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Bolt connections are widely used in construction and engineering to securely join structural elements. These connections are essential for distributing loads across components and ensuring that structures can withstand external forces. The planned failure of these bolts is of great importance in steel safety barriers (SSBs), as it can directly influence the height of the guardrail and the working width of the SSB during the vehicle impact, which consequently affects the crash consequences. Therefore, it is of great importance to determine the bolt response until fractures under different strain rates. For that purpose, experimental tensile tests of low-strength steel rods of grade 4.6 were conducted at various strain rates (0.0025–25 s−1) until fracture. Test specimens were photographed during the testing, and by means of image processing, input data for calculation of true stresses and strains up to the point of fracture were extracted. Based on the experimental data, material parameters were determined for the Cowper–Symonds model, enabling precise numerical simulations of these connections at various strain rates. A validation study was also performed successfully. [ABSTRACT FROM AUTHOR]

This work presents an analysis of the relationship between strength parameters determined in the laboratory and the results of a cone penetration test with pore water pressure measurement (CPTU) of waste soils in the "White Seas" area in Cracow. Anthropogenic soil is an alkaline waste formed during the production of soda ash and deposited in the area of the former Solvay Sodium Plant factory in Cracow, Poland. Due to the large area of the land and numerous investment plans and completed buildings, there was a need to identify reliable functional relationships enabling the determination of the strength parameters of these soils based on the results of the CPTU. Statistical analysis showed that the best correlation with the test results was provided by two logarithmic functions in which the dependent variables were the effective friction angle and effective cohesion. The dependent variable for both cases was the corrected cone resistance qt. The functional relationship combined data from labour-intensive, long-lasting and costly laboratory measurements with quick and less expensive measurements, i.e., in situ CPTUs. The obtained relationships enable the determination of the strength properties of the subsoil of these anthropogenic soils. [ABSTRACT FROM AUTHOR]

This study investigates the impact of nanomaterials on soil strength parameters. This project is carried out according to laboratory tests to determine the impact of nano-silica on the compressive strength and plasticity properties of soil. This project covers the operation of injecting nano-silica into the remoulded soil of Yazd University region, and performing the CPT test as the executive studies in addition to the analysis of nanoparticles by SEM (scanning electron microscope) and AFM (atomic force microscope) images of soil samples. These tests are done for two methods with and without nanomaterials, and then the results are compared. According to the results, nano-silica increases the Plastic Limit (PL) slightly and Liquid Limit (LL) considerably; hence, the addition of nano-silica will increase the Plasticity Index (PI) of soil. Following the increase in nano-silica, the soil compressive strength is also increased; the more the curing time increases, the more the compressive strength will be enhanced. The average rate of increase in compressive strength with time will be increased by increasing the percentage of nano-silica. Based on the results of field and laboratory tests for the injection of nanomaterials and according to silica cementation between soil particles, the nano-silica injection has resulted in the increased CPT strength of soil; hence it is offered as a suitable solution. [ABSTRACT FROM AUTHOR]

The aim of this study is to determine the effect of changes in the phase composition of Al2O3–Si3N4 ceramics that were obtained using the method of mechanochemical solid-phase grinding on their resistance to the process of long-term thermal exposure, accompanied by the processes of oxidation and softening. The relevance of this research consists of determining the influence of the phase composition of ceramics on the change in their strength and thermophysical parameters, on the basis of which, we can draw a conclusion about the optimal composition of composite ceramics that have great prospects in the field of fire-resistant, heat-resistant, or radiation-resistant structural materials. During this study, the dynamics of the changes in the phase transformations of the xAl2O3–(1−x)Si3N4 ceramics, with variations in the ratio of the components, initiated by the thermal annealing of the samples, was established. According to the assessment of the phase transformations with variations in the ratio of the components, it was found that thermal annealing in an air environment at an Al2O3 concentration in the order of 0.3–0.5 M leads to the formation of an orthorhombic Al2(SiO4)O phase and an elevation in its contribution at concentrations above 0.5 M, which causes a rise in the thermophysical parameters and resistance to high-temperature degradation. During the heat resistance tests, it was found that the formation of the composite ceramics with the Si3N4(SiO2)/Al2(SiO4)O/Al2O3 phase composition results in an increase in the stability of their strength properties when exposed to thermally induced oxidation, which has a negative impact on their resistance to softening and a decrease in hardness. Moreover, the presence of the Al2(SiO4)O phase in the composition of the ceramics causes a slowdown in the processes of thermal oxidation of the Si3N4 phase under prolonged temperature exposure, alongside an increase in the degradation resistance of strength properties by more than 4–7 times, in comparison with the softening data established for single-component ceramics. [ABSTRACT FROM AUTHOR]

Cement clay interlocking (CCI) hollow bricks have been used as a construction material in many developed and developing countries. Many emerging and underdeveloped nations have utilised cement clay interlocking (CCI) hollow bricks as building materials. In India, Andhra Pradesh local makers prepare these cement clay interlocking (CCI) hollow bricks by simply mixing clay, cement, and sand in a traditional method, without following strict design criteria or rules. Previous research has demonstrated that the mechanical characteristics of CCI hollow bricks gathered from various locations in detailed manner respect to hand books on Civil Engineering as per Indian Standards. Bricks from one region had compressive strengths that were significantly lower than the other region Indian Community Standards. Various methods were employed in this investigation to enhance the mechanical characteristics of CCI bricks. New mix patterns were created with the use of sand, cement, and fly ash in this research paper.

