As a relatively new method, vacuum preloading combined with prefabricated horizontal drains (PHDs) has increasingly been used for the improvement of dredged soil. However, the consolidation process of soil during vacuum preloading, in particular the deformation process of soil around PHDs, has not been fully understood. In this study, particle image velocimetry technology was used to capture the displacement field of dredged soil during vacuum preloading for the first time, to the best of our knowledge. Using the displacement data, strain paths in soil were established to enable a better understanding of the consolidation behavior of soil and the related pore water pressure changes. The effect of clogging on the deformation behavior and the growth of a clogging column around PHD were studied. Finite element analysis was also conducted to further evaluate the effects of the compression index (lambda) and permeability index (ck) on the soil deformation and clogging column. Empirical equations were proposed to characterize the clogging column and to estimate the consolidation time, serving as references for the analytical model that incorporates time-dependent variations in the clogging column for soil consolidation under vacuum preloading using PHDs.

The widespread utilisation of vacuum-assisted prefabricated vertical drains (PVD) for managing clayey soft ground has led to the development of numerous consolidation models. However, these models have limitations when describing the filtration behaviour of soil under high water content conditions, without the formation of a particle network. To effectively address this issue, in this work, based on the compressional rheology theory, a two-dimensional axisymmetric model incorporating the compressive yield stress Py(phi) and a hindered setting factor r(phi) was developed to couple the filtration and consolidation of soil under vacuum preloading. A novel approach for determining the unified phi-Py-r relationships was introduced. The equation governing such fluid/solid and solid/solid interactions was solved using the alternative direction implicit (ADI) method, and the numerical solutions were validated against the 1-D filtration cases, 3-D laboratory model tests, and large-scale field trials. Further parametric analysis suggests that the radius of the representative unit and r(phi) exclusively affect the dewatering rate of the clayey slurry, while the gel point and Py(phi) influence both the dewatering rate and the final deformation.

In view of the challenges posed by construction on deep soft coastal ground, this study introduces the precast drainage pile (PDP) technology. This innovative approach combines precast pipe piles with prefabricated vertical drains, installed through static pile pressing and subsequently subjected to vacuum negative pressure for the consolidation of surrounding soil. To evaluate the efficacy of PDP technology, a comparative analysis was conducted between precast pile and PDP, incorporating field testing and numerical simulation. The investigation focused on the evolution of excess pore water pressure, deformation, and pile bearing capacity. Results indicated that vacuum negative pressure drainage could induce rapid initial dissipation of pore water pressure, followed by a slower rate. Excess pore pressure decreased more rapidly and significantly closer to the drained pile, aligning with drainage consolidation theory. After 5 days of consolidation, the PDP exhibited a 16% increase in ultimate bearing capacity compared with the undrained pile. Numerical simulation outcomes closely matched field measurements. The enhancement in pile bearing capacity was found to correlate hyperbolically with drainage time, culminating in a 26.5% ultimate increase. The research achievements facilitate the development of new pile technologies in coastal soft soil areas.

The lateral cyclic bearing characteristics of pile foundations in coastal soft soil treated by vacuum preloading method (VPM) are not well understood. To investigate, static lateral cyclic loading tests were conducted to assess the impact of treatment durations and sealing conditions on pile performance. Results indicated that vacuum preloading significantly improved soil properties, with undrained shear strength (S-u) increasing by up to 36.5 times, especially in shallow layers. Longer treatment durations boosted the ultimate lateral bearing capacity by up to 125%, although the effect decreased with depth, suggesting an optimal duration. Sealing conditions had minimal impact on capacity but affected S-u distribution and pile behaviour. Analysis of p-y curves revealed that longer durations improved soil resistance in shallow layers, while shorter durations provided consistent resistance across depths. Sealed conditions enhanced displacement capacity. The API specification predicted soil resistance accurately for lateral displacements under 0.1D but showed errors for larger displacements. These findings emphasise the need for optimising VPM parameters to enhance pile-soil interaction and lateral cyclic performance. The study offers guidance for applying VPM in soft soil foundation engineering and balancing performance with cost efficiency.

The rail network invariably encounters soft subgrades consisting of shallow estuarine clayey deposits. Cyclic loading generated by the passage of trains causes deformation and corresponding development of excess pore water pressure (EPWP), which dissipates during the rest periods between two consecutive trains. This paper presents an experimental study describing the effect of yield stress and EPWP responses upon intermittent cyclic loading (i.e. with rest periods), and the associated consolidation with the combination of vertical and radial drainage by way of a prefabricated vertical drain (PVD). Based on the laboratory data, the normalised yield stress for cyclic loading (NYCL) is introduced as an insightful parameter to define a novel empirical relationship between the yield stress, cyclic stress amplitude and the initial effective stress. The experimental results indicate that, as the NYCL increases, the peak EPWP decreases and, during the rest periods, the EPWP reaches a stable equilibrium faster without causing further settlement. Furthermore, this study demonstrates that the accumulated EPWP caused by cyclic loading can be further reduced when using a larger width of PVD for a given unit cell radius. An analytical model inspired by empirical parameters for predicting EPWP is proposed, capturing the effects of NYCL and the PVD characteristics.

