EXPERIMENT 8 , Test Name: CONSOLIDATION TEST , soil and foundation
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Purpose
This test is performed to determine the magnitude and rate of volume decrease that a laterally confined soil specimen undergoes when subjected to different vertical pressures.
From the measured data, the consolidation curve (pressure-void ratio relationship) can be plotted.
This data is useful in determining the compression index, the recompression index and the preconsolidation pressure (or maximum past pressure) of the soil.
In addition, the data obtained can also be used to determine the coefficient of consolidation and the coefficient of secondary compression of the soil.
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Equipment
1. Consolidation device (including ring, porous stones, water reservoir, and load plate),
2. Dial gauge
3. Sample trimming device,
4. Metal straight edge,
5. Clock,
6. Moisture can,
7. Filter paper.
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Test Procedure
1. Weigh the empty consolidation ring.
2. Measure the height (h) of the ring and it’s inside diameter (d).
3. Extrude the soil sample from the sampler, generally thin-walled Shelby tube. Determine the initial moisture content and the specific gravity of the soil.
4. Carefully trim a sample to fit the consolidation ring and weight the sample plus the ring.
5. Carefully place the soil sample in the consolidometer with a saturated porous stone after filter paper on each face. Be sure the porous stones will enter the ring so that the test can proceed satisfactorily.
6. Being careful to prevent movement of the ring and porous stones, place load plates centrally on the upper porous stone adjust the loading device.
7. Adjust the dail gauge to a zero reading.
EXPERIMENT 8 , Test Name: CONSOLIDATION TEST
8. Soaking the soil sample in consolidometer with water.
9. At a convenient starting time, apply the first load increment and simultaneously take deformation reading at elapsed times of 0.25, 0.5, 1, 2, 4, 8, 15, 30, 60, 120, min, then 4, 8, 16 hr,……….24 hr Of elapsed time and until there is little change (plot DR vs. log t) or (plot DR vs. t) in the curve.
10.After 24 hr. or as directed or when the between two reading is sufficiently small, change the load to the next value and again take elapsed time interval reading as in step 9, above.
11.Continue changing loads and taking elapsed time vs. deformation dial reading through the load range of consolidation.
12.Place the sample in the oven at the end of the test to find the weight of soil solids (Ws) and to enable a computation of the final volume of water (Vw), compare (Ws) with the compute value from step 3.
13. Plot curve of dial reading vs. log time. Find Dْ , D100, D50, and the corresponding t50 for each load increment and find (Cv).
EXPERIMENT 8 , Test Name: CONSOLIDATION TEST
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14. Or plot dail. reading vs. find , D100, D50, and the corresponding t50. Calculated Cv or find t90 and calculated Cv from:
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A) To obtain t50 from DR. vs. log time curve
1. At first obtain D100 by draw tangents to the middle and end parts of the curve. At the intersection of the tangents, project horizontally to the curve ordinate to read D100. to obtain t100 project vertically from the tangent intersection of the curve, drawn to the abscissa for the time value.
2. To obtain (the theoretical dial reading at t =0 since one cannot plot the logarithm of time for t = 0) on the semilogarithmic plot, if the early part of the curve is parabolic, select a time t1 and atime t2=4t1
EXPERIMENT 8 , Test Name: CONSOLIDATION TEST
Measure the ordinate (y) from t1 and t2 on the curveand lay this same value of y off vertically above t1. Draw a horizontal line through this point and call the intercept of this line on the DR. ordinate Do with Do and D100 established one may obtain the dial reading corresponding to 50% consolidation D50 as:
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B)To obtain t90 from D.R. vs
1. To make a plot of dial reading vs . obtain the time corresponding to given dial reading ie. If t =25 min,
which is then plotted against the dial reading for 25 min. to find Do Taylor recommended draw a straight line through the first several (say 6 to 8) plotted point and extending this line until in intersects the ordinate. This intersection of the ordinate establishes Do
2. Next, take an abscissa value 15% greater than the value obtained by the intersection of the straight line plot of D.R. vs and time axis, and from draw straight line through this points.
Continue plotting values of DR vs and draw a smooth curve using a French curve for the curved part of the plot.
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Where the plotted curve crosses the line B (1.15 offset line), the ordinate value is arbitrarily taken as D90, we can now compute D100 as:
