Soft rock tunnels in red beds frequently encounter anchor failure issues. Improving the mechanical properties of the red-bed soft rock-grout interface is highly significant for ensuring the stability of anchor support. This study employs laboratory direct shear tests in combination with digital image correlation (DIC) technology to investigate the mechanical properties (peak shear strength zp, residual shear strength zr, and shear stiffness ks) of the grout-rock interface (GRI) among three typical soft rocks from red beds (red sandstone, mudstone, and grey sandstone) and two grout materials (ordinary Portland cement (OPC) and early high-strength cement (EHC)) under varying curing periods (6 h, 1 d, 2 d, and 7 d). The shear behavior and DIC-based failure mode are analyzed for red beds GRIs. The following key findings were observed: (1) As normal stress increases, both the shear strength (zp) and shear stiffness (ks) of the GRI also increase, following the trend: red sandstone > mudstone > grey sandstone. The cohesion values of the red sandstone, mudstone, and green sandstone with the EHC grout-rock interface at 2 days are 2.4, 0.9, and 1.2 MPa, respectively. The corresponding internal friction angles are 57.6 degrees, 38.0 degrees, and 27.0 degrees, respectively. (2) With an increase in curing age, both zp and ks at the GRI increase non-linearly. EHC exhibited superior bonding performance compared to OPC, with zp reaching 7.9 MPa at 6 hand 90% of the 7-day zp being achieved at 2 din red sandstone conditions. (3) The OPC-bonded specimens primarily exhibit grout failure near the GRI, whereas the EHC-bonded specimens show rock failure in red sandstone and mudstone conditions, and adhesive failure at the interface in grey sandstone. (4) An empirical model for the shear strength of the GRI in red bed soft rocks is proposed and validated, providing a framework for the rapid and reliable evaluation of anchorage strength in red bed soft rock tunnels.
Peaty soil,a distinct category of soft foundation soil,exhibits unique physical and mechanical properties that are strongly influenced by its microstructure.Its high water content,organic matter content,low strength and permeability often result in significant engineering challenges.Enhancing the mechanical strength of peaty soil has thus become a central focus in geotechnical engineering.Using slag-based geopolymer to synergize with cement for solidification,the mechanical properties of peaty soil before and after stabilization were examined through unconfined compressive strength and direct shear tests.The mechanisms of improvement were further analyzed through microscopic techniques,including scanning electron microscope(SEM),X-ray diffraction(XRD),mercury intrusion porosimetry(MIP),and Fourier transform infrared spectroscopy(FTIR).The results demonstrate that all three alkali activators contribute to the enhancement of the mechanical strength of the peaty soil,with NaOH showing the highest activation efficiency.Cement stabilization of peaty soil improves shear strength by reducing pore space and strengthening interparticle bonding via ion exchange,hydration product crystallization,and the formation of CaCO3 and calcium silicate hydrate(C-S-H).Four stages i.e.,dissolution activation,ion exchange,gel formation,and structural reorganization are identified in the reaction process of activated slag improving peat soil.The alkali activator facilitates the dissolution of the slag's vitreous phase,promoting ionic polymerization that leads to the formation of calcium-alumino-silicate-hydrate(C-A-S-H)gel.Simultaneously,organic functional groups in the peaty soil engage in ion exchange,forming CaSiO3 precipitates and establishing a"calcium bridge"structure.These reactions collectively contribute to the formation of a dense composite matrix,thus enhancing compressive strength.Grey relational analysis reveals that compressive strength is most strongly correlated with pore area,while shear strength shows the highest correlation with the shape factor.Modified soil specimens undergo five dry-wet cycles,with a minimum strength loss rate of 27%.These findings provide a theoretical foundation for the partial replacement of cement with alkali-activated slag in peaty soil stabilization,contributing both to soft soil improvement and the valorization of industrial byproducts.Furthermore,these results offer valuable insights for ground improvement in peat-rich regions,such as Yunnan,China.
