Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

@All.

When cohesive soils, such as clay or silty soils, become wetted, several things can happen due to the soil's unique properties.

Here's an overview of what typically occurs:

1. Increase in Moisture Content: The moisture content of the soil increases as water is absorbed by the soil particles. Cohesive soils have a high water retention capacity, so they can hold a significant amount of water.

2. Decrease in Shear Strength: The cohesion between soil particles, which provides strength, weakens when the soil becomes wet. As water fills the pores, it can reduce the friction between the particles, leading to a decrease in the soil's shear strength. This makes the soil more susceptible to slippage, sliding, or failure under load.

3. Expansion and Swelling: Some cohesive soils, particularly clays, can absorb water and expand. This is known as swelling. The degree of swelling depends on the type of clay and the amount of water it absorbs. This can cause ground heaving and changes in the volume of the soil, affecting structures built on or in the soil.

4. Compression and Consolidation: In certain situations, cohesive soils may undergo consolidation when wetted. This occurs when the weight of the water pushes the soil particles together, leading to a reduction in volume and potential settling. Over time, excess pore water pressure is dissipated, and the soil compresses.

5. Reduction in Permeability: Cohesive soils generally have low permeability, meaning water does not easily pass through them. When wetted, the pores may become filled with water, but the ability of the soil to drain or allow further water movement is limited.

6. Increase in Plasticity: Wetting can increase the plasticity of cohesive soils, meaning they become more moldable or workable. This can lead to the soil being more deformable when subjected to external forces, such as compaction or loading.

Overall, wetting cohesive soils can lead to significant changes in their behaviour, and these changes are important considerations in geotechnical engineering and construction projects.

So, the given answer is correct.

In the case of saturated dense sands if there is sudden application of stress in the field, the soil does not get time to expand and negative pore water pressures develop. This results in increased effective stresses and greater shear strength. In the case of loose sands, this is the reverse.

The loose sands try to compress by bringing their grains closer together. This results in reduced effective stress and a reduction in corresponding shear strength. If fine sands in the saturated condition are subjected to sudden loading, the tendency towards volume reduction causes pore water pressure to increase instantaneously. This causes a large decrease in the shear resistance, as the shear strength is given by;

(τ)f = σ'tanΦ' = (σ-u) tanΦ [when σ ~ u].

As shear strength = C + (σ)ntanθ.

On wetting c and (σ)n are modified and effective parameters are used, hence shear strength decreased.

As per my knowledge, on wetting cohesive soils Gain Shear Strength, so option B is correct.

Apparent cohesion of the soil increases with an increase in the moisture content.

So, Option B is right.

It is Only for cohesion soil.

Option B is right.

The study was conducted for low suction range, (i.e. 0"50 kPa). The soil at the drying had lower shear strength as compared to the soil at the wetting under the same matric suction. Furthermore, the study was extended to investigate the effects of suction and the hysteresis of SWCC on shear strength parameters such as effective friction angle and the apparent cohesion, c. Results exhibited no significant effects of suction and the hysteresis of SWCC on the effective friction angle. It was observed that the apparent cohesion at the wetting was higher than that was obtained at the drying under the same suction. The c increases as the suction increase with the decreasing rate at wetting.

Option B is to be right only.

Shear strength related with flow index. If water content increase then flow index will increase and. Shear strength will decrease.

Will you explain it clearly?