Mechanical properties of soil
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Mechanical properties of soil

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Mechanical properties of soil- Distribution of vertical and horizontal stresses in the soil.


The mechanical properties of soil are concerned with the identification and determination of its behavior under the influence of loads in terms of the extent of its resistance, its bearing, the amount of its subsidence, the degree of compaction and its various formations.

Mechanical properties include the following:

  • Distribution of vertical and horizontal stresses in the soil
  • Settlement of the soil
  • Compaction the soil
  • Shear resistance to the soil
  • Soil bearing capacity
  • Effective lateral pressure of soil
  • Slop stability of soil
  • The movement of water in the soil under the water compressor
  • Swelling pressure of the soil

In this article we will take distribution of vertical and horizontal stress in the soil and in next articles we will complete all other mechanical properties.

- Distribution of vertical and horizontal stresses in the soil


When a soil is exposed to vertical loads transported through the foundation, the soil in this case is subjected to vertical stresses below the foundation that are quickly affected by the soil grains below and on the sides of the foundation where that these stresses spread in the soil from its maximum value directly below the foundation and gradually decrease with increase in the depth from the bottom of the foundation. And, with the increase of the dimension and lateral distance from the foundation. 

The below figure shows how the vertical stresses transmitted from the foundation of the building footing are square in shape through lines equal to the vertical stresses in the soil.




Where it is noted that the vertical stresses decrease to reach about less than 20% of its value at a depth approximately equal to the width of the footing.

Based on the above, it becomes clear that the stresses on the soil not only affect the soil directly below the foundation, but affect the soil layers in the area adjacent to the foundation or the building, but to a limited degree depends on the distance of the adjacent layer in relation to this foundation. 

It must be noted that when embarking on the establishment of a specific building The study of soil properties should not be limited to the apparent layer at the depth of foundation only, but this study must be extended to include the substrate layers of the soil below the foundation due to the possibility of the presence of weak lower layers that may be compressed to a high degree despite their exposure to relatively weak stresses compared to those below the foundation and at the level Incorporation is something that which lead to falling foundations at high values and varying from each other which lead to damage to the building as a whole.

How to calculate the stress applied to the soil under the foundations.

Calculation of the vertical stress applied to the soil under foundation by approximately manner with an slope of 1 horizontal : 2 vertical and accordingly, the average vertical stress on weak soils ( at the midpoint of its height) and under foundation is as follows:

The stress on the soil directly below the foundation = loads/ foundation area.

The stress on the weak soil = the load at this level / the area exposed to the load.









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