Search Results (38)

The application of construction and demolition waste (CDW) as roadbed filler faces challenges due to the variable mechanical properties caused by fragile recycled brick aggregates. This study elucidates the breakage mechanism of CDW fillers under compaction effort through a combination of standardized laboratory compaction tests and discrete element method (DEM) simulations. Furthermore, the breakage evolution patterns of mixed fills comprising recycled concrete and brick aggregates at various mixing ratios were revealed. A DEM model was developed to characterize recycled concrete and brick aggregates, adopting polygonal clumps for particles >4.75 mm and spherical clumps for finer fractions. The results indicate that particle breakage progresses through three distinct stages: linear fragment stage (0–200 kJ/m³, 50% of total breakage), deceleration growth stage (200–1000 kJ/m³, 38% of total breakage), and residual crushing stage (1000–2684.9 kJ/m³, 12% of total breakage). Recycled concrete aggregates form a skeleton restraining deep cracks, while brick aggregates enhance stability through energy dissipation and void filling. However, exceeding 30% brick content impedes skeleton development. Critically, a 30% brick content optimizes performance, achieving peak dry density with 25% lower compression deformation than concrete-only fillers, while limiting breakage index rise. These results provide a science-based strategy to optimize CDW roadbed design, improving recycling efficiency and supporting sustainable infrastructure. Full article

This article takes alluvial silty sand in the alluvial plain area as the research object. Through a combination of theoretical analysis, finite element simulation, and on-site testing, the engineering characteristics of alluvial silty sand under traffic loads, as well as the feasibility of using alluvial silty sand as roadbed filling material in practical engineering, are systematically expounded on for the first time. The research results indicate that the influence of vehicle speed on the distribution and depth of dynamic stress is relatively small, while the moisture content (optimal 7.8%) and compaction degree (>94%) are the key factors determining the performance of the roadbed. Specifically, the displacement at the top of the roadbed varies with changes in moisture content. An increase in compaction degree is beneficial for reducing settlement and enhancing the stability of the roadbed. Through comparative analysis of finite element simulation and on-site testing, it was found that although the initial settlement of alluvial silt filling is large, the settlement rate is fast and can stabilize in a short period of time. Its long-term performance can still meet engineering requirements. Research has shown that alluvial silt can be used as an economical and reasonable roadbed filling material, but in practical applications, strict control of moisture content and compaction degree is required to optimize roadbed performance. Full article

It is difficult to meet environmental requirements via the coarse treatment methods of landfilling and open-air storage of construction waste. At the same time, the consumption of building materials in highway engineering is enormous. Using construction waste as a filling material for proposed roads has become a research hotspot in recent years. This paper starts with basic performance tests of recycled construction waste materials, and then moves on to laboratory experiments conducted to obtain the road performance of the recycled materials, the testing of key indicators of post-construction filling quality of the roadbed, and analyses of the deformation pattern of roadbed filled with construction waste. Additionally, the ABAQUS finite element software was used to establish a numerical model for roadbed deformation and analyze the roadbed deformation under different compaction levels and vehicle load conditions. The experimental results show that the recycled material has a moisture content of 8.5%, water absorption of 11.73%, and an apparent density of 2.61 g/cm³, while the liquid limit of fine aggregates is 20% and the plasticity index is 5.4. Although the physical properties are slightly inferior to natural aggregates, its bearing ratio (25–55%) and low expansion characteristics meet the requirements for high-grade highway roadbed filling materials. The roadbed layer with a loose compaction of 250 mm, after eight passes of rolling, showed a settlement difference of less than 5 mm, with the loose compaction coefficient stabilizing between 1.15 and 1.20. Finite element simulations indicated that the total settlement of the roadbed stabilizes at 20–30 mm, and increasing the compaction level to 96% can reduce the settlement by 2–4%. Vehicle overload causes a positive correlation between the vertical displacement and shear stress in the base layer, suggesting the need to strengthen vehicle load control. The findings provide theoretical and technical support for the large-scale application of recycled construction waste materials in roadbed engineering. Full article

