抽水井附近MJS桩施工引起的土体位移

Ground Movement Induced by Installing MJS Column nearby Pumping Well

在复杂的场地条件下,尤其是场地内存在抽水井等不良地质条件时,MJS桩施工对周围土体位移的影响仍然缺乏深入的认识。基于上海某基坑工程,对附近存在抽水井时MJS桩垂直施工引起的土体位移进行监测,包括地表垂直位移、深层土体垂直位移、深层土体水平位移,施工结束后在设计桩边界和抽水井之间钻孔取样。研究结果表明:MJS桩垂直施工期间地表微隆起,深层土体的水平位移比垂直位移大;在距设计桩边界1 m处,土体最大水平位移(32.86 mm)的67%是受抽水井影响。抽水试验使抽水井周围土体细粒含量减少,MJS桩在附近施工时,高压水泥浆更容易切割土体,成桩直径更大,从而土体水平位移明显增加。因此,工程上应重视附近存在抽水井时MJS桩施工引起的土体侧向位移。

The soil displacement induced by installing the MJS column in complex geological conditions, such as nearby pumping well, has been not studied in detail. Based on a deep foundation pit of Shanghai, the ground surface vertical displacement, lateral and vertical displacements of subsoils induced by installing an MJS column adjacent to a pumping well were monitored. The drilling and sampling were conducted after the installation of the column between the MJS column and the pumping well. The monitored results indicate that during MJS installation, the ground surface was slightly uplifted, and the horizontal displacement was larger than vertical displacement. The 67% of the maximum horizontal displacement(32.86 mm) is induced by the pumping well, which is 1 m away from the nominal edge of the MJS column. The fine particle content of the soils surrounding the pumping well decrease after the pumping test and thus during the MJS installation, the high-pressure grout jet can easily erode these soils, which can obtain a larger column diameter and thus further lead to greater horizontal displacement of subsoils. Therefore, the lateral displacement induced by the installation of the MJS column adjacent to the pumping well should be noticed.