Search Results (484)

In soft soil areas, cement–soil mixing piles are widely employed as a building foundation treatment measure, and their construction parameters directly influence pile uniformity and the stability of foundation reinforcement. However, visual and quantitative methods to verify on-site improvement effects are currently lacking. This study aimed to improve the mixing uniformity between jet media and soil layers and proposed a quantitative evaluation method based on numerical simulation and image recognition. Taking the silty soil in the Nansha area in Guangdong Province, China, as the research object, combined with flow tests and discrete element simulations, an experimental simulation based on a linear model of adhesive rolling resistance was established. First, the entire process of the wet water spraying soil mixing method and visualizing particle behavior was simulated. Based on the Danckwerts mixing index, image recognition technology was applied to quantify the uniformity of cement–soil mixing at different rotational speeds. The simulation results revealed that increasing the rotational speed within a certain range (0–100 r/min) significantly improved the uniformity of cement–soil mixing by 33.3%. However, increasing the rotational speed still further (100–200 r/min) resulted in only a 15.8% improvement. Furthermore, excessive rotational speed caused a significant loss of cement within the designed diameter of the pile. Second, based on the cement retention rate inside the pile, a speed balance range suitable for the working conditions of this study was obtained. A good balance was achieved between the effective cement content inside the pile and the uniformity of cement–soil mixing, further ensuring the consolidation effect of the cement–soil pile. Full article

High-speed railway embankments constructed over karst-prone ground conditions are often challenged by weak soils and subsurface cavities, which can lead to instability and excessive settlement. This study presents a full-scale field investigation conducted in the El-Gharbaniyat area, west of Alexandria, Egypt, where a pile–cap ground improvement system was implemented to support a high-speed railway embankment founded on clayey and silty soils overlying fractured limestone. A comprehensive site investigation program was performed, including 28 boreholes and integrated geophysical surveys using Electrical Resistivity Tomography (ERT) and Seismic Tomography (ST), enabling improved identification of weak zones and cavity-prone formations. Based on these findings, a pile–cap system was designed using reinforced concrete piles of 0.60 m diameter and an average length of 29 m, arranged in a 4 × 4 m grid and capped with reinforced concrete footings to ensure efficient load transfer to deeper competent strata. The system performance was validated through laboratory testing and full-scale in situ pile load tests. The average 28-day compressive strength of 122 tested piles reached approximately 50 MPa, exceeding the design value by approximately 30%. Load test results showed settlements ranging from 1.08 to 2.76 mm at the working load (2200 kN) and 2.16 to 5.10 mm at the maximum load (3300 kN), all well below allowable limits. Comparative evaluation indicated that the proposed system achieves significant material savings (>90%), lower treatment cost (150 USD/m²), reduced carbon emission (5.7 t per pile), and shorter construction duration (7 h per pile). These findings confirm that the pile–cap system provides a robust, cost-effective, and environmentally efficient solution for ground improvement in karst environments. Full article

Seasonal freeze–thaw cycling progressively rearranges pores and propagates microcracks in silty clay, reducing the reliability of cold-region earthworks. This study evaluated a bio–polymer stabilization strategy combining microbially induced carbonate precipitation (MICP) with anionic polyacrylamide (APAM) to improve mechanical performance and freeze–thaw durability. Six groups were prepared at identical moisture and compaction conditions: water, APAM, and four MICP–APAM groups with bacterial optical densities (OD600) of 0.8, 1.0, 1.2, and 1.4. Unconfined compressive strength, unconsolidated-undrained triaxial compression, ultrasonic pulse velocity, and SEM, TG/DTG, XRD, and FTIR analyses were conducted before and after freeze–thaw cycling. The M1.0-APAM group showed the best overall performance, with UCS values of 1.35 MPa before cycling and 0.89 MPa after nine cycles, together with high shear resistance and ultrasonic velocity. Lower bacterial concentration provided insufficient cementation, whereas higher concentrations promoted non-uniform carbonate deposition, pore heterogeneity, and local stress concentration. Microstructural evidence indicated that OD600 ≈ 1.0 produced a relatively homogeneous network of fine carbonate clusters and polymer-associated films, with calcite formation supported by TG/DTG and XRD. The results show that MICP–APAM treatment enhances silty clay primarily through coordinated mineralization uniformity, pore refinement, and polymer bridging, providing a sustainable stabilization option for seasonally frozen soils. Full article

