Deformation Monitoring And Numerical Simulation Analysis Of Deep Foundation Pit Excavation In Soft Soil Layer

With the increasing of underground engineering scale,the scope of the continuously augmented,then also brought a series of problems,including soft soil layer is one of the challenges faced by the people,the stability of the foundation to a large extent affects the stability of the whole project,as well as the soft soil stratum in the deep foundation pit engineering construction,if not for the bad strata pre-reinforcement ahead of time,it is bound to have a large or small impact on the construction of deep foundation pit.In addition,subway construction is often located in the city center where buildings are densely distributed.The dense urban underground buildings and various underground pipelines make the construction of deep foundation pit more difficult.Once the large displacement of the retaining structure occurs in the process of foundation pit construction,there will be huge safety risks.Such as uneven surface settlement,underground pipeline deformation and rupture,surrounding buildings cracking and collapse;Therefore,it is very necessary to pre-reinforce the soft soil layer and to analyze and monitor the displacement and deformation law of deep foundation pit excavation in real time.his paper,taking the high road station of Shenzhen metro line no.16 for engineering,combined with the geological situation of Long gang district in Shenzhen city,soft soil layer of Liuzhou road station,pre-reinforcement by FLAC3 D numerical simulation and field monitoring analysis method of combining the pre-reinforcement the supporting structure after excavation and the displacement of the deformation law of surrounding environment and situation,The results are as follows:1.In part of the boreholes,peaty soil and peat-containing silty clay were revealed,which were distributed unevenly,with wood fragments in some parts,and the surrounding buildings were dense and close to each other.Considering the construction difficulty,project cost and other reasons,cement mixing pile was adopted as reinforcement method.The soft soil layer of the foundation pit was strengthened by triaxial mixing pile,and the test pile was carried out before large-scale construction,and the optimal parameters were selected by comparison.It was verified by experiments that the unconfined compressive strength of foundation reinforcement and groove wall reinforcement was greater than or equal to0.8MPa(28d age),and the internal friction Angle of composite soil after triaxial mixing pile reinforcement was greater than or equal to 20°.The cohesive force is more than 200 k Pa,and the strength index of the reinforced composite soil has met the construction requirements.2.In order to verify the rationality of the reinforcement scheme and the effectiveness of the final reinforcement results,FLAC3 D software was used in this paper to simulate and analyze the deformation characteristics and displacement of the supporting structure of the foundation pit and the surrounding environment.Probe to connect wall on the top of the wall horizontal displacement and vertical displacement,vertical displacement on the surface of the earth around the deep foundation pits,the surface of the building settlement and horizontal displacement of deep soil,the deformation of supporting structure of deep foundation pit excavation and surrounding environment characters,the results show that the deformation law in line with the characteristics of the deformation law of foundation pit excavation,and consistent with the theoretical analysis results,The displacement values are all within the pre-warning values specified in the design,which verifies the rationality and effectiveness of the soil reinforcement scheme.3.In order to verify the feasibility and reliability of FLAC3 D for simulating and analyzing the excavation process of deep foundation pit engineering in subway station,a reasonable displacement monitoring scheme was developed.The monitoring data were obtained through real-time monitoring on the site and analyzed in detail.By comparing and analyzing the simulation results with the actual monitoring results,it is found that the deformation law of the two is basically the same and the displacement results are not much different,which indicates that FLAC3 D is feasible and reliable enough to simulate and analyze the excavation process of deep foundation pit engineering in subway station.