In situ stress determination in rock using the acoustic emission technique

John Joseph McElroy

doi:10.17918/00009621

The acoustic emission technique was used in a three phase investigation of the determination of the in situ state of stress in rock masses. A laboratory phase was performed to establish the time dependency of the Kaiser Effect. Cyclic stress tests were performed where a delay time was introduced between cycles. These tests were performed for seven delay times (0.01, 0.1, 1, 10, 100, 1000, and 10,000 hours), in both unconfined compression and indirect tension (double punch), for six rock types (gneiss, mica schist, carbonate, mudstone, limestone, and sandstone). The Kaiser Effect existed in all rock types in both loading modes for delay times below 10 hrs. Beyond 10 hrs less than perfect prestress indication occurred, which was quantified by the Felicity Ratio. The Felicity Ratio decreased with increasing delay time until little prestress predictability was obtained for a 10,000 hour delay time. A pre-field or quarry phase was performed to initially apply the Kaiser Effect phenomenon to in situ rock stress measurement. An Acoustic Rock Jack was developed to stress an NX borehole and monitor its diametrical deformation and acoustic emission response. This equipment was employed in testing of five large gneiss masses. A cyclic stress test verified the Kaiser Effect in situ. Also the in situ stress was estimated in the range of 450 to 625 psi in three of four constant stress rate tests. The field phase applied the acoustic rock jack to actual in situ testing of rock. Twenty-five tests were performed in shallow NX boreholes in rock at six field sites (gneiss, mica schist, sandstone, argillite and two shales). Pressure, borehole deformation and AE activity were monitored. The deformation response did not exhibit indications of in situ stress levels. Anomalous behavior occurred in the acoustic emission response which could be due to the Kaiser Effect predicting in situ stress levels. Anomalies were noted in the AE response of all rock types and estimations of the in situ stress levels were made based upon the frequently occurring stress indications neglecting those that were obviously deformation related. Thus a simple, easily used, and inexpensive method was developed which can estimate in situ stress levels using the Kaiser Effect phenomenon and acoustic emission monitoring techniques.

In situ stress determination in rock using the acoustic emission technique

Files and links (1)

Abstract

Metrics

Details

In situ stress determination in rock using the acoustic emission technique

Files and links (1)

Abstract

Metrics

Details

Drexel University Social media