Weakening Effect Of Water Research Articles

Parametric study to implement a water-weakening process in UDEC

Despite the prevalence and validity of the universal distinct element code (UDEC) in simulations in geotechnics domain, water-weakening process of rock models remains elusive. Prior research has made positive contributions to a presupposed link between modelling parameters and saturation degree, Sr. Nevertheless, this effort presents inaccurate results and limited implications owing to the misleading interpretation, that is, devoid of the basic logic in UDEC that modelling parameters should be calibrated by tested macroscopic properties in contrast to a presupposed relation with Sr. To fill this gap, a new methodology is proposed by coupling a computationally efficient parametric study with the simulation of water-weakening mechanisms. More specifically, tested macroscopic properties with different Sr values are input into parametric relations to acquire initial modelling parameters that are sequentially calibrated and modulated until simulations are in line with geomechanical tests. Illustrative example reveals that numerical water-weakening effects on macroscopic properties, mechanical behaviours, and failure configurations are highly consistent with tested ones with noticeable computational expediency, implying the feasibility and simplicity of this methodology. Furthermore, with compatibility across various numerical models, the proposed methodology substantially extends the applicability of UDEC in simulating water-weakening geotechnical problems.

The water weakening effect on the progressive slope failure under excavation and rainfall conditions

The water weakening effect refers to the gradual deterioration of soil mechanical properties under long-term saturation. This paper analyzed the impact of water weakening on slope stability under alternating excavation and rainfall. The field investigation speculated shale hydration as the cause of overall slope instability. The mechanical parameters of hydrated shale were determined by the parameter inversion and empirical estimation methods. The simulations were used to restore the process of parameter weakening and slope failure, and confirmed the fact that hydration causes landslide. Furthermore, the failure mechanism of slope and support structure under hydration were investigated. The results show that the mechanical parameters of the slope decreased linearly, whereas the plastic strain–time and total displacement-maximum shear stress curves of the hydrated shale exhibited three stages: slow initial growth, rapid growth in the middle term, and rapid increase in the later period; the rate of slope deformation and the factor of safety reduction also gradually increase over time; under middle stage of hydration, the middle to rear of shale were extruded, while the front first underwent tensile shear deformation, forming a plastic zone of at rear and front excavated slope; In the late stage, hydrated shale quickly reaches its yield limit (maximum shear stress of 270 kPa), the middle and rear shale is damaged and compresses the front, causing it to transform from tensile shear to compressive shear failure. The plastic zone in the rear extends forward and connects with the front ones, forming an overall landslide. Besides, preventing deep landslides caused by hydration through waterproofing, drainage, protection, and support for excavated slopes has proven difficult. Therefore, it is necessary to redesign treatment schemes based on the characteristics of stress, strain, and seepage.

Formation mechanism of loess-mudstone landslides in the Weibei Tableland Fault Active Zone of Baoji, China - Taking Wolongsi landslide as an example

The geomorphologic and environmental evolution of the Loess Plateau is greatly affected by the strong fault activity, leading to the frequent occurrence of geological hazards, particularly the loess-mudstone landslide (LML). Thus, it is crucial to investigate the formation mechanism of such landslides in active fault zones. In this study, a field survey was conducted in the Weibei tableland of Baoji where the active fault zone is developed. To study the creep behavior of LML sliding zone soil, the triaxial creep tests of multi-stage loading under different water content, confining pressure, dry density, loess-mudstone binary structure (LMBS) contact surface angle, and thickness were carried out using the sliding zone soil samples (loess, mudstone, and LMBS samples) obtained from Wolongsi landslide in the study area as an example. Experimental results revealed that: (1) Water content has a significant weakening effect on the strength of LML sliding zone soil. The strength of the LMBS sample is extremely water-sensitive. The weakening effect of water on the long-term strength of LML sliding zone soil mainly manifested in promoting the elastoplastic deformation of loess and the viscoplastic deformation of mudstone. (2) The long-term strength of the LML slip zone soil increases linearly with the increase in confining pressure and increases exponentially with the dry density. (3) The degrading effect of the stratigraphic interface dip angle on the long-term slope strength is mainly reflected in the change in the weakening degree of water on the strength of the LML sliding zone. In addition, according to the test results, the traditional Nishihara model is improved by introducing nonlinear parameters, and a new constitutive equation describing LML sliding zone soil is established. The new constitutive model can accurately describe the creep curve's whole process especially sensitively identifying the accelerated creep stage. Finally, after conducting a field investigation and laboratory tests, the main hazard factors affecting the occurrence of the LML were analyzed in the presence of fault activity on the Weibei Plateau of Baoji, China, and its formation mechanism was revealed as well.

