【Excerpts】Deep large foundation pit commonly used 7 kinds of support forms, a summary!

Generally speaking, the support mode of deep large foundation pit is divided into two forms: "internal support" and "no internal support", covering 7 commonly used support methods. Let's take a look at what ones ?

  
1、With internal support and support form

(1) Exterior-protected construction

        Its function is to directly bear the lateral soil pressure and water pressure in the foundation construction stage of the foundation pit, and transfer this pressure to the support system. Each type has different emphasis in terms of applicable conditions, engineering economy and construction period. At present, the common types of envelope structure are steel plate pile retaining wall, steel and cement-soil mixing wall, cast-in-place pile row pile, concrete continuous wall, etc.

Steel pile enclosure wall

Steel and cement concrete mixing wall

Place-in-place pile pile retaining wall

continuous concrete wall

(2) Stop the water curtain

        Its function is to block the flow of water outside the pit into the pit or increase the seepage path of the water at the bottom of the pit, to facilitate the mechanical excavation and provide the construction conditions of dry operation in the pit. The main form is the envelope structure and water stop curtain, such as ground wall, steel cement mixing pile, steel plate pile and bite pile, etc.; the form is cement mixing pile water stop curtain, its construction processes are high pressure rotary spray, two axis mixing, three axis mixing, TRD method, CSM method, etc.

High-pressure rotary spray water stop curtain

Three-axis stirring water stop curtain

TRD water-soil mixing wall

CSM cement-soil mixing wall

(3) Lateral bracing

        Its function is used to transfer and balance the soil and water pressure on the enclosure structure, and to form the supporting system together with the enclosure structure. Common support types are: steel support system, concrete support system, steel and concrete combined support system, etc.

Steel support system

Concrete support system

Steel and concrete combined support form

(4) Vertical support

        Its function is to bear the vertical load from the horizontal support, strengthen the spatial stiffness of the support system, ensure the longitudinal stability of the horizontal support, and have a better stiffness and a small vertical displacement. Common types are temporary lattice column + column pile, permanent steel column + column pile.

Temporary lattice column + column column

Permanent steel column + column pile

2、No internal support support form, no internal support support form

(1) Put slope

        Slope laying is to rely on the strength of the soil itself to maintain the stability of the whole foundation pit, suitable for shallow foundation pit, this process is simple, economic cost, the construction progress is fast.

Put slope

(2) Suspension arm support

         Cantilever support is to rely on the retaining structure to resist lateral soil pressure and water pressure. The common forms are single / double row pile cantilever pile support, cement soil gravity retaining wall, steel cement soil mixing pile, etc.

Suspension arm support

(3) Pile-anchor support

        Pile anchor support is a supporting system composed of bolt rod and pile. No internal support provides great convenience for excavation and underground structure construction, with fast construction period and low construction cost.

pile-anchor support 

——Source: Architectural Engineering Luban Union

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