Experimental Study on the Effects of Stress-Induced Damage on the Microstructure and Mechanical Properties of Soft Rock

After rocks are damaged under stress loading, the changes of their microstructural and mechanical properties are major factors that affect construction safety in geotechnical engineering projects. Studying the microstructures and mechanical behaviors of stress-damaged rocks can help better guide construction and reduce construction risks for geotechnical engineering projects. In this study, a sandstone was first artificially predamaged and then subsequently subjected to scanning electron microscopy (SEM) analysis, computed tomography (CT) scanning, and uniaxial compression testing. Afterwards, the rock microstructures were three-dimensionally (3D) reconstructed, and the pores were classified and characterized based on their diameters. Moreover, the microstructural and mechanical parameters of the rock were subjected to significance analysis. The results showed that as the stress-induced damage ( σ i ) increased, the uniaxial compressive strength ( σ c ) of the soft rock decreased by 13.7–31.8%; as σ i increased from 11.2 to 19.6 MPa, the elastic modulus (E) of the soft rock increased by up to 28.8%; and as σ i increased beyond 19.6 MPa, there was a significant (22.3%) decrease in E. Stress-induced damage significantly affected the spatial distribution of the pores’ structure of the soft rock. Changes in the spatial structure of the pores led to the formation of cracks. The microstructural parameters of the stress-damaged soft rock were correlated with its mechanical parameters.

Influence of phyllosilicates and fluid–rock interaction on the deformation style and mechanical behaviour of quartz-rich rocks in the Carboneras and Palomares fault areas (SE Spain)

Deformed quartzitic rocks from the Carboneras and Palomares fault areas (SE Spain) are enriched in phyllosilicates compared to their respective protoliths. Deformation is mainly localized in highly foliated chlorite-rich bands. Quartz-rich bands show brittle deformation developing dolomite-rich cross-cutting veins re-cementing microcataclasite areas. Undamaged lenses within the cataclastic rocks contain patches of phyllosilicates with randomly oriented chlorite and mica. Mg, Fe, water, As and Zn enrichment of the damaged rocks suggests a process of hydrothermal chloritization associated with the Cabo de Gata volcanism. Petrographic characteristics indicate that hydrothermal alteration that produced chlorite and mica-enrichment occurred before faulting. Phyllosilicates provided lubricating properties to the quartzitic rocks, favouring the predominance of creep over seismic stick-slip and reducing the possibility of large seismogenic events. Dolomite cementation as a consequence of fluid–rock interaction processes would have a limited effect, due to the presence of weak phyllosilicate surfaces.

Study on Constitutive Relation and Permeable Coefficient Tensor of Rocks under Tensile Stress Loading with Micromechanics

In the present paper, a micromechanical based damage model and corresponding permeable coefficient tensor are developed for rocks under tensile stress and hydraulic pressure loading based on the concept of the domain of microcrack growth (DMG) . After choosing an appropriate fracture criterion for microcracks, we obtain the equations from which the DMG under a monotonically increasing proportional plane stress and an invariable hydraulic pressure loading is obtained. Then the overall effective stress-strain relations and the permeable coefficient tensor of damaged rocks are calculated. The theory is verified by test.