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Stress in soil due to surface load. Dr. Suhad Dawood Salman Mechanical Engineering Department Faculty of Engineering, Mustansiriyah University, Baghdad, Iraq.
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Stress in soil due to surface load Dr. Suhad Dawood Salman Mechanical Engineering Department Faculty of Engineering, Mustansiriyah University, Baghdad, Iraq
The vertical stress on element A can be determined simply from the mass of the overlying material. If represents the unit weight of the soil, the vertical stress is
Stresses in a Layered Deposit The stresses in a deposit consisting of layers of soil having different densities may be determined as: Vertical stress at depth z1
Vertical stress at depth z2 Vertical stress at depth z3
Vertical Stresses Vertical stresses due to self weight increase with depth, there are 3 types of geostatic stresses: a. Total Stress, σ total b. Effective Stress, σ' c. Pore Water Pressure, u
Total vertical stress Consider a soil mass having a horizontal surface and with the water table at surface level. The total vertical stress at depth z is equal to the weight of all material (solids + water) per unit area above that depth ,i.e Pore water pressure
If the pores of a soil mass are filled with water and if a pressure induced into the pore water, tries to separate the grains, this pressure is termed as pore water pressure. The pore water pressure at any depth will be hydrostatic since the void space between the solid particles is continuous, therefore at depth z: Effective vertical stress due to self weight of soil The pressure transmitted through grain to grain at the contact points through a soil mass is termed as effective pressure.
Stress due to surface load To analyze problems such as compressibility of soils, bearing capacity of foundations, stability of embankments, and lateral pressure on earth retaining structures, we need to know the nature of the distribution of stress along a given cross section of the soil profile. When a load is applied to the soil surface, it increases the vertical stresses within the soil mass. The increased stresses are greatest directly under the loaded area, but extend indefinitely in all directions.
