高填黄土明洞减载结构及土压力计算方法研究

This subject adopts laboratory tests combined with theoretical analysis and numerical simulation to study the unloading mechanism of load reduction structure and distribution regularity of earth pressure for high fill loess open cut tunnel, and further obtain the calculation method of earth pressure. By using the consolidation test and triaxial test, the deformation modulus, cohesion, frictional angle of different compactness loess specimen are tested to study the changing with compactness. Guided by similarity theory, the more factors coupled action are considered, such as structure dimension, side slope angle, foundation stiffness, back filling and load reduction material mechanical properties, layer-by-layer filling and step loading on the model are carried out to simulate the construction process, the model test and numerical simulation of high fill loess open cut tunnel with EPS slab and geogrid are analyzed to study on the unloading mechanism of load reduction structure and distribution regularity of earth pressure. Based on the load reduction mechanism of a culvert and the characteristic of a high fill loess open cut tunnel, load reduction structural mechanics model is established, the earth pressure calculation method of high fill loess open cut tunnel is derived via the theory of rock and soil mechanics, providing the mutual authentication with laboratory tests and numerical analysis. Through in-depth study on experiment and theoretical systematically, it can provide a theoretical guidance and technical assistance for design and construction in the future.

本课题采用室内试验、理论分析和数值模拟相结合的方法，研究高填黄土明洞减载结构卸荷机制及其土压力分布规律，并进一步得到其土压力的计算方法。通过室内固结试验、三轴试验测试不同压实度黄土试样的变形模量、粘聚力、摩擦角等力学特性，研究其随压实度的变化规律；以相似理论为指导，考虑结构尺寸、边坡坡角、地基刚度、回填黄土及减载材料力学特性多因素耦合作用，通过逐层填土、分级加载模拟实际施工过程，进行EPS板+土工格栅减载结构的高填黄土明洞模型试验及数值模拟分析，研究减载结构卸荷机制及其土压力分布规律；基于涵洞（管）减载原理，结合高填黄土明洞特点，构建其减载结构力学模型，利用岩土力学理论，研究高填黄土明洞减载结构土压力计算方法，并与室内试验、数值分析结果相互验证。通过深入系统地进行试验和理论研究，为该类结构的设计、施工提供理论指导和技术支持。

我国黄土高原地区沟多坡陡，随着城市化进程空前加速，高速铁（公）路网正向西部地区不断延伸，无法避免要穿越黄土沟壑地段，填沟造地，从而出现了高填方明洞这种特殊结构，而额外的土压力会影响明洞使用安全。本课题首先以相似理论为指导，考虑结构尺寸、边坡坡角、地基刚度、回填黄土及减载材料力学特性多因素耦合作用，进行EPS板+土工格栅减载结构的高填黄土明洞模型试验及数值模拟分析，研究减载结构卸荷机制及其土压力分布规律。其次，基于岩土力学原理，推导了减载前后高填明洞洞顶土压力的计算公式，并通过数值模拟结果和现场实测结果验证了该计算方法的正确性。最后，进一步对影响土压力集中系数的参数敏感性进行分析。结果表明：明洞顶一定高度范围内铺设 EPS 板+土工格栅可改变土体的相对沉降方向，引起土体应力重分布，促使土拱效应的形成，从而减小明洞洞顶垂直土压力；增大填土边坡坡角、明洞顶设置低压实土、铺设土工格栅、提高明洞两侧填料压缩模量可减小明洞洞顶土压力，其中，增大边坡坡角卸载作用最优。本课题研究成果可为高填黄土明洞卸载措施的设计和施工提供参考依据。