Conference Agenda

<p>A piled embankment consists of piles, usually in a square grid, driven through the unsuitable foundation soil to a firm-bearing stratum. The piles directly reinforce the soft soil and distribute the embankment load onto the firm stratum. A geosynthetic layer is typically installed over the pile caps at the base of the embankment to further assist in the transfer of load. Piled embankments also rely on arching in the embankment fill to redistribute vertical load at the base of the embankment, increasing the load on the rigid piles and reducing the load on the soft compressible soil between pile caps.</p>

<p>Low height piled embankments arise where the height of the embankment is less than the clear spacing between adjacent pile caps. Full arching is no longer mobilised in the fill, with a danger that the embankment surface could imitate the ripple effect that is occurring at the pile level where the geosynthetic deflects downward between the piles.</p>

<p>This paper will present results from a plane strain analysis of piled embankments conducted using Plaxis. The Plaxis models will be discussed, together with validation of the models against previous studies conducted in a geotechnical centrifuge. The aim of the study is to better understand the performance of low height piled embankments. The study will also determine the minimum embankment height, pile and pile cap geometry, fill and geosynthetic properties required to minimize deformation at the surface of the embankment.</p>

<p>To determine the interface characterization of geogrid inclusion, soil-geogrid interaction is of particular importance. Tensile strength, tensile strain, and interfacial shear stress are all characteristics induced along with geogrid reinforcement. In this paper, a series of small-scale physical modelling has been carried out to investigate the stress-strain behaviour and deformation of geogrid after final loading. Therefore, a simplified expression model has been developed to model the behaviour of tensile stress-strain of geogrid inclusion. This simple model is similar to the Mohr-Coulomb model that is used in the nonreinforced soil. In general, the results have been confirmed by experimental testing and are consistent with the analytical results. In the main results, it is demonstrated that strains and deflections induced within two layers of geogrid inclusions are less than those induced within one layer. In addition, the tensile force induced in the first geogrid sheet is larger than that in the second geogrid layer.</p>

<p>Stone column technique is well established to improve soft soil performance. However, an alternative material is proposed to enhance the soft soil performance by reinforcing with geofoam materials. Expanded Polystyrene (EPS) geofoam is a super-weighted geosynthetic material used in various geotechnical engineering applications. This study deals with the innovative use of geofoam as a column material in soft soils to improve bearing capacity. This method has been developed in small-scale laboratory tests and a series of loading tests have been performed on different columns of single floating floating geofoam columns with two different diameters and a length to diameter ratio of 5. Then, a comparison was made with the results of ordinary stone columns and reinforced stone columns to obtain the advantages of geomofume columns. By considering the bearing capacity, it was found that geofoam columns could be a suitable alternative material to improve the bearing capacity of soft soils. The results showed that the efficiency of geofoam columns is almost similar to ordinary stone columns and geofoam is easy and economical to use. However, encasing the stone columns with geotextiles leads to further growth of bearing capacity.</p>

This paper conducts a 1g model test on soil foundations reinforced by geosynthetic encased granular columns (GECs) across a reverse fault. The aim is to evaluate the effectiveness and reinforcing mechanism of GEC foundations in mitigating the ground surface deformation as-sociated with reverse faulting. For comparison, 1g model tests were also performed on unrein-forced and GRS foundations. The test results indicate that GEC foundations can effectively mitigate the ground surface deformation induced by reverse fault movement; compared with the unreinforced foundation, the GEC foundations can reduce the maximum angular distor-tion at the ground surface by 23.3%–55.6%. A percentage reduction for maximum angular distortion of 23.3% was achieved as the fault offset reached 30% of the foundation height, which mitigates the risk of the surface fault hazards associated with large reverse fault move-ment.

<p>As part of the French national project (2021-2023) on the improvement and strengthening of soils by rigid inclusions (ASIRI +), the “Geotechnical Centrifuge” laboratory at the University of Gustave Eiffel is studying the effect of rolling loads on a thin granular platform based on a soil reinforced by a mesh of rigid inclusions. One describes the design and the realization of a 2D reduced model to the scale 1/10^th. This model consists of a sandy mattress, evenly reinforced by a geogrid, an analog soft polystyrene soil and spaced vertical metal plates. The scale model is then placed in a strongbox with a transparent face to allow image analysis during loading. Under an acceleration of 10xg, this model was first subjected to the static vertical loading of a shallow foundation, then of a heavy roller pulled by a mobile gantry which performances are detailed. With regard to the failure mechanisms observed in the platform in static, the tests have shown the importance of the positioning of the foundation in relation to the inclusions, and of its width in relation to the compressible thickness or the distance between inclusions. Fatigue tests on a few round-trip cycles along the length of the container were carried out in order to simulate linear traffic here. The mass of the roller can vary from test to test over the range of platform service loads up to the critical load measured statically. The first 2D traffic simulations show perturbations in arching effects in the platform on the vertical residual stress above the rigid inclusions heads, and highlight the benefic effect of an additional reinforcement geogrid on the overall stiffness of the foundation.     </p>

