Any development on soft soil requires ground improvement work prior to construction. Otherwise, the structure, such as roads and railways, would fail due to unstable soil foundation. If you have ever driven on roads riddled with potholes, chances are it might be due to poor soil foundation. Or when a house has cracks, it means the structure is unstable, probably due to the poor soil foundation of the house. Poor or soft soil condition will cause a movement in soil foundation, which will lead to the movement of the structure or anything on the soil.
Therefore, ground improvement work is crucial to ensure the soil foundation is solid. There are many types of ground improvement work that can be carried out to ensure the soil foundation resists load from structure or infrastructure. The cheapest type is excavation and replacement. This requires the excavation and removal of soft soil and replaced with the good backfill materials. The limitation of this method is the depth of excavation is only up to 3m due to the safety and stability of the cut soil.
The other low-cost method is surcharge load. Surcharge load is used to expedite the consolidation of the soft soil where the backfill soil is placed on top of soft soil for a certain period of time. The consolidation is the process to drain out water from the soft soil. The backfill represents the load of the structure to be constructed, so that when the structural load is put on the soil foundation later on, the movement of the soil foundation is minimised.
If the depth of the soft soil is deeper, prefabricated vertical drain (PVD) is preferred. PVD is installed in a soft soil area to expedite the consolidation process and it is combined with surcharge to effectively consolidate the soft soil. If the depth of soft soil is critical and the structural load is large, the pile embankment is the best option, but it is costly. This is the most effective method for deep soft-soil areas.
The current technology and research proposed the use of lightweight material as a ground improvement for soft soil. For example, the soft soil is removed at shallow depth and replaced with expanded poly-styrene foam or polyurethane foam to reduce the load imposed on the underlying soil. Apart from the cost, implementation of the ground improvement takes into consideration the time allocation and safety of the surroundings.
By: Diana Che Lat
Geotechnical Highway Engineering
Universiti Teknologi MARA (UiTM), Pasir Gudang