Analysis Of Composite Soil Nailing Safety Factor And Working Behaviours By FEM

The soil-nailing support system for deep excavation has got more and more application because of its many advantages, such as easy and rapid to implement, safe and less investment. However, there are some disputes with regard to its design, and it is short of thorough and systematic research on composite soil-nailing. In this thesis the finite element method is applied to analyze the behavior of soil nailing and composite soil nailing. Extensive computations are carried out to further reveal the behaviors of soil-nailing and to provide scientific basis for its broad application.In this thesis, the safety factor calculation by finite elements based on the concept of strength parameter reduction is carried out. By adding the function to the traditional FEM calculation, a computer program, named TCSoil, is further developed based on the proposed computation model. Its solution for the safety factor of soil slope coincides with the Bishop method, and some unconventional feature of failure behaviors in complex soil slope can be analyzed. Moreover, the comparability between the safety factor calculated by TCSoil and that by the design code formula is also discussed. After this discussion, some suggestions about the optimization of the soil-nailing design are given out by changing the inclination and collocation of soil nailing.To study the behaviors of two kinds of composite soil-nailing, abundant numerical calculations by TCSoil are also made. Some significant conclusions are drawn as follows:(a) In the analysis of composite soil-nailing with pre-stressed anchor, one can find that its failure pattern is similar to soil-nailing. Therefore, its safety factor can also be calculated by the design code formula. An easy measure to enhance the safety factor is to put the anchor in the middle of the slope. In this type of composite soil-nailing, it is better for engineering application to set the anchor's inclination less than 10 degree and nails between two rows of anchors is not recommended because the anchor has great influence on the nails close to it.(b) Two kinds of failure patterns of composite soil-nailing with cement-soil wall are found. Their mechanisms are failure of cement-soil wall under limit shear situation and overturn of whole nailed system. Their sliding planes always pass through the far end of the soil-nails. Different from people's traditional opinion that the addition of embedded depth cannot lead to decrease of slope displacement all the time, so moderate depth should be adopted. Spacing of soil-nail has great influence upon slope displacement, but it hardly has any influence on the safety factor of this type of composite soil-nailing.