3. 1. INTRODUCTION
o Consolidation is a process of time-dependent
settlement of saturated clayey soil when
subjected to increased loading.
4. 2. SIGNIFANCE
o To determine the following :
1. Void ratio-pressure curve [e-σ(log scale)].
2. Pre consolidation pressure.
3. Coefficient of consolidation (Cv with logarithm of time method
Square root of time method )
5. 3. SPECIMEN AND TOOLS
o Undisturbed cohesive soil in a sampling tube.
o One dimensional consolidation device – consolidation ring, loading
unit, weights
o Porous stones and filter paper
o Wire saw
o Balance
o Water content cans
o Stopwatch
8. 4. TEST PROCEDURE
Measure the inner diameter and height of a clean dry consolidation ring and weigh it.
2. Eject the specimen from the sampling tube and trim it to fit exactly into the inside dimension
of the consolidation ring. Weigh the specimen in the ring. Take a small quantity of remaining
soil in a can for an auxiliary initial water content determination.
3. Place the ring with the specimen in the consolidation device.
4. Put the loading plate and loading piston in position.
5. Make the loading arm in balance by adjusting the counter weight of the arm.
6. Set the vertical dial gage at zero and be ready for loading.
7. Carefully put the initial load at the zero time and record the vertical dial gage at the time
intervals of 0.1, 0.25, 0.5, 1, 2, 4, 8, 15, 30 min., and 1, 2, 4, 8, 24 hours.
9. 4. TEST PROCEDURE
8. At the end of approximately 24 hours, read the final dial gage reading for that load
application, and increase the load to the next level at the new zero time. Record the vertical dial
gage at the same (similar) time intervals.
9. Usually before the second load application, or sometimes during the middle of the first load
application, the water is poured into the device to fill above the top of the ring and it is kept at
that level until the end of the test.
10. Repeat Step 8 until the maximum pressure is attained. A typical sequence of consolidation
pressure is 0.25, 0.5, 1, 2, 4, 8, (16) kgf/cm2
(24, 48, 98, 196, 391, 792, (1584) kPa).
11. After the final reading is completed under the maximum load, the specimen is reloading. The
load is reduced with several steps (typically 4, 1, 0.25 kgf/cm2
). During each unloading step, the
initial dial gage (just before the unloading) and the final reading (typically after one to two hours
after the unloading) are needed to measure the rebounds. Therefore, this entire unloading process
usually takes one day.
12. At the end of the unloading process, remove the specimen in the ring and weigh it. The
specimen in the ring is then placed in the oven for water content determination.
13. Thoroughly clean the tools and the testing area.
(3.48, 6.96, 14.21, 28.42, 56.69, 114.84, 229.68 psi)
(56.69, 14.21, 3.48 psi)
11. 5. REPORT
1. Test procedures
2. Computation of consolidation data
3. Plot of log (t) vs. δ curve for t50 and Cv determination by log t method
4. Plot of root (t) vs. δ curve for t90 and Cv determination by root t method
5. Comparison of Cv (coefficient of consolidation) values by the 2 methods.
6. Plot of e-log σ curve
7. Determination of pre consolidation pressure Pc by Casagrande method
8. Determination of compression index Cc
9. Conclusion
14. 7. RESULTS
How to determine t50 using the log t method ( P = 0.4276kN)
15. 7. RESULTS
How to determine t50 using the log t method ( P = 0.4276kN)
16. 7. RESULTS
How to determine t50 using the log t method ( P = 0.4276kN)
1. Extend the straight line portion of primary and secondary consolidations to intersect at Point A. Point A
represents d100 (Deformation at 100% primary consolidation).
2. The initial curved portion of the deformation plot versus log t is approximated to be a parabola on a natural
scale. Select times t1 and t2 on the curved portion such that t2 = 4t1. Let the difference of the specimen
deformation between (t2 –t1) be equal to x.
3. Draw a line horizontal to DE such that the vertical distance BD is equal to x. The deformation corresponding
to the line DE is do (Deformation at 0% primary consolidation)
4.The ordinate of Point F on the consolidation curve represents the deformation at 50% primary consolidation
(d50).
5. Find t50
17. 7. RESULTS
How to determine t90 using the square root method ( P = 0.4276kN)
18. 7. RESULTS
How to determine t90 using the root method ( P = 0.4276kN)
1. Draw a line AB through the early portion of the curve.
2. Draw a line AD such that CD = 1.15OBC. The time value for Point E (i.e. the intersection of line AD and the
the data) is the square root of time for value for t90 (i.e. the time to 90% primary consolidation).
3. Find t90
19. 7. RESULTS
How to calculate Cv using the square root t and log t methods
1. Cv = T50*Htavgi² , where T50 = 0.197
t50
2. Cv = T90*Htavgi² , where T90 = 0.848
t90
Htavgi² =( Initial specimen height/2)² [ data sheet}
21. 7. RESULTS
Determination of preconsolidation pressure Pc by Casagrande method
Choose a point a with maximum curvature
Draw a horizontal line from A
Draw a line tangent to the curve at point A
Bisect the angle made by steps two and three
Extend the virgin compression line to intersect the bisector
line
