TUNNEL BORING MACHINE (TBM)

•TBM is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. •They can bore through anything from hard rock to sand. Tunnel diameters can range from a metre to 19.25 metres to date. •Tunnels of less than a metre or so in diameter are typically done using trenchless construction methods or horizontal directional drilling rather than TBMs.

•TBMs are enormous, multimillion-dollar pieces of equipment with a circular plate on one end. •The circular plate is covered with disk cutters -- chisel-shaped cutting teeth, steel disks or a combination of the two.• As the circular plate slowly rotates, the disk cutters slice into the rock, which falls through spaces in the cutting head onto a conveyor system. •The conveyor system carries the muck to the rear of the machine. Hydraulic cylinders attached to the spine of the TBM propel it forward a few feet at a time. •TBMs don't just bore the tunnels -- they also provide support. As the machine excavates, two drills just behind the cutters bore into the rock. Then workers pump grout into the holes and attach bolts to hold everything in place until the permanent lining can be installed. The TBM accomplishes this with a massive erector arm that raises segments of the tunnel lining into place.

BUILDING CONSTRUCTION- TBMNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

DEWATERING

•Dewatering used to describe removal or draining groundwater or surface water from a riverbed, construction site, caisson, or mine shaft, by pumping or evaporation. On a construction site, this dewatering may be implemented before subsurface excavation for foundations, shoring, or cellar space to lower the water table. This frequently involves the use of submersible "dewatering" pumps, centrifugal pumps, application of vacuum to well points.•The process of Dewatering can be defined as – puming from wells or sumps to temporarily lower groundwater level, to allow excavation to be made in dry & stable conditions below natural ground level.

BUILDING CONSTRUCTION- DEWATERINGNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

DEWATERING PUMPS WELL POINT DEWATEING SYSTEM EMERGENCY DEWATEING SYSTEM

VERTICAL WELL DEWATEING SYSTEM (SHAFT) EDUCATOR DEWATEING SYSTEM HORIZONTAL DEWATEING SYSTEM

GROUNDWATER CONTROL•Groundwater control describes the range of engineering techniques used to allow engineering excavations and mines to the constructed below groundwater level in workably dry, stable and safe conditions.•There are two main types of groundwater control techniques: Methods that use cut-off walls and other barriers to exclude water from the excavation (known as exclusion techniques). Methods that deal with groundwater by pumping (known as construction dewatering techniques).•There are a wide range of groundwater control methods and dewatering techniques available. The selection of the best method will depend on the geology and hydrogeology of the location, the available space and facilities and the environmental constraints at the site.Cut-off walls are used to exclude groundwater from an excavation, to minimise the requirement for dewatering pumping. Typically, the method involves installing a very low permeability physical cut-off wall or barrier around the perimeter of the excavation to prevent groundwater from entering the working area. Most commonly, the cut-off is vertical and ideally penetrates down to a very low permeability stratum (such as a clay or unfractured bedrock) that forms a basal seal for the excavation. The selection of a exclusion method used to form a cut-off barrier will depend on the conditions and constraints on a given project. Primary constraints are desired depth of wall, ground conditions, geometry of wall (some methods can be used horizontally or inclined to the vertical, while others are limited to vertical applications), and whether the barrier is intended to be permanent or temporary.

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

DEWATERING BY EXCLUSION

DEWATERING BY PUMPING

Dewatering involves controlling groundwater by pumping, to locally lower groundwater levels in the vicinity of the excavation.The simplest form of dewatering is sump pumping, where groundwater is allowed to enter the excavation where it is then collected in a sump and pumped away by robust solids handling pumps. Sump pumping can be effective in many circumstances, but seepage into the excavation can create the risk of instability and other construction problems.

The pump set for this application uses a 150-millimeter (6-inch) centrifugal pump powered by a 224-kilowatt (190-horsepower) diesel engine.

