Alternative drainage designs are developed due to high failures in retaining walls with missing or inadequate drainage. This study investigates the usage of nonwoven conical filter systems and their hydraulic compatibility with common backfill material using both laboratory and computational modeling. Computational fluid dynamics numerically solved the fluid flow and the discrete element method allowed for the modeling of particle to particle, and those methods were coupled to simulate particle-to-fluid contact. Through a combination of these methods, piping and retention performances of various soil-geotextile systems were studied. Nonwoven geotextiles were numerically modelled, partly by using the Poisson line process to simulate the inherent randomness found in fabricated nonwoven filters. The model results were compared with laboratory tests to corroborate the accuracy of the models. The soil-nonwoven filter systems, either conventional or conical, provided 6–87% lower permeability values compared to soil-woven systems and had 10–48% higher piping rates than their counterparts. A support-vector-machine algorithm was utilized to classify zones for the performance curves for woven and nonwoven geotextiles, where a clear distinction in zones was shown.

This paper provides insight into the causes of post-peak strength loss for textured geomembrane (GMX) and nonwoven geotextile (NGT) interfaces. The NGT can be part of a geosynthetic drainage composite (GDC) or a stand-alone NGT. The study used ring shear tests where one of the two interface materials was replaced after reaching a residual strength condition and restarting the test to measure the change in interface strength. The interface strength loss from peak to large displacement (LD) strength primarily comes from three mechanisms: (1) geomembrane wear, (2) breakage and combing of fibers in the NGT, and reduction of the hook and loop effect between GMX asperities and fibers of the NGT. The source of interface strength loss from LD strength to the residual value mainly comes from breakage and continuous combing of NGT fibers parallel to the direction of shear in ring shear tests. Scanning electron microscope photographs of the GMX and NGT before and after shearing confirm wear and smoothing of GMX asperities and the combing of NGT fibers in the direction of shear.

Locally available marginal soils are of great interest to use as backfill material in geosynthetic reinforced soil structures due to their cost-effectiveness. The advanced stress–strain analysis of these structures necessitates the correct evaluation and the accurate description of marginal soil-geosynthetic interface behaviour. Therefore, the primary objectives of this study are numerical and analytical analysis of the soil-geosynthetic interface behaviour with application of a hyperbolic nonlinear elastic perfectly plastic constitutive model. In this investigation a series of large-scale direct shear tests was performed to evaluate the shear stress-displacement interface behaviour considering two types of marginal soils in contact with five types of geosynthetic materials in different soil moisture conditions. Accordingly, the hyperbolic model was used to simulate the soil-geosynthetic interface behaviour. Moreover, a three-dimensional finite element model of the direct shear test was developed using ABAQUS software and a user-defined subroutine was implemented to consider the hyperbolic interface model. The results indicated a very good agreement between the experimental data and the predicted finite element simulations of the direct shear tests and analytical solutions. Finally, a numerical simulation of a pullout test is presented in this paper with application of the hyperbolic interface model.

Experiments are conducted to investigate leakage through circular GMB holes overlain and underlain by both tailings with various hole diameters and GMB thicknesses. Finite element analyses are performed to explore the effect of hydraulic conductivities (k) of subgrade (underliner) and tailings above the GMB (overliner) on water head contours dissipation. Analytical solution is developed for predicting leakage through circular GMB hole overlain and underlain by both tailings. Results show that the effect of subgrade on leakage is highly dependent on the ratio of k between the underliner and the overliner. If the ratio > 100, no head loss occurs in the subgrade; if the ratio < 0.01, all the head loss occurs in the subgrade. With the deposition of fines from overliner into subgrade, a low permeable filter cake is formed on the subgrade surface, notably increasing the impact of underliner on leakage. With the increasing ratio of k between underliner and overliner from 0.01, 0.1, 1, 10, and to 100, the ratio of leakage relative to a highly permeable subgrade increases from 0.01, 0.1, 0.56, 0.93, and to 1. An intimate interface contact can be achieved when the GMB is underlain by silty sand tailings as subgrade (foundation) material.

