A Simple Method for Assessing the Peak Friction Angle of Sand at Very Low Confining Pressures

摘要

This article presents a simple experimental method that may be used to assess the peak friction angle of sand at very low effective confining pressures (i.e., 10 kPa). Soil strength at very low confining pressures is important to a variety of geotechnical problems, including small-scale 1-g physical modeling and micro-gravity environments. It is often very difficult to assess friction angles at very low confining pressures in conventional element tests because some factors, such as specimen self-weight and machine friction, become significant. Currently, there are no published methods available to measure the peak friction angle of sands below a mean effective stress at failure of about 6 kPa. To address this need, a simple tilt test method is proposed that involves preparing a soil to a specified relative density within a steel mold and then tilting the mold to induce a shallow slope failure. Based on infinite slope analysis, the tilt angle at which the slope fails is equal to the peak friction angle. A modified stress-dilatancy relationship is also proposed that can be calibrated for a specific soil using a combination of tilt test and triaxial test data. This relationship can be used to predict peak friction and dilation angles over the low stress range.