Ketogenic diets (KDs) are an alternative to improve strength performance and body composition in resistance training participants. The objective of this review and meta-analysis is to verify whether a ketogenic diet produces an increase in the strength of resistance-trained participants. We have evaluated the effect of the ketogenic diet in conjunction with resistance training on the strength levels in trained participants. Boolean algorithms from various databases (PubMed, Scopus, and Web of Science) were used. Meta-analyses were carried out, one on the 1-RM squat (SQ), with 106 trained participants or athletes, and another on the 1-RM on the bench press (BP), evaluating 119 participants. We did not find significant differences between the groups in the variables of SQ or BP, although the size of the effect was slightly higher in the ketogenic group. Conclusions: KDs do not appear to impair 1-RM performance; however, this test does not appear to be the most optimal tool for assessing hypertrophy-based strength session performance in resistance-trained participants. [ABSTRACT FROM AUTHOR]

Summary: This paper summarizes the literature available on the behavior of concrete‐filled steel tubular (CFST) columns to evaluate the effect of geometrical properties such as shape of cross‐section, diameter‐to‐thickness ratio, and length‐to‐diameter ratio of CFST columns under axial loading. Then, the impact of different material composition for core concrete and encasing material is concluded for columns under axial loading. The performance of CFST is evaluated in terms of failure modes, ductility, stiffness, and axial compressive strength. For encasing tube, carbon steel, stainless steel, and aluminum are studied while for core, various concretes such as Normal (NSC) and high strength concrete (HSC), light weight concrete (LWC), recycled aggregate concrete (RAC), expansive concrete (EC), rubber crumb concrete(RuCC), and steel slag concrete (SSC) are covered for review in this paper. Material limitations as provided by various codes for design of composite structures is also mentioned for both tube and core concrete. Failure modes of concrete‐filled tubular(CFT) columns are most affected by geometric properties columns while materials used for concrete and encasing tube do not cause much difference. Though, ductility, axial compressive strength, and stiffness are affected by both geometric and material properties. [ABSTRACT FROM AUTHOR]

This work presents an analysis of the relationship between strength parameters determined in the laboratory and the results of a cone penetration test with pore water pressure measurement (CPTU) of waste soils in the “White Seas” area in Cracow. Anthropogenic soil is an alkaline waste formed during the production of soda ash and deposited in the area of the former Solvay Sodium Plant factory in Cracow, Poland. Due to the large area of the land and numerous investment plans and completed buildings, there was a need to identify reliable functional relationships enabling the determination of the strength parameters of these soils based on the results of the CPTU. Statistical analysis showed that the best correlation with the test results was provided by two logarithmic functions in which the dependent variables were the effective friction angle and effective cohesion. The dependent variable for both cases was the corrected cone resistance qt. The functional relationship combined data from labour-intensive, long-lasting and costly laboratory measurements with quick and less expensive measurements, i.e., in situ CPTUs. The obtained relationships enable the determination of the strength properties of the subsoil of these anthropogenic soils.

The present study explores the intricate relationship between the geotechnical and mineralogical properties of lithomargic clays in the Uttara Kannada region of south India. Lithomargic clays, characterized by their unique composition of clay minerals and calcareous content, play a crucial role in the geotechnical behavior of soils. The study aims to provide a comprehensive understanding of the interplay between the mineralogical composition and engineering characteristics of lithomargic clays, shedding light on their suitability for various construction and infrastructure projects. The research methodology involves a systematic analysis of lithomargic clay samples collected from different locations in the Uttara Kannada region. Geotechnical investigations, including particle size distribution, Atterberg limits, unconfined compressive strength (UCS), California bearing ratio (CBR) and triaxial tests, are conducted to assess the engineering properties of the clays. Concurrently, mineralogical analyses, such as X-ray diffraction (XRD) and scanning electron microscopy (SEM), are employed to identify and quantify the clay mineral constituents within the samples. The findings of this study reveal correlations between specific mineralogical features and geotechnical behaviors of lithomargic clays. Understanding these relationships is crucial for predicting the response of these clays to different engineering applications, including slope stability, foundation design and embankment construction. The research contributes valuable insights to the scientific and engineering communities, aiding in the informed utilization of lithomargic clays in geotechnical projects in the Uttara Kannada region and beyond. The outcomes of this investigation, such as the correlation of geotechnical properties with the variation in minerals in various sample locations, enhance our understanding of the complex nature of lithomargic clays, providing a foundation for more sustainable and effective engineering practices in the geologically diverse landscapes of south India. [ABSTRACT FROM AUTHOR]

The aim of this study is to determine the effect of changes in the phase composition of Al2O3–Si3N4 ceramics that were obtained using the method of mechanochemical solid-phase grinding on their resistance to the process of long-term thermal exposure, accompanied by the processes of oxidation and softening. The relevance of this research consists of determining the influence of the phase composition of ceramics on the change in their strength and thermophysical parameters, on the basis of which, we can draw a conclusion about the optimal composition of composite ceramics that have great prospects in the field of fire-resistant, heat-resistant, or radiation-resistant structural materials. During this study, the dynamics of the changes in the phase transformations of the xAl2O3–(1−x)Si3N4 ceramics, with variations in the ratio of the components, initiated by the thermal annealing of the samples, was established. According to the assessment of the phase transformations with variations in the ratio of the components, it was found that thermal annealing in an air environment at an Al2O3 concentration in the order of 0.3–0.5 M leads to the formation of an orthorhombic Al2(SiO4)O phase and an elevation in its contribution at concentrations above 0.5 M, which causes a rise in the thermophysical parameters and resistance to high-temperature degradation. During the heat resistance tests, it was found that the formation of the composite ceramics with the Si3N4(SiO2)/Al2(SiO4)O/Al2O3 phase composition results in an increase in the stability of their strength properties when exposed to thermally induced oxidation, which has a negative impact on their resistance to softening and a decrease in hardness. Moreover, the presence of the Al2(SiO4)O phase in the composition of the ceramics causes a slowdown in the processes of thermal oxidation of the Si3N4 phase under prolonged temperature exposure, alongside an increase in the degradation resistance of strength properties by more than 4–7 times, in comparison with the softening data established for single-component ceramics.

