This study comprehensively evaluated the influence of dual geogrid-geocell reinforcement and geogrid placement depth on the mechanical performance of unpaved roads constructed over weak subgrade (CBR = 2.52%) using a multiple field-testing approach i.e., Falling Weight Deflectometer, Lightweight Deflectometer, and dynamic field CBR tests combined with mechanistic analysis using IITPAVE. Six instrumented pavement test sections, incorporating different reinforcement configurations, were constructed in the field and their performance was assessed on the basis of increased stiffness, deformation reduction, stress distribution, service life, and reinforcement benefit. Results indicated that the section with combined geogrid-geocell reinforcement exhibited the superior mechanistic performance followed by the standalone geocell-reinforced section. Among different geogrid placement configurations, one-quarter of the base layer thickness was identified as the optimum placement depth for the geogrid due to its improved mechanistic behavior and reinforcement benefits. Cost-benefit analysis indicated that although reinforced sections incur higher initial material costs, the enhanced structural performance resulted in improved cost efficiency. Additionally, the study compared the performance outcomes from LWD tests with those from FWD tests to assess the reliability and consistency of LWD-based measurements for rapid and preliminary field assessment, while the FWD tests provided a more comprehensive evaluation of system-level response.
The long-term chemical, mechanical, and hydraulic performance of a styrene-butadiene-styrene (SBS)-modified bituminous geomembrane (BGM) was investigated using accelerated ageing for up to 80 months (6.7 years). The experimental program combined mechanical testing of the nonwoven polyester geotextile reinforcement (NW GTX), chemical and rheological characterization of the SBS -modified bituminous compound using Fourier-transform infrared spectroscopy, dynamic shear rheometry, gel-point analysis, and proton nuclear magnetic resonance, together with constant-head permeability testing under applied stress. Results show that degradation of the examined BGM is governed by two concurrent mechanisms. The bituminous compound undergoes thermo-oxidative ageing and progressive breakdown of the SBS polymer network, resulting in increased stiffness and loss of viscoelastic strain-accommodation capacity. Concurrently, the NW GTX reinforcement degrades primarily through hydrolysis driven by diffusive transport of water and dissolved constituents of the solution across the bituminous compound. Permeability testing showed that loss of hydraulic barrier function was stress-activated and occurred once either the SBS network collapsed or the reinforcement lost mechanical integrity. These findings indicate that nominal material failure should be interpreted as an index-based material degradation state, defined using bituminous compound and reinforcement-based criteria, with its relevance to hydraulic barrier function depending on the applied mechanical stress.
Geosynthetic-Reinforced Load Transfer Platform for Pile-Supported Embankments (GLTP-PSE) enables construction over soft soils by transferring loads into deep foundations. This research study presents a full-scale case study of the GLTP-PSE constructed at the Amite River site, Louisiana, USA. A comprehensive field instrumentation program, including multi-level piezometers, Vibrating Wire Earth Pressure (EP) cells, horizontal Shape Acceleration Array profilers, inclinometers, and geogrid strain gauges, was implemented for field monitoring and track the performance of GLTP-PSE during and after construction. The staged construction induced moderate excess pore pressures (peak≈10 kPa), which dissipated fully during a 1.5-year consolidation pause. EP cells recorded substantial soil arching, with vertical stresses on piles roughly 20-30 times those in the surrounding soil, corresponding to a high Stress Concentration Ratio (SCR) of 20-30, with 38-40% of the embankment load carried by the piles. Differential settlements between piles and soil were minimal (<20 mm) due to pile support and geosynthetic reinforcement, and total settlements remained uniform. Lateral movements of foundation soil were very small (max. 18 mm). Strain gauges showed peak geogrid strains of 1.4% in the lowest geogrid layer and <0.5% in the upper geogrid layers, confirming the conservative design. In addition, a 3D Finite Element (FE) model was developed in PLAXIS to simulate GLTP-PSE behavior, and the results showed close agreement with field measurements of pore pressures, stress distributions, settlements, and geogrid strains. The 3D FE accurately predicted the embankment response during staged construction and consolidation. Moreover, seven selected analytical design guidelines (BS8006, Nordic, EBGEO, FHWA, CUR 226, Pham (2020), and Chinese Code) were also evaluated by comparing their predictions with full-scale field measurements and 3D FE analyses for the current GLTP-PSE full-scale test site. The GLTP-PSE demonstrated effective load transfer and settlement control on soft soil. The findings provide valuable insights into GLTP-PSE performance and validate FEM for design optimization.
