Abstract The artificial ground freezing (AGF) method has been widely used in underground engineering to improve the stability and water tightness of water-rich weak ground. In projects with radial or inclined freezing pipe arrangements, the resulting deformation is strongly three-dimensional and direction-dependent, which may threaten adjacent tunnels, underground structures, and ground surface stability if it is not accurately predicted and controlled. To support deformation assessment in AGF engineering, this study develops a three-dimensional thermomechanical coupled numerical model for simulating frost heave deformation under complex freezing pipe layouts. The model incorporates the soil ice–water phase transition, convective heat transfer at the ground and structural surfaces, and orthotropic frost heave deformation associated with the heat-flow direction. In this framework, the frost heave ratio is introduced as an equivalent thermal strain, and an orthotropic deformation coefficient is used to characterize the difference between frost heave parallel and perpendicular to the heat-flow direction. A frost heave subroutine is implemented to update the temperature field, heat-flow direction, and frost heave strain during the freezing process. The proposed method is validated using field-monitored temperature and displacement data from a metro cross-passage freezing project. The results show that the model accurately reproduces the spatiotemporal evolution of the ground temperature field and effectively captures the orthotropic characteristics of frost heave. Compared with the isotropic frost heave assumption, the proposed method reduces the prediction error of ground surface uplift deformation from 17%–25% to <10%. The slightly conservative displacement predictions provide a reliable basis for safety-oriented frost heave control in AGF engineering.
Abstract This study investigates the feasibility of additively constructed concrete (ACC) under sustained subfreezing conditions (−20°C), an environment that has been largely unaddressed in the existing literature. A gantry-based ACC system was developed within a temperature-controlled enclosure, alongside a cold-weather cementitious formulation (LC-CW) using conventional materials and chemical admixtures to promote early hydration. A brief early-age heating regimen was applied after an initial 6-h subfreezing period to counter the strength suppression observed under sustained −20°C curing, after which curing proceeded at −20°C without further thermal intervention. Fresh-state evaluation confirmed that LC-CW retained approximately 84% of its initial slump flow after 60 min while achieving sufficient early-age structural buildup for continuous layer stacking. The heating regimen increased the 1-day compressive strength to 34.6 MPa and enabled the material to reach the 3.5-MPa frost-protection threshold at approximately 12 h. Laboratory-cast specimens exceeded long-term strength targets, and field-extracted cores reached higher strengths (79.6 MPa at 28 days) owing to increased thermal mass. Interlayer bond strength averaged 2.3 MPa, with a substantial portion of specimens failing in the bulk material rather than at the interface, and no mass loss or surface deterioration occurred after 300 freeze–thaw cycles. Full-scale validation was completed by printing a 1.8-m-tall wall under continuous exposure at −20°C. These results demonstrate the feasibility of ACC using conventional construction materials in extreme cold environments, broadening its applicability for cold-region and remote construction.
Abstract As a widely distributed type of degraded land, saline soils form and evolve through interactions among natural factors and human activities. Saline soil improvement technology has emerged as a core tool for land degradation management due to its multidimensional benefits, including increased agricultural yield, engineering stabilization, and ecological restoration. This paper systematically summarizes four types of improvement technologies (physical solidification, chemical improvement, bioremediation, and synergistic improvement) and the progress of their application in saline soil management. It comprehensively analyzes the mechanisms of improvement (salt washing, ion exchange, and microbial action) and the key influencing factors (soil type, climatic conditions, and amendment compounding). Additionally, the environmental risks (chemical residues from improvements, risk of biological invasion) associated with the implementation of the technology are highlighted. It has been found that physical solidification is suitable for rapid salt reduction in coastal saline soil, whereas chemical improvement is effective for inland sulfate saline soil. Bioremediation can achieve long-term stabilization of saline soil in arid regions, and synergistic improvement technologies (physical–chemical–biological combinations) demonstrate comprehensive advantages for composite saline soil. However, the large-scale application of existing technologies is still constrained by challenges such as long-term effectiveness verification, analysis of multifactor coupling mechanisms, and management of high-salt, heavy-metal composite pollution. This paper aims to provide theoretical support for the precise application and sustainable development of saline soil improvement technologies.
Recently, ice accretion on bridge stay cables has frequently occurred, posing serious safety hazards to pedestrians and vehicles. Current research on factors influencing ice accretion on stay cables primarily focuses on ambient temperature, wind speed, cable diameter, and inclination angle. However, there has been limited investigation into key factors such as wind direction and surface roughness of stay cables. Therefore, in this study, icing tests on stay cables were conducted to explore the impact of these factors on ice accretion of stay cable surfaces. The effects of wind direction and surface roughness on ice accretion at both sides of the cable surface were systematically investigated. The results indicate that wind conditions and surface roughness significantly influence the ice accretion of stay cables. Under parallel wind (where the wind direction is parallel to the ground projection of the cable axis), the average ice rib width, unit number of icicles, and maximum icicle length of the stay cables are 6.92-8.51 mm, 3.5-5.5 icicles/m, and 84-157 mm, respectively. These values all exceed those under perpendicular wind (where the wind direction is perpendicular to the ground projection of the cable axis), which are 6.04-7.05 mm, 0.5-3.5 icicles/m, and 35-47 mm, respectively. All icing parameters increase with wind speed. Ice distribution shows significant asymmetry between Sides A and B under perpendicular wind but is uniform under parallel wind. When the surface roughness parameter (Ra) is increased from Ra1 = 1.6 mu m to Ra4 = 6.4 mu m, the average ice rib width growth rate reached 37.0%-63.6% for cables with helical fillets and 17.3%-44.7% for those without. Cables with helical fillets exhibit a larger total ice accretion mass despite a lower growth rate (31.0%-61.1% versus 53.0%-143.2%). The study demonstrates that parallel wind, higher wind speed, increased roughness, and helical fillets all promote ice accretion on stay cables.
Fly ash-based geopolymers are considered sustainable binders for soil stabilization, but their curing behavior and effectiveness in subzero environments remain inadequately studied. In this study, loess was stabilized with fly ash at five different contents and three particle sizes, compacted, and cured at -10 degrees C for up to 28 days. The physical, mechanical, and microstructural properties were comprehensively evaluated using strength, surface, chemical, and microanalysis tests. The results showed that higher fly ash content and finer particle size significantly increased the compactness of geopolymer-stabilized loess under subzero curing conditions. When the fly ash content reached 20% and the particle size was < 4 & micro;m, the surface hardness increased by 45% and the ultrasonic wave velocity nearly doubled. The decreases in pH and electrical conductivity indicated progressive geopolymerization, which proceeded faster with finer particles. Strength properties also improved significantly, with the 28-day unconfined compressive strength and splitting tensile strength reaching 1.02 MPa and 52 kPa, about 2.6 and 5 times higher than those of the untreated soil, respectively. Thermogravimetric analysis results showed greater thermal stability in samples with higher fly ash content and finer particles. Meanwhile, mercury intrusion porosimetry revealed that the dominant pore diameter decreased from about 10 to 2 & micro;m, indicating the formation of a denser, more tightly bonded soil structure. These results demonstrate that adding 15%-20% finer fly ash can effectively solidify loess at -10 degrees C, providing a practical and sustainable solution for winter construction in cold regions.
