Question 2 (a) Define overconsolidation ratio (OCR) of soils and give two possible reasons for soils at a project site (

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Question 2 A Define Overconsolidation Ratio Ocr Of Soils And Give Two Possible Reasons For Soils At A Project Site 1 (108.91 KiB) Viewed 39 times

Question 2 (a) Define overconsolidation ratio (OCR) of soils and give two possible reasons for soils at a project site (not in the laboratory) to be overconsolidated. (3 marks) (b) An oedometer test was performed on a specimen of saturated clay, and the following results were obtained at different applied pressure: Pressure (kPa) 0 100 200 400 800 1600 800 Dial gauge reading after 24 hour (mm) 0 0.480 0.639 1.534 2.430 3.325 3.166 The initial thickness of the sample was 19 mm. At the end of the test, the mass of the wet soil and dry soil were 90.20 g and 72.57 g, respectively. Without considering correction of laboratory consolidation curve to in situ curve, determine the following quantities: (i) Prove that the specific gravity, Gs, can be estimated by the following relationship: Gs = Psat/Pw 1+w-w(Psat/Pw) where w=water content, Psat saturated density of soil and pw density of water. Determine G, if the diameter of the specimen was 60 mm. (4 marks) (ii) The initial void ratio (eo). (3 marks) (iii) The coefficient of volume compressibility, m,, at stress increments of 100-200 kPa and 800-1600 kPa. (2 marks) (iv) The compression index, Ce, and expansion index, Ce, if preconsolidation pressure is found to be 210 kPa. (4 marks) (v) The coefficient of consolidation, c, (in m²/year), if too was found to be 31 min during the increment of 0-100 kPa. (3 marks) (c) Explain the rationale of the root time method in determining too, by considering the approximate relationship between time factor, T,, and degree of consolidation, U: TC U < 0.6 ={-0.933 10 AUZ (-0.933 log(1-U)-0.085 U> 0.6 (6 marks) Tv =