考虑大变形特征的超深冻结壁弹塑性设计理论

Elastoplastic design theory for ultra-deep frozen wall considering large deformation features

冻结法是深厚不稳定、含水地层中最主要的凿井方法,冻结壁设计理论是冻结法凿井的技术核心之一。以往的深井冻结壁(表土层厚度超过400 m)设计理论忽略冻结壁变形对其尺寸、位置的影响,既偏于不安全,又低估开挖土方量。为了考虑超深表土层内大变形的影响,采用有限应变推导出变形前冻结壁的开挖半径与有效厚度的求解公式,建立冻结壁厚度设计新理论;与数值计算结果对比,分析了地应力、冻土黏聚力、冻土内摩擦角、弹性模量等参数对冻结壁厚度与井帮位移的影响。结果表明:新理论既能解决小变形问题,又能解决大变形问题,忽略弹性应变的理论公式能适用于应变达0.15的大变形情况,新理论还能准确地计算开挖土方量,为超深表土层冻结壁设计提供理论参考。

The freezing method is a key sinking method used in deep aquifer. The frozen-wall design theory is a key technique for the freezing method. However, the previous design theories for a deep artificial frozen wall have neglected the influences of side-wall deformation on its sizes and locations. Thus, the associated designs tend to be unsafe and the earthwork excavations tend to be underestimated. In order to consider the influences of a large deformation, new solution formulas for excavation radius and outer radii before deformation occurs are deduced by finite strains, and a new design theory for frozen-wall thickness is established. The analytical results are compared with numerical ones by analyzing the effects of various parameters, such as the crustal stress, and the cohesion, internal friction angle, and elastic modulus of frozen soil, on the side-wall displacement and frozen-wall thickness. The results indicate that both the small deformation and large deformation problems can be solved by the new formulas, the theoretical formula neglecting elastic strains can be applied to large deformation with strain up to 0.15, and the new formulas can accurately calculate the amount of excavation earthwork, and provide a theoretical reference for the design of frozen wall in ultra-deep soil layers.