STRUCTURAL GLAZING IN BUILDING–MODERN GLASS
Modern glass is not only a transparent beauty, but also has unmatched utility. Today, glass is an important building element, which not only offers aesthetics but also proves economical in the long term on account of very low maintenance expense.
Amongst the types of glass made in India,
(a) Float glass
(b) Sheet glass
(c) Plate glass
Float glass is a 100% distortion free glass, manufactured indigenously by three companies in India. Float glass is a recent development that produces a fire polished, nearly optically flat surface that does not have to be ground or mechanically polished.
Sheet glass, including the machine drawn cylinder process simulating hand-blown glass, was known for its wavy irregularities.
Plate glass, first introduced into the U.K. in the mid seventeenth century, was cast and then polished flat.
Undergraduate student, Department of Civil Engineering, NSS College of Engineering, Palakkad-08,Kerala
2.0 PROPERTIES OF GLASS
2.1 Transmission Properties
Transmission through glass can be modified by improving or modifying the
Chemical make-up of the glass to increase the absorption factor. Heat absorbing glasses are designed to absorb as much of the solar infrared radiation as possible while maintaining high transmission in the visible region. Some are also designed to absorb
visible radiation to reduce glare, which further reduces heat transmission. However, due to unavoidable impurities in the soda-lime-silica mix, typical window glass does absorb some radiation that might otherwise pass through.
2.2 Material Composition
The main components of clear glass are silica sand (73%), Calcium oxide (9%), Soda (13%) and Magnesium (4%). The amount and type of additional impurities within the glass affect the wavelength of the absorbed light and the amount of impurities determines how much it will be affected. Manufacturers often purposely add their own impurities such as ion oxides to manipulate absorption effects.
2.3 Thermal Conductivity
The thermal conductivity (K) of a soda lime glass between 5 and 7 Btu/hr Sq.ft F/in. is higher than that of insulating materials, but much lower than that of most metals. Glass of normal thickness offers negligible resistance to heat transfer between the inside and outside of a building and the thermal resistance is predominantly due to the surface films.
2.4 Strength of Glass
Glass is a brittle material and does not deform plastically before failure. It fails in tension regardless of the nature of loading. The potential tensile strength of glass is about 690107N/mm2, but failure occurs at average stresses far below this value because of the stress-raising effect of surface imperfections both inherent in the glass and mechanically created. Glass is most vulnerable at its edges, with surface imperfections from cutting and handling adding to the risk of failure. Because the effect of stress raisers is indeterminate, the allowable tensile strength of glass is determined statically and a sizable safety factor included. By using the value thus established breakage can be reduced to an insignificant level but not eliminated. Glass can be greatly strengthened by development of a “stressed skin” sandwich, where both surfaces are in compression & the middle is in tension. This can be accomplished by heating the glass to near its melting point and rapidly cooling both surfaces. The contraction of the middle (of the thickness) of the sheet develops the desired stress on final cooling.
2.5 Thermal Expansion
The co-efficient of expansion for glass is 4.5x10-6. Thermal expansion and contraction of glass is of importance in the design of glazing details, but it is even more important with respect to the development of stresses within the glass from temperature differential in a pane.
3.0 TYPES OF GLASSES
3.1 Safety glass
Safety Glass is defined as glass, which has passed specific impact tests, and must either not break or break in a manner that will not cause injury. There are 3 main types.
i. Toughened Glass
Toughened glass is obtained when a glass is heated to approximately 7000C in a furnace then chilled rapidly by cold air blown onto both its surfaces. This glass is 4 to 5 times stronger than float glass and, if broken disintegrates into small fragments with dulled edges, which are unlikely to cause serious injury, and therefore it is not termed as security glass. This is a safety glass, as it has the highest impact resistance when hit on the surface, although it is vulnerable to immediate cracking when hit on the edge. It also has a very high thermal resistivity, almost 5 times that of a normal annealed glass.
ii. Laminated glass
Laminated glass is obtained when two or more thin sheets of glass separated by layers of a plastic or resin material. The principal benefit of laminated glasses is their performance under impact, the glass may fracture, but any broken fragments will remain firmly bonded to the interlayer.
There are 2 main types.
a) PVB laminated
Two or more sheets of glass are bonded together with one or more layers of polyvinyl butyral, a plastic interlayer in sheet form. The interlayer in laminated glass provides two additional benefits: sound transmittance is reduced, particularly at the higher frequencies and UV radiation is reduced by atleast 97%.
b) Resin laminated
Such glasses are manufactured by pouring liquid resin into a cavity between two sheets of glass, which are held together until the resin cures. They are principally used for decorative and acoustic purposes, where safety performance is normally of secondary importance.
iii. Wired glass
A steel wire mesh is embedded within the glass and is intended to hold it in place if cracked. The glass breaks in almost the same way as ordinary glass, into sharp dagger-like pieces, but mostly stays in place. The visual quality of the glass is impaired by the wire mesh but this has traditionally been accepted in low-cost fire resistant and roof glazing.
3.2 Security glass
There are similar to safety glass, which has passed specific impact tests and must either not break or break in a manner that will cause injury. Laminated glass is the only glass that qualifies as a security glass.
There are 3 main types
i. Anti-bandit glass
Designed to resist manual attack, such as might be made by a man armed with a hammer, crow bar or pickaxe, and to delay access to the protected space for a short period of time.
ii. Bullet resistant glass
A multi-layered variable thickness laminated glass can function as a bullet resistant glass. A laminated glass upto 80mm thickness can resist an AK-47 bullet. A glass laminated under variable thickness specification can function as a bulletproof glass.
iii. Explosion pressure resistant glass
Basically defined as glazing that affords a defined resistance against a specified explosive blast.
3.3 Solar control glass
This type of glass reduces the amount of heat and light from the sun transmitted through the glass. This is usually done by increasing the amount energy either absorbed within the glass reflected from its surface. There are 2 different ways of producing a solar control glass.
i. Body Tinted glass
This is a mild coloured glass, available in blue, bronze and grey colour tints. They are produced by the addition of metal oxides to the raw materials during float glass manufacture. It not only restricts transparency in glass but also most importantly restricts the sunlight glare, and thereby partially insulating heat transmitted via the sunlight.
ii. Coated Glass
Solar control is achieved by applying a very thin transparent reflective metallic coating to the surface of clear or body tinted glasses. There are two different coating techniques:
Pyrolitic coating: This coating reduces the proportion of solar energy transmitted through the glass mainly by increasing the amount reflected.
Sputtered coating: The coating enables the glass to reduce the proportion of solar energy transmitted by increasing the amount absorbed and reflected.
3.4 Low-E coatings
Low-emissivity coatings, called Low-E for short, act to reduce surface emissivity of glass. These glasses provide excellent energy conservation by reflecting majority of the heat and allowing more of visible light thus reducing the heat gain without having to sacrifice much light transmission resulting in dual benefit of less energy requirement to cool the interior of the building as well as less energy for lighting requirement which in turn will help to reduce air-conditioning and lighting cost.
3.5 Spectrally selective glazing
The aim of this glass is to screen out as much ultraviolet and short wave infrared radiation as possible whilst allowing through the maximum amount of visible light. Because this type of glazing can have a virtually clear appearance, they admit more day light and permit much brighter views to outside, whilst still providing order similar to that of dark, reflective tinted glasses
.
4.0 GLASS APPLICATIONS
All the above varieties of processed glasses have ensured safe and functional use of glass in many areas of human life. Amongst them, a few special examples are
4.1Glass skylite/Glass dome
From small to very large spans of ceilings can be covered with glass allowing transmission of natural light permanently. Here, although glass is above our head, there is no fear as these are designed safely. A laminated glass is an ideal concept for glass skylites. While a glass roof does transmit heat faster during the day it also has the benefit of losing heat faster during the night.
4.2 Glass flooring
Today it is possible to walk on glass and be absolutely safe and secure. Proper structural support and adequate cushioning between glasses as well as glass and structure are inevitable. Glasses can be surface treated to prevent skidding. If used carefully, a glass floor does not involve major maintenance.
4.3 Front façade
For every architect or designer, the front facade of any building is very critical. Glass has opened wide avenues, daring opportunities for providing a grand awesome look to the building. Clear view with minimum obstructions, while the inside is cut from outside with regard to noise and pollution, yet due to transparency two worlds are merged.
Toughened or ideally toughened laminated glasses are used here.
4.4 Glass wash basin units
A clean, vibrant, novel, beautiful appearance is derived from a glass washbasin unit.
4.5 Glass furniture
With the advent of skilled workmanship and unique designing techniques, glass can speak different language in versatile styles as an element of furniture. Fusing, blasting, blowing, etching, staining, glue chipping, sticking, colouring, sculpting, chipping are some of the known techniques for beautifying transparent glass into a piece of art. Coffee tables, dining tables, T.V.Stands, corner tables, glass chairs, partitions, lampshades etc. are few of the endless forms of glass interiors.
5.0 GLASS INSTALLATION
There are five main techniques for single glazing.
1. Into rebates without beads
The glass sits in a rebate, held in place by a suitable glazing material, such as putty or a plastic-based compound, which then provides weather proof seal.
