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This paper describes a simplified numerical model for geogrid-reinforced piled embankments considering dynamic loads. Based on this model, the vertical stress acting on the geogrid is investigated comprehensively and is found to exhibit an inverse trapezoidal distribution. An analytical solution for the geogrid-reinforced piled embankment under a static load is then derived for vertical equilibrium and an assumed inverse trapezoidal load distribution on the geogrid. This is extended by considering an additional vertical stress induced by the dynamic loads, based on the Boussinesq equation. However, the characteristics of the traffic loads (i.e. frequency and load numbers) are ignored. The analytical solution is then validated against three case studies and parametric numerical studies under various geometries (pile spacing and embankment height), geogrid stiffnesses and embankment friction angles. These parametric studies show that the geogrid tension increases with the pile spacing, embankment height and geogrid stiffness but decreases with the friction angle of the embankment. The pile spacing is found to be the most influential of all the factors examined in this paper, increasing from 2.0 m to 3.0 m when the geogrid tension is increased by approximately 248%. [ABSTRACT FROM AUTHOR]

This paper presents a simplified finite-element model, based on which the arching in highway piled embankments subjected to moving vehicle loads is investigated. The analyses demonstrated that the pile spacing was a more sensitive factor than embankment height, whose increase from 2·0 to 3·0 m led to a 60–68% increase of the normalised maximum settlement at the base of the embankment. The effect of moving vehicle loads was of particular interest, increasing the normalised maximum settlement and vertical stress at the base of the embankment by approximately 23% and 19%, respectively, compared to the static situation. The influence height of soil arching related to the pile spacing and embankment height was investigated, and showed that the vertical extent of arching was within a normalised distance of 2·0 from the base of the embankment. Factors of the embankment properties – that is, elastic modulus, friction angle, dilation angle and cohesion – were examined and showed that the cohesion was a most sensitive factor, whose increase from 1 to 10 kPa reduced the normalised maximum settlement and vertical stress by approximately 56% and 42%, respectively. Also shown was that the increase in the velocity of a moving vehicle from 30 to 120 km/h slightly increased the normalised maximum settlement and vertical stress by approximately 9% and 10%, respectively. Finally, a modified analytical method was developed by considering the additional vertical stress induced by moving vehicle loads based on the Boussinesq equation, whose solution was found to be in good agreement with the finite-element results. [ABSTRACT FROM AUTHOR]

This paper presents a finite-element (FE) analysis of the effect of subsoil in a reinforced piled embankment and compares the findings with predictions from a theoretical method. It shows that the subsoil can carry as much as 75% arching embankment load for the present standard model (pile spacing of 2.5 m, geogrid stiffness of 6 MN/m, embankment height of 6 m, and subsoil compression index of 0.7). Also, the proportion is much larger for the lower value of pile spacing, geogrid stiffness, embankment height, and subsoil compression index. The maximum settlement of subsoil is found to be more sensitive to the pile spacing than to the geogrid stiffness. The theoretical method shows reasonable agreement with the FE results and can therefore be used to predict the effect of subsoil in reinforced piled embankments. The geogrid has a significant role in carrying the entire embankment load without the subsoil support. However, this effect may lead to intolerable geogrid strain due to relatively large settlement. Two case studies are assessed by the theoretical method. They show that stiff subsoil can carry a significant portion of the embankment load, whereas very soft subsoil support may result in intolerable strain on the geogrid. The effect of the subsoil, therefore, should be considered in the design. [ABSTRACT FROM AUTHOR]

In 2014, the authors of this paper considered predictions of reinforcement tension in a piled embankment from British standard BS 8006 published in 2010 and the 2012 amended version, and compared the results with finite-element model predictions. In keeping with BS 8006, any contribution from the subsoil beneath the embankment was ignored. The present paper extends that earlier work by also considering the potentially beneficial contribution of a lightly overconsolidated clay subsoil layer, both in the finite-element predictions and as a simple modification to the BS 8006 predictive method. It is assumed that there is no 'working platform' (granular) material below the pile cap level, and that the water table in the subsoil does not drop, since either of these factors would be likely to significantly reduce the ability of the subsoil to carry load from the embankment. As anticipated, the subsoil support reduces reinforcement tension. When compared to the finite-element results the proposed modified BS 8006 prediction is quite accurate. The BSI 2012 modified prediction is 'best' (but sometimes slightly unconservative), whereas the BSI 2010 modified prediction is conservative in all cases considered. [ABSTRACT FROM AUTHOR]

Biaxial geogrid in current research is oversimplified, and the three-dimensional orthotropic nature of the biaxial geogrid has not been fully understood in numerical investigations. A comparative study on three modeling approaches for the biaxial geogrid is presented in this paper, including the isotropic membrane model, the orthotropic membrane model, and the truss element model. It shows that the orthotropic membrane model yields practically identical results of the maximum geogrid tension when compared with the truss element model, whereas the isotropic membrane model tends to yield values that are approximately 33% larger. A parametric study shows that the pile spacing has the strongest influence on the maximum geogrid tension. The comparison of four analytical methods with the orthotropic membrane model shows that the British standard (BS) 8006 (published in 2010) and EBGEO (published in 2011) methods greatly overestimate the geogrid tension, while the method presented by Zhuang et al. (published in 2014) results in closer agreement. [ABSTRACT FROM AUTHOR]

The British 'Code of practice for strengthened/reinforced soils and other fills' (BS 8006) was substantially revised in 2010, with a further 'Corrigendum' in 2012. Historically, BS 8006 considered arching in a piled embankment, based on an interpretation of the 'Marston' equation. The 2010 revision included an alternative method related to the analysis of arching in a piled embankment, which was proposed by Hewlett and Randolph in 1988, and later itself amended in the 2012 Corrigendum. This contribution considers BS 8006 predictions of reinforcement tension using these methods as a basis for embankment load on the reinforcement, for a wide range of piled embankment geometries. The predictions are compared with results from three-dimensional finite-element analysis, demonstrating encouraging correspondence with the Hewlett and Randolph approach (but noting that the 2010 revision overpredicts the data whereas the 2012 revision underpredicts it). Good predictions of maximum reinforcement sag are also achieved by slight modification of the BS 8006 method. [ABSTRACT FROM AUTHOR]

The results of a series of linearly elastic-perfectly plastic plane strain finite-element (FE) analyses are reported, investigating the arching of a granular embankment supported by pile caps over a soft subsoil. The objective of the research was to contribute further to generic understanding of arching in a piled embankment, and the contribution of tensile reinforcement near the base of the embankment. The stress state in the embankment and load on the subsoil were examined. The analyses demonstrate that the ratio of the embankment height to the centre-to-centre pile spacing is a key parameter in determining the behaviour. The potential contribution of tensile reinforcement near the base of the embankment was also considered. It was found that arching in the embankment occurred at relatively small settlement of the underlying subsoil, whereas much more settlement was required for sag of the reinforcement to have significant effect in further reducing the stress on the subsoil. [ABSTRACT FROM AUTHOR]