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.

Effective erosion mitigation in the Pisha sandstone region is crucial for soil and water conservation in the Yellow River Basin, yet existing vegetation measures are inadequate in water-limited environments. This study examines the application of drought-tolerant biological soil crusts (biocrusts) for erosion control on sandstone slopes and evaluates their erosion-reducing effects under varying coverage and slope conditions through controlled artificial rainfall experiments. Key findings include: (1) biocrusts coverage demonstrated a linear relationship with initial runoff generation time and an exponential relationship with stable runoff generation time. On average, biocrusts delayed initial runoff generation by 396.32 % and extended stable runoff generation time by 153.93 %, thereby increasing the threshold for both initial and stable runoff generation on Pisha-sandstone surfaces. (2) biocrusts reduced runoff volume by an average of 23.89 %, enhanced infiltration volume by 69.19 %, decreased sediment yield by 64.24 %, and lowered the soil erosion modulus by 68.98 %. These results indicated significant promotion of water infiltration and reduction of water erosion. Both effects were positively influenced by coverage and negatively impacted by slope gradient. A critical slope angle of 15 degrees and a critical coverage of 60 % were identified. When the slope was gentle (S 15 degrees), the negative impact of slope predominated, diminishing the positive effect of biocrusts. Additionally, when coverage reached or exceeded 60 %, further increaseing in coverage accelerated the enhancement of infiltration and erosion reduction. Below this threshold, the rate of improvement gradually diminished with increasing coverage. (3) The structural equation model further elucidated that biocrusts mitigate erosion by enhancing the coverage, thereby reducing runoff velocity and modifying the runoff regime. This mechanism effectively dissipates runoff energy, leading to a decreased soil detachment rate and alleviation of soil erosion. Additionally, the relationship between runoff energy and soil detachment rate follows a power function curve, providing an effective method for predicting erosion in Pisha sandstone area. Consequently, biological soil crust technology shows considerable potential for preventing water erosion damage on Pisha sandstone slopes across various gradients.

Bridges are important social infrastructure, and in particular, the stability of the back-fill behind the abutment determines the safety of the entire bridge. Recent climate change has increased the risk of flooding, and damage caused by back-fill erosion and collapse is increasing. The objective of this study is to elucidate the damage mechanism of the back-fill of bridge abutments during floods and to propose new reinforcement techniques. In the experiments, indoor open channel tests using a scaled model were conducted to verify the effectiveness of the Gabion Faced Reinforced Soil Wall (GRW), which is a reinforcement method integrating gabions and geosynthetics to reduce the collapse of the back-fill due to flooding. The result of the study showed that the GRW was effective in preventing the collapse of the back-fill due to flooding. As a result, the time until complete collapse of the back-fill was three times longer in the case where GRW was installed than in the case where no countermeasures were taken. This suggests that GRW may be effective during flood events. However, boiling due to changes in pore water pressure occurred inside the back-fill, resulting in progressive sediment discharge. In particular, the effect of the gabion installation geometry was observed, confirming that the corner design is important to control scour. This study experimentally verified the effectiveness of the reinforced soil wall and provided knowledge that contributes to improving the durability of abutment back-fill during flooding. In the future, quantitative evaluation will be conducted to establish a more practical design method.

This study presents experimental results from scale model tests on laterally loaded bridge pile foundations in soils subjected to seasonal freezing. A refined finite-element model (FEM) was established and calibrated based on data obtained from the experiments. Furthermore, the model was utilized to investigate the impact of soil scouring depth on the lateral behavior of bridge pile foundations embedded in seasonally frozen soils. The findings indicate that soil freezing significantly enhances the lateral bearing capacity of the pile-soil interaction (PSI) system while reducing lateral deflection of the pile foundation. However, soil freezing results in increased damage to the pile foundation and upward movement of the plastic zone toward the ground surface. Under unfrozen conditions, significant plastic deformations occur on the ground surface and even inside the piles due to the extrusion effect. Additionally, increasing soil scouring depth significantly reduces the lateral bearing capacity of the PSI system while also increasing lateral deflection of the pile foundation for a given load level. Notably, when the scouring depth exceeds 2 m in unfrozen soils, the entire pile experiences obvious deformation and inclination, exhibiting a short-pile behavior that negatively affects the lateral stability of the pile under lateral loads.

