Search Results (149)

The concrete protective layer in hydraulic tunnels is prone to abrasion by high-velocity sand-laden water, reducing structural durability. Accurate prediction of abrasion depth is key to rational hydraulic structure design. Existing studies have limitations: classical empirical models consider only a single factor, while early machine learning models fail to cover two core abrasion mechanisms (friction and impact) and lack meta-heuristic algorithm-based parameter optimization, leading to insufficient generalization and stability. This study aims to (1) establish a multi-source database with 690 cases (463 friction-dominated, 227 impact-dominated) covering multiple test standards (ASTM C944, ASTM C779, BIS: 1237-1980, ASTM C1138); (2) optimize hyperparameters of LightGBM, XGBoost, and CatBoost using Genghis Khan Shark Optimizer (GKSO) to build a hybrid ensemble model; (3) verify model performance and identify key factors via SHAP analysis. After preprocessing, input features were simplified to five: water–cement ratio, FA/CA (fine aggregate/coarse aggregate), age, T/V (test duration/velocity), and WRA content. Results show that GKSO-CatBoost performed best (test set R² = 0.982, RMSE = 0.1231 mm). SHAP analysis identified T/V and the water–cement ratio as key influencing features, providing clear directions for optimizing concrete mix proportions under different standard scenarios. This study provides a new method for hydraulic concrete abrasion prediction and a scientific basis for durability design oriented to specific test standards. Full article

Aeolian sand is widely distributed in desert areas, but it has certain challenges in the application of roadbed engineering due to its loose particles and poor stability. Cement-modified aeolian sand has gradually become the mainstream improvement method of aeolian sand materials due to its good sand fixation performance. However, the mechanical properties and failure modes of cement-modified aeolian sand are still unclear. The effective characterization of the damage evolution process of aeolian sand is crucial to understanding its mechanical mechanism. This study focuses on cement-modified aeolian sand as the research subject. Utilizing an unconfined compression apparatus and an acoustic emission monitoring system, this research simultaneously monitors stress–strain data and acoustic emission signals during the deformation and failure process of cement-modified aeolian sand. This investigation analyzes the influence of cement content on mechanical performance parameters, examines the correlation between acoustic emission time–frequency characteristics and damage evolution processes, and subsequently establishes an acoustic-emission-based damage evolution model. The results show that a strong correlation is observed between the stress–strain curve and the acoustic emission (AE) evolution characteristics of the cement-modified aeolian sand. When the applied stress reaches 80% of the peak stress, the AE signals enter a relatively calm period. This characteristic can be regarded as significant precursor information for the deformation and failure of the material. The damage in the cement-modified aeolian sand follows a Weibull distribution. The shape parameter m attains its maximum value at a cement content of 7%. The material’s homogeneity transitions from being comparable to coal rock at lower cement contents to resembling granite at higher contents. These findings can provide a technical basis for using acoustic emissions to characterize damage and identify risks in cement-modified aeolian soils. Full article

Geopolymers are inorganic aluminosilicate binders formed by alkali activation of reactive powders, offering a sustainable, low-carbon alternative to Portland cement. Their rapid setting and chemical durability make them well-suited for additive manufacturing (AM) in demanding environments, including underwater construction, where chemical stability is essential for both structural integrity and environmental safety. This study evaluates two metakaolin-based formulations designed for underwater extrusion, differing in activator chemistry and rheology control. Standardized leaching tests revealed alkaline but stable leachates with strong immobilization of most ions; major anions and total dissolved solids remained within regulatory thresholds. Limited exceedances were observed—soluble organic carbon in the NaOH-activated mix and arsenic/selenium in the waterglass–sand system—highlighting specific areas for mix improvement rather than fundamental limitations of the material. Complementary radioactivity screening confirmed activity concentration indices well below the regulatory limit, with measured radionuclide activities falling comfortably within exemption ranges. Together, the leaching and radioactivity results demonstrate that both formulations provide robust matrix integrity and environmental compatibility, while highlighting clear opportunities for mix design improvements to further minimize ecological risks. Full article

