Triaxial Tests Research Articles

Effect of the particle shape on the shear mechanical behavior of coral sand

Abstract Coral sand particles exhibit a wide range of shapes, which can be divided into four shapes, e.g., blocky, dendritic and rodlike, flaky, and shell debris. The particle shape of these mixtures is defined by the sphericity, concavity, aspect ratio, flatness and overall regularity, which ranges from 0 to 1. The effect of particle shape on the strength, crushing characteristics, and critical state parameter is systematically investigated through a series of triaxial drainage shear tests under different confining pressures. And the relationship between critical state parameters and mechanical parameters is established. The test results demonstrate the existence of an evident strain-hardening phenomenon in the stress–strain curve of coral sand, accompanied by a strain-softening phenomenon when the bias stress reaches its peak value. The sample is initially subjected to shear shrinkage, followed by shear expansion. The volumetric deformation of the coral sand decreased with increasing peripheral pressure. The particles are transformed from rough irregular shapes to smooth spheres as evidenced by an increase in the shape parameter. The greater the degree of irregularity in the shape of the particles, the more pronounced the resulting change in size reduction. In addition, the critical state parameter was found to be influenced by the shape of the coral sand particles and the mode of particle accumulation. The overall shear resistance of coral sand particles was found to depend on particle rearrangement in addition to particle surface roughness and interparticle friction. It is proposed that the general regularity critical state parameter equation relates the particle shape of coral sand to its critical state mechanical properties, which is of great importance to the practical application and research of coral sand in engineering, and provides an effective means of predicting mechanical properties granular materials.

Experimental investigation of failure mechanism of fissure-filled sandstone under hydro-mechanical conditions

Fissure fillings are critical to the hydro-mechanical properties of jointed rock masses in rock engineering. In this study, triaxial seepage tests were performed on standard cylindrical fissure-filled sandstone. The characteristics of stress–strain relationships, absorption and consumption of energy, variations in deformation resistance, and permeability evolution during the experimental process, along with the crack development observed in post-failure computed tomography scan images of the sandstone specimens were analyzed. The results demonstrate that the fillings improve the energy capacity and reduce the damage accumulation of sandstone specimens, with sand-filled specimens performing better than mud-filled specimens, especially at lower bridge angles. The fillings can reduce the depth of crack extension and lessen the influence of prefabricated fissures on sandstone failure, with this effect diminishing as the rock bridge angle increases. Permeability decreases in the pre-peak failure stage as the fillings improve the deformation resistance of the sandstone specimens. In the post-peak failure stage, the fillings and rock debris generated by the sandstone failure move within the developed fractures, causing significant fluctuations in permeability. These findings deepen the understanding of the hydro-mechanical properties of jointed rocks and provide a scientific basis for stability analysis in rock engineering.

Experimental investigation on the influence of weak interlayers on sandstone rockburst and associated microcracking mechanism

Weak interlayers (WI) are common in sedimentary rock masses in deep coal mines. The qualitative effect of the WI on rockbursts is widely acknowledged; however, its influence mechanism still needs further investigation. In the present study, true triaxial unloading rockburst tests of sandstone with WI and calcite veins (CV) were conducted to explore their influence mechanisms. To explore the impact of WI, the rockburst stress, failure modes, acoustic emission (AE) parameters (energy, entropy, and b-value), and spatial energy characteristics of AE events were analyzed. The influence of the area ratio of WI and their distribution patterns (centralization and dispersion) on rockburst were further investigated. The results indicate that the rockburst stress (peak of maximum principal stress) decreased by 4 % for every 1 % increase in the sandstone's dispersion WI area ratio (1.9%–9.3 %). Namely, rockburst is more likely to occur when there is appropriate WI distributed in the sandstone because WI exacerbates the microcrack activities and energy release. The CV will reduce the weakening effect of WI on rockburst stress and can enhance the rockburst intensity, especially in samples with dispersion WI. Moreover, the more considerable AE energy is released around CV for the sandstone with dispersion WI. The interface between WI and matrix is prone to rockburst for the sandstone with centralized WI because of the concentrated energy release. The results of this paper can provide a reference for the prevention and control of rockbursts in mine sedimentary rocks containing WI and CV.

