DEWATERING METHODS IN EXCAVATION
- 2. Dewatering methods • Many excavations for basement construction will encounter groundwater. • If not suitably managed and controlled, groundwater can cause problems for excavation and basement construction. • Adequate control of groundwater is important, and is a necessary part of a well planned basement construction project. • Groundwater control methods are classified into two main types: Exclusion or Pumping.
- 3. GROUNDWATER PROBLEMS WHEN CONSTRUCTING BASEMENTS • If an excavation is made without suitable groundwater control various problems can result: • The excavation may flood as a result of groundwater inflows from water-bearing layers of soil or rocks. • High pore water pressures in batter slopes at the sides of the excavation may lead to instability or seepage erosion of batter slopes. • Groundwater uplift pressures beneath the floor of an excavation can give the risk of a base heave or piping failure in the base of the excavation. • Groundwater pressures can cause excessive hydrostatic loads on excavation retaining structures such as concrete pile walls.
- 4. GROUNDWATER CONTROL BY EXCLUSION… • Groundwater pumping can be reduced or avoided by installing a very low permeability physical cut-off wall to exclude groundwater from the excavation. If a low permeability stratum (such as a clay layer) exists at shallow depth beneath the excavation then the cut- off wall can penetrate down to that stratum to create a full cut-off. • Several different geotechnical methods can be used to form cut-off walls: • Steel sheet piles • Concrete secant pile walls • Concrete diaphragm walls • Slurry walls and trenches • Grout curtains (including permeation grouting and jet grouting) • Freeze walls (produced by artificial ground freezing) • Compressed air (for tunnels and shafts). • Concrete contiguous pile walls leave a gap between the piles and do not form an effective cut-off to groundwater flow.
- 5. … GROUNDWATER CONTROL BY EXCLUSION • Groundwater control by exclusion is widely used in situations when there is a risk of external impacts (e.g. settlement of nearby structures or detrimental effects on other water users) caused by groundwater lowering. • An exclusion system can, if carried out effectively and if ground conditions are favorable, minimize any groundwater lowering outside the dewatered site area.
- 6. GROUNDWATER CONTROL BY PUMPING… • Groundwater control by pumping involves pumping groundwater from an array of wells or sumps with the aim of temporarily lowering groundwater levels to allow excavation to be carried out in dry and stable conditions. • Groundwater control by pumping is also known as Groundwater Lowering, Construction Dewatering or simply Dewatering
- 7. …GROUNDWATER CONTROL BY PUMPING • The most common types of groundwater control by pumping are listed below • Well points • Shallow suction wells • Relief wells • Deep wells • Eductor wells • On a given site these techniques are not readily interchangeable. Each technique has a relatively narrow range of application relative to two key parameters: the drawdown required and soil permeability.
- 8. Well Point Dewatering System… • A well point dewatering system consists of a series of shallow wells, known as well points, which are installed at a pre-determined depth and appropriate spacing around an excavation. • The well points are connected to the surface, via a riser pipe, and in turn, connected to a common header main pipe through a flex bow. • This flex bow incorporates an adjustable push fit valve which allows the control of air and water entering the system, known as trimming, to give a clear view of what is being pumped. • The header main pipe is connected to a well point dewatering pump and then discharged to the designated point.
- 9. …Well Point Dewatering System • Well point Dewatering Systems are extremely versatile and can be used for a wide range of applications. • They can be used to lower and control groundwater levels in excavations, in order to create a dry and stable working environment, and are also suitable for shallow foundations and trench works.
- 10. Water Proofing methods • The application of a layer of impervious material which prevents water from penetrating. Making the structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water. • Waterproofing in building structures is required at various locations - • Basement of the building, which is directly in contact with the earth surface. This area is very much prone to seepage from the surrounding to the building structure. • Kitchen, Toilet and Bathroom, this is the place where water is continuously used for utility purpose and bathing. Always critical location for seepage. • Balcony areas, at this location water enter in monsoon season, or washing of cloths and other utility works. • Roof /Terrace/Podium of the building is always open for monsoons and other seepage. • Swimming Pool, it is filled with water and had major chances of leakage. • Water Tank, any leakge in tank can damage the terrace and seep into our rooms.
