土体抗拉强度试验研究方法的进展

理论上土体的抗拉强度与抗压和抗剪强度一样是描述土体力学性质的重要指标之一，也是研究土体张拉破坏特性的基础。由于土体抗拉强度在数值上相对较小，且难以准确测量，在岩土工程领域常常被忽视。随着工程中的张拉破坏问题越来越突出，土体抗拉强度特性引起许多学者的关注，相关研究成果也越来越多。文中对土体抗拉强度试验研究方法进行了系统的归纳和总结，对比分析了各种方法的优缺点，认识到，（1）土体抗拉强度试验方法总体上可分为直接法和间接法两大类，直接法是在试样两端直接施加拉力直到试样发生张拉破坏，根据破坏时的最大拉力及对应的破裂面面积计算出土体的抗拉强度。间接法主要通过一些理论假设，把压应力转换成相应的拉应力并基于一些理论公式计算土体抗拉强度；（2）按试样受力条件，直接法可分为单轴拉伸和三轴拉伸，一般都需要开发专门的拉伸试验设备，以实现拉力荷载的施加及其在试样内的有效传递。常用的方式有粘结、锚固、模具夹持及摩擦力传递等，都各有优缺点，但模具夹持法相对而言更具操作性。间接法中比较有代表性的有巴西劈裂试验、土梁弯曲试验和轴向压裂试验等，一般较适应于刚度较大的土体如化学固化土。最后，笔者提出了今后该课题的研究重点，包括制定土体抗拉强度试验方法规范及标准，研发简单易操作的土体拉伸试验设备，拉伸试验过程中土吸力的测量及控制方法，土体拉伸过程中应变场的准确获取方法及土体张拉特性的数值模拟研究等。

Advances in experimental testing methods of soil tensile strength

Tensile strength, like compressive strength and shearing strength, is one of the most important engineering indexes to describe the properties of soil. Tensile strength is also the base of studying the characteristics of soil tensile damage; but tensile strength is always neglected in geotechnical engineering practice because it is relatively small on the value and hard to measure. With tension failure of the project more and more problems, the tensile strength properties of the soil caused by the concern of many scholars, research results are more and more. The paper on soil tensile strength test conducted systematic research methods and summarized, comparative analysis of the advantages and disadvantages of every method; it is recognized (1) The methods used in tensile strength tests can be cataloged into two classes of direct tensile test and indirect tensile test generally; in direct tensile test, tension force is directly applied on both ends of the specimen until the fracture occurs; then, tensile strength can be calculated with the maximum tension and fracture surface area; indirect method is mainly through a number of theoretical assumptions, the compressive stress is converted into the corresponding tensile stress and tensile strength of soil calculated based on some theoretical formula. (2) According to different stress conditions, the direct tensile test can be divided into uniaxial tensile test and triaxial tensile test. Generally speaking, both these two methods need special test apparatus to apply tensile load and realize its effective transfer within the specimen. Different designs are used in the apparatuses, such as glue, anchoring, mould and friction. Every design has its advantages and disadvantages; but mould is convenient for use comparatively; indirect tensile test mainly includes the split tensile test (Brazilian test), soil beam bending test and the axial fracturing test. These methods are adapted to stiff soil better, like chemical reinforced soil. Finally, some important research topics that should be well investigated in the future are proposed, including the establishment of standard tensile strength testing methods, developing simple soil tensile test apparatus, finding the method to measure and control the suction, acquiring the strain field information and numerical simulation research during the test.