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.

This study explores the effectiveness of soft viscoelastic biopolymer inclusions in mitigating cyclic liquefaction in loosely packed sands. This examination employs cyclic direct simple shear testing (CDSS) on loose sand treated with gelatin while varying the gelatin concentration and the cyclic stress ratio (CSR). The test results reveal that the inclusion of soft, viscoelastic gelatin significantly reduces shear strain and excess pore pressure during cyclic shear. Liquefaction potential, defined as the number of cycles to liquefaction (NL) at an excess pore pressure ratio (ru = Delta u/sigma ' vo) of 0.7, is substantially improved in gelatin-treated sands compared to gelatin-free sands. This improvement in liquefaction resistance is more pronounced as the inclusion stiffness increases. Furthermore, the viscoelastic pore-filling inclusion helps maintain skeletal stiffness during cyclic shearing, resulting in a higher shear modulus in gelatin-treated sand in both small and large-strain regimes. At a grain scale, pore-filling viscoelastic biopolymers provide structural support to the skeletal frame of a loosely packed sand. This pore filler mitigates volume contraction and helps maintain the effective stress of the soil structure, thereby reducing liquefaction potential under cyclic shearing. These findings underscore the potential of viscoelastic biopolymers as bio-grout agents to reduce liquefaction risk in loose sands.

In the reinforcement of micro-cracks and soil, cement grouting often suffers from poor injectability due to particle size limitations. While ultra-fine cement produced through physical grinding can address this issue, it significantly increases cost and energy consumption. Moreover, ultra-fine cement is prone to aging when exposed to moisture and CO2 in the air. To address these issues, this study proposes a new approach for in-situ particle size reduction of cement slurry through the mild corrosion of acetic acid. The refining effect of acetic acid on cement particles was investigated, along with its impact on mechanical properties and hydration products. The results show that acetic acid accelerates cement dissolution, promoting early-stage strength development and microstructure formation. The addition of 1.2 wt% acetic acid reduced the D90 particle size of the slurry by 36.4 %. Acetic acid also enhances the release of Ca2+ from clinker, increasing the precipitation of Ca(OH)2, CaCO3, and calcium silicate hydrate (C-S-H) at early stages, which serves as the primary source of early strength. Additionally, it raises the Ca/Si ratio of the early-formed C-S-H gel. However, excessive acetic acid can inhibit the further development of strength at later stages. The research demonstrates that premixed acetic acid activation is an effective approach for enhancing the performance of cementitious grouting materials, with promising potential to reduce energy consumption associated with physical cement grinding.

As a newly emerged solution for supporting the new generation of offshore wind turbines (OWTs), the pile-bucket foundation has received wide attention. However, little attention has been paid to the grouted connection that connects the monopile and bucket foundation. As the loadtransferring, yet vulnerable component, the fatigue mechanism of the grouted connection and its influence on the cyclic laterally-loaded response of OWT foundation are still not clear. In this study, a sophisticated three-dimensional (3D) finite element (FE) model of the pile-bucket foundation with grouted connection is constructed, which incorporates a hypoplastic clay model and the concrete damage plasticity (CDP) to consider the cyclic load effect on both soil and grout material. A modal analysis is first performed to verify the rationality of the proposed model. Then the influence of cyclic load frequency, load amplitude and stiffener arrangement on the accumulation of pile head displacement, stress distribution and crack development of the grouted connection is systematically analyzed. Results indicate that as load frequency approaches the eigen-frequency, the OWT structure tends to vibrate more intensively, leading to stress concentration and fatigue damage of the grouted material and rapid accumulation of the pile-head displacement. The influence of load amplitude on grout damage seems to be limited in the contact area in the simulated cases. Meanwhile, the installation of stiffeners slightly mitigates the pile head displacement accumulation, but also raises the risk of stress concentration and fatigue damage of the grouted connection. The numerical results reveal the load-transferring function and fatigue damage of the grouted connection, which could provide some reference for an optimized structure and dynamic design for the pile-bucket foundation under cyclic load.

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.

Post-grouted shafts (PGDS) and stiffened deep cement mixed (SDCM) shafts reinforce the surrounding soils with cement to enhance the bearing capacity of shaft foundations, and their applications are becoming increasingly widespread. Field tests involving two post-grouted shafts and two stiffened deep cement mixing shafts were conducted at the bridge foundations projects, analyzing the vertical bearing performance of the shafts with cement-stabilized soil enhancement. Additionally, numerical simulations were performed to establish calculation models for single shaft and groups of drilled shafts, PGDS, and SDCM shafts, enabling a comparative analysis of their bearing capacity performance within the identical strata. The results indicate that the post- grouted shaft demonstrated significant bearing deformation capacity, as confirmed by field tests. After grouting, the ultimate bearing capacities of DS1 and DS2 improved by 124.5 % and 110.9 %, respectively. In both single and group modeling shaft foundations, the post-grouted shafts demonstrated the highest bearing deformation characteristics, followed by the identical- size stiffened deep cement mixed shaft, while the long-core SDCM shafts and the ungrouted shafts exhibited the weakest performance. Due to interaction effects among group shafts, the total bearing capacity of the group shafts is not simply the sum of the individual shafts. Specifically, the reduction factor for group shaft capacity ranges from 0.68 to 0.79 at the Baoying Large Bridge site, while at the Yangkou Canal Bridge site, it varies from 0.66 to 0.85. The findings of this study provide valuable insights for practical engineering applications.

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.