# Effective stress

Effective stress is a force that keeps a collection of particles rigid. Usually this applies to san soil, or gravel. If you pinch a stack of coins between your fingers, the stack stays together.

If you then loosen the pressure between your fingers, the coin stack falls apart. Similarly, a pile of sand keeps from spreading out like a liquid . Ground movements and instabilities can be caused by changes in total stress (such as loading due to foundations or unloading due to excavations), but they . University of Anbar College of Engineering Civil Engineering Department Iraq- Ramadi Asst. Under hydrostatic conditions, no water flow takes place, and the pore pressure at a given point is given by u = gw. It is convenient to think of pore water pressure as the pressure exerted by a column of water in an imaginary standpipe inserted at the given point. Pore Pressure within the Earth). During the previous lectures crack propagation was discussed in terms of stress risers.

The example of a stress riser was the point-to- point contact between grains. To have a good understanding of what are the stresses in a soil, imagine you are standing in your favourite swimming pool which, at first, is empty (Fig. 1a).

Try to memorize the level of the stresses (pressure) you feel under your feet. Stresses in a Saturated Soil. Volume (V) = Area (A) x height (h);. When water is present the effective vertical stress is less due to buoyancy. The effective vertical stress at the bottom . For the range of stresses usually encountered in practice the individual solid particles and water can be considered incompressible: air, on the other han is highly compressible.

In soil mechanics usually effective stress rather than the total stress is used in constitutive relationships. For saturated soils, effective hydrostatic pressure, p eff, is defined as the difference between the total hydrostatic stress, p t, minus the pore-water pressure, u w (i.e., p = p eff = p t − u w). For unsaturated soils the effective . This paper examines the effective stress in indurated clay rock theoretically and experimentally. A stress concept is derived from the analysis of the microstructure and of the pore water in the highly-indurated Callovo-Oxfordian and Opalinus clay rocks, and subsequently validated by various experiments performed on these . When a building is constructe its weight is transmitted to the ground through its foundation, thus inducing stresses in the underlying strata.

These induced stresses might cause problems such as excessive settlement or shear failure and thus are important to geotechnical engineers. Standards and Analysis Methods. Increment of Earth Pressure due to Surcharge. Using the Search Function. Many different expressions have been proposed for the effective stress principle for porous media, but none has clearly been acknowledged as being the correct one.

It should be possible to determine the correct expression, because this is fundamental principle of mechanics. Following review of the . The total stress, a acts on the entire area under consideration, namely, A (Fig. ) and the pore water pressure or the neutral stress on that area, Aw where pore water is in contact with this total area, that is, the total area, A minus the grain . In geomechanics, the Finite Element Method (FEM) is widely used for analyzing both ultimate (ULS) and serviceability limit states (SLS). Finite element modelling of a geotechnical problem at hand can offer insight into how the stresses and strains distribute . The concept of effective stress and the effective stress equation is fundamental for establishing the theory of strength and the relationship of stress and strain in soil mechanics and poromechanics. However, up till now, the physical meaning of effective stress has not been explained clearly, and the theoretical basis of the.

Equation () is referred to as the effective stress equation, and is a definition of the stress state variable for saturated soils. Evidence has shown that only a single- valued effective stress or one stress .