Wave Velocity Test Research Articles

Predictive model for shear wave velocity of gravelly soil and its application to liquefaction triggering assessment

Several studies have established empirical correlations between shear wave velocity (Vs) and standard penetration test blow count (SPT-N) for engineering use. However, these empirical correlations cannot be applied to gravel-rich soils since the measured SPT-N is often inflated in gravel. Therefore, an empirical correlation of Vs for gravel is developed in this study using the Engineering Geological Database for the Taiwan Strong Motion Instrumentation Program. The Vs predictive model considers gravel content (GC) and coefficient of uniformity (Cu) in addition to effective vertical stress, void ratio, fines content, plasticity index, and overconsolidation ratio, which have been considered previously. The proposed model indicates that Vs increases with GC and Cu. Moreover, the Vs adjusted for GC can be used with existing Vs -based liquefaction triggering relationships to rationally define the boundary between liquefaction and non-liquefaction case histories with different GCs.

Comparison of autonomic nervous system dysfunction, arterial stiffness, and heart rate recovery according to spinal cord injury level.

To investigate the differences in autonomic nervous system (ANS) dysfunction, arterial stiffness, and the degree of delay in post-exercise heart rate recovery (HRR) according to the level of spinal cord injury (SCI), and propose preventive measures against cardiovascular diseases after SCI. This retrospective study included 51 patients with SCI. Based on the neurological level of injury (NLI), patients were divided into two groups: Group A (NLI at and above T6) and Group B (NLI below T6). To assess ANS dysfunction, the head-up tilt test and 24-hour ambulatory blood pressure monitoring were conducted. Arterial stiffness was measured using the pulse wave velocity test. The exercise tolerance test was conducted to measure post-exercise HRR. Group A had significantly higher values in the head-up tilt test and 24-hour ambulatory blood pressure monitoring. In the pulse wave velocity test, both sides (left and right) had significantly higher values in Group B. One minute after the exercise tolerance test, Group A had significantly slower HRR (18.8 ± 11.1 beats/minute) than Group B. Understanding the impact of ANS dysfunction and arterial stiffness on HRR in SCI according to NLI may provide insights for clinical management and preventative strategies for cardiovascular diseases.

Non-destructive evaluation of residual strength distribution of recycled aggregate concrete and bond strength between recycled aggregate concrete and deformed bar with different cover thicknesses after freeze-thaw cycles

The thickness of a cover significantly influences both the bonding performance and the durability of materials against frost resistance. This research investigates the degradation and damage distribution of fundamental mechanical properties in two specimens of recycled aggregate concrete (RAC), each with varying sizes, following freeze-thaw cycles (FTCs). This comparison is facilitated through non-destructive and damage tests. Subsequently, the influence of freeze-thaw damage (FTD) on the bond strength of specimens with differing cover thicknesses is examined via pull-out tests on 14 groups of center pull-out specimens. Lastly, the bond strength is theoretically analyzed. The test results reveal that FTCs diminish the material strength of RAC, and the FTD distribution within RAC specimens is not uniform. The surface concrete sustains a higher degree of damage compared to the internal concrete, resulting in an average FTD of small-size specimens that surpasses that of large-size specimens. The residual strength of RAC can be assessed using a non-destructive test, specifically the ultrasonic wave velocity test. For center pull-out specimens, FTD not only decreases the material strength but also increases the wedge splitting angle while reducing the critical protective layer thickness. This paper proposes a soft sleeve correction theory that comprehensively accounts for the effects of FTD. When combined with non-destructive test results—namely those from the ultrasonic wave velocity test—this theory can effectively evaluate the bond strength of RAC post-FTD. This approach offers valuable insights for the design and assessment of recycled concrete in cold climates.