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An industrial by-product known as fly ash is produced when coal is burned for electricity production and is considered an environmental pollutant. A comprehensive fly ash utilisation programme must be implemented to reduce environmental pollution, including numerous factors at different levels. Fly ash's geotechnical qualities, including its specific gravity, permeability, internal angular friction, and consolidation characteristics, make it ideal for structural fill, particularly on clay soils, when building highways and embankments. Much research has been conducted on how fly ash affects soil stability. In order to determine the impact of fly ash addition on soil properties, this inquiry reviewed a few of these papers and conducted a critical assessment. This study also looked at combining fly ash and clay soil. Numerous investigations indicate that fly ash generally improves soil stability, notably when analysing CBR values and soil permeability, and reduces volumetric changes in the soil. The ground becomes compact due to particle size and form and a decrease in volumetric dilatation. Because the additives to the hardened soil do not dissolve, the soil's behaviour continues to be modified. [ABSTRACT FROM AUTHOR]

An appreciable quantity of cement is consumed as binder for masonry mortar, which has resulted in cost escalation and high energy consumption in building construction, in addition to contributing to greenhouse gas emissions. On the other hand, disposal of waste lignocellulosic materials as agricultural residues persists as an unsolved technical problem creating environmental pollution. This paper proposes an effective solution for these two critical issues. Coir fiber, when used as a reinforcement material in cement, was found to be effective in enhancing the mechanical properties of the binder. The application of coir fiber reinforcement on strong, moderate, and weak masonry mortars with respect to strength criteria is examined in this study. ANOVA analysis was carried out to examine the level of significance of coir fiber reinforcement on the flexural and compressive strengths of masonry mortar. The findings from the study revealed that 0.5% coir fiber reinforcement enhanced flexural strength of strong mortar by 18%–22%, moderate mortar by 21%, weak mortar by 10%, and compressive strength of strong mortars by 16%–19% by contributing strength in the early curing period. Moreover, coir fiber–reinforced mortars satisfied the compressive strength criteria required of strong mortar (7.5 to 10 N/mm2), moderate mortar (5 N/mm2), and weak (3 N/mm2) mortar for its application as mortar on masonry walls in accordance with Indian standards. The strength of masonry in compression, flexure, and shear determines how well masonry operates structurally. Cement-based structures are strong in compression but are prone to shrinkage cracks over a span of 30 years due to its weakness in tension. Flexural strength is an indirect indicator for measuring tension. Coir fiber imparts tensile strength to the matrix when used as reinforcement in cement mortar. Fiber networking dissipates the tensile stresses that develop in mortar during flexure and would bridge the gap in a better way. This prolongs the life of buildings and maintains ecological equilibrium by preventing the need for periodic repair and maintenance, which reduces cost, time, and labor. The use of fibers in mortar for plastering is found to be more beneficial in enhancing the strength of a masonry structure than adding fibers to blocks. Coir fiber content of 0.25% and 0.5% (10 mm length) by weight of cement was found to be effective at enhancing the early flexural strength of cement mortar. Coir fiber–reinforced plaster cement can be made available ready to use in bags of 25 or 50 kg for a crack-free plastered surface on ceilings and internal and external walls. [ABSTRACT FROM AUTHOR]

In this research, a multilayer feed-forward backpropagation error neural network has been used to predict the strength parameters of a concrete sample containing different additives. To achieve the most optimal neural network structure, the strength parameters of the concrete have been evaluated for different neural network arrangements. Control criteria are the use ofnumerical values of performance, the correlation between training functions, validation and,testing in the neural network, gradient and results of regression diagram to determine the most optimal neural network structure. It was found that the function of the neural network largely depends on its geometric structure. Revealed by the research findings, the most optimal prediction of the neural network has occurred in the case of using three layers with 30 neurons in each layer in the neural network. In this case, the numerical value of the neural network performance and the regression were obtained as 58.5 × (10-9) and 0.9846 , respectively. By determining the optimal neural network, different percentages of concrete raw materials based on the pre-performed experimental study are introduced to the selected neural network and the considered resistance parameters are predicted through residual analysis. According to the results, the differences between the predicted values of the neural network and the numerical values of the experimental study concerning the parameters of compressive, flexural, and tensile strength were also found to be equal to 1.68%, 1.92%, and 0.21%, respectively. Such a slight difference reflects the optimal accuracy of the chosen neural network in predicting the strength parameters.

This work investigates the behavior of a silty clay stabilized with 3, 6, 9, and 12 % of ground granulated blast-furnace slag (GGBS), respectively, and 1 % of quicklime used as an activator. The influence of the composite (Quicklime - GGBS) on the immediate behavior of the silty clay is studied by examining the Atterberg limits, the maximum dry density, the optimum moisture content, and the immediate bearing index. The evolution, at different curing periods (1, 7, and 28 days), of the mechanical characteristics of the treated soil, namely unconfined compressive strength, cohesion, and internal angle of friction is also studied. The increase, up to a dosage of 9%, of the GGBS content, leads to an increase in the optimum moisture content, the immediate bearing index, the unconfined compressive strength, and shear strength parameters. Paradoxically, a decrease in the plasticity index and the maximum dry density was observed.

