Development of a borehole pressure shear test apparatus for evaluating the in-situ geotechnical properties of intermediate geomaterial

Accurate evaluation of the geotechnical properties of weathered layers, comprising weathered residual soil and rocks, is critical for civil engineering stability. The preference for field tests over laboratory tests stems from the difficulty of obtaining undisturbed samples of weathered geomaterials for laboratory analysis. Standard field-testing techniques traditionally designed for rocks or soils face shortcomings when applied to weathered geomaterials with intermediate characteristics between those of rocks and soils. In response to this technical gap, this study introduces the borehole pressure shear tester (BPST), an innovative field-testing device integrating pressuremeter and borehole shear test methodologies. By applying horizontal and shear forces within a borehole, the BPST enables simultaneous evaluation of deformation and shear strength properties. Empirical tests on residual soils under simulated high relative densities and varied overburden stresses demonstrated its accuracy in determining deformation moduli and shear strength parameters. These results aligned well with triaxial and direct shear tests, validating the device’s reliability. By providing a novel approach for appraising the engineering properties and relevant parameters of intermediate geomaterials, the BPST contributes to the field of geotechnical engineering by enhancing the predictive capability and the design safety of infrastructure projects.