- 11. Waterproofing Methods… • Cementitious Waterproofing • This method is very commonly used for wet areas such as toilets and bathrooms. This is a semi-flexible or rigid type of waterproofing and not exposed to weathering or sunlight. Tape Crete material is commonly used for waterproofing and easy to apply. • Brick Bat Coba Waterproofing • Laying of soaked brick bats (Pieces) over fresh mortar, which acts as a insulation for thermal comfort . Surface brick layer thickness in between 70mm to 150 mm (Avg. thickness of 110mm) . • Bituminous Waterproofing • This method is basically coating of a flexible asphalt layer or in general practice we call it coal-tar. • Injection Grouting • A low viscous injection resin for water proofing application in low to medium infiltration. It can be used in bricks, concrete and other structures, as basement, tunnels etc., • Membrane Type Waterproofing • There are two methods , one is Torch seal and other is Self-adhesive membrane waterproofing. Torch seal is used for podium, external development etc., and woks at site. This is very common method used for waterproofing at site. It is more durable and cost effective method compared to Self – adhesive membrane.
- 12. Waterproofing Methods • Polyurethane Liquid Membrane Method • This is expensive method and less used at site. It is very flexible membrane carefully applied to avoid peeling after some time. Used for roof /terrace and the areas exposed to weathering. • EPDM Waterproofing Membrane • It is synthetic rubber single layer flexible membrane, durable in cold and hot weather. • Liquid Roofing with bitumen membrane coating • Excellent adhesion to all kind of surfaces (metal, concrete etc.,) and chemical resistant. It saves time and spray application allows seamless coverage and long lasting waterproofing solution. Rapid curing even in winter weather. • Waterproofing Products • Tape Crete, APP membrane, Epoxy and PU Resin, Nitobond, EPDM membrane, Pidicrete URP ,Dr Fixit 101 LW+, Dr Fixit Roofseal , AcryFlex 2k strong etc., • Waterproofing Brands • CICO, Sika, Fosroc, Dr. Fixit, Redwop, MYK Schomburg , Chowgule etc.,
- 13. Pumps • A pump is a device that moves fluids, by mechanical action. • Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift, displacement, and gravity pumps. • Pumps operate by some mechanism (typically reciprocating or rotary), and consume energy to perform mechanical work moving the fluid. • Mechanical pumps serve in a wide range of applications such as pumping water from wells, aquarium filtering, pond filtering and aeration, in the car industry for water-cooling and fuel injection, in the energy industry for pumping oil and natural gas or for operating cooling towers and other components of heating, ventilation and air conditioning systems • When a casing contains only one revolving impeller, it is called a single-stage pump. When a casing contains two or more revolving impellers, it is called a double- or multi-stage pump.
- 14. Types of pump • Centrifugal pumps Centrifugal pumps contain a rotating impeller which creates a vortex that sucks air out of the hose. Water rises to the pump as a result of atmospheric pressure. Priming involves filling the pump casing with liquid before the pump is started. This is done to prevent the casing becoming filled with gases that inhibit pumping. • Displacement pumps Displacement pumps can be either reciprocating or diaphragm pumps. Reciprocating pumps work by the action of a piston or ram moving in a cylinder. Water is drawn into the cylinder when the piston moves in one direction, and pushed out at the rear. These have high efficiency and reliability, and are able to pump against varying heads at a uniform rate. Diaphragm pumps work by drawing water into a cylinder in which a flexible diaphragm is raised and lowered. The downward motion of the diaphragm pushes the water out through the delivery pipe.
- 15. Types of pump • Submersible pumps Submersible pumps can be used for lowering groundwater or removing water from a deep sump. The pump unit is suspended from the rising main or, if a flexible hose is used, from a wire cable. The pump consists of a centrifugal unit and motor mounted in a single cylindrical unit with a space between pump and casing which allows the water to move upwards to the rising main. • Air lift pumps Air lift pumps consist, not of moving parts, but of a long vertical pipe connected to a supply of compressed air. The air carries the water up the pipe to the discharge area.
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