MJS水平桩加固在盾构下穿既有隧道中应用研究

以在富水砂层中，长沙地铁4号线近距离下穿上覆2号线运营隧道工程为背景，对Metro Jet System （MJS）水平桩加固在盾构下穿既有隧道中的应用进行研究.通过现场钻孔取芯与室内试验，并在地表和2号线隧道内布置竖向位移监测点、管片应力监测点，研究MJS水平桩的成桩效果，以及盾构掘进时周边地层与上覆隧道的变形响应规律.研究表明：MJS工法桩直径为2 m左右，抗压强度达到3 MPa以上，均满足设计要求；盾构下穿时，上覆隧道沉降呈高斯曲线分布，最大沉降4.33 mm；由于盾构开挖的卸载，相交位置处上覆隧道断面在水平方向被挤压，产生的最大附加应力为1.4 MPa；地表最大沉降为1.1 mm，其中，MJS水平桩加固区域，地表沉降相对较小.总体来看，MJS水平桩加固效果较好，可为类似工程的实施提供借鉴.
Taking a case of Changsha Metro Line 4 excavated beneath closely spaced existing Changsha Metro Line 2 twin tunnels as research background, this paper studies the application of the Metro Jet System (MJS) Horizontal Column Reinforcement in Shield Tunneling. The quality of MJS column and the response of stratum and overlying tunnels are studied during the shield tunneling by carrying out in-situ and laboratory tests, installing the additional stress sensors and vertical displacement monitoring points inside Metro Line 2 and setting up monitoring points on ground surface. The result indicates that the diameter is appropriately 2 m and the compressive strength is higher than 3.0 MPa, which satisfy the designed specifications. When the shield excavates beneath the overlying tunnels, the settlement of the overlying tunnel present Gaussian curve distribution, and the maximum settlement is 4.33 mm. Due to the unloading of the shield excavation，the maximum additional stress is 1.4 MPa and the maximum settlement is 1.1 mm. Surface settlement is relatively small in the MJS horizontal pile reinforcement area. Overall，MJS horizontal pile can effectively reduce the settlement of existing tunnel，and can offer reference for the application of similar engineering.