泡沫改良砂卵石土的试验研究

Experimental study of foam-improved sandy gravel soil

砂卵石土具有内摩擦角大、流动性差、渗透系数大等特点,在砂卵石地层的盾构施工时会引起出土困难、刀盘磨损、地下水喷涌等问题。通过泡沫优化试验,得到泡沫半衰期及发泡倍率最优时的发泡液浓度为2%~3%。基于四川成都地铁7号线茶店子站至一品天下站区间砂卵石地层,配制卵、砾石含量为20%、40%、60%、80%的土体,掺入泡沫进行室内大型剪切试验、坍落度试验和渗透试验,发现随着泡沫注入率的增加,包裹在砂卵石土周围泡沫土的含量增加,砂石分离现象逐渐消失,抗剪强度和内摩擦角呈非线性降低,坍落度逐渐增大,抗渗性能明显提高,并得到了不同含石量砂卵石土满足盾构施工中"理想状态土体"要求的泡沫注入率。研究成果对砂卵石地层盾构掘进中的相关问题解决具有一定的意义。

Sandy pebble soil has the characteristics of large internal friction angle, poor mobility and high permeability coefficient. It will be excavation difficulties, cutter head wear, groundwater spewing and other problems in the construction of shield in sandy cobble stratum. Through foam optimization test, the foam liquid concentration is 2%-3% when the foam half-life and foam expansion ratio are optimum. Based on the sand-pebble stratum of Chengdu metro line 7 in Sichuan Province, the soil with 20%, 40%, 60% and 80% of the gravel content is prepared. Large-scale indoor shearing test, slump test and permeability test are carrie out, it is shown that with the increase of foam injection ratio, the content of foam soil wrapped around sand and pebble soil increased, the phenomenon of sand and stone separation gradually disappeared; the shear strength and internal friction angle decreased nonlinearly; and the slump gradually increased. The impermeability can be obviously improved; and the foam injection ratio of different stone contents gravel soil satisfying the requirements of "ideal state soil" in shield construction is obtained. The result can be of great importance in solving the problems encountered in the construction of shield in sand pebble stratum.