Question

In a one-dimensional consolidation test the time required for 50% consolidation has been measured as 154 seconds. The settlement of the sample at the end of the test was 2.5 mm.

a) Assume that Tv for 90% consolidation is equal to 0.848 and Tv for 50% consolidation is equal to 0.197. Also recall that Tv = (cv.t)/d2. Determine the time required to achieve 90% consolidation.

b) For the same experiment, assuming double drainage (i.e. open layer/permeable boundaries) and knowing that s'0 = 60 kPa, s'1 = 120 kPa, e0 = 0.65 and H0 = 20 mm determine the coefficient of permeability (k) in m/s.

Recall that S = mv.H0.Ds' and that k = cv.mv.gw

c) How long would it take to achieve 90% consolidation for the same soil on a layer with single drainage (i.e. closed layer) with a thickness of 10 m? Please provide your answer in years

d) What would you expect to happen to (i) the coefficient of volume compressibility mv, (ii) the permeability k, and (iii) the time to reach 90% consolidation t90 if it was decided to build (in the field) an embankment twice as heavy as initially expected? (i.e. consider that s'1 = 240 kPa). Calculations are not necessary to justify your answer. You must explain your answer in terms of physical phenomena (i.e. what the soil “feels”).

e) What are vertical drains? How can they be used in the field to accelerate consolidation time? Why do they work? Answer succinctly and use as many sketches as necessary to explain your answers

Answer 1