Water effect on subcritical crack growth and fracture behavior of marble

Understanding the fracture properties and subcritical crack growth of rocks in aqueous environments is significant for the effective assessment of the long-term stability of the masonry buildings, cultural heritage structures, and art sculptures. We use double torsion techniques to systematically investigate the subcritical crack growth behavior of marble under air, fluid, saturated and saturated + fluid test conditions. In the fluid condition and the saturated + fluid condition, the load reductions during the relaxation test are larger than other conditions, reaching 12.81% and 12.26%, respectively. There is a water-weakening effect on both the subcritical crack growth index (SCI) and KIC, but the water weakening sensitivity in KIC is lower than that of SCI. Compared to the air condition, the SCI values of the marble decreased by 43.69% under the fluid condition, 17.64% under the saturated condition, and 38.09 % under the saturated + fluid condition, respectively. The introduction of water during the relaxation test results in an immediate increase in the crack velocity and the major principal strain of the specimen, as evidenced by the appearance of the Ⅳ region on the KI-V curve. Scanning electron microscope images show that the most triangular pits and dissolution pits are present in the marble under fluid and saturated + fluid conditions, leading to a more pronounced deterioration of the mechanical properties. The test results highlight the significant impact of water on subcritical crack growth in marble. In particular, during rainfall, both dry and saturated marble masonry buildings are more prone to cracking due to the introduction of water.

Molecular insight into the structural and mechanical properties of Ca-based geopolymers

Ca-based geopolymers are a principal product of introducing calcium into geopolymers. Analyzing Ca-based geopolymers structural and mechanical properties aids in optimizing mix design of geopolymers. In this paper, partially reacted low-polymerization and fully reacted high-polymerization models were constructed to examine the structural and mechanical properties of Ca-based geopolymers with varying calcium contents via molecular dynamics simulations. Results show that Ca-based geopolymers contain pentacoordinate aluminum and tricluster oxygen which is more brittle and makes the structure loose. In low-polymerization models, an increase in calcium content accelerates the polymerization rate by overcoming the low-temperature reaction barrier. However, calcium content hinders the formation of pentacoordinate aluminum, decreasing the final degree of polymerization, resulting in weakened mechanical properties. In high-polymerization models, increased calcium decreases tricluster oxygen content, resulting in improved mechanical properties. While the hydrolysis reaction reduces mechanical properties, the weakening effect of water is greater than the enhancing effect of calcium.

Influence of cure time, temperature, and moisture on mechanical properties of a fast cure adhesive for post-installed rebar application

The use of chemical adhesives to post-install rebars and anchor elements in existing concrete structures has been widely developed in the previous years. The progress of the adhesive market in civil engineering has led to various commercialized structural adhesives targeting post-installation of steel elements in existing concrete structures. Regardless of the diversity of chemistries of adhesive types on the market today, existing mechanical theoretical descriptions and product evaluation methods are common to all adhesives.This paper presents the influence of moisture, cure time and temperature on the tensile behavior (resistance and stiffness) of a fast cure industrial adhesive used for post-installed rebar application. Results are compared to other studies on slow cure (epoxy) adhesives also used for the same application. The influence of temperature of the initial cure exothermic reaction is quantified through thermal measurements. Tensile tests performed at different times with samples stored at 50 % RH and 100 % RH show increase of strength and stiffness with cure time and highlighted the weakening effect of water. Finally, tensile tests performed directly at high temperatures (50 °C, 80 °C and 110 °C) on samples that had been previously pre-heated at these same temperatures or below were performed. Material strengthening caused by thermally induced post-cure (as observed for step polymerized products designed for the same application) is not distinguishable for the fast-cure adhesive. The progressive decrease of strength and stiffness with temperature appears unchanged by the thermal history.

