2D Modelling of GeosyntheticallyReinforced Piled Embankments : Calibration Methods in PLAXIS 2D & Review of AnalyticalGuidelines

Sammanfattning: This thesis focuses on the 2D modelling of Geosyntheticaly Reinforced Piled Embankments (GRPE) in PLAXIS 2D. In doing so, it explores two main aspects: 1) the calibration of Interface Stiffness Factors (ISFs) governing the soil-pile interaction of Embedded BeamRow (EBR) elements in PLAXIS 2D, and 2) the prospects and limitations of modelling geogrids (GR) in PLAXIS 2D when underlain by EBR elements; although several studies have validates the EBR element in modelling piles, none address the geogrid-EBR interaction and its implications on modelling GRPE systems. The thesis performs the calibration and validation processes using the full-scale GRPE structure ASIRI (Amélioration des Sols parInclusions Rigide) as documented in Briançon and Simon, 2012 and Nunez et al., 2013. Calibration of the EBR’s ISFs is done against 1) load-displacement curve of a test pile, 2)load-displacement of the structure’s monitored piles, and 3) differential soil-pile settlement. Model results for soil settlement, pile settlement, and pile load are then compared to reported values from the ASIRI site. Results show that the natural deviation between the structure and test pile’s load - displacement results in a wide range of possible calibration values for the ISFs, making calibration based on a test pile’s load-displacement curve an unpractical method. Even when such natural deviations were eliminated by calibrating the model against the structure’s reported values for pile load-displacement, model predictions for subsoil displacement were compromised. It is thus advisable to calibrate the EBR element with respect to soil settlement, pile settlement, and pile load rather than solely on a load-displacement curve as to avoid high divergences in soil-pile differential settlement. Modelling geogrids in GRPE systems, PLAXIS 2D underestimates GR strain due to its inability to simulate GR deflection: EBR elements are superimposed on top of a continuous soil mesh, thus allowing the embankment soil to settle through the EBR element. This unrealistically minimizes GR deflection, which underestimates GR strain when modelling GRPEs in PLAXIS 2D. In addition to validating the 2D modelling of GRPE systems, the thesis conducts a comparative literature review of GRPE design guidelines, focusing on the British BS8006 (2010), the German EBGEO (2011), and the Dutch CUR226 (2016). It then applies the latter two to the ASIRI full scale case study and compares results for predicted maximum GR strainand displacement to those from the PLAXIS 2D model and ASIRI measurements. The literature review shows that the geogrid load distribution is highly dependent on the state of subsoil support, where a uniform distribution is more appropriate for high subsoil support, and an inverse-triangular one more appropriate for low subsoil support. However, the analytical analysis of the ASIRI case shows that the triangular distribution, previously dismissed as unrealistic by the literature review, gives satisfactory results due to a combination of soil sliding and high subsoil support at the ASIRI site.