富水粉砂地层水平 MJS 桩施工 对周边环境的影响及控制研究

全方位高压喷射工法(metro jet system，MJS)具有全方位、高精度、排泥集中等优点，在复杂地质条件 和盾构穿越既有车站等不利施工工况下有着较强的适应性。为研究水平 MJS 成桩对周围粉砂地层的影响，优化 水平 MJS 设计施工参数，以苏州轨道交通 6 号线苏锦站富水粉砂地层中 MJS 试桩工程为背景，采用现场试验的 方法研究水平 MJS 成桩引起地下水位、超静孔隙水压力、土压力和深层水平位移的变化规律。研究结果表明： 试桩期间水平 MJS 喷浆时超孔隙水压最大增加了 46.1 kPa；喷浆使地下水位最大上升 3.6 m，停止喷浆后水位最 大下降 1.5 m；土压力的变化趋势与孔压一致，喷浆时土压最大上升 40.6 kPa。由于粉砂层引孔过程中土体自支能 力不足，易塌孔，本次施工中引孔时的测斜最大发生 1.2 mm 的内倾，喷浆时测斜最大发生了 2.2 mm 的内倾。苏 州地铁 8 号线时代广场站水平 MJS 施工期间车站底板最大位移值为 0.8 mm，满足规范要求。粉砂层 MJS 施工过 程中在水泥浆液中加入 3%掺量膨润土，可防止出现塌孔和抱钻现象。

Influence and Quality Control of Horizontal MJS Pile in Water-rich Silty Sand Stratum

The metro jet system (MJS) construction method has advantages of omnidirectional, high-precision, centralized mud discharge and shows high adaptability under unfavorable construction conditions such as complex geology and traversing existing stations by shield tunneling. The objectives of this study were to investigate the effects of horizontal MJS pile constructed within a silty sand stratum and to optimize the design and construction parameters of the horizontal MJS. MJS pile tests were conducted at Sujin subway station of Suzhou Rail Transit Line 6. Field tests were performed to examine the variations in the groundwater level, excess pore-water pressure, soil pressure, and deep horizontal displacement caused by horizontal MJS pile construction. The results show that the maximum excess pore-water pressure increases by 46.1 kPa during horizontal MJS shotcreting. The water level rises by a maximum of 3.6 m during shotcreting and decreases by a maximum of 1.5 m after shotcreting. The variation trend of the earth pressure is consistent with that of the pore pressure, and the maximum increment in earth pressure is 40.6 kPa. Because of the insufficient self-supporting capacity of the soil mass, the hole tends to collapse during the hole drilling process in the silty sand layer. In-situ experimental results show that during the hole drilling and shotcreting processes, the inclinometer had maximum inclinations of 1.2 and 2.2 mm, respectively. The maximum displacement of the station floor during the horizontal MJS construction at a subway station in Suzhou is 0.8 mm, which satisfies the specification requirements. During the construction of MJS piles within a silty sand layer, 3% bentonite can be added to the cement slurry to prevent hole collapse and drilling-holding problems.