Numerical Simulation Research On Composite Retaining Of Steel Tube-Cement-Soil Pile And Soil Nailing

Composite retaining of steel tube-cement-soil pile and soil nailing (CSCS) is a new method of foundation pit bracing, that the small steel tube is inserted into the cement-soil retaining wall before the retaining wall's initial setting, and a row of soil nailing is inserted into the wall after digging a certain depth. This method is very suitable to the foundation pit retaining in soft soil area.By means of the finite element program ADINA and combining with theory analysis and indoor experimental results, the paper created 3D finite element model. The correctness of the 3D finite element model was proved by the engineering instances. Based on the 3D finite element model, the influences on soil and retaining structure's displacement and stress fields due to the change of every parameter were analyzed. The measure of ground reinforcement in the passive zone and the suitable digging depth of every category CSCS were researched. Such conclusions were got:1. The vertical displacement and stress inside of the pile can be efficiently controlled when the steel tube is inserted. The horizontal displacement of foundation pit and steel tube as well as the vertical stress outside of the pile can be minimized when the soil nailing row is increased.2. The horizontal displacement of the foundation pit and the soil nailing as well as the settlement of the soil around is increased by the increase of the digging depth. The horizontal displacement of the foundation pit and the soil nailing as well as the vertical stress inside of the pile is increased by the increase of the rigidity and the insert depth of the steel tube. The diameter's increase of the soil nailing reduces the horizontal displacement of the pit, the settlement of the soil around and the horizontal displacement of the soil nailing. To sandy cement soil, the increase of the cement's elasticity modulus reduces the settlement of the soil around. The mixing quantity of the cement should be best controlled about 15%. To silt-floury-clay cement soil, the increase of the cement's elasticity modulus reduces the settlement of the soil around and the horizontal displacement of the soil nailing. The increase of the blocking wall's thickness reduces the horizontal displacement of the pit the steel tube and the soil nailing, at the same time it reduces the vertical displacement of the soil nailing.3. The ground reinforcement form in the passive zone excels at shallow and broad. The best reinforcement width is 1.17 times of the digging depth and the depth is 0.44 times. The reinforcement length is suitable to be controlled more than 0.64 times of the digging depth. The interval is suitable to be controlled no more than 0.38 times of the digging depth and should be controlled less than 0.71.4. The suitable digging depth of foundation pit timbering structure using a row of steel tube without soil nailing is smaller than 5.02m, and that using a row of steel tube with a row of soil nailing is smaller than 5.63m. When the soil nailing is increased into 2 rows, the depth can be dug to 6.26m, and when the soil nailing is increased into 3 rows, the depth can be dug to 6.67m.