The dynamic stresses in many subgrades for old railways exceed the bearing capacity of the fillers. The geocell has been used to reinforce weak subgrades and achieve a quick attenuation in the dynamic stress. In this study, a series of field tests were conducted to investigate the dynamic stress attenuation characteristics in a weak subgrade reinforced with a geocell. A coupled finite element-discrete element model was developed to analyze the mechanism of the stress attenuation from a multiscale perspective. The results indicated that increasing the geocell height or decreasing the weld distance resulted in an increase in the attenuation rate. There was a threshold for the weld distance, below which its impact on the stress attenuation rate became negligible. When the weld distance was small, the dynamic stress attenuation was attributed to the geocell induced lateral confinement for the infilled soil. With the weld distance increasing, the deformation of the geocell increased and the membrane effect was further mobilized, which contributed to the dynamic stress attenuation. Based on the field test and numerical results, a design method was proposed to determine the reinforcement parameters of geocell-reinforced subgrade, aimed at improving dynamic stress attenuation and preventing subgrade distress.

The effects of induced trench configuration and stiffness of compressible inclusion on the high-density polyethylene (HDPE) pipe behavior were investigated through full-scale laboratory tests. Two pipe-compressible inclusion configurations (‘compressible inclusion over the pipe crown’ and ‘the pipe covered with compressible inclusion’) were tested and expanded polystyrene (EPS) Geofoam with 10 and 15 kg/m3 nominal density was used as compressible inclusion. To simulate geostatic stresses imposed by high embankment fill, the surcharge stress up to 200 kPa was applied on the surface of the burial medium. Comprehensive instrumentation was implemented to measure the pipe deflections, soil stresses on the pipe, and soil settlements in the pipe zone. Considering the pipe behavior and cost-efficiency together, the configuration in which one EPS geofoam panel with 10 kg/m3 nominal density is placed over the pipe crown arises as the optimal solution for the induced trench HDPE pipe. This solution provided a reduction in the vertical stress at the pipe crown of up to of 76% and in the horizontal stress at the pipe springline of up to 65%. The vertical and horizontal pipe deflections are reduced by 87% and 60%, respectively, under 200-kPa surcharge stress. – that is, overburden pressure imposed by a 10-m-high embankment fill.

The degradation behaviour of a 4.8 mm thick elastomeric bituminous geomembrane (BGM) immersed in pH 0.5, 9.5, and 11.5 synthetic mining solutions is examined over 26 months at 22, 40, 55 and 70°C. The low pH solution simulates the leach solutions found in copper, nickel, and uranium heap leach pads while the two high pH solutions simulate the chemistry and pH found in gold and silver heap leaching facilities. The mechanical, rheological, and chemical properties are examined at different incubation times to assess the degradation in the BGM at different temperatures. It is shown that the degradation rates of all properties are faster in pH 11.5 and 9.5 than in pH 0.5. Additionally, the BGM started to exhibit degradation in its mechanical properties even with a slightly degraded bitumen coat in all the mining solutions at elevated temperatures. The time to nominal failure of the BGM is predicted at different field temperatures using Arrhenius modelling. Due to the relatively fast degradation in the mechanical properties of the BGM, especially at temperatures above 50°C, the tensile strains in the BGM in the field should be limited so it can meet the required liner design life of heap leaching applications.

This paper presents an experimental study investigating the effect of particle shape of granular soils on the shear strength characteristics via direct shear tests. Thirty direct shear tests were conducted on spherical and crushed sand mixtures with different proportions (i.e. 0%, 25%, 50%, 75% and 100%). The overall regularity (OR) parameter of sand particles varies between 0.788 and 0.909, fairly reflecting the particle shape of sand mixture. A particular relation between OR and maximum shear strength was found, namely that maximum shear strength increases with a decrease in OR. Furthermore, a gradual increase was observed in the improvement factor (If) due to geotextile reinforcement with an increase in OR except for S25C75, representing 25% spherical and 75% crushed sand, at high and low normal stress levels (i.e. 29 kPa and 116 kPa). The interfacial friction angle (ϕ) of sand mixtures is improved by geotextile reinforcement. Additionally, geotextile reinforcement caused an apparent increase in ϕ with decreasing OR values.