Statistical damage constitutive model considering water-weakening effect based on the Hoek–Brown criterion

Statistical damage constitutive model considering water-weakening effect based on the Hoek–Brown criterion

Dynamic fragmentation and chip formation of water-soaked rock in linear cutting with a coupled moisture migration-fracture model

Water can greatly influence the mechanical properties and dynamic fracture of underground rock mass. However, the dynamic fragmentation and chip formation of water-soaked rock in linear cutting is neglected. In this work, a coupled moisture migration-fracture model is utilized to investigate this problem. First, the water weakening effect on rock mechanical parameters is introduced in the coupled model according to a fitting laboratory test. Then, the uniaxial tensile, uniaxial compression, triaxial compression, and swelling experiments are utilized to calibrate the input micro-parameters. Subsequently, a series of scratch tests are carried out on the water-soaked rock samples. The stress evolution, fragmentation mode, cutting force, crack number, extent of fracture zone, chip shape, chip area, cutting work, and mechanical specific energy (MSE) with different water content are studied. The results indicate that as water content increases, the rock sample changes from brittle failure to ductile failure in linear cutting, the peak cutting force gradually decreases, and the chip area first becomes larger and then smaller, while the MSE shows an opposite trend. Especially, a water content of 2% can bring the largest chip area and the highest cutting efficiency. Moreover, the effects of cutting velocity and cutting depth on the above indexes are discussed. Finally, a complex specimen composed of half wet and half dry rock is built to further demonstrate the influence of water on rock dynamic fragmentation and chip formation in linear cutting. The modeling results in this paper provide new insights into the influence mechanism of water on rock dynamic fragmentation, chip formation, and cutting efficiency in linear cutting.

Effect of water on the rock strength and creep behavior of green mudstone

The weakening of rock mass after immersion substantially affects slope stability. Considering the mudstone in the north slope of the Fushun West Open pit as the research object, we investigated the failure and creep characteristics of mudstone under different immersion times and confining pressures. For this, we used a self-developed experimental apparatus that applies biaxial compression loading in a water immersion environment. Water significantly changed the strength and failure mode of the mudstone. The increase in confining pressure limits the expansion of the crack aperture, reduces the rock strength-weakening coefficient, and delays the rock weakening time. The change in cohesion is primarily responsible for the weakening of shear strength during immersion. Based on the creep test results, the creep curve of the soaking specimen was identical to that of the dry specimen in the initial phase. The weakening effect of water on the specimen increased as the soaking duration increased, due to which the creep curve of the soaking specimen gradually approached that of the saturated specimen. Water entered the microcracks and reacted with the rock interior, accelerating rock failure. Consequently, the soaking specimen had the lowest stress level for creep failure and the shortest failure time. The results of this experiment provide a reference for the long-term stability of the flooded slope.

Effect of incorporating discarded facial mask fiber on mechanical properties of MICP–treated sand