Study on the time delay failure characteristics of sandstone unloading under dynamic disturbance

The rockburst caused by underground engineering excavation exhibits a significant lag effect. Studies have shown that the occurrence of lag-type rockburst is closely related to the delayed failure of rocks. This paper focuses on the delayed failure characteristics of unloading-damaged sandstone under the combined action of static load and dynamic disturbance. Numerical simulations are utilized to analyze the delayed failure evolution characteristics and failure mechanisms of sandstone. The results indicate that in triaxial unloading delay failure tests, the duration of loading decreases exponentially with the increase of initial unloading damage. Compared to static load conditions, the duration of loading under dynamic disturbance decreases by more than 43 %, and the average strain rate significantly increases. The number of cracks at the endpoint of triaxial unloading delay failure increases as initial unloading damage decreases, with a substantial increase in the number of cracks under dynamic disturbance. These findings provide a valuable reference for the timeliness and delayed rockburst analysis and interpretation of rock damage and failure under high-stress levels.

Theory and Experiment on Rock-Cutter Interfacial Friction and Rock Mohr-Coulomb Parameter Estimations

Summary The Mohr-Coulomb (M-C) failure criteria is by far the most widely used model for granular materials (including rocks and soils) in many geotechnical industries due to its simplicity. Its parameters are conventionally obtained by performing a series of pressurized triaxial compression tests (TCTs). The peak stress from each confining pressure is plotted at a single point as the maximum vs. the minimum principal stresses. The M-C parameters are obtained by the best linear fitting through the failure envelope formed by the peak stress points of interest. The TCT is time-consuming, costly, and destructive. Is there an experiment that can provide the failure envelope with one single test, even at the atmospheric pressure? This seems impossible, at least has never been rigorously reported. In this work, we present our finding of such a test. The paper first provides the experimental setup and the theoretical solution for a hemispherical scratch test of a polycrystalline diamond cutter (PDC) at low rate of cut (ROC) and low depth of cut (DOC); the theoretical characteristic response of the test is identified and validated. Next, the formula for the rock-cutter interfacial coefficient of friction (COF) is derived, which provides a theoretical guide for the friction measurement for shaped cutters. Then, the nominal average drag and thrust stresses are evaluated, which are observed experimentally and then proved theoretically to behave in a linear relation, analogous to the M-C envelope from the TCTs. We also provide a first method that can self-consistently evaluate the M-C parameters for the crushed zone, which plays a very important role in rock cutting. By comparing the M-C results for three rocks at different loading conditions, good agreements under different scratch conditions are made against the M-C parameters for several rocks from the TCTs.

Effect of Hydrate Saturation on Triaxial Shear Mechanical Properties of Methane Hydrate-Bearing Sediment

Abstract As a clean energy source, natural gas hydrate resources are essential to the development of energy in the twenty-first century. However, the degree of consolidation of the hydrate reservoir is low, and complex accidents such as wellbore instability, reservoir collapse, and gas production leakage will be caused if improperly exploited. The laboratory employs a self-developed triaxial shear test equipment that operates under high pressure and low temperature conditions. This equipment is specifically designed to determine the mechanical parameters and strength characteristics of methane hydrate bearing sediment (MHBS) samples. It is used to create water-saturated hydrate deposits with varying levels of saturation. The synthesis of MHBS samples with varying saturations is achieved by precisely regulating the amount of water. The saturation of MHBS is then determined and confirmed by the utilization of the “water content method” and the “gas collection method.” Triaxial shear tests are conducted on MHBS to examine the impact of hydrate saturation on the mechanical parameters and strength behaviours of MHBS. The experimental findings demonstrate that the presence of hydrate crystals enhances the robustness of the depositing medium. The stress-strain curves of MHBS have a hyperbolic shape, indicating strain hardening features. The stress-strain curves may be categorized into three distinct stages: the initial elastic deformation, followed by a slow shift to the initial yield deformation, and ultimately leading to strain hardening. As axial strain rises, the behaviour of the MHBS transitions progressively from elastic deformation to plastic deformation. The shear strength and initial yield strength of MHBS enhance with higher hydrate saturation. The reason for this is that as the hydrate saturation rises, the influence of hydrate crystals on the enhancement of sediment strength becomes more pronounced. However, the initial yield strain of each MHBS sample is between 0.5% and 1.5%, and the difference is not significant. When the hydrate saturation rises gradually, the cohesion of MHBS enhances. Nevertheless, the hydrate saturation has a very minor impact on the internal friction angle.