Biogrouting, a method to enhance soil properties using microorganisms and mechanical techniques, has shown great potential for soil improvement. Most studies focus on small sand columns in labs, but recent tests used 0.5 m plastic boxes filled with sand stabilized with microorganisms and fly ash. The experiments, conducted over 30 days, applied injection and infusion methods with microbial fluids, maintaining groundwater levels to simulate field conditions. Mechanical properties were analyzed through unconfined compressive strength (UCS) tests on extracted samples. Researchers also assessed calcium carbonate distribution and shear strength. Results showed water saturation significantly influenced vertical stress (qu), while UCS correlated with the permeability of sand containing varying calcium carbonate levels. Bacillus safensis, a resilient bacterium used in this process, can withstand extreme conditions. After completing its task, it enters a dormant state and reactivates when needed. The bacteria produce calcium carbonate by binding calcium with enzymes, which cements soil particles, enhancing strength and stability. center dot Testing enzymes on microbes and natural soil center dot Installation settings for drip tools using infusion center dot Soil resistance testing after stabilization using UCS

This study investigated the improvement in a type of sand using a geopolymer made of recycled glass powder (RGP) as the base material and sodium hydroxide (NaOH) as the alkaline activator. Using maximum uniaxial compressive strength (UCS), the impact of alkaline activator concentration and the RGP content were investigated to determine the optimum mix design. Groundwater level increments were simulated through a laboratory procedure to study the effect of curing age and capillary action on the behavior of stabilized soil. The UCS of samples at different ages (14, 28, 45, and 60 days) and different degrees of saturation (Sr=0%, 20%, 50%, 80%, and 100%) were determined and their stress-strain diagrams were drawn. Using the stress-strain relationships, UCS, modulus of elasticity (Es), shear modulus (G), and resilient modulus (Mr) of the stabilized soil were estimated. The results showed that fully saturated stabilized samples did not disintegrate and exhibited a considerable UCS of up to 1.88 MPa at the age of 60 days. The greatest observed reduction in the UCS through saturation was between Sr=0 to 20%. To further investigate and validate the mechanical results, chemical and microstructural studies including X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction analysis (XRD), and Fourier transform infrared spectroscopy (FTIR) were carried out. The results showed that during the curing period, the silicon/aluminum (Si/Al) ratio increased from 2.98 in untreated soil to 4 in stabilized samples, indicating active geopolymerization, which enhanced UCS and reduced the potential for disintegration. Additionally, the crystal size decreased from 53 to 24 nm for the 45-day stabilized samples when the degree of saturation changed from 0% to 100%. This finding suggests that if RGP-based geopolymer-stabilized soil contacts water after fully drying, geopolymerization reactions will resume that involve the dissolution of both crystalline and amorphous phases.

If building loads cannot be transferred into the soil, ground improvements are often used, which require the addition of cement with considerable emissions of CO2. Thermo-mechanically processed crushed concrete fines can partially replace the required cement. This article deals with comprehensive laboratory tests to improve the soil mechanical properties of a typical sand as a building ground and demonstrates the applicability of thermo-mechanically processed concrete fines for the substitution of 25 wt.-% to 50 wt.-% of cement for practical construction purposes. Processing temperatures of 400 degrees C and 600 degrees C proved to be particularly effective, with greater reductions in strength and stiffness occurring outside this temperature range.

The recycling and reuse of construction and demolition materials offer significant environmental and economic benefits. This study investigated the performance of aggregates with varying proportions of recycled concrete aggregate (RCA) and natural aggregate (NA) as base materials. Key parameters, such as compaction behaviour, California bearing ratio (CBR), and resilient modulus, were evaluated. The findings revealed that the mixture with 50% RCA and 50% NA exhibited the highest CBR and resilient modulus values. Small-scale cyclic loading tests were then conducted on the samples of NA, RCA, and a 50% RCA-50% NA mixture to assess the suitability of RCA as a base material. Additionally, RCA and NA samples were reinforced with biaxial geogrids for material optimisation. The results showed that the 50% RCA-50% NA mixture exhibited the smallest permanent deformation, and the geogrid, placed at the middle depth of the base, significantly reduced rut depth. Findings of this experimental study suggest that RCA can be used as an alternative base material to partially replace NA in road construction. The results can help conserve natural resources, promote sustainability through the reuse of waste materials, and reduce the environmental impact associated with the use of NA in road construction.

Cinder gravel, a porous, lightweight, and durable volcanic byproduct, has the potential to be a sustainable and cost-effective alternative to conventional stone columns for ground improvement applications. Its use in soft soils, however, requires sufficient confining pressure to prevent bulging and thus performance degradation. Geotextile-encased cinder gravel (GECG) columns are therefore an innovate method to overcome this, however their bearing response and pressure-deformation characteristics have received limited study. This paper presents a comprehensive numerical analysis for GECG columns using a coupled discrete element and finite difference method (DEM-FDM). The hybrid DEM-FDM framework enables the simulation of individual particle behavior while maintaining efficiency in modeling continuous, homogeneous materials. The key novelties are examining the macro and mesoscopic behavior of GECG columns under triaxial compression. To do so, the development of the numerical model is introduced, followed by its validation and calibration against triaxial test results. Subsequently, a parametric analysis of GECG columns investigates the influence of relative density and gradation on the compression behavior and load capacity. Upon triaxial compression, the findings reveal a significant radial expansion near the column top, with stress and deformation fields aligning with the column's bearing capacity. The relative density exerts limited influence on the geotextile's radial deformation, and the higher content of coarse particles in the gradation enhanced the bearing capacity of the GECG columns.