Determination of Prestress in Granular Soils Using AE

This project is aimed at the development of a technique, based on acoustic emission (AE) monitoring, to assess preconsolidation pressures (in all soils) in the field. Envisioned is a three part program: (1) Technical feasibility via testing granular soils in the laboratory; (2) technical feasibility via testing fine-grained soils in the laboratory; and (3) field verification, in all soil types, using an "acoustic pressuremeter." This paper presents the first part of the overall program. Remolded granular soils were loaded in a standard consolidometer, where the prestress load was first released, then reapplied in an in cremental manner. Deformation and AE were monitored during this reloading process. As the load equivalent to the originally applied preconsolidation pressure was exceeded, both deformation and AE increased markedly. The original prestress was easily detectable by both methods. Separate tests were performed on five different granular soils, each at four different saturation levels and for four different prestress conditions. Eighty (80) tests were performed in total. Results show that both deformation and AE predicted the originally applied preconsolidation pressure to within about 5% error, the exception being AE at the lowest value of prestress, which was somewhat higher. These results are presented and reviewed. It is concluded that AE is a viable method to predict prestress in granular soils, and should be extended to fine grained soils. If rea sonable results are obtained, field verification will be commenced.