Detailed Lab Report: Oedometer Test for Soil Consolidation Analysis

This lab report details an Oedometer test conducted to determine the consolidation properties of soil, a crucial aspect of civil engineering for construction projects. The report begins with an introduction to soil consolidation and the experiment's objective: to identify the consolidation properties of soil. It explains the theory behind the test, which focuses on one-dimensional consolidation of low-permeability soils, and outlines the principle of the experiment, emphasizing the reduction of soil volume due to water expulsion under pressure. The report describes the apparatus used, including the Oedometer, and provides the formulas necessary for calculations. The procedures followed in the experiment, including the loading sequence and data collection, are thoroughly documented. The results are presented in tables, showing the dial gauge readings over time for different load increments, alongside calculations for void ratio changes and the coefficient of consolidation using Taylor and Casagrande methods. The report includes graphs illustrating the relationships between time and deformation, and void ratio and pressure, to derive key soil properties like the compression index. The findings are essential for understanding the settlement behavior of soils and the stability of structures.

Lab Report of Oedometer test

Table of Contents
OEDOMETER or CONSOLIDATION TEST................................................................................1
1.1 Introduction............................................................................................................................1
1.2 Objective of Experiment........................................................................................................1
1.3 Theory....................................................................................................................................1
1.4 Principle of Experiment.........................................................................................................1
1.5 Apparatus used.......................................................................................................................2
1.6 Formulae used for experiment...............................................................................................3
1.7 Procedures of experiment......................................................................................................3
1.8 Result.....................................................................................................................................5
1.9 Calculation.............................................................................................................................8

