Abstract: The self-boring pressure meter tests (SBPT) and seismic dilatometer tests (SDMT) are conducted in the granite residual soil to obtain the in-situ shear modulus and shear modulus degradation. The shear modulus decay by shear strain was measured by resonant column tests(RCT), and the approximate in-situ shear modulus decay curves were deduced from the data of RCT and SDMT to analyze the suitability of the proposed approach. The results show that complete in-situ shear modulus degradation curves can be directly derived using‘Stokeo model’ from the combination of initial shear modulus G0 measured by SDMT and G- decay curve measured by SBPT. By comparing the results of resonant column tests under different stress states, a deduction is found in laboratory process of sampling, transporting and preparing of soil, causing unrecoverable damage in the soil. By comparing the results of the forecasting method by RCT and SDMT, the initial stage of the G- decay curves are found consistent with the proposed method. However, the stiffness attenuation rates of the proposed method are lower. After a comprehensive comparison of the three methods, the proposed approach proved to show a good suitability in the stiffness analysis of structural soil. The result provides an important reference for the selection of engineering parameters in relative soil layers.

Key words: granite residual soil, G- decay curves, self-boring pressure meter test, seismic dilatometer test, suitability