L04-effective_stress

L04-effective_stress - Soil Mechanics CIVL2410 1 4....

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Soil Mechanics CIVL2410 4. Effective Stress Contents 1. Saturated Soil ........................................................................................................................... 1 2. Calculation of Effective Stress .................................................................................................. 3 a) Calculation of Vertical (Total) Stress. ................................................................................... 3 b) Calculation of Pore Water Pressure. .................................................................................... 4 c) Example:. .............................................................................................................................. 5 3. Effective Stress under general conditions ................................................................................ 7 4. Example – Effects of groundwater level changes .................................................................... 7 1. Saturated Soil A saturated soil is a two phase material consisting of a soil skeleton and voids which are saturated with water. It is reasonable to expect that the behaviour of an element of such a material will be influenced not only by the forces applied to its surface but also by the water pressure of the fluid in the pores. Suppose that a soil sample having a uniform cross sectional area A is subjected to an applied load W, as shown in Fig la, then it is found that the soil will deform. If however, the sample is loaded by increasing the height of water in the containing vessel, as shown in Fig lb, then no deformation occurs. Figure 1: Loading on soil. W W Fig(1a) Soil loaded by an applied weight W Fig(1b) Soil loaded by water weighing W Soil Soil In examining the reasons for this observed behaviour it is helpful to use the following quantities: 1
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Soil Mechanics CIVL2410 σ v Vertical Stress Vertical Force Cross Sectional Area = = (1) and to define an additional quantity the vertical effective stress, by the relation w v v u - = (2) Let us examine the changes the vertical stress, pore water pressure and vertical effective stress for the two load cases considered above.
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L04-effective_stress - Soil Mechanics CIVL2410 1 4....

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