3D printing has emerged as a valuable tool for studying the mechanical behavior of rock replicas under various stress-strain states.This technique enables the creation of an unlimited number of replicas with predetermined properties and a homogeneous structure.Among various 3D printing methods,liquid crystal display(LCD)-based printing offers a cost-effective and high-quality approach for rapid prototyping of rock samples.This study investigates the feasibility of using 3D LCD printing to create rock analogs for geomechanical investigations.We evaluate the microstructure of LCD-printed samples and its influence on their elastic and mechanical properties.To assess these properties,we subjected cylindrical samples to elastic wave propagation and uniaxial compression tests.Our results demonstrate that LCD-printed samples exhibit high homogeneity of elastic properties.The velocities of elastic wave propagation across and along the layers are essentially identical,differing only by the error value.Moreover,Young's moduli obtained under uniaxial loading are in good agreement with non-destructive test results,indicating a high degree of homogeneity in elastic properties up to 20 MPa.These findings suggest that 3D LCD-printed rock analogs are well-suited for investigating processes in rocks under purely elastic loading.Additionally,the technology's versatility allows for the creation of rock replicas with various features,providing researchers with the ability to study the mechanical behavior of rocks with specific characteristics.We demonstrate the potential of 3D LCD-printed rock analogs through a case study investigating the impact of cyclic deformations on the conductivity of thin capillaries in a porous medium.Our results provide a strong foundation for utilizing 3D LCD printing to advance our understanding of geomechanical processes in rocks.
Open-ended precast hybrid reinforced concrete (PRC) piles exhibit distinct vertical bearing behavior compared to closed-ended counterparts, primarily due to soil plug formation during installation. To quantitatively assess this difference, fiber Bragg grating sensors were embedded during pile fabrication, and vertical static load tests (SLTs) were conducted on piles P1-P6 with two end configurations and pile lengths. Experimental results for piles P1-P3 were validated through numerical simulations, and length optimization was performed. A parametric study was conducted to evaluate the effects of key geometric parameters on vertical bearing capacity. Results showed that, under identical pile length and stratigraphic conditions, open-ended piles exhibited lower ultimate bearing capacity (UBC), top settlement, and rebound rate than closed-ended piles. However, longer open-ended piles demonstrated significantly greater settlement and rebound than shorter counterparts. Optimization analysis indicated that the closed-ended pile could be reduced from 40 m to 35 m. With constant concrete volume, the D800t130 pile type yielded optimal performance, achieving the highest compressive coefficient (0.42) and material utilization rate (783.1 kN/m3). Both UBC and end resistance ratio increased with pile diameter. For closed-ended piles, diameter significantly influenced axial force distribution and side resistance, while wall thickness had minimal effect on end resistance but reduced side resistance. In contrast, open-ended piles exhibited greater sensitivity to both diameter and wall thickness in terms of axial force and lateral resistance. Inner wall friction was concentrated within twice pile diameters above the soil plug base, although its magnitude remained low. The height-to-diameter (h/D) ratio of the soil plug critically affected vertical bearing behavior. Compared to closed-ended piles, open-ended piles showed reduced lateral friction, with reduction coefficients ranging from 0.78 to 0.92. Notably, when diameter increased from 600 mm to 800 mm, open-ended piles outperformed as closed-ended piles in stiff plastic silty clay.