Shield tunneling in soft soil is prone to losing control of posture and seriously deviating from the designed tunnel axis, which can cause significant ground settlement and tunnel misalignment. This paper develops a large-scale indoor shield tunneling model test platform and conducts shield posture adjustment model tests to examine the interaction between the shield and soft soil. Based on these tests, the distribution and evolution of earth pressure and pore water pressure around the shield, as well as the surface displacement under in-situ posture adjustment and tunneling posture adjustment modes are investigated. The results indicate that the earth pressure around the shield and ground displacement are significantly related to the shield tunneling posture mode. When the shield is in the constant posture angle tunneling mode, the sudden changes in earth pressure and ground displacement are mainly due to the in-situ posture adjustment at a large angle before excavation. However, under the subsequent dynamic tunneling effects of the shield shell approaching and leaving the soil in the excavation, the mutation amount gradually dissipates. When the small-range dynamic posture adjustment mode is adopted, the earth pressure around the shield and surface displacement will change synchronously with the shield posture mode and reach their peak value when the posture angle of the shield is maximum. Moreover, there is a plastic limit in the earth pressure around the shield during the posture adjustment, and under the plastic deformation and flow of the soil, the formation will cause soil loss and ground settlement. These findings offer important information on how the shield interacts with the surrounding soil as well as recommendations for constructing shield tunnels in soft soil.

To study the effect of increased rainfall on the heat and mass transfer and deformation characteristics of sulfate saline soil, a geometric similarity ratio model (1:6) of the natural site was created inside the self-developed indoor baseplate-atmospheric dual-temperature control model box. For the first time, combined with the characteristics of the surface energy change, the characteristics of water-heat-salt-mechanical coupling changes within sulfate saline soil under normal rainfall and twice the increase in rainfall were studied. The results show that the increased rainfall leads to a more significant decrease in upward shortwave radiation and downward longwave radiation, as well as a more significant increase in the surface net radiation and surface evaporation rate. Additionally, the increase in rainfall leads to an obvious cooling trend in the surface temperature. Compared with normal rainfall, an increase in rainfall leads to a significant increase in soil water content and conductivity, while soil heat flux and temperature significantly decrease. The increased rainfall caused a temperature drop of 1.6 degrees C at 5 cm of saline soil. Moreover, the increased rainfall leads to an increase in the heat release time of sulfate saline soil. Meanwhile, the impact of increased rainfall on the soil water content, conductivity, and temperature gradually weakens with increasing depth. The increased rainfall can exacerbate thawing settlement deformation and alleviate salt frost heave deformation. Compared with normal rainfall, twice the increase in rainfall results in a 0.9 mm increase in thawing settlement deformation and a 2.5 mm decrease in salt frost heave deformation.

Integrating liquid CO2 phase transition blasting (LCPTB) technology with hydraulic fracturing (HF) methods can help reduce wellbore damage, create multiple radial fractures, and establish a complex fracture network. This approach significantly increases the recovery efficiency of low-permeability oil and gas fields. Accurately calculating the number of fractures caused by LCPTB is necessary to predict production enhancement effects and optimize subsequent HF designs. However, few studies are reported on large-scale physical model experiments in terms of a method for calculating the fracture number. This study analyzed the initiation and propagation of cracks under LCPTB, derived a calculation formula for crack propagation radius under stress waves, and then proposed a new, fast, and accurate method for calculating the fracture number using the principle of mass conservation. Through ten rock-breaking tests using LCPTB, the study confirmed the effectiveness of the proposed calculation approach and elucidated the variation rule of explosion pressure, rock-breaking scenario, and the impact of varying parameters on fracture number. The results show that the new calculation method is suitable for fracturing technologies with high pressure rates. Recommendations include enlarging the diameter of the fracturing tube and increasing the liquid CO2 mass in the tube to enhance fracture effectiveness. Moreover, the method can be applied to other fracturing technologies, such as explosive fracturing (EF) within HF formations, indicating its broader applicability and potential impact on optimizing unconventional resource extraction technologies. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

