Enzyme-Induced Carbonate Precipitation (EICP) is an innovative technique to improve soil strength and reduce permeability. However, the use of EICP for reinforcing underwater sand beds remains largely unexplored. To advance EICP implementation in various geotechnical applications, this paper develops a model box system to investigate the effectiveness of the EICP technique in reinforcing underwater sand beds. An ''injection-extraction'' system is designed to facilitate the flow of the EICP solution through underwater sand layers. Key parameters, including conductivity, pH, and Ca2+ concentration of the solution, are measured and analyzed. Electrical resistivity tomography (ERT) is utilized to evaluate the reinforcement effect in the underwater sand bed. The permeability of the model is tested to verify the feasibility of EICP technology for strengthening underwater sands. Furthermore, scanning electron microscope (SEM) is performed to investigate the growth mechanisms of calcium carbonate (CaCO3) crystals. The results show that the permeability of the model decreases from 1.28 × 10−2 m/s to 9.66 × 10−5 m/s, representing a reduction of approximately three orders of magnitude. This verifies that the EICP technology can greatly reduce the permeability of underwater sand beds. With increasing grouting cycles, the resistivity of the underwater sand initially decreases and then increases. This variation in sand resistivity is significantly influenced by the ion concentration in the solution, resulting in marked differences in resistivity at various depths and positions within the sand. The findings from this study offer a theoretical basis for the application of EICP technology in reinforcing seabed foundations and supporting marine infrastructure such as offshore pipelines, wind turbines, and oil platforms.

Enzyme-induced carbonate precipitation (EICP) is a potential ground improvement method that can reduce the permeability of sands. However, the traditional mathematical models are hard to accurately predict the permeability of EICP-treated sands. In this study, the mathematical model was established for predicting the permeability of EICP-treated sands based on Kozeny-Carman equation. The effects of calcium carbonate precipitation on the porosity, tortuosity, and specific surface area of the EICP-treated sands were considered in the model. To validate the model, the bio-cemented sand column tests with different grain size distributions (coarse, medium, and fine sands) and treatment numbers (6, 8, and 10 times) were conducted. The calcium carbonate content (CCC) and permeability of EICP-treated sands were measured. The validation of the model was confirmed through a comparative analysis of theoretical and experimental results. Furthermore, the impacts of porosity, particle size, CCC, and specific surface area on the hydraulic conductivity of EICP-treated sands were analyzed. The results showed that the model can reflect the hydraulic conductivity of EICP-treated sands under different particle size distributions and degrees of cementation, demonstrating broad applicability. Parametric analysis indicated the hydraulic conductivity gradually decreases with increasing CCC and specific surface area. Conversely, the hydraulic conductivity gradually increases with increasing porosity (n) and particle size (d50), with porosity exhibiting a significantly higher sensitivity than particle size. In summary, this study contributes theoretical foundations for the practical implementation of EICP technology in reducing soil permeability.

The rock mass integrity index (Kv) is a widely used parameter for characterizing rock mass integrity. Kv is defined as the square of the ratio of the P-wave velocity of a rock mass to that of intact rock. Usually, due to the presence of structural planes in rock mass, the P-wave velocity of rock mass is lower than that of intact rock, resulting in Kv values ranging from 0 to 1. However, during a rock mass integrity investigation in a water-conveyance tunnel excavated through diabase and quartz schist in Hubei Province, China, Kv values exceeding 1 were observed. To investigate this phenomenon, a detailed geological survey was first conducted, followed by physical property tests, microscopic structural observations, and macroscopic mechanical experiments. Uniaxial loading tests at different stress levels showed a nonlinear reduction in P-wave velocity as stress decreased. The foliated structure and microcracks in layered rocks are considered the dominant factors that reduce P-wave velocity after stress is released. A relationship model between P-wave velocity and stress variation in intact rock was introduced to explain the mechanism underlying Kv values greater than 1. It is recommended to use the P-wave velocity of intact rock corresponding to crack closure conditions rather than stress-free conditions when calculating Kv. The present study enhances understanding of Kv, helps to standardize testing conditions, and improves its accuracy in evaluating rock mass integrity.

