Development of an Instrumented Portable Soil Test Device that Measures Shear, Sinkage, and Friction Parameters of Soil in Situ

Abstract

The objective of this study was to develop an instrumented, portable soil test device that can measure sinkage, shear, and frictional parameters of soil in situ. The device is composed of a cone tip (ASABE standard small cone) that will provide cone index values with depth as well as soil-metal friction when the unit is rotated. Moreover, the device consists of a conical shear vane unit to measure soil shear characteristics. Furthermore, it is equipped with an ultrasonic sensor to monitor the depth at which the cone index, soil-metal friction, and soil shear characteristic measurements are obtained. The operation of the device consists of pushing the unit into the soil just as is done with a cone penetrometer to obtain cone index values with depth. At desired depths, the whole unit is rotated to obtain soil-metal friction and shear characteristics. Tests conducted in a Capay clay soil, which had been sieved through a 0.85 mm sieve (U.S. sieve #20) had 2.0% d.b. moisture content, revealed that the cone index values obtained using this device agreed quite well with those obtained using a commercial cone penetrometer. Failure torque and axial loading graphs obtained from the tests showed a very high coefficient of determination (r2 = 0.99) between cone torque and cone index, and a lower correlation (r2 = 0.53) between shear vane torque and shear vane cone index. These relationships were similar to the typical results obtained when a Cohron sheargraph is used to conduct soil tests. A second prototype was developed that was similar in design to the first prototype except that it used commercial combination torque/force load cells to provide independent measurements of torque and force. In addition to the ultrasonic depth sensor, it was equipped with an angular displacement sensor for measuring angle of rotation.