Shaking table tests were performed on reduced-scale models of integrated and two-tiered mechanically stabilised earth (MSE) walls to evaluate the effect of a tiered configuration on the seismic behaviour of metal-strip and geogrid reinforced soil walls. The results showed that, although inextensible reinforcements could reduce the fundamental period, acceleration amplification and lateral deflection and improve wall stability, these benefits declined with the use of a tiered configuration and gradually faded with an increase in the offset distance. This made changing the degree of extensibility a low-impact factor in two-tiered MSE walls with a sufficiently large offset distance (D > (0.4–0.5)H). In order to benefit from the advantage of a tiered configuration, it was found that 0.22H should be considered as the minimum offset distance. The findings indicated that preventing the development of a slip surface in the lower half of the wall, improving the seismic stability by increasing the failure threshold acceleration, mitigating acceleration amplification and decreasing the reinforcement load were the main advantages of a tiered configuration. Moreover, it was concluded that the Mononobe–Okabe method could be used to find the upper bound for estimating the reinforcement forces in two-tiered MSE walls.

Inclined anchors are used in civil engineering structures where the foundations are expected to resist pullout forces during their operational period. This paper presents a three-dimensional numerical analysis of inclined anchors placed in unreinforced and reinforced sand. The influence of several parameters on the response of inclined anchor plates has been investigated in this study. Results indicate that geogrid reinforcement placed on top of the anchor plate significantly influences the anchor plate's performance. The ultimate pullout capacity is found to increase with the inclination angle (varied from 30° to 60°) of the anchor plate both in unreinforced and reinforced sand. The anchor capacity is also affected by other parameters such as friction angle of sand (varied from 35° to 45°), embedment depth of the anchor plate (varied from 2 to 10) and tensile stiffness of the geogrid. Besides, the comparison between piles and anchors has been presented with the help of an illustrative example of a transmission tower foundation. The design calculations indicate that inclined anchors placed in reinforced sand can lead to economical design at shallow depth as compared to piles.

This paper interprets the results from field monitoring which was carried out during vacuum-PVD improvement in a site located near an actively moving slope. Interestingly, the monitoring results showed, among other things, mitigation in the outward lateral movements during and after the preloading process indicating relative stability in the slope and the efficiency of vacuum to mitigate lateral movements during the preloading period. Analyses were made on other field parameters such as pore pressure and settlement, as well as back-calculation of flow parameters to be considered during vacuum preloading design, such as permeability ratio (kh/ks) and horizontal consolidation coefficient (Ch) due to vacuum-PVD, were carried out. Post improvement, appropriate geotechnical properties were obtained from laboratory tests of clay specimens from borehole samples and undrained shear strengths were measured from unconfined compression and field vane shear test. The obtained properties indicated improvement in soft soil properties with a reduction in water content and an increase in maximum past pressure, OCR and undrained shear strengths. The prediction made for final shear strength using past literature, where applied additional incremental stress was reduced with depth, matched well with the shear strengths recorded from field testing.

An explosion on the ground surface can cause considerable damage to underground structures. In this study, a series of experimental and numerical investigations were conducted to examine the performance and reinforcing mechanism of reinforced soil subjected to blast loads. An excavated pit backfilled with sand only (unreinforced soil) and sand reinforced with three layers of geotextiles (reinforced soil) were used as test models in a field explosion test. In the field explosion test, blast pressures in air and soil, ground deformation, and mobilized reinforcement tensile strain were measured. The test results obtained for the reinforced and unreinforced soil were compared to evaluate the effectiveness of using soil reinforcement as a protective barrier against blast loads. The test results indicated that peak blast pressure in the reinforced soil was only 10–28% of those in the unreinforced soil. Two reinforcing mechanisms were identified in this study: the tensioned membrane effect and lateral restraint effect. Moreover, a series of numerical analyses were performed to evaluate the effects of reinforcement parameters on the blast pressure. This study provides useful insights into the application and design of soil reinforcement as an alternative antiexplosion measure to protect underground structures against surface explosions.

