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Soldier Pile & Contiguous Pile
This type of retaining wall is formed by a row of bored piles installed in some spacing or close contact with one another. Soldier piles are usually installed at wide spacing (3 - 5 times pile diameter depending on soil conditions), while contiguous piles are installed at close spacing (less than 1 pile diameter). The exposed soil during excavation can be self supporting or retained by a shotcrete depending on ground conditions. This piles can be applied for temporary as well as permanent wall for deep excavation and suitable for varies of soil conditions.
For conditions where groundwater lies above the excavation level or the retaining wall design shall exclude any heavy inflow behind the wall, a bentonite-cement pile between the bored piles can used to provide an impermeable layer. The intermediate piles will interlock with the bored piles and form a wall similar to a Secant system of interlocking bored piles (concrete to concrete). This method is often applied as an alternative of secant pile wall.
A sheet pile wall is constructed by driving series of sheet piles connected to one another by locking mechanism, into a depth sufficient to develop a cantilever beam type reaction to resist the active pressure on the wall. The sheet pile material widely available is usually from steel with various shapes depending on the design and requirement, and also concrete precast piles.
The most commonly driving method used for sheet piling is by vibration. Not only for installation, a vibro hammer can be used for extracting sheet piles which are necessary for short term use, and the verticality and straightness of sheet piles can be adjusted with this method. Alternatively, a diesel hammer can also be used but for installation only as in the case of permanent type use. For difficult soil especially into sand or sandy gravel stratum, water jetting at the base of sheet pile may be used to aid the penetration.
A secant pile wall is formed by constructing a row of interlocking female (primary) and male (secondary) bored piles (concrete to concrete). The sequence is carried out with the primary pile installed first then cut (typically 0.15 to 0.2m) by the secondary pile forming a continuous wall and watertight at some degrees. The diameter of pile is usually ranges from 0.8m to 1.2m. The primary pile is cast from either weak mix concrete (less than 15 MPA) or full strength concrete, while the secondary pile as the main structural member is cast from full strength reinforced concrete. Particularly for high strength primary pile, a high torque drilling rigs and special drill casings and extractors are required.
A guide wall is compulsory for this method to ensure the piles accurately positioned to achieve the interlocking cut. This piles can be applied for temporary as well as permanent wall for deep excavation and suitable for varies of soil conditions.
A diaphragm wall is constructed by excavation in a narrow trench using a grabber or cutter depending ground conditions which is temporarily supported by a bentonite / polymer slurry, and followed with installing steel reinforcement and concreting to replace the slurry. The excavation of the trench is undertaken in alternate panels, with each length is usually about 4m to 6m in stable ground and the width design ranges from 0.6m to 1.2m thickness. To provide a watertight wall, the joint between panels is sealed with a water stop material (installed prior to concreting) or using grouting method. Alternative to cast-in-situ, precast concrete panels can be also used. A guide wall is very important for this method to accurately line the grabber and ensuring a proper watertight joint achieved.
Diaphragm walls are best suited for urban areas that requires deep excavations and in the proximity of existing structures or building, such as deep basements, tunnel approaches, underground rail stations and often used in top down constructions. As a permanent retaining structure, for deeper excavation diaphragm wall is considered more economical compare to the secant pile system.