How Can Water Infiltration Change the Properties of Soil?

In this week’s episode of IAM News, the effects of extreme heat on roads and railways were explored. Such effects lead to moisture changes in soil, leading to large volume changes in certain soils and  desiccation cracks; these cracks then leave the soil vulnerable to water infiltration. But how can water infiltration change the properties of soil?

Soil particles are held together by various forces, including friction and cohesive forces. When water infiltrates the soil, it fills the void spaces between particles and can weaken these forces. Initially, capillary forces might enhance the stability of the soil particles, but as water content increases, the capillary forces dissipate. When the voids become saturated with water, the buoyancy of the solid particles reduces their effective weight and frictional strength.

The shear strength of soil is a critical parameter in geotechnical engineering, influencing slope stability and foundation design. Water infiltration can reduce the frictional forces between soil particles, leading to a decrease in shear strength. This is especially evident in cohesive soils like clays, where water can effectively lubricate the particles and weaken their bonds.

In some cases, water infiltration can cause soil to swell. Certain clay minerals have the ability to absorb water and expand, increasing the volume of the soil. On the other hand, sandy soils might undergo a reduction in volume due to the rearrangement of particles as water infiltrates. Both compaction and swelling can significantly impact the soil’s engineering properties, affecting factors like settlement, and bearing capacity.

Permeability refers to a soil’s ability to transmit water. Water infiltration can influence permeability by altering the arrangement of soil particles. In well graded soils, infiltration can help create better particle interlocking, reducing permeability. In poorly graded soil, water might create pathways for faster flow, increasing permeability.

Excessive water infiltration can lead to erosion, where water flow removes soil particles from one location and deposits them elsewhere. This can weaken slopes and undermine structures. Additionally, when soil becomes saturated with water, it loses its ability to bear additional loads, potentially leading to failures.

In geotechnical engineering, understanding how water infiltration impacts soil properties is essential for designing safe and stable structures. Engineers consider the type of soil, its composition, and the expected water conditions (rainfall, groundwater levels, etc.) to make informed decisions about construction techniques, foundation design, and slope stability analysis.