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Analytical Chem Soil HW Solutions 49

Analytical Chem Soil HW Solutions 49 - of the...

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49 Q4.2 (a) Describe with the aid of a diagram the important features of a conventional oedometer, and define the parameters that this apparatus is used to measure. (b) Data from an oedometer test on a sample of clay are given below. σ ' v , kPa 50 100 200 400 800 600 400 Equilibrium sample height h, mm 17.123 16.912 16.701 15.496 14.300 14.390 14.521 Cross-sectional area of sample = 80 000 mm 2 G s = 2.61 Two-way sample drainage Water content at start of test: 45.14% Water content at end of test: 32.84% Calculate the specific volume at the end of the test, assuming S r =1 at this stage. What was the saturation ratio at the start of the test? Show that the specific volume is related to the sample height by the expression v/h = A/v s = constant, where A is the cross sectional area of the sample and v s is the volume occupied by the soil grains. Plot a graph of the specific volume against the natural logarithm of the vertical effective stress. Explain the shape of this graph. Calculate the preconsolidation pressure and the slopes
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Unformatted text preview: of the one-dimensional normal compression line and unloading/reloading lines. [University of London 2nd year BEng (Civil Engineering) examination, King's College (part question)] Q4.2 Solution (a) A diagram of the oedometer is given in the main text Figure 4.2. The apparatus is used to measure i) the stiffness of the soil in one dimensional compression, E' , over a given stress range; ii) the coefficient of consolidation, c v = k v .E' / γ w iii) by inference, the vertical permeability k v . (b) Assuming that the sample is fully saturated at the end of the test, the specific volume at this stage is given by v f = (1 + e f ) = (1 + w f . G s ) = 1 + (0.3284 × 2.61) = 1.857 At the start of the test, the specific volume is equal to 1.857 (17.123 ÷ 14.521) = 2.190. The saturation ratio may be calculated using...
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