Experimental Study on Strength Enhancement and Porosity Variation of 3D-Printed Gypsum Rocks: Insights on Vacuum Infiltration Post-Processing

Three-dimensional printing (3DP) technology has shown great potential in rock mechanics and mining engineering due to its ability to create complex and customized objects with high precision and accuracy. At present, an emerging research focus is improving the mechanical properties of 3D-printed samples, which originally has low strength and stiffness, to match those of natural rocks. The objective of this study was to investigate the effectiveness of different post-treatments on the strength enhancement of 3D-printed gypsum samples. To achieve this goal, 3D-printed gypsum samples were subjected to different post-treatments including dipped infiltration treatment and vacuum infiltration treatment using different infiltrants: water, saltwater, ColorBond, and StrengthMax. Subsequently, each sample was subjected to ultrasonic wave velocity testing and uniaxial compression experiments to characterize their mechanical properties, CT scans to investigate their microstructural characteristics. Additionally, X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) tests were conducted to explore the underlying reasons for changes in macroscopic strength. Finally, the physical characteristics and mechanical properties of untreated and post-processed 3D-printed gypsum samples were compared with natural rocks. The results showed that the strength of samples treated with water and saltwater was much lower than that of those treated with ColorBond and StrengthMax, while the porosity was the opposite. In water-treated and saltwater-treated samples, water or saltwater treatment can alter particle characteristics, but weak adhesive bonding and numerous pores result in low mechanical strength. Samples treated with Colorbond or StrengthMax exhibit improved strength due to effective gap filling and cohesive structure formation, with StrengthMax-treated samples showing higher strength despite having more pores than Colorbond-treated ones. Moreover, the physical and mechanical properties of these treated samples matched a wider range of natural rock types compared to the untreated samples.

Effect of freeze‒thaw cycles on root-Soil composite mechanical properties and slope stability.

Natural disasters such as landslides often occur on soil slopes in seasonally frozen areas that undergo freeze‒thaw cycling. Ecological slope protection is an effective way to prevent such disasters. To explore the change in the mechanical properties of soil under the influence of both root reinforcement and freeze‒thaw cycles and its influence on slope stability, the Baijiabao landslide in the Three Gorges Reservoir area was taken as an example. The mechanical properties of soil under different confining pressures, vegetation coverages (VCs) and numbers of freeze‒thaw cycles were studied via mechanical tests, such as triaxial compression tests, wave velocity tests and FLAC3D simulations. The results show that the shear strength of a root-soil composite increases with increasing confining pressure and VC and decreases with increasing number of freeze‒thaw cycles. Bermuda grass roots and confining pressure jointly improve the durability of soil under freeze‒thaw conditions. However, with an increase in the number of freeze‒thaw cycles, the resistance of root reinforcement to freeze‒thaw action gradually decreases. The observed effect of freeze‒thaw cycles on soil degradation was divided into three stages: a significant decrease in strength, a slight decrease in strength and strength stability. Freeze‒thaw cycles and VC mainly affect the cohesion of the soil and have little effect on the internal friction angle. Compared with that of a bare soil slope, the safety factor of a slope covered with plants is larger, the maximum displacement of a landslide is smaller, and it is less affected by freezing and thawing. These findings can provide a reference for research on ecological slope protection technology.

Experimental investigation on the deterioration of the physical and mechanical properties of autoclaved aerated concrete at elevated temperatures

Abstract Autoclaved aerated concrete (AAC) has been extensively studied and applied in the past decades because of its excellent thermal insulation and acoustic performance, energy efficiency, and outstanding structural performance. To investigate the deterioration characteristics of AAC under high temperatures, the physico-mechanical properties of AAC at different temperatures were tested by mass loss, wave velocity, and compressive tests, and the deterioration mechanism was discussed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) tests. The results showed that after exposure to elevated temperatures, the parameters of apparent form, mass loss, wave velocity, and compressive strength underwent remarkable conversions. It was observed that the ultrasonic behavior of AAC was affected at high temperatures as it increased at 100°C and decreased beyond 100°C. In addition, the compressive strength exhibited a two-stage transformation, slightly increased from ambient temperature to 300°C, and exhibited a rapid reduction beyond 300°C. At 900°C, the specimen lost its strength. By XRD, TGA, and SEM, it was confirmed that a series of physicochemical changes in AAC, such as the water escape and evaporation, decomposition of calcium silicate hydrate and calcium carbonate, and structural damage, were the primary reasons for the deterioration of the physical and mechanical properties at elevated temperatures.

Correlation between obesity and early vascular aging in middle-aged and young adult health check-up populations.

