Abstract
A pressuremeter test (PMT) is a representative and highly reliable in situ test for assessing the stress–strain behavior of weathered granite. Its application, however, is restricted by its cost and time requirements. Many researchers have also investigated the correlations between the SPT-N value and the pressuremeter modulus (Em) and limit pressure (PL) of soils, but they have mostly focused on sand, silt, and clay and have employed simple regression analysis. In this study, equations for Em and PL were derived for weathered granite through multiple nonlinear regression analyses using a chemical weathering index that quantitatively represents the degree of weathering. Nonlinear multiple regression analyses were conducted by combining the allometric models that produced the optimal correlations between Em, PL, energy corrected SPT-N (SPT-N60), and normalized VR (Vogt’ ratio) with vertical effective stress. The obtained equations for Em and PL had higher R2 values (0.76 and 0.46, respectively) compared with the simple regression equations reported in previous studies. Because local characteristics are important determinants of the engineering properties of geo-materials, the Em and PL equations proposed in this paper are intended for use in geotechnical surveys of weathered granite in South Korea.
Highlights
Weathered granite, including residual soil and highly and completely weathered rocks, is widespread in South Korea and is used as the support base in the construction of major roads, bridges, and tunnels
The converted standard penetration test (SPT)-N value was corrected to SPT-N60, which corresponds to 60% of the energy efficiency for the energy transfer rate of the equipment used in the test
A chemical weathering index was calculated based on the weight percentage of the major oxides in the rock formed by weathering through the X-ray fluorescence (XRF) analysis
Summary
Weathered granite, including residual soil and highly and completely weathered rocks, is widespread in South Korea and is used as the support base in the construction of major roads, bridges, and tunnels. Bozbey and Togrol [8] proposed nonlinear relationships between the same parameters for sandy soil and clayey soil using the results of tests conducted in Istanbul, Turkey, while Cheshomi and Ghodrati [9] did the same for silty sand and silty clay based on SPTs and PMTs conducted in Mashhad, Iran. Most of these previous studies dealt with soils with SPT-N values of ≤50; none considered weathered granite with an N value of ≥50. The values of Em and PL determined by the proposed equations were compared with those obtained in previous studies and by field measurements
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