Small- and large-scale 1g experiments were conducted to investigate the bearing capacity failure of geosynthetic-reinforced soil walls. The small-scale experiments (1/10) provided fundamental insights into the development of failure based on digital image correlation analysis. Since these tests suffered from scale effects, large-scale tests (1/1.67) were performed to quantify the ultimate load-bearing capacity of a 1.2 m high wall. A vertical load was applied on top of the structures and internal soil movements and stresses, wall deformations and reinforcement strains were measured. The experimental results revealed that the failure was initially triggered at the rear end of the bottom reinforcement. The wall rotated to the backfill and the ground surface in front of the wall was uplifted. The results confirmed the quasi-monolithic behaviour of the reinforced zone. A multi-body failure mechanism was observed below the base of the wall, consisting of an active and a passive wedge connected by a transition zone. Important scaling factors were discussed using the two different scales which has shown important conclusions that are relevant for experimental studies. The analytical calculations revealed that a reduced reinforcement length needs to be considered in the analytical approach to predict a rather conservative load-bearing capacity.

High-density polyethylene (HDPE) geomembranes (GMs) are frequently used as fluid barrier components of cover systems for mine site reclamation in regions that are prone to freeze–thaw cycles (FTCs). However, HDPE GMs are more susceptible to stress cracking than linear low-density polyethylene (LLDPE) GMs. Hence, LLDPE GMs are increasingly considered as alternatives to HDPE GMs in cover systems. Nevertheless, little information is available on LLDPE compared to HDPE GMs. Moreover, little is known about the changes in the fluid barrier properties (the equivalent hydraulic conductivity and the oxygen sorption and diffusion coefficients) for these two materials with FTCs. The purpose of this study is therefore to compare the effects of FTCs on the tensile, hydraulic, and oxygen sorption and diffusion properties of HDPE and LLDPE GMs. To do so, GM sheets were subjected up to 300 FTCs. Mechanically, both GMs got stiffer and their tensile break properties increased with increasing number of FTCs. However, although the GM fluid barrier properties changed with FTCs, the equivalent hydraulic conductivity and the oxygen permeation coefficient remained within an order of magnitude of 10−14 m/s and 10−13 m2/s, respectively. Up to 300 FTCs would therefore have no adverse effects on HDPE and LLDPE GMs.

Geosynthetics have been used to reinforce soils for over four decades. They can also be used as reinforcement in buried pipe installations to reduce stresses and strains in the pipe, as well as the consequences of pipe explosions. This paper investigates the use of geosynthetic reinforcement to protect a flexible buried pipe from the effects of a localised surcharge on the soil surface. Large scale tests were carried out on an instrumented PVC pipe buried in a rather loose sand. Different types and arrangements of the reinforcement layer were investigated. The results obtained address the relations between stresses on the pipe, pipe strains and pipe deflections and show that the presence of the reinforcement can reduce significantly vertical and horizontal stresses on the pipe as well as pipe deformations. An elastic solution for the prediction of strains at the pipe crown was employed, whose predictions compared well with the experimental results.

In practice, little attention has been paid directly to freeze-thaw (FT) cycles during the design and analysis of geogrid-reinforced soil (GRS) walls due to a lack of relevant literature. This study investigates the pavement vertical deformation (s), panel lateral deformation (d), lateral earth pressure (σh), and geogrid strain (ε) of a field GRS wall using an ABAQUS-based numerical model considering variations of the recorded five-year ambient temperature (TR). Numerical results show that the s distribution follows a convex shape instead of the initial concave shape after FT cycles and can be divided into high, transition, and stable deformation zones. FT action alters both location and amplitude of the maximum d within the first two cycles, making the d distribution evolve from a J-shaped curve into an S-shaped one. During freezing, the developments of s and d are coordinated and can be described using a unified model; σh is larger than the Rankine active earth pressure; ε state depends on the interplay of two factors resulting from d and frost heave force. Furthermore, the hysteresis of s, d, σh, and ε with TR was discussed and several beneficial suggestions were proposed for GRS walls to avoid such FT destruction.