The obesity rate among middle-aged and young adults in China is increasing annually, and the incidence of cardiovascular diseases is becoming more prevalent in younger populations. However, it has not yet been reported whether obesity is associated with early vascular aging (EVA). This study aims to explore the correlation between obesity and EVA in middle-aged and young adult health check-up populations, providing a reference for the prevention of cardiovascular diseases. A total of 15 464 middle-aged and young adults aged 18-59 who completed brachial-ankle pulse wave velocity (baPWV) test in the Third Xiangya Hospital of Central South University from January to December 2020 were included. Among them, 1 965 individuals with normal blood pressure and no cardiovascular risk factors were selected as the healthy population. The baPWV thresholds for determining EVA in each age group for males and females were calculated based on the baPWV values of the healthy population. The number and percentage of individuals meeting the EVA criteria in the middle-aged and young adult health check-up populations were statistically analyzed by age and gender. The differences in obesity indicators [visceral adiposity index (VAI), body mass index (BMI), waist circumference (WC)] between the EVA and non-EVA groups for males and females were compared. Using EVA as the dependent variable, VAI, BMI, and WC were included as independent variables in a Logistic model to analyze the correlation between each obesity indicator and EVA before and after adjusting for other influencing factors. Furthermore, the correlation between each obesity indicator and EVA in each age group was analyzed. In the health check-up populations, the detection rate of EVA in different age groups was 1.65%-10.92% for males, and 1.16%-10.50% for females, the detection rate of EVA increased with age in both males and females. Except for the 40-<50 age group, the EVA detection rate was higher in males than in females in all other age groups. Regardless of gender, obesity indicators VAI, BMI, and WC were significantly higher in the EVA group than in the non-EVA group (all P<0.01). Before and after adjusting for other influencing factors, VAI and WC were both correlated with EVA (both P<0.05). BMI was a risk factor for EVA before adjusting for other influencing factors (P<0.01), but after adjustment, the correlation between BMI and EVA was not statistically significant (P=0.05). After adjusting for other influencing factors, the correlation between VAI and EVA was statistically significant in the 18-<40 and 50-<60 age groups (both P<0.05), while the correlation between BMI and WC with EVA was not statistically significant (both P>0.05). In the 40-<50 age group, the correlation between VAI and BMI with EVA was not statistically significant (both P>0.05), but the correlation between WC and EVA was statistically significant (P<0.01). VAI is closely related to the occurrence of EVA in middle-aged and young adults aged 18-<40 and 50-<60 years, while WC is closely related to the occurrence of EVA in those aged 40-<50 years.

Effect of glass fibre on the strength and durability of artificially cemented alluvial clay

ABSTRACT Using cement with fibers is a cost-effective way to improve soft clays’ engineering properties. This study investigates the strength, stiffness, and durability of artificially cemented alluvial clay stabilized with glass fiber. Unconfined compressive strength and shear wave velocity tests were used, along with microstructural analysis via scanning electron microscopy and energy-dispersive spectroscopy. Durability and resistance to harsh weather were evaluated using wet-dry cycles. The combination of cement and glass fiber improved the mechanical response, with 0.4% glass fiber being the most effective. A blend of 0.4% glass fiber with 13% cement showed the highest strength and stiffness improvement and reduced mass loss. This mixture, supported by unique power functions forecasting its properties, is suitable for various civil engineering projects, such as unbounded sub-layers, highway barriers, stone columns, and ground improvement.

Prediction of liquefaction of gravelly soils based on a cost-sensitive Bayesian network combined with rough set weighting

Existing liquefaction prediction approaches for gravelly soils rely on in situ test data, which neglects the in-suit test cost sensitivity. Furthermore, these approaches do not consider the effect of the weights of the factors on the model performance. Therefore, in this paper, a cost-sensitive Bayesian network with rough set theory (CSW-BN) and model hierarchies and factor weighting are combined to address the two aforementioned challenges in research on gravelly soil liquefaction prediction. A two-layer model is constructed using the proposed CSW-BN approach. The first layer of the model reduces the data costs by utilizing conventional soil parameters, without necessitating specific in situ tests such as shear wave velocity tests. In the second layer of the model, variable weights calculated using rough set theory are incorporated into the parameter learning to enhance the generalization of the model. The results show that the learning and prediction accuracies of the new approach are 0.968 and 0.95, respectively. Compared with existing models, the proposed method not only reduces the number of required in situ tests but also improves the prediction accuracy and interpretability. Furthermore, the effectiveness of the CSW-BN model is evaluated using new cases for the 2008 Wenchuan earthquake, with a prediction accuracy of 0.89. Finally, a software tool is developed using Visual Basic for Applications programming to facilitate its application in engineering practice.

