Study On Design And Numerical Simulation Of Foundation Pit Support For Chengde Zhongliang Building

In the rapid development of the economy today,the city faces large population density,low land use rate,traffic congestion,serious environmental pollution and other issues are increasingly apparent,including traffic congestion and air pollution has become a prominent problem in urban development,in order to solve the problem of traffic congestion and other issues fully developed And the use of underground space has been urgent.Deep foundation pit engineering is to solve the development of underground space on the basis of came into being,foundation pit engineering focused on structural engineering and geotechnical engineering in one of the systematic project,with a comprehensive,practical,regional and risk Characteristics,is the basis of underground engineering and construction of a traditional subject,but also a comprehensive geotechnical problems.Taking the foundation pit of Chengde Zhongliang Building as an example,firstly,on the basis of geotechnical engineering investigation report and geotechnical test data,the geological conditions of foundation pit of Zhongliang building are analyzed,and the geological conditions,hydrogeological conditions and main physical The paper analyzes the actual engineering geological conditions of the project,analyzes the types of common supporting structures in Chengde area and the corresponding applicable conditions,and selects the scheme suitable for the project.By using the deep foundation pit design software,Finally,based on the analysis and analysis of the software design of the deep foundation pit,the finite element theory is introduced,and the geometrical analysis based on geotechnical analysis is used to analyze the stability of the foundation.Software Midas GTS NX to establish the finite element analysis model,the support structure of the numerical simulation analysis,the analysis results and field monitoring test results to verify the Chengde Building,foundation pit support program feasibility.The conclusions of this paper are as follows:(1)Site topography from top to bottom:Quaternary system(Q4ml)miscellaneous fill,Quaternary new system(Q4al+pl)of the silt,gravel,local powder folder thin layer of silt,Local gravel sanded with silt,sand sandwich,under the Cretaceous(J2t)andesite.There is a layer of groundwater within the depth of the survey,belonging to the type of diving.The seismic intensity of the area is 6 degrees,the design of the basic seismic acceleration value of 0.05g,the design of the earthquake group for the third group,the design feature period of 0.45s.From the nature of the soil to determine,belonging to the hard soil,site cover layer thickness greater than 5m,site type II,is a general site can be built.(2)The particularity of the project and the protection requirements of the surrounding environment,combined with the Chengde area commonly used foundation pit support type,to determine the Chengde building base pit with pile type pile anchor fixed support form,the upper part of the soil to meet the slope The requirements of the use of soil nailing support form,the lower part of the use of anchor-type row of pile support structure,the construction of the beam in the form of optimization design,in different sections using a different support program.That is,the upper part of the foundation on the west side of the foundation pillar support form,the lower part of the use of slope protection pile with anchor support form,and in the other three sides of the upper part of the use of grading combined with soil nail support,the lower part of the use of anchor support Waterproof pile support form.The stability of the support scheme,the anti-overturning stability and the anti-uplift and so on are verified by the deep foundation pit calculation software,and the scheme is feasible to meet the design requirements.Determine the pit monitoring,water drainage program.(3)The excavation of the foundation pit is carried out by numerical simulation of the whole process.The proposed support scheme can effectively support the excavation of the foundation pit,and the deformation of the foundation pit and the surrounding environment can be within the stipulated range The The surface subsidence of the main road on the west side of the foundation pit is calculated and the trend curve is drawn.The theoretical calculation of the surface subsidence of the main road on the west side of the foundation pit is compared with the monitoring value.The maximum deformation of the CS1 is 4.44mm,the deformation of the surface is 4.65mm,which is 0.21mm larger than the simulated value.The maximum deformation of the numerical simulation is 4.43mm,the deformation of the surface is 4.57mm,which is 0.14mm higher than the simulated value.The maximum deformation of the simulated value in CS3 is 9.67mm,which is 0.65mm and the deformation is 10.32mm.In the working condition CS4,the maximum deformation is 9.94mm,the surface deformation is 10.98mm,which is larger than the simulated value 1.04mm.The maximum deformation of the simulated value is 22.72mm,the actual surface deformation is 23.15mm,0.43mm larger than the simulated value The The results show that the measured value is slightly larger and the simulated value,the main reason may be the excavation of the earth pit excavation faster,the foundation pit exposed to a longer time caused.(4)The analysis of the internal force of the second anchor cable on the west side of the foundation pit is carried out.The anchor cable adopts the tensioned truss element,and the axial internal force change value of the cable is from 135 ?to 190KN,250KN.From the change value of the internal force of the second anchor in the west side,it can be concluded that the internal force of the anchor is increasing with the excavation of the foundation pit,especially when the foundation pit is unloaded.(5)The horizontal stress and vertical stress of soil are analyzed,and the distribution and trend of the two are similar.The stress of the bottom of the pit is relatively small,and the stress relief effect is more obvious.When the depth of the bottom of the pit reaches 1?1.2 times of the excavation depth,the distribution of the soil stress cloud tends to be stable,indicating its effect on the stress Depth of about 1 to 1.2 times the depth of excavation pit.The design plan of the foundation pit in Zhongliang Building has reached the safety,economic and reasonable requirements,which is of great significance to solve the problem of insufficient foundation pit design and uncertainties encountered in Chengde area.Engineering provides a reference.