Simple shear tests, three-dimensional morphology scanning, and fractal analysis were combined to investigate the relationship between interface morphology and shear resistance. Two granular soils with different particle characteristics were considered, and the effects of normal stress, soil relative density, EPS geofoam density, and preload duration were systematically evaluated. Results showed that increasing normal stress enhanced particle penetration into the EPS geofoam surface, producing rougher and more complex interface morphologies. The fractal dimension D of the interface morphologies increased rapidly with normal stress and then approached a stable value once EPS geofoam densified. Coarse granular soil produced larger D values and higher interface friction than finer sand due to stronger particle interlocking. Increasing soil relative density reduced both D and interface friction, whereas EPS geofoam density had only a minor effect within 15–25 kg/m3. A strong relationship was observed between the interface friction coefficient μ and D, with μ increasing approximately linearly with D and the increment in friction coefficient showing a near-linear relationship with the increment in fractal dimension. These findings indicate that interface shear behavior is governed primarily by the evolution of real contact morphology.
In this paper, the results of experimental and numerical investigations into the effectiveness of geogrid-reinforced backfill in improving the performance of surface-loaded precast cut-and-cover tunnels (CCTs) are presented. A series of reduced-scale model tests was first conducted using a 1/35 scale model, designed with due consideration of the similitude law, to examine the governing mechanism. Additional two-dimensional finite element analyses were performed to complement the experimental observations and enable quantitative evaluation at prototype scale. The primary variables considered were geogrid arrangements, length, vertical spacing, number of layers, and axial stiffness. The results indicate that geogrid reinforcement significantly reduces soil deformation and shear strain in the backfill, thereby mitigating the impact of surface loading on the tunnel. Also revealed is that unlike conventional geogrid applications for shallow foundations, the system performance is most effectively improved when geogrid layers are placed in close proximity to the tunnel crown. Based on a parametric study, critical values of key geogrid design parameters are also identified. The findings confirm that geogrid-reinforced backfill is an effective means for improving the load carrying capacity of cut-and-cover tunnel systems.
This study investigates lateral deformation and strain localization in soft ground improved by prefabricated vertical drains (PVDs), vacuum consolidation, and a sheet-pile system. A two-dimensional finite element model was developed in PLAXIS for a real embankment project on very soft marine clay in Ho Chi Minh City, Vietnam. The modelling framework introduces two practical approximations: an equivalent plane-strain consolidation method using line drains calibrated against an axisymmetric unit-cell model, and a vacuum simulation method that better reproduces the theoretical vacuum-induced effective stress increase. The model was validated using field measurements of surface settlement, lateral displacement, and observed damage patterns. Parametric analyses were then performed to examine the effects of embankment width, PVD length, sheet-pile depth, and sheet-pile stiffness. The results show that sheet-pile system reduces maximum lateral displacement by approximately 50–70%, although deformation may still propagate into adjacent ground. Increasing embankment width and PVD length expand both the lateral displacement zone and the deviatoric strain localization zone. A critical condition occurs when the PVD length equals or exceeds the sheet-pile depth, causing shear bands to initiate near the sheet-pile tip and propagate toward the protected side. The findings provide practical guidance for designing PVD–vacuum consolidation systems near sensitive structures.
Back-to-back mechanically stabilized earth (BBMSE) walls have been used for bridge abutments, highway and railway embankments. FHWA guidance for BBMSE walls emphasizes the effects of reinforcement configuration on wall interaction and external stability. However, their behavior under footing loading has received less attention. In this study, five BBMSE wall models with separated, meeting, overlapped, continuous, and mixed configurations were tested under static footing loading to investigate the effects of reinforcement configuration on pressure-settlement response, lateral earth pressure distribution along the wall facing, reinforcement strain, and facing deformation. Continuous or overlapped configurations exhibited higher bearing capacities, whereas the separated configuration showed 80% reduction in ultimate bearing capacity compared to the continuous configuration. Separated or meeting configurations developed localized peak lateral pressures at intermediate elevations while the overlapped and mixed configurations shifted the pressure concentration to lower elevations. In all tests, peak tensile strains developed at a horizontal distance of approximately 0.3 times the wall height from the wall facing, reaching up to 0.45%, although their magnitudes and distributions varied among reinforcement layers and configurations. Reinforcement continuity strongly influenced deformation and failure mechanisms: separated configurations exhibited pronounced bulging and localized failure, while overlapped and mixed configurations promoted more distributed deformation and integrated behavior.