The application of buffer layer provides an effective solution to the problem of secondary lining failure.Different buffer layer materials exhibit significant variations in mechanical properties,making it essential to establish a widely applicable theoretical model.For this purpose,this study firstly divides the nonlinear compressive stress-strain curve of buffer layer materials into n deformation stages,and the deformation characteristic of each stage is described by replacing with a straight line.Secondly,an interaction mechanical model between rheological surrounding rock and support considering the effect of the buffer layer is established.By using the deformation coordination in both the surrounding rock-buffer layer interface and the buffer layer-secondary lining interface during the whole interaction process,analytical solutions for tunnel displacement and contact pressures at different interfaces during various deformation stages of buffer layer materials are presented.Furthermore,the effectiveness of the proposed theoretical model is validated by comparison with previous studies and numerical results.Finally,a parametric analysis of the mechanical responses of tunnels with polyurethane and polyethylene foam buffer layers(with differing deformation characteristics)is carried out based on the theoretical model.The results show that the proposed model is applicable to different buffer layer materials.The division of deformation stages in buffer layer materials significantly impacts prediction outcomes.For polyurethane foam buffer layer,the prediction result of the secondary lining pressure without considering the deformation stage division is 35.2%higher than that under consideration,while for polyethylene foam buffer layer,the predicted value is even 96%higher than that considering the deformation stage division.For a given tunnel,the thickness of buffer layer has a reasonable range,with an optimal thickness of 25 cm for both polyurethane and polyethylene foam buffer layers under these conditions.Installing a buffer layer is more beneficial for tunnels subject to significant long-term deformation,as it effectively reduces secondary lining pressure and ensures long-term safety.
Understanding and utilizing the laws of heat and moisture migration in loess under climate change is crucial for slope engineering safety and agricultural production. A custom-designed vertical temperature-controlled heat and moisture migration test device, coupled with non-contact continuous measurement technology for temperature and moisture fields, was used to perform heating tests with varying temperature levels and initial water content conditions at the bottom of loess samples. The study investigates the vertical heat and moisture migration in loess under the combined effects of thermal potential, gravitational potential, and matric potential. The results show that: (1) At heat source temperatures ranging from 45 degrees C to 75 degrees C, the temperature field of the loess samples stabilizes within approximately 24 hours. (2) Between 0 and 40 cm in height, samples with higher heat source temperatures and initial water content exhibit larger stable temperatures and thermal gradients. (3) As the heating time increases, the vertical moisture content of the soil sample shows a significant peak in the height distribution curve, with the position of the peak gradually shifting upward and the peak magnitude progressively increasing. (4) The thermal potential plays a dominant role in the upward migration of moisture in loess, with higher temperatures significantly increasing the driving force for moisture movement. (5) The upward migration of water is most pronounced when the initial moisture content is moderate.
The pullout performance of the anchorage system is a key indicator for assessing the effectiveness of rock mass reinforcement.However,existing pullout tests,though widely used,fail to accurately simulate the stiffness of the actual rock mass,reveal the radial mechanical response,and analyze failure modes.To address these issues,this study designed a combination of aluminum sleeves and rock to simulate a soft rock environment and conducted pullout tests on the anchorage system under the stiffness conditions of a soft rock environment.Results indicate two dominant failure modes in a soft-rock environment:rock-splitting failure and unsplit failure,with the corresponding pullout curves showing post-peak sharp drop and post-peak gradual drop,respectively.A significant correlation exists between radial stress and failure mode:peak radial stress ranges from 4 MPa to 10 MPa for rock-splitting failure and 2 MPa to 4 MPa for unsplit failure.Moreover,the anchorage length has the most significant impact on the peak load,while the anchorage length and grout strength are the main factors affecting the failure mode of the anchorage system.
The cavern constructed in the layered inter-bedded salt rock contains significant insoluble sediment, whose heat storage and utilization potential remains underexplored. To investigate the feasibility of integrating compressed gas energy storage in salt caverns with heat storage in the sediment, a thermo-hydro-mechanical numerical model was developed using Comsol Multiphysics, accounting for the porous medium characteristics of the sediment layer. Firstly, the thermal response of the cavern was analyzed under varying sediment contents during conventional compressed gas storage. The specific heat capacity of the sediment was found to mitigate the thermal impact of hot air on the cavern wall. Temperature fluctuations in the surrounding rock decreased when the sediment layer's vertical thickness exceeded 30 m. During the gas production stage, temperature fluctuations were restricted to below 0.5 V, while during the gas injection stage, they were less than 1 'C. Subsequently, a dual-cavern model with connected channels was constructed to study the temperature field changes under short-term heat storage, respectively. Simulations showed that temperature fluctuations at the outflow interface during operation ranged from 45 degrees C to 55 degrees C, which is 66% lower than at the injection interface, ranging from 30 degrees C to 60 degrees C. After three operation cycles, sediment temperature was observed to vary periodically between 49 and 53 , validating the feasibility of using sediment as an underground heat storage module for compressed air energy storage systems. Results demonstrate that the sediment's heat capacity contributes to cave wall stability and offers a reference for developing a comprehensive system for utilizing compressed air and heat energy storage in sediment-filled salt caverns.