2. Into rebates with beads
As before the glass sits in a rebate, but is held in place by the beading. The glazing compound provides the weather seal.
3. Into grooves or channels.
It is usually used for glazing into concrete, store or timber frames with a rebate and bead at the sill, but it can also be modified to suit frames that have beads at the head and sill and grooves at the jambs.
4. Using structural gaskets.
Gaskets are used to hold the glass in a groove or rebate and to provide a weather seal. They can include H-shaped, Y-shaped or single-sided gaskets.
5. Using non-structural gaskets
The glass is held in place by a combination of pressure beads and gaskets.
Check that the clearance is appropriate for the thickness and type of glass. If the glass is in direct contact with the framing materials, it could lead to breakage.
Frameless glass glazing
The use of glass without using wooden or aluminum frames has become a necessity in the present and future concept with the change in the methods of use of thicken float glass in spacious buildings like airports, seaports, multistory buildings, banks, showrooms and spacious offices etc. It is therefore important that the development of such a glass glazing should be accurate and well designed, in accordance with the requirement of the situation and the architectural layout. It is also an important factor that such glass glazing should be fully supported by the hardware used in it with a capacity to sustain wind pressure and structural strength safety based on the necessary material and technique.
6.0 MAINTENANCE OF GLASS
Site Clean up
It is essential that all external glass be thoroughly washed with clean water to eliminate all abrasive and chemical laden dust. Excess glazing compounds and sealants should be carefully removed from the glass and frame surrounds, taking care not to scratch the finished surfaces with tools or abrasives. A solvent such as white spirit or professional glass cleaner may be used to remove any glazing compound, finger marks or grease. Frequent washing is required whilst construction continues on site, since chemicals in dust and particularly in cement may be activated by rain and cause permanent corrosion of the glass surface.
Normal Cleaning
Use a mild liquid detergent solution, then rinse the glass well with clean water and dry off. Under no circumstances may abrasive cleaning products or contaminated cloths be used. If rainwater coming from cement mortar contaminates the surface of the glass, frequent cleaning is necessary to prevent permanent staining.
Regular maintenance
It is essential that all installations are inspected and maintained during the lifetime of the building at regular intervals as recommended by the sealant and framing manufacturers.
7.0 PROTECTION OF GLASS
Glass can be a dangerous material .When standard annealed glass breaks, it forms potentially lethal shards and splinters. Glass manufactures have developed a range of safety glasses adding strength and integrity to this beautiful building material and allowing glass to be used in areas where safety is critical in unprecedented situation. Safety glass is defined as glass, which must have passed an impact test (as per BS 6206: 1981). There are 3 levels of impact: C, B and A, ‘A’ being the highest. Each involves the glass being impacted by a leather bag containing 45kg of lead shot.
Class A - 1219 mm
Class B - 457 mm
Class C - 305 mm
All security glasses automatically qualify a class A safety glasses.
Glass in doors and side panels to doors must be at least:
# a class B safety glazing material if the smaller dimension of the glass is more
than 900 mm.
# a class C safety glazing material if the smaller dimension of the glass in less than 900 mm.
Non safety glass in small panes may be permitted under certain controlled circumstances.
7.1 Permanent screen protection
The use of annealed glass is permitted in a critical location if protected by a permanent, robust screen. The screen must prevent the passage of a 75mm diameter sphere and must not be climbable.
7.2 Bathing areas and areas of special risk
BS 6262 requires that any glazing, forming part of a bath or shower screen or adjacent to or surrounding a bathing area, swimming pool or other wet areas must be at least a class C material. Consideration should also be given to the breakage characteristics. The fragmentation of toughened glass into small dice-like particles would result in, should it enter the pool, being invisible practically impossible to remove, practically causing damage to pumps filters. This can be avoided by using a laminated safety glass an account of the glass fragments remaining adhered to the plastic interlayer. This requirement also applies to all glazing in areas of special risk such as gymnasia and other places of energetic activity. In such areas, the designer must consider whether a higher class is required, or if additional safeguards such as protective rails or screens, or manifestation are necessary.
7.3 Commercial frontage
Robust glass (non-safety thick annealed glass) when fully framed is considered suitable for use in large areas in non-domestic applications, for eg: forming fronts to shops, showrooms, offices, factories, and public buildings.
Glass thickness / size limits for annealed glass that may be used in these locations are shown in the Table 1. Wind loads & other load must be considered when selecting the glass thickness.
Table1 Glass thickness and pane size
Normal Glass Maximum pane size
thickness (mm) (four edge supported )(mm)
8 1100 x 1100
10 2250 x 2250
12 4500 x 4500
15 or thicker No limits
7.4 Glass in furniture
Standard advises minimum BS 6206 classification, glass thickness and support details to insure the reasonable safety of flat glass having a total area of at least 0.02m2.
1. Glass in tables or trolleys
Glass that is not supported over its entire area:
The minimum horizontal area of each support shall be 36mm2. Annealed glass shall be supported for not less than 50% of its total perimeter and the support should be in at least two non-adjacent regions and shall be not more than 100mm from the edge of glass. Minimum BS 6206 classification and nominal thickness for glass that is not supported over its entire area as shown in table 2.
Table 2 Minimum BS 6206 classification and nominal thickness
Area of Nominal Thickness Minimum Nominal thickness
glass (m2) (mm) BS 6206 (mm)
annealed glass classification
Toughened glass Laminated glass
<= 0.25 >=10 Class C >=4.0 >=6.4
< 0.25 to >=10 Class C >=5.0 >=6.4
<=0.5
> 0.5 to >=12 Class C >=6.0 >=6.4
<=0.75
> 0.75 to >= 15 Class B >=8.0 >=8.4
< =1.5
>1.5 >=19 Class A >=10.0 >=10.8
Glass that is supported over its entire area.:
Glass which has an area not greater than 1.5m2 shall comply with the relevant nominal thickness given in table3 below.
Table 3 Nominal thickness of glass
Area of glass (m2) Nominal thickness (m)
Annealed
Toughened glass
Laminated glass
<=0.5 >=4.0 >=4.0 >=4.4
>=0.5 to <=1.0 >=5.0 >=4.0 >=4.4
>=1.0 to <=1.5 >=6.0 >=4.0 >=4.4
>1.5 N/A >=4.0 >=4.4
Contact of glass with other materials:
Hard materials such as other glass, metal or stone should not be allowed to come into direct contact with the edges or surface of the glass. Separation should be ensured by the use of suitable bushes and gaskets. Glass in furniture other than tables or trolleys. Horizontal glass supported over its entire area should comply with Table 3. Glass used to form the external surfaces (excluding horizontal glass supported over its entire area) and which is unbaked should comply with the requirements of table 4.
Table 4 Requirements of glass for external surfaces and unbaked conditions
Smaller dimension (width or height)
Less than 900mm
BS 6206 Class C
Minimum Thickness More than 900mm
BS 6206 Class B
Minimum Thickness
3 mm Fully framed 4 mm
4 mm Partially framed or unframed 6 mm
For sliding door and fixed glass retained in a rebate or groove, the edge cover provided by the rebate or groove shall be at least 4 mm.
7.5 Glass shelves
Glass shelves that are not fully enclosed in a cabinet shall be a class C safety glass to BS 6206 as a minimum. This requirement is most easily met by using toughened glass. Annealed glass is acceptable for use as shelves only when fully enclosed within a cabinet. The maximum evenly distributed safe load that a shelf can support is dependent on glass type, thickness, width and span of the glass between supports.
8.0 DEVELOPMENTS IN SAFETY GLAZING
8.1 Fire resistant glass products
Acceptable glazing products for fire – rated, hazardous locations include transparent glass ceramic and in tumescent glass. Glass ceramic are single glazed products that meet both impact resistance requirements and provide up to a 3-hour fire resistance rating.
In tumescent glass are double – glazed products with an inner layer of transparent sodium silicate that when exposed to high temperature, turns opaque and forms an insulating layer that can provide up to a two hour fire resistance rating. Unlike glass – ceramic, in tumescent glass becomes insulating when exposed to fire. It is also more expensive than glass ceramic.
8.2 Blast resistant glazing
When a building is subjected to bombing it is noted that 60% of the non-lethal injuries sustained in that event were due to shattered glass, shattered glass was found as far as 1 mile from the blast site.
The GSA standard defines performance condition based on the response of glazing to a specified blast event, and the level of protection provided by glazing system as shown in the table below.
Table 5 The level of protection provided by glazing system
Performance Criteria Protection Level Hazard Level Description of Window Glazing Response
1
Safe
None Glazing does not break.No visible damage to glazing or frame.
2 Very high None Glazing cracks but is retained by the frame. Dusting or verysmall fragments near sill or on floor acceptable.
3a High Very low Glazing cracks. Fragments enter space and land on the floor no further than 0.99m from the window.
3b High Low Glazing cracks. Fragments enter space and land on floor no further than 3m from the window.
4 Medium Medium Glazing cracks. Fragments enter space and land on the floor and impact a vertical witness panel at a distance of no more than 3m from the window at a height no greater than 0.6m above the floor.
