岩溶地区某浅埋箱型隧道沉降成因及控制

研究目的:岩溶地区侧方基坑桩基施工及土方开挖过程中,浅埋明挖箱型地铁隧道结构出现突发沉降,尤其是变形缝部位沉降显著,本文通过箱型地铁隧道沿线及变形缝两侧的位移监测数据,分析隧道结构突发沉降产生的原因,并研究了浅层回灌水、深层回灌水和注浆加固等沉降控制措施的效果。研究结论:(1)支护桩施工诱发浅埋箱型隧道最大累计沉降为3. 3 mm,应重视其在岩溶地区的施工影响;(2)嵌岩工程桩施工揭露溶洞,承压岩溶水突涌桩孔,是侧方浅埋箱型地铁隧道结构突发沉降的主要原因;(3)浅层回灌水可短时间内使地层补水,抬升隧道,抑制隧道急剧沉降;长期实施深层回灌、桩基泥浆护壁施工,可维持地下水位,控制侧方隧道沉降,但存在深层回灌水可能通过岩溶裂隙或通道进入溶洞,降低回灌水补充效率的问题;(4)"双排桩+对拉钢绞线+对称开挖"有效控制隧道的最大水平位移为3. 0 mm;(5)箱型地铁隧道周围进行垂直和斜向钻孔注浆可起到加固和止水的效果,考虑到变形缝的敏感性,应实时控制注浆压力;(6)该研究成果可供类似岩溶地区浅埋箱型地铁隧道侧方基坑工程参考。

Causes and Controls of Settlement of a Shallow Buried Box Tunnel in Karst Area

Research purposes: In the process of pile foundation construction and earth excavation of lateral foundation pit in karst region,the shallow buried box metro tunnel structure has sudden subsidence,especially the deformation joint performed significantly. This paper depends on the displacement monitoring data along the box metro tunnel and on both sides of the deformation joint to analyze the causes of sudden subsidence of tunnel structure,and studies the effect of subsidence control measures including the shallow layer recharge water,deep layer recharge water and grouting reinforcement.Research conclusions:( 1) The maximum cumulative settlement of shallow buried box tunnel induced by support pile construction is 3. 3 mm,which should be paid attention to in karst area.( 2) The sudden settlement of lateral shallow buried box tunnel structure is mainly caused by the exposure of karst cave and the burst of confined karst water in the construction of foundation pit rock-socketed engineering pile.( 3) The shallow recharge water can replenish the stratum in a short time,uplift the tunnel and restrain the steep settlement of the tunnel;long-term implementation of deep recharge and pile foundation mud wall protection construction can maintain the underground water level and control the subsidence of side tunnel,but there are problems that deep recharge water may enter the karst cave through karst cracks or aisles and decrease the replenishment efficiency of recharge water.( 4) The maximum horizontal displacement of the tunnel under the effective control of " double row pile + steel strand + symmetrical excavation" is 3. 0 mm.( 5) Vertical and oblique grouting around box tunnel can reinforce and stop water,and the grouting pressure should be controlled in consideration of the sensitivity of deformation joints.( 6) The research results can be used as a reference for the lateral foundation pit engineering of shallow buried box tunnel in similar karst areas.