Measuring three-dimensional soil deformation

Abstract

A laboratory system has been developed in which controlled surface loading can be applied to a constructed soil profile and the resultant deformation can be measured accurately in three dimensions. The system utilizes a 10m × 0.9m × 1.3 m rectangular bin composed of ten modular sections. A hydraulically powered carriage controlled by a microcomputer is used to construct soil profiles and apply surface loading via a pneumatic wheel. Soil deformation is measured by placing 6.4mm(diameter)x25.4mm white polypropylene markers in the soil at prescribed three-dimensional coordinates during profile construction and then determining their corresponding coordinates after deformation by means of a sonic digitizer. Experiments were conducted to determine: (a) the accuracy of measurement of marker coordinate dimensions and (b) the accuracy of initial placement of markers during soil profile construction. The 95% confidence interval of measurement accuracy for the sonic digitizer was ± 0.2 mm for the x and y coordinate directions and ± 0.8 mm for the z direction (parallel to the direction of wheel travel). The 95% confidence interval for marker placement accuracy was ± 2.0 mm, ± 3.4 mm, and ± 7.1 mm for the x, y, and z coordinate directions, respectively. The mean marker dislocation for the x and y directions was approximately equivalent to the accuracy limit of the sonic digitizer, whereas that of the z direction was an order of magnitude greater.