BMI-based metabolic syndrome severity score and arterial stiffness in a cohort Chinese study

Background and aimsTo investigate the relationship between metabolic syndrome severity z score(MetS-Z) and arterial stiffness(AS). Methods and resultsA total of 7621 participants who took three physical examination and brachial-ankle pulse wave velocity(ba-pwv) test from 2006 were enrolled. Cumulative MetS-Z(cMetS-Z) was calculated by using blood pressure, triglycerides, HDL cholesterol, blood glucose and BMI. AS was assessed by ba-pwv. Cox regression model was used to evaluate the risk of AS. All participants were divided into four groups according to cMetS-Z(Q1-Q4). The average age of the participants was 43.06 ± 8.91 years old. During a median follow-up of 6.27 years, 1831cases of AS were identified. The incident rate of AS increased gradually from group Q1 to Q4. Compared with the lowest cMetS-Z(group Q1), the adjusted hazard ratio (HR) and 95% confidence interval (CI) of group Q2-Q4 for AS were 1.27 (1.09–1.47),1.28(1.10–1.48) and 1.45 (1.24–1.69) respectively. The cubic spline model indicated cMetS-Z had a liner relationship with AS and the cut-off value was lower than zero. Sub-group analysis suggested cMetS-Z was related to AS especially among participants who were younger and without obesity or hypertension or diabetes. ConclusionHigher cMetS-Z was associated with an increased risk of AS in this cohort community study, and this relationship seemed to be stronger among normal healthy subjects. Registration numberChiCTR-TNC-11001489. Clinical trialJanuary 1st 2006, ChiCTR-TNC-11001489 and 2011.

Evaluating deterioration of the properties of lightweight foamed concrete at elevated temperatures

This paper presents the results of an experimental study of varied properties of lightweight foamed concrete (LFC) at high temperatures. The key objective of this experimental study is to investigate the thermal, rheological, physical, and mechanical properties of LFC after being exposed to high temperatures up to 800 °C. To achieve that goal, an extensive study has been carried out to obtain 10 properties, i.e., slump flow, the colour of the surface, mass loss, porosity, thermal conductivity, compressive, split tensile, and flexural strength, modulus of elasticity, and wave velocity tests. In addition, the scanning electron microscopy (SEM) test provides the compositional details of materials. All mixes with varied densities were investigated after exposure to 20, 100, 150, 200, 400, 600, and 800 °C predetermined temperatures. Results also showed that mixes have different behaviours after being exposed to elevated temperatures, yet these behaviours, mass losses in particular, can be generally categorized into three phases based on temperature levels, i.e., 20–200 °C, 200–400 °C, and 400–800 °C. According to the SEM images, it is clear that the pore distributions and void sizes were significantly affected by the density value and the level of high temperature. As the temperature elevated, the void sizes also increased, and in some cases, groups of pores combined to form giant pores. However, by increasing the density, the pores' number, size, and distribution are less influenced by increasing temperature.

Evaluation and analysis of liquefaction potential of gravelly soils using explainable probabilistic machine learning model

Majority of the presently available machine learning (ML) models employed to assess the liquefaction potential of soils are for sands or sands containing silt fraction. In the current study, an explainable ML (EML) model has been developed using the updated liquefaction database of gravelly soils. The Chinese dynamic cone penetration test (DPT) and shear wave velocity test results of gravelly soils are used in the analysis. A new empirical correlation between these two in-situ tests’ results is developed using the final processed database. The light gradient boosting machine (LightGBM) is trained using this processed dataset and further tuned using Fast and Lightweight AutoML library (FLAML). The final tuned model shows relatively better deterministic and probabilistic predictive performance for the test sites as compared to the conventional method. An EML technique, SHapley Additive exPlanations (SHAP) is applied to provide further comprehension into the predictions. The developed LightGBM-SHAP model has achieved a right balance between explainability and accuracy. The obtained SHAP plots are consistent with almost all the existing domain knowledge (DK) in gravelly soil liquefaction. The developed model thus fills the gap between the ML-based procedures and the traditional DK of gravelly soil liquefaction.

