Study On The Influence Of Secondary And Multistage Slop On The Deformation And Stability Of Foundation Pit

With the development of foundation pit engineering,the complicated geological conditions of the foundation pits are the problems faced by the foundation pit engineering.Combining the relevant factors,it's essential to choose the appropriate foundation pit support method to solving the problem.Considering the economy and safety,in the foundation pit of the soil dual structure,the secondary and multi-stage grading foundation pits could combine the stability of the soil and the composite soil nail wall structure,this is a local adaptation and an advantage that other supporting structure does not have,so it's worthy of extensive application and promotion in the foundation pit engineering.Based on the research status of existing composite soil nail support,this paperanalyzed the influence of secondary and multi-stage retreat on the deformation and safety of soil binary structure pit(Refers to the difference between the nature of the two layers of slope).Relying on the third phase foundation pit project of Hangzhou Fuxing No.4 block,the model was established by using the finite element analysis software Abaqus according to the actual foundation pit excavation support sequence,the second grade grading in the composite soil nailing wall support structure and the influence of the deformation characteristics of the binary foundation pit was studied,the influence law of the width of the retreating platform and the slope coefficient of the foundation pit is also studied in depth,then the safety performance and the position of the sliding surface under various influencing factors are calculated by using Lizheng deep foundation Software,The reliability of the conclusions was further verified by comparing the results obtained by Abaqus.In this basis,taking the foundation pit project of Luoyang Zhengda International City Plaza as an example,the influence of multi-stage grading on the deformation characteristics of soil binary pits in composite soil nailing wall support structure is further studied.The main research contents and conclusions of this paper are as follows:1.Introduced the theoretical,experimental and simulation results of the predecessors in the composite soil nailing wall,as well as the stability check of the composite soil nail wall and the mechanism.2.Simulated and analyzed the composite soil nailing wall engineering case with finite element software Abaqus,Comparing the actual monitoring data,it's can be known that the finite element simulation results are in good agreement with the actual monitoring,which proves that the results are true and reliable,and it can provide a reliable basis for numerical simulation research.3.When the width of the secondary grading and retracting is increased,the maximum settlement displacement at the top of the foundation pit,the horizontal displacement of the deep pit of the foundation pit,the horizontal displacement at the retreat,and the vertical displacement can be effectively reduced.However,the influence of the uplift displacement on the bottom of the foundation pit is weak;in addition,as the width of the retreat increases,the influence range of the settlement at the top of the foundation pit decreases gradually.4.When the upper slope coefficient of the secondary retreat foundation pit,the slope coefficient of the lower pit of the foundation pit,and the slope coefficient of the upper and lower pits of the foundation pit are changed,the degree of influence of the foundation pit deformation is affected when the respective influencing factors are considered respectively,the slope coefficient of the upper and lower part of the foundation pit should not be adjusted synchronously,the two should be considered separately.The values of the two are consistent with the “slow up and down”.5.Changing the multi-stage grading and retracting up-platform,retracting the low-platform,and retracting the up-platform and low-platform width,the change of the width of the retracting up-platform could has an obvious influence on the deformation of the upper part of the foundation pit;the change of the width of the low-platform has no effect on the foundation pit above the low-platform,and the influence on the deformation of the lower part of the foundation pit is also not obvious.Only when the width of the retreating low-platform is large,the influence is gradually revealed;When the width of the retracting up-table and low-table is changed synchronously,the comparison only changes the width of the retracting up-table 1 and only changes the width of the retracting low-table,and the widths of the two retracting stages should be considered separately,and the values should be in accordance with "upper width and lower width".6.The slope coefficient of each slope section should be considered separately when changing the upper slope coefficient of the multi-stage grading foundation pit,the slope coefficient of the central pit,the slope coefficient of the lower pit of the foundation pit,and the slope coefficient of the middle and lower part of the foundation pit,The slope coefficient value of each slope section is close to the trend of “slow up and down steep”,and the value of the middle slope section is reasonable between the two.7.The safety factor of the second-level grading foundation pit and the multi-stage grading foundation pit is simulated by using the LIZHENG deep foundation pit 6.01.By considering the influence of the width of the retraction and the slope coefficient,and analyzed the influence of each influencing factor on the safety factor of the foundation pit,the correctness of the Abaqus simulation of the finite element software was verified.8.The slip surface of the secondary grading foundation pit and the multi-stage grading foundation pit was simulated by using the LIZHENG deep foundation pit 6.01,compared with the influence range of the foundation pit top settlement obtained by Abaqus simulation.it shows that the curves obtained by the two were highly consistent.Especially when the retreat is closer to the top of the foundation pit,the regularity of the two is much more closer;When the retreat is far from the top of the foundation pit and the slope coefficient of the lower pit is changed,the distance from the slip surface to the slope of the foundation pit is relatively slow.