富水弱胶结大粒径砂卵石地层盾构施工技术

兰州地区富水弱胶结砂卵石地层中修建的第一条盾构法隧道工程，施工中遇到许多技术难题，如掘削面前方大粒径卵石难以有效破碎；掘削面平衡土压力难以建立与欠压掘进；渣土改良效果较差与螺旋机喷涌；地层超挖明显、隧道上方地层出现空腔以及地表沉降现象难以控制等。针对以上问题进行深入分析，发现弱胶结砂卵石地层中高强度大粒径卵石的存在与渣土改良效果难以保证是导致盾构掘进困难、地层超挖与沉陷的主要原因，从施工技术角度提出了相应的应对措施，如加大盾构机额定扭矩和总推力，确保在有足够动力的前提下，适当减少滚刀数量，同时增加贝壳刀与撕裂刀的数量。从施工技术角度提出相应措施，可为今后类似工程提供参考。

Shield tunneling technology in weak cemented gravel formation

As the first shield tunnel constructed in weak cemented gravel formation with rich water in Lanzhou area, there are many technical difficulties encountered during construction. For instance, low tunneling speed under relatively larger drive torque for cutterhead and total jack thrust forces, the large size pebbles encountered in front of the cutterhead and are very hard to be crushed, the balanced earth pressure at excavation face is difficult to be established, effect of muck improvement cannot be ensured, and the overexcavation and ground settlement are very difficult to be controlled. All of the technical difficulties encountered during construction are deeply analyzed, and the primary causes are the existence of relatively higher strength and larger size pebbles and the poor effect of muck improvement. The corresponding countermeasures are put forward from the perspective of construction technology. This study can lead a reference for similar project in the future.