A investigation was conducted within a slurry pond to propose a sustainable method for improving engineering properties of ultra-soft sludge. The ground improvement technique employed was Prefabricated Vertical Drains (PVDs) in combination with preloading, with the usage of green construction materials. Finite element model (FEM) analysis was conducted to ensure the stability of working platform construction under undrained condition and to control the field construction sequence. The waste sand reinforced with bamboo grids and a geotextile was utilized as the working platform. The waste chipped rock and excavated claystone were employed as drained layer and loading surcharge. The FEM results suggested factor of safety greater than minimum criterion of 1.2 for a 2-layer working platform construction. The field monitoring results demonstrated that the reinforced working platform provided sufficient bearing capacity for heavy machinery and allowed safe PVD installation. The rapid and uniform consolidation settlement of sludge after PVD installation under surcharge loading was observed, indicating acceptable capacity of chipped rock drainage blanket. Using Asaoka method, the average degree of consolidation of > 90% was attained within 19 days after backfilling. The output of this study confirm both the technical viability and the practical effectiveness of the proposed approach.
The study reports the results of a testing program to evaluate the pullout response of PET strap reinforcement of different grades at various vertical stresses and in-soil temperatures. Tests were carried out using a well-graded, granular soil with small fines content. Pullout response and reinforcement longitudinal stiffness were evaluated using measured pullout loads and front- and tail-end displacement measurements. Pullout resistance was observed to increase non-linearly with increasing vertical pressure (or depth). Overall, temperature variations in the range of 15°C to 35°C did not result in practical differences in peak pullout resistance. However, in-soil temperature appears to influence reinforcement longitudinal stiffness, more so than vertical pressure calculated, at peak pullout load. The accuracy of four analytical models for pullout resistance and friction interaction factor was quantified using bias statistics. Data showed higher spread between measured and calculated values at shallow depths, attributed to a greater sensitivity of the dilatant response to vertical pressure and compaction conditions. Model accuracy dependency with calculated pullout resistance and vertical pressure was explored. Bi-linear and non-linear pullout models were found to be statistically more accurate than the linear pullout model which appears in many design codes.
The effectiveness of Geocell Anchor Cage (GAC) system as a structural add-on to conventional geocell reinforcement was earlier established by the authors. However, design parameters for this GAC system to achieve enhanced reinforcing benefits and its applicability to different soil-geocell systems remain unexplored. This paper presents comprehensive investigation on the design of geocell-GAC systems for load-bearing applications through experimental, analytical, and numerical studies. To eliminate scaling issues, customised 3D printed geocells made of polypropylene and GACs made of polylactic acid are used in experiments. The specific contribution of GAC to the overall increase in load capacity and settlement reduction with changing geocell and GAC parameters and soil density is quantified. Further, various design parameters of GAC system, including pin diameter and rib dimensions for deriving improved reinforcing benefits, are obtained from plate load tests. The benefits of GAC are found to be more significant for geocells of lower stiffness, larger pocket sizes, shorter geocell heights, and for soils of lower density. Width of GAC can be limited to 1.5 times the foundation width in a geocell layer of 3.5 times the foundation width for optimal benefits. A semi-empirical analytical equation is developed to predict pressure-settlement response of geocell-GAC sand beds.
This paper presents an analytical framework for geocell-reinforced unpaved roads based on Layered Elastic Theory (LET). The proposed model integrates LET with a stress-dependent analytical approach for the calculation of the Modulus Improvement Factor (MIF). It explicitly accounts for the surface load, geometric and elastic properties of the geocell, the infill material, the compaction effort, and the subgrade properties. The formulation provides a rational means to evaluate surface deflections and vertical stresses and strains at the top of the subgrade, which may support subsequent coupling with empirical performance relationships for unpaved roads. Validation was performed using data from 42 field and laboratory sections with measured deflections and 21 experiments with subgrade stress measurements, covering a broad range of testing types, loading conditions, magnitudes, subgrade and infill soils, compaction levels, and geocells with different geometries, polymers, and wall stiffnesses. The comparison demonstrated good overall agreement between analytical predictions and experimental measurements. The proposed framework reproduced the structural response of geocell-reinforced systems with consistency across different conditions. Although the formulation focuses on the analytical evaluation of short-term responses, the results highlight its potential as a basis for subsequent integration with empirical performance approaches.