An experimental study of tensile stress and deformation in an anisotropic rock

Anisotropy is a very common condition in rock mass; it can be due to different factors and directly affects the failure mechanisms affecting the rock mass. For example, metamorphic rocks that are foliated, sedimentary rocks that are stratified or volcanic formations with alternating layers. Despite the existence of several studies related to anisotropy those specifically addressing the tensile strength of anisotropic rocks are quite limited. The present study is focused on the determination of the deformability, compressive and tensile strength of anisotropic rocks. It must be highlighted that the mechanical behavior of the anisotropic rock mass is dependent on the angle between the inclination of planes of weakness (e.g. foliation) and the direction of the load. Assuming a vertical load, the two extremes of tensile strength are 0°(horizontal) and 90° (vertical). A series of laboratory tests has been done in anisotropic sandstone (lithic arkose), from Burgos (Spain), including uniaxial compressive strength tests, direct tensile strength tests, and diametric compression (Brazilian tests). The tests were carried out with strain gauges that allowed estimating the elastic modulus. To determine the anisotropic direction, ultrasonic pulse wave velocity tests were also performed. The variation of strength and deformability as a function of anisotropy is analyzed, as well as the variation of elastic behavior in tensile and compressive.

Pore characteristics and mechanical behaviors of autoclaved aerated concrete produced from coal bottom ash and tailings

AbstractThe solid wastes such as coal bottom ash and tailings are currently widely used in various building materials, but further research on their application in autoclaved aerated concrete (AAC) is needed. To study the physical and mechanical properties of AAC produced from coal bottom ash and tailings, the pore characteristics of two different density grades of AAC were extracted and analyzed, and wave velocity and uniaxial compressive tests under water‐saturated and dry conditions were carried out. The results show that the AAC produced from solid waste has excellent performance. The specimen is anisotropic, and the pore size distribution of its cross‐section is mainly concentrated in the ranges of &lt;0.1, 0.1–0.5, and 0.5–1.0 mm. The pore size perpendicular to the direction of rise is smaller and the pores number is greater. The wave velocity and uniaxial compressive strength of the test specimens in the water‐saturated state are significantly lower than those in the dry state. The strengths of specimens loaded perpendicular to the direction of rise are higher than those loaded parallel to the direction of rise whether water‐saturated or dry. The failure mode of the water‐saturated specimens are different from those of dry specimens, which is manifested in the act that there are fewer surface cracks when the specimens fail in the water‐saturated state, while there are more surface cracks in the dry specimens, and their morphology is irregular. The physicochemical effect between water and components and the mechanical effect of pore water are the reasons for the deterioration of AAC's mechanical properties. The results help to reveal the performance of AAC produced from solid waste and have good practical significance.

Investigation of the Deterioration of Basu Granite Mechanical Properties Caused by Freeze–Thaw Cycles in High-Altitude Mountains in the Eastern Part of the Tibetan Plateau, China