To prevent significant groundwater seepage into the excavation and to ensure stability of excavation side slopes and base it may be necessary to lower groundwater levels in advance of excavation. This is known as ‘pre-drainage’.Pre-drainage methods include:Deep wells Wellpoints Eductors Vacuum wells Horizontal wells

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

DEEP WELL TECHNIQUES

•A deep well system consists of an array of bored wells pumped by submersible pumps. Pumping from each well lowers the groundwater level and creates a cone of depression or drawdown around itself. Several wells acting in combination can lower groundwater level over a wide area beneath an excavation. Because the technique does not operate on a suction principle, large draw downs can be achieved, limited only by the depth of the wells, and the hydrogeological conditions.•The wells are generally sited just outside the area of proposed excavation, and are pumped by electric submersible pumps near the base of each well. Water collection pipes, power supply generators, electrical controls and monitoring systems are located at the surface.

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

Deep Well - Electric Submersible Pump System

•The technique is particularly suited to deeper excavations or where artesian groundwater pressures threaten base stability. The system is reliable and the wide spacing of the wells reduces access restrictions to a minimum.

WELL POINT DEWATERING

Wellpoint dewatering is widely used for excavations of shallow depths, especially for pipeline trench excavations. In appropriate ground conditions a wellpoint system can be installed speedily and made operational rapidly. A typical wellpoint system consists of a series of small diameters wells (known as wellpoints) connected via a header pipe, to the suction side of a suitable wellpoint pump. The pump creates a vacuum in the header pipe, drawing water up out of the ground. For long pipeline trenches, horizontal wellpoints may be installed by special trenching machines.Wellpoints are typically installed in lines or rings around the excavation, and are pumped by diesel or electrically powered pumps, with associated header mains, water discharge pipes, power supply generators, electrical controls and monitoring systems.

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

EDUCTORS / EJECTORS WELLS DEWATERING

•The eductor system (also known as the ejector system) is specialist technique used to control pore water pressure in low permeability soils such as very silty sands, silts, or clays with permeable fabric. Eductors are typically used to help stabilise the side slopes and base of excavations in soils that would be difficult to dewater with wellpoints or deep wells.•Eductors have the advantage that they can allow vacuum-assisted drainage, to draw water out of poorly draining fine-grained soils. The system works by circulating high pressure water (from a tank and supply pumps at ground level) down the well to a small-diameter nozzle and venturi located in the eductor in each well. This generates a vacuum of up to 9.5 m of water at the level of the eductor. The vacuum draws groundwater into the well from where it is piped back to ground level via a return riser pipe and through the reservoir tank back to the supply pump for recirculation.

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

EDUCTOR PUMP SETUPMore than 100 eductor wells are commonly activated by a single pumping station . The volumes of water which can be pumped by each system are generally low, typically less than 200 gpm.

HORIZONTAL WELL DEWATERING

•Horizontal wells for dewatering are of two principal types: Horizontal drains installed by specialist trenching machines Horizontally directionally drilled (HDD) wells.Horizontal drains installed by specialist trenching machinesThis technique uses a horizontal flexible perforated pipe, pumped by a wellpoint pump, to lower groundwater levels. The perforated pipe is installed by a special trenching machine. One end of the pipe is unperforated and is brought to the surface and connected to a wellpoint suction pump. The method can be very effective for dewatering long pipeline excavations.Horizontally directionally drilled (HDD) wells. HDD wells are used where groundwater must be abstracted from beneath inaccessible areas or from areas where the disruption associated with surface drilling is undesirable. Applications for HDD wells include:Installation of permanent dewatering systems beneath existing built up (urban) environments.Pumping for remediation of contaminated groundwater without the risks of cross-contamination associated with vertical drilling Dewatering for tunnel construction Recharge wells to re-inject water as part of artificial recharge schemes.

