Soil nailing wall is developed in more than 30 years to maintain stability of foundation pit side or slope soil excavation for a soil retaining structure.
There are several kinds of components such as soil nail, prestressed anchor, micropiles and concrete surface, water-stopping curtain wall will be added with the higher underground water. By the role of soil nail, the surface layer and the combined action of undisturbed soil, formed on the basis of the active restriction mechanism of complex, has greatly improved the structure of the slope soil strength and resistance to deformation ability, decrease the lateral deformation of soil, enhance the stability of the slope. Supporting effect is mainly set by the length of soil nail, density, soil nail tensile and bending and shear strength of soil, soil nail and the bonding strength, stiffness, soil nailing wall and side wall combined with degree and undisturbed soil properties, the top load and excavation depth factors such as comprehensive decision.
One foundation pit completed in 2002, the largest vertical opening of digging depth of 19 m, used the anchor cable composite soil nailing wall for success, marked the soil nailing wall technology has reached a very high level .
Soil nailing wall is suitable for the underground water level above or by artificial precipitation after artificial filled soil, cohesive soil and weak cementation sand foundation pit supporting or slope reinforcement. Soil nailing wall should not be used for water rich in silty sand layer, sandy gravel layer and silt soil, the lack of self stabilizing ability should not be used for silt and saturated soft soil layer.
In order to better control the deformation, anchor should be set in the excavation of the upper.
When no slope space or limited to constructed the scheme of composite soil nailing wall is used. Soil nailing should be stipulated in the design of stratified excavation depth according to the operation sequence of construction, at the completion of the upper surface of soil nailing and shotcrete, before may not be on to the next layer depth of excavation.
Steel pipe pile composite soil nailing wall has flexible,wide applicable range, low cost, short construction period and the characteristics of safe and reliable. In practical engineering, the composite soil nailing wall in all kinds of technology according to the organic combination of engineering need to be flexible, so that the construction is simple, economic and reasonable, comprehensive performance is outstanding, and deformation and the overall stability of the slope can meet the requirements.
Steel pipe pile stiffness and strength of composite function. The stiffness and strength, the greater the composite support system, the more have pile anchor.
Failure morphology and mechanical properties of the support, can be used for the analysis of the principle of the combined
bolting; The smaller, the closer to the soil nailing wall, can be reference to the design theory of soil nail wall. In order to make the micro pile can play a role of a whole, usually at the top of the pile setting crown beam. In general, the greater the stiffness of pile and composite soil nailing wall effect. Steel pipe pile composite soil nailing wall, usually are not destroyed by shear, but washed curved or between sliding out from the pile soil. Although there are many kinds of practice of micro pile, the pile stiffness difference, the research of stiffness of pile impact on the soil nailing wall needed.
Steel pipe pile composite soil nailing wall failure mode has two kinds: (1)Similar to the mixing pile composite soil nailing wall shear instability destruction, pile was cut, soil nail bent, pull out or surface. (2) Mainly for soil shear failure,
after the collapse of earthwork from pile, micro pile is not damaged, or destroyed by collapsed earthwork shearing break. When steel pipe pile stiffness is bigger, which can significantly reduce the levels of slope displacement and
ground settlement, therefor stiffness of pipe is important point in the design work.