OEDOMETER or CONSOLIDATION TEST
1.1 Introduction
A state of stress is normally set up when a saturated soil is loaded, where entire load at
initial level is carried in the soil pores by water. The pressure in the water causes a saturated soil
to drain away towards the surrounding materials, which will result in producing a change within
water contents of soil consolidation. This is mainly depended on number of voids which is
present in soil. Before construction of any structure like building and more, properties of soil are
needed to be studied firsts, especially settlement is of great concern for constructing a site. For
this purpose, coefficient of consolidation helps in determining information about amount of
settlement and stability of structures after construction.
1.2 Objective of Experiment
“To identify the consolidation properties of soil by using Oedometer test.”
1.3 Theory
The present test is performed for determining the consolidation characteristics of soil
having low permeability, one-dimensional consolidation test is used. This test is carried on
specimens which are prepared from undisturbed samples, which helps in obtaining the tests by
classification of data and knowledge of soils loading. This would enable in estimating the
behaviour of foundation within load. For this purpose, variations of deformation under different-
different time with each load increment is recorded. This will be used to plot the relationship
between Void ratio versus Logarithmic of Pressure (e – logσ’v) relationship from the
measured data. Further, to determine properties relevant for one dimensional consolidation of
soil from oedometer test, values of Compression Index (Cc), Swelling Index (Cs), Coefficient
of Consolidation (Cv) and Coefficient of Permeability (kv) are calculated. After then, final void
ratio in given soli efinal is determined by finding the values of void ration increments △e and
initial variance e0.
1.4 Principle of Experiment
A soil having consolidation type of property consider as silty-clay, where volume of soil is
reduced after mixing up water, therefore, two situations prevail here –
 Excess pore pressure exist only within silty-clay stratum
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 Settlement will arise predominantly when volume change within clay
As per the above conditions, equation which will govern the consolidation are equilibrium, One-
dimensional continuity and Stress-strain distribution. By combining these equations, co-efficient
of consolidation can be calculated by using –
Cv = kv / Vw x mv
Here, Vw = unit weight of water and mv = coefficient of volume compressibility
1.5 Apparatus used
 Oedometer
 A mould and collar
 A drop hammer
 Oven
 Loading piston
 Dial gauging
 Porous stone
 Pans for weighing and mixing
 Stop watch
 Trimming knife
 A metal straightedge
 Meter Scale
 An electronic balance
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Figure 1: Experiment Set up
1.6 Formulae used for experiment
a. Volume of solid by dry weight after end of test
Vs = Ws / Gs Ѵs
b. Initial Volume of voids
Vv = Vi – Vs
c. Initial void ratio
e0 = Vv / Vs
d. Change of void ratio
△e1 = △H1 / Hs where Hs = Vs /A
e. New void ratio
e1 = e0 - △e1
f. Repeat both last two process for other load increments
1.7 Procedures of experiment
1. Set up Oedometer test carefully
2. Measure the internal diameter and height of ring
3. Mass of the ring take near about 0.001g (mg)
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4. Specimen is taken as trimmed till the Oedometer ring fitted where accuracy of measured
weight is approx. taken as 0.01(m1)
5. Determine the sample height (H0) and diameter of sample (D)
6. For determining the initial water content take some trimmed material
7. Place specimen in given setup experiment within Oedomter having a saturated porous
stone as shown in given figure
8. Pour water within Oedometer till water level reach at top of loading platform
9. Apply the seating load of 0.1kg and left it for a while
10. Now, wind up screw jack till it touch the beam then reset the timer of stop watch to zero
11. Apply the first load increment which is of 100kPa where beam support then winded
down. Now record readings in the dial gauge at different time period as per instruction
Table 1:
Loading sequence Weight (Kg) Approx. Stress (kPa)
1 2 100
2 4 200
3 8 400
4 4 200
5 2 100
12. After ending the experiment, consolidation cell will be disassembled, where soil sample
will weight and use to determine the final water content.
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1.8 Result
General data
Mass of the soil specimen = 76.5g
Height of specimen H1 = 20mm
Area of specimen A = 1862 mm2
Specific gravity of soil, Gs = 2.7
After test
Mass of can = 71.5g
Mass of can +wet soil = 144.00g
Mass of can + dry soil = 128.00g
Table 2:
Day 1
Load: 2 Kg 100kN/m2
Time
24hrs
Elapsed
time
(sec)
Log (t) √t Dial Gauge
Reading
(0.001mm)
△H x 10-3 mm △e △e1
0 0 0 0.693 2.693
10 1 3.1623 0.705 4.705
20 1.3010 4.4721 0.712 4.712
30 1.4771 5.4772 0.718 4.718
40 1.6020 6.3246 0.722 4.722
50 1.6989 7.0711 0.726 4.726
60 1.7781 7.7460 0.729 4.729
120 2.0791 10.9545 0.748 4.748
240 2.3802 15.4919 0.771 4.771
480 2.6812 21.9089 0.803 6.803
900 2.9542 30 0.835 6.835
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1800 3.2552 42.4264 0.856 8.856
3600 3.5563 60 0.862 8.862
86400 4.9365 293.9387 0.873 8.873
Table 3:
Day 2
Load: 4 Kg 200kN/m2
Time
24hrs
Elapsed
time
(sec)
Log (t) √t Dial Gauge
Reading
(0.001mm)
△H x 10-3 mm △e △e1
0 0 0 1.071 9.071
10 1 3.1623 1.083 9.083
20 1.3010 4.4721 1.096 9.096
30 1.4771 5.4772 1.103 11.103
40 1.6020 6.3246 1.110 11.110
50 1.6989 7.0711 1.114 11.114
60 1.7781 7.7460 1.118 11.118
120 2.0791 10.9545 1.145 11.145
240 2.3802 15.4919 1.188 13.188
480 2.6812 21.9089 1.230 14.230
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900 2.9542 30 1.244 14.244
1800 3.2552 42.4264 1.251 14.251
3600 3.5563 60 1.256 14.256
86400 4.9365 293.9387 1.260 14.260
Table 4
Day 3
Load: 8 Kg 400kN/m2
Time
24hrs
Elapsed
time
(sec)
Log (t) √t Dial Gauge
Reading
(0.001mm)
△H x 10-3 mm △e △e1
0 0 0 1.410 15.410
10 1 3.1623 1.441 18.441
20 1.3010 4.4721 1.452 18.452
30 1.4771 5.4772 1.458 18.458
40 1.6020 6.3246 1.463 18.463
50 1.6989 7.0711 1.467 18.467
60 1.7781 7.7460 1.470 20.470
120 2.0791 10.9545 1.489 20.489
240 2.3802 15.4919 1.517 22.517
480 2.6812 21.9089 1.580 26.580
900 2.9542 30 1.593 28.593
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1800 3.2552 42.4264 1.600 29.600
3600 3.5563 60 1.605 29.605
86400 4.9365 293.9387 1.609 29.609
Data by unloading to 4kg
Time
24hrs
Elapsed
time
(sec)
Log (t) √t Dial Gauge
Reading
(0.001mm)
△H x 10-3 mm △e △e1
600 2.7882 24.4948 1.244
Data by unloading to 2kg
Time
24hrs
Elapsed
time
(sec)
Log (t) √t Dial Gauge
Reading
(0.001mm)
△H x 10-3 mm △e △e1
600 2.7882 24.4948 1.224
1.9 Calculation
1. Before test
Mass of solids
Ms = Mc+s – Mc
= 76.5g
Mass of dry solid
Md = Mc+d – Mc
Mass of water
Mwi = Ms – Md
Initial moisture content of specimen, wi (%)
wi = Ms – Md x 100%
Ms
Void ratio
eo = Gs wi
S
2. After test
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Mass of solids
Ms = Mc+s – Mc
= 144.0 – 71.5
= 72.50g
Mass of dry solid
Md = Mc+d – Mc
= 128.0 – 71.5
= 56.50g
Mass of water
Mwi = Ms – Md
= 72.50 – 56.50
= 16.00
Final moisture content of specimen, wi (%)
wi = Ms – Md x 100%
Ms
= 72.50 – 56.50 x 100%
72.50
= (16/72.50) x 100%
= 22.06%
Change of Void ratio
△eo = △H1
Hs
New void ratio
e1 = eo – △e1
Coefficient of consolidation using Taylor method, where T90 = 0.848
1. Draw a tangent to the initial straight portion as AB of the curve
2. Then draw AC in such a manner OC = 1.15OB where abscissa of point D gives √t90
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Figure 2 Taylor's method Deformation v/s Square root of time
Now Casagrande construction, to plot graph between void ratio and effective pressure as log
scale, in following way –
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Figure 3 Relationship between void ratio and pressure
Now, Compression index (Cc) can be obtained by plotting graph between log pressure
relationship and linear void ratio
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Figure 4: Linear relationship graph between log pressure and void ratio
Now, coefficient of consolidation using Casagrande method –
T50 = 0.197
Then, log (t50) =
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