The experimental testing and analysis of strength and deformation characteristics of hydrate reservoirs is an integral part of natural gas hydrate exploitation. However, studies so far have failed to deeply explore samples from the South China Sea. Especially, there is a lack of a simple and applicable method to estimate their mechanical behaviors. Thus, based on test data, an improved Duncan-Chang model is established in this paper to characterize the strength and deformation of reconstituted samples with various hydrate saturation and stress states from this area. This model can accurately describe the strainhardening characteristics, and failure strength is estimated by the improved Drucker-Prager criterion with high fitting accuracy. The initial elastic modulus and failure ratio are given by the proposed empirical models, which are obtained from experimental data and fitting methods. Generally, this model has several advantages including simple structure, favorable performances, and a limited number of model parameters. Therefore, it could be widely used in strength and deformation analysis. This study can support the prevention and control of geological risks during natural gas hydrate exploitation in the South China Sea. [ABSTRACT FROM AUTHOR]

The present study explores the intricate relationship between the geotechnical and mineralogical properties of lithomargic clays in the Uttara Kannada region of south India. Lithomargic clays, characterized by their unique composition of clay minerals and calcareous content, play a crucial role in the geotechnical behavior of soils. The study aims to provide a comprehensive understanding of the interplay between the mineralogical composition and engineering characteristics of lithomargic clays, shedding light on their suitability for various construction and infrastructure projects. The research methodology involves a systematic analysis of lithomargic clay samples collected from different locations in the Uttara Kannada region. Geotechnical investigations, including particle size distribution, Atterberg limits, unconfined compressive strength (UCS), California bearing ratio (CBR) and triaxial tests, are conducted to assess the engineering properties of the clays. Concurrently, mineralogical analyses, such as X-ray diffraction (XRD) and scanning electron microscopy (SEM), are employed to identify and quantify the clay mineral constituents within the samples. The findings of this study reveal correlations between specific mineralogical features and geotechnical behaviors of lithomargic clays. Understanding these relationships is crucial for predicting the response of these clays to different engineering applications, including slope stability, foundation design and embankment construction. The research contributes valuable insights to the scientific and engineering communities, aiding in the informed utilization of lithomargic clays in geotechnical projects in the Uttara Kannada region and beyond. The outcomes of this investigation, such as the correlation of geotechnical properties with the variation in minerals in various sample locations, enhance our understanding of the complex nature of lithomargic clays, providing a foundation for more sustainable and effective engineering practices in the geologically diverse landscapes of south India.

Myokines represent important regulators of muscle metabolism. Our study aimed to explore the effects of a cyclical ketogenic reduction diet (CKD) vs. a nutritionally balanced reduction diet (RD) combined with regular resistance/aerobic training in healthy young males on serum concentrations of myokines and their potential role in changes in physical fitness. Twenty-five subjects undergoing regular resistance/aerobic training were randomized to the CKD (n = 13) or RD (n = 12) groups. Anthropometric and spiroergometric parameters, muscle strength, biochemical parameters, and serum concentrations of myokines and cytokines were assessed at baseline and after 8 weeks of intervention. Both diets reduced body weight, body fat, and BMI. Muscle strength and endurance performance were improved only by RD. Increased musclin (32.9 pg/mL vs. 74.5 pg/mL, p = 0.028) and decreased osteonectin levels (562 pg/mL vs. 511 pg/mL, p = 0.023) were observed in RD but not in the CKD group. In contrast, decreased levels of FGF21 (181 pg/mL vs. 86.4 pg/mL, p = 0.003) were found in the CKD group only. Other tested myokines and cytokines were not significantly affected by the intervention. Our data suggest that changes in systemic osteonectin and musclin levels could contribute to improved muscle strength and endurance performance and partially explain the differential effects of CKD and RD on physical fitness. [ABSTRACT FROM AUTHOR]

Gas production by depressurization can significantly increase the effective stress in hydrate-bearing sediments. Therefore, strength and deformation characteristics of sediments under high effective confining pressure should be fully understood before large-scale extraction. In this study, a series of triaxial tests on artificial methane hydrate-bearing specimens were conducted under effective confining pressures of 0.2–20 MPa, and the effects of effective confining pressure and hydrate saturation on the strength parameters and the stress–dilatancy characteristics were discussed. The results demonstrate that the strength and stiffness of hydrate-bearing sediments increase with increasing effective confining pressure. Shearing under high effective confining pressure leads to significant breakage of host particles, which is independent of the hydrate saturation. The increase in the effective confining pressure decreases the internal friction angle while increasing the cohesion of hydrate-bearing sediments. By linking the effective confining pressure and hydrate saturation with strength parameters of Mohr–Coulomb criterion and Drucker–Prager criterion, the strength of sediments in a high range of effective stress can be accurately predicted. With increasing effective confining pressure, the shear–dilation transfers to shear–contraction, the critical stress ratio gradually decreases to attain a constant value, and the effects of hydrate saturation and effective stress on the dilatancy characteristics gradually become less notable. [ABSTRACT FROM AUTHOR]

Approximately 30 million tons of tailings are being stored each year at the KGHMs Zelazny Most Tailings Storage Facility (TSF). Covering an area of almost 1.6 thousand hectares, and being surrounded by dams of a total length of 14 km and height of over 70 m in some areas, makes it the largest reservoir of post-flotation tailings in Europe and the second-largest in the world. With approximately 2900 monitoring instruments and measuring points surrounding the facility, Zelazny Most is a subject of round-the-clock monitoring, which for safety and economic reasons is crucial not only for the immediate surroundings of the facility but for the entire region. The monitoring network can be divided into four main groups: (a) geotechnical, consisting mostly of inclinometers and VW pore pressure transducers, (b) hydrological with piezometers and water level gauges, (c) geodetic survey with laser and GPS measurements, as well as surface and in-depth benchmarks, (d) seismic network, consisting primarily of accelerometer stations. Separately a variety of different chemical analyses are conducted, in parallel with spigotting processes and relief wells monitorin. This leads to a large amount of data that is difficult to analyze with conventional methods. In this article, we discuss a machine learning-driven approach which should improve the quality of the monitoring and maintenance of such facilities. Overview of the main algorithms developed to determine the stability parameters or classification of tailings are presented. The concepts described in this article will be further developed in the IlluMINEation project (H2020).

