Abstract
Three-dimensional finite element (FE) simulations were performed to further develop the Swedish design guidelines for geogrid-reinforced timber pile-supported embankments, also known as lightly piled embankments. Lightly piled embankments are constructed mainly in areas which typically have highly compressible soils, and the method utilises untreated timber piles as its key feature. The timber piles are installed in a triangular arrangement instead of the more common square arrangement, with a centre-to-centre distance of 0.8–1.2 m. The aim of this study was to evaluate the current standard using FE modelling setups with square and triangular pile arrangements with varying centre-to-centre distances, based on a typical road foundation case. The evaluation mainly focused on comparing the embankment settlements, as well as the load and stress distribution in the embankment, the piles and the geosynthetic reinforcement. As part of the evaluation, a state-of-the-art study was done on international design guidelines and analytical models. From the FE simulations, no evident difference in mechanical behaviour was found between the triangular and square piling patterns. The maximum allowed centre-to-centre distance between piles can potentially be increased to 1.4 m, decreasing the number of piles by as much as one third.
Highlights
Piled embankments with basal reinforcement are widely used as a foundation method for roads and railways on soft soils
The remaining two simulations were performed without piles, with the respective soil profiles of the semi-floating and floating pile groups, in order to assess the relative reduction of embankment settlement when reinforcing the embankment with a triangular and square pile arrangement
The total settlement of the pavement is limited to 35 cm for the type of road studied in order to avoid seasonal flooding
Summary
Piled embankments with basal reinforcement are widely used as a foundation method for roads and railways on soft soils. This foundation method, known as geosyntheticreinforced pile-supported embankment (GRPSE), has a short construction time and creates an efficient reduction of both the vertical and the horizontal displacements. There is some uncertainty in the Swedish industry concerning the optimum design of GRPSE with untreated timber piles, called the lightly piled embankment method. The uncertainty lies in the optimal centre-to-centre pile spacing and pile arrangement, as well as the need for geosynthetic reinforcement to fulfil the serviceability state of the road or railway construction. The lightly piled embankment method is currently used in Sweden mainly for loose clays and silts, with untreated timber piles as its key feature.
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