内撑式深基坑承压水抗突涌稳定数值模拟技术

承压水作用下,内撑式深基坑的突涌稳定状态与围护墙水平位移、土压力分布及坑底回弹变形等因素密切相关。建立了深基坑突涌稳定的数值分析模型,分析不同承压水位作用下的坑底突涌破坏机制、稳定性及相应的基坑变形性状,并与已有分析方法作对比。分析结果表明,承压水作用下,基坑围护墙内侧隔水层表面剪切应变最大,是突涌破坏的最危险位置。随着坑底承压水位的升高,隔水层内的剪切应变增量逐渐变大并向下部土层发展,最终在隔水层与承压含水层界面处产生楔裂破坏,隔水层整体顶升破坏。同时,基坑变形状态表现为,围护墙弯矩和水平位移逐渐增大,被动侧土压力逐渐减小,最终围护墙发生踢脚破坏,坑底土体大量隆起回弹。相对于压力平衡法和均质连续梁板法等理论方法,数值分析方法可以分析坑底土体的突涌渐进发展过程,较好地反应内撑式基坑抗突涌稳定性与围护墙及土体变形性状的相互影响,计算结果更为符合工程实际。

Numerical Simulation Technology for Hydraulic Heave Stability of Deep Braced Excavation under Confined Water

Under the effect of confined water, hydraulic heave stability of braced excavation is closely related to horizontal displacement of retaining wall, earth pressure distribution, and uplift of pit bottom, etc. Numerical models of deep braced excavation under confined water were established, hydraulic failure mechanism, hydraulic heave stability, and deformation of excavation at different confined water levels were investigated. In addition, the computed stabilities were compared with that of the limit equilibrium method and cohesive soil strength considering method. The results illustrate that: shear strain in cohesive aquiclude at the medial surface of retaining wall is the largest, and soil in this region is most easy failure at high hydraulic gradient. When confined water level rise, shear strain increment of aquiclude increase gradually and develop to lower soil layer. At last, soil at interface between aquiclude and confined aquifer appear wedge failure and the whole cohesive aquiclude uplifts. Accordingly, bending moment and horizontal displacement of retaining wall increase with the raised of confined water level, earth pressures at passive side of retaining wall gradually decrease, and excavation collapses because of the great pit bottom uplift. By numerical analysis method, the gradual development process of hydraulic failure can be gained, and interaction effect of hydraulic heave stability, retaining wall displacement and rebound of cohesive aquiclude can be well considered. Computed results would be consistent with actual excavation stability.