The purpose of this study is to solve the problem of the harmless treatment of dredged silt and soil extraction during road construction in lake areas. The silt in the project area is used as the research material to evaluate its engineering applicability as an improved filling material for the roadbed of the lake’s surrounding road. Through indoor pretreatment and a series of mechanical performance tests, including compaction tests, unconfined compressive strength tests (UCS), bearing ratio tests (CBR), triaxial compression tests (CU consolidated undrained), and consolidation tests, we obtained key mechanical parameters of modified sludge soil, such as maximum dry density, optimal moisture content, unconfined compressive strength, bearing ratio, shear strength, and compression characteristics. The research results show that with the increase in modifier dosage, the optimal moisture content of modified sludge soil increases, the maximum dry density decreases, and its compressive strength and shear strength significantly improve. The CBR value also meets the technical requirements of each layer of the roadbed. Specifically, after 7 days of curing, the compaction degree of 10% modified sludge soil can exceed 96%, the unconfined compressive strength reaches 0.819 MPa, the CBR value reaches 17.5, the cohesion measured by triaxial tests is 78 kPa, the internal friction angle is 27°, and it exhibits low compressibility. These findings provide new solutions for environmentally friendly treatment, resource utilization, and road engineering in river and lake sediments. Full article

Large-scale engineering projects frequently involve pit excavation and wetland landfill operations, resulting in significant silt accumulation that occupies land and adversely affects the environment. Curing technology offers a solution for reusing this waste silt. In this study, straw ash and calcium carbide slag are proposed as effective curing agents for silt soil. Various indoor tests were conducted to evaluate the mechanical properties of the cured silt soil, while X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze its mineral composition and micro-morphology. The results showed that increasing the curing agent dosage significantly improved soil strength. Specifically, at a 10% dosage, the California bearing ratio (CBR) value increased to 18.7%, which is 13.4 times higher than untreated silt soil and exceeds road specifications by 8%. At a 20% dosage, the unconfined compressive strength (UCS) value reached 1.38 MPa, meeting the ≥0.8 MPa requirement for roadbeds. Based on economic considerations, a 20% dosage of straw ash–calcium carbide slag was selected as optimal. Microscopic analysis revealed that the addition of these agents promoted the formation of hydrated calcium silicate, filling pores and enhancing the mechanical properties of the cured soil, resulting in a more dense and stable structure. Full article

To achieve resourceful utilization of dredged sludge, lightweight treatment was performed on sludge from Xunsi River in Wuhan using fly ash, cement, and expanded polystyrene (EPS) particles. Density tests and unconfined compressive strength (UCS) tests were conducted on the composite stabilized sludge lightweight soil to determine the optimal mix ratio for high-quality roadbed fill material with low self-weight and high strength. Subsequently, microstructural tests, including X-ray diffraction (XRD) and scanning electron microscopy (SEM), were conducted. The Particle (Pore) and Crack Analysis System (PCAS) was used to analyze the SEM images, investigating the cement–fly ash composite stabilization mechanism. The experimental results showed that the optimal lightweight treatment was achieved with an EPS content of 80% (by volume ratio to dry soil), cement content of 7.5% (by mass ratio to dry soil), and fly ash content of 5% (by mass ratio to dry soil). The density of the optimized lightweight soil was 1.04 g/cm³, a reduction of 28.27% compared to the density of raw sludge soil (1.45 g/cm³). The UCS increased significantly from 110 kPa for raw sludge soil to 551 kPa. The addition of fly ash enhanced the hydration and secondary hydration reactions between cement and sludge, generating more calcium silicate hydrate (C-S-H) gel, which filled the larger pores between the EPS particles and soil particles, as well as those between the soil particles themselves, making the structure denser. Compared to single cement stabilization, composite stabilization resulted in a lower content of expansive ettringite crystals, a more uniform pore distribution, fewer pores, and a lower surface porosity ratio. These research findings can provide theoretical support and practical references for the lightweight treatment of dredged sludge in the Yangtze River Basin of Central China. Full article