Geosynthetic encased stone column (GESC) has higher strength than conventional stone col-umn due to the radial confinement of geosynthetic encasement. This technology has been used for ground improvement in soft soils. In this study, the shear strength behavior of GESC under direct shear loading was investigated using the three-dimensional finite difference pro-gram FLAC3D. The stone column and surrounding soil were modeled using the linearly elas-tic-plastic Mohr-Coulomb model, and the geosynthetic encasement was characterized using linearly elastic elements with isotropic behavior. The model also considered the interaction be-tween geosynthetic encasement and adjacent soils (i.e., stone column and surrounding soil). The shear stress-strain response and the development of longitudinal and circumferential strains of GESC during the shear process were presented and discussed. Simulation results in-dicated that the geosynthetic encasement can increase the shear resistance of stone column, and the longitudinal strains of GESC are greater than the circumferential strains under direct shear loading.

<p>A wide range of treatments has been proposed to improve soft soils. However, increasing construction costs and combining with today's environmental considerations will undoubtedly make the need for alternative materials. Expanded Polystyrene (EPS) geofoam is a superlight weight geosynthetic material used in various geotechnical engineering applications. This study deals with the innovative use of geofoam as a column in the soft soil for improving the load-carrying capacity. A series of numerical analysis was carried out on the various single floating geofoam columns with diameters of 80 mm and 100 mm and the length of 400 mm and 500 mm, respectively. Then, the results of the analysis were compared with the results of ordinary stone columns and vertical encasement stone columns with the geotextile to obtain the benefits of geofoam columns. The load-carrying capacity of the geofoam column is almost equal to the load-carrying capacity of an ordinary stone column. However, this amount is smaller than vertical encasement stone columns. The lateral deformation of the columns was investigated for all types of columns. The bulging in geofoam columns is smaller than the ordinary stone column. According, finite element numerical analysis was performed to implement the full-scale geofoam columns.</p>

<p>Existing studies confirmed that the response of geosynthetics-reinforced beds is directly affected by contributory factors, including soil’s grains, reinforcement’s characteristics, and surface loading geometries. In this paper, a series of plate load tests has been carried out for the further understanding of the behaviour of geocell and geogrid-reinforced soil. The considered variables were included with four different soil grains sizes, two different geocell’s opening sizes, two different geogrid’s aperture sizes and three different loading plate sizes. As it was expected, the geocell and geogrid-reinforced soil exhibited a few times higher bearing capacity than the unreinforced status, up to 524% and 635%, respec-tively. The results further focused on the important role of scale effect on the response of reinforced foundations. The optimum nominal aperture size of geocells and geogrids were obtained about 15 and 4 times of medium grain size of soil. Also, it was found that in or-der to obtain the highest reinforcement benefits, the footing’s width should be in the range 13 to 27 (20 in average) times of medium grain size of the backfill. Finally, to provide more stable and reliable geocell-reinforced backfill, it is recommended that the aperture size of geocells and geogrids should be selected smaller than 0.67 and 0.2 times of footing width.</p>

<p>The Aquitaine Basin is a sedimentary basin widely compounded by karstic limestones aged from Jurassic to Oligocène series. Throughout years and particularly in the future, designers would have to consider resilient structures regarding climate changes that, for instance, emphases karst issues. Therein, a methodology based on hydraulic and geological criteria, is provided to assess karst collapse hazard. Applied to a roadway study-case (Departmental Road n°1215 – Le Taillan-Medoc), the methodology carries on a set of disposals to ensure the robustness of the design. Amongst them, a strengthening of the road by a geosynthetics is designed according to the French standards. The importance of the karst diameter and the limiting value of the accepted deformation of the roadway structure, on the required strength resistance of the geosynthetics is enlighten. That confirms the relevance of the methodology to assess a reasonable hazard.</p>