Mekanika Tanah : Tegangan Efektif Tanah part1 - Hinawan T. Santoso, ST, MT

Summary

This educational script explains the concept of effective stress in soils, a crucial aspect of soil mechanics. It delves into how soil behavior changes under load, focusing on the role of water in bearing the initial load due to its incompressible nature. Over time, as water pressure decreases, the load shifts to the soil particles, creating effective stress. The script covers important terms like total stress, effective stress, and pore water pressure, providing a practical understanding through examples and formulas, with a strong emphasis on their application in construction and geotechnical engineering.

Takeaways

• 😀 Effective stress is a critical concept in soil mechanics, representing the portion of stress transmitted through soil particles after pore water pressure dissipates.
• 😀 Total stress in soil includes both the effective stress and the pore water pressure acting on the soil.
• 😀 Soil consists of three main components: solid particles (grains), water, and air, which occupy the voids between the particles.
• 😀 When soil is subjected to a load, pore water pressure is initially generated due to the incompressible nature of water in the soil.
• 😀 The total stress in soil is the combined effect of the stress from soil particles and the pressure exerted by the water in the voids.
• 😀 Pore water pressure first absorbs the load in saturated soils, but this pressure dissipates over time, transferring the load to the soil particles.
• 😀 Effective stress can be calculated using the formula: Effective Stress = Total Stress - Pore Water Pressure.
• 😀 In real-life applications, buoyant forces reduce the apparent weight of the soil when it is submerged in water, due to the contribution of pore water pressure.
• 😀 The weight of the soil in water can be used to calculate the pressure acting on the soil using the unit weight of the soil and water.
• 😀 The effective unit weight of the soil is calculated as the difference between the saturated unit weight of the soil and the unit weight of water, denoted as γ_effective = γ_saturated - γ_water.

Q & A

What is effective stress in soil mechanics?

Effective stress refers to the stress carried by the soil particles in a saturated soil mass. It is the difference between the total stress applied to the soil and the pore water pressure within the soil.

What factors influence the effective stress in soil?

Effective stress in soil is influenced by total stress, pore water pressure, and the interaction between soil particles, which changes when the soil is saturated with water or exposed to external loads.

How is total stress in soil calculated?

Total stress in soil is calculated as the total load or weight applied to the soil divided by the area over which the load is applied. The formula is Sigma = P / Aa, where P is the applied load and Aa is the cross-sectional area.

What is pore water pressure, and how does it relate to effective stress?

Pore water pressure is the pressure exerted by water within the soil pores. It reduces the effective stress because part of the load is supported by the water in the soil, not just the soil particles.

Why does water in the soil initially absorb most of the applied load?

Water is incompressible, meaning that it cannot shrink when a load is applied. Therefore, when a soil sample is loaded, the water pressure (pore pressure) first absorbs the load before the load is transferred to the soil particles.

How is effective stress distributed in soil?

Effective stress is distributed among the soil particles at contact points, where the load is transferred from the pore water to the solid soil particles after the pore water pressure dissipates.

What happens to the pore water pressure when the water in the soil flows out?

When the pore water pressure is relieved (i.e., the water in the soil escapes), the load that was initially absorbed by the water is gradually transferred to the soil particles, increasing the effective stress on the soil.

How is the effective stress in soil related to total stress and pore water pressure?

Effective stress is the difference between total stress and pore water pressure. The formula is Sigma effective = Sigma total - Pore water pressure.

What does the term 'Gamma effective' represent?

'Gamma effective' represents the effective unit weight of the soil, which is the difference between the saturated unit weight (Gamma saturated) and the unit weight of water (Gamma water). It is used to calculate effective stress in soils.

Why is understanding effective stress important in soil mechanics?

Understanding effective stress is crucial because it helps in predicting soil behavior under different loading conditions, particularly in geotechnical engineering, where soil stability and strength are influenced by the distribution of effective stress.