Identifying soil nutrient limiting factors and fertilization effects in the irrigated silty soil region of Ningxia is key to improving wheat (Triticum aestivum L.) quality and yield. A field experiment was conducted with five treatments: conventional fertilization (TF), recommended fertilization (RF), nitrogen deficiency (RF-N), phosphorus deficiency (RF-P), and potassium deficiency (RF-K). The results showed that under RF, soil nutrients remained at relatively high levels, with no significant differences compared with TF. In contrast, RF-N significantly reduced soil mineral nitrogen, total nitrogen, and organic matter compared with TF, and inhibited plant growth, photosynthesis, and plant accumulation of nitrogen, phosphorus, and potassium. Wheat yields under RF and RF-K showed no significant differences from those under TF, whereas RF-N and RF-P significantly reduced yields by 42.68% and 22.69%, respectively, relative to RF, mainly due to decreases in spike length and grain number per spike. The increase in yield was associated with synergistic increases in grain number per spike, spike number per hectare, and spike length. Yield components were significantly positively correlated with soil organic matter, total phosphorus, and mineral nitrogen, with soil total phosphorus identified as the environmental factor most strongly associated with wheat yield. Grain protein content was significantly positively correlated with soil mineral nitrogen, while starch content was significantly negatively correlated, indicating that mineral nitrogen is a key factor regulating grain quality. In summary, nitrogen fertilizer is the primary limiting factor in this region. Applying nitrogen, phosphorus, and potassium together synergistically enhances wheat yield by increasing soil total phosphorus levels and improves grain quality by regulating soil mineral nitrogen. Thus, this combined fertilization strategy provides a foundation for precise nutrient management and the simultaneous improvement of both yield and quality. Full article

As a result of long-term groundwater overexploitation, the thickness of the vadose zone in the NCP has significantly increased, leading to changes in moisture transport patterns and groundwater recharge processes. This research gathers data on soil water potential and moisture content by conducting in situ profile monitoring of a 30.4 m thick vadose zone. A 44.5 m geological borehole was drilled for the purpose of measuring the hydraulic parameters of undisturbed soil samples, collecting ³⁶Cl isotope tracer samples, and constructing a coupling model of the unsaturated–saturated zone with a depth of 47 m. The research objectives were to examine the moisture transport law and infiltration recharge mechanisms in deep vadose zones. Comprehensive analysis shows that the average infiltration velocity is 0.661–0.743 m/a and the average recharge intensity is 103.1–115.9 mm/a. The depth and silty clay play an important role in affecting the infiltration process. The characteristics of infiltration can be divided into three segments: rapid, slow, and stagnant. The residual pore gases in the clay strata have a certain inhibitory effect on moisture transport. The time required for precipitation infiltration is 75.14 years for a 44.5 m thick vadose zone; thereafter, new water replaces old water to continue recharging the aquifer. In recent years, the government has taken multiple actions to alleviate this continuous downward trend in groundwater levels, including river ecological flow replenishment and groundwater extraction reduction. Additionally, increased precipitation since 2021 has objectively halted the previous thickening trend of the vadose zone. It is recommended to further strengthen groundwater resource management and enhance groundwater-level monitoring and warning to prevent further declines. This research holds significant implications for the evaluation and sustainable management of groundwater resources in large-scale plains in semi-humid areas. Full article

Rice (Oryza sativa L.) straw-return can improve soil carbon (C) sequestration, but its adoption in intensive rice systems is limited by short fallow periods (<30 days), which likely lead to incomplete straw decomposition and increase methane emissions under continuous flooding (CF). Brittle rice straw, characterized by lower recalcitrant fiber content and rapid decomposition, may overcome this constraint; however, its environmental performance under alternate wetting and drying (AWD) remains unclear, such as broader C allocation. This 150-day microcosm study evaluated the interaction of straw type (brittle vs. non-brittle) and water management (CF vs. AWD) on greenhouse gas (GHG) emissions, dissolved C production, soil C storage, and aggregate formation in two contrasting paddy soils (sandy loam vs. silty clay loam). Compared with non-brittle straw, brittle straw returns reduced net GHG emissions by approximately 28.4% under CF and 39.6% under AWD. The combination of brittle straw with AWD produced the lowest net GHG emissions (0.61 kg CO₂-eq m⁻²), indicating that intermittent oxygen input effectively mitigated the early decomposition-related emission risk. Brittle straw also increased the concentrations of dissolved inorganic C by 14.2% and nitrate by 64.3% under AWD, suggesting enhanced mineralization and potential inorganic C stabilization. Regardless of straw type, straw return improved soil C stocks by 27.3% in sandy loam and 29.6% in silty clay loam, while also promoting macroaggregate formation. Overall, this study demonstrated that coupling brittle rice straw with AWD can reduce GHG emissions while maintaining soil C benefits, offering a promising residue management strategy for intensive rice cultivation. Full article

