This paper aims to investigate the tunnelling stability of underwater slurry pressure balance (SPB) shields and the formation and evolution mechanisms of ground collapse following face instability. A laboratory SPB shield machine was employed to simulate the entire tunnelling process. Multi-faceted monitoring revealed the responses of soil pressure, pore water pressure, and surface subsidence during both stable and unstable phases. The morphological evolution characteristics of surface collapse pits were analyzed using three-dimensional scanning technology. The experimental results indicate that: (1) The key to stable tunnelling is balancing the pressure in the slurry chamber with the tunnelling speed, which ensures the formation of a filter cake in front of the cutterhead. (2) The torque of the cutterhead, soil pressure, and surface subsidence respond significantly and synchronously when the tunnel face becomes unstable, while the soil and water pressures are relatively less noticeable. (3) Excavation disturbance results in a gentler angle of repose and a wider range of collapse in the longitudinal direction of the collapsed pit. (4) A formula for predicting the duration of collapse is proposed, which effectively integrates the evolution patterns of the collapse pit and has been well-validated through comparison with the experimental results. This study provides a reference for the safe construction of tunnel engineering in saturated sand.

Freeze-thaw cycles pose a serious threat to the protection and preservation of earthen sites. To investigate the effects of freeze-thaw cycles on the shear strength and permeability of site soil, this study took artificially prepared site soil as the research object. Through triaxial shear tests and permeability tests, the strength and permeability characteristics of site soil under different sticky rice slurry content, sticky rice slurry density and freeze-thaw cycles were analyzed. In addition, the mineral composition, chemical structure, and microstructural characteristics of the samples were investigated by combining X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) tests. The results showed that the addition of sticky rice slurry could increase the shear strength and decrease the permeability coefficient of the soil, while the opposite effect was exhibited after freeze-thaw cycle. The optimum ratio of loess to sticky rice slurry was 95:5, and the optimum density of sticky rice slurry was 1.04 g/cm3. The addition of sticky rice slurry and the increase in the number of freeze-thaw cycles did not significantly change the mineral composition of the soil. The SEM results showed that the morphology and arrangement of soil particles became complex after freeze-thaw cycle, the inter-particle connections became loose, and the pore morphology became irregular. The surface porosity of the soil increased, and the proportion of large and medium pores increased. The directionality of the pores was enhanced, and the complexity of the pores increased. The pore arrangement became relatively stable after 15 freeze-thaw cycles. These findings can provide a reference for the restoration of ancient sites in loess areas.

The stability of soil in high-altitude regions is significantly affected by freeze-thaw cycles, which alter its mechanical and physical properties. This study investigates the impact of 12 consecutive freeze-thaw cycles on poorly graded sandy-silt soil collected from Arunachal Pradesh. To enhance soil resistance, a bio-slurry containing urea (60 g/L) and calcium chloride (111 g/L), along with vetiver and bamboo fibers (by soil weight), was introduced as a stabilizing agent. The durability of the treated soil was evaluated by measuring the weight fluctuations after each cycle and assessing unconfined compressive strength (UCS) after 5, 10, and 12 cycles. The results revealed that untreated soil experienced a 50% reduction in UCS, while bioslurry-treated soil retained 70-80% of its original strength after 12 freeze-thaw cycles. The greatest strength retention was observed in soil treated with bioslurry and bamboo fiber, which retained 80% of its strength, followed by vetiver-treated soil at 75% strength retention. Weight loss measurements indicated that untreated soil samples lost 9.5% of their initial mass, whereas bioslurry-treated samples exhibited only a 3-5% weight loss. The findings of the study highlight the potential of bioslurry and natural fibers in mitigating freeze-thaw-induced soil degradation, making them suitable for applications in geotechnical engineering in cold-climate regions.