Mountains composed of granite are generally regarded as stable geological formations. However, in Alpine and high-altitude mountains in the eastern part of the Tibetan Plateau, geological hazards such as collapses and landslides occur frequently due to the deterioration of granite mechanical properties caused by the freeze–thaw cycles. To investigate this phenomenon, a freeze–thaw cyclic mechanical test is conducted on granite from the Basu area, and the rock’s damage trend during the freeze–thaw process is analyzed through wave velocity and nuclear magnetic resonance (NMR) tests. The results indicated that the internal damage of granite increases and its wave velocity decreases significantly with increasing the freeze–thaw cycles, implying a decline in the rock’s integrity. Furthermore, the development pattern of the NMR T2 relaxation time distribution indicates that the crack size range of naturally weathered rock samples further increased after freeze–thaw cycles, whereas less-weathered rocks showed a more concentrated range of crack sizes. Triaxial compression tests conducted on rock samples after the freeze–thaw cycles showed that parameters such as the uniaxial compressive strength, elastic modulus, internal friction angle, and cohesion of the rock decreased with increasing freeze–thaw cycles, while a significant change of Poisson’s ratio was not observed. Based on the test data and theoretical analysis, a freeze–thaw damage constitutive model of the Basu granite can be established to simulate and predict the overall variation in rock stress and strain under various confining pressures and freeze–thaw cycles. Hopefully, the present study will provide useful guidance for research on the hazard mechanism and hazard prevention of granite sand-sliding slopes in the Basu area.

Hypertension combined with atherosclerosis increases the risk of heart failure in patients with diabetes.

The increase in heart failure risk in the diabetic population when hypertension and atherosclerosis are both present is still inconclusive. The aim of this study was to explore the effects of hypertension combined with atherosclerosis in diabetic population on the risk of heart failure. We selected 10,711 patients with diabetes who participated in the Kailuan study and completed brachial-ankle pulse wave velocity (baPWV) testing for statistical analysis. The subjects were divided into the non-hypertensive non-atherosclerotic, hypertensive, atherosclerotic, and hypertensive atherosclerotic groups based on their history of hypertension and atherosclerosis. At a median follow-up of 4.15 years, 227 cases of heart failure occurred. Compared with the non-hypertensive non-atherosclerotic group, the multifactorial Cox proportional risk regression model showed that the hazard ratio (HR) for heart failure in the hypertensive atherosclerotic group was 3.08 (95% confidence interval [CI]: 1.32-7.16), whereas the HR decreased to 2.38 (95% CI: 1.01-5.63) after gradual correction of lipid-lowering, glucose-lowering, and antihypertensive drugs. The subgroup analysis and sensitivity analysis were consistent with that of total population. In conclusion, patients with diabetes exposed to both hypertension and atherosclerosis had an increased heart failure risk, which was attenuated by the use of lipid-lowering, glucose-lowering, and antihypertensive drugs.

The combined effects of arteriosclerosis and diabetes on cardiovascular disease risk.

The morbidity and mortality of cardiovascular disease (CVD) rank first among common diseases. Arteriosclerosis and diabetes are risk factors for CVDs, which influence each other. However, their combined effects on CVDs are still unclear. In this study, people who participated in brachial-ankle pulse wave velocity (baPWV) testing and the annual physical examination of the Kailuan Group Finance Co., Ltd., from January 1, 2010, to December 31, 2020, were selected, and their anthropometric, biochemical and epidemiological data were collected. The participants were divided into four groups according to diabetes and arteriosclerosis diagnosis and follow-up. Cox proportional hazards regression and subdistribution hazard models were used to analyse the combined effects of arteriosclerosis and diabetes on CVDs. Multiple sensitivity analyses were also performed. A total of 59,268 Asian populations were selected, including 14,425 females (28.11%) with an average age of 48.10 (± 12.72) years. During follow-up, 1830 subjects developed CVDs (mean follow-up period, 4.72years). The cumulative incidence rates of the healthy control, diabetes, arteriosclerosis, and comorbidity groups were 5.04% (807/38781), 15.17% (253/3860), 17.04% (465/5987), and 25.59% (305/2684), respectively. The results of multivariate Cox regression analysis showed that compared with the healthy control group, the risk of CVD in the diabetes, arteriosclerosis, and comorbidity groups was significantly increased. Their HR values were 1.88 (95% CI 1.62-2.18), 1.40 (95% CI 1.23-1.60), and 2.10 (95% CI 1.80-2.45), respectively. The results of the sensitivity analysis were robust. For each one standard increase in fasting blood glucose or baPWV, the HR values for CVDs were 1.16 (95% CI 1.12-1.20) and 1.22 (95% CI 1.16-1.28), respectively. The results indicated that both arteriosclerosis and diabetes lead to an increased risk of CVDs. The risk of CVDs, coronary atherosclerotic heart disease, heart failure, stroke, coronary artery bypass grafting and ischemic stroke in patients with arteriosclerosis and diabetes was significantly higher than that in patients with arteriosclerosis or diabetes alone. Therefore, the primary prevention of CVDs in patients with arteriosclerosis complicated with diabetes needs more attention.

