富水地层中重叠隧道施工引起土体变形研究

Soil deformation induced by overlapping tunneling in water-bearing strata

重叠隧道施工易产生隧道结构不稳定和地层变形等问题。重叠隧道富水地层施工时,土层开挖应力释放和地下水渗流共同作用使得地层和隧道变形问题显得更加突出,增加了施工难度。以深圳地铁5号线重叠隧道为背景,采用数值方法研究了开挖应力释放和渗流作用在重叠隧道施工不同阶段对隧道结构和土层变形的影响,得到富水地层重叠隧道施工土层变形规律,同时提出了控制地层变形措施。重叠隧道下洞施工时,采用设置超前注浆支护能有效控制开挖应力释放引起拱顶沉降,开挖完成后隧道拱顶在渗流作用下沉降稳定,而隧道上覆土层因失水固结产生较大工后沉降,同时地表沉降槽深度和半径在渗流作用下不断增大;为避免下洞隧道在渗流作用引起上洞隧道整体沉降,上洞在下洞施工引起土体变形稳定后进行施工。上洞开挖应力释放引起较大地层沉降,开挖应力释放引起较大地层沉降,渗流因素引起地层工后变形较小,地表沉降槽深度迅速增大而影响半径保持稳定。

Tunnel construction instability and soil deformation are usually encountered in overlapping tunneling, especially in water-bearing strata. Based on the background of overlapping tunneling of Shenzhen Metro Line 5, numerical analysis is adopted to study the effects of stress relaxation and seepage on the tunnel construction and soil deformation during different tunneling stages. The disciplines of soil deformation are obtained, and the relevant measures are proposed. When the lower tunneling is processed, the soil deformation induced by earth relaxation can be effectively controlled by pre-reinforcement and grouting. After the excavation, the crown settlement becomes steady under the action of groundwater seepage. However, the settlement of the covering layer subsequently comes out because of the soil consolidation induced by groundwater loss. At the same time, the settlement tank develops deeper and wider gradually under the seepage. To avoid its entire settlement, the upper tunnel is recommended to be constructed when its settlement caused by the construction of the lower tunnel is steady. During the construction of the upper tunnel, the earth pressure release induced by excavation brings about large soil settlement, but the seepage causes small settlement. The depth of the ground surface settlement tank develops rapidly, while the radius of the tank keeps constant.