Paalfundaties onderworpen aan tijdsafhankelijke horizontale belastingen door zachte bodems / Piled foundations subjected to time dependent lateral loads by soft soils

Paalfundaties onderworpen aan tijdsafhankelijke horizontale belastingen door zachte bodems / Piled foundations subjected to time dependent lateral loads by soft soils

Schadee, L.W.

Van Tol, A.F. (mentor)
Everts, H.J. (mentor)
Bakker, K.J. (mentor)
Hoefsloot, F.J.M. (mentor)

Civil Engineering and Geosciences

Geoscience & Engineering

Geotechnical Engineering

2012-11-06

In 2010 design guidelines for piles that are subjected to lateral loads by soils were published in CUR-report 228. The design guidelines are developed by a committee who did several case studies. A few recommendations were made from these case studies. To complement the case studies a long term field test on time dependent soil behavior and a study of the shell factor to take account for 3D pile-soil interaction in a 2D model are desired. Two previous students made their master thesis on these recommendations. This master thesis is a follow-up of the previous studies. A long term field test to investigate both time dependent behavior and lateral pile loads by soils is situated in the Bloemendalerpolder. It consists of a 3 m height embankment made of sand on a 3.6 m thick peat layer, see figure. In the embankment a number of measurement devices are installed. Like casings to measure lateral soil deformation with an inclinometer and two HEA300 piles, which are also equipped with a casing for measurements. From this field test a previous thesis student developed a FEM 3D model in Plaxis 3D. Results of the site investigation and laboratory tests are used for parameter determination for this model. Validation was done in Plaxis 2D with available measurements of deformations and pore pressures. The field test was still ongoing when the 3D Plaxis model was ready. A comparison of the modeled piles and more recent field data shows a good resemblance at depth. However the soil and water pressures are falsely simulated in the model and the modeled embankment shows too stiff pile-soil interaction. The falsely simulated pressures can be solved by using the updated water pressure function in Plaxis 3D, which isn’t available yet. One can cope with the stiff pile-soil interaction by using a more advanced soil model for the embankment sand. The use of the Hardening Soil Model instead of the used Mohr-Coulomb Model may offer a solution. For more insight in the lateral behavior of pile and soil the stress development around the pile in the 3D simulation is looked into. Three depths spread over the peat layer are looked at. In the stress points in front of the pile lateral soil pressure increases and the soil relaxes behind the pile. The difference in lateral soil pressures around the pile increases mainly in the beginning of the consolidation phase. Lateral pile displacements also show the fastest build-up in this phase. During the creep phase the soil pressure around the pile do not change significantly. This is also seen for the bending moments of the pile, which do not change or even decreases in the creep phase. The decrease of bending moments is due to the pile head displacement, as the rest of the pile doesn’t move. The pile head displacement causes the upper part of the pile to stretch, whereby the bending moments decrease. With 2D FEM one models a cross section, whereby piles are modeled as walls. The shell factor translates the pile stiffness to a wall stiffness. A 2D simulation of the 3D model is made. Only one of the piles is modeled in this 2D model to avoid inclusion of the soil between the wall elements. A high and low shell factor is applied and results of the lateral pile behavior are compared with the 3D model and the field test. On the short term a higher shell factor shows the best results. On the long term the high and the low shell factor show insignificant differences in pile displacements, however the higher shell factor shows better results for the bending moments in the pile.

Bloemendalerpolder
horizontaal belaste funderingspalen
kruip
plaxis
CUR-rapport 228

http://resolver.tudelft.nl/uuid:ef8b8914-a3cd-4cbc-a5c0-d3ced832580e

Student theses

master thesis

(c) 2012 Schadee, L.W.