The collapse of surface goaf beneath highways can result in instability and damage to roadbeds. However, filling the goaf areas with foam concrete can significantly enhance the stability of the roadbeds while considerably reducing the costs of filling materials. This study analyzes the effects on destructive characteristics, mechanical properties, stress–strain curve features, and relevant metrics, while also observing the microstructure of basalt fiber-calcined gangue-silty clay foam concrete (BF-CCG-SCFC). The results indicate that the water–binder ratio significantly influences the cubic compressive strength, split tensile strength, and fluidity of BF-CCG-SCFC. Silty clay reduces the cubic compressive strength, split tensile strength, and fluidity of BF-CCG-SCFC. Conversely, an appropriate amount of calcined gangue and basalt fiber significantly increases the cubic compressive strength and split tensile strength, while decreasing fluidity. To satisfy the strength and fluidity requirements of the filler material in hollow areas, the optimal water–binder ratio for BF-CCG-SCFC is 0.55, the ideal mixing ratio of calcined gangue to silty clay is 2:2, and the basalt fiber content should be 1%. The study examines the influence of varying water–binder ratios, the combined proportions of calcined gangue and silty clay, and different basalt fiber contents on the elastic modulus, peak stress, and peak strain of BF-CCG-SCFC. Additionally, the water–binder ratio influences the matrix strength through the non-hydration reactions of doped particles, while gangue and clay induce a “gradient hydration effect” during the hydration process. The incorporation of basalt fibers enhances the mechanical interlocking between the fibers and the matrix. Full article

Using silty clay as roadbed filling can lead to roadbed diseases. In this paper, silty clay was modified with lignin and BFS (GGBS). Then, the mechanical properties, freeze-thaw characteristics, and microscopic mechanisms were investigated using unconfined compression tests, California bearing ratio tests, rebound modulus tests, freeze-thaw cycling tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that as the curing age increased, the unconfined compressive strength (UCS) of modified silty clay gradually increased, and the relationship between the stress and axial strain of the samples gradually transitioned from strain-softening to strain-hardening. As the lignin content decreased and the BFS content increased, the UCS, California bearing ratio (CBR), and rebound modulus of the modified silty clay first increased and then tended to stabilize. Adding lignin and BFS can effectively resist volume increase and mass loss during freeze-thaw cycles. When the ratio of lignin to BFS was 4%:8%, the growth rate of the UCS, CBR, and rebound modulus was the largest, the change rate in volume and mass and the loss rate of the UCS under the freeze-thaw cycle were the smallest, and the silty clay improvement effect was the most significant. The microscopic experimental results indicated that a large amount of hydrated calcium silicate products effectively increased the strength of interunit connections, filled soil pores, and reduced pore number and size. The research results can further improve the applicability of silty clay in roadbed engineering, protect the environment, and reduce the waste of resources. Full article

The construction of roads in saline soil areas usually involves using coarse-grained soil as roadbed fill material; studying the water–vapor–salt migration mechanism in coarse-grained saline soil subgrades is crucial for ensuring the stability of highway infrastructure. In order to clarify the influence of fines content and initial moisture on the water–salt migration and to clarify the water–vapor–salt migration patterns in coarse-grained saline soil, a model test of coarse-grained saline soil was conducted to study the response patterns of external water replenishment, final moisture content, final salt content, and liquid level height of coarse-grained saline soil. The results indicated that the water vapor migration amount only causes a change in the final moisture content, albeit not enough to cause salt redistribution. With increasing initial moisture content in coarse-grained saline soil, the migration characteristics of water vapor are weakened, and it imposes a significant inhibitory effect on liquid water migration at the same time. Increasing fines content in coarse-grained soil significantly inhibits water vapor migration, whereas liquid water migration is promoted. Water and salt accumulate in the liquid and vapor coupling migration mode at different heights. Based on the mechanisms of water vapor and salt transport characteristics, this study proposes a novel roadbed structure, which is vital for ensuring the long-term service performance of coarse-grained saline soil roadbeds in saline soil areas. Full article

