| With the development of the city,the population of the city increases sharply.In order to alleviate the traffic pressure,the construction of Metro has gradually risen in major cities.At the same time,the safety of metro station construction has become increasingly severe.Based on a deep foundation pit project of a subway station in Jinan City,this paper studies the variation law of horizontal displacement of retaining pile,surface settlement outside pit,transverse support axial force,column heave and groundwater level outside pit by means of theoretical derivation,field measured data and numerical simulation,and analyses the stability of retaining structure and soil outside pit.The main research results are as follows:(1)When foundation pit is excavated in the upper soil without bracing,the top of the pile inclines to the pit,and the deformation curve of the pile body is similar to that of the cantilever beam.In the later construction,the deformation of the pile body gradually increases,the maximum deformation position moves downward from the top of the pile gradually,and the maximum deformation position is about 15m deep.The deformation curve of the pile body is similar to that of the "parabola".The deformation of the pile is larger in the middle part with less deformation at both ends.The maximum deformation is less than the control value,and the construction environment is relatively safe.With the increase of excavation depth,the ground subsidence increases gradually.Because the friction between the retaining pile and surrounding soil restricts the settlement of the soil near the pit to a certain extent,the overall settlement deformation curve is close to the "spoon" shape.The location where the maximum ground subsidence occurs is approximately 0.4H-0.6H away from the pit edge.The ground subsidence in the standard section is larger than that in the end section,and the foundation.Pit excavation does not bring safety problems to the surrounding environment.The axial force of the first concrete support is obviously greater than that of the lower steel support,the maximum axial force of the standard steel support appears in the third way,and the maximum axial force of the end shaft steel support appears in the second way;the upheaval of the column is always in the process of excavation,and the change of the column is within the controllable range,which does not affect the stability of the foundation pit.The water level outside the pit drops by 600 mm.Within the range of normal water level change,the method of water curtain combined with seepage diversion and drainage has played a good role in water resources protection in this area.(2)The maximum horizontal deformation of the enclosure structure obtained by the method of stability safety factor and the maximum settlement value estimated by the exponential curve settlement curve in the method of stratum loss are close to the actual results.These two methods can be used to estimate the maximum deformation of the enclosure structure and the maximum settlement value generated by the ground in advance.(3)FLAC3D software is used to simulate the construction process of foundation pit.When the distance from the edge of the foundation pit is 35m,the surface settlement of the soil outside the pit tends to be stable.Based on the analysis of shear stress,horizontal displacement of the soil and shear stress of retaining structure,the stability of retaining structure and soil outside the pit is further analyzed.The comparison and analysis between the measured data and the simulation results show that the deformation law and trend of the two are basically the same,which indicates that the simulation of the construction process of foundation pit is reasonable.Using FLAC3D software to simulate the enclosure structures with different depth of soil entry,it is concluded that when the embedding ratio is 28%-32%,the enclosure structure can prevent kicking phenomenon,make the pile produce smaller deformation,and make more reasonable use of resources. |
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