The growing application of nonwoven wicking geotextiles for capillary water drainage in transportation embankments highlights the need to better understand the hydraulic mechanisms governing their field performance efficiency. Accordingly, this study investigated wettability and wickability in nonwoven geotextiles, emphasizing pore structure as the critical link between these two distinct phenomena. Experimental characterization was conducted through contact angle (CA) measurements using water, glycerin, and mineral oil droplets, alongside horizontal radial wicking tests with an infinite water source. The latter test provided a more representative assessment of material-scale wicking behavior than CA measurements. Two nonwoven wicking geotextiles (WGv1 and WGv2) and one nonwicking control (NG) were evaluated. The use of a wide range of probe liquids and nonwoven geotextiles enabled the assessment of diverse wetting interactions and the measurement of wicking rates for various liquid–geotextile combinations. Notably, enhanced wettability did not always result in higher wicking rates. WGv1, with its more open and porous structure, consistently exhibited a greater wicking rate than WGv2, which featured a denser configuration. Additional tests on a wicking sample impregnated with fine glass beads showed lower gravimetric liquid retention and diminished water wicking performance, highlighting the importance of evaluating soil–geotextile interaction.
Prediction of the lateral displacement and the associated impact zone under the coupled effect of vacuumsurcharge loading remains significant challenges in design of vacuum consolidation method (VCM). Following an earlier field study by the authors, where extensive investigations on lateral displacement in VCM sites were conducted, this paper details development of numerical modelling and proposes a novel analytical method. Finite element method is adopted to reproduce the test embankments with close validation with field data, followed by a comprehensive parametric study on the influence that varying the vacuum-surcharge load ratio and distance from the embankment can cause on the lateral displacement. The numerical results reveal the nonlinear relationship between the load ratio and lateral displacement of soil, allowing for assessment of the lateral impact zone. By forming empirical correlations between the displacement and load ratios, the study proposes a novel analytical procedure to estimate the lateral displacement according to distance from the embankment toe. The proposed method is validated against six different case studies, demonstrating its great reliability and robustness in predicting spatial lateral displacement. This study enables the lateral impact zone to be determined based on lateral displacement profile, giving a simple yet accurate approach for safe and cost-effective design and construction planning.
Laboratory model tests and field implementation confirm the effectiveness of prefabricated horizontal drains combined with vacuum preloading (PHDs-VP) in treating dredged sludge, but analytical solutions for its large strain nonlinear consolidation are rarely reported. This study first reveals the symmetric distribution of excess pore water pressure (EPWP) in a PHDs-VP improved disposal site using existing numerical solutions, then decomposes its representative unit into two simplified models (single and double drainage boundaries), and derives their semi-analytical solutions via variable substitution, Laplace transform, finite Fourier cosine transform, and numerical inverse transform. The accuracy and applicability of the proposed solutions are validated against existing numerical solutions and laboratory model test results. On this basis, a series of analysis were further conducted to evaluate the effects of the key parameters on consolidation behavior. Finally, the proposed analytical solution for the large strain consolidation model is applied to the settlement and water content calculation of the dredged sludge disposal site in Aomori Prefecture, which further demonstrates the applicability of the consolidation model. This study provides theoretical support for predicting the consolidation of highly compressible sludge dredger treated by PHDs-VP in engineering practice.
To address the late-stage issues of clogging, nonuniform consolidation, and low monitoring efficiency in soft ground improved by vacuum preloading with prefabricated vertical drains (PVDs), a comparative field study of intermittent vacuum preloading was carried out at the Xuanmen Bay project in Yuhuan. Three test areas were established to implement intermittent vacuum preloading with intermittent ratios of 1:3 and 1:2, alongside a conventional continuous vacuum preloading scheme. During improvement, settlement, vacuum pressure, pore water pressure, and energy consumption were monitored in real time; after improvement, water content tests and field vane shear tests were conducted. The results indicate that, relative to continuous vacuum preloading, the final degrees of consolidation under the 1:3 and 1:2 intermittent schemes were 4.9% and 10.3% lower respectively, whereas the potential consolidation settlement was greater. Intermittent operation markedly alleviated deep-soil clogging, improved drainage, and produced more uniform foundation consolidation. In terms of energy performance, the 1:3 and 1:2 schemes achieved energy savings of 27.0% and 40.3%, respectively; particularly in the late stage of consolidation, their energy efficiency was about 44% higher than that of the continuous scheme. These findings demonstrate that intermittent operation effectively mitigates late-stage clogging in vacuum preloading and enhances energy efficiency.