In recent years, highway infrastructure in the Ningxia region of China has rapidly advanced. Cement–loess is extensively utilized in the roadbed and foundation reinforcement. It is necessary to conduct micro–macro-analysis and model derivation of the electrical resistivity on Ningxia cement–loess, which are beneficial for both the practical application of electrical resistivity and the evaluation of the geotechnical properties of cement–loess. Therefore, a series of electrical resistivity measurements, microstructural observations (scanning electron microscopy), mineral analyses (thermogravimetric analysis), and theoretical analyses were adopted on the cement–loess. The following conclusions can be drawn: The electrical resistivity is negatively related to dry density and water content, while it is positively related to cement dosage and curing age. A cement dosage of 6% exhibits a lower hydration reaction potential compared to 12%, causing a slower increase in electrical resistivity. The formation of calcium silicate gel around particles results in particle clustering and pore filling, reducing the pore area and increasing electrical resistivity. Increased hydration also decreases microscopic orientation, contributing to a higher electrical resistivity of cement–loess. Finally, a new three-dimensional electrical resistivity model was created, finding that the electrical resistivity of Ningxia cement–loess was determined by the dry density, water content (ρ_d·w), cement dosage, and curing age (a_w·T) in an exponential function form. The new three-dimensional electrical resistivity model could be used in the high-efficiency evaluation of the cement–loess geotechnical parameter, offering valuable insights for the monitoring and maintenance of road infrastructure. Full article

Saturated sand foundations are susceptible to liquefaction under dynamic loads. This can result in roadbed subsidence, flotation of underground structures, and other engineering failures. Compared with the traditional foundation reinforcement technology, enzyme-induced calcium carbonate precipitation technology (EICP) is a green environmental protection reinforcement technology. The EICP technology can use enzymes to induce calcium carbonate to cement soil particles and fill soil pores, thus effectively improving soil strength and inhibiting sand liquefaction damage. The study takes EICP-solidified standard sand as the research object and, through the dynamic triaxial test, analyzes the influence of different confining pressure (σ₃) cementation times (CT), cyclic stress ratio (CSR), dry density (ρ_d), and vibration frequency (f) on dynamic strength characteristics. Then, a modified dynamic strength model of EICP-solidified standard sand was established. The results show that, under the same confining pressure, the required vibration number for failure decreases with the increase in dynamic strength, and the dynamic strength increases with the rise in dry density. At the same number of cyclic vibrations, the greater the confining pressure and cementation times, the greater the dynamic strength. When the cementation times are constant, the dynamic strength of EICP-solidified sand decreases with the increase in the vibration number. When cementation times are 6, the dynamic strength of the specimens with CSR of 0.35 is 25.9% and 32.4% higher than those with CSR of 0.25 and 0.30, respectively. The predicted results show that the model can predict the measured values well, which fully verifies the applicability of the model. The research results can provide a reference for liquefaction prevention in sand foundations. Full article

Freeze–thaw cycling has a significant impact on the energy utilization and stability of roadbed fill. Given the good performance of basalt fiber (BF) and plant fiber (PF), a series of indoor tests are conducted on fiber-reinforced red clay (RC) specimens to analyze the shear strength, thermophysical, and microstructural changes and damage mechanisms of the RC under the freeze–thaw cycle–BF coupling, meanwhile, comparing the improvement effect of PF. The results indicate that the RC cohesion (c) first increases and then decreases with the increasing fiber content under BF improvement, reaching the maximum value at the content of 2%, and the change in the internal friction angle (φ) is relatively small. As the number of freeze–thaw cycles increases, cohesion (c) first decreases and then gradually stabilizes. The thermal conductivity increases with increasing moisture content, and the thermal effusivity increases and then decreases with increasing moisture content and fiber content. The heat storage capacity reaches the optimum level at a moisture content of 22.5% and a fiber content of 1%. Microanalysis reveals that at 2% fiber content, a fiber network structure is initially formed, and the gripping effect is optimal. The shear strength of PF-improved soil is higher than that of BF at a fiber content of 4–6%, and the thermal conductivity is better than that of BF. At the same fiber content, the heat storage and insulation capacity of BF-improved soil is significantly higher than that of PF. Full article

