Earth pressure at rest

Earth pressure at rest rest is the horizontal pressure acting on the rigid structure. It is usually assumed in cases, when it is necessary to minimize the lateral and horizontal deformation of the sheeted soil (e.g. when laterally supporting a structure in the  excavation pit up to depth below the current foundation or in general when casing soil with structures sensitive to non-uniform settlement), or when structures loaded by earth pressures are due to some technological reasons extremely rigid and do not allow for deformation in the direction of loading necessary to mobilize the active earth pressure.

Earth pressure at rest is given by:

For cohesive soils the Terzaghi formula for computing K_r is implemented in the program:

where:

ν

-

Poisson ratio

For cohesionless soils the Jáky expression is used:

where:

φ

-

angle of internal friction of soil

When computing the pressure at rest for cohesive soils σ_r  using the Jáky formula for the determination of coefficient of earth pressure at rest K_r, it is recommended to use the alternate angle of internal friction φ_n.

The way of computing the earth pressure at rest can be therefore influenced by the selection of the type of soil (cohesive, cohesionless) when inputting its parameters. Even typically cohesionless soil (sand, gravel) must be introduced as cohesive if we wish to compute the pressure at rest with the help of the Poisson ratio and vice versa.

For overconsolidated soils the expression proposed by Schmertmann to compute the coefficient of earth pressure at rest K_r is used: 

where:	Kr	-	coefficient of earth pressure at rest
	OCR	-	overconsolidation ratio

The value of the coefficient of earth pressure at rest can be inputted also directly.

Influence of the inclined ground surface at the back of structure on earth pressure at rest is described here.

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Literature:

Arnold Verruijt: Soil mechanics, Delft University of Technology, 2001, 2006, http://geo.verruijt.net/