This study examines the zonal micromechanics of geogrid-ballast interaction using integrated large-scale triaxial tests and Discrete Element Method (DEM) simulations. Tests were conducted on loose and compacted ballast with and without geogrid inclusion, incorporating SmartRock sensors to capture local contact forces and particle rotations. Corresponding DEM models with representative ballast particles, an explicit geogrid, and a flexible membrane boundary were developed and validated against experimental responses. Results reveal that geogrid inclusion alters particle-scale load-transfer mechanisms. Stabilization promotes the formation of a more connected contact network and redistributes loads toward regions near and above the geogrid, while suppressing force transmission and particle kinematics below it. The stabilization effect is more pronounced in loose ballast, whereas compacted ballast retains higher inherent strength due to pre-existing interparticle interlocking. Although overall volumetric change is only marginally affected, the geogrid redistributes deformation, shifting dilation and bulging away from the specimen mid-height. These findings provide direct mechanistic evidence of how geogrids regulate force transmission and deformation in ballast, offering a basis for optimizing geogrid design and placement in railway tracks.
This study examines the bearing performance and load-transfer mechanisms of triaxial geogrid-reinforced unpaved roads over soft clay subgrades using large-scale testing and three-dimensional finite-element modeling. Eleven plate-bearing tests were performed on geogrid-reinforced unpaved roads over compacted high-plasticity (CH) and low-plasticity (CL) clays, considering granular base thicknesses of 0.05-0.20 m. Numerical simulations using the Hardening Soil model reproduced load-settlement response, stress redistribution, failure mechanisms, and geogrid strain development. Unreinforced granular bases increased bearing stress at a normalized settlement of 0.1B by approximately 2.0-3.5 times compared with soft clay alone. With triaxial geogrid reinforcement, bearing stress at 0.1B increased to about 520-860 kPa for CH clay and 650-1000 kPa for CL clay. Granular bases, with and without geogrid reinforcement, reduced vertical stress transmitted to the subgrade by approximately 23-77%, with consistently higher stress reductions observed for the CL subgrade due to its greater stiffness and lower plasticity, which promote more effective stress diffusion within the granular base. Failure modes shifted from localized punching to distributed deformation, while geogrid strains remained low at serviceability settlements, typically below 200 mu epsilon. Numerical results closely matched experimental observations, supporting performance-based design of geogrid-reinforced unpaved roads over soft clay.
Integral abutment bridges (IABs) eliminate bearings and joints but intensify soil-structure interaction during earthquakes. EPS geofoam is used as a compressible backfill, though its seismic performance under saturated conditions is not well understood. This study presents a 60 g centrifuge test of a single-span IAB on spread footings in saturated loose sand, comparing conventional backfill with a 1 m EPS inclusion behind each abutment. Six earthquake motions (PGA up to similar to 0.35 g) were applied, measuring settlements, rotations, accelerations, bending moments, excess pore pressures, and soil deformation. EPS effects were found to be strongly earthquake-intensity dependent. At low shaking levels (PGA < 0.1 g), responses were similar for both configurations. At higher intensities (PGA approximate to 0.25-0.35 g), EPS significantly reduced excess pore-pressure generation and foundation settlements despite higher recorded base accelerations. Settlements beneath the left and right abutments were reduced by approximately 70% and 40%, respectively, relative to the conventional backfill configuration. In contrast, EPS increased global rocking, with peak bridge rotations during the strongest motion increasing by approximately an order of magnitude (from similar to 0.004(degrees) to similar to 0.05 degrees). EPS also amplified structural demand: deck accelerations increased by roughly 10%-40%, while cyclic oscillations of abutment and deck bending moments were nearly doubled, whereas soil-surface accelerations remained broadly similar. These findings show that EPS geofoam does not uniformly reduce seismic demand. Its compressibility lowers earth pressures and settlements but shifts more inertial demand to the bridge superstructure, underscoring the need for design approaches that account for demand redistribution.
A full-scale test using vacuum consolidation method with an airtight membrane and vertical-band drains was implemented for the first time in Mexico and at a high-altitude site (2227 m. a.s.l). The trial embankment was constructed at the former Texcoco Lake on an extremely compressible clayey soil. This paper describes the soil conditions, characteristics of the embankment, phases of construction, instrumentation, monitored results, and the application of observational methods to estimate the degree of consolidation. The embankment monitoring period was one year, with six months of vacuum application. The maximum vacuum pressure applied was -73 kPa and an average vacuum pressure of -63 kPa. The decrease in the pore pressures due to the vacuum was 57.14% of the average vacuum pressure. The monitoring results show that the vacuum preloading system effectively accelerated consolidation. At the end of the vacuum application period, the settlement at the center of the embankment was 2.90 m. Given the above, it was estimated that a consolidation degree of 87.8% was reached accordingly to the settlement plates records. Field observations additionally highlight the importance of maintaining the vacuum pumps at elevations similar to the prefabricated horizontal drains to preserve effective vacuum transmission during large settlements.
