Experimental Study On Failure Process Monitored By Multi-physical Methods And Water Weakening Laws Of Sandstone

Composed of mineral particles,commented composition and pore structures,rock is one of the most widely distributed and complex solid materials due to the long-term effect of internal and external geological force.Rock mass is usually composed of rock and structural planes in a certain range.Knowledge of rock mechanical behavior is very important for ensuring the stability and avoiding the disaster in rock engineering such as stope,tunnel,chamber,slope and dam.In this thesis,the characteristics of deformation and energy release were monitored by multiple methods on mesozoic sandstone in Yulin zone,then the effects of the meso structure and water weakening on the rock mechanical parameters and stability were analyzed.Based on laboratory experiments and site investigation,the parameters of rock mass with different water content were obtained.Furthermore,the numerical models of coal mining with different excavation lengths and water content states were established,and the distribution of stress and the extension of plastic zone during coal excavation process were discussed.The works can be summarized as follows:(1)The uniaxial loading and cyclic loading experiments were conducted on homogeneous sandstone specimens with acoustic emission,displacement field,infrared radiation and average temperature monitored.The inner damage characteristics(acoustic emission)and surface evolution characteristics(displacement field and infrared radiation)of rock were analyzed simultaneously.On the basis of the damage evolution process of horizontal and vertical displacement field,acoustic emission and temperature,the evolution order of the multiple physical parameters was summarised.(2)The calculating code for determining the mineral particles shape was compiled by the Matlab language,and the morphological parameters of mineral particles such as particle size,roundness and main direction,as well as the statistical parameters such as particle content,sorting feature and grading curve were described quantitatively by the code.Furthermore,the effects of particle shape and cementation structure on the strength and dissipated energy under the uniaxial and triaxial experiments were analyzed.In addition,the Kaiser effect and load/unloading response ratio were used to study the characteristic of dissipated energy in the form of acoustic emission during the cyclic loading experiments.(3)The dry specimens and saturated specimens with different soaking time were chosen for the acoustic emission experiments,and the water weakening effects on mechanical parameters including strength,deformation and acoustic emission parameters were discussed.In addition,the acoustic emission energy release characteristics of specimens with different water content and loading stages were analyzed based on energy accelerating release theory and probability density distribution method.(4)Considering the laboratory tests and geological information of coal mine,the mechanical parameters of surrounding rock and coal with different water content and lithologies were obtained.And the geological strength index(GSI value)was modified by interpolation method.Based on Hoek-Brown strength criterion,a graphical user interface for calculating the rock mass parameters was compiled by Matlab language.The mechanical parameters such as rock strength and deformation with different conditions were obtained,which provided a basis for the following numerical simulation.(5)Based on the rock mass mechanical parameters obtained by the graphical user interface and coal mine geological information,the FLAC model of coal excavation was established.The characteristics of stress distribution and plastic state zone extension in rock mass with different water content conditions and different mining processes were discussed.In addition,the effect of water on the stability of rock strata in the coal mine was also discussed.