5 Low High Glazing cracks and window system fails catastrophically. Fragments enter space impacting a vertical witness panel at a distance of no more than 3m from window at a height greater than 0.6m above floor.
9.0 CONCLUSION
1. Structural glass tends to influence modern architecture more and more. It defines not only modernity, but also value, richness and future technology.
2. There have been thousands of other developments in glass manufacture that make it one of the most useful and versatile materials available.
Thursday, January 19, 2012
Nature and Behaviour of Soft Clays and their improvement
The growth of Indian port city’s over the last few decades has been phenomenal
and Cochin is no exception with the increase of population, housing and construction of
various facilities have been a problem with urbanization. Having exhausted all the trouble
free hand, man is now on the look out for techniques to improve areas which were
originally considered uninhabitable. Thus studies on the nature and engineering behavior
of
soft clay’s covering long stretches of coastal line and methods to improve there geotechnical properties have been of great relevance, and is explained in the following pages.
2. REVIEW OF COCHIN MARINE CLAY
According to King (1884), 2500 years back, the sea washed up to the high ranges
of Western Ghats. The land between the Western Ghats and the present coastal line was
once well above the sea and was subsequently submerged. It was uplifted again by volcanic
action and again partially covered by sea water. The uplifted area includes the coastal belt
(10 to 30Km wide and 150 Km long) starting from Crangannore at the north to Quilon
at the south. Most of the Cochin city is situated in this belt.
3. PHYSICAL PROPERTIES OF COCHIN MARINE CLAY
Marine clay is formed by the sedimentation of clay soils in marine environments
exhibit unusual physical properties. They posses very high liquid limit and their natural
water content is close to the liquid limit values. The most striking feature of the physical
properties is the phenomenal changes that are caused by drying of sample. Some physical
properties of the Cochin marine clay is shown in the following table.
PHYSICAL PROPERTIES OF COCHIN MARINE CLAY
Sl No Physical properties (%) Moist soil Air dried soil Oven dried soil
1 Liquid limit 131.5 94.5 62.0
2 Plastic limit 53.9 45.2 40.5
3 Plasticity index 77.6 49.3 21.5
4 Shrinkage limit 18.1 18.8 19.2
5 Grain size distribution
(a) Clay
(b) Silt
(c) sand
48
34
18
33
47
20
13
55
32
4. SHEAR STRENGTH
In greater Cochin area the layers of shallow depth have their natural moisture
content quite close to their liquid limit. The clay deposits below vary widely in consisting up
to 40 to 50m where good load bearing stratum can be met with.
The shear strength of clayey soils is dependent on its water content. Any
increase in water content is necessarily accompanied by the reduction in cohesion or shear
strength. But at the same water content, different soils have different shear strength. From
the test results that were conducted at different places in Cochin, it was found that, the shear strength is very low and it is around 0.01Kg/cm² and 0.02Kg/cm².
5. CONSOLIDATION CHARACTERISTICS OF COCHIN
MARINE CLAY
Several series of consolidation tests were carried out on samples of Cochin arine clay varying different parameters like duration of loading, effect of pore fluid, effect
of washing. In the consolidation test which served as the reference test. It was found that
about 2 days were required for a complete dissipation of pore pressure and for reaching
an equilibrium void ratio for a particular loading stage. The clay deposits are highly
compressive with Cc value around 1.5 and natural moisture content
very close to liquid limit. It has been observed that almost all the structures, founded on
spread footings or raft footings invariably show actual settlement far below the computed
values.
6. PROBLEMS DUE TO THICK MARINE CLAY
Cochin City and the surroundings are covered with thick marine clay deposit
extending to a large depth (30 to 40m) below the ground level. Due to the presence of this
soft clay layer, following problems are observed.
Low bearing capacity
Higher settlement
High seepage losses
Liquefaction during earthquake
Instability of foundation excavations
Higher earth pressure on retaining structures
IS: 1904(1966) permits a maximum settlement of 40mm for isolated foundations on
sand and 65mmfor those for clay. The allowable settlement is higher for clay because
progressive settlement on clayey soils permits better strain adjustments in the structural
members. The maximum settlement for raft foundations on sand is 40mm to 65mm and that
on clay is 65mm to 100mm.
For typical industry following issues are to be addressed:
Large area is covered with thick vegetation. If the area is reclaimed without removal of the vegetation. It will result in a fill with high organic content and high compressibility. On the other hand, if the vegetation is to be removed, it requires dewatering of the area so that powered vehicle can operate on the surface and clear slush and vegetation before selected soil is placed for reclamation.
While reclaiming the area, particularly for industry requiring very large area, for example refinery, oil terminal, gas bottling plant, etc. the drainage pattern of the area needs to be planned carefully. The flow surface water which was taking place through the area prior to reclamation has to be diversified through special drains/culverts such a way that it does not create any inundation.
The area avail is low-laying and often inundated with water. Unless the area is raised by soil fill (3 to 4m thick) it is difficult to carryout any construction.
In many projects, the height of the fill required is 2 to 3m. This will require boundary wall which has a high retaining wall plus a compound wall. In the absence of retaining wall the fill material can encroach in the neighboring areas beyond the property line which may not be acceptable in many cases. Alternately, fill is placed with toe of the slop within the property line .in this case, large area with a width of 6 to 7m all along the periphery of the area remain unutilized.
The placement of fill can lead to the following foundation problems.
Negative drag force on pile foundation.
Lateral flow under surface loading leading to settlement and lateral force on the adjacent foundations.
Deep-seated slop failure for construction of embankment and heavy surface loading.
Difficulty in executing foundations requiring deep excavation.
7. GROUND IMPROVEMENT
The clay deposit also needs to be improved to meet the foundation requirements. In early days, areas having clay deposit was avoided for construction. But with scarcity of land in urban areas, we do not have choice and structures have to be built on weak deposits. Pile foundation is of course a possible approach as it by pass the weak deposit and transfer the load on next component layer. Where thickness is very large, pile foundation is uneconomical and time consuming.
The methods of ground improvement that can be adopted depend basically on nature of strata and purpose of improvement. The methods available are as follows.
8 METHODS OF GROUND IMPROVEMENT
8.1 VERTICAL DRAINS
This method is suitable for deep deposit of soft clay. The natural moisture content in this strata can brought down substantially by installing vertical drains with preloading. The pressures of vertical drains reduce the drainage path of water in the pores of the soil and thereby reduce the time required for consolidation. The spacing of drains depends upon the speed at which required improvement is to be achieved.
In earlier days, such vertical drains were installed by driving a close ended steep pipe o 100 to 200mm diameter up to the full thickness of such clay deposit. The pipe is then filled with sand and withdrawn in stage to form a vertical drain. The pipe is generally refused for installing other drains.
In the recent past, there has been number of different materials developed to replace the sand drains. These are basically plastic sections having thickness varying from 5 to 10mm and width from 100 to 150mm. The sections have channels to permit flow of water. The perimeter of the section is covered with a layer of geo-textile to prevent the entry of soil particles in to the channel. The advantages of such drain are that it results in minimum remoulding of surrounding soil during installation. The process of installation is very fast. The machine is mounted on a crane and typical drain up to 10m depth can be installed in the period of varying 1 to2 minutes including the time for shifting the machine to a new location.
The percentage of consolidation, which can be achieved by such vertical drains, can be theoretically predicted from the design charts developed based on the theory of three-dimensional consolidation. Typically, a deposit, which requires a period of over ten years for 95% consolidation, can complete the same consolidation within a short period of 3 to 6 months when vertical drains are installed.
After the drains are installed, the magnitude of preload to be placed on the required shear strength of the layer after improvement. Depending on the time available for improvement, the degree of consolidation is worked out and the effective over burden pressure (p) is computed. From the plasticity index I\of the soil, the ratio Su/p is determined. The ratios normally remain constant and therefore with increase in value of p the shear strength after treatment increases.
8.2 IN-SITU DEEP MIXING
In- site deep mixing using hydraulically operated helical augers penetrate the ground to the required depth. The hollow stem of the auger is used to inject cement / lime / any other stabilizing compound into the ground. A pair of 2 or 3 augers is operated simultaneously. After injecting the stabilizer in to the ground, the augers are rotated such that the soil along with the stabilizer is churned in-situ and mixed the stabilizer thoroughly with the soil without necessity of taking out the soil. The auger configuration can be chosen such that either a stabilized wall can be formed (to act as a barrier) or the entire area can be stabilized.
8.3 STONE COLUMN
Stone columns are cylindrical columns made below ground level which comprises of granular material of size varying from 25 to 100mm. The hole is made in the soft clay deposit by different techniques and then filled with stones in layer and compacted to form the complete column. When the structure is placed over the area treated by stone column, majority of the load (80 to 90%) is transmitted to the stone columns because of their higher stiffness. Balance 10 to 20%of the load is taken by the clay deposit. With the help of this 10%of surcharge load, the soft clay able to provide adequate confinement to the cylindrical column.
The area treated stone columns can be used to support only flexible structures such as embankment, oil storage tank, etc. because the settlement even after treatment with stone column can be large (50 to200mm). Without stone column the settlement could have been 3 to 4times higher and also the bearing capacity would have been much less.
