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Alternative calculation principle for design of piled embankments with base reinforcement

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Abstract

Grouting soil improvement, geosystems including reinforcement
... Different methodologies were developed for the design of RI systems considering the load transfer mechanism through soil arching under static loadings (Terzaghi 1943;Guido et al. 1987;Combarieu 1988;Kempfert et al. 1997;Russell and Pierpoint 1997;Svanø et al. 2000;Collin 2004;Filz 2006;van Eekelen and Bezuijen 2008;Zhang et al. 2016). Some comparisons demonstrate a good agreement between the analytical models and the real projects (Xing et al. 2014;Ariyarathne and Liyanapathirana 2015), different results are noted for the same situation using various design methods (Bhasi and Rajagopal 2015), and neither of them considers the influence of complex loading (e.g., eccentric loading). ...
Article
In the absence of high-quality soils, the rigid inclusion reinforcement technique has been extensively used in geotechnical engineering practice to meet the serviceability requirements of construction projects. This article aims to investigate the behavior of a single footing placed on soft soil reinforced by four rigid inclusions using three-dimensional (3D) finite difference modeling (FDM). A set of full-scale experimental tests are used as references for the development of the numerical approach. The concurrence of the numerical and experimental data allows us to assess the load transfer platform thickness influence on the system under centered and eccentric loading conditions. Some preliminary insights can thus be obtained based on this analysis for the soft soil improvement using rigid inclusions at the design stage.
... The mechanical response of these 'geo-structures' is commonly studied by analysing the stress redistribution taking place within the embankment, usually named 'arching effect'. In the past, numerous theoretical arching mechanisms (Carlsson, 1987;Chen et al., 2008;Collin, 2004;Handy, 1985;Hewlett & Randolph, 1988;Kempfert et al., 2004;Marston & Anderson, 1913;McKelvey, 1994;Rogbeck et al., 1998;Russell & Pierpoint, 1997;Svanø et al., 2000;Terzaghi, 1943;Van Eekelen et al., 2013;Zaeske, 2001) were proposed. The employment of some of these mechanisms is also suggested by the most used design standards (e.g. ...
Article
The use of piles as settlement reducers in the design of artificial embankments on soft soil strata is nowadays very common. The design methods employed in the current engineering practice are based on simplified approaches not allowing the assessment of average and differential settlements at the top of the embankment. In this paper, a model to estimate both differential and average displacements at the top of the embankment is introduced. This, based on the choice of substructuring the spatial domain and employing a suitably conceived upscaling procedure, is an extension to the case of rough pile shafts of a model originally conceived by the authors for smooth piles. To conceive and calibrate the model, the authors performed a series of numerical simulations mainly aimed at highlighting the mechanical processes taking place at the pile shaft. From a practical point of view, this model can fruitfully be employed in displacement based design approaches and to optimize pile diameter and spacing.
... Five existing design methods are selected for the comparison, which are design standards or design Guidelines. These design methods consist of the CUR226 method (adapted from the concentric arches model of Van Eekelen et al., 2013), EBGEO method (adapted multi-arching model from Kempfert et al., 2004), BS8006 method (adapted from the model of Hewlett and Randolph, 1988), NGG method (adapted from the model of Svanø et al., 2000), and the Geogridge bridge method (adapted from the model of Filz and Smith, 2006;Filz et al., 2019). Liu et al. (2007) described a case study with measured results for a geogrid-reinforced and pile-supported (GRPS) embankment that has an improvement area ratio of 8.7%. ...