When shield TBM tunnelling in abrasive sandy gravel ground, the higher ripper tooth plows the excavation surface, and then the lower scraper cuts the loose sandy gravel. The plowing effect refering to the mitigation of ripper tooth on scraper wear by loosing the dense sandy gravel is related to cutter height difference, inherent soil properties and foam additive parameters. However, the previous studies focus mainly on the former two factors, and the influence mechanisms of foam additives on the plowing effect are unclear. To fulfill the evaluation of plowing effect under various foam additive conditions, the WHU-SAT test apparatus that can continuously change cutter height difference was developed. The plowing coefficient was proposed to quantify the plowing effect of ripper tooth on dense sandy gravel ground. The variations in plowing coefficient, ripper tooth wear and modelled cutterhead torque with foam additive parameters were analyzed under various cutter height difference conditions. The influence mechanisms of solution concentration and injection ratio on plowing effect were revealed based on particle contact analysis. Cutter height difference and foam additive parameters were optimized for abrasive sandy gravel ground tunnelling. The results indicate that under the lubrication of active material on particle surface and the cushion of air bubble on particle contact, the plowing coefficient increases rapidly and then slowly with increasing solution concentration and injection ratio. The ripper tooth wear and modelled cutterhead torque decrease first rapidly and then slowly with increasing solution concentration, while they decrease first and then stabilize with increasing injection ratio. The optimal cutter height difference stabilizes with solution concentration, while it decreases first and then stabilizes with increasing injection ratio. The present study provides a reference for optimizing cutter height difference and foam additive parameters in abrasive sandy gravel ground tunnelling using shield TBM.

Pipe jacking is a key trenchless technology for urban underground construction. Accurate jacking force prediction is critical for safe and efficient construction. Existing models often fail to properly account for the contact conditions at the pipe-soil interface caused by lubricant injection. This study develops a novel mathematical model for jacking force prediction that considers the pipe-soil/slurry contact state and soil arching effect. The proposed model was validated by comparing theoretical results with monitoring data from three field pipe jacking projects. The results demonstrate that the proposed model can accurately predict the field jacking forces,with an average error of less than 15%. The sensitivity of the jacking force to soil unit weight, internal friction angle, pipe-soil friction coefficient, and burial depth was investigated. Parametric analysis revealed that the pipe-soil friction coefficient is of paramount importance, followed by soil unit weight, burial depth, and soil internal friction angle. The evolution of the contact angle and effective friction coefficient in response to variations in burial depth, construction gap, contact pressure, and pipe diameter was also analyzed. A construction gap of more than 30 mm was identified as an effective measure for friction reduction, as it ensures the formation of the slurry sheath. The influence of contact pressure and burial depth diminishes beyond specific thresholds. The present study can provide a reference for predicting the jacking force and optimizing pipe jacking design.

The coalescence behavior of flaws critically governs rock mass stability. Despite established coalescence classification systems, ambiguities in the mechanisms of morphologically similar crack trajectories and limitations in universality and accuracy persist. To address these issues, the present study employed the bonded particle model to generate a comprehensive range of flaw geometries with fine incremental steps and simulate the coalescence process between parallel flaws under uniaxial compression. By tracking the dynamic evolution of force chains and displacement fields, the physical origin of the long-unexplained compression-induced tensile (CIT) crack is identified. Findings reveal that CIT cracks are driven by the accumulation of nested tensile contact forces within dominant compressive forces; the confinement effect within the rock bridge leads to delayed but abrupt energy release, resulting in sudden internal failure. Furthermore, the present study deciphers the divergent mechanical mechanisms underlying various coalescence patterns in overlapping and stepping geometries, resolving controversies where identical crack morphologies arise from distinct stress states. Additionally, results demonstrate that coalescence patterns are governed not only by macroscopic flaw geometry, but also by stress heterogeneity induced by random particle distribution and dynamic stress redistribution during crack propagation. These insights facilitate a refinement of Wong’s classification system that prioritizes mechanical criteria over geometric morphology. Ultimately, this mechanism-driven framework eliminates previous observational ambiguities, establishing a robust foundation for predicting the failure behavior and stability of jointed rock masses.

The contact pressure distribution at the disc cutter-rock interface is fundamental to estimating rock cutting force, optimizing cutter head design, and predicting tunnel boring machine (TBM) performance. In the present study, pre-existing microcracks were explicitly incorporated into a three-dimensional discrete element method (DEM) model to simulate the rock material more realistically. The linear cutting tests (LCTs) were simulated using cuboid numerical specimens containing distributed microcracks. First, to simulate the continuous cutting process accurately, three different numerical preprocessing methods were compared, and the most representative approach was selected. Second, three probability distribution functions, namely the Gaussian distribution, Lorentzian distribution and Extreme distribution, were employed to fit the contact pressure distribution between the disc cutter and the rock surface. This approach enables quantitative characterization of both the magnitude (p0) and position (xc) of the maximum contact pressure. Based on the fitting performance, the Gaussian function was selected for describing the stress distribution in the present study. Third, LCT simulations were conducted under various conditions, including different cutting velocities, tip widths, penetration depths, and rock strengths. Both the magnitude and position of the maximum contact pressure (p0 and xc) are significantly influenced by disc cutter geometry, cutting parameters, and rock strength. Furthermore, the maximum contact pressure (p0) showed a positive correlation with both the normal force and the rolling force. These findings may enhance understanding of the fragmentation mechanism under the cutting tool and advance the comprehension of cutting force prediction in practical field operations.