Stabilizing weak soils is a well-known pavement and geotechnical engineering technique. This technique involves introducing minimal cementitious materials to improve the soil’s geotechnical characteristics. This paper investigates the use of recycled industrial polymer waste (IPW) as a reinforcement material in the presence of cementitious binders to stabilize weak silty sand soil (SM), supporting sustainable engineering practices. The randomly distributed IPW were added as percentages of 0%, 5%, and 10% to a mixture of lime soil and cement soil, with varying amounts of 0% to 6% of lime (L) and 0% to 6% of ordinary Portland cement (OPC), respectively. The laboratory experiments were conducted on natural and stabilized samples in wet (unsoaked) and submerged (soaked) conditions. The experimental program included Proctor compaction, California bearing ratio (CBR), unconfined compressive strength (UCS), durability tests, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction analyses. The resilient modulus (Mr) was estimated using an empirical equation. The outcomes of this experimental study show that adding a combination of IPW shreds with a small amount of L and/or OPC to the SM soil provides a significant increase in the UCS, CBR, durability and Mr values compared with case of SM with only L, which allows for superior characteristics and increases strength and stiffness parameters throughout any phase of earthwork construction design, resulting in stronger and stiffer subgrades. These results were reinforced by microstructural observations from SEM, EDS, and DRX, confirming the formation of cementitious gels and chemical compounds, consistent with the macro-scale mechanical improvements. The expected practical outcomes include potential reductions in pavement thickness, which can help lower pavement stabilization costs and extend its service life. Additionally, the use of waste materials to replace raw materials contributes to decreased energy consumption and emissions, although detailed assessments are needed to quantify these effects. Full article

Structural and functional soil degradation under conventional tillage has reached a critical point, requiring a shift towards conservation practices to mitigate the negative effects of climate change. This study evaluated the multi-year effects (2021–2024) of conventional tillage (CT), conservation deep tillage (CD), and conservation shallow tillage (CS) on soil physical properties (density, air capacity, and water content), water distribution, infiltration rate, and maize yield in a silty Gleysol. Soil water content (SWC), i.e., distribution, was monitored using PR2 profile probes at depths of 10, 20, 30, and 40 cm. CT treatment resulted in impaired soil physical properties, characterized by a significant increase in air capacity (+233.9%) and with a significant decrease in volumetric water content (qw, ≈40%). In contrast to CT (47.91 cm h⁻¹), the CS treatment resulted in more favorable hydraulic properties, i.e., and infiltration rate of 102.29 cm h⁻¹, by 2024. Statistical analysis (R², RMSE) confirmed that CS provides the most reliable and consistent environment for monitoring SWC. While maize yields were significantly higher in CT during the initial year (2021; 9.5 t ha⁻¹ vs. 8.4 t ha⁻¹ in CS), no significant differences were observed by 2024, and all tillage systems reached yields of ≈13.0 t ha⁻¹. The results suggest that after the four-year study period, CS tillage stabilized soil hydraulic properties and pore continuity, thereby resulting in maize yields equivalent to those of CT. Therefore, CS has proven to be a more resilient and effective strategy for sustainable water management in silty Gleysols. Full article

The aim of this research was to evaluate the efficacy of water-soluble epoxy resin (ER) in regard to stabilising clay soils, specifically for the design of column-type reinforcement in soft ground. An extensive laboratory program was conducted to assess the mechanical enhancement of a silty clay soil via ER, both as a standalone stabiliser and in combination with cement, bentonite, and sodium polyacrylate (PA). In addition, the study investigated the impacts of thermal stabilisation and electro-osmotic dewatering on resin–soil specimens. Specimens stabilised solely with ER exhibited poor strength development due to the inhibition of polymerisation by water. The addition of bentonite at low concentrations resulted in low early strength development and a moderate increase in the final strength. The use of cement provided the most significant strength gains, which were further enhanced by optimising the dosage of PA, although an excessive PA content significantly reduced the strength properties. In terms of physical treatments, thermal stabilisation at an optimal temperature of 60 °C for 24 h substantially improved the performance of ER. Electro-osmotic treatment accelerated the development of early strength but failed to provide appreciable strength improvement, and resulted in brittle behaviour and reduced toughness in the later stages (90–180 days). These findings offer critical guidelines for optimising mix designs and treatment protocols for geotechnical ground improvement projects. Full article