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

HORIZONTAL WELL DEWATERING

•Horizontal Dewatering drainage makes it possible to lower ground water levels in such a short time that the groundwork for sewer’s, building excavations, cables and pipes can be done in the dry, without any risks in a short space of time.•It is achieved by special designed trenching machine systems to drain the ground water from the soil. Pumping out the ground water lowers the water table and modifies the subsurface flow pattern. The system can be installed accurately by means of laser depth control.•PRINCIPLE OF HORIZONTAL DEWATERINGThe principle of Horizontal Dewatering is simple. A trench is dug by means of a specially constructed dewatering trenching machine. During the digging a flexible synthetic filter pipe is inserted in this trench directly behind the digging chain, through a steel case. The beginning of the flexible pipe is not perforated and is dug in from the surface level.When it has reached the desired depth the non perforated pipe becomes a horizontal perforated pipe that is connected to a vacuum pump. The groundwater is sucked through the perforations because of the under pressure. Then it is pumped up through the blind pipe by the vacuum pump. In this way it can be controlled and drained off.

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

TRENCHING MACHINE SYSTEM HORIZONTAL DEWATERING SYSTEM

RELIEF/ ARTESIAN WELL DEWATERING

•Relief wells (also known as pressure relief wells or bleed wells) are used to reducing pore water pressures in confined aquifers or in stratified ground conditions. The relief wells are typically drilled before the excavation has extended below the piezometric level in the aquifer. As excavation continues, the wells will begin to overflow, relieving pore water pressures in the aquifer and ensuring stability. The water flowing from the relief wells is typically disposed of by sump pumping. A granular drainage blanket and network of drains can be used to direct water to the sumps and prevent ponding in the excavation.

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

•Pressure relief wells are a method of controlling excess pore water pressures in confined aquifers.•The artesian or sub-artesian head within a confined aquifer can be dangerous if the overburden pressure is equal or less than that of the confined pore water pressure, and if not dealt with it will result in piping or heaving of the base of the excavation.•There are two basic means of relieving this pressure The use of Passive Pressure Relief Wells ; and The use of active pumping pressure relief wells, which can consist of either deep wells or wellpoints.

In flood control, a relief well is used adjacent to earthen levees to relieve the pressure on the lake or river side of the levee and thus to prevent the collapse of the levee.The greater flow of water in the water source, typically during a flood, creates a pressure gradient such that more water infiltrates the soil of the levee.Water may then flow through the soil towards the dry side of the levee, resulting in sand boil, liquefaction of the soil, and ultimately destruction of the levee.Relief wells act like valves to relieve the water pressure and allow excess water to be diverted safely, for example, to a canal.Pressure relief wells can prevent sand boils from occurring by relieving the water pressure as described.

RELIEF/ ARTESIAN WELL DEWATERING

BUILDING CONSTRUCTION- DEWATERING TECHNIQUESNAME – NEDA SHAKILROLL NO. - 13CLASS – 3RD YEAR, B

Artesian Pressure beneath an excavation is sometimes referred to as the silent enemy. During the construction period there can often be no apparent issue with groundwater, then with little or no warning, the base of the excavation can fail, with water flooding the structure. It is, therefore, essential to establish if artesian conditions are present, before any deep excavation is carried out. If artesian conditions are anticipated, then a system of either active or passive pressure relief wells can be designed and installed in order to prevent heave.

Before the ground is reduced and the water pumped out, the upward water pressure is less than the downward weight of soil.

When the ground is excavated, the artesian water pressure becomes greater than the pressure from the ground above causing the base to heave and crack.

•Before the ground is reduced and the water pumped out, the upward water pressure is less than the downward weight of soil. •To prevent heave it is necessary to reduce the uplift pressure to below the weight of the overlying soil (in the temporary works condition) or structure (in the permanent works condition). •This can be achieved by one of two methods: actively pumping from below the confining layer(installation of active pumping wells) by providing a pathway through the confining layer allowing water to bleed into the excavation when artesian pressure rises

A dewatering system reduces the groundwater uplift pressure to less than the weight of the overlying soil, so preventing ground heave.