8.4 VACUUM DEWATERING
In this technique also the layer is provided with vertical drains as mentioned above. The surface is then covered with a layer of a sand blanket 150 to 300mm thick and covered with a thin plastic sheet which is suitably anchored along the perimeter. Vacuum is then applied with a sand blanket which creates a suction pressure up to 50 to60mm height of mercury and forced the pore water out from the deposit through vertical drains. The area is also subjected to atmospheric pressure which then acts as preload. The vacuum pressure is maintained till the required improvement is achieved.
8.5 VIBROFLOTATION
Vibroflotation involves the use of a vibrating probe that can penetrate granular soil to depths of over 100feet. The vibrations of the probe cause the grain structure to collapse thereby densifying the soil surrounding the probe. To treat an area of potentially liquefiable soil, the vibroflot is raised and lowered in a grid pattern. Vibro replacement is a combination of vibroflotation with a gravel backfill resulting in stone columns, which not only increase the amount of densification, but provides a degree of reinforcement and potentially effective means of drainage.
Figure:1
VIBROFLOTATION.
SCHEMATIC DIAGRAM:1
8.6 DYNAMIC COMPACTION
In dynamic compaction, a heavy weight of 15 to 20ton is raised to a height about 20m above the ground level and freely dropped on the ground surface. The impact on the ground surface transmits compression waves, which spreads radially from the point of impact. The compression waves travels fast and creates Liquefaction of the strata, which is saturated. It is followed by shear waves reorients the soil particle which are liquefied state to denser state and compacts the configuration. The spacing between the treating point, number of impact at each point, etc. can be varied depending on the required improvement.
Figure : 2
DYNAMIC COMPACTION.
8.7 COMPACTION BY DEEP BLASTING
In this technique, a borehole is made to a depth approximately 3/4 or 2/3 of the total depth. Suitable explosive is lowered to the bottom of the borehole and the space above is back filled with compacted soil (known as stemming). The explosive is attached with cordex, which is taken up to the surface and connected to electric detonator. When the explosive is detonated, it creates a cavity, which expands instantaneously. The cavity expansion generates shock waves. Propagation of these waves densifies the soil to certain extent. After blast, a large conical depression is observed at the place of blast. The water within the pores of the deposit gets expelled out and comes up to the ground and form a large pool in the cone of depression.
The quantity of charge and spacing between the explosive can be suitably selected to achieve the required densification. As a thumb rule, about 15 to 45 grams of explosive is required for densification of every 3m of the deposit. Initial loose deposit which has relative density of about 50% and susceptible to liquefaction can be densified to a relative density of over 60% which is adequate to prevent liquefaction. The vibrations created during the blast are within permissible limits for construction purpose.
8.8 COMPACTION GROUTING
Compaction grouting is a technique where by a slow-flowing water /sand /cement mix is injected under pressure into a granular soil. The grout forms a bulb that and densifies the surrounding soil. Compaction grouting is a good option if the foundation of an existing building requires improvement, since it is possible to inject the grout from the side or at an inclined angle to reach beneath the building.
Figure:3
COMPACTION GROUTING.
SCHEMATIC DIAGRAM:2
9. CASE STUDY
PILE FOUNDATION FOR VYPEEN ISLAND BRIDGE
The new bridge connecting Ernakulam town with Bolgatti Island and Vypeen Island is supported on 1m diameter bored cast in-situ pile. The design load for each pile is 450tones. The strata comprise of soft marine clay of 20 to 30m. This is followed by alternative layers of dense sand and stiffing clay which contains decayed wood within the deposit. The SPTN value of clay with decayed wood is generally >100 and the pile length were estimated as 45 to 50m.
During excavation of the work, it was noticed that even pile length 45m was not adequate to meet the loading requirement. Due to the large depth of pile, stabilization of the borehole and cleaning of the bore before concreting was found to be difficult. The load test results revealed that the end boring resistance offered by the strata was not significant and particularly all the load was resisted by side friction. To meet the requirement of loading, the pile length had to be increased from 45 to as high as 65 to 70m depending on the strata condition. For the certain piers, before the load test results were available, the piles were terminated with depth of 45m. Additional piles were provided at these locations to meet the loading requirements. It is very rare that large diameter piles have been installed to meet large depth.
The variations in the strata conditions and uncertainty about the behavior of stiff clay with the decayed wood made the designers to adopt a conservative approach which has resulted in large depth of pile. Apart from construction of piles, the strata condition posed followed technical problems.
Reclamation of large area by dredged material on Vypeen Island.
Construction of 6 to 8m high approach embankments on soft clay deposit created problems of settlement and negative drag of the pile. To reduce this 2 structural span have been added at the Ernakulam end so that the height of the embankment get reduced and approach embankment can be supported on the available weak strata.
Figure:4
PILE FOUNDATION FOR VYPEEN ISLAND BRIDGE
10. CONCLUSIONS
Due to the increase in construction activities and urbanization the availability of suitable soils are decreasing. Cochin City and its surroundings are covered with marine clay to large depth. Which posses very low shear strength, low physical and engineering properties. Whenever the soft clay deposits are very loose sand or soft clay and are unsuitable for resting the foundation, the following options can be considered.
Adopt deep foundation such as pile foundation so that the top soil can be bypassed.
Treat the existing soil to improve the bearing capacity and reduce the settlement and place the foundation directly over the top soil.
and Cochin is no exception with the increase of population, housing and construction of
various facilities have been a problem with urbanization. Having exhausted all the trouble
free hand, man is now on the look out for techniques to improve areas which were
originally considered uninhabitable. Thus studies on the nature and engineering behavior
of
soft clay’s covering long stretches of coastal line and methods to improve there geotechnical properties have been of great relevance, and is explained in the following pages.
2. REVIEW OF COCHIN MARINE CLAY
According to King (1884), 2500 years back, the sea washed up to the high ranges
of Western Ghats. The land between the Western Ghats and the present coastal line was
once well above the sea and was subsequently submerged. It was uplifted again by volcanic
action and again partially covered by sea water. The uplifted area includes the coastal belt
(10 to 30Km wide and 150 Km long) starting from Crangannore at the north to Quilon
at the south. Most of the Cochin city is situated in this belt.
3. PHYSICAL PROPERTIES OF COCHIN MARINE CLAY
Marine clay is formed by the sedimentation of clay soils in marine environments
exhibit unusual physical properties. They posses very high liquid limit and their natural
water content is close to the liquid limit values. The most striking feature of the physical
properties is the phenomenal changes that are caused by drying of sample. Some physical
properties of the Cochin marine clay is shown in the following table.
PHYSICAL PROPERTIES OF COCHIN MARINE CLAY
Sl No Physical properties (%) Moist soil Air dried soil Oven dried soil
1 Liquid limit 131.5 94.5 62.0
2 Plastic limit 53.9 45.2 40.5
3 Plasticity index 77.6 49.3 21.5
4 Shrinkage limit 18.1 18.8 19.2
5 Grain size distribution
(a) Clay
(b) Silt
(c) sand
48
34
18
33
47
20
13
55
32
4. SHEAR STRENGTH
In greater Cochin area the layers of shallow depth have their natural moisture
content quite close to their liquid limit. The clay deposits below vary widely in consisting up
to 40 to 50m where good load bearing stratum can be met with.
The shear strength of clayey soils is dependent on its water content. Any
increase in water content is necessarily accompanied by the reduction in cohesion or shear
strength. But at the same water content, different soils have different shear strength. From
the test results that were conducted at different places in Cochin, it was found that, the shear strength is very low and it is around 0.01Kg/cm² and 0.02Kg/cm².
5. CONSOLIDATION CHARACTERISTICS OF COCHIN
MARINE CLAY
Several series of consolidation tests were carried out on samples of Cochin arine clay varying different parameters like duration of loading, effect of pore fluid, effect
of washing. In the consolidation test which served as the reference test. It was found that
about 2 days were required for a complete dissipation of pore pressure and for reaching
an equilibrium void ratio for a particular loading stage. The clay deposits are highly
compressive with Cc value around 1.5 and natural moisture content
very close to liquid limit. It has been observed that almost all the structures, founded on
spread footings or raft footings invariably show actual settlement far below the computed
values.
6. PROBLEMS DUE TO THICK MARINE CLAY
Cochin City and the surroundings are covered with thick marine clay deposit
extending to a large depth (30 to 40m) below the ground level. Due to the presence of this
soft clay layer, following problems are observed.
Low bearing capacity
Higher settlement
High seepage losses
Liquefaction during earthquake
Instability of foundation excavations
Higher earth pressure on retaining structures
IS: 1904(1966) permits a maximum settlement of 40mm for isolated foundations on
sand and 65mmfor those for clay. The allowable settlement is higher for clay because
progressive settlement on clayey soils permits better strain adjustments in the structural
members. The maximum settlement for raft foundations on sand is 40mm to 65mm and that
on clay is 65mm to 100mm.
For typical industry following issues are to be addressed:
Large area is covered with thick vegetation. If the area is reclaimed without removal of the vegetation. It will result in a fill with high organic content and high compressibility. On the other hand, if the vegetation is to be removed, it requires dewatering of the area so that powered vehicle can operate on the surface and clear slush and vegetation before selected soil is placed for reclamation.
