Settlement in three dimensions
With our recently acquired tool Settle 3, we now have the capability to determine settlement in three dimensions. This opens up the ability to model and analyse complex interactions, e.g. between excavations, surcharges, foundations and crane loads.
Settle3 by Rocscience is a commonly used tool across the globe for calculating elastic, consolidation and creep settlement in three dimensions. The program combines straightforward and proven one-dimensional settlement models, such as Janbu and Koppejan, with complex ground profiles and load combinations.
Most settlement calculations use in two-dimensional models, such as D-Settle. This is generally appropriate in situations that are easily simplified. One such example is the modelling of road embankments. In that case, the geotechnical engineer models a number of cross sections (e.g. at every 100 m road alignment) to get an understanding of expected absolute and differential settlement due to consolidation and creep.
A 3D approach is more suitable to complex situation. Examples of such cases are combinations of excavations and crane loads. Or of embankments and piling plant near existing foundations.
Ground deforms (strains) as a result of loading or surcharge. The time in which this deformation or settlement develops depends strongly on the soil type and profile, geological history, ground water levels and permeability of the ground.
Time-dependent deformation, or consolidation settlement, occurs when the surcharge is first resisted by the present ground water. In low-permeability soils, such as clay, the ground water cannot dissipate immediately. Over time, as ground water dissipates from the loaded soil, the soil compresses under the load. This process can take many months to occur and this can lead to problems on superstructures. If a road is paved, for example, but settlement is still ongoing, cracks and bumps may form. This is why road alignments are often preloaded prior to construction on soft soils.
In highly permeable soils, such as clean sand, the ground water can dissipate almost immediately. Here, compression of the soil occurs almost instantly and can be mitigated during construction.
Loads are spread by the ground, reducing with depth. But where multiple loads are present, these may overlap and lead to higher local settlements. If this is not accounted for, tilting of structures can occur, causing extensive damage. An engineer using Settle 3 can account for this effect by calculating loads and their interaction in three dimensions. We can thus predict the risk of settlements in a more accurate way.
We have used Settle 3 in a number of applications already, such as:
– Determining environmental impacts from fill placement;
– Clarify the impact of foundation pressures interacting as part of a forensic investigation;
– Expected deformation of a gas pipe from mobile crane loading.
Contact us if you have a query about settlements for you project.