Conference Agenda

<p>Polyethylene has temperature dependent properties. As a thermoplastic material, it softens on heating and hardens on cooling. This behavior affects the contact surface areas of materials made out of polyethylene, such as geomembranes, adjacent to other materials. Interface strength properties depend on the contact area and stress at the interface. Since the soil-geomembrane interfaces are relatively weak and potentially form the critical failure planes, modeling temperature dependent soil-polyethylene contact surfaces is important. A theoretical model to determine temperature dependent soil-polyethylene contact areas was developed during this study and presented in this paper.</p>

<p>The results of an experimental campaign of reinforcement of thin cohesive soil embankments in the case of cavity collapse are presented in this paper. In particular, the aim is to test the effectiveness of a new type of double stiffness geosynthetic. A coupled DEM-FEM numerical model is validated based on these results and allows a better understanding of the soil-geosynthetic interaction phenomena mobilized during the collapse. Comparisons between the numerical and experimental results obtained with the two types of reinforcement (mono-stiffness and inverted bi-stiffness) make it possible to underline the interest of the innovative product developed.</p>

<p>As part of an endeavor to develop a laboratory scale device for testing freeze-thaw behaviors of geosynthetics-reinforced soils, this study synthesizes outcomes from a survey of plate loading apparatuses developed in various labs in different countries. The survey specifically investigated the setup of each component, loading mechanism, instrumentation, and materials tested. The functions of the apparatuses and the implications of the test results are examined. The results from the survey were utilized to develop a new model test apparatus capable of performing freeze-thaw and plate loading tests. The apparatus was further upgraded to incorporate a water supply system. The preliminary tests based on the open system were conducted, and the results are discussed.</p>

<p>As a contribution to solving environmental problems, some attempts at recycling waste into geomaterials have been carried out. The authors have also been investigating the possibilities to effectively use of crushed expanded plastic waste, which was circulated for recycling, as a component of light-weight mixed soil. As a result, this plastic waste was shown to be available as a geomaterial, because it was found that the strength parameters such as internal friction angle remained almost unchanged, while its compressibility became larger. However, it is necessary to clarify the deformation characteristics of such a soil in considering the actual use. Moreover, a similar situation may also be a problem in the case of layering a flexible geosynthetic in the ground, it is also necessary to know the deformation characteristics of soil when integrated with geosynthetics. For this reason, the authors have promoted research to elucidate the deformation characteristics of soil mixed with deformable particles, considering the mechanism of compressive deformation from a microscopic point of view. Generally, in the case of soil mixed with deformable particles such as rubber, it is thought that two more compression components, one is compression of the deformable particle themselves and the other is the following reduction of pore space, are added to the ordinary volumetric compression. Therefore, a series of one-dimensional compression tests was executed using rubber and aluminum tips to estimate these compression components, then the calculation method of these compression amount was examined considering the deformation of constituent particles geometrically. As a result, it was found that each compression components of the mixture could be predicted almost well, under the condition that the specimen is in the densest particle arrangement state and the skeletal structure is not disturbed by compression.</p>

<p>Passive grout-anchors are widely used in mountainous areas as foundations for rockfall and avalanche barriers. In many cases the foundations are set in porous ground, where fluid grout flows into void space, resulting in large amounts of grout loss associated with increased cost and a negative environmental impact. Application of geotextile bags can control grout losses to porous ground. However, the interaction of geotextile, grout, and ground properties form a complex system with multiple interactions, which is difficult to model with finite element method (FEM). In this study, data acquired from laboratory pull-out tests is applied to investigate the behavior and failure mechanism of passive anchors in geotextile bags (PAGB) under tension loads. The study has shown, that depending on the permeability of the geotextile, a grout mantle can be formed at the outer interface of the geotextile bag with the porous ground, contributing to the strength of the PAGB. However, this intermediate layer creates new possible failure surfaces, which need to be considered. The pull-out tests have been modelled numerically in 3D with OPTUM G3. Mohr Coulomb models have been successfully implemented to model the strength properties of the multiple interfaces. A parametric analysis has shown that geotextile-ground friction plays a crucial role in the strength of PAGB. If an intermediate layer is created, the strength of the bag is limited to the geotextile-grout pealing strength. In summary, PAGB could provide a sustainable solution to anchoring problems in mountainous areas. Multiple interfaces can be modelled from a practical point of view, using simple Mohr-Coulomb models. For optimal PAGB design, the permeability of the geotextile and the creation of an intermediate layer needs to be considered.</p>

<p>Geogrids are widely used as a soil reinforcement technique in many engineering applications, however a detailed study of the mutual interaction between these structures and the granular soil is complex and generally faced only with specific laboratory tests. In the last decades, the recourse to numerical methodologies has experienced a large growth, and among the different methods the discrete element method (DEM) has proven its reliability in understanding both the micro and macro aspects of the soil-geogrid interaction.</p>

<p>In this study, 3D discrete element simulations of pull-out tests are performed. The shape of the numerical geogrid and the contact properties of its elements are calibrated using the results of laboratory tests referring to a real PET woven geogrid.</p>

<p>The geogrid mechanical properties investigated controls its strength and stiffness. Their role and influence on pullout behaviour are investigated in different soil conditions about the confinement stress, the soil particles size and shape. The granular soil is modelled using both spheres and clumps to simulate different fine graded gravels. The role of the initial geogrid pretension is also investigated.</p>

<p align="left">The authors developed a hybrid type rigid plastic finite element method (RPFEM) for a stability problem of a ground. This method is based on limit analysis with a spatial discretization of finite element to evaluate a maximum load which a ground can carry under the constraint conditions of equilibrium of forces and no ground failure. In this study, from the point of computational mechanics, the authors focus on the modification of RPFEM to handle with a stability of a reinforced ground with reinforcement members.</p>

<p align="left">The principle of a ground reinforcement method is a confining effect of soils by the reinforcement members, i.e., confining forces or pressures by the reinforcement members contribute to the resistance against ground failure.</p>

<p align="left">Theory of mechanics tells velocity and stress fields are dual to each other. This indicates deformation constraint between two nodes in a velocity field can be converted into confining forces acting between two nodes. So, a confining force term is added to the equilibrium to deal with a reinforced ground problem. Limit of a confining force is also introduced to reflect a reinforcement member strength. It should be noted that only a mesh of a ground is necessary and no special FEmesh of reinforcement members is required.</p>

<p align="left">Furthermore, to treat a sticking / slipping interaction between reinforcement members and surrounding soils, a limit of a change in confining forces between adjacent two segments is introduced. This model is similar to an interaction between piles and soils, i.e., a change of axial forces of piles at two sections is due to skin frictions. This newly proposed method can predict various failure modes including member-failure and pull-out failure as solutions without any assumption of failure modes. Some numerical examples are presented to demonstrate the features of the proposed method.</p>

<p>Geosynthetic-reinforced soil (GRS) structure has been received much attention recently due to its advantages of less over-excavation, ease of construction, cost-effective and excellent performance in practice. The backfill gradation may influence the bearing capacity of a GRS mass. This paper conducts a series of plane strain model tests with transparent soil to investigate the effect of backfill gradation on the bearing capacity of a GRS mass. The particle image velocimetry technique was adopted to monitor the deformation field change in the backfills during testing. The results showed that the maximum aggregate size of backifll affected the bearing capacity of a GRS mass, while the test with well-graded aggregates yielded larger bearing capacity than that with poor-graded aggregates although both backfill had the same maximum aggregate size. Moreover, the well-graded aggregates reduced the deformation of GRS mass.</p>