During the design phase, SOCOTEC can investigate for you which settlement has to be taken into account for your project and whether any provisions are required to meet the settlement-related requirements upon completion of the project.
With a design for the construction phase (or possibly as part of the final design), SOCOTEC can examine what the aforementioned provisions are and which specifications they must meet. This can be done in combination with the establishment of a fill schedule.
With regard to the aforementioned measures, you could consider (a combination of):
- Observing a settlement / waiting period if there is sufficient time so that the majority of the settlement has occurred by the time the project is delivered
- Applying a temporary pre-load to accelerate the settlement process
- Using vertical drains to accelerate the settlement process
- A combination of the previous two measures
- Applying light filling material
- In special cases, using a stabilising construction, consisting of light filling material such as expanded polystyrene (EPS) or foam concrete
In order to control uncertainties in the properties and composition of the underground, and the calculation models used for the design (see Site Engineering) with regard to settlement, a so-called ‘back analysis’ is performed. The settlement parameters are recalculated until the calculated development over time of the settlement corresponds as closely as possible to the measured actual development of settling over time. The recalculated settlement parameters are then used to predict the expected final and residual settlement.
The calculations for the settlement analyses are generally made using the validated Deltares D-series software.
SOCOTEC can conduct settlement analyses for you according to the Koppejan models and the Den Haan (abc isotach) and Bjerrum isotach models. Preference is given to the isotach models since they are more advanced. SOCOTEC has some 15 years of experience with the more advanced isotach models.
In general, settlement analyses are performed deterministically. SOCOTEC has the experience to perform probabilistic settlement analyses for you. Depending on the type of probabilistic analysis, it can be investigated for you which parameter(s) has/have the greatest influence on the calculation of settling, or it can be investigated how likely it is that you will meet the intended residual settlement requirement.
In addition to Deltares software, SOCOTEC has developed a spreadsheet in-house that can be used to effectively calculate for you the final settlement resulting from a change in stress based on the results from large numbers (hundreds) of CPTs.
Infrastructure and site preparation
As a result of embankments, for example for dike reinforcement, the construction of infrastructure or site preparation, excavations, for example for construction pits, or groundwater level lowering, deformations in the subsurface can occur.
The aspects mentioned above cause a certain degree of influence on the surroundings, such as influence on above- and underground infrastructure, archaeological finds in the subsurface or (foundations of) buildings. Depending on the degree of influence, damage may occur to the aforementioned objects.
SOCOTEC can advise you on this environmental impact. This can include making:
- Settlement analyses for groundwater level reductions
- Settlement and horizontal deformation analyses for embankments
- Horizontal deformation analyses (horizontal) for excavations
Predicting horizontal deformations can be done in two ways:
- Fast and indicative (weighted average over the height of the soil layer package subject to deformations) with analytical computational models (De leeuw, Mieusses and Bourgeses)
- More precisely with a Finite Element Model (Plaxis for example) where a detailed picture of the deformations of the different soil layers with different stiffnesses is obtained
For these analyses we use a geotechnical soil investigation as well as geotechnical laboratory investigations that we can perform ourselves. For the calculations we use the Dseries of Deltares (D-Settlement) and Plaxis 2D/3D.
To minimize the impact on the environment as much as possible, environmental monitoring plays an important role during the execution of earthworks (excavations and embankments). With monitoring, uncertainties during execution can be identified so that, if necessary, risk-mitigating measures can be taken at an early stage.