含粉砂层软土地基真空预压密封性及现场试验研究

Vacuum preloading sealing performance and field test of soft soil foundations with silty sand layer

针对含有高渗透性含砂层软土地基采用真空预压处理时,设置黏土密封墙是保持真空系统密封性的有效措施。粉砂夹淤泥在微观上呈现絮状结构,取土扰动对土体渗透性影响较大。通过室内渗透–固结试验,建立土体渗透系数(k_(v))与有效应力(σ′)、黏粒含量(N_(c))的关系式,作为打设密封墙的评判依据,进而在该类地基上开展不同排水板(PVD)间距的真空预压现场试验,试验结果表明:考虑上覆土压力(σ′)作用,粉砂夹淤泥的渗透系数小于10^(-5 )cm/s;膜下真空度维持在83 k Pa左右,真空系统密封性良好,表明该类地基无须打设密封墙;加固后含水率降低了20%,淤泥孔隙比降低了30%;十字板剪切强度提高了22.3~32.23 k Pa。

When using vacuum preloading for soft soil foundations that contain high permeability sand layers,it is effective to establish a clay sealing wall to maintain the integrity of the vacuum system.The silt mixed with silt forms a flocculent structure at a microscopic level,which significantly affects the soil permeability when subjected to external disturbance.Experiments were conducted to determine the relationship between soil permeability coefficient(k_v),effective stress(σ′),and clay content(N_c).This relationship can be used as a basis for evaluating the construction of sealing walls.Subsequently,field tests were conducted on this type of foundation with different PVD spacing.The test results revealed that the permeability coefficient of silty sand and silt is less than 10~(-5) cm/s,considering the effect ofσ′.The vacuum pressure under the membrane was maintained at around 83 k Pa,indicating good sealing performance of the vacuum system and suggesting that a sealing wall is unnecessary for this type of foundation.After reinforcement,the moisture content is reduced by 20%and the void ratio of silt is reduced by30%.The vane shear strength increased by 22.3–32.23 k Pa.