construction dewatering

Construction Equipments- A project report on

Construction Dewatering…

Team members…

• Tote Vipul• Salunkhe Harish• Parab Shubham• Kakamare Mrinali • Katkam Rahul• Thorat Omkar• Jadhav Yatiraj

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Definitions...

Dewatering may be defined as separation of water from soil. OR

Dewatering may also be defined as taking the water out of the particular construction problem/ site.

Permanent ground water control is the permanent stoppage of flow of water within the ground.

Difference...

Construction dewatering• It is separation or taking out

water from a particular construction site.

• Purpose of dewatering is to control sub - surface hydrologic movement in such a way so as to permit construction activities in dry environment.

Permanent ground water control• It is permanent stoppage of

flow of water within the ground.

• Purpose of permanent ground water control is to prevent entry of water in underground constructions during and even after construction activities are over.

Difference...

Construction dewatering• It involves temporary

lowering of ground water table at the construction site to permit sub - surface constructions.

• It is required only at the time of construction.

• It is a dynamic process.• Eg. During construction of

foundations, lift pits etc.

Permanent groundwater control• It blocks the flow of ground

water, without interfering with ground water table.

• It is required during and even after construction.

• It is a static process.• Eg. Areas of mining,

tunnels, basement, subways etc.

Groundwater Control…• Control of ground water always referred to

temporary and permanent exclusion.• Temporary exclusion: lowering of the

water table and within the economic depth range of 1500mm using subsoil drainage methods, for deeper treatment a pump or pumps are usually used.• Permanent exclusion: the insertion of an

impermeable barrier to stop the flow of water within the ground.

Groundwater Control…

Groundwater Control…

• Water can be classified by its relative position to or within the ground.

Groundwater Control…• Problems of water in the subsoil:• A high water table could cause flooding

during wet period.• Subsoil water can cause problems during

excavation works by its natural tendency to flow into the voids created by the excavation activities.• It can cause an unacceptable humidity level

around finished building and structures.

Dewatering techniques…Pumping methods

Sump pumping.

Shallow well pumps.

Well points.

Deep wells.

Exclusion methods

Ground freezing

Sheet freezing

Slurry trench cut-off walls with bentonite.

Impervious soil barriers

Grounted cut-offs.

Construction Dewatering…

Sump and Sump pumping.

• Water is collected in deeper part of excavations (called sumps) and pumped away.

Sump and Sump pumping…

ADVANTAGES-• Simple and cheap method of dewatering.DISADVANTAGES-• The sump takes up space within the

excavation.• Can lead to water pollution problems silt-

laden water.

Construction Dewatering…Shallow Wells• These are suitable

for sandy gravels and water-bearing rocks for depth not in excess of 5 meters and principle upon which they operate is similar to that of well point system.

Shallow Wells

ADVANTAGES• It is used to extract large quantities of water

from a single hole.DISADVANTAGES• The limiting depth to which this method is

employed is about 8 m.

Construction Dewatering…Well point system.• A line or ring of small

diameter shallow wells (called well points) installed at close spacing (1 to 3 m centres) around the excavation.

• Commonly used for dewatering of pipeline trenches.

Well point system

ADVANTAGES-• Can be very flexible and effective method of

dewatering in sands or sands and gravel.DISADVANTAGES-• Drawdown limited to 5 to 6 m below level of

pump due to suction lift limits.

Construction Dewatering…

Deep wells system• Wells are drilled at wide

spacing (10 to 60 m between wells) to form a ring around the outside of the excavation

• An electric submersible pump is installed in each well.

Deep wells system

ADVANTAGES• Effective in a wide range of ground conditions,

sands, gravels, fissured rocks.DISADVANTAGES-• Drawdown limited only by wells depth and

soil stratification.

Permanent groundwater Control…• Ground Freezing Techniques• Slurry Trench Walls• Steel sheet Piling• Thin Grouted Membranes• Contiguous Piling• Diaphragm Wall• Precast Concrete Diaphragm Walls• Grouting Methods

Ground Water control…

Ground freezing

Ground freezing…

Permanent groundwater Control…Ground Freezing• Principle: To change the water in the soil

into a solid wall of ice.• Seepage into a excavation or shaft can be

prevented by freezing the surrounding soil. However, freezing is expensive and requires expert design, installation, and operation.

Permanent groundwater Control…Ground Freezing Techniques• Suitable for all types of saturated soils and

rock and for soils with a moisture content in excess of 8% of the voids.• The basic principle is to insert into the

ground a series of freezing tubes to form an ice wall thus creating an impermeable barrier.• Takes time to develop and the initial costs

are high.

Permanent groundwater Control…Ground Freezing Techniques• The freezing tubes can be installed vertically for

conventional excavations and horizontally for tunneling works.

• Normally using magnesium chloride and calcium chloride with a temperature of -15 to -25 degree Celsius which takes 10 to 17 days to form an ice wall 1m thick.

• Liquid nitrogen could be used as the freezing medium to reduce the initial freezing period if the extra cost can be justified.

Ground freezing

ADVANTAGES• Ground freezing is an extremely versatile method

for temporary ground improvement or cutoff. • It is applicable to the entire range of soils,

provided that the soil is near saturation or completely saturated.

• It is also applicable to difficult ground conditions including large boulders and cobbles, or debris-rich non-engineered fills.

Ground freezing

DISADVANTAGES• Ground freezing is a highly energy intensive

process, requiring refrigeration of massive quantities of soil over extended periods of time, which is very expensive.

