Consolidation Test (IS 2720- part 15 - 1986 )

AIM: This test is performed to determine the consolidation properties of a given soil as listed below:

1. Co-efficient of compressibility
2. Co-efficient of volume change
3. Co-efficient of consolidation Cv
4. Compression Index
5. Pre-consolidation Pressure, Cc
6. Co-efficient of permeability, K

STANDARD REFERENCE: IS: 2720(part 15) - 1986 - Determination of consolidation properties.

THEORY: Consolidation is the process of removal of pore water present in the soil gradually due to the application of sustained static load. Because of consolidation, there will be decrease in volume of soil mass.

SIGNIFICANCE: The consolidation data of soil is used to predict the rate and amount of settlement of structure founded on clay primarily due to volume change. In addition, the following information can be obtained for foundations resting on clay using consolidation data.

1. Total settlement of foundation under any given load.
2. Time required for total settlement due to primary consolidation.
3. Settlement for any given time and load.
4. Time required for any percent of total settlement or consolidation.
5. Pressure due to which soil already has been consolidation or compressed.

APPARATUS REQUIRED: 

1. Consolidometer
2. Loading device (Jack or lever system)
3. Ring of non-corrosive material
4. Porous stone
5. Water reservoir
6. Soil trimming tool like wire saw, knife or spatula etc.
7. Balance (0.01 gm sensitivity)
8. Dial gauge (0.01 mm accuracy)
9. Oven
10. Desiccators
11. moisture content cans
12. Stopwatch.
13. Scale ( 0.5 mm least count)

PROCEDURE: 

1. Clean the ring and weigh it empty.
2. Measure the height and diameter of the consolidation ring.
3. For undisturbed soil specimen, insert the ring in the soil mass by pressing with hand and remove the material around the ring.  The soil specimen so cut should project about one centimeter on either side of the ring.
4. Trim the specimen to flush it with the top and bottom of the ring.
5. Remove any soil sticking outside of the ring and weight the ring with the soil specimen.
6. For remoulded specimen, compact the soil in the ring to the desired density and weigh it.
7. Determine the moisture content of the extra soil removed from outside the ring.
8. Assemble the consolidometer with the ring having the soil specimen and saturated porous stones on top and bottom of the specimen. Place the filter paper between the soil specimen and the porous stone.
9. Mount the assembly on the loading frame and the dial gauge is set in position in such a way that the dial is at the beginning of its release run.
10. Connect the system to a reservoir with the same level as that of specimen. Allow the water to flow into the sample till its saturation is achieved.
11. After saturation, note initial reading of the dial gauge.
12. Apply the normal load to give the desired pressure intensity of 2.5 N/cm^2 on the soil specimen. 
13. Not the dial gauge reading at elapsed times of o, 0.25, 1.0, 2.25, 4, 9, 16, 25, 36, 49, 64, 81, 100, 169, 256, 361, 600, 1440 - minutes from the instant of  application of load. The dial gauge readings are taken until 90% consolidation is reached or atleast for 24 hours.
14. Increase the normal load to give the doubled pressure intensity of the previous pressure or 5 kN/cm^2.
15. On successive days, apply the loads to give the pressure of 10, 20, 40 and 80 N/cm^2 for the desired pressure intensity.
16. After the last load is applied, decrease the load 1/4 th the value of the last laod i.e. 20 N/cm^2 and allow to stand for 24 hours.
17. Note the dial gauge reading after 24 hours.
18. Further reduce the load in steps of 1/4th the previous load and repeat the observations.
19. If data for repeated loading is required, the load intensity is increased and observations are repeated.
20. Finally reduce the load to the initial setting load, keep for 24 hours and final dial gauge reading is recorded.
21. Dismantle the consolidation ring and weigh it after gently removing any surface water present.
22. Dry the specimen in the oven for 24 hours and weigh the dry soil specimen.
23. Draw graphs between:

               (a) Dial gauge reading versus under root of time on normal graph sheet and determine t90 for all the pressure by square root of time fitting method.

               (b) Dial gauge reading versus root of time on semi log graph sheet and determine t50 for all pressure by logarithm of time fitting method.

               (c) Void ratio 'e' versus pressure curve.

               (d) Void ratio 'e' versus load of pressure on semi-log graph sheet.

Square root time fitting method

RESULTS AND COMMENTS: 

Average value of the co-efficient of compressibility =

Average value of co-efficient of consolidation, Cv = 

Average value of co-efficient of volume compressibility =

Average value of co-efficient of permeability, K = 

Compression Index, Cc =