Study on mechanical properties and statistical damage constitutive model of red sandstone after heating and water-cooling cycles

To investigate the effect of hydro-mechanical coupling characteristic in low-permeability hard rocks during the excavation of groundwater-sealed energy cavern and hydraulic engineering tunnels or chambers, triaxial compression tests were conducted on engineering granite under different confining and seepage pressures. The mechanical properties, such as the strength and deformation parameters, of granite under hydro-mechanical coupling condition were studied. The permeability of the granite under different stresses first decreases, then stabilizes, and then increases significantly until the final abrupt change, and the inflection point of the abrupt change in permeability tends to be in advance as the confining pressure increases or the seepage pressure decreases. Based on the statistical damage theory and test result, combined with the Mogi-Coulomb strength criterion, a hydro-mechanical coupling statistical damage constitutive model that considers the rock damage threshold and the initial compaction effect was proposed, and the proposed mechanical model was verified based on the test results under different confining and seepage pressures. The proposed mechanical model was further applied to predict permeability catastrophes during rock fracturing and achieves good results. This study provides a theoretical basis for the prevention and control of hydro-mechanical coupled disasters in rock engineering.

Section: Test Results and Analysismentioning

confidence: 99%

Hydro-mechanical coupling characteristics and damage constitutive model of low-permeability granite under triaxial compression

Zheng

Wang

et al. 2022

“…Moreover, the numerical results reflect the macroscopic fracture, but the accumulation of microscopic damage is responsible for the occurrence of the macroscopic fracture. Although we do not conduct microscopic experiments on shale after thermal shock, different rock types have similar evolution characteristics at the microscopic level (Jiang et al., 2022). We previously carried out a cyclic heating and cooling experiment on hot dry granite (Zhang et al., 2021), as shown in the SEM images in Figure 24.…”

Section: Discussionmentioning

confidence: 99%

Numerical simulation on hydraulic fracture propagation in laminated shale based on thermo-hydro-mechanical-damage coupling model

Zhang

Guo

et al. 2023

The temperature of a deep shale reservoir may reach more than 100°C, and the effect of thermal shock on shale hydraulic fracturing has rarely not been considered in previous studies. Based on mesoscopic damage mechanics and the finite element method, a thermo-hydro-mechanical-damage (THMD) coupling model considering temperature, seepage, stress, and damage fields was constructed to investigate the effects of reservoir temperature, convective heat transfer coefficient ( h), in-situ stress difference and bedding plane angle ( αθ) on shale hydraulic fracturing. The results show that multiple hydraulic fractures (HFs) can occur under thermal shock and that HFs control the distribution of seepage, temperature, and stress fields. Reservoir temperature, in-situ stress difference and αθ are primary factors affecting hydraulic fracturing, whereas h is a secondary factor. When the reservoir temperature rises from 50°C to 150°C, the initiation and breakdown pressures decrease by 65.5% and 16.7%, respectively. HFs cross the bedding plane more easily, and fracture complexity is obviously enhanced. A higher h is favourable for slightly reducing the initiation and breakdown pressures, but it has little influence on the fracture complexity. Once the in-situ stress difference is low, there is a high fracture complexity, but HFs are more easily captured by bedding planes to limit the propagation of fracture height. When the in-situ stress difference is high, HFs are more likely to form bi-wing fractures. Whether αθ is too large or small, it is not conducive to improving the fracture complexity. In this study, when αθ is 30°, HFs and bedding planes intersect to form a fracture network. Essentially, thermal shock plays a key role in reducing the initiation pressure and forming multiple HFs during the fracturing process, and fracture propagation mainly depends on the injection pressure. The results can serve as reasonable suggestions for the optimization of shale hydraulic fracturing.

“…The loading damage variable of rock during the failure process can be indicated as the ratio of numbers of damaged microelements ( S f ) to that of total microelements ( S ), i.e., Df=SfS. Assuming that the microelement strength inside the rock conforms to Weibull distribution (Chen et al., 2020; Jiang et al., 2022; Onodera and Okabe, 2020; Weibull, 1951; Zachariev, 2016), and the probability distribution function of damaged microelements is defined as: where f is a variable representing microelement strength. β and η are parameters related to Weibull distribution.…”

Section: Damage Constitutive Models For Frozen-thawed Rockmentioning

confidence: 99%

“…Although the changes in physical and mechanical properties can be taken as an indicator of the freeze-thaw induced damage of rock in a macro perspective, the mechanical behavior of frozen-thawed rock with uniaxial or triaxial compression tests cannot be represented. Under conventional uniaxial or triaxial compression, some damage constitutive models of rock (Bian et al., 2019; Ji et al., 2018; Jian and Gu, 2011; Li et al., 2012; 2015; 2017; Wang et al., 2018, 2021; Xie et al., 2020; Zhu et al., 2020) were built on account of the equivalent strain theory proposed by Lemaitre (Lemaitre, 1984, 1985; Liu et al., 2018) and probability statistical distribution of strength originally from Weibull (Jiang et al., 2022; Weibull, 1951; Zachariev, 2016). Later on, some damage constitutive models of frozen-thawed rocks (Chen et al., 2020; Fang et al., 2019; Lu et al., 2018; Zhang et al., 2019) were build using the statistical damage mechanics.…”

Section: Introductionmentioning

confidence: 99%

Mechanical properties and two damage models of frozen-thawed rocks under triaxial compression

Jiang

Lai

et al. 2022

Freeze-thaw induced damage in rock engineering is common in cold regions. However, a damage model for capturing the whole failure process of frozen-thawed rocks is still lacking. In this paper, triaxial compression tests of red sandstone experienced with different freeze-thaw cycles (FTCs) were conducted. Subsequently, the variation of mechanical properties with the numbers of FTCs under different confining pressures were obtained, including peak deviator stress, peak strain, linear elastic modulus, residual strength, friction angle and cohesion. The completely compacted point on stress-strain curve of rock was determined by calculating the strain difference between the stress-strain curve and a reference line. On theses bases, two damage constitutive models considering the initial compaction phase and residual deformation phase were established by means of the continuum damage mechanics and statistical microelement strength theory together with the random exponential function of strain difference. The calculated data obtained from the two proposed models and measured data were then compared. The results shows that the proposed model I is suitable for all rocks samples experienced with FTCs, while the proposed model II is suitable for rocks with small residual strength or large stress difference between peak strength and residual strength. Meanwhile, the two proposed models were compared with the existing ones by evaluating the factor Ω . The influence of confining pressure and FTCs on damage evolution of rock was discussed, and the physical meanings of the parameters in the two models were analyzed in details. The findings are beneficial for providing a reference in developing a constitutive damage model for rocks in cold regions.