Influence of Pre-excavation Dewatering in Pit on Foundation Pit Deformation
In order to study the influence of pre-excavation dewatering in a pit on foundation pit deformation and water level change before excavation,based on the foundation pit project of a subway station,the influences of pumping speed and dewatering depth on the deformation of envelope structure,surface settlement,water level change outside the pit,pore water pressure and earth pressure are studied with laboratory model test method.MIDAS GTS NX finite element software is used to simulate the actual project,and the test data is compared with the numerical calculation results.The result shows that(1)With the increase of the distance between the water level and the envelope structure,the water level drops less,and the slope of the precipitation curve is smaller,which is consistent with the results of first concave and then convex type precipitation curve obtained with the experiment.(2)The lateral displacement of the enclosure structure increases with the increase of the precipitation depth,and the increased amplitude gradually decreases.The overall pattern is cantilever type,a kick deformation pointing to the pit is generated at the bottom due to the action of seepage force,and the maximum lateral displacement of the enclosure structure appears at the top of the enclosure structure.(3)Surface subsidence outside the pit presents a cross-hook type distribution.The location of surface subsidence outside the largest pit does not change when the precipitation depth changes,and the location appears about 10 m away from the envelope structure.(4)The lateral movement of the envelope structure and the ground settlement increase with the increase of precipitation depth or pumping speed.(5)After foundation pit dewatering,the pore water pressure decreases both inside and outside the pit,the pore water pressure in the pit decreases significantly more than that outside the pit,and the change rule of the two is different.The pore water pressure in the pit decreases first and then increases,while the pore water pressure outside the pit decreases all the time.(6)The lateral earth pressure inside and outside the pit decreases significantly with the increase in precipitation depth.(7)The soil pressure in the pit does not change obviously with the increase of pumping speed,but the soil pressure outside the pit decreases obviously with the increase of pumping speed.
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