Recently this happened in mumbai in metro construction. It is very important to understand the nature of the soil and associated risk under different conditions


If you keep an excavation poorly retained in red fat clay or any expansive soil during the monsoon season, several risks may arise due to the nature of the soil and the increased moisture content. Here are some potential risks:

1. Soil erosion : Expansive soils, including red fat clay, have a tendency to erode when exposed to water. The high clay content makes the soil susceptible to erosion by runoff or flowing water. Un-retained excavations can lead to significant erosion, causing the sides of the excavation to collapse or slope failures to occur.

2. Soil Instability: The presence of excess water in the expansive soil can cause it to become highly saturated and lose its strength. Un-retained or poorly excavations can experience soil instability, leading to slope failures, landslides, or soil slippage. This poses a risk to workers on-site and can result in damage to nearby structures or property.

3. Groundwater Inflow: During the monsoon season, the water table tends to rise, increasing the risk of groundwater inflow into the un-retained/ poorly retained excavation. This influx of water can further destabilize the soil, increase pore pressures, and potentially cause heave or collapse of the excavation walls.

4. Surface Runoff and Flooding: Un-retained or poorly retained excavations can contribute to increased surface runoff during heavy rainfall events. This can result in localized flooding and water accumulation around the excavation, posing safety hazards and making it difficult to carry out construction activities.

5. Contamination and Water Quality Issues: In areas where the red fat clay soil is contaminated, leaving the excavation unretained during the monsoon season can lead to the spread of contaminants through runoff. This can pose environmental risks and impact water quality in nearby water bodies or groundwater sources.