黄土抗拉强度和各向异性研究

Loess is a special kind of soil due to its structural strength and water sensitivity.Numerous systematic studies have been conducted to investigate the collapsibility and shear strength, which had yielded great achievements both at home and overseas. In contrast, the tensile strength and anisotropy of loess have attracted much less attention and the related research were very poor. So some error or inaccuracy might occur when the fundamental mechanical properties of loess need to be considered correctly and the calculation parameters of loess engineering need to be determined rationally. This research is going to investigate the experimental method of tensile strength, stress and strain characteristics and anisotropy of intact loess in Lanzhou and the adjacent areas, to grasp the major influencing factors of tensile strength and anisotropy of loess by using experimental tests and statistical analysis. Combined with the comparative experimental research on unconfined compressive strength and shear strength of intact loess, the related calculation mechanical parameters and constitutive model would be proposed, which will take the anisotropy of loess into consideration. This research could also provide the basic data and lay the theoretical foundation to comprehensively understand the structural strength and vertical joints of loess and their engineering application.

黄土是典型的结构性和水敏感性特殊岩土材料，国内外针对其湿陷性和抗剪强度等方面已展开了大量的系统研究，成果颇丰。相比而言，国内外对其抗拉强度和各向异性特点的研究相对较少。这给正确理解黄土的地质力学特性和合理确定黄土工程设计的计算参数带来一定的偏差。本课题拟以兰州及其附近地区的典型黄土为研究对象，通过对原状黄土抗拉强度试验方法、拉伸应力应变规律和各向异性特点的试验研究和统计分析，结合黄土无侧限抗压强度和抗剪强度的对比试验研究，掌握影响黄土抗拉强度和各向异性的主要影响因素，考虑黄土的各向异性特点，提出相应的计算力学参数建议和本构模型，为全面认识黄土的结构性和垂直节理等特性及其工程应用提供数据支持和理论依据。

本项目以兰州、定西、延安等地区的典型黄土为研究对象，通过对大量原状黄土和重塑室内轴向劈裂抗拉强度试验、抗剪强度试验、无侧限抗压强度试验等，分析研究了黄土拉、压和剪应力作用下的变形破坏特点及规律。主要工作和成果如下：.（1）推导了轴向劈裂法测定岩土抗拉强度的计算公式以及抗拉强度与抗压强度和粘聚力的相关性，用不同类型的原状和重塑黄土进行验证，分析了轴向劈裂破坏的力学机理及影响因素，结果显示重塑黄土无侧限抗压强度与抗拉强度的比为13.19，粘聚力与抗拉强度比为3.93，原状黄土无侧限抗压强度与抗拉强度比为9.81，粘聚力与抗拉强度比为2.50。.（2）系统讨论了黄土密度、含水量、饱和度等物性参数和试验条件（如加载速率、制样方法、试样尺寸等）等因素对黄土抗拉强度的影响，给出了适合于黄土抗拉强度的试验参数，亦即加载速率在1.0mm/min下测定的不同试样强度值间的变化幅度为最小，高径比为1:1的试样的抗拉强度值既位于不同试样强度值变化过程中的中间位置又处于强度相对差值的最小处，静压制样优于击实制样且其抗拉强度较大。.（3）通过系列对比试验，研究了水平和垂直两个不同方向黄土强度与变形特征，给出了建议的变形与强度参数取值方法，初步提出了考虑抗拉强度和各向异性的黄土本构模型及其参数确定方法，研究表明：垂直方向黄土试样在强度、变形方面均优于水平方向的黄土试样，对传统 E-B 模型进行修正，将试样破坏阶段分为线弹性阶段、弹塑性应力峰值阶段和塑性破坏阶段，按硬化规律可将黄土应力应变曲线划分为强硬化、硬化、弱硬化、弱软化、软化、强软化等六类。.（4）结合试验研究，将黄土工程力学特性研究在黄土隧道工程中加以推广应用，提出了隧道工程中黄土围岩变形破坏的三种类型，并针对黄土隧道工程提出围岩分级的方法和建议参数，为理论研究与工程实践提供技术指导与数据支持。.