复杂应力路径下过湿低路堤永久变形特性研究

The permanent deformation of subgrade is the result of the coupling effect of complex stress and humidity. Due to the inadequacy of existing subgrade design methods, the permanent deformation of low embankment is often underestimated. The key to improve the prediction accuracy of permanent deformation of low embankment lies in the accurate grasp and scientific expression of the law of plastic strain and pore water pressure accumulation under actual traffic load. Starting from the actual stress and equilibrium humidity state of the low embankment, based on the saturated porous media theory, a mechanical model of the low embankment considering the influence of pore water was established to analyze the actual stress history and stress path characteristics of the low embankment. According to the principle of graded loading and hollow cylinder torsional shear test, partial drainage intermittent cyclic torsional shear test was designed to simulate the complex stress path action in soil under discontinuous traffic load. The effects of initial stress, cyclic stress, loading frequency and humidity on the plastic strain and pore pressure accumulation of low embankment were studied. Combined with the layered summation method and unidirectional drainage consolidation mechanism of taisha foundation, a experiential model for predicting the permanent deformation of low-wetting embankment is established, and the characteristics of plastic stability and cumulative failure of permanent deformation are analyzed. The research results can provide theoretical guidance for improving the prediction accuracy of permanent deformation of excessively wet low embankment.

路基永久变形是复杂应力与湿度耦合作用的结果，长期处于高应力过湿状态的低路堤永久变形问题尤为严峻。现有路基设计方法的不足使低路堤永久变形常常被低估。提高低路堤永久变形预估精度的关键在于，对实际交通荷载作用下土体塑性应变累积规律与孔隙水压力累积-消散规律的准确掌握与科学表达。项目从低路堤实际应力与平衡湿度状态出发，基于饱和多孔介质理论建立考虑孔隙水影响的低路堤力学模型，分析低路堤实际应力历史与应力路径特征；根据分级加载与空心圆柱扭剪试验原理设计建立部分排水间断循环扭剪试验，模拟非连续交通荷载下土中复杂应力路径作用；采用该试验研究初始应力、循环应力、荷载作用次数及湿度对低路堤土体塑性应变与孔压累积规律的影响；结合分层总和法与太沙基单向排水固结机理，推导建立经验型过湿低路堤永久变形预估模型，并分析永久变形的塑性安定与累积破坏行为特征。研究成果可为提高过湿低路堤永久变形预估精度提供理论指导。

随着低路堤高速公路建设需求不断扩大，过湿低路堤永久变形问题日益突出，但是由于对低路堤的实际状态考虑不足，现有路基设计与永久变形控制方法对过湿低路堤的适用性存疑。因此，有必要对交通荷载在过湿低路堤中引起的复杂应力特征进行系统分析，建立更符合实态的模拟加载方法对复杂应力路径下过湿低路堤土体塑性应变及土中孔隙水压力累积规律进行深入研究，采用更直观方法对过湿低路堤永久变形行为进行表达，从而提高过湿低路堤永久变形预估精度。路基填土作为典型的弹塑性体，在随机交通荷载作用下将产生土颗粒破碎、相对位置重新排布及土中孔隙水排出等变形响应，随着荷载作用次数的不断增加，在竖向逐渐形成了可观的路基永久变形。路基永久变形是复杂应力与湿度耦合作用的结果，长期处于高应力过湿状态的低路堤永久变形问题尤为严峻。项目从低路堤实际应力与平衡湿度状态出发，基于饱和多孔介质理论建立考虑孔隙水影响的低路堤力学模型，分析低路堤实际应力历史与应力路径特征，研究了多层低路堤动荷载理论计算方法，掌握了交通荷载作用下过湿低路堤应力水平、应力历史与应力路径特征。根据分级加载与空心圆柱扭剪试验原理设计建立部分排水间断循环扭剪试验，模拟非连续交通荷载下土中复杂应力路径作用，建立了模拟复杂应力作用的部分排水间断循环扭剪试验方法，开展了不同应力路径下典型过湿低路基填土累计塑性应变室内试验，明确了过湿低路堤土体塑性应变累积发展规律。结合分层总和法与太沙基单向排水固结机理，甄选恰当的模型形式，构建了过湿低路堤土体塑性应变预估模型，提出了过湿低路堤土体永久变形计算方法。针对过湿低路堤永久变形防控技术的不足开展了深入研究，预期成果有望提高过湿低路堤永久变形计算精度，并可为建立低路堤永久变形防控新技术提供理论指导。