Responding to environmental challenges associated with the waste generated from discarded facial mask fiber (DFMF), this study introduces an innovative approach to integrate DFMF as a beneficial additive to Microbial-induced calcium carbonate precipitation (MICP) technology - an eco-friendly soil stabilization method. Despite its merit of enhancing soil strength and permeability, MICP often incurs substantial soil brittleness. The incorporation of DFMF, a material conventionally destined for landfill, demonstrates an enhancement in the ductility of MICP–treated sand. Various proportions of DFMF were incorporated (0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% by weight), leading to an observable improvement in unconfined compressive strength (UCS), splitting tensile strength (STS) and in the microstructural configuration of MICP-treated sand. The presence of DFMF fostered bacterial immobilization, catalyzed CaCO3 production, and culminated in an optimum DFMF content at 0.2%. This not only mitigated soil brittleness by introducing ductility via calcite precipitation but also culminated in a “sand particles-fibers-sand particles” spatial configuration, reducing the weakening effect of water on MICP-treated sand samples. This study, therefore, highlights the potential of DFMF as a promising additive in MICP-treated sand, thereby offering an effective method for recycling and reusing discarded facial mask fibers.

Acoustic Emission Characteristics of the Water Weakening Effect on Cretaceous Weakly Cemented Sandstone

Rock mass stability is often affected by water–rock interaction in underground engineering construction. Cretaceous sandstones often have weak cementation, low strength and strong water-holding capacity, and their rock mass strength is easily weakened by these activities. In this paper, the uniaxial compressive strength (UCS) and tensile strength (TS) of weakly cemented Cretaceous sandstones from different sedimentary facies under natural and saturated conditions were tested, and the loading process was monitored by the acoustic emission (AE) technique. The results show that the existence of water obviously weakened the mechanical properties of weakly cemented sandstone. The UCS and TS of saturated braided river facies sandstone decreased to 41.24% and 35.95% of their natural states, respectively, while those of desert facies sandstone decreased to 32.90% and 26.98% of their natural states, respectively. The AE characteristics of sandstone from different sedimentary facies were similar during loading due to weakening by water, including a decrease in cumulative AE energy, b-value fluctuation and reduction in the peak frequency distribution range. Fracture in the Brazilian splitting test was mainly due to the rapid initiation and coalescence of microcracks near the peak point. However, in the uniaxial compression test, the macro fractures were caused by many microcracks that occurred continuously during loading and finally connected. The high quartz and low feldspar contents strengthened the mechanical properties of braided fluvial facies sandstone compared to those of desert facies sandstone and lessened the effect of water weakening.

Optimum spacing and rock breaking efficiency of TBM double disc cutters penetrating in water-soaked mudstone with FDEM

Cutter spacing is one of the key factors affecting the rock breaking efficiency of Tunnel Boring Machine (TBM). In the excavation of deep soft rock tunnels, the water content can change the fragmentation behavior by TBM cutters, and further influence rock breaking efficiency. This study takes mudstone as an example to study the influence mechanism of water content on the optimum cutter spacing and rock breaking efficiency when TBM disc cutters penetrate soft rock. Firstly, the FDEM water migration-fracture coupled model considers the water weakening effect based on existing experimental fitting results. Secondly, several numerical experiments are conducted to calibrate the microscopic parameters input in FDEM. Finally, a series of numerical experiments of TBM double disc cutters penetrating in water-soaked mudstones are carried out using the coupling model. The crushing characteristics, cutter force, acoustic emission (AE), and crack pattern with different water content and cutter spacing are discussed in detail. Moreover, a novel recognition algorithm is proposed to calculate the rock chip distribution and area. The crack number, work done by the cutters, and specific energy (SE) are quantitatively analyzed. The results indicate that the water content of 2%–3% and the cutter spacing of 60–80 mm can lead to the lowest SE and highest rock breaking efficiency. Overall, the optimum cutter spacing decreases with the increase of water content. The modeling results can supply guidance for the optimization of cutter spacing during TBM tunneling in water-rich soft rock ground.

