上海软土深埋盾构施工引起的土压时效规律分析

针对上海软土地区深埋盾构开挖所引起的土压力时效性发展规律,选取4倍直径埋深盾构,布设土压力全断面长期监测点,获取盾构开挖阶段及后期固结蠕变阶段的土压力数据,以得到深部地层的土压时效变化规律。通过现场试验可得,盾构开挖所采取的土仓压力按照理论静止土压力取值时,刀盘周围会形成半径为1~1.5D的被动土拱效应作用区域,土拱范围内会产生20%的被动土压力增幅,土拱以外的范围不受开挖扰动影响。盾构掘进所产生的被动土拱挤压效应在盾尾注浆浆液硬化后开始逐渐衰减,衰减主要作用阶段为开挖后1~3年,深层土体衰减后进入长期蠕变阶段。试验表明,软土深部地层盾构开挖会产生一定程度的土拱效应,且土拱效应在后期固结蠕变过程中逐步衰减,可为今后软土深部地层盾构隧道设计及施工的土压力取值提供一定参考依据。

Field Measurement of Time-dependent Variation of Earth Pressure Caused by Deep Tunneling in Shanghai Soft Soil

Aiming at the time-dependent development law of soil arching effect caused by shield excavation in deep stratum in Shanghai soft soil area, the shield crossing section with tunnel in buried depth of four times diameter is selected to lay the long-term monitoring points for the earth pressure of the whole section, which can help to obtain the full-section earth pressure data of shield excavation stage and consolidation creep stage in deep soft soil stratum. The test results show that when the theoretical static earth pressure is adopted to be shield chamber pressure in tunneling process, an ellipsoidal passive soil arching effect zone with radius of 1~1.5 time diameter will be formed around the shield cutter-head. The passive earth pressure will increase by 20% in the range of soil arching action, and the earth pressure outside the soil arching zone will not be affected by excavation disturbance. The passive soil arching effect produced by shield tunneling in deep soft soil stratum begins to attenuate gradually after the grouts hardening at the tail of shield. The main stage of attenuation is 1-3 years after the completion of excavation. After the soil arching effect attenuating, soil in deep stratum enters the long creep stage. The test results show that shield tunneling in deep soft soil stratum will produce a certain degree of soil arching effect. The soil arching effect will gradually attenuate during the later consolidation creep process, which provides a certain reference for the earth pressure in the design and construction of shield tunnels in deep soft soil.