While reclaiming the area, particularly for industry requiring very large area, for example refinery, oil terminal, gas bottling plant, etc. the drainage pattern of the area needs to be planned carefully. The flow surface water which was taking place through the area prior to reclamation has to be diversified through special drains/culverts such a way that it does not create any inundation.
The area avail is low-laying and often inundated with water. Unless the area is raised by soil fill (3 to 4m thick) it is difficult to carryout any construction.
In many projects, the height of the fill required is 2 to 3m. This will require boundary wall which has a high retaining wall plus a compound wall. In the absence of retaining wall the fill material can encroach in the neighboring areas beyond the property line which may not be acceptable in many cases. Alternately, fill is placed with toe of the slop within the property line .in this case, large area with a width of 6 to 7m all along the periphery of the area remain unutilized.
The placement of fill can lead to the following foundation problems.
Negative drag force on pile foundation.
Lateral flow under surface loading leading to settlement and lateral force on the adjacent foundations.
Deep-seated slop failure for construction of embankment and heavy surface loading.
Difficulty in executing foundations requiring deep excavation.
7. GROUND IMPROVEMENT
The clay deposit also needs to be improved to meet the foundation requirements. In early days, areas having clay deposit was avoided for construction. But with scarcity of land in urban areas, we do not have choice and structures have to be built on weak deposits. Pile foundation is of course a possible approach as it by pass the weak deposit and transfer the load on next component layer. Where thickness is very large, pile foundation is uneconomical and time consuming.
The methods of ground improvement that can be adopted depend basically on nature of strata and purpose of improvement. The methods available are as follows.
8 METHODS OF GROUND IMPROVEMENT
8.1 VERTICAL DRAINS
This method is suitable for deep deposit of soft clay. The natural moisture content in this strata can brought down substantially by installing vertical drains with preloading. The pressures of vertical drains reduce the drainage path of water in the pores of the soil and thereby reduce the time required for consolidation. The spacing of drains depends upon the speed at which required improvement is to be achieved.
In earlier days, such vertical drains were installed by driving a close ended steep pipe o 100 to 200mm diameter up to the full thickness of such clay deposit. The pipe is then filled with sand and withdrawn in stage to form a vertical drain. The pipe is generally refused for installing other drains.
In the recent past, there has been number of different materials developed to replace the sand drains. These are basically plastic sections having thickness varying from 5 to 10mm and width from 100 to 150mm. The sections have channels to permit flow of water. The perimeter of the section is covered with a layer of geo-textile to prevent the entry of soil particles in to the channel. The advantages of such drain are that it results in minimum remoulding of surrounding soil during installation. The process of installation is very fast. The machine is mounted on a crane and typical drain up to 10m depth can be installed in the period of varying 1 to2 minutes including the time for shifting the machine to a new location.
The percentage of consolidation, which can be achieved by such vertical drains, can be theoretically predicted from the design charts developed based on the theory of three-dimensional consolidation. Typically, a deposit, which requires a period of over ten years for 95% consolidation, can complete the same consolidation within a short period of 3 to 6 months when vertical drains are installed.
After the drains are installed, the magnitude of preload to be placed on the required shear strength of the layer after improvement. Depending on the time available for improvement, the degree of consolidation is worked out and the effective over burden pressure (p) is computed. From the plasticity index I\of the soil, the ratio Su/p is determined. The ratios normally remain constant and therefore with increase in value of p the shear strength after treatment increases.
8.2 IN-SITU DEEP MIXING
In- site deep mixing using hydraulically operated helical augers penetrate the ground to the required depth. The hollow stem of the auger is used to inject cement / lime / any other stabilizing compound into the ground. A pair of 2 or 3 augers is operated simultaneously. After injecting the stabilizer in to the ground, the augers are rotated such that the soil along with the stabilizer is churned in-situ and mixed the stabilizer thoroughly with the soil without necessity of taking out the soil. The auger configuration can be chosen such that either a stabilized wall can be formed (to act as a barrier) or the entire area can be stabilized.
8.3 STONE COLUMN
Stone columns are cylindrical columns made below ground level which comprises of granular material of size varying from 25 to 100mm. The hole is made in the soft clay deposit by different techniques and then filled with stones in layer and compacted to form the complete column. When the structure is placed over the area treated by stone column, majority of the load (80 to 90%) is transmitted to the stone columns because of their higher stiffness. Balance 10 to 20%of the load is taken by the clay deposit. With the help of this 10%of surcharge load, the soft clay able to provide adequate confinement to the cylindrical column.
The area treated stone columns can be used to support only flexible structures such as embankment, oil storage tank, etc. because the settlement even after treatment with stone column can be large (50 to200mm). Without stone column the settlement could have been 3 to 4times higher and also the bearing capacity would have been much less.
8.4 VACUUM DEWATERING
In this technique also the layer is provided with vertical drains as mentioned above. The surface is then covered with a layer of a sand blanket 150 to 300mm thick and covered with a thin plastic sheet which is suitably anchored along the perimeter. Vacuum is then applied with a sand blanket which creates a suction pressure up to 50 to60mm height of mercury and forced the pore water out from the deposit through vertical drains. The area is also subjected to atmospheric pressure which then acts as preload. The vacuum pressure is maintained till the required improvement is achieved.
8.5 VIBROFLOTATION
Vibroflotation involves the use of a vibrating probe that can penetrate granular soil to depths of over 100feet. The vibrations of the probe cause the grain structure to collapse thereby densifying the soil surrounding the probe. To treat an area of potentially liquefiable soil, the vibroflot is raised and lowered in a grid pattern. Vibro replacement is a combination of vibroflotation with a gravel backfill resulting in stone columns, which not only increase the amount of densification, but provides a degree of reinforcement and potentially effective means of drainage.
Figure:1
VIBROFLOTATION.
SCHEMATIC DIAGRAM:1
8.6 DYNAMIC COMPACTION
In dynamic compaction, a heavy weight of 15 to 20ton is raised to a height about 20m above the ground level and freely dropped on the ground surface. The impact on the ground surface transmits compression waves, which spreads radially from the point of impact. The compression waves travels fast and creates Liquefaction of the strata, which is saturated. It is followed by shear waves reorients the soil particle which are liquefied state to denser state and compacts the configuration. The spacing between the treating point, number of impact at each point, etc. can be varied depending on the required improvement.
Figure : 2
DYNAMIC COMPACTION.
8.7 COMPACTION BY DEEP BLASTING
In this technique, a borehole is made to a depth approximately 3/4 or 2/3 of the total depth. Suitable explosive is lowered to the bottom of the borehole and the space above is back filled with compacted soil (known as stemming). The explosive is attached with cordex, which is taken up to the surface and connected to electric detonator. When the explosive is detonated, it creates a cavity, which expands instantaneously. The cavity expansion generates shock waves. Propagation of these waves densifies the soil to certain extent. After blast, a large conical depression is observed at the place of blast. The water within the pores of the deposit gets expelled out and comes up to the ground and form a large pool in the cone of depression.
The quantity of charge and spacing between the explosive can be suitably selected to achieve the required densification. As a thumb rule, about 15 to 45 grams of explosive is required for densification of every 3m of the deposit. Initial loose deposit which has relative density of about 50% and susceptible to liquefaction can be densified to a relative density of over 60% which is adequate to prevent liquefaction. The vibrations created during the blast are within permissible limits for construction purpose.
8.8 COMPACTION GROUTING
Compaction grouting is a technique where by a slow-flowing water /sand /cement mix is injected under pressure into a granular soil. The grout forms a bulb that and densifies the surrounding soil. Compaction grouting is a good option if the foundation of an existing building requires improvement, since it is possible to inject the grout from the side or at an inclined angle to reach beneath the building.
Figure:3
COMPACTION GROUTING.
SCHEMATIC DIAGRAM:2
9. CASE STUDY
PILE FOUNDATION FOR VYPEEN ISLAND BRIDGE
The new bridge connecting Ernakulam town with Bolgatti Island and Vypeen Island is supported on 1m diameter bored cast in-situ pile. The design load for each pile is 450tones. The strata comprise of soft marine clay of 20 to 30m. This is followed by alternative layers of dense sand and stiffing clay which contains decayed wood within the deposit. The SPTN value of clay with decayed wood is generally >100 and the pile length were estimated as 45 to 50m.
During excavation of the work, it was noticed that even pile length 45m was not adequate to meet the loading requirement. Due to the large depth of pile, stabilization of the borehole and cleaning of the bore before concreting was found to be difficult. The load test results revealed that the end boring resistance offered by the strata was not significant and particularly all the load was resisted by side friction. To meet the requirement of loading, the pile length had to be increased from 45 to as high as 65 to 70m depending on the strata condition. For the certain piers, before the load test results were available, the piles were terminated with depth of 45m. Additional piles were provided at these locations to meet the loading requirements. It is very rare that large diameter piles have been installed to meet large depth.
The variations in the strata conditions and uncertainty about the behavior of stiff clay with the decayed wood made the designers to adopt a conservative approach which has resulted in large depth of pile. Apart from construction of piles, the strata condition posed followed technical problems.