Biopolymers have recently been introduced as eco-friendly alternatives to other chemical cementitious additives for sandy soil stabilization, especially in pavement construction. The resilient modulus (M_R) is a key metric considered in the mechanistic design of pavement layers that ensures a safe and economic design based on guaranteed accurate values. This study investigated the effects of dehydration on the M_R of biopolymer-treated sand. Prepared specimens were subjected to two different curing conditions. The first set underwent closed-system curing (CSC) for periods of 7, 14, and 28 days. The second set of specimens was cured at different levels of suction by controlling relative humidity (RH) using different salt solutions (0.27, 1.0, 9.7, 21.0, 54.6, 113.7, and 294 MPa), referred to as dehydration curing (DC). The soil water retention curve (SWRC) was measured over the entire suction range to evaluate the dehydration curing and to link the results of suction levels and dehydration regime. M_R tests were conducted on both sets of specimens using a dynamic triaxial system to simulate different confining, traffic, and dynamic stresses. The results showed a significant increase in M_R (i.e., up to eight times) for specimens cured under DC conditions that was proportional to the suction level across different zones of the SWRC. Scanning electron microscopy revealed a phase change from hydrogel to film, which enhanced cementation and bonding between particles. in addition, CSC treatment resulted in a 10–30% reduction in M_R. A new regression model is proposed to predict the M_R of biopolymer-treated sand as a function of confining stresses, dynamic stresses, and suction. These findings will assist pavement engineers and designers in achieving safe, sustainable, and economic designs. Full article

The study considers the development of a paraffin-based additive for cement–sand injection mortars intended for deep soil stabilisation under the geological conditions of Central Kazakhstan. The present study investigates the influence of the additive on mobility, water separation, setting time, and strength characteristics of mortars, for concentrations ranging from 0.2 to 1.0% by cement mass. The findings demonstrated that the additive enhanced the slump flow area by up to 62%, diminished water separation by 30–32% and extended the setting time by 45–76%. It was demonstrated that compressive and flexural strength were preserved with moderate increases of up to 8–9% in comparison with the reference mixture. The range of 0.6–0.8% was identified as optimal, providing enhanced mobility and stability while maintaining structural integrity. The findings indicate that paraffin-based additives can be effectively applied in deep cementation technologies for enhancing the injectability and performance of soil stabilization mixtures. Full article

The building sector is under increasing pressure to lower its environmental impact, prompting renewed interest in raw soil as a low-carbon and locally available material. This study investigates the mechanical and thermal properties of clay-based masonry walls through a comprehensive experimental program on earthen mortars, bricks, and their interfaces, considering both stabilized and non-stabilized formulations. Compressive, bending, and shear tests reveal that strength is strongly influenced by mortar composition, hydration time, and the soil-to-sand ratio. The addition of 5–7.5% cement yields modest gains in compressive strength but increases the carbon footprint, whereas extended pre-hydration achieves similar improvements with lower environmental costs. Thermal characterization of the studied samples (SiO₂ ≈ 61.2 wt%, Al₂O₃ ≈ 11.7 wt%, MgO ≈ 5.1 wt%) revealed that SiO₂-enriched compositions significantly enhance thermal conductivity, whereas the presence of Al₂O₃ and MgO contributes to increased heat capacity and improved moisture regulation. These findings suggest that well-optimized clay-based mortars can satisfy the structural and thermal requirements of non-load-bearing applications, offering a practical and sustainable alternative to conventional construction materials. By reducing embodied carbon, enhancing hygrothermal comfort, and relying on locally available resources, such mortars contribute to the advancement of green building practices and the transition towards low-carbon construction. Full article

