Abstract
The paper presents numerical simulations investigating the settlement reduction caused by stone columns in a natural soft clay. The focus is on the influence of the soft soil alteration caused by column installation. A uniform mesh of end-bearing columns under a distributed load was considered. Therefore, the columns were modelled using the “unit cell” concept, i.e. only one column and the corresponding surrounding soil in axial symmetry. The properties of the soft clay correspond to Bothkennar clay, which is modelled using S-CLAY1 and S-CLAY1S, which are Cam clay type models that account for anisotropy and destructuration. The Modified Cam clay model is also used for comparison. Column installation was modelled independently to avoid mesh distortions, and soft soil alteration was directly considered in the initial input values. The results show that the changes in the stress field, such as the increase of radial stresses and mean stresses and the loss of overconsolidation, are beneficial for high loads and closely spaced columns but, on the contrary, may be negative for low loads, widely spaced columns and overconsolidated soils. Moreover, whilst the rotation of the soil fabric reduces the settlement, in contrast the soil destructuration during column installation reduces the improvement.
Highlights
Stone columns are one of the most common ground improvement techniques to improve soft soil deposits
To clarify the influence that the changes in the state of soil due to column installation have on the settlement reduction caused by the columns on soft cohesive soils, the authors carried out numerical simulations using two advanced constitutive models, namely S-CLAY1 [23] and S-CLAY1S [24], which have been especially developed to represent natural structured soft soils, a common type of soils to be treated with stone columns
The analysis of the results focuses on the settlement reduction factor, and the influence of the soil model (Figure 13)
Summary
Stone columns are one of the most common ground improvement techniques to improve soft soil deposits. Kirsch [19] simulated the settlement reduction caused by installation effects of a group of floating columns in a sandy silt He distinguished between individual installation effects, which were modelled applying a small cavity expansion (2-8%), and a global installation effect in an enhanced zone around the group of columns with a higher stiffness (around twice the initial one). To clarify the influence that the changes in the state of soil due to column installation have on the settlement reduction caused by the columns on soft cohesive soils, the authors carried out numerical simulations using two advanced constitutive models, namely S-CLAY1 [23] and S-CLAY1S [24], which have been especially developed to represent natural structured soft soils, a common type of soils to be treated with stone columns. Depending on the analysed case, the effects of column installation either improve or reduce the settlement reduction of the stone column foundation
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