Reclamation of large area by dredged material on Vypeen Island.
Construction of 6 to 8m high approach embankments on soft clay deposit created problems of settlement and negative drag of the pile. To reduce this 2 structural span have been added at the Ernakulam end so that the height of the embankment get reduced and approach embankment can be supported on the available weak strata.
Figure:4
PILE FOUNDATION FOR VYPEEN ISLAND BRIDGE
10. CONCLUSIONS
Due to the increase in construction activities and urbanization the availability of suitable soils are decreasing. Cochin City and its surroundings are covered with marine clay to large depth. Which posses very low shear strength, low physical and engineering properties. Whenever the soft clay deposits are very loose sand or soft clay and are unsuitable for resting the foundation, the following options can be considered.
Adopt deep foundation such as pile foundation so that the top soil can be bypassed.
Treat the existing soil to improve the bearing capacity and reduce the settlement and place the foundation directly over the top soil.
Marina Bay Sands
Following four years of construction in Singapore opened Hotel Marina Bay Sands. The three tower 200 meters is a huge terrace in the form of a gondola with pools and green gardens with total area of 120 thousand square meters. The main pool is located outdoors, is not visible to the rim, because of what the impression that the water's edge terminates at a height. Swimming pool stretches for 150 meters and is the largest swimming pool, built on this level. The hotel has 2,560 rooms, shopping center, conference hall, 2 theaters, a museum and several restaurants. Marina Bay Sands is one of two winning proposals for Singapore's first Integrated Resorts, the other being the Resorts World Sentosa,
Bidders were assessed based on four criteria:
• Tourism appeal and contribution
• Architectural concept and design
• Development investment
• Strength of the consortium and partners
Las Vegas Sands initially committed to invest S$3.85 billion in the project, not including the fixed S$1.2 billion cost of the 6,000,000 square feet (560,000 m2) site itself. With the escalating costs of materials, such as sand and steel, and labour shortages owing to other major infrastructure and property development in the country, Sheldon Adelson placed the total cost of the development at $8.0 billion as of July 2009.
2. DESIGN
Fig(2.1) Architectural model showing the layout of the Marina Bay Sands Integrated Resort:
The hotel and Sky Park are in and on the towers in the background, respectively; the shopping mall, theatre and casino are in the long lower building; and the ArtScience Museum is in flower-shaped building in the foreground.
The resort is designed by Moshe Safdie, who says it was initially inspired by card decks. In addition to the casino, other key components of the plan are three hotel towers with 2,560 rooms and suites, a 200,000-square-foot (19,000 m2) Art Science Museum and a convention centre with 1,200,000 square feet (111,000 m2) of space, capable of accommodating up to 45,000 people.
Conceptually, each tower is composed of two slabs of east and west-facing rooms. The double-loaded towers spread at the base forming a giant atrium at the lower levels, and converge as they rise . the tower slabs also give further character to the massing and relate to the site context: the glazed west side faces the city center while the east side is planted with lush bougainvilleas facing the botanical gardens and ocean beyond in plan, as the parcel varies in width, the cross section is decrease from one tower to the next. The three void spaces are connected by one continuous and conditioned glazed, filling the space between the towers with restaurants, retail spaces, and a public thoroughfare. Each tower slab from is also twisted slightly in relation to its pair, creating a dance-like relationship between the two parts and accentuation the slenderness of the buildings, resulting in the appearance of six towers, rather than three.
In addition to the million square meters of built space the project program also called for the development of extensive exterior gardens with swimming pools, jogging paths, and public spaces. As one of the aims of the project had been to minimize the geight of the podium buildings, seeking to reference Singapore’s pastoral hills more than its urban core, the problem emerged that the complex program left no vacant land suitable for these amenities. Creating gardens on top of the roof of the casino and the convention center was studied, however these vast spaces lacked views, overshadowed and overpowered by the adjacent hotel towers. The idea emerged to bridge between the three towers in order to reclaim exterior garden space and create a 2.5-acre park in the sky.
2.1 THE BELLY
The façade of the project which required careful consideration was thus the “belly” of the sky park. Made of more than 9000 silver-painted metal –composite panels, this skin encloses the mega trusses which bridge the buildings at level 55,as well as a multitude of back of house spaces(i.e., large mechanical rooms with water tanks supporting the pools and a network of corridors and offices for hotel operations staff). The geometry of the sky park began with a platonic torpid form, which was then further shaped to streamline the cross sections of the building. The resulting surface was then regularized and panelized using a computer script, triangulation the façade into simple shapes, the shapes were water-jet cut from flat sheet panels and shipped to the building site in containers pre-designed to be lifted to the top levels of the building.
Once on top of the building, the panels were installed via temporary aluminum frame under slung mobile gantries which traveled on a permanent track of steel rails. The gantry system track serves double day as a building maintenance unit, therefore the track was designed to be hidden within the reveal pattern of the facade panels.
3. CONSTRUCTION
Fig(3.1) When construction started in 2007.
Fig(3.2) Marina bay sands
In May of 2006, after a highly-competitive bidding process, the Singapore government selected Las Vegas sands corp. to build the country's first integrated resort property. It will be one of only two resort-casino properties in the South East Asian city-state and will operate as such for a period of 30 years. the gigantic complex complete with three 60-story hotel towers with 3 stories underground will house 2,600 hotel rooms / suites and a 4,000 car garage; topped by a two acre sky park bridging across the towers consisting of a garden, swimming pool, jogging paths, spas; ‘floating’ crystal pavilions; on the promontory a lotus-shaped museum; a grand, a multi-leveled retail arcade for international luxury brands. Celebrity chef restaurants; an outdoor event plaza; entertainment theaters and night clubs plus a Las Vegas-style casino; highly flexible exhibition halls and a convention centre that can host over 45,000 delegates.
Fig(3.3) Marina bay sands
Fig(3.4) Marina Bay Sands
Skypark is beginning to look like a park with more than 20 trees now planted 200 meters in the air.Closer to the opening, the roof top gardens will be home to 250 trees and 650 plants.
Fig(3.5) The grand arcade trave rse of the MBS hotel
The 340m-long skypark, which will house a 1,2 hectares swimming pools -
equivalent to the size of 10 olympic size swimming pools -, observation decks, gardens, restaurants, spas, and walking trails.it will be cantilevered out some 70m without any support underneath.once completed, the skypark is expected to be a leading tourist spot where one can enjoy a panoramic view of the beaches and downtown singapore.drawing by lim vong marina bay is a bay near central area in the southern part of singapore, and lies to the east of the downtown core. it is an artificial bay and was formed when land reclamation created the marina centre and marina south areas, which form a body of sheltered waters of what was once open sea. This land was reclaimed as part of the long-term strategy for singapore’s growth about 30 years ago, with a view to the downtown core eventually out-growing itself.The reclamation is about more than just increasing land area. The large area of sea which has been embraced by the reclamation has now been isolated from the larger ocean by the building of a dam across the narrow inlet so that, gradually as the singapore river discharges its fresh water load into this area over the next decade or so, it will dilute the sea-water and eventually create a fresh-water reservoir, making singapore politically less dependant on malaysia for its fresh water needs, and creating a great recreational resource in the heart of the city to boot.
Fig(3.6) Marina resort
Fengshui master says the integrated resort has many auspicious elements going for it. The sky park is curved, planes that come around will see a smile from their bird's eyes view. The towers represent three mountains or three warriors guarding the gateway to singapore. Despite fengshui being open to many interpretations, there are rules and principles to the practice, which are guided by the so-called balance of the five elements. its silvery white facade represents metal, while other elements represent fire. wood is in the landscaping and greenery, while water surrounds it.
Fig(3.7) The marina bay sands art and science museum
The lotus shaped art science museum sits at the front of the development. The building's shaped steel frame was among the most difficult parts of all the structural design. However, using software scripting it was possible to analyze this one petal at a time, altering the parameters for each subsequent part. An international team of PERI specialists from singapore and germany created a comprehensive formwork and scaffolding solution for the korean building company, ssang yong engineering & construction. in particular, the skytable large slab tables as well as PERI ACS self-climbing technology have optimised construction progress with reduced crane times. These rised steadily upwards with each floor being completed in only four days.
During construction, three iron structures were propped temporarily at places with the severest inclination beside the post-tension method. Through this, the quantity of temporary work for the main work was reduced by a great deal so that the work could be executed without interference from structures. as a result, constructors succeeded in early march 2009 in connecting at 23F above ground and a height of 70m for the east-side building and the west-side building that were inclined at 52 degrees maximum for towers I, II and III that were rising in the form.
In each case, two asymmetrically curved legs have been positioned against each other which grow together like bridge pylons to form units. although the three hotel towers are still identical with regard to the height and number of floors, the forms of the respective building elements nevertheless have considerable differences in terms of the base width, curvature radius and lateral offset dimension. Furthermore, the individual floors are also offset from one another in a longitudinal direction. Only two cranes per tower were available to the Construction crews, therefore crane independent and crane-saving formwork solutions were used to construct the core walls and floor slabs respectively.