To study the deep rock strength, this paper proposes a five-parameter deviatoric function to modify the deviatoric function of the Hoek–Brown (HB) criterion, introduces an intelligent optimization algorithm (IOA) to determine the material parameters, thereby constructing a modified three-dimensional (3D) HB criterion, namely MMCHB criterion. The MMCHB criterion avoids the defects of the traditional HB criterion, which neither considers the Intermediate principal stress (IPS) nor meets the smoothness requirement, and overcomes the shortcomings of parameter determination based on conventional methods, which can lead to a single deviatoric plane envelope shape. This modified criterion can be degenerated into the HB criterion under triaxial compression and tension. The proposed criterion is verified using true triaxial test data for six types of intact rock, and the modified 3D HB criteria are selected for comparative study. The results show that the proposed criterion under the IOA has the best prediction error for the six rock types, ranging from 1.6636

A partly clumped-particles combined with joint planes model was developed to simulate the microstructure of quartz mica schist. It considers grain-scale heterogeneity including microgeometry heterogeneity and grain-scale elastic heterogeneity. Clumped-particles with larger volume and larger stiffness were used to represent stiff minerals such as quartz, the rest of unclumped particles with smaller stiffness were used to represent soft minerals such as mica. The joint planes, which have smaller stiffness and strength than mica, were used to describe schist. The extensive sensitivity studies have shown that the clump’s radius, clump’s content and joint plane’s strength affect the microscopic and macroscopic behaviors of sample. For DanBa quartz mica schist, the model calibrated uniaxial tests and well matched with the stress-strain curves, crack initiation stress and crack damage stress of laboratory test.

When shield TBM tunneling in dense sandy ground, the installation height of the ripper tooth is higher than that of the scraper. The ripper tooth plows the excavation surface, followed by the scraper cutting the loose sand. The plowing effect refers to the mitigation of scraper wear by the ripper tooth, which loosens the dense sand on the tunnel surface. Although it has been analyzed qualitatively over the past few decades, there is still a lack of reliable parameters for quantitative evaluation. The influence of cutter height difference, sand density and particle size on plowing effect is unclear. In the present study, the WHU-SAT test apparatus that can continuously change cutter height difference was developed to explore plowing effect of ripper tooth. The plowing coefficient was proposed to quantify the plowing effect on dense sandy ground. The influence mechanism of cutter height difference, sand density and particle size on plowing coefficient was revealed based on excavation process analysis. The cutter height difference between ripper tooth and scraper was optimized for dense sandy ground tunneling. The results indicate that as cutter height difference increases, the loosening depth of ripper tooth on tunnel face increases. The bulk density of sand samples cut by scraper decreases first and then stabilizes, leading to a similar trend in the plowing coefficient. With the increase of sand density, the loosing depth corresponding to the stable plowing coefficient increases first and then stabilizes, resulting in a similar pattern for the optimal cutter height difference. As the average particle size increases, the loosing depth corresponding to the stable plowing coefficient increases, leading to an increase in the optimal cutter height difference. The present study provides a reference for optimizing cutter height difference in dense sandy ground tunneling.

Excessive tool wear in abrasive ground has become a critical factor restricting tunneling efficiency. To evaluate soil abrasion and tool wear, a series of testing methods have been proposed. However, the lack of comprehensive analysis on the soil-tool tribology system prevents them from accurately reflecting the contact conditions between tunnel face and cutting tool. Moreover, the tunneling parameters are determined subjectively by designers, potentially skewing test results. In the present study, the deficiencies of existing test methods have been analyzed, and the WHU-SAT test method has been developed. Compared with existing test methods, the rational design of cutterhead structure and cutter geometry enables a more realistic simulation of cutting process and wear mechanism. The high-precision monitor system promotes a more rigorous test process. The influence of tunneling parameters on scraper wear has been studied for parameter determination to avoid inappropriate parameters interfering with test reliability. The results indicate that scraper wear increases first and then stable with increasing rotation speed, with a recommended value of N = 100–200 r/min. With increasing tunneling speed in nature sand (or quartz sand), scraper wear decreases (or increases) first and then stable, with a recommended value of V = 10–30 mm/min. As the increase of cutterhead penetration depth, scraper wear increases slowly and then rapidly, with a recommended value of h = 120–150 mm. Since sand particles are crushed during the cutting process, the increase rate of scraper wear decreases with increasing test time. Considering the constraints between weighing error and test efficiency, the recommended value is t = 60–90 min.