Performance of geocell reinforced rubber sand mixtures under undrained triaxial test

Large quantities of scrap tires are produced by the automobile industry each year, which causes disposal challenges and impacts the environment. However, scrap tires exhibit various properties, including tensile strength, abrasion resistance, durability, thermal conductivity, elasticity, and more. Due to their versatile characteristics, these scrap tires can be utilized as construction materials for various civil engineering works to reduce their negative environmental effects and conserve natural resources. This study aims to understand the shear strength behaviours exhibited by geocell-reinforced mixtures of rubber and sand through the unconsolidated undrained triaxial test. Various parameters, including rubber sizes (425 μm to 12 mm), rubber contents (10% to 40% by volume), confining pressures (50 to 300 kPa), and geocell heights (0.2H to 0.8H, where H is the height of triaxial sample), were systematically examined to understand their impact on shear strength characteristics. The experimental findings reveal that deviatoric stress is enhanced with increasing confining pressure and rubber sizes. The maximum benefits of the rubber-sand mixture were observed at 30% rubber content. Geocell-reinforced rubber sand mixture has a higher shear strength with respect to the unreinforced mixture. Furthermore, the energy absorption capacity of the geocell-reinforced rubber sand mixtures was much better as compared to either the clean sand or rubber-sand mixture. The findings of this research demonstrate that geocellreinforced rubber sand mixtures are suitable for various geotechnical engineering works.

Prediction of resilient modulus with pre-post experimental data of undisturbed subgrade soils using machine learning algorithms

The resilient modulus (MR) of subgrade, which shows relationship between stress and unit deformation of a pavement systems under traffic loads, is a design parameter of the pavement structure. Although a cyclic triaxial test apparatus can be used to directly determine the MR of the subgrade in the laboratory, utilizing prediction models based on easily obtainable soil parameters, is a more efficient method when taking time and cost considerations into account. A comprehensive laboratory testing program is designed to create MR prediction models using machine learning (ML) algorithms. 70 undisturbed soil samples are subjected to MR tests, as well as physical and engineering soil properties tests (water content, field density, specific gravity, gradation, consistency limits, unconfined compressive strength, swell pressure, swell percentage). Soil samples are drilled from a highway that has been in operation for over five years.First, a linear model like MLR is used in the study. Next, nonlinear regression models like RF, GBM, LightGBM, CatBoost, and XGBoost algorithms are used. Research findings showed that nonlinear regression models outperformed linear regression models in predicting the MR (R2 > 0.85), with the XGBoost algorithm yielding the best accuracy (R2 = 0.90). Apart from the primary effects such as confining pressure (σ3) and deviatoric stress (σd), it was found that unconfined compressive strength (qu), natural water content (wn), and swelling percentage (SR) are significant parameters in the prediction of MR among all parameters.

Impact of rubber membrane on lunar regolith mechanical properties under low effective confining pressure

The existing lunar exploration activities and associated equipment interactions are limited to the surface environment, where the stress state of the lunar regolith is significantly lower than that in laboratory tests conducted on Earth. To address this, this paper proposes a new framework for discrete modeling of large-scale triaxial tests on lunar regolith under low confining pressure. The framework incorporates particle shapes from the Chang’E-5 mission (CE-5) and flexible boundary conditions. Firstly, the shape characteristics of the lunar regolith particles were adopted in the Discrete Element Method (DEM) model to reproduce the mechanical properties of the lunar regolith as accurately as possible. Then, experiments with varying membrane particle stiffness ratios were conducted to explore the effect of the rubber membrane’s properties on the mechanical characteristics of lunar regolith under low effective confining pressure. Topological Data Analysis (TDA) tools from persistent homology were utilized to quantify the dynamic response of particles during the onset and development of strain localization. The results indicate that under low effective confining pressure, selecting appropriate rubber membrane types is crucial for accurately determining the mechanical properties of lunar regolith.

Using well log data to predict rock compressibility and elasticity in Zubair formation/ southern of Iraq

The mechanical characteristics of rocks such as elasticity (Young's modulus, Poisson's ratio, and unconfined compressive strength) play an essential in sand production analysis, well design, and borehole stability assessment. In this study, the mechanical characteristics of rocks were indirectly estimated using gamma ray, density, and acoustic (compressional and shear) log data from well RU-X in the Rumaila oil field, specifically for the Zubair Formation. These estimated properties were compared to direct measurements obtained from triaxial and uniaxial mechanical tests conducted on well RU-X. The results showed a significant similarity between the indirect estimates and the direct measurements, indicating their reliability for sand production analysis and their valuable contribution to constructing the geomechanical model. Moreover, the static profile of Poisson's ratio was validated using laboratory core test results, demonstrating reasonable agreement. The validation process involved comparing laboratory-derived measurements with actual field measurements in the Zubair Formation. The higher Poisson's ratio observed in the shale was attributed to the slower propagation of acoustic waves, resulting in a good matching with an R2 value of 0.77. On the other hand, the lower Young's modulus in the shaly formations indicated lower resistance to deformation, with a comparative ratio of R²=0.96. Static measurements, which consider various influencing factors, provide a more realistic representation of rock behavior under different conditions. Regarding unconfined compressive strength, the comparative ratio was R²=0.83.

Influence mechanism of initial mechanical damage on concrete permeability and tunnel lining leakage

The stress state is not effectively considered in existing studies when researching the permeability evolution of concrete with initial mechanical damages, causing ambiguity in the influence mechanism of initial mechanical damage on tunnel lining leakage. This deficiency can lead to significant uncertainty in predicting the probability and evaluating the consequences of tunnel leakage diseases, further affecting the formulation of relevant prevention strategies. Therefore, mechanical damage is induced to concrete specimens by subjecting them to certain stress levels, and triaxial compression seepage tests are subsequently conducted to study the influence of initial mechanical damage on permeability evolution and macrocracks. Furthermore, the relationship between microcrack characteristics and concrete permeability is studied, ultimately revealing the influence mechanism of initial mechanical damage on tunnel lining leakage. Research results indicate that the concrete permeability decreases first, becomes stable, and then continuously increases during testing, and is positively related to changes in horizontal deformation ratio. When the damage-inducing stress reaches 80% of the uniaxial compressive strength (UCS), the impact of initial mechanical damage on concrete permeability increases significantly. The increase in initial mechanical damage can lead to a significant rise in permeability, even when the crack volume is in a compacted state. Additionally, cracks on the surface of the specimen become clearly visible when the test terminates, once the damage-inducing stress reaches 85% UCS. Two factors contribute to the gradual increase in concrete permeability with the rise in initial damage-inducing stress. Firstly, microcracks inside the concrete gradually widen and propagate. Secondly, the microcracks resulting from the initial damage progressively enlarge due to water pressure during the triaxial compression seepage test. Influenced by the blockage of seepage channels, concrete permeability can occasionally decrease during testing. The accidental load induces the gradual propagation of microcracks inside the mechanically damaged concrete. Then, the rebound deformation of concrete after the removal of the accidental load causes the closed microcracks to reopen significantly, leading to an increase in permeability and subsequent tunnel lining water leakage.

A Numerical Study of the Mechanical Behavior of Jointed Soft Rocks under Triaxial Loading Using a Bonded Particle Model.