The ability to conduct conventional triaxial compression tests on multiple identical specimens is restricted by available sample quantity, sample homogeneity, as well as testing duration. Multistage triaxial testing is an alternative method to tackle these issues by using a single specimen sheared under different confining stresses to attain the strength parameters. Although there are widely accepted procedures to decide when to stop each shearing stage and proceed to the next stress level, the applicability of these procedures on different soil types is still a question. This study examines the applicability of combinations of two multistage triaxial testing procedures (Rational Procedure and Minimum Slope) under two different deviator stress conditions (Sustained or Cyclic) during confining stress increase. The outcome is compared to conventional triaxial test results for undrained and drained shearing of reconstituted specimens of high-plasticity Ankara Clay. Out of the four options, the rational procedure with cyclic deviator loading and minimum slope with cyclic deviatoric loading conditions, are found to give the most accurate strength parameters in reference to single-stage test results. The maximum number of the shearing-reconsolidation sequences applicable before strength loss is also investigated for each multistage triaxial testing procedure.

Physical properties and mechanical parameters of intact rocks are essential in defining geomechanical characteristics of rock masses. The latter are fundamental in the geotechnical design and numerical modelling of engineering-geological applications involving slope stability analyses as well as the design of dams, foundations, tunnels, open and underground mines, nuclear storage repository etc. Time and financial constraints of many projects often do not allow to perform all the laboratory tests necessary for physical-mechanical characterization of the rock matrix. In these cases, existing published data are the only tools for appropriate definition of the geomechanical characteristics of the intact rocks and subsequent development of engineering-geological performances.This paper reports the values of major physical properties and mechanical parameters for several intact rock samples of limestone, collected from the Central Apennines region (Italy). The main physical properties measured for the rock samples are unit weight, density, and porosity. The mechanical parameters derived from the laboratory tests on the samples include uniaxial compressive strength, cohesion, friction angle, tensile strength, elastic modulus, and Poisson's ratio. Only for a few of samples, the index parameters (point load index) and the dynamic characteristics (P-wave velocity) were also measured. The laboratory tests for these samples were performed following the standards by the International Society for Rock Mechanics (ISRM).

Mixing cement and soil is a traditional technique used to improve their mechanical properties. Other studies proposed a rational dosage methodology for soil-cement mixtures. This method is based on the void-cement ratio and aimed at obtaining a particular strength level. The present study evaluated the validity of the void-cement ratio (η/Civ) and analysed the stress – strain – strength behaviour of aeolian dune sand from Natal, Brazil, mixed with cement. Isotropically consolidated drained triaxial compression tests (CID-C) were conducted with moulded samples containing 0.0, 2.5, 5.0 and 7.5% cement by weight of dry soil. Void ratios corresponded to three conditions of relative density: loose, medium and dense, with confining stresses of 50, 100, 200 and 300 kPa. The effect of void ratio, cement content and void-cement ratio on the stress-strain-strength behaviour of the mixtures was determined. The results showed that the void-cement ratio is an appropriate parameter to assess the effective strength of the cement-sand mixture studied. [ABSTRACT FROM AUTHOR]

The freezing technique has been employed for a long time to strengthen the mechanical properties of intact rock and rock mass; however, it has not received as much attention as it deserves. This paper thoroughly reviews the effect of freezing on the essential mechanical properties, including uniaxial compressive strength, tensile strength, and Young’s modulus. The laboratory tests include the determination of density, ultrasound speed propagation, and strength parameters such as uniaxial compressive strength, tensile strength, and Young’s modulus. According to previously published results, the strength of different rocks such as marl, limestone, sandstone, tuff, granite, and marble increased significantly due to freezing when the samples were tested in frozen conditions. However, there is variation in strength increase based on rock type. It is outlined here that freezing increases rock strength by a factor of 4 in porous rock and by a factor of 1.8 in crystalline rock. Additionally, Young’s modulus increases with a decrease in temperature; however, a further decrease in temperature from -10 to -20 °C has no effect on Young’s modulus. Moreover, mathematical modelling for frozen rock has been reviewed comprehensively. It was found that porosity, the density of rock grains, density of water, residual unfrozen water content, minimum unfrozen water content at freezing point, material parameters, the initial temperature of rock, crystal size, orientation and alignment of minerals, and the loading rate are the most critical parameters that influence frozen rock strength.

Slope failure is a recurring natural hazard in the western margin of the Main Ethiopian Rift and especially around the Debre Sina area. To minimize the damage caused by failure events, a detailed investigation of landslide-prone areas identified using numerical modelling plays a crucial role. The main aim of this study is to assess the stability of slopes and to evaluate and compare safety factors calculated by the different available numerical methods. Stability analyses of slopes prone to different types of failures were performed with different techniques. The stability was assessed for slopes of complex geometry composed of aphanitic basalt, porphyritic basalt, tuff, and colluvium (poorly sorted clayey sand to silty sand) using the limit equilibrium method and the shear strength reduction method based on finite elements. Furthermore, numerical analysis was done under static and pseudo-static loading using the horizontal seismic coefficient to model their stability during a seismic event. Satellite images were used to select failure-prone slopes based on slope properties and identified past landslides, as well as to derive structural and geological information for the numerical models. The slope stability analysis indicates that the studied slopes are unstable, and any small-scale disturbance will further reduce the factor of safety and cause failure. The slope stability of landslide prone hills in the study area strongly depends on the saturation conditions and the seismic load. [ABSTRACT FROM AUTHOR]