Article
An analytical model is presented for the design of geosynthetic-reinforced and pile-supported (GRPS) embankments in this paper. The originality of the proposed solution lies in the fact that it allows considering the influence of the subsoil consolidation on the soil arching and geosynthetic strain. A nonlinear function is implemented to describe the subsoil behavior with the consolidation process in a closed-form solution. A simplified approach is then presented to link the arching development with the subsoil consolidation. The arching theory is combined with the tensioned membrane theory and the soil-structure interaction mechanisms to provide a simple and suitable design approach that enables a realistic approximation for designing soil–geosynthetic systems. The analytical model is capable of performing an ultimate and serviceability limit state design of GRPS embankments. While current methods cannot fully address the important effects of the subsoil consolidation, the analytical results suggested that arching and differential settlements increase with an increase of the subsoil consolidation degree. The analytical model is compared to field measurements and five other design standards for several full-scale field tests to study its validity. The results showed a satisfactory agreement between the proposed model and measured data, and generally better results are obtained as compared with other design methods
... To study the behaviour column supported embankments, several analytical models have been proposed in the literature. Van Eekelen et al. (2013) summarised and classified them as (a) frictional models (Terzaghi, 1943;McKelvey, 1994;Russell and Pierpoint, 1997;Naughton, 2007;McGuire et al., 2012), (b) rigid arch models (Carlsson, 1987;Rogbeck et al., 1998;Svanø et al., 2000;van Eekelen et al., 2003), (c) models using mechanical elements (Deb, 2010;Filz et al., 2012;Zhang et al., 2012aZhang et al., , 2012bDeb and Mohapatra, 2013;Zhao et al., 2019) and (d) limit-state equilibrium models (Marston and Anderson, 1913;Hewlett and Randolph, 1988;Jones et al., 1990;Zaeske, 2001). BS8006 (2010), later discussed by Van Eekelen et al. (2011), adopted the empirical model proposed by Jones et al. (1990) to examine the geosynthetic reinforced column supported embankments. ...
Article
Generally numerical modelling can provide an accurate and cost-effective approach to understand the behaviour of geosynthetic-reinforced column-supported embankment. When the problem geometry cannot be simplified to the two-dimensional plane-strain or axisymmetric, a full three-dimensional solution is required to obtain sensible results. This study presents a modelling of the geosynthetic-reinforced composite ground supporting a road embankment. Response of soft soil is captured by adopting Modified Cam-Clay model. In addition, Hoek-Brown constitutive model is considered to simulate non-linear stress-dependent yield criterion for Concrete Injected Columns (CIC) that describes shear failure and tensile failure by a continuous function. To assess whether the proposed numerical model can capture real behaviour of composite ground, field monitoring data of deep soft clay deposit improved by CIC from Gerringong Upgrade is used to validate the model. The settlement and lateral displacements of ground, stress transferred to column, and pore water pressure results for the embankment during and after the construction, measured using the field instrumentations including settlement plates, inclinometers, earth pressure cells on CIC, and pore pressure transducers, are compared with numerical predictions. In addition, the numerical results provide insights to investigate load transfer mechanism in the composite ground, capturing response of soil – column - embankment system.
... To validate calculation steps 1 and 2 separately, arching AR needs to be measured ( Step 1 has been evaluated previously by means of centrifuge tests on piled embankments without GR by Fagundes et al. (2015) and Girout et al. (2016) by comparing the results obtained with the three methods evaluated here plus Svanø et al. (2000)'s method. Fagundes et al. (2015) and Girout et al. (2016) found that the EBGEO (DGGT 2011) and BS8006 (BSI 2012) guidelines resulted in a better agreement with the measured forces acting on the piles (arching AR). ...
Article
Full-text available
This paper presents numerical and analytical models to complement experimental data obtained from 40 centrifuge tests of geosynthetic-reinforced piled embankments, 12 of which had a surcharge applied at the embankment surface. The main parameters of study were pile diameter, pile spacing, embankment height and geosynthetic stiffness. The tests measured the force transferred to the piles, the embankment surface settlements and the maximum geosynthetic reinforcement deflections below the embankment under conditions without any support from the underlying soil. Maximum geosynthetic deflections measured longitudinally between piles were then compared with values predicted by European design guidelines. A 3D numerical model, initially validated by centrifuge tests, was then used to compute those geosynthetic tensile forces not measured in the reduced-scale physical models. Numerical values of geosynthetic tensile forces were also compared with corresponding values predicted by European guidelines.
... To validate calculation steps 1 and 2 separately, arching AR needs to be measured ( Step 1 has been evaluated previously by means of centrifuge tests on piled embankments without GR by Fagundes et al. (2015) and Girout et al. (2016) by comparing the results obtained with the three methods evaluated here plus Svanø et al. (2000)'s method. Fagundes et al. (2015) and Girout et al. (2016) found that the EBGEO (DGGT 2011) and BS8006 (BSI 2012) guidelines resulted in a better agreement with the measured forces acting on the piles (arching AR). ...
Article
Full-text available
This paper presents numerical and analytical models to complement experimental data obtained from 40 centrifuge tests of geosynthetic-reinforced piled embankments, 12 of which had a surcharge applied at the embankment surface. The main parameters of study were pile diameter, pile spacing, embankment height and geosynthetic stiffness. The tests measured the force transferred to the piles, the embankment surface settlements and the maximum geosynthetic reinforcement deflections below the embankment under conditions without any support from the underlying soil. Maximum geosynthetic deflections measured longitudinally between piles were then compared with values predicted by European design guidelines. A 3D numerical model, initially validated by centrifuge tests, was then used to compute those geosynthetic tensile forces not measured in the reduced-scale physical models. Numerical values of geosynthetic tensile forces were also compared with corresponding values predicted by European guidelines.