Shear strength and modulus of mine waste rock – Large scale laboratory testing results

This paper presents the sampling and laboratory testing results of mine waste rock consisting of limestone, siltstone, and intrusive materials collected from the Ok Tedi open pit mine in Papua New Guinea. The laboratory tests included specific gravity measurements, index testing, large-scale direct shear tests using a 720 mm square direct shear apparatus, large-scale consolidation tests using a 550 mm diameter consolidation apparatus, and shear wave velocity tests conducted on compressed waste rock samples. The obtained strength values, as well as small and larger strain modulus values, were subsequently compared with existing literature data from the literature. These findings can serve as a valuable reference for mine waste materials with similar lithology, particle size distribution, and stress condition, particularly in the context of static and seismic slope stability designs.

Experimental Study On Acoustic Emission Characteristics of SAP Mortar Self-Healing Process

Self-healing properties of super absorbent polymer (SAP) concrete can reduce the harmful effects of concrete cracking in structures. This study examines the self-healing process of mortars with different SAP content under dry and wet conditions through acoustic emission testing (AE) and elastic wave velocity testing. Findings indicate that the SAP mortar healing process has three stages: rapid water absorption, smooth water absorption, and drying. In a dry environment, increasing SAP content enhances AE activity, indicating internal crack self-healing via further hydration of unhydrated cement particles. In a wet environment, AE activity increases with increasing SAP content during the second healing cycle, indicating self-healing of the mortar matrix. These results suggest the use of SAP concrete could potentially mitigate future structural damage.

Microseismic Signal Characteristics of the Coal Failure Process under Weak-Energy and Low-Frequency Disturbance

In deep mining, “critical static stress + slight disturbance” is an important inducing form of coal mine rockburst disasters. In previous studies, the critical static stress has been shown to be consistent with the loading direction of a slight disturbance but cannot reflect all types of rockbursts. In addition, the research that uses microseismic (MS) signals to reflect the overall process and critical stages of coal failure and instability under weak-energy and low-frequency disturbance conditions is immature, and more information, such as the critical state, has not been fully revealed. The aims of this paper are to further elucidate the important role of weak-energy and low-frequency disturbances in the occurrence of rockburst disasters. First, briquette samples were prepared from the Tashan Coal Mine, which is severely affected by rockbursts, and their homogeneity was verified using ultrasonic longitudinal wave velocity. Second, the natural frequency of the coal sample specimens was measured using a testing system. Then, based on the self-developed static pressure loading system, dynamic and static combined loading test system and MS signal monitoring device, the MS signal characteristics during the process of coal body failure and instability were comprehensively analysed. Finally, a comparison was made between weak-energy and low-frequency disturbances and impact disturbances. The results are summarized as follows. (1) The longitudinal wave velocity test results reflect that the briquette samples prepared in the experiment have high homogeneity. The smaller the particle size is, the higher the density and moulding pressure, and the denser the sample. (2) The natural frequency of the briquette samples is between 30.79 Hz and 43.34 Hz, and most of them fluctuate at approximately 35 Hz. (3) During the static loading stage, the occurrence of more than three MS signals of larger magnitude in a continuous cluster is an important criterion for the critical failure of the samples. (4) The weak-energy and low-frequency disturbance actually leads to fatigue damage, and the briquette sample experiences three stages: the near-threshold stage, the high-speed expansion stage and the final fracture stage. The smaller the particle size of the coal sample, the denser the specimen, the stronger the amplitude and energy of the single effective MS signal formed during the destruction process, the longer the time duration of crack expansion from the near-threshold stage to the high-speed expansion stage, and the stronger the ability of the coal sample to resist weak-energy and low-frequency disturbances. This study may contribute to a more comprehensive understanding of the destabilization mechanism of coal bodies and MS signal characteristics under weak-energy and low-frequency disturbances and provide a reference for further research and discussion.