G1-Lecture29-Plastic-Settlement

G1-Lecture29-Plastic-Settlement - CEG CEG-4011 Geotechnical...

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Unformatted text preview: CEG CEG-4011 Geotechnical Engineering I 4011 Geotechnical Engineering I Lecture Lecture 29 29 Plastic Settlement (Consolidation) L. Prieto-Portar 2010 Loads placed on saturated fine-grained soils may come from (a) added soil deposits, or (b) from man- made structures. Both produce settlement of the ground surface due to the squeezing out of the water and air volumes (much like pressure on a water-soaked sponge). The behavior of the soils under these loads is modeled by the Theory Plastic Compressibility of Soils (Consolidation). This theory assumes a one-dimensional (vertical) compression over a large area squeezing out of water and air from the voids. This type of settlement is typical for clays, and characteristically is very slow. Consolidation is time dependent and may take place over years or decades. e The mechanical behavior of soils can be elastic or viscoelastic (non-conservative). The elastic behavior can be either linear or non-linear. Figure 2. Elastic - plastic behavior V isco-elastic behavior is when stress is time-dependent on strain and non-conservative behavior is where soils have strain memory (permanent deformation after unloading). For example, although stress at point A may be construed to be due to the overburden of h above it, the soil recalls the stress induced by a higher h , now eroded away. h A Past surcharge from a now eroded soil Present ground surface Pressure at A > h Soil particle at A recalls past condition of surcharge. Figure 3. Visco-elastic behavior The clay stratum is sandwiched between two strata of sand, which permits the excess pore water pressure to escape either to the top layer or the bottom layer of sand. As the water escapes, the volume previously occupied by the water is lost, and the clay stratum is reduced in thickness. This reduction is what is called settlement . 1 2 3 4 5 6 7 8 9 10 11 P 1 2 3 4 5 6 7 8 9 10 11 P+ P (b) (a) t=t u = u + u u=u Drain holes h o e h 1 2 3 4 5 6 7 8 9 10 11...
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This note was uploaded on 09/11/2011 for the course CEG 4011 taught by Professor Staff during the Summer '10 term at FIU.

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G1-Lecture29-Plastic-Settlement - CEG CEG-4011 Geotechnical...

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