In the context of the rapid development of new energy technologies, energy storage has emerged as a crucial strategic capability. As a new energy storage technology, compressed air energy storage in aquifers (CAESA) is receiving attention due to its advantages of wide distribution and large scale. It has more significant advantages in carrying out compressed air energy storage in aquifers with high exploration and development levels in oil regions. In CAESA, the sealing performance of the caprock system controls the storage capacity and safety. Fully tapping into the sealing potential of the caprock system requires the use of quantitative evaluation indicators. This article proposes a maximum sealing pressure model (P-max model) to define the sealing capacity of a caprock segment, and provides a method for determining P-max via mathematical modeling. This model can accommodate various sealing mechanisms, and for the first time, it explains the sealing mechanism of the thickness of the caprock layer from a mathematical and physical perspective. This indicator can be used as a single indicator to measure the sealing performance of the caprock layer during the site selection stage. Based on this indicator and in combination with the short-board principle, we propose the safe sealing pressure index Aare to quantify the sealing performance of the entire caprock system. We also provide the calculation method and a flowchart, which can be applied during the engineering development and design stage. Finally, using the KD642-7 pilot project planned by Sinopec Shengli Oilfield as an example, the model's validity has been preliminarily demonstrated.
A large strain nonlinear radial consolidation model RVTCS for saturated soil foundation under vacuum preloading combined with heating is developed by using piecewise-linear difference method.This model couples radial heat conduction in a soil layer with large-strain thermo-consolidation.It accounts for thermal stress and thermal expansion during consolidation,self-weight,radial and vertical seepage,time-dependent heat-source temperature,nonlinear relationships between compressibility and permeability,and rebound-recompression behavior.The model can analyze large-strain thermo-consolidation under various combinations of vacuum preloading and heating.The model is verified by large-scale vacuum preloading combined with heating consolidation test,and the RVTCS numerical solution of settlement is in good agreement with the indoor test results.The variation laws of excess pore water pressure,settlement,degree of consolidation,temperature and energy consumption under different combined conditions are deeply studied through the analysis of numerical examples.The combination of vacuum preloading and heating can significantly improve the settlement and consolidation rate of soil layer.
The cross-sectional shape of an underground gas storage in a compressed air energy storage(CAES)power plant significantly influences its stress state,thereby affecting gas tightness and stability.It is conventionally considered that a circular cross-section yields the most favorable stress distribution.However,under anisotropic in-situ stress conditions,the hoop stress around a circular cavern is uneven and can induce localized lining cracking and gas leakage.To address this issue,this study investigates elliptical cross-section storage caverns using theoretical analysis based on elasticity theory.First,we propose a gas-tightness criterion based on the elastic stress state and derive an analytical solution for the elliptical cross-section's optimal axial ratio.Second,we establish a stability criterion for lined rock caverns under anisotropic in-situ stress and develop a method to determine the operating pressure range for elliptical cross-sections,comparing it with the circular cross-section.Furthermore,we perform a parameter sensitivity analysis using FLAC3D to evaluate how factors affect the elliptical cross-section's optimal axial ratio and operating pressure range.Finally,we establish an integrated calculation process to determine the optimal axial ratio and pressure range.Results show that,under anisotropic in-situ stress conditions,an elliptical cross-section designed with an optimal axial ratio can produce uniform hoop stress around the cavern.When an elliptical cross-section gas storage facility is designed with the optimal axis ratio,its pressure operating range is maximized.The lateral pressure coefficient,in-situ stress and internal pressure of gas storage are the main factors affecting the operating pressure range of elliptical section gas storage.These findings provide theoretical guidance for the shape optimization and pressure design of underground gas storage caverns.