In order to master the strength and deformation characteristics, including the macro-micro failure mechanism of soft rock samples with penetrating joints under triaxial loading, a series of numerical triaxial tests have been carried out. The strength and deformation characteristics, failure modes, crack propagation, distribution of force chains, and the influences of joint dip angles and confining pressures have been analyzed and compared with the laboratory test results. The results show that (1) the residual strength ratio of jointed rock samples generally increases first and then decreases with the increase in joint dip angles under the same confining pressure and reaches the maximum value around 23-24°. Poisson's ratio increases with the increase in the confining pressure or the joint dip angle. The elastic modulus increases with the increase in the confining pressure and decreases with the increase in the joint dip angle. (2) The jointed rock samples with different joint dip angles compact with relatively small volumetric strains and then dilate up to failure with relatively large volume expansions. Lower confining pressure and smaller dip angles will lead to a more pronounced dilation phenomenon and less obvious volume shrinkage rules. (3) The low-angle jointed rock samples all exhibit the X-type shear failure. The jointed rock samples with a joint dip angle of 45° exhibit hybrid failure with both slippage and shearing, which are controlled by both the matrix and the joint. (4) The change in the number of cracks includes three stages: the slow crack initiation stage, rapid growth stage, and crack coalescence stage. The total number of shear or tensile cracks all decrease with an increase in the joint dip angles, with the number of tensile cracks being approximately twice that of shear cracks. The tension cracks are mostly horizontal, and the shear cracks are mostly vertical. (5) The number of force chains shows a decreasing trend after the cracks begin to grow. The jointed rock samples for the intact, 15° and 30° cases all form a main force chain during the failure process, while there is no main force chain for the 45° case.

Analysis of Liquefaction in Tailings Deposits by Fem Modeling of Undrained Cyclic Triaxial

In this article, a numerical calibration procedure for undrained cyclic triaxial tests is presented to evaluate the liquefaction potential in sand and silt samples from mining tailings in northern Chile. The numerical modeling of an axisymmetric specimen involved two stages: isotropic consolidation using the Hardening Soil Small (HSS) model and a cycling phase employing the UBC3D-PLM model to simulate the onset of liquefaction using the criterion that the excess pore pressure ratio Ru should exceed 0.8. The results demonstrate that the UBC3D-PLM modeling calibrated with experimental data from cyclic triaxial tests effectively represents the excess pore pressure in both sandy and silty soils from mining tailings. The accuracy of the modeling decreases when a single set of parameters is applied to the same soil at different cyclic stress ratios (CSR), highlighting the need for specific calibrations for each loading.

Experimental study on pore structures and mechanical properties of ferroaluminate cement under sulfate attack

Ferroaluminate cement (FAC) emerges as a special cement with outstanding durability, offering promising applications. However, the resistance to sulfate attack of FAC remains inadequately understood. In this paper, the impact of sulfate attack on the pore structure of FAC concrete is explored through nuclear magnetic resonance (NMR) tests from a microscopic perspective. Meanwhile, the macroscopic mechanical characteristics of concrete attacked by sulfate are investigated under different loading conditions, including splitting tensile and conventional triaxial compression. NMR test analysis shows that as the degree of erosion increases, the number of mesopores and macropores in FAC concrete decreases while the number of micropores increases. The changes in pore structure distribution alter the mechanical response of specimens. The discussion of strength characteristics, deformation behavior, and energy parameters in conventional triaxial tests reveals that FAC concrete attacked by sulfate exhibits superior mechanical properties under confining pressure. Uniaxial strength results indicate that sulfate attack has less impact on specimens under tensile stress state than under compression. Based on the experimental findings, this paper introduces a sulfate attack impact factor to capture the uniaxial strength changes. Further, a multiaxial strength criterion is developed to describe the strength properties of sulfate-attacked concrete under triaxial stress conditions.