High water-content silty soft soils are widely distributed across coastal regions. Their low strength and high compressibility render them unsuitable for direct use as foundation or subgrade materials. While ordinary Portland cement is the most prevalent chemical stabilizer for ground improvement, its manufacturing process generates substantial CO₂ emissions, significantly exacerbating global climate change. While limestone calcined clay cement (LC³) has emerged as a promising low-carbon alternative in concrete engineering, its multicomponent hydration mechanisms and engineering applicability for geotechnical soft soil stabilization remain a critical knowledge gap. To address this, this study investigates the application of LC³ in ground improvement by systematically evaluating and comparing three novel LC³ blends formulated with distinct types of calcined clay. The mechanical properties of LC³-stabilized soft soil were investigated through unconfined compressive strength and direct shear tests. Furthermore, the underlying stabilization mechanisms and microstructural evolution were revealed using X-ray diffraction and supplementary microanalytical techniques. The results demonstrated that LC³ significantly enhanced the mechanical properties of soft soils by generating abundant C-S-H and C-A-S-H gels, which bound soil particles into a stable, interlocking network. Among the evaluate variants, the calcined kaolin-based cement (LC³-K) exhibited the highest pozzolanic activity, providing to be the optimal stabilizer. However, this stabilization effect was dosage dependent; while an appropriate LC³ application markedly improved soil strength, excessive dosage or elevated clinker proportions induced a highly alkaline environment. This led to charge over-neutralization and deflocculation, ultimately compromising the structural integrity and mechanical performance of the solidified soil. The findings of this study provide a solid theoretical foundation for the application of eco-friendly LC³ in soft soil stabilization, promoting the broader adoption of sustainable, low carbon geomaterials in geotechnical engineering. Full article

This study explains how an extremely low electrical earthing resistance was achieved in challenging gravelly soil conditions. In the existing soil, a resistance of 5 ohms was measured using traditional earthing techniques. After excavating and removing the granular soil, it was replaced with fine-grained, sandy-silty clay, then compacted after moistening, reducing earthing resistance to 2.5 ohms. The goal was to achieve a resistance below 0.5 ohms, which is necessary for the precise operation of robotic welding machines. To achieve this, a hybrid strategy was employed, combining deep earthing by drilling with ground-enhancing compounds in the gravelly soil. In İzmir-Torbalı, a 40 m-deep borehole was drilled to install a copper electrode in water-saturated clay below the groundwater level. To increase the conductivity of the granular soil and ensure contact with the electrode, the borehole was filled with graphite powder. As a result, the earthing resistance reached only 0.28 ohms, proving the effectiveness of this method in high-resistance soils. Full article

Solid-waste-based cementitious materials have been widely applied in soil stabilization. However, their durability in practical engineering applications remains inadequate, which may lead to performance degradation and challenges for long-term serviceability. In this study, the durability of solid waste-based cementitious materials (CSD)-solidified soil was improved by adding RL and polypropylene fibers (PP). The research results indicate that the addition of RL hinders the ingress of water into the sample, which is beneficial for improving the water stability and resistance to dry–wet cycles of CSD solidified soil. The addition of PP can suppress crack propagation and effectively enhance the freeze–thaw cycle resistance of solidified soil. When the dosage of RL and PP is both 0.2%, CSD-RP solidified soil exhibits excellent durability performance. After 28 days, the water stability coefficient reached 82.8%, representing a 9.5% increase compared to the control group. After undergoing dry–wet and freeze–thaw cycles, the strength loss of the samples was 36.7% and 47.3%, which was 8.6% and 10.5% lower than that of the control group. Microscopic test results show that cyclic failure promotes the formation of pores and cracks in the sample, while the hydration products generated by the reaction of cementitious materials densify the soil. Compared with the control group, the total porosity of CSD-RP samples decreased by 2.45% and 2.19% after wet–dry and freeze–thaw cycles, further indicating that co doping of RL and PP is beneficial for reducing the degree of structural degradation of the samples. Full article

