Dynamic Construction Numerical Simulation And Parameter Analysis Of Deep Foundation Pit Internal Bracing System

With the continuous development of society and economy,the land for the urban construction has got in a shortage increasingly.Massive construction of underground engineering,such as subway,underground utility tunnel and large underground emporium,make the foundation pit engineering develop towards greater and deeper.Internal bracing system in deep foundation pit engineering has good safety and applicability,but the present frequently-used design method of two-dimensional section cannot truly reflect the interaction among the internal bracing,the retaining structure and soil.Therefore,it is necessary to study the overall performance of the internal bracing system.Based on the deep foundation pit engineering,the internal bracing system was analyzed by the method of actual measurement and numerical simulation,the finite element software MIDAS/GTS of geotechnical engineering was used to simulate the dynamic construction process of the project.The internal force and deformation laws of the deep foundation pit support system were analyzed and studied.The influence of design parameters value on support structure was explored.The original design scheme was optimized.The main contents are as follows:(1)By consulting relevant documents and materials,the characteristics of foundation pit support engineering and the application of different support methods in practical engineering were outlined,the calculation of foundation pit deformation at home and abroad and the practical design method of supporting structure were summarized to provide a basis for the follow-up.(2)According to the geological conditions and the surrounding environment,the supporting scheme was designed,the monitoring scheme was produced combined with the requirements of the site deformation and the key parts of the supporting structure,the monitoring equipment were selected for data collection and sorting.According to the foundation pit deformation monitoring results,the dynamic change law of horizontal displacement of retaining pile top and deep,axial force of concrete bracing were analyzed,the grey theory prediction model was established,and the accuracy and feasibility of the model were discussed based on the monitoring data,to provide the suggestion for the design and construction process of similar foundation pit engineering.(3)According to the design documents of the engineering,the three-dimensional finite element model of internal bracing system in deep foundation pit was established.Based on the specific construction procedure,the internal force and displacement of thesupport system in the dynamic construction process were analyzed,and the influence of the excavation on the surrounding environment was analyzed.At the same time,the simulation results were compared with the monitoring results to verify the feasibility and effectiveness of the finite element method,and an effective numerical model were provided for subsequent studies.(4)Based on the three-dimensional finite element model,the influence of the design parameters on the performance of the support system was analyzed,the sensitivity analysis of the supporting stiffness,support structure stiffness and the ring beam(crown beam)stiffness was performed.The results show that the most important influence on the performance of the support system is the bracing stiffness,followed by the retaining structure stiffness and the ring beam stiffness.Based on the above research,the optimization design of the original pit support scheme was carried out.The results show that the cost was reduced in the case of less displacement growth.The optimization scheme has good economic benefits.