含大粒径漂石复合地层地下连续墙槽壁稳定性三维极限分析与控制研究

Three-Dimensional Limit Analysis and Control Study on the Stability of Diaphragm Wall Trench Walls in Composite Strata Containing Large-Grain Boulders

摘要: 针对含大粒径漂石、卵石等非均质复合地层中地下连续墙成槽极易失稳塌孔的工程难题，本文依托北京地铁1号线支线工程，提出了一套理论评价、数值揭示、现场控制的完整方案。首先，突破传统均质地层假设与二维平面应变局限，基于塑性力学上限极限分析定理与空间刚体离散技术，构建了适用于三维复合地层的二阶锥规划(SOCP)优化模型，推导并反演了维持槽壁稳定的极小泥浆重度。其次，构建三维非线性有限差分模型，揭示了复合地层槽壁的宏观失稳机理与空间应力–应变演化规律。最后，基于理论预测的极限目标参数，研发了适用于大孔隙地层的高分子聚合物改性泥浆，并通过现场高频超声波探测验证了控制效果。试验结果表明复合地层临界滑移面受抗剪强度空间突变控制，呈现显著的“折射”与“土拱”效应；最危险破坏面具有极强的“地层靶向性”，优先发育于低黏聚力卵石层；理论优化的聚合物泥浆(密度1.12 g/cm³)成功在深部易扰动地层孔隙中水化固结出3~5 mm厚的致密低透泥皮，实现了长达8小时、深36 m槽壁的全尺度稳定。

Abstract: To address the critical engineering challenge of extreme vulnerability to instability and trench collapse during the excavation of diaphragm walls in heterogeneous composite strata containing large boulders and cobbles, this paper proposes a comprehensive scheme integrating theoretical evaluation, numerical investigation, and on-site control, based on the Branch Line Project of Beijing Subway Line 1. First, breaking through the limitations of the traditional homogeneous stratum assumption and two-dimensional (2D) plane strain, a Second-Order Cone Programming (SOCP) optimization model applicable to three-dimensional (3D) composite strata was constructed. This model, based on the upper bound limit analysis theorem of plasticity and 3D rigid block discretization technique, deduced and back-calculated the minimum slurry unit weight required to maintain trench wall stability. Second, a 3D nonlinear finite difference model was established to reveal the macroscopic instability mechanism and the spatial stress-strain evolution patterns of the trench wall in composite strata. Finally, based on the theoretically predicted limit target parameters, a polymer-modified slurry suitable for highly porous strata was developed, and its stabilization effect was verified through in-situ high-frequency ultrasonic detection. The experimental results demonstrate that the critical slip surface in composite strata is controlled by the spatial abrupt variation in shear strength, exhibiting significant “refraction” and “soil arching” effects. Furthermore, the critical failure surface displays a strong “stratum-targeting” characteristic, preferentially developing in the low-cohesion cobble layer. The theoretically optimized polymer slurry (density 1.12 g/cm³) successfully hydrated and consolidated within the pores of the deep, easily disturbed strata to form a dense, low-permeability filter cake with a thickness of 3~5 mm, achieving full-scale stability of the 36 m deep trench wall for up to 8 hours.