Abstract:
When the footings are constructed on weaker soils, several structural enhancement techniques
such as use of larger footings, micro piles, or different ground improvement techniques such
as use of concrete cylinders and use of filling materials or low-grade concrete are being used
in practice. However, there is a limited understanding of the effectiveness of these different
techniques. The aim of this research is to provide a design guideline/ framework for design
engineers when constructing column footings in domestic buildings on weaker soils. This study
pursue the following objectives: Identifying current design practices used by the engineers
when constructing domestic buildings on weaker soils, Developing comprehensive Finite
Element (FE) models using MIDAS software to investigate the behaviour of column footings
with the varying embedment depths, Conducting a parametric study to investigate the
behaviour of column footings with the implementation of identified strength enhancement
techniques, and comparison of the results to identify feasibility of identified strength
enhancement techniques.
This research investigates the structural adequacy of the above techniques by using the MIDAS
GTS-NX FE analysis software. Footing and soil were modelled two dimensionally and three
dimensionally in drained conditions incorporating soft clay soils and dense sand. Validation
process was carried out comparing theoretical settlements and settlements from the FE model.
Mesh sensitivity analysis was carried out to optimise the computational process. A
comprehensive study was carried out with developed models to investigate the effect of
embedment depth of the footing, effect of use of concrete cylinders, influence of soil
replacement with quarry dust and impact of low-grade concrete layers below the footing. The
comprehensive modelling techniques developed in this research could be used for further
studies in different ground improvement techniques and will provide an idea about the
feasibility of enhancement techniques to make necessary structural enhancements and ground
improvements when constructing domestic buildings on weaker soils, thus reducing the costs.
This study concluded that for a typical footing stress range of 150-175 kN/m2, optimum
embedment depth lies within the range of 0.6 m to 1 m. Within this range, the load versus
settlement curve demonstrates a desirable linearity, suggesting that the footing can
accommodate the expected stresses while minimising excessive settlement, and increasing the
depth of the cylinder has a noticeable effect on reducing settlement by 16% -17% but beyond
approximately 1.2 m in height, there is no noticeable impact on the settlement. This study also
concluded that use of quarry dust replacement can reduce overall settlements in drained
conditions by 50% - 60% while bearing capacity can be increased by 45% to 55%. Optimum
depth of soil replacement can be taken as between 1m – 1.2 m for the embedment depth of 0.8
m. and use of Grade 15 concrete layer below the footing can reduce the settlements and enhance
the bearing capacity. Implementation of 150 mm – 250 mm thick M15 concrete layer
underneath the footing can reduce settlements by 55% - 60% for 210 kPa of pressure.