Cumulative effects of cyclic train loading on strains in reinforced soils around tunnels

Metro tunnels often experience uneven settlement of the soil beneath them during operation, a problem that is especially pronounced in soft soil layers such as silt. This uneven settlement negatively affects the operational safety of subways, prompting engineers to use soil reinforcement techniques to mitigate ground deformation. However, there is a lack of research on the cumulative deformation of reinforced soils under cyclic train loading. In this study, dynamic triaxial tests were conducted to obtain the deformation parameters of silty reinforced soils under cyclic loading. The principal dynamic relationship was summarized, and the effect of loading frequency on soil deformation was analyzed. The results indicated that as the loading frequency increased, the cumulative deformation of the soil decreased. Using the dynamic constitutive relationship derived from the tests, the finite element method was employed to model the interaction system between the load, tunnel, and strata, as well as the dynamic modulus attenuation behavior of the reinforced soil layer. This approach was used to investigate the cumulative deformation characteristics of reinforced soils under cyclic loading. The findings indicated that the dynamic modulus of the reinforced soil decayed rapidly at the beginning of the loading period, leading to an accelerated increase in the cumulative deformation. Additionally, the cumulative deformation was measured at different train speeds, revealing that when the speeds exceeded 80 km/h, the cumulative strain of the soil increased gradually with speed.

Study on Pore Water Pressure Model of EICP-Solidified Sand under Cyclic Loading

Under traffic load, earthquake load, and wave load, saturated sand foundation is prone to liquefaction, and foundation reinforcement is the key measure to improve its stability and liquefaction resistance. Traditional foundation treatment methods have many problems, such as high cost, long construction period, and environmental pollution. As a new solidification method, enzyme-induced calcium carbonate precipitation (EICP) technology has the advantages of economy, environmental protection, and durability. Through a triaxial consolidated undrained shear test under cyclic loading, the impacts of confining pressure (σ3), cementation number (Pc), cyclic stress ratio (CSR), initial dry density (ρd), and vibration frequency (f) on the development law of pore water pressure of EICP-solidified sand are analyzed and then a pore water pressure model suitable for EICP-solidified sand is established. The result shows that as σ3 and CSR increase, the rise rate of pore water pressure of solidified sand gradually accelerates, and with a lower vibration number required for liquefaction, the anti-liquefaction ability of solidified sand gradually weakens. However, as Pc, ρd, and f rise, the increase rate of pore water pressure of solidified sand gradually lowers, the vibration number required for liquefaction increases correspondingly, and its liquefaction resistance gradually increases. The test results are highly consistent with the predictive results, which show that the three-parameter unified pore water pressure model is suitable for describing the development law of A-type and B-type pore water pressure of EICP-solidified sand at the same time. The study results provide essential reference value and scientific significance in guidance for preventing sand foundations from liquefying.

Damage constitutive model of RAC under triaxial compression based on weibull distribution function

Fly ash (FA) and ground blast furnace slag (GGBS) can be used to densify the pore structure of recycled aggregate concrete (RAC). However, there remains a lack of deep exploration into the effects of confining pressure and mineral admixtures on RAC's crack formation and damage analysis. This study thus focused on investigating the combined impact of the replacement rate of recycled coarse aggregate (RCA), FA, and GGBS contents on the damage mechanisms of RAC under varying stress conditions by microscopic tests and triaxial compression tests. Results identified that increasing confining pressures enhance the peak stress, peak strain, and elastic modulus of RAC, with shear cracks predominating under triaxial compression. Whereas higher the replacement rate of RCA reduced the mechanical performance of RAC, incorporating 20 % FA and 20 % GGBS can significantly enhance its strength and modulus. Electron microscopy (ESEM) images proved that the incorporation of FA and GGBS lead to a denser internal structure compared to that of RAC without mineral admixtures. The constructed damage constitutive model agreed well with experimental data of this study and literatures, showing slower increases in damage variables (D) under triaxial stress compared to uniaxial compression. Model parameters indicated that increasing confining pressure decreased parameter m and increased F0, resulting in flatter post-peak stress-strain curves, and RAC incorporated with 20 % FA and 20 % GGBS had smaller m value under different stress states. These findings provide valuable insights for applying mineral-admixed RAC in diverse engineering scenarios, offering a robust reference for optimizing RAC formulations with FA and GGBS in practical applications.

