Abstract:

Completely weathered granite exhibits distinctive engineering behavior, making it difficult to obtain its shear-strength parameters using conventional methods. At present, most researchers determine shear strength through direct shear tests and triaxial shear tests, yet these approaches often overlook the influence of specimen size on geomaterial strength and weaken boundary effects. As a result, the derived shear-strength parameters tend to be higher than those under actual field conditions, which may compromise engineering safety. By comparing results from large-scale in-situ direct shear tests with those from conventional laboratory direct shear tests on undisturbed samples and further comparing direct shear results of remolded completely weathered granite specimens of different sizes, this study analyzes the discrepancies in shear-strength parameters obtained under various indoor and outdoor shear conditions. The test results indicate that cohesion c decreases with increasing specimen size, while the internal friction angle φ shows an increasing trend. Additionally, the strength of undisturbed samples is greater than that of remolded samples. These findings demonstrate that soil structure and specimen size exert significant influence on the shear strength of completely weathered granite.

Key words: Completely Weathered Granite, Shear Strength Index, Direct Shear Test, Sample Size