不同热冲击过程花岗岩Ⅰ型和Ⅱ型断裂特性研究

Study on Mode Ⅰ and Mode Ⅱ Fracture Characteristics of Granite Under Different Thermal Shock Process

在岩石工程中发生的与高温相关的灾害中,快速降温的影响(热冲击)不可忽视,因此,研究在不同程度的热冲击作用下花岗岩的断裂特性可以对遭受高温灾害后岩石工程的稳定性分析提供理论依据和技术支撑。在本研究中,花岗岩被加热至目标温度(200℃、400℃、600℃),利用制冷剂的不同温度(-20℃、20℃、60℃)为高温试样提供不同速率的降温处理。热处理前后对试样干密度、孔隙率和纵波波速进行测定,并通过巴西劈裂试验测试试样Ⅰ型、Ⅱ型断裂韧度。试验结果表明:干密度、纵波波速以及Ⅰ型、Ⅱ型断裂韧度均随降温速率的增大而减小,孔隙率则随降温速率的增大而增大;快速冷却引发的拉应力是造成花岗岩损伤的主要原因,且与岩石试样和制冷剂之间的温差呈正相关。

In the high temperature related disasters occurring in rock engineering,the effect of rapid cooling(thermal shock)can’t be ignored.Therefore,the study on modeⅠand modeⅡfracture toughness of granite under different degrees of thermal shock can provide theoretical basis and technical support for the stability analysis of rock engineering after thermal shock disasters.In this experiment,the granite is heated to the target temperature(200℃,400℃,600℃).According to the characteristics of low freezing point of calcium chloride solution,calcium chloride solution is used as refrigerant,and refrigerants of-20℃,20℃and 60℃are obtained by means of freezing and heating respectively,and thermocouple thermometer is used to ensure that the temperature of refrigerating liquid reached the set temperature.Use refrigerants(-20℃,20℃,60℃)for three different cooling rate of the high temperature granite processing,namely the three different levels of thermal shock.The physical properties of the samples are measured before and after heat treatment,including dry density,porosity and P wave velocity.In the end,modeⅠand modeⅡfracture toughness of specimens is tested by Brazilian splitting test.The experimental results show that the dry density and P-wave velocity of heated granite samples decrease with the increase of cooling rate,while the porosity increases with the increase of cooling rate.These phenomena are related to the opening and expansion of pores and micro-cracks caused by thermal shock,that is,more violent thermal shock will cause more serious damage to granite.In addition,with the increase of heating temperature,the sensitivity of the physical properties of heated granite to the temperature change of refrigeration liquid decreases during the cooling process.In terms of fracture toughness,the fracture toughness of granite as a whole decreases significantly with the increase of heating temperature.In addition,at the same high temperature level,the modeⅠand modeⅡfracture toughness of heated granite decreases linearly with the decrease of cooling liquid temperature,which is roughly the same as the change trend of physical properties of granite.The main causes of thermal shock damage are the non-uniform expansion and contraction of minerals inside the rock and the disharmony of deformation caused by the temperature gradient inside and outside the rock.The tensile stress generated by the temperature gradient inside and outside the rock is positively correlated with the temperature difference between granite and refrigerant.