URS FREE FIELD SOIL STRESS GAUGE DESIGN, CONSTRUCTION, AND EVALUATION

摘要

The report describes the design fabrication and evaluation of a static-dynamic free-field soil stress gauge. The gauge is disc shaped with a thickness of 0.060 in. and a diameter of 1.500 in. The sensing element is a piezoresistive semiconductor strain gauge located in a field cavity. The gauge was evaluated in two soils - Ottawa 20-30 sand at two densities (108 and 101 pcf), and a kaolinite clay at two water contents (25% and 30% by weight). All tests were conducted in the soil testing facilities developed at URS which are essentially free of side wall or boundary effects. With these facilities, the soil stress field in the absence of a gauge (the free-field stress) can be accurately determined, so that when a gauge is included in the soil its influence on the free-field stress field in its vicinity can be found. Both static and dynamic tests were conducted at various stress levels and depths of burial of the gauge in soil columns to determine gauge accuracy, repeatability, linearity, stability, and its sensitivity to various possible sources of spurious signals. Waterproofing techniques to protect the gauge from adverse moisture conditions were also evaluated. (Author)