砂卵石地层土压平衡盾构施工渣土改良试验

Soil Conditioning Tests for Earth Pressure Balance Shield Applications in Sandy Cobble Strata

砂卵石地层土压平衡盾构施工时需进行渣土改良,提高渣土的流塑性.针对成都砂卵石地层采用泡沫、膨润土和聚合物进行改良,进行室内塌落度试验、搅拌试验和泥浆黏度试验来确定配比.研究结果表明,钠基膨润土比钙基膨润土具有更好的膨化能力,且不发生分层,更适用于渣土改良.案例中膨润土单独改良的合理配比为泥浆质量分数14.3%,注入量体积比20%.泡沫改良时注入率受渣土含水率影响较大,土体含水率越大,泡沫最佳注入率越小.泡沫加膨润土共同改良比两者单独改良效果要好,选择泡剂质量分数为3%、泥浆质量分数为14.3%,添加量在某一个范围,有多种组合都可以满足要求;当泥浆注入量体积比为12%时,泡沫最优注入量体积比为15%～20%;当泥浆注入量体积比为6%,泡沫最优注入量体积比为30%～35%.当地下水丰富时,需要添加聚合物;正常情况下也可降低膨润土泥浆浓度,添加聚合物,来节省膨润土用量,从而降低工程成本.

Soil conditioning is used to improve the plastic flow capacity of earth pressure balance (EPB) in sandy cobble strata. Conditioning tests were conducted for sandy cobble strata in Chengdu by using foam, bentonite, and polymer, including the slump test, the stirring test as well as the viscosity test. The results show that sodium bentonite has a better bulking capacity than Ca-bentonite and is not layered, which is more suitable for soil conditioning. The reasonable ratio for bentonite alone is to have a concentration of 14.3% and an injection rate of 20%. The foam injection rate is influenced by soil moisture content with a negative correlation. Using foam and bentonite together for conditioning can have a better result than using foam or bentonite alone. The concentration is proposed to be 14.3% for bentonite and 3% for foam while the injection rate is a range. There are many assembles which can meet the demand. For instance, the optimum injection rate is about 15% to 20% for foam and 12% for bentonite, or 30% to 35% for foam and 6% for bentonite. Polymer is proposed under rich underwater environment. Besides, under normal circumstances, polymer also can be used for lowing bentonite concentration, which can save bentonite consumption to reduce project cost.