Mechanical Properties of Gravel Deposits Evaluated by Nonconventional Methods

Gravel deposits are materials that contain large particles. The mechanical behavior of such materials is conventionally examined using large-scale tests such as large-scale triaxial and in situ shear tests. However, the large-scale tests may not fully represent the gravel deposits in the field or cannot obtain the deformation parameters. This study estimated the elastic and shear-strength properties of gravel deposits using nonconventional methods. Field investigations at various locations were performed to obtain the material factors, including the gravel content, the diameter in the grain size distribution curve that corresponded to 50% finer ($D_{50}$), the unconfined compressive strength of the gravel, and the penetration strength of the matrix. Seismic-wave testing was conducted to obtain the elastic parameters at each location. Around each location, the critical slope profiles with greatest gradients or heights were back-calculated to obtain c-phi curves, of which the envelope represents the shear strength of the gravel deposit. The mechanical properties of the gravel deposits were correlated with the four material factors and P-wave velocity using regression analysis. The Young’s modulus was correlated with the P-wave velocity, the unconfined compressive strength of the gravel, and the penetration strength of the matrix. The cohesion of a gravel deposit was correlated with the penetration strength of the matrix. The Poisson’s ratio and the friction angle were correlated with the four material factors. The results were successfully tested using data on two gravel deposits at other locations. For the gravel deposits in central Taiwan, the unconfined compressive strength of the gravel and the penetration strength of the matrix significantly affect the elastic properties, and the penetration strength of the matrix controls the shear-strength properties. Although the proposed regression models serve as a preliminary evaluation of the elastic and shear-strength properties of the gravel deposits in central Taiwan, these nonconventional concepts are applicable to gravel deposits elsewhere.