Effects of zeolite on rheological properties of asphalt materials and asphalt-filler interaction ability

The rheological properties of asphalt materials (asphalt binder and mastic) and asphalt-filler interactions play critical roles in the performance of asphalt mixtures. However, the rheological properties of zeolite-foamed asphalt materials and zeolite-foamed asphalt-filler interactions are significantly influenced by zeolite, which is used as a foaming additive. To study the effects of zeolite on the rheological properties of asphalt materials and asphalt-filler interaction, the base asphalt, limestone filler, and two kinds of zeolites in two dehydrated states were selected to prepare zeolite asphalt/mastic and zeolite-foamed asphalt/mastic. First, the effects of zeolite on the chemical composition and micromorphology of asphalt binders were evaluated using a Fourier transform infrared spectrometer (FTIR) and fluorescence microscopy (FM), respectively. Then, the rheological properties of asphalt binders and mastics were measured by rotational viscosity (RV) and dynamic shear rheometer (DSR) tests. The results indicated that zeolite did not chemically react with the components of asphalt, and zeolite minerals played a role in volume filling and physical adsorption in asphalt, which dispersed in the asphalt in the form of floccules. Adding zeolite minerals to asphalt binders and mastics enhanced the elasticity, which was beneficial to high-temperature performance and adverse to fatigue performance. Conversely, the effect of zeolite water released by zeolite was the opposite. The effect of zeolite on the rheological properties of asphalt materials was consistent with that of zeolite minerals because the enhancing effect of zeolite minerals was dominant, offsetting the weakening effect of zeolite water in asphalt binders and mastics. The three indices, namely, intrinsic viscosity [η], Palierne-C-G* parameter, and Ziegel-B-δ parameter, were selected to evaluate the zeolite asphalt-filler interaction ability and zeolite-foamed asphalt-filler interaction ability. The results showed that the asphalt-filler interaction ability was enhanced after adding zeolite minerals to asphalt, and the influence of zeolite on asphalt-filler interaction was consistent with zeolite minerals. However, the opposite effect was observed for zeolite water.

Energy Evolution Characteristics of Water-Saturated and Dry Anisotropic Coal under True Triaxial Stresses

During deep underground coal mining, water-injection-related engineering methods are generally carried out to reduce the hazards of coal dynamic disasters. The energy evolution characteristics of coal can better describe the deformation and failure processes, as it is more consistent with the in situ behavior of underground mining-induced coal. In this study, experimental efforts have been paid to the energy evolution characteristics of water-saturated and dry anisotropic coal under true triaxial stresses. The effects of water saturation, intermediate stress, and anisotropic weak planes of coal on the true triaxial energy evolution were systematically evaluated. The results show that the overall energy is weakened due to the water adsorption for water-saturated coal samples. The water-weakening effect on the overall energy of water-saturated coal is more pronounced when perpendicular to the bedding plane direction than in the other two cleat directions. The accumulation elastic energy anisotropy index of dry and water-saturated coal samples is higher than 100.00%. Both accumulation and residual elastic energy of dry and water-saturated coal samples show an increasing-then-decreasing trend with intermediate stress increase. The results obtained in this study help understand the in situ behavior of coal during deep underground mining and control coal dynamic disasters.

Experimental study on the competing effects of strain rate and water weakening on compressive strength of saturated rocks

Measuring the rock compressive strength under combined effects of strain rate and water weakening is of great importance and at the same time a major issue for engineers. In this study, we explore the ability to detangle the contributions of strain rate and water-weakening effects on rock compressive strength within a wide static and dynamic strain rate range. To this end, we conduct a series of compression tests and acoustic emission (AE) tests on two types of rock with specific mineral compositions (i.e., limestone and granite). The correlations between rock compressive strength, including static compressive strength σcs and dynamic compressive strength σcd, and water-weakening factors fw with strain rate are derived. The experimental AE waveform data is analyzed using a new methodology named statistical analysis of dominant frequency, from which we infer the intrinsic rock progressive failure and evaluate the competing effects of water weakening and strain rate. Our results show that water saturation causes a drastic loss in the compressive strength of limestone and a small reduction in the compressive strength of granite. The strain rate effect governs the changes in the compressive strength of dry rocks, characterizing a reduction in low dominant frequencies of AE waveforms with increasing strain rates. Whether the strain rate effect or water-weakening effect plays a dominant role depends largely on the rock types and loading regimes. We proposed that the primary effects on σcs of saturated limestone are strain rate under relatively low static strain rate (lower than 8.33 × 10−5 s−1) and pore water pressure under relatively high static strain rate (beyond 8.33 × 10−5 s−1), respectively, and that on σcd of saturated limestone is strain rate. The variations of σcs and σcd of saturated granite are both determined by the strain rate effect within the strain rate range investigated. Additionally, the exertions of various water-weakening effects of limestone and granite at different strain rates, which are responsible for their fw variations, are evaluated in detail.

