砂卵石地层盾构施工引发的滞后地面塌陷机理

针对砂卵石地层盾构施工地面突发塌陷频发的情况,结合成都地铁1、2号线地面塌陷实例,研究了盾构施工引发的滞后地面塌陷机理；分析了砂卵石地层地质条件,利用大型三轴剪切试验获得其力学特性；选用颗粒离散元法进行数值计算,通过三轴数值试验标定了土体的细观参数；通过数值计算模拟了开挖面失稳和空洞向地表移动.研究结果表明,当开挖面支护压力较小时,位移大于0.1m的颗粒接触力极低,该区域的土体孔隙率变大、力学性质也降低,该区域是开挖面失稳区,掘进过后将在盾构上方形成空洞；砂卵石层开挖面上方土体成拱作用明显,即使土层内部形成空洞,也不会立刻引起地面塌陷,这是地面滞后塌陷的重要原因.

Lagged Surface Collapse Mechanism of Shield Construction in Sandy Pebble Stratum

As for many lagged surface collapse cases that shield crosses the sandy cobble stratum in Chengdu metro No.1 and 2 lines, lagged surface collapse mechanism in sandy pebble stratum was studied. Conditions of engineering geology about sandy cobble stratum were analyzed. Mechanical behavior of sandy pebble was obtained via large-scale tri-axial test. Discrete element method was adopted for numerical computation on lagged surface collapse mechanism. According to the tri-axial numerical test method, the relation between the micro parameters and macro parameters of the sandy pebble stratum layer in Chengdu was calibrated. The face failure of shield tunneling and upward movement of cavity was simulated by numerical calculation. When supporting pressure is small, the particles with the displacement of over 0.1 m have low contact force. The porosity of earth in the region becomes larger and its mechanical behavior becomes worse. Therefore the region can be identified as instability region. Cavity in the ground will be caused after shield tunneling. Soil arching effect is obvious under shield construction. Even though there is cavity in the ground, surface collapse will not bring about immediately. This is important reason for lagged surface collapse phenomena of shield construction in sandy pebble stratum.