Investigating crack evolution characteristics in expansive soil under dry–wet cycle conditions is essential for analyzing the shallow instability of embankments and roadbeds filled with this type of soil. Indoor tests on remolded expansive soil specimens were performed under dry–wet cycle conditions, and digital image processing technology (PCAS) was used to quantitatively analyze the process of crack evolution. The study examined how initial moisture content, compaction degree, thickness, and expansibility affect crack development in expansive soil. Additionally, the study discussed the mechanism of crack evolution, considering the characteristics of crack structures in expansive soil. The findings suggest that crack development in expansive soil specimens is influenced by various factors including initial moisture content, compaction degree, thickness, and expansibility. The crack ratio increases with the initial moisture content, thickness, and expansibility, but decreases with the compaction degree. Furthermore, a significant linear relationship exists between the attenuation rate of soil strength and the crack ratio. The development of cracks is governed by the variance in soil shrinkage, which leads to the formation of distinct shrinkage centers at various locations and is markedly influenced by the soil’s thickness. This research explores the laws governing the evolution of cracks in expansive soils, elucidating the mechanisms by which these cracks evolve under the influence of various factors. It addresses a significant gap in the theoretical understanding of crack evolution in expansive soils under conditions of multiple influences, thereby offering crucial insights into the characteristics of soil evolution. Full article

Steel slag micronized powder, granulated blast furnace slag, and cement were used as cementitious materials to prepare a foamed lightweight soil for roadbed filling to reduce the settlement and additional stress of the foundation and to solve the environmental problems caused by the storage of large amounts of steel slag. However, the instability of steel slag and the multi-angular nature of its surface limit the resource utilization of steel slag. Currently, concrete technology is unable to achieve a large amount of steel slag. Therefore, it is necessary to deeply explore the influence of steel slag content and the specific surface area of steel slag on the working performance, compressive strength, durability, and micro-mechanism of foam light soil. Through the modification of steel slag and the improvement of the production process, the preparation of foam light soil with a large amount of steel slag can be realized. In this study, the foamed lightweight soil with 1.0 Mpa was prepared by cementitious materials composed of 40% cement and 60% multi-mixture of steel slag micronized powder and granulated blast furnace slag. The study of SEM images and BET demonstrated that the larger specific surface area of steel slag powder was more conducive to improving the durability of the foamed lightweight soil. Meanwhile, XRD analyses confirmed that the reactions of f-CaO and f-MgO in steel slag were slowly released in the porous foamed lightweight soil system, which compensated for the shrinkage properties of porous materials. When the SSMP content was 0%, the shrinkage rate was 2.34 × 10⁻³, while when the SSMP content was 60%, the shrinkage rate was only 0.54 × 10⁻³. Furthermore, our study of the hydration process of samples indicated that the strong alkalinity of steel slag micronized powder hydration was helpful to stimulate the potential activity of the slag powder, which was beneficial to the improvement of the compressive strength of foamed lightweight soil. Thus, this study provides a valuable idea for reducing the settlement and additional stress of the original foundation and for solving the environmental problems caused by a large amount of steel slag storage. Full article

Black shale, as a type of soft rock, exhibits high strength when freshly exposed. However, it easily disintegrates upon contact with water, making it unsuitable for direct use in roadbed construction. Using it as discarded material not only increases construction costs but also pollutes the environment. Therefore, the reuse and modification of black shale have become particularly important. Based on the theory of composite material equivalent inclusions, this study investigates the strength and water stability characteristics of black shale gravel after being mixed with cement and compacted with clay. The results show that the strength of cemented soil increases linearly with the cement content. The water absorption properties of the modified soils with different amounts of black shale added are similar, with an average water absorption rate of about 2.53%. The strength of black shale modified soil is generally positively correlated with the cement content, although the linear correlation is not significant. The modified black shale soil used in the experiment is suitable for the subgrade of medium- and light-grade secondary roads and below. The recommended mass ratio is M_shale:M_clay:M_cement = 70:21:9. The unconfined compressive strength of the material under 7-day curing is 1.36 MPa. The relationship between the strength of modified soil, clay strength, cement content, and gravel addition has been established, clarifying the physical significance of each parameter. The “drying and soaking” cycle can accelerate the strength degradation of modified soil. It is recommended to strengthen the construction of roadbed drainage facilities during construction to maintain a stable and dry environment for the modified soil as a roadbed filling material. The research results not only provide clear technical indicators for the reuse of discarded black shale in engineering but also serve as a basis for proportion of crushed stone discarded material as roadbed fill. Full article