Ground freezing

DISADVANTAGES• Ground freezing requires plenty of monitoring:

brine temperatures, soil temperatures, deflections of adjacent or nearby structures, heaving and settlement at the ground surface, groundwater salinity, pressures within freeze pipes (leak detection), frozen wall thickness, and the location and dimensions of possible windows within the frozen wall, among other site specific measurements.

Permanent groundwater Control…

Slurry trench walls• These are used to contain or

divert contaminated groundwater from drinking water intake, divert uncontaminated groundwater flow from contaminated sites and or provide a barrier for the groundwater treatment system

Slurry trench cutoff walls

Soil-bentonite

Cement –bentonite

Soil-cement bentonite

Slurry trench wall

ADVANTAGES• This is the only method that permits the visual

inspection of key material.• Depth up to 200ft can be reached.DISADVANTAGES• Large excavation site, excavated soil storage,

slurry mixing, material storage etc.• It is hard to ensure integrity of the wall.

Permanent groundwater Control…

Cutoff wall• Vertical barriers or “cutoff walls” are often

used in geo-environmental engineering to control the spread of contaminants.

• Cutoff curtains can be used to stop or minimize seepage into an excavation where the cutoff can be installed down to an impervious formation.

Cut off wall construction…

Permanent groundwater Control…Steel sheet piling• Steel sheet piles are long structural sections with a

vertical interlocking system that creates a continuous wall. The walls are most often used to retain either soil or water.

Steel sheet piling

ADVANTAGES• It is extremely light weight and makes it easier

to lift and handle.• Steel sheeting is reusable and recyclable.• The pile length is easily adaptable and can be

welded or bolted to make it work

Steel sheet piling

DISADVANTAGES• It is extremely difficult to install steel sheeting

in soil that is rocky or has large boulders. • Driving the sheets may cause neighborhood

disturbance.

Permanent groundwater Control…Grouted barrier walls• It consists of injecting a fluid material at a certain

pressure into soil or rock in order to decrease the permeability and strengthen the formation.

• Grout walls are typically formed by overlapping grout columns which form a single row.

Grouted barrier walls

ADVANTAGES • Depths greater than 200 ft can be achieved.• Little waste material is generated.DIS-ADVANTAGES• This configuration involves more cost.• Relatively high hydraulic conductivity values

are obtained.

Permanent groundwater Control…Thin Grouted Membranes• Work as permanent curtain or cut-off non

structural walls or barriers inserted in the ground to enclose the proposed excavation area.• Suitable for silts and sands and can be

installed rapidly but they must be adequately supported by earth on both sides.• The only limitation is the depth to which the

formers can be driven and extracted.

Permanent groundwater Control…

Permanent groundwater Control…Contiguous Piling• Forms a permanent structural wall of

interlocking bored piles.• Alternate piles are bored and cast by

traditional methods after which the interlocking piles are bored using a special auger or cutter.• To ensure a complete interlock of all piles over

the entire length may be difficult therefore the exposed face of the piles is usually covered with a mesh or similar fabric and face with rendering or sprayed concrete.

Permanent groundwater Control…Contiguous Piling• Suitable for most types of subsoil and has the

main advantages of being economical on small and confined sites; capable of being formed close to existing foundations and can be installed with the minimum of vibration and noise.• Suitable for structures such as basements,

road underpasses and underground car parks.

Contiguous Piling…

Permanent groundwater Control…Diaphragm Wall• Are structural concrete walls which can be

cast in-situ or using pre-cast concrete methods.• Suitable for most subsoil and their

installation generates only a small amount of vibration and noise.• The high cost of these walls makes them

uneconomic unless they can be incorporated into the finished structure.• Normally use for basements, underground

carparks and similar structures.

Diaphragm Wall…

Permanent groundwater Control…Pre-cast Concrete Diaphragm Wall• Have some applications with in-situ concrete

diaphragm walls.• Lack in design flexibility.• The panel or post panel units are installed in a

trench filled with a special mixture of bentonite and cement with a retarder to control the setting time.• This mixtures ensures that the joints between

the wall components are effectively sealed.• To provide stability, the panels of posts are tied

to the retained earth with ground anchors.

Pre - cast diaphragm wall…

Permanent groundwater Control…

Grouting Methods• Are used to form a curtain or cut-off wall in

high permeability soils where pumping methods could be uneconomic.• The curtain walls formed by grouting methods

are non-structural therefore adequate earth support will be required and in some cases this will be a distance of at least 4m from the face of proposed excavation.

Permanent groundwater Control…Grouting Methods• Grout mixtures are injected into the soil by

pumping the grout at high pressure through special injection pipes inserted in the ground.

• The pattern and spacing of the injection pipes will depend on the grout type and soil conditions.

• Grout types:• Cement grouts• Chemical grouts• Resin grouts

Grouting Methods…

240m lengthx150mwidthx21m depth

Equivalent Radius and Influence Range

Equivalent radius of excavation r= √800ft * 500ft/√ = 357ft 112.5m Height of water level in well h = 160 – 70 – 5 = 85ft 25.5mInfluence range R=C’(H-hw)√k =3000*(140-85)*0.3*√9.2*10^-5 =2200ft 670mC= 3000 for wells

Layout of deep wells

Rate of flow in wells

Multiple wells For circular arrangement of wells Q = 3.14k(H^2-h^2) / ln R – ln r =3.14 * 0.00181*(140^2 – 85^2) / ln 2200 - ln 357 = 38.7 cubic ft /min = 290gal / min = 290/8 = 36.3 gal/min per well

Multiple Wells

Deep wel l size: 4” dia. for 36.3 gal/min Header pipe: 4” dia. for 5*36.6 gal/min=181 gal/min

Discharge pump: 4” dia. Pump for 290 gal/min

THANK YOU…Questions please…