MJS reinforcement of foundation pits adjacent to existing stations and settlement analysis of surrounding buildings
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摘要: 宁波市轨道交通7号线外滩大桥站为7号线与既有2号线换乘站，该车站基坑位于软土地层，基坑东侧紧邻既有2号线车站且周边环境复杂，基坑施工易引起围护结构及周边建（构）筑物过大变形，为此采用MJS工法对既有车站西侧土体进行加固，并对基坑及周边建筑进行监测。基坑监测结果表明：基坑施工期间周边建筑沉降量整体呈增大趋势，沉降的最大值更多出现在基坑影响范围内的建筑转角区域；在基坑开挖前，经MJS加固的基坑东侧变形基本控制在−2～4 mm，基坑西侧变形则在−5～7 mm；基坑开挖后，东西两侧的变形量则均控制在−6～4 mm，相比开挖前基坑变形增量较小，且总体变形远低于监测控制值25 mm。本研究表明MJS工法加固可有效控制基坑周边建（构）筑物变形，增加基坑开挖的安全性，可以为后续类似工程施工提供借鉴。Abstract: During the construction of the transfer node at Waitan Bridge Station on Line 7 of Ningbo Rail Transit, it was recognized that the proximity of the new building to the existing Line 2 station, within a complex environment characterized by soft soil layers, posed a risk of excessive deformation to both the project structure and surrounding buildings. To address this concern, the MJS construction method was employed to reinforce the soil on the west side of the existing station, while closely monitoring nearby buildings. The monitoring results revealed an overall increase in settlement of surrounding buildings, with maximum settlement occurring primarily in corner areas within the influence range of foundation pit. Prior to excavation, deformation on the east side of the foundation pit—strengthened by MJS—was effectively controlled within −2 ~ 4 mm; meanwhile, deformation on its west side ranged from −5 ~ 7 mm. Post-excavation, deformations on both sides were managed within −6 ~ 4 mm. In comparison with pre-excavation increments in deformation levels around foundation pit—which remained significantly lower than a monitored control value set at 25 mm—it is evident that implementation of MJS construction method has effectively mitigated structural deformations in surrounding buildings and enhanced safety during foundation pit excavation. These findings can offer valuable insights for similar projects moving forward.
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表 1 换乘节点位置主要地层物理力学参数
层号 土层 天然含水率
w/%天然重度
γ/(kN·m−3)孔隙比
e压缩模量
Es /MPa土体静止侧压力
系数K0渗透系数
k/(×10−6cm·s−1)黏聚力
c/kPa内摩擦角
φ/(°)层底
标高/m①1a 杂填土 20.0 2.5 0.55 2500 1.67 ①2 黏土 28.9 19.3 0.825 3.5 0.52 0.15 18 13 −0.33 ②2t 黏土 31.6 18.8 0.895 5.0 0.46 150 −2.83 ②2c 淤泥质粉质黏土 44.4 17.3 1.250 2.6 0.58 3.5 13.9 16.1 −13.83 ③2 粉质黏土 32.8 18.6 0.950 3.0 0.49 0.15 13 14 −16.83 ④1b 淤泥质粉质黏土 37.9 18.3 1.067 2.8 0.58 0.35 19.9 18.9 −17.83 ④2a 黏土 39.6 18.1 1.118 3.0 0.56 0.8 13.9 16.3 −21.33 ⑤1a 黏土 29.2 19.4 0.824 6.0 0.38 0.28 39.4 16.1 −28.03 ⑤2 粉质黏土 30.7 19.2 0.856 5.5 0.43 0.08 14.3 18.7 −30.93 ⑥3a 粉质黏土 33.0 18.8 0.929 4.2 0.47 0.65 24.7 18.6 −39.93 ⑦1 粉质黏土 23.2 19.4 0.656 6.5 0.40 0.4 −44.23 ⑧1 中砂 19.7 0.700 10 0.42 3500 −59.33 ⑧2 粉质黏土 27.4 19.3 0.775 6.5 0.40 0.65 −63.63 
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表 2 周边主要建筑基本信息
序号 建构筑物 与车站基坑相对位置 结构形式及层数 基础形式 基础埋深情况 1 2号线外滩大桥站主体 位于车站东侧，距离基坑0.8 m 单柱双跨钢筋混凝土
箱型结构，地下2层叠合墙形式，无桩基 基坑底埋深15.77 m 2 2号线1号出入口及风亭 位于车站北侧，紧邻基坑 钢筋混凝土结构，地下1层 ϕ800钻孔灌注桩基础 基坑底埋深8.76 m，
桩底埋深约57 m3 凯德置地 位于车站北侧，距离基坑23.6 m 框剪结构，13层 ϕ800钻孔灌注桩基础 桩底埋深约53 m 4 雨辰文星 位于车站西北侧，距离基坑44.3 m 框架结构，7层 ϕ400预应力混凝土管桩基础 桩底埋深约33 m 5 来福士广场 位于车站南侧，距高基坑17.2 m 框架及框剪结构，4～19层 ϕ700（800）钻孔灌注桩基础 桩底埋深约56 m 6 凯德汇豪 位于车站西南侧，距离基坑18.2 m 框剪结构，23～25层 ϕ700钻孔灌注桩基础 柱底埋深约56 m
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表 3 MJS工法施工参数
参数 数值 参数 数值 桩径/mm 2500 削孔水压力/MPa 10～30 水灰质量比 1.0 成桩角度误差控制 ≦1/300 水泥浆压力/MPa 40 提升速度/(min·m–1) 20～40 水泥浆液流量/ (L·min–1) 90 步距行程/mm 25 主空气压力/MPa 0.70～1.05 步距提升时间/s 60 主空气流量/(m3·min–1) 1.0～2.0 转速/(r·min–1) 3 倒吸水压力/MPa 5～20 地内压力系数 1.3～1.6 倒吸水流量/(L·min–1) 5～60 水泥掺量/% 40
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