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Stress Calculation in Soil - Stress in Soil, Soil Mechanics | Soil Mechanics Notes- Agricultural Engineering PDF Download

Stress calculation in Soil

The following example shows the stress calculation at different level within the soil.

Problem 1: Calculate total, effective stress and pore water pressure at different level of the soil as shown in Figure 5.2.

Stress Calculation in Soil - Stress in Soil, Soil Mechanics | Soil Mechanics Notes- Agricultural Engineering


Fig. 5.2. (a) Soil profile (b) Stress diagrams


 Solution:

The bulk unit weight of the partially saturated sand

\[{\gamma _{t(sand)}}={{{G_s} + Se} \over {1 + e}}{\gamma _w}={{2.6 + 0.5 \times 0.65} \over {1 + 0.65}} \times 10=17.72\;kN/{m^3}\]


The unit weight of the water is taken as 10 kN/m3. The saturated unit weight of sand is

\[{\gamma _{sat(sand)}}={{{G_s} + e} \over {1 + e}}{\gamma _w}={{2.6 + 0.65} \over {1 + 0.65}} \times 10=19.7\;kN/{m^3}\]

The saturated unit weight of the clay-I is.

\[{\gamma _{sat(clay - I)}}={{{G_s} + e} \over {1 + e}}{\gamma _w}={{{G_s} + {G_s}w} \over {1 + {G_s}w}}{\gamma _w}={{2.65 + 2.65 \times 0.55} \over {1 + 2.65 \times 0.55}} \times 10=16.71\;kN/{m^3}\]

[Se = Gsw and for fully saturated soil S =1]

The saturated unit weight of the clay-II is

\[{\gamma _{sat(clay - II)}}={{{G_s} + e} \over {1 + e}}{\gamma _w}={{{G_s} + {G_s}w} \over {1 + {G_s}w}}{\gamma _w}={{2.7 + 2.7 \times 0.6} \over {1 + 2.7 \times 0.6}} \times 10=16.49\;kN/{m^3}\]

At elevation -2.5 m

Total stress (σ) = 17.72 ´ 2.5 = 44.3 kN/m2

Pore water pressure (u) = 0

Effective stress () = 44.3 - 0 = 44.3 kN/m2

At elevation -6 m

Total stress (σ) = 17.72 ´ 2.5 + 19.7 ´ 3.5 = 113.25 kN/m2

Pore water pressure (u) = 10 ´ 3.5 = 35 kN/m2

Effective stress ( \[\sigma '\] ) = 113.25 - 35 = 78.25 kN/m2

At elevation -10 m

Total stress (σ) = 17.72 ´ 2.5 + 19.7 ´ 3.5 + 16.71 ´ 4 = 180.1 kN/m2

Pore water pressure (u) = 10 ´ 7.5 = 75 kN/m2

Effective stress ( \[\sigma '\] ) = 180.1 - 75 = 105.1 kN/m2

At elevation -14 m

Total stress (σ) = 17.72 ´ 2.5 + 19.7 ´ 3.5 + 16.71 ´ 4 + 16.49 ´ 4 = 246.1 kN/m2

Pore water pressure (u) = 10 ´ 11.5 = 115 kN/m2

Effective stress ( \[\sigma '\] ) = 246.1 - 115 = 131.1 kN/m2

The document Stress Calculation in Soil - Stress in Soil, Soil Mechanics | Soil Mechanics Notes- Agricultural Engineering is a part of the Agricultural Engineering Course Soil Mechanics Notes- Agricultural Engineering.
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FAQs on Stress Calculation in Soil - Stress in Soil, Soil Mechanics - Soil Mechanics Notes- Agricultural Engineering

1. What is stress calculation in soil?
Ans. Stress calculation in soil refers to the process of determining the distribution and magnitude of stresses within the soil mass. It involves analyzing the forces acting on the soil particles and quantifying the resulting stresses. This calculation is essential in understanding the behavior of soil under different loading conditions.
2. How is stress in soil measured?
Ans. Stress in soil is measured using various instruments such as stress cells or pressure transducers. These devices are placed within the soil at different depths to directly measure the stress or pressure exerted by the soil. Additionally, stress can also be indirectly calculated using formulas and principles of soil mechanics, considering factors such as the weight of the soil, applied loads, and soil properties.
3. What factors affect stress distribution in soil?
Ans. Several factors influence stress distribution in soil, including the magnitude and distribution of applied loads, soil properties (such as density, moisture content, and shear strength), and the presence of any external constraints or boundaries. Additionally, the type of soil and its behavior under loading also play a significant role in determining stress distribution.
4. Why is stress calculation important in agricultural engineering?
Ans. Stress calculation in soil is crucial in agricultural engineering as it helps in understanding the behavior of soil under different agricultural practices. By accurately calculating stresses, engineers can design efficient irrigation systems, determine suitable foundation designs for agricultural structures, and assess the stability of slopes or embankments in agricultural fields. This knowledge allows for the optimization of agricultural processes and the prevention of soil-related problems.
5. How does stress calculation help in soil mechanics?
Ans. Stress calculation is fundamental in soil mechanics as it aids in predicting the behavior of soil under different loading conditions. By quantifying stresses, engineers and researchers can assess the deformation characteristics of soil, determine its shear strength, and evaluate the stability of structures built on or within the soil. This information is vital for designing safe and sustainable foundations, retaining structures, and geotechnical engineering projects.
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