Post-grouting pile technology has gained extensive application in collapsible loess regions through the injection of slurry to compress and consolidate the soil at the pile base, thereby forming an enlarged base that enhances the foundation's bearing capacity and reduces settlement. Despite the prevalent unsaturated state of loess in most scenarios, the conventional design methodologies for piles in collapsible loess predominantly rely on saturated soil mechanics principles. The infiltration of water can significantly deteriorate the mechanical properties of loess due to the reduction in matric suction and the occurrence of collapsible deformation, leading to a substantial degradation in the bearing behavior of piles. To explore the variations in load transfer mechanisms of post-grouting piles in collapsible loess under conditions of intense precipitation, a comprehensive large-scale model test was conducted. The findings revealed that the post-grouting technique effectively mitigates the adverse effects of negative pile shaft friction in saturated zones on the pile's bearing behavior. Furthermore, the failure criteria for piles may shift from the shear failure of the base soil to excessive pile settlement. By incorporating principles of unsaturated soil mechanics, modified load transfer curves were developed to describe the mobilization of both pile shaft friction and base resistance. These curves facilitate the extension of the traditional load transfer method to post-grouting piles in collapsible soils under extreme weather conditions. The proposed revised load transfer method is characterized by its simplicity, requiring only a few soil indices and mechanical properties, making it highly applicable in engineering practice.

To address the material requirements for grouting reinforcement in fine sand strata, a novel silicate-modified polymer two-component grouting material was designed. In this material, the traditional organic polyol component of the two-component polymer was replaced with an inorganic silicate (water glass) component, along with the addition of tertiary amine catalysts, organotin catalysts, water. The response surface methodology (RSM) was used to statistically predict the performance of the modified polymer grouting material. The effects of four parameters (two-component mass ratio, tertiary amine catalyst content, organotin catalyst content, and water content) and their interactions on response variables (gelation time, polymer solids strength, cemented body strength) were investigated. Based on a comprehensive consideration of various performance requirements for grouting materials in loose fine sand strata, multi-objective optimization was employed to determine the optimal formulation of the modified polymer grouting material (A/B ratio of 0.85, tertiary amine catalyst at 2.48 %, organotin catalyst at 0.63 %, and water at 1.87 %). A series of experimental tests were conducted to evaluate the material properties of the optimal formulation, and its mechanical performance and microstructural characteristics were compared with those of traditional polymer grouting materials to verify the proposed formation mechanism of the modified polymer. The results demonstrated that the proposed design method effectively determines the optimal grouting material formulation. The optimized modified polymer grouting material exhibited excellent comprehensive performance. Finally, the optimized modified polymer grouting material was applied in a pavement repair project on a of a highway. After grouting, the structural layer's uniform integrity was significantly restored, the damaged areas were effectively repaired, the modified polymer slurry showed good diffusion, and the repair effect was satisfactory, meeting the engineering requirements for grouting in loose fine sand strata.

The grouting method plays a critical role in preventing seawater intrusion in submarine tunnels, particularly in regions with highly weathered rock that are susceptible to erosion and shifting seawater. The long-term properties of the strength and impermeability of the grout-soil composite are related to the durability of the tunnel lining structure, which is an important focus of the present research. This study introduces a new method for calculating material ratios to determine the optimal proportions of each component in grout-soil composites. A specialized experimental setup was designed to replicate the erosive conditions of seawater in environments characterized by significant rock weathering. The primary objective of this investigation was to analyze the weakening effects of seawater ions (e.g., Mg2+, SO42-, Cl-) on the grout-soil composite under dynamic seawater flow conditions. Therefore, the influence of water-cement (W-C) ratio, grouting pressure, and erosion duration on the compressive strength and permeability coefficient of the composite was studied. Furthermore, microscopic analyses were conducted to investigate the microstructure and composition of the weakened composite specimens. Finally, the model of damage weakening in grouted composite has been established. The experimental results indicate that the erosive ions (Cl-, SO42-) initially enhance and then weaken the strength and impermeability of the grouted composite, while Mg2+ ions continuously degrade the strength of the composite. Reducing the water-to-cement ratio and increasing the grouting pressure can improve the strength and impermeability of the grouted composite, but once a certain threshold is reached, the enhancement effect becomes negligible. Under different dynamic water environments and with various erosive ions (Cl-, SO42-, Mg2+, and seawater), the compressive strength of the specimens at the end of the erosion process decreased by 25.49%, 31.21%, 50.34%, and 39.70%, respectively, compared to static freshwater. The permeability coefficient increased by 8.5 times, 3.2 times, 5.8 times, and 8.9 times, respectively. As the W/C ratio increased from 0.8 to 1.2, the compressive strength decreased by 27.67%, 38.97%, 65.70%, and 44.58%, respectively, and the permeability coefficient increased by 55.24%, 59.70%, 134.23%, and 44.49%. As the grouting pressure increased from 1.5 MPa to 2.5 MPa, the compressive strength increased by 48.90%, 162.60%, 163.71%, and 48.35%, respectively, while the permeability coefficient decreased by 53.76%, 40.05%, 73.69%, and 32.89%. The findings of this study offer valuable insights into the erosion mechanism of grout-soil composites induced by seawater ions, thereby contributing to enhanced durability and longevity of submarine tunnel infrastructure.