Although adding phosphorus (P) and zinc (Zn) fertilizers to rhizobial inoculation improves nutrient accumulation in chickpeas, it is unclear which is most effective. This study evaluated whether inoculating chickpeas grown in silty-loam or silty-clay-loam soil with liquid- or peat-based rhizobial inoculants, in addition to P and/or Zn fertilizer, alters shoot nutrient concentration. The following genotypes were used: ICCV3110, ICCV8101, ICCV97024 and ICCV92944. The following levels of fertilizer were used: no addition of fertilizer, 10 kg/ha Zn, 40 kg/ha P, and Zn plus P. The following combinations of fertilizer and rhizobial inoculation were used: Zn plus P (peat-based inoculant), denoted as Zn + P + R_P, and Zn plus P (liquid-based inoculant), denoted as Zn + P + R_L. Our results showed that ICCV97024 exhibited increased shoot P, Ca, Mg, Fe and Zn concentrations when grown in silty-loam soil and increased shoot Ca, Zn, Mn and B concentrations when grown in silty-clay-loam soil. Adding P, or P plus Zn, increased shoot P, while adding Zn, or Zn plus P + R_L, enhanced shoot P, Fe and B. Adding Zn increased shoot Zn, K and Ca, and adding Zn plus P + RP increased shoot Ca. Overall, chickpeas grown in silty-loam soil accumulated the most nutrients. Adding P, P plus Zn and Zn + P + R_L improved shoot P, while adding Zn and Zn + P + R_P enhanced shoot Zn and Ca, respectively. Full article

Water-induced deterioration of silty soil subgrade in the lower Yellow River floodplain poses a critical, long-standing engineering challenge. Most existing studies on silty soil modification prioritize strength enhancement via traditional cementitious binders (i.e., cement, lime), yet these strategies fail to fundamentally block water migration in the soil matrix. A distinct scientific gap persists: the capillary water inhibition mechanism of nano-superhydrophobic modified Yellow River alluvial silt, along with the correlation between its microstructural evolution and macroscopic engineering performance, has yet to be systematically elucidated. To fill this gap, we conducted hydrophobic modification of the targeted silt using a nano-superhydrophobic material (NSHM), and performed a systematic suite of laboratory tests to characterize its hydrophobicity, mechanical properties, water stability, and microstructural characteristics. Quantitative experimental results demonstrate that NSHM imparts remarkable water resistance to the silt: at an NSHM dosage ≥0.5%, the modified soil exhibits stable superhydrophobicity across all tested compaction degrees, with over a 99% reduction in saturated hydraulic conductivity. Notably, the hydrophobic modification only incurs a <12% reduction in the dry unconfined compressive strength (UCS) of the silt. Microscopic characterization results reveal that NSHM modifies the silt via two core pathways: uniform particle encapsulation and pore infilling, without altering the inherent mineral functional groups of the soil. This microstructural regulation reduces the average pore diameter by 38.2% and total porosity by 15.6%, while optimizing the uniformity of pore size distribution. Based on comprehensive evaluation of overall performance, a minimum NSHM dosage of 0.5% is recommended for in situ application in local silty soil subgrade. This study provides critical theoretical guidance and technical support for water damage mitigation in alluvial silty soil subgrade. Full article

Soil thermal conductivity is a key parameter in modeling heat transfer, temperature-driven moisture migration, artificial ground freezing, and geothermal systems. However, most existing thermal-conductivity models do not account for temperature effects. This study aims to determine the temperature-dependent thermal conductivity of silty and fine sandy soils at elevated temperatures using a steady-state heat cell method, addressing the limitations of transient probe techniques, which are affected by air voids and heat loss at the needle–soil interface. The experiment employs a heat cell under one-dimensional steady-state heat-transfer conditions, with sufficiently small temperature gradients to prevent temperature-induced moisture migration, and measures the soil’s thermal properties at steady state by indirect temperature and heat-flux measurements using various sensors. The test observations showed well-correlated thermal conductivity readings from steady state and transient probe methods at room temperature. Furthermore, the measured thermal conductivity of the sandy soil demonstrated a near-linear increase with temperature, with the highest dependence at 15.1% and 22.5% saturation for Benbrook (SM) and fine-grained Ottawa (SP) sands, respectively. Several commonly used existing thermal conductivity models were used to fit the measured thermal conductivity. A new thermal conductivity model was developed, incorporating a temperature-dependent correction based on the best-fit model. The proposed model could more accurately capture the increased thermal conductivity of soils with temperature. The findings will significantly improve the modeling of soil-temperature-dependent multi-physics behavior. Full article