Research On Bearing Characteristic Of Energy-saving Support Structure For Foundation Pit

With the continued progress of urbanization in China,a large number of high-rise residential buildings appear. Basement and cellars of high-rise building are often used in the construction of foundation pit support. Moso bamboo have high tensile strength,and the short-term strength is relatively stable,it meet the requirements of the application of temporary construction foundation pit support. The steel is replaced by the moso bamboo, can reduce the non-renewable steel of high pollution and high energy consumption,reducing emissions in line with the national energy policy. Therefore,it has certain theory and practical value to study the ecological supporting structure on the foundation pit.By the basic physical and mechanical tests of bamboo and finite element numerical analysis software MIDAS/GTS,two kinds finite element model of composite support of micropiles & soil nailing & moso bamboo and composite support of micropiles & soil nailing were build, compared the effect on the the surrounding ground settlement, micropiles bending moment and soil nail axial force.(1)The experiment results show that moso bamboo has excellent mechanics performance, the compressive strength is about 70 MPa. Elastic modulus is about 14 GPa, and along with the body increases gradually from bottom to top. Besides, the compressive bearing capacity of moso bamboo is little effected by bamboo joint.(2)The composite supports of micropiles & soil nailing & moso bamboo and micropiles & soil nailing on surrounding ground settlement have similar basic regular, but there are obvious differences. After each step excavation, around the pit wall ground slightly uplift, due to outer soil of foundation pit slide to the inner side of foundation pit, the micropiles limit soil deformation and large diameter moso bamboo squeeze surrounding soils. Through the contrastive analysis of two kinds composite support, the difference of the maximum settlement on surrounding ground is 5 mm. This suggests that, to some extent, moso bamboo has clear effect to control surrounding ground settlement.(3)The changing curve of micropiles bending moment of the composite supports is similar after each step excavation, the maximum value of plus and minus bending moment of the micropiles both increase with the increase of excavation depth of foundation pit and the position moves down. Bending moment on the composite support of micropiles & soil nailing & moso bamboo is bigger than for the latter, due to micropiles is not only by soil pressure from the active zone, but also from soil nailing, moso bamboo common restriction. the difference of the maximum on bending moment is 2.71 k N.m. Traditional soil nailing is replaced by the moso bamboo, to a certain degree, it increases the bending moment, but the safety of foundation pit was effected.(4)Moso bamboo has strongly flexibility. Soil nailing is replaced by the moso bamboo, moso bamboo can share part of the original soil nail axial force, and the soil nail axial force of all rows were reduced obviously entirety. After the excavation of foundation pit, the difference of the maximum value on soil nail axial force of two composite supports is 8kN, moso bamboo can reduces soil nail axial force obviously.