In field exploration, disaster rescue, and complex terrain operations, the accuracy of ground type recognition directly affects the walking stability and task execution efficiency of legged robots. To address the problem of terrain recognition in complex ground environments, this paper proposes a high-precision classification method based on single-leg triaxial force signals. The method first employs a one-dimensional convolutional neural network (1D-CNN) module to extract local temporal features, then introduces a long short-term memory (LSTM) network to model long-term and short-term dependencies during ground contact, and incorporates a convolutional block attention module (CBAM) to adaptively enhance the feature responses of critical channels and time steps, thereby improving discriminative capability. In addition, an improved whale optimization algorithm (iBWOA) is adopted to automatically perform global search and optimization of key hyperparameters, including the number of convolution kernels, the number of LSTM units, and the dropout rate, to achieve the optimal training configuration. Experimental results demonstrate that the proposed method achieves excellent classification performance on five typical ground types—grass, cement, gravel, soil, and sand—under varying slope and force conditions, with an overall classification accuracy of 96.94%. Notably, it maintains high recognition accuracy even between ground types with similar contact mechanical properties, such as soil vs. grass and gravel vs. sand. This study provides a reliable perception foundation and technical support for terrain-adaptive control and motion strategy optimization of legged robots in real-world environments. Full article

Significant risk of water and sand inrushes is commonly encountered during coal seam mining when thin bedrock is directly overlain by thick, water-bearing, unconsolidated layers. Achieving effective strata control and establishing reliable water-isolating mechanisms under these conditions represent critical scientific and technological challenges for safe mining operations. Furthermore, this is a vital research direction for advancing the extraction limit (or recovery height) in coal seams. Initially, drawing on key stratum theory, ground pressure behavior patterns, and mining operation characteristics, the weathered zone was identified as the critical grouting horizon. During the initial mining stage, the first two periodic weighting intervals (approximately 60 m) were identified as the key area. Subsequently, a strategy of high-pressure grouting was proposed to modify the weathered stratum. Numerical simulation methods were employed to optimize the grouting parameters, with the core specifications determined as follows: grouting pressure ≥30 MPa, water–cement ratio of 0.7:1, and grouting hole spacing ≤30 m. Ultimately, a grouting system was designed that used directional drilling from the surface to access the weathered zone, followed by branched horizontal boreholes for staged high-pressure grouting. The borehole trajectory was predominantly L-shaped. Field implementation demonstrated that the grouting intervention increased the first weighting span by an average of 17.3%. Critically, no water inflow was observed throughout the initial caving period, and significant roof falls or rib spalling were effectively mitigated. This confirmed a substantial improvement in key stratum stability, ensuring the safe and efficient advancement of the mining face. This study provides essential technical support and a practical model for safely and efficiently extracting coal seams under thin bedrock under similar complex hydrogeological conditions. Full article

Microbial Induced Carbonate Precipitation (MICP) is regarded as a promising eco-friendly alternative to traditional Portland cement for soil stabilization. However, the feasibility of applying bio-cemented soil as a road base material remains inadequately studied, particularly in terms of the relationships between MICP treatment parameters—such as solution content, curing age, and the ratio of bacterial solution (BS) to cementation solution (CS) —and key mechanical and durability properties under realistic road conditions. In this study, an optimal curing condition for bio-cemented sand was first determined through unconfined compression strength (UCS) tests and calcium carbonate content (CCC) determination. Subsequently, dynamic triaxial tests were conducted to evaluate its resistance to cyclic loading. Further road performance tests, including splitting tensile strength, freeze-thaw resistance, temperature shrinkage, and arch expansion assessments, were carried out to comprehensively evaluate the material’s applicability. Scanning electron microscopy (SEM) was employed to elucidate the microstructural mechanisms underlying strength development. The results show that the strength (4.28 MPa) of bio-cemented sand cured under optimal conditions (12% bio-cured solution content, a BS-to-CS ratio of 1:4 and 7-d curing age) satisfies the criteria for road base applications. MICP treatment significantly improved the dynamic properties of aeolian sand (AS), reducing the cumulative plastic axial strain (ε_p) by nearly 11–46% and increasing the dynamic elastic modulus (E_d) by approximately 7–31% compared to untreated sand. The material also demonstrates satisfactory performance across all four road performance metrics. Microstructural analysis reveals enhanced interparticle bonding due to calcium carbonate precipitation, with samples prepared near the optimum moisture content exhibiting superior integrity and strength. Overall, bio-cemented sand demonstrates excellent potential as a sustainable road base material. These findings provide a theoretical foundation for practical applications of similar bio-cemented soils in road engineering. Full article