This study addresses the cracking issue of airport foundations in marine and coastal regions by proposing an unsaturated reinforcement method based on Microbially Induced Calcium Carbonate Precipitation (MICP) combined with coconut fibers. Composite sand columns incorporating coconut fiber and bioslurry were prepared, and the effects of fiber length and content on the mechanical properties of MICP-treated sand columns were investigated. Experimental results revealed that the addition of short fibers (1-5 mm) significantly improved the unconfined compressive strength and ductility of the MICP-treated sand columns. As the bioslurry content decreases in the sand columns, the enhancement effect of short fibers on the unconfined compressive strength becomes more pronounced, with fiber addition improving compressive strength by up to 98 %. However, the inclusion of medium fibers (5-10 mm) and long fibers (10-15 mm) negatively affected the mechanical properties of the sand columns. Microstructural analysis further confirmed the synergistic reinforcement effect of short fibers and calcium carbonate precipitation. Short fibers acted as bridges, forming additional contact points between sand particles, which facilitated calcium carbonate precipitation at critical contact points, thereby enhancing the overall stability and strength of the sand columns. This characteristic was more pronounced under unsaturated conditions. This study provides a feasible technical solution for the effective reinforcement of airport foundations and demonstrates potential in unsaturated reinforcement and improving the ductility of sandy soil foundations.

The physicochemical combination method (PCCM) is a new integrated method for treating and reusing large volumes of slurry-like mud (MS). To study the effects of freezing-thawing (FT) cycles on the mechanical properties of MS treated by the PCCM, unconfined compression tests (UCTs) and microstructural tests are both conducted on PCCM-treated MS samples with different combinations of FT cycles, initial water contents (wei), and cementitious binder contents (wc). The experimental results indicate that the unconfined compressive strength (UCS) and the elastic modulus (E) of PCCM-treated MS decrease exponentially when the FT cycles increase from 0 to 15. For the PCCM-treated MS samples subjected to 15 FT cycles, the reduction degree of their strength, as well as deformation resistance, is more sensitive to the variation of wc compared to that of wei. Meanwhile, the UCS and E of PCCM-treated MS samples are higher than those of the corresponding MS samples treated by the conventional cement solidification method (CCSM). The superior resistance to FT cycles of PCCM-treated MS is attributed to the presence of APAM, which not only facilitates the aggregation of soil particles but also enhances the dewatering efficiency of MS. Notably, the E/UCS value of CCSM-treated MS is 1.25 times larger than that of PCCM-treated MS, indicating the application of PCCM can significantly enhance the toughness of the treated MS.

This investigation focused on the cementation mechanisms and mechanical properties of soil-rock mixtures-slurry cement (SRM-SC) to ensure the safety of tunnels during operation. SRM-SC specimens were prepared with different types of slurry and rock contents based on an actual slurry injection ratio. The macroscopic level analysis involved measuring the specimens' uniaxial compressive strength and shear strength, determining the strength parameters, and analyzing the damage forms. At the microscopic level, the surface morphology and composition of the specimens were examined using scanning electron microscope imaging. This allowed for a comparative analysis of the cementation ability and mechanism of the slurry under different control conditions, providing a basis for determining the mechanical properties of SRM-SC. The results indicated that the rock content significantly impacts the macromechanical properties of SRM-SC. The compressive strength and stiffness of SRM-SC initially increase and then decrease with the increasing rock content, with an inflection point observed between a 20% and 60% rock content. On the other hand, the shear strength and stiffness both increase with the increasing rock content. Additionally, the macroscopic mechanical properties of SRM-SC formed by different types of grout exhibit noticeable differences. These findings serve as a reference for regulating the mechanical properties of SRM-SC.

This study investigated the rheological and compression-permeability attributes of dredged slurry reinforced using waste rice straws. Recognizing the potential of natural waste fibers in geotechnical applications, this study aimed to elucidate the effects of fiber length and pretreatment processes on the relocation dynamics of the cemented slurry. A series of laboratory evaluations were conducted to gauge critical parameters such as flow consistency, viscosity, one-dimensional compression, and hydraulic conductivity. Results indicated that straw lengths greater than 0.075 mm significantly increased slurry slump flow due to altered surface area and water adsorption. Dynamic viscosity decreased with increasing straw length, yet overall performance improved with straw inclusion. The influence of immersing straws in pure water emerged as a determinant in the study. A 24-h pretreatment duration influenced the flowability, viscosity, and the structural integrity of the fibers. Based on the observations, the study deduces that straw powder finer than 0.075 mm, subjected to a 24-h immersion in pure water, optimally bolsters the flow properties of cemented waste slurry. While the benefits associated with elongated straw fibers necessitate exploration and validation, this work underscores the potential of rice straw as a sustainable reinforcement material in geotechnical endeavors, promoting waste recycling and reducing environmental impact.

