Displacement Dynamic Coupling Stability Evaluation Method And Dynamic Information Design Of Deep Foundation Pit Anchor Composite Soil Nailing

Instability of foundation pit is a kind of harmful environmental geological hazard phenomenon. With the development and growing of urban construction scale and underground space, deep foundation pit engineering also followed has a great increase, the foundation pit engineering is forward to the development of the trend which has a large excavation area、 deep excavation and more complex environment. At present, the theoretical research on the form of composite soil nailing is not clear, it is also not clear that how to realize the synergy and failure modethrough the soil medium load transferring in the study of deep foundation pit support, and assume that soil and soil nail, bolt, etc all play a role and in accordance with the circular slip failure, etc,these assumptions are often quite different from the actual situation in the project.Therefore, the design and construction process of the whole project is still in the stage of "experience design" and "experience construction".The current specification for its design is often static,but the process of foundation pit excavation and support is dynamic.According to the current design codes, it is often not possible to make a reasonable assessment of the stability of the foundation pit, there is a certain risk or cause unnecessary waste in the process of foundation pit excavation. As a very important working procedure in the construction of underground, the excavation and support of foundation pit slope is the construction problems involved in the recent ten years. So the stability of the foundation pit supporting engineering is more and more high. Therefore, an economical and efficient method for optimizing the supporting method and safety of the method is needed for the deep foundation pit engineering. On the basis of previous studies, this paper provide a theoretical basis for the parameter design and stability evaluation of supporting structure for deep foundation pit engineering by establishing a theoretical model of stability evaluation parameters and using the finite element software ABAQUS take a simulation analysis for dynamic coupling stability evaluation method and dynamic information design of the displacement dynamic coupling stability of deep foundation pit anchor composite soil nailing. This method changes the thought that the traditional displacement time-series forecasting method only select landslide displacement or displacement rate as the monitoring and evaluation parameters, synchronous calculating and monitoring the lateral sliding dynamic loads and foundation pit displacement or displacement rate produced by unloading of the excavation of foundation pit. And giving a specific coupling monitoring and warning value, providing a new evaluation method of dynamic coupling stability for deep foundation pit engineering. By using the displacement dynamic coupling parameter to evaluate the stability of foundation pit,Change the way of thinking that the traditional displacement time sequence prediction method, the method of selecting the landslide displacement or displacement rate as a method for monitoring and evaluating the parameters, simultaneous calculating and monitoring of the lateral slip of the foundation pit and displacement or displacement rate of foundation pit. And giving a specific coupling monitoring and warning value, providing a new method of dynamic coupling stability evaluation for deep foundation pit engineering.The main contents of this paper are as follows:(1) For shortage of the research of the traditional mechanism of compound soil nailing structure and form, the dynamic stability evaluation of foundation pit excavation process is realized in this paper by introducing nonlinear dynamic parameters and the displacement response ratio of excavation which can reflect the deformation failure mechanism. In turn, according to the critical criterion of the response ratio--early warning value,to determine whether a foundation pit need to support in a moment in order to achieve the real-time dynamic monitoring and evaluation of the foundation pit excavation(overall stability of foundation pit).(2) Under the premise of ensuring the stability and safety of deep foundation pit, finding out the optimum angle、the optimal anchorage length and the optimal layout position of the bolt through theoretical deduction,then comparing and analyzing the reliability of the theoretical research results by using the stability evaluation parameters- response and combining with a specific example of a project.(3) Simulating and analyzing the regular of dynamic displacement field caused by each step of excavation by taking a foundation pit engineering in Jinan as an example and using the finite element analysis software ABAQUS to simulate the whole process of excavation. Implementing dynamic information construction and finding out the optimal parameters of the supporting design scheme by combining theoretical derivation and numerical simulation and using the stability evaluation parameters of the dynamic response ratio.(4) Through comparative analysis of the actual monitoring data and simulation results of the foundation pit,finding out the changing trend and the difference between the two and summing rule. Providing theoretical basis and technical support for the design and construction of composite soil nailing of deep foundation pit.