The deviating interpretation of Almere to the NEN-6743: The consequence of a heterogeneous soil profile, or a result of misinterpreted overconsolidation?

The deviating interpretation of Almere to the NEN-6743: The consequence of a heterogeneous soil profile, or a result of misinterpreted overconsolidation?

De Vries, L.

Hoogendoorn, R.M. (mentor)
Van Paassen, L.A. (mentor)
Ngan-Tillard, D.J.M. (mentor)

Civil Engineering and Geosciences

Geoscience & Engineering

Geo-engineering

2011-05-01

Actual bearing capacity of piles in Almere often differs from the expected values as calculated using nearby CPT data; the calculated strength is often higher than can be achieved in the field. To calculate the bearing capacity of foundation piles within Almere an addition has therefore been made to the standard NEN6743-1. The proposed hypotheses for these deviations include heterogeneous soil behavior and overconsolidation. These hypotheses are tested by a multiple data acquisition approach in which available data such as geological data and available maps have been used along with new acquired data including GEM-2, CPT, core logs and laboratory tests to obtain a better insight in the problem. The investigated maps, Begemann core logs and CPT data has shown that the subsurface of Almere indeed reflects a heterogeneous character at multiple scales. Comparing CPT soil behavior type profiles to Begemann-, grain size- and micro scale CT scan data concludes that the translation from CPT data to in situ soil parameters can be inaccurate; different soil types can show a similar behavior. Inaccurate CPT interpretations can result in bearing capacity miscalculations, but by itself cannot be the result of the deviating soil behavior of Almere. Overconsolidation of the soil has been proven by vertical stress calculations and multi-stage triaxial test results of two samples. Overconsolidation ratio (OCR) calculations based on steady state vertical stress profiles might have been underestimated in the Holocene clay layers: as a result of ongoing pore pressure dissipation resulting from the land reclamation the OCR and soil strength increases over time. Overconsolidation may have also resulted in an overcompacted soil which has the tendency to dilate when applied to vibratory sources, such as during the installation of pile foundations. Both statements have to be verified.

NEN-6743
overconsolidation

http://resolver.tudelft.nl/uuid:07a33267-fe81-40c3-b0e7-33936fcddce1

Student theses

master thesis

(c) 2011 De Vries, L.