Stress measurement in a rock bed based on emission memory effects

Abstract

1, 2.3. E(-1) -----E(-3) = Ec-5~ = E(-7) = E(-9) ----E(+I ) =Ec+3 ~ = Er = Ec+Tt = = Ec+9) = E(+11) = Ec+13) = E(+,5) = 0,73 X t05 MPa ; Ec_2) =Ec+4t = =Ec+8 ~ = 0,89 X t05 MPa; Ec_4~ = t,2t >< t05 MPa ; e(-s) = 1,48X t0 ~ MPa ; E~-s~ = 1,38 • 105 MPa, E(-io) = E(.~B) = t,3 Xi0 s ,!MPa; E(+2) = =1,2X`105 MPa; /~c+12) = 0,91 X `105 MPa E(+I4) = 1,4X ~05 MPa; p0 = PC+6) = P(+IO) = ~t,4 X `10 4 N/m 3; PC-l) = toe-3) = Pc-St = PC-7) = PC-g) = A considerable body of experimental data has been accumulated over the past few years concerning acoustic emission (AE) and electromagnetic radiation (EMR) observed during cyclic loading of rock specimens [1][2][3][4]. These characteristics, known as emission memory effects (EME), indicate that under certain conditions rocks can retain and reproduce information on impacts experienced at an earlier time. Although the basic possibility of utilizing EME for quantitative estimates of stresses in a rock bed is obvious, no such estimates had been obtained before now. This was due to the following: it was unclear which of the stresses acting in a bed could be determined from EME in specimens or what effect was exerted on signal-to-noise ratios in monitoring dynamic loads experienced by rock when the core was extracted and processed. Also, how disruptions of the core might affect EME was not known. These questions are the subject of the present study.Institute of Mineralogic Studies, Academy of Sciences of the USSR.

The rock stress memory unrecoverable by the Kaiser effect method

“…The Kaiser effect method is based on the assumption that under repeated load, the rock will not generate new cracks or extend the pre-existing cracks when the stress is lower than the previous maximum stress. Therefore, the source of acoustic emission under compression is believed to be the crack generation/growth [3][4][5][6][7][8][9][10][11][12][13][14]. Hereafter we will refer to this mechanism as damage accumulation.…”