Measurement of Earth Pressures Near Vertical and Horizontal Boreholes during Packer Tests

ABSTRACT: Packer tests in vertical and horizontal boreholes were conducted in sand placed within a test pit. A packer was inserted after the vertical (or horizontal) boreholes were cut by a Shelby Tube. Packer inflation (and deflation) was used to provide loading (and unloading) sequences to simulate borehole expansion. Null gauges were buried in the sand adjacent to the borehole to measure radial, hoop and axial stresses during packer inflation and deflation. For the vertical borehole tests where sand was in dense state, all sensors were buried at the same depth and it was found that increments of axial stresses increased with increasing increments of radial stresses. Stress measurements made with the null gages indicate that increases in radial pressures applied by the packer lead to decreases in hoop stress corresponding to initially elastic soil response. After the soil experienced shear failure, increases in stress associated with plastic behaviour were observed. When unloading, an elastic change in hoop stresses and radial stresses were observed. For the horizontal borehole configuration, tests were conducted where the sand was tested in loose or dense state, and the sensors were buried a distance three times the borehole radius above the crown. Like the stress behaviour observed in the vertical borehole tests, stress increments changes in the axial, hoop and radial stresses were similar to those seen in the horizontal borehole tests. Geo-PIV was used to calculate soil movements for the horizontal borehole tests, monitoring ground movement during packer inflation, though the magnitude of the ground movements was minimal (less than 1 mm). These data provide insights into stress changes during pressuremeter testing, a database for future analytical and numerical developments.