The study of the geomechanical parameters is necessary for field planning and development. Two of the most critical parameters used to describe the rock strength are the tensile (Ts) and the uniaxial compressive strength (UCS). Measuring these two parameters in the lab is time-consuming. Consequently, non-destructive methods have been developed to predict these parameters fast and reliable. Field drilling data can be reliable, continuous, and rapid technology in predicting UCS and Ts. Herein, an artificial neural intelligence network (ANN) predicts Ts and UCS from actual drilling data collected from two fields in the Middle East. The data include rate of penetration (ROP), weight on bit (WOB), torque (T), drilling fluid injection rate (Q), and the standpipe pressure (SPP). Several sensitivity analyses were conducted to optimize the models' parameters and inputs, followed by extracting the weights and biases for developing ANN-based relations for Ts and UCS. The results showed that the ANN was highly accurate during the training phase in predicting UCS with an AAPE of 0.28%, and Ts with an AAPE of 0.28%. The developed correlation effectively predicted Ts and UCS for an average AAPE of 0.59 % during the testing phase and only 0.65 % for the validation data set for both parameters. This method provides a real-time effective tool for predicting the strength parameters in continuous, fast, and reliable measurements from the drilling field data. [ABSTRACT FROM AUTHOR]

The subject of this paper is the evaluation of the use of waste material, which is the native soil. On the example of the base ground taken from the village of Lipie (Podkarpackie voivodeship), soil-aggregate mixtures were prepared with a different degree of addition of natural aggregate. The study analysed the quantitative and qualitative parameters of the prepared mixtures and assessed their physical and mechanical properties to determine their suitability for the construction of nfrastructural facilities. It should be noted that most specifications recommend the use of primarily aggregate mixtures. The paper presents the results of a study analysing the effect of aggregate admixture to the native soil on selected physical and strength properties of the mixtures developed. The obtained results confirmed the validity of research on the use of soil-aggregate mixtures for construction purposes. [ABSTRACT FROM AUTHOR]

Various adverse effects and hydro-mechanical failures of soil are the dominant effects of global warming. At the same time, rapid industrial development has produced several by-products on a large scale. The reuse of industrial residues in different engineering fields without compromising the technical characteristics is propitious from the engineering, environmental, ecological and economic points of view. Phosphogypsum (PG) can be used as an alternative civil engineering material as it is rich in calcium sulphate, although it contains some radioactive molecules. Researchers are continuing to investigate the utilisation of PG by mixing it with other traditional materials to convert into alternative materials when the radioactive minerals are within the permissible limits. However, the contamination effect can be reduced by treating with citric acid. This review paper presents details of the increase in strength parameters and permeability of PG when combined with other wastes materials used in different geotechnical fields.

This study examines the application of nano-colloidal silica (NCS) in enhancing the mechanical properties of sandy clay soils. Consolidated undrained (CU) triaxial tests were performed on specimens containing varying percentages of NCS (0 %, 5 %, 10 %, and 20 %), which were then cured for different curing periods (1, 7, and 28 days) and subjected to three different confining pressures (50, 100, and 200 kPa). The findings revealed that the inclusion of 10 % NCS resulted in a significant 65 % increase in strength after 28 days compared to the untreated sample. However, higher NCS percentages, exceeding 10 %, led to a decline in strength as the excess NCS was not effectively utilized. The inclusion of NCS and increased curing time led to an increase in the brittleness of the soil and the application of confining pressure was able to reduce this brittleness.Furthermore, the use of 10% NCS and a curing period of 28 days significantly increased the stiffness and absorbed energy of the soil. Despite boosting the peak shear strength, NCS reduced the residual strength. Finally, polynomial modeling (Poly4) provided an excellent fit, enabling the characterization of the stress-strain and pore pressure-stain responses from the triaxial test. • A series of CU tests were conducted to investigate the strength behavior of sandy clay soil with NCS additive. • 10 % was the optimal content of NCS to modify sandy clay soil, which can improve strength. • The addition of NCS to the sandy clay soil enhances the strength and reduces the failure strain. • Empirical models were developed to predict and satisfactorily simulate q-ɛ and u- ε curves. [ABSTRACT FROM AUTHOR]

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With the increasing global demand for clean and renewable energy sources, many underground hydropower caverns are built in deep mountain valleys in high-stress regions. The evolution of the mechanical properties of the surrounding rock of underground caverns under high-stress excavation requires urgent investigation. According to the deep-buried granite in the underground caverns of the Shuangjiangkou hydropower station, triaxial tests under confining pressures of 10, 30, 40, and 50 MPa were conducted by the MTS815 rock mechanics test system. Based on the stress–strain curve, the evolution law of the strength parameters of rock samples with the crack volume strain and energy with the energy consumption ratio under different confining pressures was analyzed. Our results showed that the stress–strain curve of the sample is divided into five stages with four characteristic points: the closed point, initiation point, volume expansion point, and peak point. The strength of each stage increases with an increase in the confining pressure. In addition, the failure of this granite is characterized by apparent shear failure. The internal friction angle and the cohesion increase rapidly with the increase in the crack volume strain, and they gradually tend to be constant. Furthermore, the confining pressure profoundly influences energy evolution during the loading in the stable and unstable crack growth stages. In these stages, total energy, dissipated energy, and elastic strain energy increase with an increase in the confining pressure. Finally, the energy consumption ratio can represent the preliminary criterion of rock failure in terms of energy. With the increase in the confining pressure, the energy consumption ratio of rock samples gradually increases to approximately 1.0 at the peak stress point. The research results can provide a reference for the instability prediction of surrounding rock masses of high-stress underground caverns.

