Numerical Analysis of a PVD-improved Embankment on soft clay - Class A and class C prediction of the Ballina test embankments
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Infrastructure and environmental engineering (MPIEE), MSc
Publicerad
2023
Författare
Sundström, Salomon
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The construction of embankments on soft soil is challenging to engineers due to
difficulties associated with their short and long-term stability. This thesis aims to
utilize numerical modelling to analyse the behaviour of embankments on soft clay,
with special focus on the Ballina test embankments. Two distinct predictions are made:
one considering the presence of prefabricated vertical drains (PVDs) installed in the
soil and another completely without PVDs. The constitutive model used is the Creep-
SCLAY1S model in PLAXIS 2D. The obtained results are compared with on-site
measurements to evaluate the effectiveness and reliability of the modelling approach.
The thesis involves analysing available soil data and creating a representative soil
profile, deriving input parameters for the constitutive model. Furthermore, a simple
homogenisation technique is implemented to model the global effect of the PVDs,
through changing the vertical hydraulic conductivity in the soil. A comprehensive
sensitivity analysis is conducted to identify factors with a significant influence on the
simulation results. The results for the PVD-improved embankment demonstrate
satisfactory predictions with vertical and horizontal deformations aligning reasonably
well when compared with measurement data over a 3-year period. Moreover, the
implemented averaging technique effectively captures the enhanced consolidation
settlements introduced by the PVDs over the time period. Comparisons with the
unimproved embankment indicate little actual improvements in stability for the
improved case in the first 3 years. However, spanning over a 40-year period, the
vertical settlements approach the same order of magnitude for the two cases, and the
horizontal displacements are significantly less for the improved embankment.
Indicating a time-dependent nature of stability improvement using PVDs.
Ultimately, the parameter derivation process and high-quality laboratory data are vital
for accurate simulations. As revealed by the sensitivity analysis, there is significant
variations in the results depending on which laboratory test is used to derive the preconsolidation
pressure. The discrepancy can likely be attributed to the unusually high
strain-rates used for the CRS laboratory tests, in combination with the unusually low
strain rates adopted for the IL-tests – emphasizing the experience and skill required of
the engineer in order to arrive at accurate predictions.
Beskrivning
Ämne/nyckelord
Numerical modelling , creep , soft clay , test embankment , Creep- SCLAY1S , Vertical Drains , Prefabricated Vertical Drains , PVD