Determination of Prestress of in Situ Soils Using Acoustic Emissions

This paper is the culmination of a three‐phase research effort to estimate the preconsolidation pressure $p_c$ of in situ soils using a conventional Menard pressuremeter modified for acoustic emission (AE) monitoring. The first two phases involved determination of the feasibility of the AE technique using controlled laboratory tests on both granular and cohesive soils that were prestressed to known $p_c$ values. These results were previously reported and have shown that the AE data manifested itself as a bilinear response curve that “broke” at pressures approximately $\pm 10\%$ of the known $p_c$ of the soil. This paper reports on the complementary field phase in which six field sites were tested. The in situ soils were all finegrained residual soils derived from weathering of the parent bedrock. All had some degree of preconsolidation. In general, the results of this investigation have shown that the AE data again produced bilinear response curves that “break” at a particular value of applied horizontal pressure. This value of horizontal pressure was found to compare reasonably well [i.e., within $\pm 143.6$ kPa ($\pm 1.5$ tsf) with the horizontal component of $p_c$ (i.e., $p_{\mathrm{cH}}$) determined from laboratory tests. These latter test results were determined from conventional consolidation tests performed on Shelby tube samples of the residual soils, which were trimmed vertically so as to yield their horizontal compression properties. Presently, the described “acoustic pressuremeter” appears to be ready for general use by the profession to assess its advantages and/or disadvantages.