兰渝铁路含水弱胶结砂岩隧道地层特性试验研究

Experimental investigation on the formation characteristics for weakly cemented sandstone aquifer tunnels in Lan-Yu Railway Line

在兰渝铁路桃树坪、胡麻岭隧道施工中,遭遇了前所未见的第三系含水弱胶结砂岩地层,施工异常困难,为此进行了地层特性的常规室内试验和土样特性随时间变化的试验,并在桃树坪隧道现场进行了土压测试。研究表明,该含水弱胶结砂岩地层为密实细砂,渗透系数在7.58×10-5~2.49×10-4cm/s范围,小于一般砂土。含水弱胶结砂岩具有一定的黏聚力。随着开挖暴露时间的延长,围岩含水率逐渐减小,密度也减小,围岩的内摩擦角减小。现场试验表明隧道围岩侧向压力较大,大于铁路隧道设计规范计算数值。施工上应选择在控制水平收敛方面具有显著优势的CRD法,并应尽量缩短开挖后围岩暴露时间。该地层渗透系数小,小导管注浆困难,应研究超细水泥+速凝剂浆液,降水方面应采用真空泵+轻型井点降水。

Special Tertiary weakly cemented sandstone aquifer is encountered during tunneling in Taoshuping and Humaling tunnels,Lan-Yu railway line,it is very difficult to tunneling in this ground. A series of indoor regular and time-relevant tests are designed to analyze the formation characteristics, and in-situ tests are done to measure the grounding pressure. The study indicates that this special aquifer is composed of compact fine sand, its permeability coefficient is between 7.58×10-5~2.49×10-4cm/s,which is smaller than that of the ordinary sand. This weakly cemented sandstone aquifer has some cohesive strength. With elongation of exposure, the water content decreased, and the density and internal friction angle are also reduced. The in-situ test indicates that the lateral ground pressure is far bigger than that calculated by Railway Tunnel Design Code. So the method that has the significant dominance in controlling horizontal convergence should be selected, such as CRD method. At the same time, the time of exposure of ground should be shorted as soon as possible. Because of the low permeability coefficient, it is very difficult for grouting with small pipe. So superfine cement and quick setting agent should be studied, and ground dewatering method of vacuum pump and the light well point drainage should be considered.