Water significantly modifies rock mechanical performance and fracture characteristics through water content and water distribution. Nevertheless, the evolution laws of rock mechanical properties and underlying fracture mechanisms under variable water conditions remain incompletely clarified. In this study, uniaxial compression tests were carried out on sandstone samples with diverse water immersion durations. Experimental observations reveal that the uniaxial compressive strength (UCS) and elastic modulus of sandstone follow negative exponential attenuation with prolonged immersion time, with maximum reductions of 50.1% and 25.6%, respectively. Under equivalent water contents, samples featuring dry exteriors and wet interiors possess lower strength than those with wet exteriors and dry interiors. A self-developed numerical code incorporating humidity diffusion effects was subsequently adopted to interpret water-controlled sandstone fracture behaviors. Numerical outputs verify that water-induced softening and heterogeneous water distribution exacerbate rock material heterogeneity and internal stress non-uniformity, triggering tensile microcracks along dry–wet interfaces. As the immersion duration rises, the rock failure mode transitions from shear-dominated mixed failure to tension-dominated failure, and finally reverts to shear-dominated mixed failure. Macroscopic rupture is predominantly governed by the gradual coalescence of tension-generated microcracks. This study offers a theoretical foundation to advance the understanding of water-triggered mechanical degradation and fracture mechanisms in sandstone.
To reveal the mechanical degradation, damage evolution, and failure mechanism of dense sandstone under varying water content, uniaxial compression tests were conducted on sandstone with different water contents. Combined with acoustic emission monitoring, scanning electron microscopy, and energy evolution analysis, constitutive models of damage evolution in sandstone with different water contents were established. The deformation and failure characteristics of water-bearing sandstone were systematically studied at both macroscopic and microscopic scales. The results show that with increasing water content, the peak strain, compressive strength, and elastic modulus of sandstone generally decrease, and the degradation pattern is initially steep and then gradual. Increasing water content gradually lowers the damage threshold of sandstone, leading to earlier damage evolution. The cumulative acoustic emission count and cumulative energy decrease overall, and moisture has a significant inhibitory effect on crack propagation and energy release. In terms of failure mode, sandstone gradually shifts from shear failure to tensile failure, with the proportion of tensile cracks increasing significantly with increasing water content. Microscopically, the fracture morphology gradually transforms from relatively smooth transgranular fractures in the dry state to rougher intergranular fractures and coupling fractures. These findings can provide a theoretical basis for the analysis of the mechanical properties of deep water-bearing dense sandstone surrounding rocks and their engineering applications.
This study examines the small-strain shear modulus (
G
max
) and water retention behavior of unsaturated sand–silt mixtures with a focus on the effects of fines content (FC), mean net stress (
p
n
), and hydraulic hysteresis. A comprehensive experimental program was conducted, incorporating saturated and unsaturated bender element tests, soil water retention curve measurements, and scanning electron microscope imaging. The tests were performed on compacted specimens of Firuzkooh No. 161 silica sand mixed with varying silt contents (0-100%) as fines under
p
n
of 50, 100, and 200 kPa along both drying and wetting paths. Two unsaturated triaxial systems equipped with bender elements and a hanging water column controlled matric suction (
ψ
) via axis translation and water head control techniques. The results revealed significant changes in soil structure and hydromechanical behavior with increasing FC. In contrast to other soil mixtures, clean sand exhibited distinct hydraulic and mechanical behaviors, with
G
max
demonstrating a nonmonotonic variation with
ψ
. As FC increased, a pronounced reduction in
G
max
emerged at FC of 20%, at which point the soil structure began to transform from a fines-in-sand to a sand-in-fines structure. Notably, the impact of hydraulic hysteresis became increasingly prominent with FC: for mixtures with 10%–100% FC,
G
max
during wetting was higher than during drying at the same
ψ
levels, whereas an opposite trend was observed for clean sand. Additionally, for sand specimens, the suction stress concept effectively described the variation of
G
max
with
ψ
, while for sand–silt mixtures (10%–100% FC), an extended framework incorporating the equivalent void ratio into a double hardening mechanism concept was adopted. The consistency between experimental observations and theoretical interpretations suggested that these concepts could provide a robust basis for predicting
G
max
behavior in unsaturated sand–silt mixtures.
B. Sadollahzadeh, S. Haeri, Ali Khosravi· Journal of Geotechnical and...· 0 citations