Analytical Chem Soil HW Solutions 44

Analytical Chem Soil HW Solutions 44 - Westfield College...

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44 Q3.11 Figure 3.45 shows a true cross-section through a sheet-piled excavation in a laminated soil of permeability k v = 10 -6 m/s (vertically) and k h = 1.6 × 10 -5 m/s (horizontally). The laminated soil is overlain by 4 m of highly permeable gravels, and the natural groundwater level is 2 m below the soil surface. By means of a flownet sketched on a suitably-modified cross-section estimate: (a) the minimum capacity required of the dewatering system, and (b) the pore water pressure at the point A. Comment briefly on the stability of the base of the excavation. (Transformation factor α = k v /k h ) [University of London 2nd year BEng (Civil Engineering) examination, Queen Mary and
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Unformatted text preview: Westfield College] Q3.11 Solution The flownet must be sketched on a transformed section, with the horizontal distances reduced by a transformation factor α = √ (k v /k h ) to account for the relatively higher horizontal permeability (see main text Section 3.14). = (k v /k h ) = (10-6 ÷ 1.6 × 10-5 ) = (1/16) = 0.25 The cross section is re-drawn with the horizontal dimensions reduced by the transformation factor 0.25, and the flownet is sketched according to the rules and procedures set out in main text Sections 3.8 and 3.9, in Figure Q3.11. Figure Q3.11...
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