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.

Excess-sulfate phosphogypsum slag grouting material (EPSGM) has strong advantages for stabilizing the coral sand foundation, which requires establishing a groutability prediction model involving multi-factors to ensure better stabilization. Specifically, the grain size (d85) d 85 ) and water-to-cement ratio (w/c) w/c ) of the grout, particle size (D15), D 15 ), relative density (Dr), D r ), and fine content (FC) FC ) of coral sand, and grouting pressure (P) P ) are considered. The results show that the optimal particle size d 85 of EPSGM is 15.567 mu m. As the w/c increases from 1.0 to 3.0, the compressive strength of mortar (EPSGM + coral sand) decreases from 11.74 MPa to 0.32 MPa, and the California Bearing Ratio (CBR) value meets the typical requirements (>= 15%). The groutability criterion (N) N ) is positively correlated with the D15, 15 , w/c, , and P , while it is negatively correlated with the Dr r and FC , namely, the model writes: N = (1- 1- 0.071Dr)(1- D r )( 1- 1.54FC)0.024D15 FC ) 0.024 D 15 + 0.42(w/c) w / c ) + 0.897(P) P )- 0.86. Particularly, the predictive accuracy can d 85 attain a level of 87.50% for systems characterized by varying grain sizes ( D 15 >= 0.431 mm) and densities (Dr D r <= 0.67) of EPSGM stabilizing coral sand foundations. Furthermore, it also applies to other systems in literature that exhibit accuracy ranging from 33.33% to 62.50%. Therefore, the derived predictive model performs greater engineering relevance in informing the selection of grout factors.

Application of biopolymers to improve the mechanical properties of soils has been extensively reported. However, a comprehensive understanding of various engineering applications is necessary to enhance their effectiveness. While numerous experimental studies have investigated the use of biopolymers as injection materials, a detailed understanding of their injection behavior in soil through numerical analyses is lacking. This study aimed to address this gap by employing pore network modeling techniques to analyze the injection characteristics of biopolymer solutions in soil. A pore network was constructed from computed tomography images of Ottawa 20-30 sand. Fluid flow simulations incorporated power-law parameters and governing equations to account for the viscosity characteristics of biopolymers. Agar gum was selected as the biopolymer for analysis, and its injection characteristics were evaluated in terms of concentration and pore-size distribution. Results indicate that the viscosity properties of biopolymer solutions significantly influence the injection characteristics, particularly concerning concentration and injection pressure. Furthermore, notable trends in injection characteristics were observed based on pore size and distribution. Importantly, in contrast to previous studies, meaningful correlations were established between the viscosity of the injected fluid, injection pressure, and injection distance. Thus, this study introduces a novel methodology for integrating pore network construction and fluid flow characteristics into biopolymer injections, with potential applications in optimizing field injections such as permeation grouting.

In many densely populated cities, buried networks of urban services, such as facilities and sewage tunnels or sewer pipes are constructed adjacent to or beneath nearby building foundations. It is vital to consider the seismic interaction of shallow tunnels with these foundations in liquefiable deposits. In such circumstances, segmental tunnels are of interest due to being considered non-rigid structures, and their utilization has increased in shallow urban tunneling. Using a two-dimensional finite difference code, a shallow tunnel subjected to uplift pressures due to soil liquefaction is studied. An advanced constitutive model (PM4Sand) is employed in the numerical model along with a fully coupled Fluid-Solid solution to simulate soil liquefaction. First, a centrifuge laboratory model was used to validate the coupled hydrodynamic numerical simulations. Additionally, it allows for the use of real sand properties. The validation results indicated a good agreement between the numerical simulations and the centrifuge tests for tunnel uplift (maximum difference of 7 %) and the excess pore water pressure ratio (ru). Next, based on the results, segmentation of the tunnel lining was found to be effective in reducing ground surface uplift by 23 %. Then, a segmental tunnel lining with and without a five-story building on a combined footing foundation is considered under soil liquefaction. The interaction between the shallow foundation of the five-story building and the segmental lining highlights the significant influence of tunnel uplift on shear force, bending moment, tilting and rotation of the foundation and surface structure. Additionally, the presence of the foundation and surface structure leads to a reduction in tunnel uplift (by 29 %) and ground surface uplift (by 21 %). Lastly, a permeation grouting method has been utilized to mitigate seismic soil-surface structure-underground structure interaction (SSSSUSI) during liquefaction, resulting in a 90.7 % reduction.

Low-pressure injection of nanosilica aqueous suspensions is often adopted to either waterproof or increase the liquefaction resistance of granular soils. The basic principle behind this ground improvement technique consists in filling the soil pores with a low-viscosity fluid that changes its consistency with time, first into a gel, then into a solid. From an application point of view, the simulation of the time-dependent permeation process is crucial to relate the in situ distance covered by the grout to the operational parameters. A comprehensive investigation was performed, combining laboratory experiments with theoretical approaches, to characterize the phenomenon and then derive predictive relations useful for designing treatment executions. The time-dependent rheological properties of different nanosilica aqueous suspensions were first quantified by means of rheometric tests, then described with Bingham's law. Grout permeation in granular media was then simulated by suitably modifying Darcy's law to incorporate the temporal evolution of Binghamian grout rheology. After validating the modified Darcy's law employment for nanosilica grout flows with respect to laboratory experimental data, simplified analytical equations, capable of predicting the temporal evolution of the distance covered in situ by the grout and the flow rate-injection pressure relation, are provided. Nanosilica aqueous suspensions are environmentally nontoxic materials with the consistency of a low-viscosity fluid, suitable for injections into fine-graded soils, but, when mixed with a sodium-chloride solution, they transform with time into a gel of solid consistency. Thanks to these properties, they are frequently adopted to provide a fast remedial against piping induced by excavation, seal contaminants or reduce the liquefaction potential of sands. Nanosilica grout is commonly injected at low pressure, leading to filling soil pores during seepage. The previously mentioned transient evolution of the suspension rheological properties, controlled by nanosilica and sodium-chloride proportions, starts during the injection-seepage phase, playing a paramount role in affecting the geometry of the treated soil domain. The present work provides an accurate description of the time-dependent grout rheology and a predictive seepage analytical tool to simulate the diffusion of nanosilica grouts, characterized by variable compositions and injected from sources of different geometrical layouts into homogeneous soils with different grain size distributions. This tool allows tailoring of the injection parameters (pump pressure, nozzle spacing, injection time) on in situ soil hydraulic properties and rheology of the selected nanosilica suspension.

An attractive approach to reduce the carbon footprint for ground improvement application is to replace Portland cement-based binders by non-cementitious binders for instance by geopolymers based on metakaolin in deep soil mixing applications or by colloidal silica and acrylates in permeation based applications. Safe design requires a good understanding of the mechanical and hydraulic properties of the improved ground but little is known about how soil is improved by these products. Besides, for permeation grouting applicability criteria are frequently set in terms of the host soil water permeability. However, for novel binders the threshold value is not known and published empirical basis for available criteria is relatively scarce. This paper summarizes results from a laboratory characterization campaign of soils of variable permeability improved with different novel binders, focusing on the effect on strength, stiffness and permeability. Observations relative to the effect of curing conditions are also provided, as well as the insight gained by examining the injection process outcomes with computed tomography. Results show how these novel products have the potential to significantly improve the mechanical properties and reduce permeability in a large range of soils.