浅埋地铁隧道施工影响下含空洞地层的变形特征分析

地层空洞的存在使得隧道结构周围的地层环境变得更为复杂,在地铁隧道施工的影响下极易引起地表沉降加剧甚至地表坍塌。针对V级围岩地铁隧道,采用三维模型试验和数值模拟研究了不同位置地层空洞对地表沉降的影响规律以及空洞的变形特征,同时通过修正后的Peck公式对试验结果进行拟合分析。研究结果表明:空洞的存在使得地层损失加剧,地表沉降槽深度和宽度均有所增大,沉降槽曲线整体向空洞一侧偏移,通过修正后的Peck公式能较好地拟合出沉降曲线形态;从地表整体沉降形状上看,空洞上方一定范围内地表沉降较大,地表会出现明显的沉降盆形态;综合考虑空洞对地表沉降槽宽度和深度以及地层损失率的影响,认为空洞位于隧道斜上方是最不利位置,在施工过程中对这一方位地层空洞应重点关注;不同方位空洞的变形模式不同,主要表现为立式椭球体和卧式椭球体等变形模式。

Deformation characteristics of ground with voids induced by shallow metro tunnelling

The existence of the ground voids makes the ground conditions around the tunnel more complex, which may increase the ground surface settlement and even induce collapse during shallow metro tunneling. Concerning the metro tunnels in the surrounding rock grade V, a series of model tests and 3D numerical simulations are conducted to investigate the characteristics of the void deformation and the impact of different void positions on the ground surface settlement. Besides, an improved Peck formula is proposed to perform the curve-fitting analysis on the model test results. The main conclusions are as follows: the ground voids increase the ground loss, depth and width of settlement trough of the ground surface, and the settlement trough moves towards the ground voids. The curve-fitting results of the improved Peck formula correspond well with those of the model tests and numerical simulations. Furthermore, from an overall perspective of the settlement trough shape of the ground surface, the ground surface settlements are relatively larger within a certain range above the void, and a basin-shaped groove occurs on the ground surface. Considering the overall influences of the ground loss, depth and width of settlement trough, the void locating on the inclined top of the tunnel is the worst position for the tunnel construction, in which case the engineers should pay more attention to monitoring of the ground movement. According to the results of the numerical simulations, the void deformation modes are different with different positions of the void, and the main deformation modes are vertical ellipsoid and horizontal ellipsoid.