Research On Field Test Of Soil Nailing And Numerical Simulation For Deep Excavation

Soil nailing is a new technology and retaining structure developed from abroad in recent years,to be used in excavation of soil, stability of deep excavation.The method had been widely used in ninties after the techique introduced.But,it is very different from other uniform soil at working performance when there exists sand layer at the bottom of foundation pit.This paper comprehensively discusses support mechanism,working performance,and stability analysis of soil nailing. Take a typical foundation pit engineering of soil nailing for example, analysed the distribution laws of deep excavation soil nails tensile forces and the slip surface through the field test of stress and strain. Based on all the analysis above,we discuss the stability of deep excavation on different geologic conditions by FLAC2D software.Main conclusions are as follows:1. The tension of soil nailing is related with its position and the potential sliding surface of deep excavation. The tension is the biggest in the middle of the excavation,small on the top and at the bottom. The biggest tension is at the potential sliding surface,whose distance is about two meters to surface course.The sliding surface is fixed initially through the position of the biggest tension.2. On the basis of traditional active earth pressure method and expirical earth pressure method,and calculating model of the lateral earth pressure which is a tetragon with the largest value in the center side is addressed. This new model presents the distribution of lateral earth pressure of soil nailing more accurately and concisely.3. According to the normal geological conditions of foundation pits in Shijiazhuang area, this paper chooses one kind of slip surfaces and the lateral earth pressure model, suitable for the soil structural characteristics in this area. A predigested method based on the limit equilibrium method is also presented in this paper, which is suitable for Shijiazhuang area.The method can be used to the engineerings that exists sand layer at the bottom of foundation pit.4. Based on the data of the field measurements and the calculation's results of numerical analysis with FLAC2D(Fast Lagrangian Analysis of Continuain)program.The biggest horizontal displacement of the typical foundation pit that exits sand layer at the bottom is ten centimes more compare with other common soil.Shear plastic yield area is much larger.Maximum shear tension at the bottom of typical foundation pit increased fifty percent.Therefore,the stability of deep excavation is worse.This paper has given some beneficial advices on design and work. Taking slope toe seriously and refined monitoring, overexcavation prohibited, bracing in time in process of excavation.