Soil structural stability is fundamentally linked to soil functionality and sustainable productivity. Rheological properties describe the deformation and flow behavior of soil under external stress, playing a crucial role in understanding soil structure stability. Despite their importance, the studies about rheological properties of black soils in Northeast China remain limited. This study aims to assess the rheological properties of two kinds of black soil with different degrees of degradation in Northeast China. The rheological parameters of these soils under various water contents and shearing were quantified by conducting Amplitude Sweep Tests (ASTs) and Rotational Sweep Tests (RSTs). Both AST and RST results showed that as soil water content and shear rate increased, shear strength, viscosity, and hysteresis area all decreased in Keshan and Binxian black soils. The increase in soil water content reduces the friction between soil particles, leading to a decrease in soil structure stability. Additionally, the viscosity and hysteresis area of the two soils decreased with the increase in water content, making it more flowable and exhibiting shear-thinning behavior. Keshan black soil exhibited stronger recovery and shear strength compared to Binxian black soil; this is mainly due to the higher organic matter content in Keshan soil, which could increase structural stability by bonding the soil particles at the micro-level. These findings enhance our understanding about the structure stability of the black soils based on the rheological parameters via rheometer.

Sandy soils are prone to engineering issues due to their high permeability and low cohesion in the natural environment. Therefore, eco-friendly reinforcement techniques are required for projects such as subgrade filling and soft soil foundation reinforcement to enhance their performance. This study proposes a synergistic reinforcement method that combines Enzyme-Induced Calcium Carbonate Precipitation with Glutinous rice slurry (G-EICP). The macroscopic mechanical properties and pore structure evolution of reinforced sand were systematically investigated through triaxial permeability tests, unconfined compressive strength (UCS) tests, and microstructural characterization based on Scanning Electron Microscope (SEM) and Micro- Computed Tomography (CT) tests. The results indicate that when the glutinous rice slurry volume ratio (VG) reaches 10%, the UCS of G-EICP-reinforced soil peaks at 449.2 kPa. The permeability coefficient decreases significantly with increasing relative density (Dr), VG, confining pressure (sigma 3), and seepage pressure (p). Microstructural analysis reveals that glutinous rice slurry may promote calcium carbonate crystal growth, potentially by providing nucleation sites, establishing a dual mechanism of skeleton enhancement and pore-throat clogging. The increased incorporation of glutinous rice slurry reduces the number of connected pores, lowers the coordination number, and elevates tortuosity, thereby inducing marked enhancements in both the strength and permeability of the treated soil compared to plain soil.

This study evaluates the potential of using rice straw waste as a sustainable alternative for managing the dredge sediment. The rice straw was used to reinforce the dredge slurry to realize treating the wastes with wastes. The dredge slurry could be relocated with altered rheological properties or reclaimed cultivable land by in-situ management. In this framework, the rheological and fertility properties of straw-reinforced dredge slurry were investigated with a 90-day degradation period. The increased liquid limit and fine content were observed regardless of the straw content and degradation time, and a decreased slump flow and increased dynamic viscosity were obtained after the addition of straw. Nutrients, including SOC, TN, P, and K, increase over time after straw reinforcement, suggesting effective land reclamation by straw blending. The increases were abrupt in the first 14 days, followed by a gently increasing rate. Soil pH decreases over time to the range more suitable for planting. Results suggest that effective straw reinforcement alters the rheological properties beneficial for vehicle transportation and improves the soil fertility for in-situ tillage. This study supplements the societal image of dredge materials and waste straws in engineering and environmental applications.