Measuring soil pressure within a soil mass

Abstract

Reliable measurement of pressure within a particulate media has frustrated researchers in the field of soil mechanics and soil structure interaction for many years. The difficulty stems from the fact that most sensing systems involve compliance in the measurement concept. This compliance imparts a parasitic output to the measurement. In the past, researchers have attempted to calibrate this disturbance. Research has demonstrated that calibrations of this sort are dependent upon soil type, particle size, sensor geometry, and soil stiffness. Response of such sensors has been shown to be stress history–dependent: the response upon unloading may be highly nonlinear, resulting in a high degree of hysteresis. Complications in the measurement of soil pressure within a soil mass are significantly more complex from those met in the measurement of soil pressure at a structural boundary and must be considered separately. This paper utilizes a concept called the Null Soil Pressure System. Null pressure sensors were embedded and tested in a series of uniformly graded soils with particle diameters ranging from less than 0.15 to 15 mm. The data indicates that the response of the null pressure sensor consistently exceeds the actual soil pressure by a value of 4% ± 3%. This outcome is seen to be independent of soil type, particle size, stiffness, and stress history. No hysteresis is noted between loading and unloading, and additional loading cycles align with that of the virgin loading segment.