The use of contiguous / secant piling and diaphragm wall construction techniques to construct retaining walls is common in large commercial basement projects. The nature of these construction techniques is such that the only practical option is to apply waterproofing systems to the internal face of the retaining wall.
Any excavation done to go down in basement and if the extent of basement is up to plot limit, then the soil or earth need to be stopped, retained or shored by diaphragm wall, shoring, secant or sheet piling or other methods.
Selection of type of retaining wall:
Selection of retaining wall type and support system are usually made on the basis of:
a) Foundation of adjoin properties and services
b) Designed limits on wall and retained ground movements
c) Subsoil conditions and ground water level
d) Working space requirements and site constraints
e) Cost and time of construction
f) Flexibility of the layout of the permanent works
g) Local experience and available construction plant
h) Maintenance of the wall and support system in permanent condition
The commonly used retaining walls to support excavations are as follows:
a) Sheet pile wall (vertical members
of interlocking profiled steel plate driven into the ground to support the sides of a major excavation - also called trench sheeting).
b) Soldier pile wall (soldier piles (steel H sections @ 3m c/c) and horizontal wood logging)
c) Continuous bored piles wall (these are all primary piles with reinforcement in each and placed next to each other)
d) Secant piles wall (primary piles and secondary piles slightly overlap each other with reinforcement in alternative pile)
e) Diaphragm wall (mostly is rcc precast wall 1.2 m to 1.5 m wide with end to end interlocking joints, but sometimes also cast in-situ)
Diaphragm wall is commonly used as permanent wall system. Diaphragm wall offers most water tightness compared to other wall systems. Similar to continuous bored piles wall secant piles wall, diaphragm wall also causes minimum noise and vibration disturbance. However it is not suitable for highly collapsible soil during trenching.