How Loads and Forces Act on Retaining Wall and Related Calculations
There are numerous kinds of loads and forces that acting on retaining wall. They are as follows: 1. Lateral earth pressure, 2. Surcharge loads, 3. Axial loads, 4. Wind on projecting stem, 5. Impact forces, 6. Seismic earth pressure, 7. Seismic wall self-weight forces.
1. Lateral Earth Pressure Acting on Retaining Wall: The key reason that lies behind the retaining wall construction is to preserve soil as soil lateral earth pressure is the chief concern in the design. The theory that is mostly used to compute lateral earth pressure is sliding soil wedge theory.
The wedge theory implies that a triangular wedge of soil would slide down if retaining wall was removed all on a sudden and the wall has to protract this wedge soil. The figure below shows free body lateral forces acting on retaining walls.
The Coulomb process of Lateral Earth Pressure Calculation: This equation acquires backfill slope, friction angle at wall face, rupture plan angle, and internal friction angle into contemplation:
Where the following signs stand for:
Ka: Coefficient of active pressure
: Angle of internal friction
: Angle of backfill slope
: Angle of friction between soil and wall (2?3 to 1?2 is assumed)
: Slope angle of the wall which is measured from horizontal (equal to 90 degree for vertical wall)
Besides, in the case of flat level backfill soil, assuming zero friction at soil-wall interface, and soil-sidewall is vertical, the coulomb equation is diminished as follows:
The Rankine procedure of Lateral Earth Pressure Calculation
William Rankine is the developer of coulomb formula. He extended and modified this equation.
Where : : Backfill slope angle : Internal friction angle of soil.
Rankine equation is reorganized when backfill is level as:
2. How Surcharge loads Acts on Retaining Wall: Surcharge loads performing on retaining wall are supplementary vertical loads that used to the backfill soil above the top of the wall. Either dead loads or live loads as an instance could outcome from highway or parking lot, paving or adjacent footing.
Live load surcharge is taken into account when vehicular actions act on the facade of backfill soil at a distance which equal or less than the wall height from the wall back face. Active pressure from uniform surcharge is elucidated in the figure below.
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