Experimental study on mechanical behaviour and pore evolution of borehole-sealing materials under different confining pressures

To investigate the differences of mechanical behaviour and pore evolution characteristics of new solidified borehole-sealing materials, traditional triaxial compression tests, Brazilian splitting test and nuclear magnetic resonance test were conducted to analyse the deformation, strength characteristics and pore evolution characteristics of three types of sealing materials under different confining pressures. The results are as follows: the improvement of elastic modulus and deformation modulus of borehole-sealing materials under the influence of confining pressure is proportional to the elastic modulus and deformation modulus at a low confining pressure. There is little difference in the cohesion among the three types of sealing materials and the differences in the strength thereof are caused by the difference in the internal friction angle. The influence coefficients of confining pressure show a negative exponential decreasing trend with increasing confining pressure. When the confining pressure is 3 MPa, turning points appear in the plot of confining pressure coefficient versus confining pressure. The ratio of tensile strength to uniaxial compressive strength of the sealing material is between 9.2 and 15.2%. The T 2 spectra of the internal pore-fracture system of the three types of borehole-sealing materials all exhibit a three-peak distribution, in which the proportion of adsorption pores is the highest, and the proportion of seepage pores and fractures is relatively small. Under different confining pressures, the stress sensitivity of different pore structure types in the new solidified sealing material is all lower than that of traditional sealing materials and cement mortar. This study on mechanical behaviour and pore evolution of those samples was conducted to facilitate the knowledge of different sealing material performance, and to deliver practical meanings on the progress and development of borehole-sealing technology.