Experimental Study On The Effect Of Carbonate Solubility To Fault Friction

The fault zone is the place where the most intense deformation occurs during the earthquake.Meanwhile,it is always accompanied by formation of fault gouge.The past researches suggest that the fault material has a significant effect in controlling the damage of rock.Hence,study on the composition,the change of structure and the mechanical dependence of the fault gouge on temperature,pressure,strain rate and fluid-chemical effect,is of great significance to study the friction strength and sliding mode of fault zone.We performed frictional experiments of Scaglia Bianca limestone gouge on a gas medium tri-axial deformation apparatus at temperatures of 50~300°C,confining pressure of 150 MPa for three different water conditions:(1)pore pressure of 50 MPa,(2)no pore pressure but saturated with water,(3)completely dry condition.To understand the speed dependence of friction sliding stability,the sliding rate switched in the range of 1.0 ?m/s and 0.2 ?m/s.The results show that:(1)The friction sliding stability of limestone fault gouge changed with temperature,controlled by the dissolution and precipitation of calcium carbonate in the fluid.Mechanical data and microscopic analysis show that slow slip occurs at120°C with completely dry condition,slow slip occurs,without dissolution and precipitation in deformed gouge sample.At 100°C,120°C,150°C and no pore pressure but saturated with water condition,typical slow slip occurs,accompanied by little dissolution and precipitation.Whereas at 300°C,accompanied by a lot of dissolution and precipitation,stick-slip occurs.At 50°C and pore pressure of 50 MPa,it shows steady-state slip with main mechanism of dissolution.At 100~150°C temperatures,it shows slow slip,with main mechanism of dissolution and supplemented by precipitation in deformed gouge sample.At 200~300°C temperatures,it displays typical stick-slip with main mechanism of precipitation.(2)The decrease of strain rate does not change the friction properties of fault gouge.Under 50 MPa pore pressure and 50 °C,it shows steady-state slip withincreasing frictional strength over time at high sliding speed(1.0?m/s),and at low speed(0.2?m/s)it shows steady-state slip with slightly decreased frictional strength.Under condition of zero pore pressure,saturated water and 150°C,it shows steady-state slip with increasing frictional strength over time at high sliding speed(1.0?m/s),and at low speed(0.2?m/s)it shows slow slip with slightly increased frictional strength.At completely dry condition and 120°C,it shows slow slip with decreasing frictional strength over time at high sliding speed(1.0?m/s),and at low speed(0.2?m/s)it shows slow slip with slightly increased frictional strength.At other conditions,the decreasing of rate resulted in slightly increase of frictional strength,and the friction mode did not change.(3)Peak vale of friction coefficient and friction mode are both controlled by saturation and precipitation rate of calcite in water.As the temperature increases,the saturation of calcium carbonate increases and the precipitation rate increases,cracks and pores of the fault are healed,which may cause the coefficient of friction increases.At 150°C,the break of dissolution and precipitation corresponds to the break of the friction coefficient.(4)Mechanical data,microstructures analysis,and dissolution and precipitation curves of calcium carbonate suggests that,at temperature of 50°C it shows steady-state slip with main mechanism of dissolution;at temperature of 100~150°C,it shows slow slip with main mechanism of dissolution and supplemented by precipitation;stick-slip occurred at 200~300°C with main mechanism of precipitation.The sliding mode was controlled by dissolution and precipitation of limestone gouge.