Experimental study on Brazilian split test and acoustic emission characteristics of high temperature granite under different cooling methods

Abstract

High-temperature rock cooling can occur in the whole process of the drilling, fracturing, and heat exchange during the geothermal energy exploitation in hot dry rock. To reveal the evolution law of rock damage, based on the Brazilian splitting test and acoustic emission technology, the effects of different high temperatures and cooling methods on the tensile properties of granite were studied. The results showed that: ①The tensile strength of granite decreases with increasing temperature from 25℃ to 600℃, and the temperature threshold, at which it decreases greatly, is advanced to 200℃ after cooling with water. After 500℃, the tensile strength is more sensitive to water cooling. ②When the load reaches the peak value, the cumulative ringing count of acoustic emission suddenly increases, and the fracture zone forms in the rock sample. Under the influence of water cooling, the ringing count peak value and energy peak value of the rock sample decrease, which indirectly reflects that the internal cracks of the rock are more developed, and both of their decrease range is larger at 200~300℃. The granite is more sensitive to heat treatment at 300℃ and after 500℃. ③With the increase in temperature, the fracture surface of granite changes from flat to rough and tortuous, from brittle to ductile; Cooling in water promotes rock fracture and advances the temperature range from brittleness to ductility. The research results provide a theoretical reference for the stability evaluation of high-temperature rocks in geothermal exploitation.

Keywords

• high temperature granite
• cooling mehtod
• brazilian split test
• acoustic emission
• thermal damage