Question

1. The following table contains the results of an oedometer test on a sample of Boston Blue Clay. Initial conditions were: void ratio e.-0.925, natural water content wa-32.8%, initial seating load o,,-15 kPa, specific gravity of the solids G 2.78. o,' (kPa) 25 50 100 200 300 400 600 o,' (kPa) 800 400 200 100 200 400 800 o,' (kPa) 1200 1600 800 400 200 100 0.916 0.905 0.890 0.870 0.847 0.826 0.790 0.757 0.769 0.783 0.800 0.790 0.775 01743 0.696 0.655 0.666 0.681 0.701 0.723 0.768 The data are available separately in a text file "smassn11_Q1_data.txt" (which includes the seating load σ,' and es). Plot the e-log σ' data (using semilog graph paper or a spreadsheet) and: (a) estimate the maximum past pressure on' using Casagrande's method (b) estimate the lab Ce and CR (c) estimate the insitu C (extend the virgin compression line to 0.42eo etc) (d) compute the compression & recompression ratios CR and RR (e) estimate the axial strain (%) due to loading from σ,'-150 to 650 kPa

Answer 1

Draw the graph between e-log o' as follows: Void ratio (e) 100 1000 10000 Effective pressure (o')

joid ratio e Void ratio (e) 10 100 430 kPa 1000 430 kPa 10000 Effective pressure (kPa)(o') Consider the calculation procedure for maximum past pressure as follows: • Locate the maximum curvature point O by observation. • Draw a horizontal line ox. Draw a tangent oy at point o. • Bisect the angle made by the lines ox and oy, which is oz. Extend the straight-line portion (shown red in color) to intersect the bisector oz and project the intersection point on to x-axis which gives the value of maximum past pressure. Therefore, the value of maximum past pressure is 430 kPa.

(b) Calculate the value of C, from the graph as follows: Void ratio (e) 10 10000 100 1000 Effective pressure

0.696 -0.655 (1600 log 1200 = 0.328 Cc = 0.33 Calculate the value of Cg from the graph as follows: 0.783-0.769 ( 400 log 200 = 0.0465 Ce = 0.0465

(c) Extend the virgin compression line to 0.42e, as follows: Calculate the value of 0.42e. 0.42e, = 0.42 x0.925 = 0.3885 Void ratio (e) 0.42e, 10 1000 10000 100 Effective pressure

Calculate the value of C. when the virgin compression line extends upto 0.42e. 10% 01 0.4-0.5 4000 log7700 = 0.351 CCO = 0.351 (d) Calculate the compression ratio by using the following relation. CR= Cc 1teo 0.33 1+0.925 CR = 0.171 Calculate the recompression ratio by using the following relation: RR= Ce teo 0.0465 1+0.925 RR = 0.0241