Development of a New Method for Estimating the Indirect Uniaxial Compressive Strength of Rock Using Schmidt Hammer

Abstract

Uniaxial compressive strength as one the mechanical properties of rock has various applications in rock engineering. This parameter can be determined directly either in laboratory tests or estimated indirectly using a cheap and conventional method such as Schmidt hammer rebound test and unit weight. Schmidt hammer rebound, unit weight, porosity and uniaxial compressive strength were determined for 104 specimens of different types of sedimentary, igneous and metamorphic rocks. Relationships of Schmidt hammer rebound value, unit weight and porosity of different types of rock and uniaxial strength were analyzed statistically using test results. Present relationships of estimating the indirect uniaxial compressive strength of rock were evaluated on the basis of the test results. Statistic analysis of the results showed that estimating indirect uniaxial compressive strength using the present relationships yields different re- sults compared to measured uniaxial compressive strength. Various relationships of estimating uniaxial compressive strength (σc) as a function of combination of three properties of Schmidt hammer rebound (Hs), unit weight (γ) and porosity (P) were applied to find improved relationships. For the relationship between uniaxial compressive strength (σc) and (Hs-P)γ a correlation (R2 =0.9501) was achieved. When effect of porosity as one of the weakness points of rock on the relationship was applied to analyze the test results, a relationship with a better correlation was obtained to estimate uniaxial compressive strength.