Shear strength characteristics of unsaturated compacted GMZ bentonite considering anisotropy

Anisotropic microstructure would be generated in the bentonite block during unidirectional compactions. Working as buffer materials, the compacted bentonite will inevitably experience shearing processes during the long-term operation of geological repositories. In this paper, high-pressure triaxial tests were conducted on unsaturated compacted GMZ bentonite specimens with different water contents, dry densities and confining stresses, with the compaction surface of the specimens oriented in both horizontally (H-type) and vertically (V-type) configurations. Results demonstrate that an increase in water content leads to a reduction in both peak strength and residual strength, while higher confining stresses enhance these strength parameters. Normally consolidated and lightly over-consolidated bentonite specimens display substantial shear deformation, whereas heavily over-consolidated specimens tend to experience brittle failure. Water content plays a significant role in shaping both the critical state line (CSL) and the Hvorslev surface (HS), with increasing water content resulting in decreased slope parameters for both and an increased intercept parameter for the HS. Generally, V-type specimens demonstrate a steeper CSL and an outwardly extended HS in contrast to that of H-type specimens. The critical state ratio for V-type specimens is about 10 % higher, and the friction angle is 2.8° greater, than that of the H-type ones. Moreover, this difference appears to increase with increasing water content. The difference of the HS slope parameter between the two specimens is minor, while the intercept parameter is higher for the V-type specimens.

Modelling permanent strain behaviour of soil for flexible pavement design utilizing LWD measurements

ABSTRACT This study aims to improve understanding of unbound material behavior by modeling permanent strain using Light Weight Deflectometer (LWD) measurements, as part of VTI’s broader LWD research. By comparing permanent strain modelling from LWD data with Repeated Load Triaxial (RLT) tests on silty sand soils, it validates LWD data accuracy and explores material property influences on permanent strain parameters, revealing a clear correlation with water content and stress levels. Using LWD data validated against RLT tests, the study delves into material behaviour understanding under varied conditions, focusing on comparing model parameters of permanent strain prediction derived from LWD and RLT tests. Despite minor differences, both methods produce acceptable values, affirming the modelling approach’s robustness. The findings demonstrate LWD’s potential to improve pavement design by providing insights into permanent strain behavior that supports mechanistic-empirical approaches, leading to more efficient designs and better resource use for improved performance.

Experimental investigation on the fracture process and infrared radiation characteristics of structure rockburst under gradient loading

To investigate the macroscopic failure characteristics and infrared thermal imaging evolution of structure rockburst under gradient stress, gradient stress loading simulation tests were conducted using a true triaxial rockburst testing apparatus with combined gradient and hydraulic-pneumatic loading. Tests included three stress gradient coefficients and four structural surface angles. Macroscopic failure observations and infrared thermal imaging of the unloading surfaces were analyzed to understand the characteristics of structure rockburst and the influence of structural surfaces. Two infrared thermal imaging evolution parameters, the relative temperature mean (HRT) and the coefficient of variation (COV), were introduced to explore precursor indicators of structure rockburst. The results indicated that: (1) The dip angle of the structural surface (θ) and the stress gradient coefficient (k) both affect the peak stress during rockburst. (2) The structural surface angle significantly influences rockburst characteristics: θ = 30° or 60° results in shear slip-type rockbursts along or exposed on the structural surface, while θ = 0° or 90° manifests as buckling and tensile cracking-type rockbursts. (3) Infrared thermal imaging reveals that from initial loading to rockburst, temperature distribution transitions from uniform to normal, and then to non-normal. Accumulation of high-temperature points near rockburst indicates failure locations, with increased k intensifying non-normal distribution. (4) Peak values of HRT and COV positively correlate with k. (5) Fluctuations or sharp increases in HRT and COV values serve as precursors for predicting debris spalling and rockburst events.