承压水地层管廊基坑开挖变形特征及抗突涌稳定性分析

管廊穿越富水软弱地层时,对其安全建设产生了不容忽视的影响。为了研究富水地层管廊基坑开挖变形的稳定性,依托济南新东站开源路富水地层管廊基坑工程,分析影响基坑开挖变形的关键因素,提出基坑周边土体变形破坏影响因素的敏感性评价指标,建立基坑底板抗突涌稳定性系数及隔水层临界厚度公式。结果表明:随开挖深度和承压水头增加,水平位移具有分层现象,深层呈“月牙形”,最大变形位于基坑底部两侧下部,呈现向桩后和基坑中心靠拢趋势;地表沉降呈凹槽形,从基坑边向两侧呈先增大后减小趋势,而隆起变形越靠近基坑中心越大,施工中应注意基坑底部两侧向中间过度时出现的较大隆起值。基坑周围土体变形破坏影响因素指标敏感性大小依次为开挖深度、加固厚度和承压水头,施工时要适当采取降水措施,预留足够的隔水层厚度,加固坑底以增强其稳定性,更要适当控制基坑开挖深度;与传统法相比,考虑土体抗剪强度所计算的基坑抗突涌稳定性系数较大,隔水层临界厚度较小,与现场情况更加吻合。

Analysis of deformation characteristics and stability against water inrush during excavation of foundation pit for utility tunnel in confined water stratum

Based on the foundation pit project for utility tunnel of water-rich stratum on Kaiyuan Road near the Jinan New East Railway Station, the key factors affecting the deformation of foundation pit excavation are analyzed, and the sensitivity evaluation index of the factors affecting the deformation and failure of soil around the foundation pit are put forward.Then the formula of stability coefficient against water inrush of foundation pit floor and critical thickness of impermeable layer are established. The results show that with the increase of excavation depth and confined water head, the horizontal displacement has a stratification, and the deep layer is crescent-shaped, and the maximum deformation is located at the bottom of both sides of the foundation pit, which tends to converge to the rear of the pile and the center of the foundation pit. The surface settlement is in a groove shape, which increases first and then decreases from the edge of the foundation pit to both sides. The closer the uplift deformation is to the center of the foundation pit, the larger the uplift value will be. During construction, attention should be paid to the large uplift value when the two sides of the bottom of the foundation pit are excessive to the middle. The order of sensitivity of the influencing factors of soil deformation and failure around the foundation pit is the depth of excavation, the thickness of reinforcement and the confined head. During construction, appropriate dewatering measures should be taken, enough thickness of the impermeable layer should be reserved, the bottom of the pit should be strengthened to enhance its stability, and the depth of excavation of the foundation pit should be properly controlled. Compared with the traditional method, the stability coefficient against water inrush calculated by considering the soil shear strength is larger and the critical thickness of impermeable layer is smaller, which is more consistent with the field situation.