Tensile Behavior of Weak Rocks
Jyh Jong Liao
|關鍵字:||軟岩;張力強度;直接張力試驗;破壞準則;應力應變關係;weak rocks;tensile strength;direct tension test;failure criterion;stress-strain relationship|
Due to the difficulties of direct tensile testing, neither direct tensile behaviors of weak rocks are not understood completely, nor are tensile properties adopted for rock engineering design. A suitable direct tensile grip for weak rock has been developed for not only measuring the direct tensile strength but also the axial displacement during tests. Besides, a series of direct tensile tests and indirect tensile tests (Brazilian tests) was conducted using a weak rock. Then, the experimental results were adopted for investigating the direct tensile behaviors and the relationship of indirect and direct tensile strength.All tests were performed on specimens cored from rock blocks collected from a construction site at the Dakeng hilly area of the Taichung City, Taiwan. Experimental results indicate that the direct tensile strength is about 0.05 MPa - 0.58 MPa, the average uniaxial compressive strength is15 - 40 times higher than the direct tensile strength. Also, the tensile strength decreases with the increase of the water content in the specimens. Incorporating with the results of consolidated undrained triaxial tests and using a regression analysis, it is found that the experimental data match well with the Hoek-Brown failure criterion. Hence, the author recommends that the criterion can be used for predicting the direct tensile strength of weak rocks.Stress-strain curves obtained from direct tensile tests exhibit nonlinear relationships. Most of the specimens failed while the axial strain is lower than 0.1 %, and the curve are linear for the axial strain less than0.005%. The curves can be simulated well by a hyperbolic function. Also, the characteristics of material bi-modularity exists in the rock which Young's modulus in tension is lower than compression.