Piled embankments with geosynthetic reinforcement: Numerical analysis of scale model tests

Piled embankments with geosynthetic reinforcement: Numerical analysis of scale model tests

Den Boogert, T.J.M.

Van Tol, A.F. (mentor)
Everts, H.J. (mentor)
Van Eekelen, S.J.M. (mentor)
Van Duijnen, P.G. (mentor)
Bakker, K.J. (mentor)

Civil Engineering and Geosciences

Geo-Engineering

2011-02-22

In the last few years, the CUR committee 159B has been working on the new Dutch Design Guideline for the design of piled embankments. To validate the guideline several field tests have been performed. From the field measurements is concluded that the design method is very conservative. Improving the design guideline will reduce the construction costs. To understand the physical behaviour of the piled embankment and to validate the theory, experimental scale tests have been performed. During these tests the load distribution, deformation and strains were measured. The results of the scale tests are analysed and published. To improve the understanding of the phenomenon arching and where possible, to confirm the observed load distributions and displacements, numerical analysis of the scale tests have been performed and reported in this thesis. The numerical analysis of the scale test is performed with Plaxis 3D Tunnel version 2.4 (Plaxis). The geometry of the Plaxis model is one quarter of the geometry of the scale test. This reduces the amount of elements and therefore the calculation time. In the scale test circular piles are applied. Circular geometry cannot be modelled in Plaxis, therefore the circular pile is mathematically converted to a square pile. The sand and granular material are modelled with Mohr Coulomb (MC) model and Hardening Soil (HS) model. The scale test is driven by applying top load and by drainage of the foam cushion. The top load is modelled as the measured equally distributed load on the embankment. To model the drainage of the foam cushion, the measured water pressure is assigned to the subsoil clusters in Plaxis by a water pressure head. From the Plaxis results can be concluded that arching is immediately found after the first drainage of the foam cushion. Increasing the top load and drainage of the foam cushion in Plaxis results in an increase of loads transferred to the pile by arching and GR, thus results in improvement of arching. The by Plaxis calculated tensile forces in the GR are concentrated in ‘tensile strips’ that lie on top and between adjacent piles. The largest displacement of the GR is found at the middle of four piles. The results of the Plaxis calculations are compared to the scale test results. The total load on the pile and water pressure in the foam cushion found with Plaxis are corresponding with the scale test results. During the first part of the test, the load distribution shows similar results as the measured load distribution. During the second part of the test the load transferred to the pile by arching is overestimated and the load transferred to the pile by the GR is underestimated. The displacement of the geosynthetic reinforcement calculated with Plaxis is underestimated compared to the scale test results. In general the results of the HS model are better than the MC model. By varying a number of parameters in the model, possible causes for the underestimated displacement are investigated. This research concludes that the stiffness of the foam cushion and the water pressure in the foam cushion does not have influence on the GR displacement. The vertical effective stresses are concentrated on and directly next to the pile and are relatively small between the piles. The internal friction angle does have a large influence on the geosynthetic reinforcement displacement, because when the internal friction angle is decreased, the arch decreases and the settlements increase. However, the measured geosynthetic reinforcement displacement from the scale test is still not found in the numerical results calculated in Plaxis.

plaxis 3D tunnel
piled embankment
geosynthetic reinforcement
scale test
arching

http://resolver.tudelft.nl/uuid:05ed172b-dcfc-4752-b575-0d155a6bb4a0

Student theses

master thesis

(c) 2011 Den Boogert, T.J.M.