Dynamic Mechanics and Energy Dissipation of Saturated Layered Phyllite

This paper is a study of the dynamic mechanics and energy dissipation of saturated layered phyllite. Using the Split-Hopkinson pressure bar system, the mechanical properties and energy dissipation law of the sample during dynamic loading in the test were analyzed. The results show that the weakening effect of water on the phyllite rock body will have a great impact on its mechanical properties, strain rate sensitivity damage mode, and fracture energy dissipation. The values of mechanical parameters such as the modulus of elasticity and compressive strength of the specimens in the test varied with the dip angle of the layer with 0° > 90° > 30° > 60°, and the mechanical parameters of the specimens in the saturated state were smaller than those of the dry specimens. The damage of the sample is mainly in the form of crushing damage at 0° dip angle, shear damage along the laminar surface at 30° and 60°, and destabilization damage of the compression bar at 90° dip angle, with higher fragmentation of the sample in the saturated state. The energy dissipation densities of different inclination samples in the saturated state of schist are greater than those in the dry state, with the highest energy dissipation density in the 0° inclination sample and the lowest in the 90° inclination sample. Both the mean strain rate and compressive strength of the samples showed a multiplicative power relationship with the crushing energy dissipation density of the samples, showing a strong strain rate correlation. These results indicate that the use of rock crushing energy dissipation density can better reflect the strength characteristics of phyllite samples under dynamic loading.

A model combining patchy saturation and moisture-induced elastic weakening with application to ultrasonic monitoring under varying water saturation

SUMMARY Water is known to induce weakening on the static mechanical properties of rocks. However, injection-based operations such as EGS or EOR are commonly monitored through seismic methods involving dynamic moduli. It is therefore important to understand and quantify the effect of water-weakening on dynamic properties. In this study, we performed water injection tests on microporous carbonate rocks (two chalks from the Mons Basin) with ultrasonic monitoring of P-wave velocity and attenuation in order to observe the evolution of the rock moduli with varying water saturation. Our experimental results were interpreted through (i) a classical patchy saturation or PS model and (ii) the same model coupled with water weakening effect through modulus reduction induced by surface energy decrease induced by water in the fluid–rock system, called the WW-PS model. We show that the WW-PS model can better fit the experimental data than the PS model for both selected chalks, but also the previously published data for Sherwood sandstone. Therefore fluid–rock interaction needs to be taken into account when dealing with a fluid not in equilibrium with the host reservoir in fluid injection operations. An extension to reservoir scale modelling is proposed to emphasize the potential impact of water weakening at larger scales.

Water Weakening of Artificially Fractured Chalk, Fracture Modification and Mineral Precipitation during Water Injection—An Experimental Study

