Conference Agenda

<p>The interface shear strength between geomembranes and other materials plays an important role as design parameter in waste landfills and water transportation systems. Over the years, many investigations have been conducted in order to better understand its behavior as well as estimating it. However, there is a lack of publications regarding the influence of the type and distribution of surface roughness of the geomembrane on its interface resistance with other materials.</p>

<p>This paper aims at evaluating the interface shear strength between geomembranes and geotextiles as well as assessing the applicability of several roughness parameters as additional design parameters for geotechnical engineering applications.</p>

<p>The experiments concerning the interface shear strength were conducted by means of inclined plane tests. The tested interface was 0.5 m wide and 1.80 m long. For each test, three low normal stresses were applied. One smooth and three textured geomembranes were used in contact with the ramp which had a rough surface provided by a sandpaper glued to it. Two different geotextiles were tested on the geomembranes. The topography of the geomembranes was measured by means of a powerful microscope which can provide the macro and micro surface roughness of the material and bidimensional and tridimensional parameters were obtained.</p>

<p>The results highlighted that there are several roughness parameters which can help evaluating whether the increase of the geomembrane asperity height may influence on the interface shear strength. Results also showed that using only the asperity height or the surface roughness as a control parameter is not an accurate way to relate them to the interface shear strength.</p>

The massive generation of construction waste is one of the priority urban environmental problems in recent years, causing losses in urban populations' quality of life, where 54% of the world population currently lives (84.3% of the Brazilian population) (IBGE, 2019). In this context, this paper presents the results of an experimental investigation on the interac-tion between synthetic strips with sand and low-cost alternative material (recycled Construc-tion and Demolition Waste). The objective is to determine their possible suitability as land-fill material in Mechanically Stabilized Earth retaining structures. Large-scale reinforcement pullout tests were carried out. Based on the results, it was possible to carry out a compara-tive analysis of the mobilized resistance, allowing to determine design parameters. The ex-periments also showed favorable results, and the CDW can be considered a viable option for partial and/or total replacement of commonly used natural materials.

The pullout mechanism (skin friction and bearing) is influenced by the type of reinforcing material and the soil properties. Coir geotextiles, being a low-stiffness material will affect their interfacial behaviour with the surrounding matrix to an extent. In this study, in order to quantify the soil-coir geotextile interaction, a series of pull-out experiments were carried out with geotextiles having different mass density. For a particular normal stress, it was observed that geotextiles with higher mass density exhibit higher shear resistance during pullout. Further, for the coir geotextile having a specific mass density, a better shear mobilization was realized at a particular normal load. In order to predict the soil-coir geotextile interaction behaviour precisely, a three-dimensional (3D) numerical model was developed in this study. Using an appropriate constitutive law for the geomaterial and soil-geotextile interface, the numerical model was validated with the experimental results. This numerical model will be helpful in quantifying the extent of shear mobilization under different boundary conditions.

<p>In this study, confinement effects of geocell were investigated by conducting direct shear tests using medium-scaled shear box: 160mm×90mm×65mm (length×width×height). This shear box has a transparent side wall made from acryl plate to capture soil deformation in the box. The quartz sand with having 0.32mm average particle diameter was used. Cell reinforcing materials were prepared by using PET sheet. The test sample was made by compaction using a steel rod. The direct shear was conducted in a constant rate as 1mm/min under constant confining pressure as 10kPa. In a series of tests, the effects of three kinds of cell-geometry on the soil-geocell interface shear resistances were investigated and compared with the soil shear strength. Moreover, the soil strain localization behavior in all test case was visualized by the particle image velocimetry (PIV) technique.</p>

<p>Main conclusion are as follows.</p>

<p>(1) The soil-geocell interface shear resistance is higher than soil shear strength. This tendency increases with smaller cell-length in the shear direction.</p>

<p>(2) The geocell confines not only soil shear deformation but also volumetric deformation i.e., dilatancy.</p>

<p>(3) The soil-geocell interface shear resistance can be shown by a simple empirical formulation. The proposed equation is based on Taylor-Bishop energy correction formula and expressed by the shear resistance angle and dilatancy angle of soil, the ration of cell confinement area to the total shear area, and an empirical coefficient on the dilatancy confinement.</p>

To predict the performance of engineered structures such as composite liner systems in landfills, constitutive modelling of soil–geosynthetic interfaces is required. This paper pre-sents a numerical model that was developed to simulate the shear stress versus shear dis-placement responses of single and multi-layer soil-geosynthetic interfaces. A series of large direct shear tests were initially carried out to investigate the behaviour of the inter-face of a typical composite liner system made up of compacted clay and three geosynthet-ics: Geotextile (GTX), Geomembrane (GMB), and Geosynthetic Clay Liner (GCL). The numerical model developed in MATLAB R2022a was then utilised to simulate the behav-iour of the soil-geosynthetic interfaces using the experimental data. The shear stress–displacement response of the soil-geosynthetic interfaces was modelled by dividing it into two parts: pre-peak and post-peak behaviour. The modelling parameters were then deter-mined based on the results of the large direct shear tests performed on these interfaces. Subsequently, the shear stress–displacement response of the interfaces was evaluated and compared with the experimental results. For both single and multi-layer soil-geosynthetic interfaces, the predicted shear stress–displacement response was shown to be in good agreement with the experimental results.

