| With the accelerating process of urbanization and the continuous development of engineering technology,the construction environment of modern subway station is more and more complex,and the system structure of construction technology is also more and more complex.The construction technology of deep foundation pit in soft soil is widely used as the basic civil engineering technology in the construction of subway station.It plays an important role in the overall quality of the project,and its construction effect directly affects the overall stability of the later operation of the subway station.Taking the deep foundation pit in soft soil of Nanjing West Railway Station as an example,this paper analyzes the structure of the deep foundation pit in soft soil with FLAC3D software after detailed engineering geological investigation and combined with the actual construction technology of foundation pit excavation and support system.Through the analysis of the actual monitoring data in the construction site and the finite element numerical simulation in the process of foundation pit support and excavation,the displacement and settlement caused by the excavation of deep foundation pit in soft soil are studied comprehensively.The main work and research results are as follows.1)The total length of Nanjing West Station of Nanjing Metro Line 5 is 180m,and the study area is the station phase I project,with a length of 95.6m.The station is an island station with two underground floors in the middle.The platform slab is 11m wide,the standard section is 20.1m wide and about 16.79m deep,and the end shaft is 24.3m wide and about 18.55m deep.According to the geological lithology,geological structure,meteorological conditions,hydrological conditions and unfavorable geological conditions of the project,the analysis shows that the buried bedrock has little impact on the shallow buried station.The main structure of the station is located in the muddy silty clay layer.Due to the deep buried confined water layer,the main body of the station is mainly affected by the pore phreatic water of the surface fill layer,The main adverse geological conditions are the poor water bearing capacity of the fill layer and the characteristics of low strength,high compressibility and high sensitivity of the soft soil layer,so as to obtain a large number of effective parameters and boundary constraints.2)According to the characteristics of soil layer and physical and mechanical properties of soil layer in the site ②-2b4 the bearing capacity of mucky silty clay is 100KPA.Then,according to the site and foundation seismic effect,support design principle,foundation pit water stop and dewatering measures,the underground diaphragm wall+internal support is finally determined as the support system of the research project after scheme comparison.3)Important coefficient of side wall of diaphragm wall γ0 is 1.10,the ground elevation is 9.4m,the underground diaphragm wall elevation is 7.55m,the additional load outside the foundation pit is 150kPa,the crown beam size is 1200mm*800mm,and the concrete strength grade is C35;The concrete support size is 800mm*1000mm,and the concrete strength grade is C35;The diaphragm wall is 800mm thick,the standard section is 36.5m long,the end well is 39m long,and the concrete strength grade is c35p10;Q235 steel support is adopted,Φ609 steel,under the condition that the setting elevations of 1 concrete support and 3 steel supports in the standard section are 8.05m,3.05M,-1.45m and-4.667m respectively,the envelope displacement,bending moment and The changes of shear force and surface settlement are analyzed.With the increase of foundation pit excavation depth,the horizontal displacement of support structure gradually increases and then decreases,and the deformation is the largest about 3M above the bottom of foundation pit excavation.The surface settlement increases first and then decreases away from the foundation pit with the increase of excavation depth.4)Compared with other finite element software,FLAC3D shows more advantages.Under the Moore Coulomb constitutive model established by this software,the lining element and support element are selected as the research object,and then the simulation model is established by FLAC3D software for numerical simulation analysis.The distance between the left and right boundary of the actual simulation model and the foundation pit is 3～5 times,and the size of the numerical model is X×Y×Z=176m×106m×60m。According to the formation physical and mechanical parameters,structural material parameters and input the actual boundary constraints,the model is analyzed under five construction conditions,and the maximum unbalanced force is infinitely close to 0 after being calculated to 3100,indicating that the generated model tends to be stable;From the initial and final horizontal stress fields,it can be seen that after the completion of foundation pit excavation and support,the horizontal stress field increases from top to bottom relative to the original state,and the active earth pressure in the middle and upper parts increases significantly due to the unloading of passive earth pressure in the foundation pit.5)According to the characteristics of the foundation pit,the appropriate foundation pit excavation method is selected,and the FLAC3D software is used for the numerical simulation analysis of the simulation model.Under five construction conditions,the model is analyzed,and the simulation model shows that the maximum horizontal displacement of the ground wall is 23.15mm at the depth of the foundation pit of about 14.15m.The maximum deep horizontal displacement of the wall is about 3M above the foundation pit base.The maximum settlement of the simulation analysis is 20.23mm.The relationship between the ground surface settlement and the distance from the edge of the foundation pit is parabolic.The settlement gradually increases with the increase of the distance from the foundation pit,and begins to show a downward trend when it reaches a certain range.With the increase of excavation depth,the base uplift value also increases,and the distance from the central axis of the foundation pit increases,and the base uplift value of the foundation pit decreases slowly.Finally,the horizontal displacement simulation value,design value,monitoring value and surface settlement design value and simulation value of the support structure are compared and analyzed.The simulation analysis value is more in line with the actual working conditions and has more reference value,so as to verify the rationality of the design and the correctness of the simulation.Figure 56 table 7 reference 76... |
