Geotextiles and Geomembranes最新文献

Reinforcing calcareous sands with geogrids is a potentially effective method for large-scale geotechnical constructions in coastal lands. The breakable nature of polygonal calcareous sands determines the complex particle-geogrid interactions. A three-dimensional numerical model of geogrid reinforced calcareous sand (GRCS) was established to investigate the potential mechanical laws based on the discrete element method (DEM), and the reasonableness of the numerical model was verified by comparing with the indoor triaxial test. It follows that the macro-microscopic mechanical behavior of GRCS under the influence of aperture size and tensile resistance of geogrids was further investigated via effective DEM simulations. The presented results show that the decreased aperture size and increased tensile resistance are beneficial to enhance the macro-mechanical properties of GRCS, including strength, internal friction angle and pseudo cohesion. Particle crushing is mainly affected by shear strain and confining pressure. The bulging deformation of GRCS is partially suppressed due to the confining effect of geogrids. Besides, the source of strength enhancement of GRCS is revealed based on the microscopic particle-geogrid interactions, and the calculation method of horizontal and vertical additional stresses in the reinforced soil element considering the effects of tensile resistance and aperture size is further established.

Decades of research has been dedicated to investigating inverted pavement as an alternative to traditional flexible pavement structures. While previous studies have largely focused on the stress dependency of the unbound aggregate base (UAB) layer using numerical simulations, there is limited research on the construction and use of geogrid reinforcement in inverted pavement. This study presents a comprehensive evaluation of full-scale inverted pavements, specifically assessing the impact of geogrid reinforcement on rutting performance. The results indicate that adding geogrid to the UAB layer improves rutting resistance, with optimal results achieved when the geogrid is placed in the upper third of the layer. On the other hand, when the geogrid was positioned in the bottom two-thirds of the layer, it led to inferior rutting performance compared to the inverted pavement where geogrid reinforcement was placed in the upper one-third of the UAB layer. Numerical simulations validate the field test results, demonstrating that higher tensile strains in the upper third location enhance aggregate interlocking and stiffness due to the geogrid's enhanced constraining capacity and reinforcement. Conversely, lower tensile strains in the bottom two-thirds location limit geogrid constraints, leading to increased rutting and surface deformation.

In this study, a fiber-reinforced rubber-sand mixture (FRRSM) was produced by adding random distribution reinforcement of polypropylene fiber recycled from waste plastic, which can strengthen the RSM. The mechanical parameters of FRRSM were tested using indoor experiments. Moreover, the seismic behavior of a wrapped reinforced earth retaining wall backfilled with FRRSM was investigated using the finite element method. First, by comparing the model test results, the accuracy of the nonlinear finite element analysis method, which simulated the earthquake response of a retaining wall well, was verified. Subsequently, the soil used in the model test was replaced with FRRSM, and the facing displacement, vertical settlement, and acceleration response of the retaining wall were analyzed. The results indicate that the seismic performance of the retaining wall was significantly enhanced with an increase in the fiber content (F_C) of the FRRSM. According to the present research, the optimal mixture ratio that can ensure the seismic performance of FRRSM-RW is 10% rubber and 1.5% fiber, that is, R_C = 10% and F_C = 1.5%.

The horizontal displacement of a reinforced-soil retaining wall is a common deformation mode of seismic damage. The horizontal displacement time history and accumulative deformation after earthquakes are important parameters for evaluating the seismic performance of a reinforced-soil retaining wall, but theoretical study on this issue is scarce at the moment. In this study, an analytical method is proposed to calculate the horizontal displacement time history of a block-faced reinforced soil retaining wall. The method is based on the pseudo-dynamic method and differential kinematics equations, and this method was used to calculate the reinforcement material's tensile displacement and overall displacement in the reinforced area under earthquake motion, while simultaneously taking into account the accumulative deformation. The rationality and accuracy of this method are verified through comparison with model experiments and existing theories. Besides, parameter analysis was carried out to further confirm the applicability of this method. The study shows the method takes into account the influence of the accumulated deformation, and can effectively calculate the horizontal displacement time history of the block-faced reinforced soil retaining wall under larger magnitudes. Although the calculated values are smaller than the actual deformation, they are still relatively close.

This paper presents a new approximate solution to study the settlement of rigid footings resting on a soft soil improved with groups of encased stone columns. The solution development is fully analytical, but finite element analyses are used to verify the validity of some assumptions, such as a simplified geometric model, load distribution with depth and boundary conditions. Groups of encased stone columns are converted to equivalent single encased columns with the same cross-sectional area and the same ratio of encasement stiffness to column diameter. In this way, the problem becomes axially symmetric. Soft soil is assumed as linear elastic but plastic strains are considered in the column using the Mohr-Coulomb yield criterion and a non-associated flow rule with a constant dilatancy angle. Soil profile is divided into independent horizontal slices and equilibrium of stresses and compatibility of deformations are imposed in the vertical and horizontal directions. The solution is presented in a closed form and may be easily implemented in a spreadsheet. Comparisons of the proposed solution with numerical analyses show a good agreement for the whole range of common values, which confirms the validity of the solution and its hypotheses.