Ground vibrations from operating railway in tunnels is a significant obstacle to sustainable development of subway. The backfill grouting layer, formed during shield tunneling, serves as a critical medium in propagation of tunnel vibrations, highlighting its potential in vibration mitigation. A semi-analytical model for the tunnelgrouting layer-soil system is proposed in this study, in order to clarify the influence of backfill grouting layer on the dynamic responses in a half-space, subjected to tunnel vibrations. In establishment of the closed-form solution, the tunnel and grouting layer are considered as two nested hollow cylinders embedded in a halfspace, with applying the Fourier transform and wave transformation. As a validation, the numerical results from the proposed semi-analytical model are compared with those reported in literature. Parametric studies, with respect to the geometric configuration (i.e., the thickness) and material parameters (i.e., the Young's modulus, material damping, and density) of the backfill grouting layer in the mitigation of tunnel vibrations, are carried out. It is found that incorporation of the backfill grouting layer significantly changes the dynamic responses of the soil and, by appropriately designing its material parameters, especially the Young's modulus, effective mitigation of tunnel vibrations can be achieved.

Collapse pits are highly susceptible to secondary hazards such as underground debris flows and slope instability under mining disturbances. These hazards significantly damage the ecological environment of the mining area. To reduce the geological hazards of collapse pits, grouting is used for management. The diffusion pattern and curing mode of slurry under different grouting pressures were investigated through indoor grouting simulation tests, and industrial tests were carried out to assess grouting effects. The results indicate that the slurry is dominated by penetration diffusion and supplemented by splitting diffusion in the moraine. The penetration distance and diffusion radius of the slurry increase linearly with grouting pressure, while the splitting uplift distance and cured volume increase exponentially with grouting pressure. Splitting diffusion consists of three stages: bulging compaction, splitting flow, and passive uplift. Horizontal splitting has a vertical uplift effect on the formation. The slurry primarily consolidates individual moraine particles into a cohesive mass by filling fractures, binding soil particles, and reinforcing interfaces with the rock mass. For different moraine layer structures, full-hole, segmented, and point-based grouting methods were applied. A composite grouting technique, layered grouting with ring solidification, was also introduced, achieving excellent grouting results. This study provides technical support for managing geological hazards in collapse pits caused by block caving mining disturbances and for green mining practices.

Current studies on soil tortuosity models typically assume a single particle size, neglecting the impact of particle gradation and spatial arrangement on pore channels and structures. To address this limitation, we develop a tortuosity model that incorporates multiple factors by assuming ellipsoidal particles and accounting for their arrangement and gradation. This model, combined with the Bingham fluid flow equation in porous media, elucidates the spherical penetration grouting mechanism of Bingham fluids, considering both tortuosity and time-varying viscosity. Using COMSOL Multiphysics, we simulate seepage to create a numerical program for Bingham fluid spherical seepage grouting that accounts for tortuosity and time-varying viscosity. Theoretical analysis and simulations validate our proposed tortuosity model and diffusion mechanisms. Additionally, we examine the sensitivity of the diffusion radius to Bingham grout rheology, grouting pressure, groundwater pressure, and grouting pipe radius. The research results demonstrate that the established tortuosity theoretical model is in excellent agreement with numerical simulations, with a maximum error of less than 3%. The spherical permeation grouting diffusion mechanism of Bingham fluid, which accounts for the tortuosity effect of porous media, more closely matches the experimental test values, achieving an average error of 10.13% and a minimum error of 3%. Grouting pressure and groundwater pressure are key factors, and their interaction with the grouting pipe radius has the strongest effect. These research findings provide valuable theoretical support for designing construction controls related to restoration projects involving porous medium earth-rock dams.

