季冻区土体冻融损伤及边坡冻融滑塌机理研究

In Seasonally frozen region, due to natural freeze-thaw cycles, structure of undisturbed soil in slope is damaged in seasonally frozen layer and its mechanical characteristics are reduced; meanwhile water field of freeze-thaw soil is redistributed and plenty of water extraordinarily accumulates on the freeze-thaw interface of slope soil, which finally result in freeze-thaw slope-collapse. What's more, the engineering problem of freeze-thaw slope-collapse is quite general on a large scale almost at the same period and in the same seasonally frozen area,and the problems of freeze-thaw hazards are more and more significant, which have cased enormous damage and economic loss to water and transport projects, country and people. .Through site investigation on freeze-thaw collapsed slope, experiments on physical and mechanical capacity of freeze-thaw soil and freeze-thaw model tests of slope will be performed, and freeze-thaw damage mechanism of soil and influence of freeze-thaw on soil structure and water redistribution of slope will be researched. Results of tests and site monitoring of freeze-thaw soil slop will be applied to reveal the mechanism of freeze-thaw slope-collapse and main reasons of different types of slope-collapse. . Constitutive model of freeze-thaw soil will be found through the relationship of soil structure, water ratio and soil mechanical capacity. By finite element method software and coupling model of water (ice), heat and force, the mechanism research will be developed on freeze-thaw collapse of soil slope with different weather conditions and seepage action in seasonally frozen region. Analysis method and management technique of freeze-thaw stability of soil slope in seasonally frozen region will be proposed to conduct the design of slope engineering, early warning of freeze-thaw slope-collapse and freeze-thaw hazard control.

季节冻土区土质边坡因遭受天然冻融作用，土体的结构受到损伤、力学特性衰减，冻融土体内水分场重分布、冻融界面处大量融水异常聚积，导致季冻区土质边坡冻融滑塌问题十分普遍，常同时同地大规模发生，冻融滑塌灾害问题逐年增多，对交通水利工程和国民经济均造成巨大危害和损失。本项目通过冻融滑塌边坡现场勘测、冻融条件下土体物理力学性质室内试验和模型试验相结合，研究土体冻融损伤机理、冻融循环对土体结构和冻融边坡内部水分重分布、聚积的影响，并结合边坡工程现场监测，揭示边坡土体冻融滑塌机理，不同类型冻融滑塌的产生要因与机理分析，利用土体结构与土体力学性能的关系以及力学性能与含水量的关系，建立冻融土体本构模型，借助大型有限元软件在考虑水（冰）、热、力耦合条件下分析不同气象环境渗流作用下季节冻土区土质边坡冻融滑坡的机理研究，提出季节冻土区土质边坡冻融稳定性分析方法与治理措施，指导边坡工程的设计、冻融滑坡预警及灾害治理。

季节冻土区边坡工程冻融滑塌事故频发、造成巨大经济损失，严重影响关系国计民生重大项目的建设、运营与发展，现有工程技术不能有效防治冻融滑塌灾害，因此季冻区边坡冻融灾害机理研究已成为亟待解决的重要基础性科研问题。为此项目组开展了如下关键研究工作：季节冻融边坡土体力学性能损伤研究及其本构模型建立，季节冻融—渗流导致土质边坡滑塌的破坏机理，季节冻融土质边坡潜在冻融破坏位置稳定性及特有整体发展规律。项目研究获得了以下关键成果：经历季节冻融后原状土抗剪强度大幅降低、可达50%以上，7次冻融后稳定，对冻融土内摩擦角随冻融次数增加而增长的趋势给予了全新机理解释。分析了原状土季节冻融损伤，提出相对初始切线模量损伤率的定义，并建立了原状土的季节冻融损伤模型。根据模型试验获得了季冻区土质边坡冻融—渗流滑塌类型：浅层滑塌破坏、局部滑塌破坏和整体滑塌破坏，分别主要发生在季节冻土层融化前期、中期和完全融化后期。春融期降雨对边坡坡顶和坡脚稳定性影响较大；坡脚积土量与降雨强度具有一个动态平衡点；降雨停止后的一段时间内，降雨对土体产生持续影响。春融期降雨7小时后，由于孔隙水压力的消散，季节冻融边坡土体有效应力增加，冻融土层基质吸力增加，边坡内部仍然存在非饱和渗流，导致降雨停止一段时间后边坡更易发生滑坡。对季节冻土区边坡处于冻融过渡带土体的抗剪强度参数进行理论分析研究，推导出粘聚力和内摩擦角的冻融损伤模型。建立了季节冻融边坡数值模型，并得到了分析方法与季节冻融土质边坡滑塌破坏的特点与规律。春季融沉阶段，随着气温的升高，边坡融化的土体逐渐增多，融化深度逐渐增大，冻融过渡带的位置从0.5m发展到1.6m左右，在极限状态下，季冻区边坡在融沉期的滑移破坏形式为：靠近坡顶处滑移面近似为平行于土体的平面，坡底部滑移面为圆弧面。综上研究成果可知，对边坡土体施以具有排水或排水固结作用的工程措施，将会使冻融后土体的抗剪强度得到一定的恢复或提高，利用这些成果可以全面掌握季冻区边坡稳定性的变化规律，直接分析边坡的最不利稳定状态，可大大减少对边坡稳定性分析和评价的工作量为解决季冻区土体边坡冻融稳定性问题提供了新的思路和理论支持。