Anchored earth is a derivative of reinforced soil. The pullout resistance and corresponding displacement of square mild steel anchor plates 100mm x 100mm, 200mm x 200mm and 300mm x 300mm, were investigated. Good repeatability of the pullout resistance – dis-placement was observed. However, both the peak pullout resistance and corresponding displacement indicated some scatter. The early stiffness, at displacement less than 10mm, was consistent with the post-peak behaviour and was found to vary from softening to plastic, to hardening behaviour. The peak pullout resistance increased with area of plate anchor. The smallest plates (100mm x 100mm) reached peak resistance at displacement less than 5mm, the large plates (200mm x 200mm and 300mm x 300mm) reached peak at similar values between 10 – 30mm. The peak pullout resistance for the 200mm x 200mm and 300mm x 300mm was found to reduce as the in-situ vertical stress in the wall in-creased.

<p>One of the most important aspects regarding the design of geosynthetic-reinforced soil structures is to predict the long-term behaviour of reinforcements and interfaces.<br />The paper describes a new large-scale laboratory apparatus capable to investigate the behaviour under pullout conditions of a geosynthetic reinforcement embedded in a compacted granular soil, and subjected to sustained tensile loading. By using the long-term pullout test results, the writers suggest a procedure for the determination of the interface parameter necessary to design the length of the reinforcement in the anchorage zone that can take into account the viscous effects of the polymeric material arising under serviceability conditions during the design working life.</p>

<p>This paper presents a prediction of geosynthetics interface friction angle by using random forest algorithm. Considered interfaces include geomembrane and cohesionless soil. In this work 495 interfaces, for each interface eleven parameters and three equipment types are identified from various literature sources. The collected data has been split in two sets, 80% for training the developed model and 20% for evaluation purpose. Nonlinear Random Forest regression has been applied to make interface friction angle forecast. The technique easily adapts to nonlinearity found in data and tends to make a better prediction (Schonlau et al 2020). Additionally, linear regression has been employed for analysis, comparison and measurement purposes. The influence level between pair of affecting factors and by pairing predicting elements with interface friction angle, was analyzed by simple linear regression. Results showed that the Pearson's correlation heat map showed the influence level indication from simple linear regression analysis is less reliable in accordance with the laboratory experiments. In addition, linear regression approach was employed by Random Forest to compare with the main nonlinear model. By resulting R²= 0.92 the nonlinear model performed better by far than the linear regression approach which resulted R²= 0.63. The accuracy of interface friction angle estimation as well was measured by a linear regression in accordance with laboratory test data. Regression metrics measures shows R²= 0.93 and RMSE = 1.94 for training set. For testing set, the performance measure results R²= 0.92 and RMSE = 2.09. It is observed that only for 3% of the training set the estimation has a maximum ±5° variation from the laboratory recorded friction angles. Similarly, the assessment for the testing set shows only 6% predicted friction angles deviate at most ±5° from actual laboratory record. Thus, random forest has predicted interface friction angle adequately.</p>

<p>Previous behavior studies on the direct shear interface between geogrids and sands are mostly focused on situations where geogrids are put horizontally on the shear plane. However, when it comes to reinforced soil structure, the potential damage plane will usually form an angle with the reinforced soil materials. Therefore, it is of great significance to conduct a study on shear behavior of interface between geogrids and sands in cases where geogrids and shear plane form an angle. This paper uses the HM-5780 large direct shear instrument to carry out a series of direct shear tests where the reinforcement is arranged at different angles, explores the laws of the shear strength of the direct shear test with the angle of the reinforcement, and uses PFC3D, a discrete elements software, to stimulate direct shear tests under different geogrids reinforcing angles, this paper analyzes the shear behaviors from multiple macro perspectives like shear strength, cohesion and internal friction angle, reaching a conclusion that compared to non-reinforced structure, the 60-degree-reinforeced structure have greatest shear strength, while a 120-degree weaken the structure’s shear strength. Additionally, from such micro factors as force chain evolution, coordination number, porosity and displacement, this paper also studies reasons that cause the differences of shear strength: during shearing process, 30/60-degree-reinforced geogrids are in tension whereas the 120/150-degree-reinforced geogrids are in compression; and the closer setting angle of geogrids is to the direction of maximum extensional strain during shearing process, the stronger of shear strength of soil structure will be.</p>