In this project, a Cyclic Borehole Shear Test (CBST) device was developed to enable rapid in situ measurement of cyclic behavior and monotonic shear strength properties of the soil. The CBST is unique in its ability to measure the parameters in the soil’s natural setting, under cyclic loading, and in a matter of minutes whereas present laboratory techniques can take several weeks. By testing the soil in situ, the device saves time and money, while reducing effects of soil sample disturbance which can significantly affect laboratory test results. Based on the results of several field testing trials, numerous refinements and modifications were made to the system that included the physical testing apparatus inserted into the borehole, the electronic and pneumatic measurement and control system, and the software control program. Comparisons of the field CBST results to those of conventional laboratory cyclic direct simple shear tests demonstrated that the device can measure meaningful cyclic behavior of soils in situ. Further research will be pursued to more rigorously relate the measured displacements to shear strains in the soil surrounding the borehole, and to explore applications of the device to in situ measurement of the liquefaction behavior of soils. With further research, the device has the potential to fundamentally transform the presently empirical techniques used in practice for assessment of soil liquefaction resistance into a more mechanistic physics-based framework.
The final report is available.