1782
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
artesian pressures are present in the underlying Pleistocene
sands. The surface water table is at 0.6 m below ground level.
Figure 1. Project area with subdivision according to subsoil lithology.
2.3
Function Analysis Phase
The road administrator demands that post-construction
settlements should not exceed 0.15 m in 30 years, to prevent
differential settlements from compromising driver comfort.
Construction should not create connections between surface
water and the Pleistocene aquifer. The feasibility stage of the
project will not consider relocation of utility networks.
2.4
Creative Phase
Two construction methods will be considered in the study: a
basal reinforced piled embankment and traditional construction,
using prefab vertical drains and a sand fill with temporary
surcharge.
2.5
Evaluation and Selection Phase
The main failure mechanisms identified for the traditional
construction method are: excessive post-construction
settlements and differential settlements, contamination of
surface water and water in the Pleistocene aquifer, damage to
constructions and utility networks. Failure mechanisms for piled
embankment construction include: insufficient end bearing
capacity of the piles, failure of piles or load transfer platform.
Shared failure mechanisms are: instability of embankment
slopes, insufficient bearing capacity of pavements and verges,
and noise and vibration nuisance during construction.
A subsoil hazard is defined as the likely occurrence of a
subsoil phenomenon that promotes failure. Figure 2 identifies
these subsoil phenomena for the project area. This simplified
geological section is redefined in terms that geotechnical
engineers can understand (Baynes, 2005). Table 2 lists the
associated subsoil hazards. On the basis of expert judgement
and local experience both construction methods were
considered feasible, and included in the further process.
2.6
Development Phase, first stage
A sensitivity analysis was performed to determine which
parameters have the largest contribution to the uncertainty in
whole life costs of the traditional construction method.
Variations of peat thickness, total thickness and unit weight of
the soft layers, compression parameters and consolidation
coefficient account for 95% of the variation of the costs. These
critical parameters were selected for the further study.
Table 1. Activities in a Value Engineering study, applying the ‘Building with the Subsurface’ concept
Value Engineering study
‘Building with the Subsurface’ process
Acquisition of geological and geotechnical data
Preparation Phase
Bring together a multidisciplinary team
Create commitment with stakeholders and decision makers
Define output of the study
Information Phase
Collect information on design
Collect geotechnical data
Topography, general geomorphology, geology
and hydrology, surface elevation
Function Analysis Phase
Collect and analyse data on end user specifications, impacts
on the surrounding area, natural and manmade hazards
Creative Phase
Prepare a long list of construction methods and materials
Evaluation and Selection
Phase
Define failure mechanisms for construction methods
Define and assess subsoil hazards for construction methods
Assess feasibility of construction methods
Prepare a shortlist of construction methods
Development Phase
Define design methods for evaluation of failure mechanisms
Define critical parameters of the subsurface model
Collect all available geological and geotechnical data
Synthetize sets of discrete soil profiles; define average values
and uncertainty of all critical parameters
Perform design calculations for all soil profiles
Analyse the design results in terms of the output of the study
Optimize the design and the construction methods
First stage
Data on geology, geotechnical parameters and
hydrology from public sources
Second stage
Local site investigation
Presentation Phase
Present the output in maps, 3D models
Select preferred construction methods and materials
Implementation Phase
Update the list of subsoil hazards, define actions for
mitigation of hazards
Present recommendations for later site investigation