Compressed air energy storage lined rock caverns are subject to various complex failure modes during operation,particularly under high-pressure conditions,where tensile and shear failures are prone to occur,posing serious threats to structural stability and operational safety.Focusing on the coupling characteristics of failure mechanisms,an analytical model of the surrounding rock failure zone was developed based on the full stress path from excavation to operation.The influences of rock mass quality,burial depth,tensile strength,and in-situ stress anisotropy on the evolution of failure zones were systematically analyzed.The results indicate that the failure mode during operation is significantly affected by the initial state of the surrounding rock after excavation:for high-quality rock masses that remain elastic after excavation,both high-pressure tensile and shear failures may occur during operation;whereas for lower-quality rock masses where shear failure zones have already developed after excavation,only further shear zone expansion is observed during operation.When the excavation-induced failure zone is smaller than the high-pressure failure zone,increasing burial depth effectively suppresses the expansion of both tensile and shear failure zones.The occurrence of tensile failure under high pressure significantly increases the overall degree of surrounding rock failure.However,relatively low tensile strength can inhibit its initiation.The critical tensile strength required for suppression decreases with increasing burial depth.In-situ stress anisotropy generates direction-dependent.As anisotropy increases,the critical internal pressure for high-pressure failure decreases,whereas the tensile strength required to suppress tensile failure increases.
The surrounding rock mass serves as the primary load-bearing structure in underground CAES caverns,making its stress and deformation behaviour during the charging and discharging process critically significant.Nevertheless,the theoretical framework for elastoplastic deformation of the surrounding rock mass under long-term cyclic expansion dynamic loading remains poorly understood,and the stress paths of the whole process from excavation to cyclic charging and discharging operations are not clear.Accordingly,based on the stress characteristics of the CAES caverns,an analytical solution for elastoplastic deformation of surrounding rock mass throughout the excavation and operational phases is proposed in this study.The reliability of the proposed solution is verified by comparing with the numerical simulation results of commercial software FLAC3D.Furthermore,a parametric sensitivity analysis is conducted using a fixed computational scheme.The analysis evaluates how geological conditions and operational parameters influence the mechanical response of the surrounding rock mass.The main conclusions are as follows:(1)The mechanism that surrounding rock mass will not continue to expand outward is clarified.Under the set working conditions,surrounding rock mass mainly exhibits plastic cumulative deformation inward,resolving the long-standing issue of CAES caverns expansion that has plagued engineering practice.(2)The evolution of the stress path in the surrounding rock mass from excavation through operation is revealed,and the stress path remains between the high-and low-pressure yield lines throughout this period.(3)A method for determining the elastic operating pressure range of the surrounding rock mass of the CAES caverns is developed.This range depends on cohesion and internal friction angle.Operating within this range ensures the surrounding rock mass remains in an elastic state without plastic deformation,thereby addressing a theoretical gap in CAES caverns operating pressure range theory.(4)It is clear that the deformation of surrounding rock mass is most significantly influenced by the minimum and maximum gas storage pressures,while the frequency of charging-discharging also plays an important role.These findings provide theoretical support for the design and construction of CAES power plants.
The performance and mix ratio of industrial residue-cement fluid solidified shield muck were studied for promoting the utilization of urban solid wastes. The shield muck collected in Wuhan city were solidified by cement and industrial residues, including blast furnace slag, carbide slag, phosphogypsum, rice husk ash, fly ash and silica fume. The effects of water-cement ratio, cement-soil ratio, industrial residue type and replacement ratio on sample fluidity, shrinkage deformation and strength were discussed. Results indicate that sample fluidity is determined by the water-cement and cement-soil ratios. As the fly ash replacement ratio increases, sample fluidity continuously increases. With increasing replacement ratios of other industrial residues, sample fluidity gradually decreases. The order of reduction is silica fume > rice husk ash > phosphogypsum > slag > carbide slag. The shrinkage deformation mainly occurs within 3-.28 d, and the shrinkage rate is significantly reduced when the industrial residue replaces the cement. Sample strength depends on the water-cement ratio and the cement-soil ratio. A low water-cement ratio enhances long-term sample strength, while a high cement-soil ratio boosts early strength. Blast furnace slag and phosphogypsum in the industrial residue promote long-term strength development. Finally, a design method of fluid solidified soil mix ratio based on the theory of slurry rheology and strength development is proposed, providing reference for subsequent construction.
