The Technique Of Sediment Improvement In Sandy Bed Without Water

EPB has good adaptability for the cohesive soil.But for sand layer with lower underground water level,the poor plastic flow and the big internal friction angle cause a series of problems,for example,it will increase cutter torque and will reduce the efficiency of screw conveyor and seriously influence on construction safety and progress.In order to solve the inadaptability of EPB for anhydrous sand,we based on the shield construction of Shijiazhuang Metro Line 2 and study the improvement of anhydrous sand in this paper.Evaluation of the improved results of different kinds of remolded soils by slump test and direct shear test,it is concluded that the optimal proportion of different kinds remolded soil improvement;Based on particle discrete element software PFC2 D,the mesoscopic parameters of coarse sand are calibrated brfore and after the improvement,and applied to the TBM model of the discrete element software PFC3 D.Based on the mesoscopic parameters of coarse sand and established the model of the TBM,compared the unearthed rate of the TBM before and after the improvement of the coarse sand.Research conclusions:(1)According to the direct test in the laboratory,the internal friction and cohesive force of different sand soil are obtained.(2)The bentonite mud and foam agent have obvious effect on the improvement of anhydrous sand soil.(3)With the volume ratio is 15% and the concentration is 1:10 bentonite mud,and foaming agent with the volume ratio is 15% are the best optimum modified ratio of medium-coarse sand;The optimum modified ratio of fine sand and silty clay bentonite mud is 10%~20% and with density 1:6 and 1:8,and foaming agent with the volume ratio is 15%~20%;For medium-coarse sand and silty clay,the the ratio of bentonite mud is 10%~16.5% and the concentration is 1:8,and foaming agent with the volume ratio is 15%~25%.(4)The trend of shear displacement and shear strength are consistent compared the indoor direct shear with the simulated shear test by PFC2 D.Mesoscopic parameters of medium-coarse sand are determined before and after improvement.(5)In the PFC3 D shield model,the improved medium-coarse sand unearth efficiency is larger 14.86% than unimproved in five seconds.