In recent decades, there have been individual cases of damage to geotextile filters due to clogging by flocculated ochre products. This process is defined as ochre clogging and has been extensively explained in recent theoretical studies (Tophoff et al., 2022). Several revetments of tidally influenced German North Sea estuaries have been damaged due to a severe reduction in the permeability of geotextiles. Therefore, experimental investigations of granular and geotextile filter constructions were carried out to better understand filter clogging. The investigations reproduce a revetment section at a scale of 1:1. For this purpose, the clogging process in the fluctuating water level or clogging zone was reproduced as a purely chemical iron precipitation. Ten short-term tests (10 h) and one long-term test (50 h) were carried out in total. The tests show that the process involves internal clogging and that the iron precipitates adhere immovably to the filter structure, reducing the pore space and permeability of the filter. This process is considered less problematic for granular filters. A reduction in permeability was measured in some cases for geotextile filter designs. Different geotextile material parameters appear to influence the iron ochre clogging tendency.

In this paper, an experiment study was carried out to identify the fundamental behavior of geosynthetic-encased stone column (GESC) reinforced foundation under freeze-thaw cycles. Three loading tests under four freeze-thaw cycles were considered. A 10-m thick reinforced foundation unit consisted of four floating GESCs with 2.5-m underlain clay layer, and the foundations were preconsolidated to three different initial degrees of consolidation (U = 1.0, 0.6 and 0.3, respectively). The results showed that soil near GESCs had a larger frozen depth due to the excellent heat transfer ability of GESCs. An extra uneven subsidence of soil also appeared around GESCs. Voids could be found between foundation soil and the loading plate after thawing, which indicated that only GESCs carried the overburden pressure. The GESCs showed outward bending under lower initial degree of consolidation, while inward bending under higher one. A bulging failure was observed on frozen part of GESCs, especially at the connection of encasement in foundation with lower initial degree of consolidation. In the first freezing process, a rapid decrease in frost heave force was noticed, inferring the fracture of frozen soil. The stress on GESC was found to almost have no change until complete freezing, when the soil was freezing and the stress on soil exceeded that on GESC. Negative pore pressure was observed in the foundation soil, and the absolute value decreased with the increasing overburden pressure. Both the peak positive and negative pore pressures were reduced as the foundation was preconsolidated to a higher degree. The freeze-thaw cycles were also found to generate excess pore pressure in soil during thawing. Moisture migration was also analyzed using Electrical Resistivity Tomography (ERT) method, and the results showed that moisture tended to go upwards and outside the reinforced unit from thawing to freezing, while downwards and inside the unit from freezing to thawing.

Experiments are conducted to investigate the effect of a drainage layer in/below saturated tailings on leakage through a hole of various shapes and sizes in a 2-mm-thick HDPE geomembrane. Three cases: no drainage (Case 1), drainage layer between two layers of tailings (Case 2), and drainage layer below tailings and above the GMB (Case 3) are examined. Analytical solutions predicting leakage through a circular GMB hole overlain by tailings with an internal drainage in (Case 2) and below (Case 3) tailings are developed, and match the experimental and numerical results well. Results show that a drainage layer separated from the GMB by a thin layer of tailings (Case 2) gives leakage slightly greater than if no drainage layer is present, but 3-5 orders of magnitude lower than when the drainage is placed directly over the GMB (Case 3). In Case 3, leakage is dependent on the hydraulic conductivity k of both the drainage and subgrade, and is not affected by the tailings. Unlike Cases 1 and 2 where the subgrade has negligible effect on leakage, a low permeability subgrade with k less than 10% of k for the drainage layer is recommended in Case 3 to minimize leakage through geomembrane defects.

In this pioneering study, the performance of an eccentrically loaded strip footing on geocell-reinforced sand was assessed with instrumented laboratory model tests in terms of pressure-settlement response, surface displacement profiles, failure mechanisms and ultimate bearing capacity considering load eccentricity, geocell height, geocell material stiffness and the relative density of the soil. The results indicated that strip footings on the geocell-reinforced sand outperformed those on unreinforced soils, with up to a 6.5-fold increase in the bearing capacity and significant improvements in the initial slope of the pressure-settlement curve. Furthermore, the strip footing under centric loading on the geocell-reinforced loose and dense sand exhibited either only punching or local shear failure while load eccentricity on the strip footing could lead to the shear failures including punching, local and general. In this research, both a design chart for predicting failure modes of geocell-reinforced strip footings and a new interpretation method to evaluate ultimate bearing capacity were proposed. Increasing the relative density of the soil and material stiffness enhanced the ultimate bearing capacity of geocell-reinforced strip footings under both centric and eccentric loading conditions, with stiffer materials resulting up to 25% increase. However, increased geocell height had no significant impact on bearing capacity.

The self-healing capacities of a GCL with natural bentonite (NB) as core (NB-GCL) and a GCL with a polymerized bentonite (PB) as core (PB-GCL) were investigated under simulated field conditions, i.e. geomembrane-GCL-a clayey subsoil layer composite liner system with a damage hole on the geomembrane and the GCL. The clayey subsoils tested had initial water contents of 22.2% and 26.8%. The liquids used were deionized (DI) water and 0.3 M NaCl solution. The test results indicate that for both the PB-GCL and NB-GCL only hydrated on the subsoils for 1–3 months, a damage hole of 15 mm in diameter was almost not self-healed. For cases of applying a constant liquid head on the top of the geomembrane of 100 mm, the sizes of damage holes were self-healed in term of diameter is about half of the values reported in the literature for tests with plenty liquid supply to the damaged GCLs. Further, for the conditions tested and for the cases self-healed, DI water leaked into the subsoil was less than about 60 g, and 0.3 M NaCl solution leaked was less than 150 g.