The interlocking L-shaped caisson,as a new type of caisson structure,exhibits enhanced performance under complex marine loading conditions.This structure shows significant potential for applications in marine infrastructure,including deep-water port terminals,breakwaters,and artificial islands.The feasibility of replacing the conventional L-shaped caisson(CLC)with the proposed interlocking L-shaped caisson(ILC)is investigated through indoor loading model tests.The paper investigated the effects of filling materials,foundation types,and load forms on the stability of caisson docks formed by adjacent ILCs within a hexagonal prism cavity.Compared to CLC quay wall,the ultimate bearing capacity of the ILC quay wall,when pinned by gravel or concrete blocks,increased by 15.5%and 20.1%under strip load.The ILC quay wall with concrete block interlocking reinforcement exhibits superior load-bearing performance.When the sand ground is replaced with a soft soil interlayer ground,the ultimate bearing capacity of the ILC quay wall decreases.The ultimate failure mode of the ILC quay wall shifted from overturning to overall instability failure,with the failure surface changing from arcs and straight lines to multi-segmented lines.When strip loads are replaced by concentrated loads with a smaller range of action,the integrity of the ILC quay wall deteriorates,its ultimate bearing capacity significantly decreases,and the settlement of the backfill soil surface near the caisson increases.
The quartet-parameter structure generation set (QSGS) method is a commonly used modeling algorithm for porous media. The fractal dimension D and pore autocorrelation distance lambda of porous media are important indicators for evaluating modeling effect. There is currently a lack of research on the relationship between the parameters of the QSGS method and the fractal dimension, as well as the pore autocorrelation distance of porous media. A method for normalizing the probability distribution of the cores of growth phase is proposed, and a set of numerical simulation schemes for modeling porous media with different grid sizes N, porosities phi and normalized distribution probability p(eta )is designed on this basis. Then the variations of D and lambda with the modeling parameters N, phi and p(eta) are analyzed based on the numerical simulation results, and the sensitivity of the modeling parameters is analyzed based on the orthogonal tests. Finally, the fitting relationships between the modeling parameters N,phi , p(eta ) and D,lambda are established. The results show that the modeling parameters N,phi and p(eta) all have a certain degree of influence on D, and the degree of influence is phi , p(eta ) and N in descending order. The main influencing factor of lambda is p(eta) , and the other parameters have less influence. The constructed multiple regression fitting models have high precision and can be used to guide the modeling of the QSGS method.
Deep-sea pipelines are typically laid on the seabed.Under the influence of their own weight and pipeline-laying operations,they become embedded into the seabed.The embedment depth wini significantly affects the lateral soil resistance exerted by the seabed on the pipeline.Existing research has primarily focused on pipelines with embedment ranging from 0.1 to 0.5 times the pipe diameter D.However,recent studies show that some pipelines embed deeper than 0.5D.We employed the radial point interpolation method-remeshing and interpolation technique with small strain(RPIM-RITSS)to perform large-deformation analyses of the lateral pipe-soil interaction for initial embedment from 0.1D to 1.0D.The method's effectiveness was validated by comparisons with centrifuge tests and other numerical results.Subsequent analyses examined how initial embedment and pipe weight influence the lateral-buckling mode and soil resistance.A residual-resistance model for lateral buckling,applicable to initial embedment from 0.6D to 1.0D,was proposed to support the safe design of deep-sea pipelines.