Aeolian sand is the primary geological material for construction in desert regions, and its stabilization with industrial solid wastes-based geopolymer (ISWG) provides an eco-friendly treatment replacing cement. This study comparatively investigated the enhancement effects of chemical activators and expansive agents on compressive strength of aeolian sand stabilized by ISWG (ASIG). Three chemical activators—NaOH, Ca(OH)₂, and CaCl₂—along with two expansive agents—desulfurized gypsum and bentonite—were considered. Through X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, mercury intrusion porosimetry and pH values tests, the enhancement mechanisms of the additives on ASIG were elucidated. Results demonstrate that the expansive agent exhibits significantly superior strengthening effects on ASIG compared to the widely applied chemical activators. Chemical activators promoted ISWs dissolution and hydration product synthesis, thereby densifying the hydration product matrix but concurrently enlarged interparticle pores. Desulfurized gypsum incorporation induced morphological changes in ettringite, and excessive desulfurized gypsum generated substantial ettringite that disrupted gel matrix. In contrast, bentonite demonstrated superior pore-filling efficacy while densifying gel matrix through a compaction effect. These findings highlight bentonite superior compatibility with the unique microstructure of aeolian sand compared to conventional alkaline activators or expansive agents, and better effectiveness in enhancing the strength of ASIG. Full article

This study formulates an efficient, affordable, and low-carbon binder based on locally excavated earth from Yaoundé, offering sufficient mechanical strength and water resistance for rendering applications. Through material characterization, a binary binder composed of Portland cement (PC) and calcined laterite (CL) was developed, reducing the PC content by up to 30%. The mortar used laterite sand with varying fine particle contents in place of river sand, and its mechanical strength and water absorption via capillarity action were evaluated. Due to the porosity of the laterite fines, all mixes were prepared at equivalent workability. The mechanical strength was the same as if the binder solely consisted of PC and reached 11 MPa when the laterite sand contained no fine particles. As the fine particle content increased, the mechanical strength decreased to a minimum value of 4 MPa when raw laterite was used, and the coefficient of water absorption via capillarity action decreased. Overall, the formulated class Wc2 mortar is suitable for rendering applications. The valorization potential of fine particles and coarse aggregates of the crushed mortar was assessed: the crushed mortar fines had pozzolanic properties and could serve as supplementary cementitious materials; the largest particles are suitable for lime stabilization. Full article

The United States of America could build 20,000 bases for the Statue of Liberty every year using its construction and demolition waste, and 456 bases using waste glass from jars and bottles. However, some sectors of the population still face a shortage of affordable housing. The challenges of disposing of such large amounts of waste and solving the housing shortage could be addressed together if these materials, considered part of a closed-loop system, were integrated into new building blocks. This research studies compressed earth blocks that incorporate soils and gravels excavated in situ, river sand, crushed concrete from demolition waste, and recycled glass sand. To stabilize the blocks, cement is used at 5, 10, and 15% (by weight). The properties studied include the following: density, apparent porosity, initial water absorption, simple compression, modulus of elasticity, and thermal conductivity. Optical image analysis proved to be a tool for predicting the values of these properties as the stabilizer changed. To assist in decision making regarding the best overall performance of the total 12 mix designs, a ranking system is proposed. The best blocks, which incorporate the otherwise waste materials, exhibited simple compression values up to 7.3 MPa, initial water absorption of 8 g/(cm² × min^0.5) and thermal conductivity of 0.684 W/m·K. Full article

