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To investigate the influence of confining pressures and temperatures on the seepage characteristics of fractured rocks, seepage tests were conducted on a fractured silty mudstone using a self-developed experimental system, and the effects of different factors on coefficient of permeability were discussed. The results showed that the increasing confining pressure will gradually decrease the coefficient of permeability, and this process is divided into two stages: 1) the fast decrease stage, which corresponds to a confining pressure less than 30 kPa, and 2) the slow decrease stage, which corresponds to a confining pressure larger than 30 kPa. Unlike confining pressure, an increase in temperature will increase the coefficient of permeability. It is noted that fracture surface roughness will also affect the variation of coefficient of permeability to a certain extent. Among the three examined factors, the effect of confining pressure increases is dominant on fracture permeability coefficient. The relationship between the confining pressure and coefficient of permeability can be quantified by an exponential function.

To study the mechanical characteristics of the disintegrated carbonaceous mudstone (DCM), consolidated drained triaxial tests were conducted on the DCM with three degrees of compaction (i.e., 90%, 93%, and 96%). Then, the nonlinear constitutive model suitable for the DCM was established based on test results using a logarithmic function. The stress-strain characteristics of the DCM were analyzed. The results revealed that the axial strain of the DCM was positively correlated with the deviatoric stress and lateral strain. The slopes of deviatoric stress-axial strain curves decreased with the increase of axial strain and so did the slopes of the axial strain-volumetric strain curves. The strength of the DCM increased with the increase of the confining pressure and the degree of compaction. In addition, the axial strain induced by dilatancy was also positively correlated with the degree of compaction and the confining pressure. Furthermore, under triaxial loading conditions, the relationship between the stress and strain of the DCM can be expressed by a logarithmic function; based on this, a nonlinear constitutive model with ten material parameters was derived. In addition, the results of numerical tests using the model showed similar stress-strain characteristics of the DCM comparing with the triaxial tests. Hence, it indicated that the nonlinear constitutive model based on the logarithmic function can reflect the nonlinear stress-strain characteristics of the DCM.

Grouting operation in karst aquifers is difficult due to the rapid underground water flow in large karst voids, which may scour and destroy the integrity of the slurry before solidification and, therefore, lead to a grouting curtain of poor quality. An important aspect of using grouting material in karst aquifers is to ensure that the slurry has a strong scour resistance and stability. For this purpose, a highly stable sandy cementitious grout is developed for karst aquifers, and the main components of this grout are cement, water, well-graded natural river sand, and sodium metaaluminate (NaAlO2, as the additive). The sand can improve the grain size distribution of the slurry and further enhance its scour resistance. To assess the mechanical performance of the newly presented grout, the bulk shrinkage rate, water-bleeding rate, setting time, weight retaining ratio, rheological properties, compressive strength and permeability are obtained by a series of indoor experiments. The results show that grout with an additive content of 1.0% has a very low bulk shrinkage rate of nearly 0% and a high weight retaining ratio of 85% under water scouring. All the physical and mechanical properties of the grout meet the requirements of curtain and consolidation grouting, including the requirements that the 28-day compressive strength of the grout reaches approximately 5–10 MPa and the permeability of the grout stone is less than 7.7 × 10–7 cm/s. Compared with clay–cement paste and cement–water–glass paste, using sandy cementitious grout can reduce the material costs by at least 43.1%. Finally, engineering applications in a dam foundation surrounded by karst aquifers are conducted, and the seepage problem is solved.