New Result of the Experiment on Self‐Potential Change of Rocks Under Biaxial Compression

Abstract

An experiment on self‐potential (SP) and strain changes during elastic deformation and fracture of rock samples was conducted by means of a biaxial servo‐control loading‐machine and a detecting array of strain gauges and electrodes. Some correlated and widespread pulse‐like transient variations in self‐potential and strain‐field appeared at some special situations, including sudden loading/ unloading, stick‐slip and fracture of rocks. The results indicate that though sometimes the stress ‐ is rather high, there is no SP anomaly occurring if the stress change‐rate γ = dσ/dt equals zero or keeps positive or negative constants. On the contrary, at the moment changes suddenly the pulse‐like SP change γV will always arise no matter the increment Δ;γ is positive or negative. The positive or negative sign of Δγ gives opposite effect on ΔV. The anomalous amplitude of ‐V is proportional to that of Δγ. The observed clear temporal and spatial self‐potential changes at the moment of sudden stress‐rate change and rock fracture mean that it is possible to detect the precursory and co‐seismic electric and corresponding strain variations if the above‐mentioned conditions can be met near a seismogenic zone. It is a support to the seismic precursory research of self‐potential and strain.

Research on the Charge Inducing Regularity of Coal Rock at Different Loading Rates in Uniaxial Compression Tests

“…The result shows that the induced charge increases dramatically when marble is suddenly unloaded, and then gradually decreases. Hao et al [16] have made experimental study on strain and the potential in the process of rock elastic deformation and damage process under biaxial stress. Sun et al [17] have calculated the quantity of electricity at failure surface to be 5.2×10 −4 C according to the magnetic field strength during main rupture.…”

The Theoretical and Experimental Research on Self-Potential Tomography

“…The experimental result indicates that the potential changes during the sample cracking can be reasonably attributed to the mechanism of charge-separation on the tip of the crack induced by micro-fracturing [17,19] . The electronic emission during the fracture developing results in the generation and balance of the positive charge in the local volume around the tip of the crack and the pulse-like SP variation similar to a charge-discharge process.…”

Laboratory Studies of Electric Current Generated during Fracture of Coal and Rock in Rock Burst Coal Mine

“…The crack propagation destroys the chemical bonds between atoms at crack front and the charge separation at crack surfaces produces a large amount of free charges. Therefore, the dominant mechanisms responsible for production of free charges and electric current are triboelectrification and charge separation during crack propagation in the deformation and fracture process of coal [17,30,31]. As shown in Figure 6(b), the main component of roof rock is quartz.…”

“…Both granite and marble would generate negative electric potential signal during deformation and fracture under double-axial pressure and uniaxial pressure. In addition, the variation of electric potential has good congruity with the sudden change of stress [17,18]. Precursory electric potential signals before failure were observed in both saturated and dry samples of the quartz-rich sandstones but only observed in the water-saturated quartz-free limestone [19].…”