... In the past, the mechanical response of this type of system was studied by analysing the 'arching effect'that is, the stress redistribution taking place within the embankment; numerous theoretical arching mechanisms (Marston & Anderson, 1913;Terzaghi, 1943;Krynine, 1945;Handy, 1985;Carlsson, 1987;Hewlett & Randolph, 1988;McKelvey, 1994;Russell & Pierpoint, 1997;Rogbeck et al., 1998;Svanø et al., 2000;Zaeske, 2001;Collin, 2004;Kempfert et al., 2004;Chen et al., 2008;van Eekelen et al., 2013), allowing the estimation of stresses applied on both the top of the pile and the foundation soil, were proposed. These approaches, which are commonly adopted in engineering practice (the employment of some of these approaches is suggested by the most used design standards e.g. ...
... In the past, the mechanical response of this type of system was studied by analysing the 'arching effect'that is, the stress redistribution taking place within the embankment; numerous theoretical arching mechanisms (Marston & Anderson, 1913;Terzaghi, 1943;Krynine, 1945;Handy, 1985;Carlsson, 1987;Hewlett & Randolph, 1988;McKelvey, 1994;Russell & Pierpoint, 1997;Rogbeck et al., 1998;Svanø et al., 2000;Zaeske, 2001;Collin, 2004;Kempfert et al., 2004;Chen et al., 2008;van Eekelen et al., 2013), allowing the estimation of stresses applied on both the top of the pile and the foundation soil, were proposed. These approaches, which are commonly adopted in engineering practice (the employment of some of these approaches is suggested by the most used design standards e.g. ...
Chapter
In recent years, the employment of deep foundations as settlement reducers has become increasingly popular in the design of earth embankments over soft soil strata. To further improve the system response, geosynthetic layers are often positioned at the embankment base. Owing to the presence of both piles and geosynthetics, complex interaction mechanisms, transferring stresses towards the piles and reducing those on the soft foundation soil, take place. Although these mechanisms are governed by the relative stiffness of the various elements constituting this system (piles, foundation soil, embankment and georeinforcements), the approaches commonly adopted to design these “geostructures” do not explicitly take into consideration the stiffness of the single element as design parameters. Moreover, the effect of the stepwise embankment construction process is often disregarded. As a consequence, the settlements at the top of the embankment cannot quantitatively be estimated.
... To validate calculation steps 1 and 2 separately, arching AR needs to be measured ( Step 1 has been evaluated previously by means of centrifuge tests on piled embankments without GR by Fagundes et al. (2015) and Girout et al. (2016) by comparing the results obtained with the three methods evaluated here plus Svanø et al. (2000)'s method. Fagundes et al. (2015) and Girout et al. (2016) found that the EBGEO (DGGT 2011) and BS8006 (BSI 2012) guidelines resulted in a better agreement with the measured forces acting on the piles (arching AR). ...
Thesis
Piled foundations are commonly employed to reduce settlements in artificial earth embankments on soft soil strata. To limit the number of piles and, consequently, construction costs, popular is the use of geosynthetic reinforcements laid at the embankment base. Due to the complex interaction phenomena occurring between (i) piles, (ii) foundation soil, (iii) embankment soil and (iv) geosynthetics, different aspects such as either time dependency or friction between piles and surrounding soil are often ignored. Moreover, simplified displacement-based approaches to choose reinforcements, pile diameter and spacing are missing in the literature. In this thesis, a series of numerical analyses are performed and, by using an upscaling procedure based on both the concept of sub-structuring of the spatial domain and plane of equal settlements, a theoretical method capable of represent the mechanical behaviour of geo-reinforced piled embankments is introduced. The effect of: (i) friction between piles and soil; (ii) consolidation occurring within the foundation soil and (iii) settlements at the pile base is considered. By sub-structuring the spatial domain, rheological models are provided to evaluate settlements at the top of the embankment. In particular, predictive tools allowing a rapid assessment of both (i) differential and average settlements at the top of the embankment and (ii) (when geosynthetics are present) the maximum tensile force acting within the basal reinforcement have been conceived.
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