This experiment was designed to study the water-weakening effect of artificially fractured chalk caused by the injection of different compositions of brines under reservoir conditions replicating giant hydrocarbon reservoirs at the Norwegian Continental Shelf (NCS). NaCl, synthetic seawater (SSW), and MgCl2, with same ionic strength, were used to flood triaxial cell tests for approximately two months. The chalk cores used in this experiment originate from the Mons basin, close to Obourg, Belgium (Saint Vast Formation, Upper Cretaceous). Three artificially fractured chalk cores had a drilled central hole parallel to the flooding direction to imitate fractured chalk with an aperture of 2.25 (±0.05) mm. Two additional unfractured cores from the same sample set were tested for comparison. The unfractured samples exposed a more rapid onset of the water-weakening effect than the artificially fractured samples, when surface active ions such as Ca2+, Mg2+ and SO42− were introduced. This instant increase was more prominent for SSW-flooded samples compared to MgCl2-flooded samples. The unfractured samples experienced axial strains of 1.12% and 1.49% caused by MgCl2 and SSW, respectively. The artificially fractured cores injected by MgCl2 and SSW exhibited a strain of 1.35% and 1.50%, while NaCl showed the least compaction, at 0.27%, as expected. Extrapolation of the creep curves suggested, however, that artificially fractured cores may show a weaker mechanical resilience than unfractured cores over time. The fracture aperture diameters were reduced by 84%, 76%, and 44% for the SSW, MgCl2, and NaCl tests, respectively. Permeable fractures are important for an effective oil production; however, constant modification through compaction, dissolution, and precipitation will complicate reservoir simulation models. An increased understanding of these processes can contribute to the smarter planning of fluid injection, which is a key factor for successful improved oil recovery. This is an approach to deciphering dynamic fracture behaviours.

A Study on the Strain-Softening Constitutive Model of Cementitious Sandstone

In order to further investigate the impacts of the water environment on the mechanical properties of rocks for an engineering project, taking the water-rich conditions in a coal mine as the engineering background, a series of tests were conducted, including the uniaxial compression test, the conventional triaxial compression test, and the constant axial pressure test on the cementitious sandstone. This was conducted along with the establishment of a multi-linear strain softening constitutive model. According to the tests, the following conclusions can be drawn. Firstly, as the water content increases, the weakening effect of water on the rock mass was obvious. Under various stress paths, the water weakened the rock body to various degrees. In other words, the weakening effect of water on the rock mass was either inhibited or promoted under different stress path conditions Secondly, under various stress paths, the turning point strength and strength variance rate of the rock mass’ mechanical properties decreased linearly with the increase of water content. This further proves that water has a weakening effect on the rock mass, showing that the failure of the specimen changes from brittleness to ductility. Thirdly, the test sample demonstrated different types of damages including the tensile failure, transformation from tensile-shear composite failure to shear failure, and expansion failure under three stress path conditions. In addition, the unloading process demonstrated some dynamic failure characteristics. The research aims to provide some foundational insights for the scientific design and safe construction of the mine and other underground engineering, especially rock mass engineering in the multi-water environment.

Research on the Mechanical Properties and Damage Constitutive Model of Multi-Shape Fractured Sandstone under Hydro-Mechanical Coupling

In this paper, mechanical property tests of sandstone with multiple shapes of prefabricated fractures (single, T-shaped, and Y-shaped fractures) are carried out through the MTS815 rock mechanics testing machine and the Teledyne ISCO D-Series Pumps system. Considering the hydro-mechanical coupling effects, the experiments reveal the key thresholds, strength characteristics and deformation laws of multi-shape fractured sandstones during the progressive failure process. According to the elastic-plastic theory, the continuous damage theory and the statistical damage theory, a new damage model is constructed, which fully reflects the coupled effects among water, micro flaws and macroscopic prefabricated fractures. The crack closure stress σcc, crack initiation stress σci and damage stress σcd of multi-shape fractured sandstone samples are determined by the proposed volumetric strain response method. In the range of 0–90°, the σcc and σci of the multi-shape fractured sandstone samples are different, as well as the angles when the σcd and peak strength (σc) reach their peak values. The stress ratios (the σcc/σc, σci/σc, and σcd/σc are collectively referred to as stress ratios) are hardly affected by the shape and inclination of the fractures inside the rock. According to strength analysis and deformation characteristics, the weakening effect of water has less of an influence on the strength than prefabricated fractures. The stress–strain curve obtained, based on the hydro-mechanical coupling test, is in good agreement with the theoretical curve generated by the damage constitutive model, verifying the rationality of the damage constitutive model. In addition, the fracture inclination only affects the numerical value of the total damage variable of multi-shape fractured sandstone samples, and has minor effects on its variation trend.