温度梯度诱导的冻土非均质机制及力学响应研究

The engineering background of the current application is the stability control of thick frozen shaft with non-uniform temperature. The heterogeneities induced by thermal gradient present the non-linear behavior, and that can not be obtained by the current test method or theories. The key scientific issue of the current application is aiming at the action mechanism of thermal gradient to the deformation fracture of frozen soils. In this application, we will take the heterogeneities induced by thermal gradient on as the basic object, and the emphasis will be put on the existing form of the heterogeneities and the evolution laws. The comprehensive research approaches including frozen hollow cylinder test with single radial thermal gradient, numerical simulation tests on the frozen hollow cylinder with combinatorial radial thermal gradients based on the 3D deformable distinct element method, physical simulation test on the frozen shaft (frozen hollow cylinder with combinatorial radial thermal gradients) ,and theoretical analysis will be all under consideration. In addition, the K0DCGF (K0 consolidation, freezing with thermal gradient under loading) method, distribution strain measurement sensors composed by carbon black and silicon rubber, and digital photography technologies will be adopted according to the distinguishing features of the object investigated. On the basis of above mentioned, we will then carry out the investigation on the basic characteristics and basic laws for the formation and variation of the cracked frozen structures with non-uniform temperature. Furthermore, both the local and total deformation and strength for the frozen hollow cylinder will be further studied. In the end, the responses of non-uniform deformation-local fracture- the overall instability of the frozen hollow cylinder to the thermal gradient will be obtained. The anticipated achievement will provide a scientific and fundamental support for the stability dynamic control of the frozen shaft in thick alluvium.

课题以非均匀温度厚冻结壁稳定控制为背景；针对现有试验方法和理论不能揭示温度梯度诱导的冻土非均质特性及其非线性力学行为的现状；紧紧围绕温度梯度对冻土体变形破坏的影响机理这一关键科学问题；以温度梯度诱导的冻土非均质效应为研究对象；以非均质性赋存形态与演变规律为研究重点；采用径向单一温度梯度冻结圆筒试验、基于三维可变形离散元理论的径向组合温度梯度冻结圆筒数值试验、冻结壁物理模拟试验与理论分析相结合的综合研究方法；应用K0DCGF(K0固结-保持荷载冻结-形成温度梯度-再试验)、基于炭黑-硅橡胶复合导电传感元件的分布式变形测量、数字照相等技术与手段；研究冻结圆筒中非均匀温度冻土破裂体形成、演化的基本特征与基本规律；明确冻结圆筒变形-承载性能与温度梯度之间的相互关系；揭示冻结圆筒非均匀变形-局部破裂-整体失稳过程对温度梯度效应的力学响应机制。研究成果将为特厚冲积层中冻结壁稳定性动态调控提供科学依据。

课题以非均匀温度厚冻结壁稳定控制为背景，针对现有试验方法和理论不能揭示温度梯度诱导的冻土非均质特性及其非线性力学行为的现状，首次研制出温度梯度冻结圆筒实验系统，温度梯度控制精度≤0.05℃/cm，构建了竖直—水平—组合—二维温度梯度冻土试验、温度梯度冻土相似材料制备等方法体系。在此基础上，以室内试样试验、离散元数值试验为主，以基于冻土材料的理模拟试验和基于相似材料的试样尺度模型试验为辅，深刻揭示出温度梯度诱导的冻土非均质机制和“梯度非均质”力学行为。温度梯度诱导的冻土非均质机制为细观冰—水—土骨架空间排列结构的非均匀性及其非线性演化。以位移增量、细观颗粒配位数等空间分布表征温度梯度诱导的冻土非均质，发现“梯度非均质”行为具有非连续、非平衡、非线性、多尺度等特征。温度梯度的出现和增加不改变冻土的宏观变形响应曲线，但是会弱化冻土的峰值强度和变形模量，并导致冻土表观脆性程度增加。温度梯度出现和增加导致冻土变形呈现显著的局部化分叉行为，局部化区内具有剪切和劈裂两种力学行为，局部化区外具有弹性卸载和局部化区内的继续损伤两种力学行为。且局部化区具有“移动”现象。冻土峰值强度随温度梯度与加载方向间的夹角增加而增加。加载方向与温度梯度方向垂直时随温度梯度增加，冻土试样的宏观破坏角逐渐增加，整体劈裂趋势加强。加载方向与温度梯度方向平行时随平均温度增加，温度梯度冻土的局部化区变形量减小、高度增加、整体劈裂趋势增强，相同平均温度随温度梯度增加，剪切破坏趋势减弱。保持平均温度和温度梯度，温度梯度冻土强度随高度增加而逐渐降低，随平均颗粒尺寸增加而降低，且不同温度条件下存在“临界”特征尺寸，小于该尺寸冻土强度基本不随尺度变化而变化，破坏行为受剪切控制为主。临界状态下梯度非均质度与冻土强度、峰值体应变间具有一阶线性响应关系，该关系与温度、土质、加载方式无关。研究成果为发展特厚冲积层中冻结壁设计和稳定控制理论提供科学依据。