击实粘性土断裂韧度KIC的试验研究

LABORATORY STUDY ON FRACTURE TOUGHNESS KIC OF COMPACTED CLAY

用线弹性断裂力学理论,研究土体中裂缝的产生和扩展过程的可行性已经为很多学者所认可,但对土体断裂韧度断裂韧度KIC的测试方法尚未形成共识。标准的三点弯曲试验中,土梁可能仅在自重作用下就发生断裂破坏,即使不发生这种试验前的断裂破坏,由于试样自重与断裂荷载相比是不可忽略的,试样自重对试验结果也存在较大影响。首先对标准三点弯曲试验方法进行了改进,研制了适于测试土体断裂参数的测试仪,并用其对某堆石坝心墙料的室内击实试样进行了断裂韧度KIC的测试,论证了线弹性断裂力学的适用性,研究了试样干密度和试验含水量对断裂韧度KIC的影响。

It is widely accepted that the linear elastic fracture mechanics （LEFM） can be used to investigate the induction and propagation of cracks in soil, especially for over-consolidated and hard clay, but no method is acknowledged to be perfect to determine fracture toughness Kic of soil in laboratory. In conventional three-point bending beam test, the single edge cracked beam （SECB） may be fractured only due to gravity itself. Even if no fracture failure of specimen occurs before test, the influence of the gravity of the specimen on test results can not be ignored because it is not little enough compared with fracture load. In this study, an improved method of three-point bending beam loading test is suggested, which can avoid the fracture failure before test and remove the influence of the gravity of the specimen because the loading direction is horizontal. Based on the improved method, an apparatus to determine fracture toughness Kic of soil is developed. The apparatus does have very simple structure, but its operation is very easy and its test result is reasonable enough. Using the improved testing method and the new apparatus, the fracture toughness Kic of compacted clay which is used to build the core wall of a high rock-fill dam in West China is investigated. The reasonability of LEFM used to describe the characteristics of the clay in the course of fracture failure is testified. The influences of dry density and water content in testing of specimen on Kic are also investigated. For the specimens which are made under the same water content, the values of Kic increase with the increase of the dry density. But for those that are made under both the same water content and dry density, with the variation of water content in test a maximum value of Kic appears.