To address the critical challenge of ensuring bottom water-inrush stability during the excavation of ultra-deep foundation pits for riverside suspension-bridge anchorages under complex geological conditions involving high-pressure confined groundwater, we investigate the application of D-RJP high-pressure rotary jet grouting pile technology for ground improvement. Its effectiveness is systematically validated through a case study of the South Anchorage Foundation Pit for the North Channel Bridge of the Zhangjinggao Yangtze River Bridge. The D-RJP method led to the successful construction of a composite foundation within the soft soil that satisfies the permeability coefficient, interface friction coefficient, bearing capacity, and shear strength requirements, significantly improving the geotechnical performance of the anchorage foundation. A series of field experiments were conducted to optimize the critical construction parameters, including the lifting speed, water–cement ratio, and stroke spacing. Core sampling and laboratory testing revealed the grout columns to have good structural integrity. The unconfined compressive strength of the high-pressure jet grout columns reached 5.45 MPa in silty clay layers and 8.21 MPa in silty sand layers. The average permeability coefficient ranged from 1.67 × 10⁻⁷ to 2.52 × 10⁻⁷ cm/s. The average density of the columns was 1.66 g/cm³ in the silty clay layer and 2.08 g/cm³ in the silty sand layer. The cement content in the return slurry varied between 18% and 27%, with no significant soil squeezing effect observed. The foundation interface friction coefficient ranged from 0.44 to 0.52. After excavation, the composite foundation formed by D-RJP columns was subjected to static load and direct shear testing. The results showed a characteristic bearing capacity value of 1200 kPa, the internal friction angle exceeded 24.23°, and the cohesion exceeded 180 kPa. This study successfully verifies the feasibility of applying D-RJP technology to construct high-performance artificial composite foundations in complex strata characterized by deep soft soils and high-pressure confined groundwater, providing valuable technical references and practical insights for similar ultra-deep foundation pit projects involving suspension bridge anchorages. Full article

This study presents the results of research on the use of Portland cement as a binder for producing semi-permanent molds intended for large-scale castings made from complex alloyed steels. Based on the conducted experiments, the optimal composition of a molding mixture based on Portland cement was determined to manufacture large molds with high operational performance. The technological properties of the mixtures were investigated, focusing on the flowability, sedimentation stability, and strength after curing. The recommended mixture composition is as follows: Portland cement—18.75%; sand—56.5%; quartz powder—25%; water—25%. To accelerate the hardening process, the use of curing accelerators is advised. The most effective additives are a 9% aluminum nitrate solution at 0.6–1.5% by weight or sodium aluminate at 3–4%. This composition ensures the required strength within a short curing time. A specific thermal treatment regime is also recommended to further stabilize the mold structure: heating to 450 °C at a rate of 75 °C per hour, holding for 2 h, followed by controlled cooling together with the furnace. Full article

Backfilling materials are commonly employed materials in mines for filling mining waste, and the strength of the consolidated backfill formed by the binding material directly influences the stability of the surrounding rock and production safety in mines. The traditional approach to obtaining the strength of the backfill demands a considerable amount of manpower and time. The rapid and precise acquisition and optimization of backfill strength parameters hold utmost significance for mining safety. In this research, the authors carried out a backfill strength experiment with five experimental parameters, namely concentration, cement–sand ratio, waste rock–tailing ratio, curing time, and curing temperature, using an orthogonal design. They collected 174 sets of backfill strength parameters and employed six population optimization algorithms, including the Artificial Ecosystem-based Optimization (AEO) algorithm, Aquila Optimization (AO) algorithm, Germinal Center Optimization (GCO), Sand Cat Swarm Optimization (SCSO), Sparrow Search Algorithm (SSA), and Walrus Optimization Algorithm (WaOA), in combination with the CatBoost algorithm to conduct a prediction study of backfill strength. The study also utilized the Shapley Additive explanatory (SHAP) method to analyze the influence of different parameters on the prediction of backfill strength. The results demonstrate that when the population size was 60, the AEO-CatBoost algorithm model exhibited a favorable fitting effect (R² = 0.947, VAF = 93.614), and the prediction error was minimal (RMSE = 0.606, MAE = 0.465), enabling the accurate and rapid prediction of the strength parameters of the backfill under different ratios and curing conditions. Additionally, an increase in curing temperature and curing time enhanced the strength of the backfill, and the influence of the waste rock–tailing ratio on the strength of the backfill was negative at a curing temperature of 50 °C, which is attributed to the change in the pore structure at the microscopic level leading to macroscopic mechanical alterations. When the curing conditions are adequate and the parameter ratios are reasonable, the smaller the porosity rate in the backfill, the greater the backfill strength will be. This study offers a reliable and accurate method for the rapid acquisition of backfill strength and provides new technical support for the development of filling mining technology. Full article