With the help of ACS self-climbing technology and the large-area sky table slab tables, crews were able to finish a complete floor with a standard height of 3 m in only four days. Twelve elevator shafts climbed three cycles in advance and a total of 110 sky table slab tables were required for constructing two complete floors in each case.
Fig(3.8) Construction of deck
Fig(3.9) Construction of deck
Fig(3.10) Construction of deck
Fig(3.11) The marina bay sands construction site
Up to 20 m long and 5 m wide, the 100 m² sky table units could be easily moved with only one crane lift. the innovative moving method ensured that the table was always pulled out of the building in a horizontal position and the operating personnel were always standing in a safe and secure place on the slab edge. Due to the large lowering height of the multiprop props, 20 cm slab offsets and, at the same time, 50 cm parapet wall heights presented no problems. Connected to MRK frames, the tables could be additionally used for the 9 m high intermediate floors.
Fig(3.12) The marina bay sands towers
With the help of ACS, the different-sized shafts with dimensions ranging between 2.30 and 10.10 m, could be shuttered, struck and climbed without the need of a crane. Altogether, five working levels rose at the same time to the next section:
Two platforms for forming, reinforcement work and concreting the shaft walls as well as three finishing platforms for pretensioning the subsequent storey slabs. in combination with CB climbing scaffold and the vario GT 24 girder wall formwork, operational sequences on the construction site were optimized.
The technical team of ssang yong E&C applied the post-tension method that is used mainly in constructing bridges to construct a building inclined at 52 degrees at its highest, which is 10 times more inclined than the leaning tower of pisa. The team adopted a tension method whereby post-tension is installed on a 600 mm thick bearing wall and wire is stretched from inside.
Fig(3.13) Close-up to the marina bay sand middle tower
Fig(3.14) With only one crane lift, 100 square meters of slab formwork could quickly and safely moved.
The project's foundations have had to be massive because of building on marine clay. the team has had to get through the clay to make room for the underground car-parks and railway tunnels which sit beneath the facility. bored piles which go down to over 50m with large bored piles up to 2.8m in diameter have been necessary, typical of many singapore construction projects.
4. OPENING
Fig(4.1) During the 2010 Summer Youth Olympics opening ceremony
Marina Bay Sands was originally planned to be completed in a single phase in 2009, but rising construction costs and the financial crisis forced the company to open it in phases. The first phase's preview opening was further delayed until 27 April 2010, and the official opening was pushed back to 23 June 2010. The rest of the complex remained under construction and was opened after a grand opening on 17 February 2011.On 27 April 2010, Marina Bay Sands had the first of a planned 3 to 4 phase openings. The casino, parts of the conference hall, a segment of the Shoppes, 963 hotel rooms and the event plaza were opened.
The Inter-Pacific Bar Association (IPBA) held the first conference at Marina Bay Sands Convention Centre on 2–5 May 2010, but the event was marred by uncompleted facilities and power failure during a speech. IPBA withheld payment of S$300,000 and was consequently sued by Marina Bay Sands. In June IPBA counter-sued, describing the venue as a complete disaster and that its earlier payments had been imposed by duress, fear and force. An amicable settlement with undisclosed terms was announced in August. On 23 June 2010, the resort had its official opening with a 2-day celebration, this includes the Sands Sky Park, the Event Plaza along Marina Bay, more shops, additional dining options and nightlife offerings, and the rest of the hotel room
5. SPECIALITIES
5.1 CASINO
Marina Bay Sands casino is housed in its own building and offers four levels of gaming in a luxurious, spacious setting. Patrons can enjoy a wide variety of popular table games including roulette, blackjack, baccarat and sic bo, and slot machines featuring the latest games such as video poker, and electronic sic bo and roulette. Premium players and Paiza members have access to exclusive gaming and dining privileges at the casino’s upper two levels, which feature over 30 private gaming rooms.
5.2 SKY PARK
The Sands Sky Park is an architectural masterpiece sitting on top of the three hotel towers at Marina Bay Sands. This 1.2 hectare tropical oasis is longer than the Eiffel Tower is tall and large enough to park four-anda-half A380 jumbo jets. It extends to form the one of the world’s largest public cantilevers. It is 200 meters in the sky. Landscaped gardens are home to 250 trees and 650 plants and 12,400 square meters of space big enough to fit three football fields.
5.3 INFINITY POOL
The Infinity Pool is part of the 380 metre long Sands Sky Park, which spans across the three towers of the Marina Bay Sands complex and covers a total area of 12,000 sq mts. The length of this roof-top deck can be equated to the height of the Eiffel Tower.
The Infinity Pool is one of the world’s largest outdoor pools at three times the length of an Olympic pool and 55 storeys high. The pool creates an illusion of the water extending to the horizon while in reality, the water spills over the edge into a catchment below and is then pumped back into the pool. It has two circulation systems, with the first filtering and heating the water in the main pool and the other, filtering the water in the catch basin and returning it to the upper pool.
Fig(5.1) Infinity Pool
6. CONCLUSION
Marina bay sand is a magnificent destination for entertainment, business, and shopping.
The success of project lies in the fact that the inventiveness of the design was matched by an equally inventive and novel approach developed by engineering and constructon teams.
Delivers once in lifetime experiences.
This landmark building is situated in the heart of Singapore’s central business district.
With a luxury hotel, state of art convention, exhibition facilities, and some of the best shopping &dining in the region.
This is the place to go for world class entertainment.
Bidders were assessed based on four criteria:
• Tourism appeal and contribution
• Architectural concept and design
• Development investment
• Strength of the consortium and partners
Las Vegas Sands initially committed to invest S$3.85 billion in the project, not including the fixed S$1.2 billion cost of the 6,000,000 square feet (560,000 m2) site itself. With the escalating costs of materials, such as sand and steel, and labour shortages owing to other major infrastructure and property development in the country, Sheldon Adelson placed the total cost of the development at $8.0 billion as of July 2009.
2. DESIGN
Fig(2.1) Architectural model showing the layout of the Marina Bay Sands Integrated Resort:
The hotel and Sky Park are in and on the towers in the background, respectively; the shopping mall, theatre and casino are in the long lower building; and the ArtScience Museum is in flower-shaped building in the foreground.
The resort is designed by Moshe Safdie, who says it was initially inspired by card decks. In addition to the casino, other key components of the plan are three hotel towers with 2,560 rooms and suites, a 200,000-square-foot (19,000 m2) Art Science Museum and a convention centre with 1,200,000 square feet (111,000 m2) of space, capable of accommodating up to 45,000 people.
Conceptually, each tower is composed of two slabs of east and west-facing rooms. The double-loaded towers spread at the base forming a giant atrium at the lower levels, and converge as they rise . the tower slabs also give further character to the massing and relate to the site context: the glazed west side faces the city center while the east side is planted with lush bougainvilleas facing the botanical gardens and ocean beyond in plan, as the parcel varies in width, the cross section is decrease from one tower to the next. The three void spaces are connected by one continuous and conditioned glazed, filling the space between the towers with restaurants, retail spaces, and a public thoroughfare. Each tower slab from is also twisted slightly in relation to its pair, creating a dance-like relationship between the two parts and accentuation the slenderness of the buildings, resulting in the appearance of six towers, rather than three.
In addition to the million square meters of built space the project program also called for the development of extensive exterior gardens with swimming pools, jogging paths, and public spaces. As one of the aims of the project had been to minimize the geight of the podium buildings, seeking to reference Singapore’s pastoral hills more than its urban core, the problem emerged that the complex program left no vacant land suitable for these amenities. Creating gardens on top of the roof of the casino and the convention center was studied, however these vast spaces lacked views, overshadowed and overpowered by the adjacent hotel towers. The idea emerged to bridge between the three towers in order to reclaim exterior garden space and create a 2.5-acre park in the sky.
2.1 THE BELLY
The façade of the project which required careful consideration was thus the “belly” of the sky park. Made of more than 9000 silver-painted metal –composite panels, this skin encloses the mega trusses which bridge the buildings at level 55,as well as a multitude of back of house spaces(i.e., large mechanical rooms with water tanks supporting the pools and a network of corridors and offices for hotel operations staff). The geometry of the sky park began with a platonic torpid form, which was then further shaped to streamline the cross sections of the building. The resulting surface was then regularized and panelized using a computer script, triangulation the façade into simple shapes, the shapes were water-jet cut from flat sheet panels and shipped to the building site in containers pre-designed to be lifted to the top levels of the building.
Once on top of the building, the panels were installed via temporary aluminum frame under slung mobile gantries which traveled on a permanent track of steel rails. The gantry system track serves double day as a building maintenance unit, therefore the track was designed to be hidden within the reveal pattern of the facade panels.
3. CONSTRUCTION
Fig(3.1) When construction started in 2007.