Existing studies on the dynamic response of tunnel linings and surrounding soil under explosive shocks primarily treat the soil as isotropic, however, it is actually a transversely isotropic medium. To investigate the axisymmetric dynamic response of transversely isotropic soil under explosive loading, we derive the governing equations for the lining and the surrounding transversely isotropic saturated soil based on Biot's theory and the theory of transversely isotropic elastic mechanics. The potential function was introduced and Laplace transform and Fourier transform were performed to obtain the general solution. The results indicate that as the transversely isotropic parameter & varsigma; increases, both the radial displacement and the peak effective circumferential stress of the soil decrease. The peak values of radial stress, circumferential stress, and pore water pressure in transversely isotropic soil occur almost simultaneously at the moment of the explosion. In the axial direction of the tunnel, these responses decay exponentially as the distance from the explosion source increases. When the axial distance reaches six times the tunnel radius, the transient response of the soil approaches zero.
To investigate the temporal influence of thermal ageing on the thermal conductivity of bentonite buffer material under high temperature conditions, MX80 bentonite powder was pretreated at 100 degrees C and 200 degrees C for durations of 0, 15, 30, 60, 90, 120 days. The thermal conductivity of the compacted bentonite samples after pretreatment was measured using the thermal probe method, and the temporal influence was analyzed. The microscopic mechanism underlying the temporal influence on thermal conductivity 2 of bentonite samples was revealed through particle size analysis, X-ray diffraction and thermogravimetric analysis tests. The experimental results indicate that: 1) After high-temperature aging (100 degrees C and 200 degrees C), the thermal conductivity 2 of bentonite samples decreased significantly with increasing thermal aging time t, demonstrating a significant temporal effect. A sharp decline was observed from 0 to 15 days, followed by stabilization after 30 days. The effect was more pronounced at 200 degrees C compared to 100 degrees C. 2) High temperatures (100 degrees C and 200 degrees C) result in the gradual desorption of various forms of water, thinning of the bound water film, and a reduction in the particle size of bentonite samples. Additionally, at 200 degrees C, some montmorillonite minerals in the samples transform into sodium mica. These microstructural evolutions are consistent with the temporal influence observed in the thermal conductivity 2 of the samples. 3)The fundamental reason for the temporal influence of thermal aging on the thermal conductivity of bentonite materials is as follows: At 100 degrees C, as thermal aging time t increases, the temperature effects lead to the gradual desorption of various forms of water, thinning of the bound water film, reduction in particle size, decrease in solid volume, and increase in gas volume, while the mineral composition remains unchanged. At 200 degrees C, as the thermal aging time t increases, the aforementioned temperature become more pronounced, and the high temperature causes some montmorillonite minerals to transform into sodium mica, which exhibits a lower thermal conductivity lambda.
The heterogeneity in breccia content and geometry significantly influences the variability of the mechanical properties of sandstone containing breccia clasts.However,previous studies have often neglected the distribution of breccia geometry,resulting in inaccurate assessments of mechanical behavior.To investigate mechanical properties and determine the minimum number of samples for testing,particle-shape indices were introduced to quantify breccia geometry and its statistical distribution.Using laboratory experiments and numerical simulations,we developed a model that incorporates breccia content and the distribution of breccia geometry.The study explored the effects of breccia area,slenderness,and roughness on the mechanical properties of sandstone containing breccia clasts,along with their impact on the minimum sample number.The findings reveal a strong positive correlation between breccia content and fine length with the uniaxial compressive strength of sandstone containing breccia clasts,with Pearson correlation coefficients of 0.87 and 0.62,respectively.In contrast,breccia roughness exhibited a weaker correlation,with a Pearson coefficient of 0.31.Increasing the variability of the fine length of the breccia significantly elevated the minimum sample number,while variability in breccia roughness had no significant effect.Although the area of individual breccia particles did not alter the minimum required sample number,it contributed to an increase in the uniaxial compressive strength of the sandstone with breccia clasts.This study reveals the underlying causes of the variability in the mechanical properties of sandstone containing breccia clasts and establishes a dynamic approach to determine the minimum sample number,which was found to be 14.The proposed method achieved a relative error of less than 2%in predicting the uniaxial compressive strength.These findings provide valuable insights into evaluating mechanical properties and determining its minimum required sample number.
