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| Effect of segregated pit construction on displacement of adjacent strata and tunnel |
Dingwen ZHOU1,2( ),Lei HAN3,Hongwei YING1,4,*(),Chengwei ZHU1,Huihui LI5 |
1. Research Center of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China
2. Zhejiang Seaport Marine Engineering Construction Limited Company, Ningbo 315899, China
3. China Construction Eighth Engineering Division Limited Company, Shanghai 200112, China
4. Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098, China
5. Hangzhou Investigation and Design Institute, Hangzhou 310013, China |
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Abstract A finite element numerical model of the segregated foundation pit was established based on the case of a deep foundation pit in Hangzhou adjacent to an operating underground shield tunnel in order to analyze the influence of the construction sequence, the separation wall location and other factors on the deformation of deep and large foundation pits and adjacent facilities caused by the segregated-pit construction. The reasonableness of the parameters of the HSS model was verified by combining with the measured data. The influence of the construction sequence of the "platform" type segregated pit on the displacements of out-of-pit strata and existing adjacent tunnels were analyzed by combining with a simplified model based on the case. Results show that the displacements of strata and tunnels caused by the excavation of the segregated pit in Hangzhou soft soil are related to the construction sequence, the location of the separation wall, the thickness of the soft clay, and the relative position of the tunnel and the pit. The deformation of the close pit retaining wall, the surface settlement and the tunnel displacement will be greater with a wider far sub-pit when the close sub-pit is firstly constructed. An opposite finding is observed if the far sub-pit is firstly excavated, and the optimal control effect on the deformation of the retaining wall and adjacent tunnels is achieved by dividing the ratio of the far sub-pit width to the close one by 3.0 to 4.0 and the width of the close sub-pit by 15 m to 20 m. The deformation of the close pit retaining wall, the surface settlement and the tunnel displacement caused by the two sub-pit construction sequences will increase as the thickness of the soft clay layer increases. The concept of the displacement impact zone resulting from different sub-pit construction sequences was proposed, and the demarcation line of the zone can be simplified to be a straight line with an angle of 45° to the wall of the pit. The range of the displacement impact zone which is defined as the strata displacement caused by the close-first-then-far construction sequence is smaller than that of the far-first-then-close construction sequence gradually decreases with the increase of the width of the far sub-pit and the thickness of the soft clay layer. A parametric analysis was conducted to propose formula for fitting the demarcation line of the impact zones related to the location of the separation wall and the thickness of the soft soil layer.
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Received: 17 May 2024
Published: 25 April 2025
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| Fund: 国家自然科学基金资助项目（51678523）；浙江省建设科研项目（2018K119）. |
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Corresponding Authors:
Hongwei YING
E-mail: zhoudingwen1998@zju.edu.cn;ice898@zju.edu.cn
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分隔型基坑施工对邻近地层及隧道位移的影响
为了研究远近分坑的施工顺序、分隔墙位置及其他因素对分坑施工引起软土深大基坑及周围设施变形的影响，基于杭州某邻近运营地铁盾构隧道的深基坑案例，建立分隔型基坑的有限元数值模型. 结合实测数据，验证各土层小应变刚度硬化（HSS）模型参数的合理性. 结合在实际案例基础上简化的基坑算例，研究“平台”式分隔型基坑的分坑施工顺序对坑外地层及既有隧道位移的影响. 结果表明，杭州软土地层分隔型基坑开挖引起的坑外地层和隧道位移与分坑施工顺序、分隔墙位置、软黏土厚度及隧道与基坑的相对位置等因素相关. 当采用先近后远施工时，远坑宽度越大，近坑围护墙变形、地表沉降和隧道位移越大. 对于先远后近施工，则反之，此时远坑与近坑宽度之比取3.0~4.0、近坑宽度取15 ~20 m的分坑方案对近坑围护墙和邻近隧道变形的控制效果最佳. 随着软黏土层厚度的增大，先近后远和先远后近2种分坑施工顺序引起的近坑围护墙变形、地表沉降和隧道位移均明显增大. 提出分坑施工顺序对坑外地层位移的影响分区的概念，影响分区的分界线可以简化取为与坑壁夹角近似为45°的直线，随着远坑宽度和软黏土层厚度的增大，先近后远施工引起的地层位移小于先远后近施工的影响分区的范围逐渐减小. 通过参数分析，提出与分隔墙位置和软土层厚度相关的影响分区分界线拟合公式.
关键词：
分隔型基坑,
既有隧道,
分坑施工,
变形,
位移影响分区
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