A pipeline with long-term hidden leakage will greatly reduce the stability of the ground between the pipeline and tunnel in the process of tunneling through existing pipelines in unsaturated soil. Excessive settlement of the surrounding strata and pipelines can occur when the shield excavation face approaches below a pipeline, which can lead to engineering accidents. This study is based on a self-developed model experimental system for tunneling through an existing pipeline with a double-line tunnel shield. The ground settlement and pipeline deformation caused by shield construction with small-scale and no leakages are investigated. An experimental study is conducted and the accuracy of the results is verified through a comparison with theoretical solutions. The results demonstrate that there is a significant increase in ground settlement and pipeline deformation under the influence of leakage water. It is also determined that the displacement field generated by the excavation of a double-line tunnel is not simply a superposition of the displacement field generated by the excavation of a single-line tunnel. The repeated disturbances caused by the excavation of a double-line tunnel significantly influences the redistribution of the displacement field. Additionally, a three-dimensional (3D) model of shield construction considering the influence of pipeline leakage is established. This study discusses the ground settlement and pipeline deformation patterns caused by changes in the vertical and horizontal leakage diffusion ranges. The computational results indicate that the diffusion depth of a leakage is the primary factor controlling the extent of settlement.

The practical application of micropiles in landslide reinforcement and prevention advanced before theoretical research, significantly limiting their application and promotion. To determine the damage patterns and stress distribution of micropiles during sliding failure in reinforced shallow landslides, three sets of physical modeling tests were performed. These tests examined the stability of shallow soil slopes with and without micropiles, including single-row and three-row configurations. During the tests, the foot displacement of the landslide, the top displacement of the micropiles, and the strain within the micropiles were monitored throughout the loading process. Following the tests, the landslide was excavated to observe the damage patterns in the micropiles. The experimental results showed that the pile-soil composite structure formed by three rows of micropiles, together with the soil between them, significantly improved the stability of the landslide and demonstrated effective anti-sliding effects. The stress distribution curve of the micropile was inversely S-shaped, with the peak stress located near the sliding surface. Within the micropile group, the first row exhibited the highest stress, and the micropiles nearest to the free face experienced the greatest displacement. Through the micropile-reinforced landslide tests, we identified three stages in the slope's sliding damage process and the stress distribution pattern of the micropiles. The research findings offer valuable insights into the anti-sliding mechanism of micropiles, which can guide design and construction.

The loess structural planes of different formation, scales, origin, and types are widely developed in loess slopes, which can significantly control the structure, hydro-mechanical properties, damage regulations and deformation failure pattern of the slope. A series of major engineering projects have been implemented on the Loess Plateau of China. These projects have formed many loess slopes, which are prone to failure induced by loading. However, the failure mechanism of heap-loading loess slope, especially the influence of structural plane on slope failure, is not clear. Therefore, based on the investigation and analysis of the characteristics of loess structural planes, a large-scale model experiment was carried out, and the deformation process and failure mechanism of loess landslide induced by loading were systematically investigated. The soil pressure distribution, plastic state, and deformation characteristics of the slope were analyzed to reveal the influence of the structural plane on slope failure. The results show that the existence of the structural plane changed the stress field of the loess slope, forming a preferential yielding region around the structural plane, making the structural plane more likely to become a potential sliding surface. Different increases of earth pressure in the x- and z-direction is the main reason for the change in the extension angle of the structural plane. The propagation of the shear zone presents a typical double slip surface structure. The failure process of the loess slope induced by loading could be generalized into structural plane extension, shear band initiation, shear band penetration, and sliding failure stages.