The main goal of this research is to study the failure behavior of cement-fiber-treated sand under triaxial direct tension condition tests. Thus, a new loading system and triaxial cell was designed and built for tensile loading. Samples were prepared with content cement of 3 and 5% (dry wt.) of the sand, while two types of polypropylene fibers 0.024 m in length and 23 μm and 300 μm thick were added at 0.0% and 0.5% (dry wt.) of the sand and cement mixture. After a seven-day curing period, the samples were loaded under triaxial direct tension tests under confining pressures of 100, 200, and 300 kpa in drained conditions. Stress-strain behavior, changes in volume and energy absorbed by cement-fiber reinforced sand were measured and compared with the results of other studies. Adding fibers resulted in reduced peak deviatoric stress and increased residual deviatoric stresses of the cement-fiber reinforced sand, with changes from brittle to ductile behavior. The initial stiffness and stiffness at 50% maximum tensile stress of the samples is decreased with the addition of fibers and with an increase in fiber diameter, the reduction rate of this stiffness is more evident. The absorbed energy for fibers with a thickness of 23 μm is less than fibers with a thickness of 300 μm. The effect of adding fibers to strength parameters showed that the cohesion intercept decreases, while the internal friction angle increases. [ABSTRACT FROM AUTHOR]

A significant increase in effective stress can be induced in hydrate-bearing reservoirs when the depressurization method is applied. A series of drained triaxial shear tests were performed on hydrate-bearing sediments with various hydrate saturations to investigate their mechanical characteristics under effective confining pressures of up to 20 MPa. The results show that significant particle crushing of the host sand occurs during shearing under high pressures, and there is no remarkable effect of hydrate saturation on the degree of particle breakage. As the effective confining pressure increases, the stress–strain curves of the hydrate-bearing specimen transformed from strain-softening to strain-hardening. The peak stress ratio and internal friction angle of the sediments gradually decrease and tend to be constant with the increased confining stress, whereas the cohesion in hydrate-bearing sediments exhibits an increasing tendency. The critical state line (CSL) of hydrate-bearing sediments in the e-lnp′ space under low-to-high effective confining pressures intersects with the normal consolidation line under the same hydrate saturation. Furthermore, the CSL moves upward and rotates clockwise as the hydrate saturation increases. [ABSTRACT FROM AUTHOR]

In this research, the potential improvement of some geotechnical characteristics of soft clay soil using the low Calcium fly ash was evaluated. (These characteristics include unit weight, shear strength, compaction characteristics and soil plasticity characteristics). In addition, the X-ray diffraction test was performed to measure the mineralogical changes in the soft clay soil when the low Calcium fly ash is added. The ordinary Portland cement was used to activate the fly ash. The total percent of flash and cement was10% to investigate the variation in the effectiveness of activation. The optimum moisture content that which computed by the compaction test was adopted in the rest of the experimental program. The test results revealed that the cement could be used to improve the activating of the fly ash efficiently. The maximum value of dry density was marginally affected due to activation from 1.747 to 1.738 g/cm3 along with a corresponding change in optimum water content from 17.45 to 15.5 %. The soil cohesion parameter increased from 188 to 206 kN/m2 whereas the angle of internal friction rose from about 56.7o to 59.1o. Finally, the results of the unconfined compression test reveal that the cement-activated fly ash could present better results than those obtained from a 28-days curing cement.

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This paper presents the impact of selected essential aspects of geological structure on the state of slope stability as assessed by changes in the safety factor (SF). The engineering geological slope features that were analysed include: (i) changes in soil cohesion and internal friction angle, (ii) presence of a weak soil layer and its span, (iii) structural discontinuity (i.e. fault), (iv) soil permeability properties and water conditions (i.e. groundwater level, long and heavy rainfall). A certain scheme of slope stability calculations has been proposed for a case involving complex geological conditions. The numerical modelling of a hypothetic slope was performed using the shear strength reduction method based on the finite element method.

In the current paper, we explore the effect of temperature changes in seasonal frozen areas on the strength parameters of unsaturated soil under low matric suction, as well as the impact of the parameters under different temperatures on an overwintering deep foundation pit in unsaturated soil under low matric suction. In particular, we take unsaturated silty clay in its original state as the research object and Global Digital Systems Ltd. (GDS) unsaturated silty soil as the triaxial tester to perform triaxial shear tests on unsaturated silty clay under several temperatures. The strength parameters obtained from the laboratory tests are then combined with Abaqus numerical simulations to analyze the stress and deformation of the overwintering deep foundation pit supporting structure in unsaturated soil within seasonal frozen areas. Experimental results under low matric suction demonstrate that temperature variations have a greater effect on the total cohesive force of unsaturated silty clay, yet their impact on the effective internal friction angle is relatively small. The influence of the frost heaving force produced by the freezing of the unsaturated soil on supporting structures is observed to be greater than the earth pressure during the freeze-thaw process. When the unsaturated soil is frozen, the horizontal frost heaving force of the retaining structure at the top and bottom of the foundation pit is relatively large. Furthermore, the selection of strength parameters for unsaturated soil during the freeze-thaw process has a great influence on the surrounding environment of the deep foundation pit, as well as the stress and the deformation of the supporting structure. Numerical simulations using strength parameters under different temperatures (20°C, - 15°C, 20°C -15°C--20°C) resulted in the following general trend for the horizontal displacement of the retaining structure, the horizontal force of the pile side and the displacement of the top of the deep foundation: simulation results of frozen soil parameters > simulation results of dynamic changes of parameters with temperature > simulation results of normal temperature soil parameters. [ABSTRACT FROM AUTHOR]

Based on the triaxial test results of 30 types of rocks, by analysing the confining pressure function and defining a new plastic internal variable, the evolution laws of the strength parameters and shear dilation angle with a defined plastic internal variable are studied, and the corresponding evolution models are established. First, the complete stress-strain curves of 30 types of rocks are collected from published literature; from these curves, the critical equivalent plastic strains under different confining pressures are extracted. With the confining pressure and critical equivalent plastic strain data of the 30 types of rocks, fitting is performed for 23 different functions. The results demonstrate that the three-parameter allometric power-type function is the best to serve as the confining pressure function to define the plastic internal variable. Second, the strength and plastic strain data of the 30 types of rocks are extracted and transformed into the strength and plastic internal variable data. By analysing the evolution laws of the strength parameters considering the plastic internal variable, the Gaussian function is adopted to uniformly characterise the variation in the strength parameters with the plastic internal variable. Third, the shear dilation angle, confining pressure and plastic strain data of the 30 types of rocks are extracted and transformed into shear dilation angle, confining pressure and plastic internal variable data. By analysing the evolution law of the shear dilation angle considering the confining pressure and the plastic internal variable, a negative exponential function is adopted to uniformly characterise the nonlinear evolution of the shear dilation angle. Finally, the proposed evolution models of the strength parameters and the shear dilation angle are integrated into ABAQUS. By comparing the simulated complete stress-strain curves with the experimental curves of the different rock types, it is verified that the proposed models can be used to correctly simulate the nonlinear deformation and failure of different rock types. This research overcomes the shortcomings of the existing models and has wide application prospective. [ABSTRACT FROM AUTHOR]