In urban regions with karst developments, grouting is commonly utilized to fill cavities. However, the extent and control standards of grouting reinforcement are primarily determined through experience and field testing, which poses challenges in ensuring its effectiveness. Based on the instability mechanism of surrounding rocks in underwater karst shield tunnels, this study develops a mechanical model for analyzing the grouting reinforcement extent of such tunnels using strength theory. The reinforcement range for karst formations at various tunnel locations is clarified, and corresponding grouting reinforcement control standards are proposed based on cusp catastrophe theory. The findings indicate the following: the primary cause of surrounding rock instability in underwater karst shield tunnels is that the reduction in surrounding rock thickness during shield tunneling modifies the original constraints and boundary conditions and disrupts the initial equilibrium state. These changes influence the water content of the surrounding rocks and disturb the surrounding rock and soil mass, leading to surrounding rock instability. When grouting causes damage to the surrounding rocks between the karst and tunnel, the system is simplified into cantilever beam and plate models for analysis. It is determined that the grouting reinforcement extent is primarily influenced by factors such as karst size, properties of the karst filling material, and tunnel span. The total potential energy of the rock mass between the karst and tunnel is calculated, leading to the development of an instability and catastrophe model for the surrounding rocks. The proposed grouting reinforcement control standards are mainly dependent on factors such as the distance of the karst, characteristics of the reinforced surrounding rocks, shield machine support force, material properties post-reinforcement, and karst size.

Erosion and seepage control is a prime concern for embankments, dams, and other hydraulic structures constructed with alluvial sandy soil due to its highly porous characteristics. Permeation grouting has been a popular solution for controlling seepage situations in such structures. In this study, unconfined compression tests and triaxial tests were performed to determine the strength properties of grouted alluvial sandy soil located in the Ganges-Brahmaputra-Meghna delta. A simple method was devised to prepare cylindrical grouted samples with water-cement ratios (W/C) of 2:1, 3:1, 4:1, and 5:1. Here, unconfined compressive strength test results revealed that the highest compressive strength of the grouted sandy soil samples was achieved at the 2:1 W/C ratio at all curing ages. Different failure patterns are observed for different W/C samples during unconfined compressive tests. Furthermore, triaxial tests were conducted on the grouted samples prepared at the 2:1 W/C ratio under consolidated undrained conditions. Dilation occurred during the volume change, and the pore pressure decreased with increasing confining stress. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy were conducted to discern the microstructural behavioral changes and the chemical characteristics of the grouted sandy samples, respectively. Here, SEM images revealed a reduction in porosity with decreasing W/C ratio and increasing curing age. Permeation grouting leads to a reduction in permeability without disturbing the soil microstructure. Therefore, permeation grouting is a very effective technique for improving the mechanical behavior of grouted alluvial sand.

Groundwater is widely distributed in various rock and soil media and underground structures. Groundwater seepage inside the silty-fine sand layer causes infiltration erosion, leading to uneven settlement and cracking damage to the foundation and its structures. An analysis was conducted on the mechanisms of flowing soil and piping, and it was pointed out that flowing soil is caused by the effective gravity of sand particles, resulting in the floating and failure of sand particle groups due to the permeability greater than that of sand particles; Pipe surge refers to the migration and loss of movable fine particles, and the formation of water inflow channels through the interior of the silty-fine sand layer. Propose technical measures to improve the physical and mechanical properties of silty-fine sand layers and prevent infiltration damage through grouting. The mechanism of infiltration, splitting and compaction grouting was explained and analyzed, and the grouting materials such as plant glue modified cement sodium silicate, geopolymer, microbial solution, nano silica sol, emulsified asphalt, polyurethane, etc. were discussed and sorted out, aiming to contribute to improving the quality of silty-fine sand layer engineering projects.

Grouting below the tunnel invert is commonly used to remediate the settlement. Case histories demonstrate that the tunnel settlement still develops after the grouting is completed, especially in structured clay. The principal mechanism behind this is the grouting-induced soil disturbance, including the generation of excess-pore-water pressure (EPWP), degradation in soil structure, and changes in compressibility. To date, the mechanism behind the grouting-induced soil disturbance and responses of the ground heave is not yet fully understood. Toward this end, laboratory tests on grouting in mud with different sand content are carried out. Earth pressure, pore water pressure, shear stiffness, undrained shear strength, and ground heave are measured and analyzed. The results indicate that grouting causes increases in the lateral earth pressure and significant EPWP in the surrounding soil. Changes in undrained shear strength and shear stiffness are closely related to the comprehensive effects of increases in stress level and shear disturbance. The increased stress level leads to the growth in stiffness and strength, while shear disturbance causes degradation. The soils right nearby the grouting zone are subjected to significant shear disturbance and also increases in stress level. As a result, the soil stiffness and strength exhibit negligible change. In comparison, the soils above and below the grouting zone mainly experience an increase in stiffness and strength, because shear disturbance is comparatively smaller than the influence of the increases in stress level. Furthermore, the development of the vertical displacement of the ground surface demonstrates two stages of initial uplift during grouting and then settlement after the grouting is completed. In addition, stronger soil structure corresponds to larger settlement after the grouting is completed.