Low-permeability liners are required at the base of municipal solid waste (MSW) landfills to minimize leachate leakage and contaminant migration into groundwater. This paper uses a two-dimensional coupled groundwater flow and contaminant transport model to examine the performance of three types of low-permeability liners specified by the current Chinese landfill standard: (1) a compacted clay liner (CCL), (2) a geomembrane (GMB) overlying a CCL, and (3) a GMB overlying a geosynthetic clay liner (GCL) on a CCL. The model simulates leachate leaking and contaminant migrating over the entire base of the landfill for the CCL and through the holed GMB wrinkles for the GMB composite liners. The performance of each type of low-permeability liners was evaluated and compared in terms of leakage rate and peak impact of chloride on the aquifer. Based on liner cases and conditions examined in this paper, the results show that the three types of low-permeability liners are not equivalent for minimizing the leakage rate and chloride impact on the aquifer. The GMB + GCL + CCL performs the best among the three low-permeability liners, and is effective for limiting the peak chloride impact on the aquifer below the acceptable level in drinking water.

This paper reports on a series of static and cyclic plate loading tests performed on a weak unreinforced sand bed in a test pit. The weak sand was covered by a 160 mm thick layer comprised of one of three compacted soil types which was either unreinforced or geocell-reinforced. The purpose was to investigate the effects of soil density and grain size as filler materials for the covering layer. The three covering soils were granular with average particle sizes of 2.2 (Soil 1), 6.14 (Soil 2), and 8.47 (Soil 3) mm. Under static loading, the bearing pressure increased on average 23% when the average grain size of the upper, unreinforced, soil layer changed from 2.20 mm to 8.47 mm. The improvement in bearing pressure was about 37% due to the use of a soil-filled geocell but, unlike the unreinforced situation, employing larger soil grains to fill the geocell pockets didn't show significant further improvement. For cyclic loading tests, the maximum settlement reduction by employing a geocell layer was about 50% for Soil 1. Whether loaded statically or cyclically, increasing soil density likely would be more efficient for improving geocell performance than employing a soil having larger particle sizes.

Interface shear characteristics have an important impact on the stability of geosynthetically reinforced soil structures. The shear characteristics of three-dimensional (3D) geogrid–sand interfaces were investigated using large-scale direct shear tests and the discrete element method (DEM). Geogrids were manufactured by 3D printing. The effect of mesh pattern and transverse-rib thickness on the stress–displacement relationship, strength parameters, coordination number and porosity distribution were evaluated. The results showed that the mesh pattern and transverse-rib thickness have an impact on the interface shear characteristics. The peak and residual interface shear strength of the modified geogrid mesh pattern exceeded that of biaxial geogrids. The average coordination numbers of the modified geogrid mesh pattern were greater than those of biaxial geogrids. The variability of particle compactness, as characterised by the porosity distribution, shows how the modified mesh pattern increases the interface shear strength. The interface shear strength of the geogrid–sand interface was improved by thickening the transverse ribs of the modified geogrid mesh pattern.

A new rubber dam with two layers of dam bodies anchored together into a rigid concrete base was proposed to improve the water-retaining capacity of a traditional rubber dam. A series of large-scale model tests was conducted to evaluate the static behaviour of a double-layer rubber dam under conditions of different internal and external water heads, anchoring distances and cross-sectional perimeters. It was found that the maximum tensile force of the Layer-1 dam is located at the anchoring point but that of the Layer-2 dam is located at the extruded free section. The optimal cross-sectional perimeter ratio was concluded as 0.8 with an optimal anchoring distance of 0.06 L1 and an internal water head in the upstream dam and in the downstream dam of 0.40 L1 and 0.36 L1, respectively, where L1 is the cross-sectional perimeter of the upstream dam.