Fig(3.2) Marina bay sands
In May of 2006, after a highly-competitive bidding process, the Singapore government selected Las Vegas sands corp. to build the country's first integrated resort property. It will be one of only two resort-casino properties in the South East Asian city-state and will operate as such for a period of 30 years. the gigantic complex complete with three 60-story hotel towers with 3 stories underground will house 2,600 hotel rooms / suites and a 4,000 car garage; topped by a two acre sky park bridging across the towers consisting of a garden, swimming pool, jogging paths, spas; ‘floating’ crystal pavilions; on the promontory a lotus-shaped museum; a grand, a multi-leveled retail arcade for international luxury brands. Celebrity chef restaurants; an outdoor event plaza; entertainment theaters and night clubs plus a Las Vegas-style casino; highly flexible exhibition halls and a convention centre that can host over 45,000 delegates.
Fig(3.3) Marina bay sands
Fig(3.4) Marina Bay Sands
Skypark is beginning to look like a park with more than 20 trees now planted 200 meters in the air.Closer to the opening, the roof top gardens will be home to 250 trees and 650 plants.
Fig(3.5) The grand arcade trave rse of the MBS hotel
The 340m-long skypark, which will house a 1,2 hectares swimming pools -
equivalent to the size of 10 olympic size swimming pools -, observation decks, gardens, restaurants, spas, and walking trails.it will be cantilevered out some 70m without any support underneath.once completed, the skypark is expected to be a leading tourist spot where one can enjoy a panoramic view of the beaches and downtown singapore.drawing by lim vong marina bay is a bay near central area in the southern part of singapore, and lies to the east of the downtown core. it is an artificial bay and was formed when land reclamation created the marina centre and marina south areas, which form a body of sheltered waters of what was once open sea. This land was reclaimed as part of the long-term strategy for singapore’s growth about 30 years ago, with a view to the downtown core eventually out-growing itself.The reclamation is about more than just increasing land area. The large area of sea which has been embraced by the reclamation has now been isolated from the larger ocean by the building of a dam across the narrow inlet so that, gradually as the singapore river discharges its fresh water load into this area over the next decade or so, it will dilute the sea-water and eventually create a fresh-water reservoir, making singapore politically less dependant on malaysia for its fresh water needs, and creating a great recreational resource in the heart of the city to boot.
Fig(3.6) Marina resort
Fengshui master says the integrated resort has many auspicious elements going for it. The sky park is curved, planes that come around will see a smile from their bird's eyes view. The towers represent three mountains or three warriors guarding the gateway to singapore. Despite fengshui being open to many interpretations, there are rules and principles to the practice, which are guided by the so-called balance of the five elements. its silvery white facade represents metal, while other elements represent fire. wood is in the landscaping and greenery, while water surrounds it.
Fig(3.7) The marina bay sands art and science museum
The lotus shaped art science museum sits at the front of the development. The building's shaped steel frame was among the most difficult parts of all the structural design. However, using software scripting it was possible to analyze this one petal at a time, altering the parameters for each subsequent part. An international team of PERI specialists from singapore and germany created a comprehensive formwork and scaffolding solution for the korean building company, ssang yong engineering & construction. in particular, the skytable large slab tables as well as PERI ACS self-climbing technology have optimised construction progress with reduced crane times. These rised steadily upwards with each floor being completed in only four days.
During construction, three iron structures were propped temporarily at places with the severest inclination beside the post-tension method. Through this, the quantity of temporary work for the main work was reduced by a great deal so that the work could be executed without interference from structures. as a result, constructors succeeded in early march 2009 in connecting at 23F above ground and a height of 70m for the east-side building and the west-side building that were inclined at 52 degrees maximum for towers I, II and III that were rising in the form.
In each case, two asymmetrically curved legs have been positioned against each other which grow together like bridge pylons to form units. although the three hotel towers are still identical with regard to the height and number of floors, the forms of the respective building elements nevertheless have considerable differences in terms of the base width, curvature radius and lateral offset dimension. Furthermore, the individual floors are also offset from one another in a longitudinal direction. Only two cranes per tower were available to the Construction crews, therefore crane independent and crane-saving formwork solutions were used to construct the core walls and floor slabs respectively.
With the help of ACS self-climbing technology and the large-area sky table slab tables, crews were able to finish a complete floor with a standard height of 3 m in only four days. Twelve elevator shafts climbed three cycles in advance and a total of 110 sky table slab tables were required for constructing two complete floors in each case.
Fig(3.8) Construction of deck
Fig(3.9) Construction of deck
Fig(3.10) Construction of deck
Fig(3.11) The marina bay sands construction site
Up to 20 m long and 5 m wide, the 100 m² sky table units could be easily moved with only one crane lift. the innovative moving method ensured that the table was always pulled out of the building in a horizontal position and the operating personnel were always standing in a safe and secure place on the slab edge. Due to the large lowering height of the multiprop props, 20 cm slab offsets and, at the same time, 50 cm parapet wall heights presented no problems. Connected to MRK frames, the tables could be additionally used for the 9 m high intermediate floors.
Fig(3.12) The marina bay sands towers
With the help of ACS, the different-sized shafts with dimensions ranging between 2.30 and 10.10 m, could be shuttered, struck and climbed without the need of a crane. Altogether, five working levels rose at the same time to the next section:
Two platforms for forming, reinforcement work and concreting the shaft walls as well as three finishing platforms for pretensioning the subsequent storey slabs. in combination with CB climbing scaffold and the vario GT 24 girder wall formwork, operational sequences on the construction site were optimized.
The technical team of ssang yong E&C applied the post-tension method that is used mainly in constructing bridges to construct a building inclined at 52 degrees at its highest, which is 10 times more inclined than the leaning tower of pisa. The team adopted a tension method whereby post-tension is installed on a 600 mm thick bearing wall and wire is stretched from inside.
Fig(3.13) Close-up to the marina bay sand middle tower
Fig(3.14) With only one crane lift, 100 square meters of slab formwork could quickly and safely moved.
The project's foundations have had to be massive because of building on marine clay. the team has had to get through the clay to make room for the underground car-parks and railway tunnels which sit beneath the facility. bored piles which go down to over 50m with large bored piles up to 2.8m in diameter have been necessary, typical of many singapore construction projects.
4. OPENING
Fig(4.1) During the 2010 Summer Youth Olympics opening ceremony
Marina Bay Sands was originally planned to be completed in a single phase in 2009, but rising construction costs and the financial crisis forced the company to open it in phases. The first phase's preview opening was further delayed until 27 April 2010, and the official opening was pushed back to 23 June 2010. The rest of the complex remained under construction and was opened after a grand opening on 17 February 2011.On 27 April 2010, Marina Bay Sands had the first of a planned 3 to 4 phase openings. The casino, parts of the conference hall, a segment of the Shoppes, 963 hotel rooms and the event plaza were opened.
The Inter-Pacific Bar Association (IPBA) held the first conference at Marina Bay Sands Convention Centre on 2–5 May 2010, but the event was marred by uncompleted facilities and power failure during a speech. IPBA withheld payment of S$300,000 and was consequently sued by Marina Bay Sands. In June IPBA counter-sued, describing the venue as a complete disaster and that its earlier payments had been imposed by duress, fear and force. An amicable settlement with undisclosed terms was announced in August. On 23 June 2010, the resort had its official opening with a 2-day celebration, this includes the Sands Sky Park, the Event Plaza along Marina Bay, more shops, additional dining options and nightlife offerings, and the rest of the hotel room
5. SPECIALITIES
5.1 CASINO
Marina Bay Sands casino is housed in its own building and offers four levels of gaming in a luxurious, spacious setting. Patrons can enjoy a wide variety of popular table games including roulette, blackjack, baccarat and sic bo, and slot machines featuring the latest games such as video poker, and electronic sic bo and roulette. Premium players and Paiza members have access to exclusive gaming and dining privileges at the casino’s upper two levels, which feature over 30 private gaming rooms.
5.2 SKY PARK
The Sands Sky Park is an architectural masterpiece sitting on top of the three hotel towers at Marina Bay Sands. This 1.2 hectare tropical oasis is longer than the Eiffel Tower is tall and large enough to park four-anda-half A380 jumbo jets. It extends to form the one of the world’s largest public cantilevers. It is 200 meters in the sky. Landscaped gardens are home to 250 trees and 650 plants and 12,400 square meters of space big enough to fit three football fields.
5.3 INFINITY POOL
The Infinity Pool is part of the 380 metre long Sands Sky Park, which spans across the three towers of the Marina Bay Sands complex and covers a total area of 12,000 sq mts. The length of this roof-top deck can be equated to the height of the Eiffel Tower.
The Infinity Pool is one of the world’s largest outdoor pools at three times the length of an Olympic pool and 55 storeys high. The pool creates an illusion of the water extending to the horizon while in reality, the water spills over the edge into a catchment below and is then pumped back into the pool. It has two circulation systems, with the first filtering and heating the water in the main pool and the other, filtering the water in the catch basin and returning it to the upper pool.
Fig(5.1) Infinity Pool
6. CONCLUSION
Marina bay sand is a magnificent destination for entertainment, business, and shopping.
The success of project lies in the fact that the inventiveness of the design was matched by an equally inventive and novel approach developed by engineering and constructon teams.
Delivers once in lifetime experiences.
This landmark building is situated in the heart of Singapore’s central business district.
With a luxury hotel, state of art convention, exhibition facilities, and some of the best shopping &dining in the region.
This is the place to go for world class entertainment.
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