This paper investigates the effects that the spatial variability of a soil's undrained shear strength has on lateral wall movements and ground surface settlements when performing a deep excavation stability analysis. A random finite-element method is employed to statistically assess a deep excavation. A case study based on an actual deep excavation project in Bangkok's subsoils was used to validate the methodology. The two-dimensional spatial variability of the undrained shear strength in the clay layers of Bangkok's subsoil is simulated using the random field theory and Monte Carlo simulation. The Mohr–Coulomb model is used to predict lateral wall movements and ground surface settlements, while the stability analysis of the deep excavation is evaluated by the factor of safety using the strength reduction approach. The results show that spatial variability highly affects the distribution of lateral wall movements and ground surface settlements, as well as the scatter of the factor of safety corresponding to progressing stages of excavation. [ABSTRACT FROM AUTHOR]

It is necessary to master the characteristics of rock mass to develop the mine safely and efficiently, and then to reduce the environmental pollution of mining. The strength parameters of rock mass are the basic problem in rock mechanics research. An important characteristic of the strength parameters of the jointed rock mass is size effect. According to the physical and mechanical significance of the representative element volume(REV) of the strength parameters of the jointed rock mass, the real rock mass discontinuities was measured by the advanced ShapeMetrix 3D photogrammetry system in tunnel of an iron mine, then the 3-D solid model of underground rock mass is established is used to obtain the geometrical distribution parameters of rock mass discontinuities. Aaccording to the geometrical distribution parameters of rock mass discontinuities, a 3D-discontinuities network model is generated based on the Monte-Carlo simulation of joint network. And then, the joint data are imported into the RFPA in order to simulate uniaxial compression test and shear test of the jointed rock mass with different sizes. The REV size of the strength parameters of the jointed rock mass is estimated to be 10mx 10m after the comprehensive numerical analysis on the compressive strength and shear strength of the jointed rock mass with different sizes, which may lay the basis for further stability evaluation of the jointed rock mass in mines. This study can provide a reliable theoretical basis for the efficient, safe and environmental protection mining of mines. [ABSTRACT FROM AUTHOR]

Sandy soils constitute a large part of the soils of the northern part of Iran. The construction of structures on these soils will have some problems due to a lack of proper strength properties. On the other hand, in recent years, bottles of polyethylene terephthalate (PET) plastics, such as water and soda bottles, have led to the emergence of an environmental threat due to their prolonged durability in the environment. The utilization of these materials for soil improvement seems to be a sustainable approach. In this research, the effect of recycled PET on the mechanical properties of Babolsar sandy soil is investigated through an extensive experimental analysis carried out using direct shear and Consolidated Drained (CD) triaxial compression tests. Various concentrations of PET were mixed to sand with 3%, 5%, and 7% cement contents. The curing time and relative density of samples were 7 days and 70%, respectively. The results showed that the addition of this fiber improved strength parameters such as cohesion and internal friction angle. Furthermore, the effect of the fiber was not significant with an increase in cement content in samples. The samples with 3% cement showed better results in both direct shear and triaxial tests. By adding 0.5% and 1% PET fibers to the samples containing 3% cement at 100 kPa pressure, the ratio of strength in direct shear tests increased by 13% and 24%, respectively, and increased in the triaxial test by 50% and 93%, respectively. [ABSTRACT FROM AUTHOR]

A simple concrete - based structure model is proposed by developing it from nano to macro structure. In this model, the structure is divided into four levels and each level is represented by a parametric model. The parameters of the four based structures are identified, in terms of elastic modulus (EM) and poisson's ratio at any time period (t) at Calcium silicate hydrates (CSH), cement paste, mortar and concrete levels. Then, by integrating the proposed model with Bazant - Baweja (B3) model, the compressive strength (CS) and EM of concrete at different curing periods is estimated. Further, it is analyzed and validated by other international models such as B3 model alone, Comite Euro - International Du Beton (CEB) model and Indian standards (IS) method. Few tests were done to investigate the CS of concrete with the inclusion of 25% fly ash (fa) and varying ratios of waste foundry sand (WFS) - 0, 25, 50, 75 and 100%. The results are compared with the obtained values by other models and validated with the experimental results. It is found that the proposed model (PM) i.e., Multiscale modeling (MS) can be used reliably integrated with the other models and builds the interaction between the various matrix to estimate and study the strength parameters of the concrete. MS is a new technique which is based on the mathematical formulation, it doesn't require any earlier data about the mechanical properties of the concrete except the intrinsic values of the cement-based materials and mix details to evaluate the strength of the concrete. [ABSTRACT FROM AUTHOR]

Curing is the process of maintaining hardened concrete under moist condition. Curing must be undertaken for reasonable period of time, to ensure that the concrete achieves its potential strength and durability. Efficient and uninterrupted curing contributes to the superior quality of concrete. This paper aims to compare the strength parameters of M40 and M25 grade concrete under various methods of curing. For this study, we adopted curing by Immersion and Surface Curing methods. We also adopted Membrane Curing, in which the curing would be done by the application of pigmented emulsions of linseed oil on the concrete surface. Finally, after the concrete specimens have undergone curing for a certain period of time, they are tested for strength parameters such as Compressive Strength and Flexural Strength and the conclusions are drawn from it. [ABSTRACT FROM AUTHOR]