Slurry pressurized effect on strength and deformation characteristics of clay soil at excavation fac

Based on the true triaxial tests and ESEM apparatus,the effect of the slurry infiltration on the strength and deformation characteristics of clay soil at excavation face in slurry shield under various stress conditions is investigated,and the stability mechanics of the excavation face in clayey geological condition is proposed from the macroscopic aspect and microscopic aspect.The results show that:(1) For the soil strata with too low permeability parameter(K<10-8 m/s),the face stability mechanics can not be built by filter cake,because there is not any filter cake formation as the slurry hardly infiltrates into the strata.However,the compression imposed by slurry supporting pressure and the friction from filtering solution between the soil particles have considerable effects on the face stability.(2) The effect of the compression that exerts on the soil mass at the excavation face has upper and lower limit values,generally speaking,when the support pressure of slurry is less than the lower limit value,the slurry infiltration has less effect on the soil strength and deformation,when the support pressure of slurry is greater than the upper limit values,the infiltration of water from slurry softens the soil mass,resulting in strength reduction and deformation increase,and when the support pressure of slurry is within the upper and lower limit values,the compression effect compacts the soil particles and increases the molecular force between the soil particles,and also reduces the infiltration capacity to a great degree.As a result,the soil strength has a certain improvement and the deformation reduces considerably.(3) When the shield-driving stops for segment assembly,it is recommended that the slurry support pressure should not be used alone to maintain the face stability due to the softening characteristic of clay soil,and the pressure produced by the shield cutter and transferred to the excavation face shoule be taken full use to sustain the face stabilization.