Theory
Unconfined compressive test is perform in order to measure compressive strength of a cylinder of soil to which no lateral support is offered the shear strength is taken as equal to as times the compressive test because no lateral pressure is employed in unconfined compressive test it has the following features.
1. It is used cohesive soil only because the cohesive less soil not term and un-support cylinder.
2. It is the simplest and cheapest method for measuring the shear of cohesive soil.
Items required
1. Compressive device of any suitable time
2. Sample measuring dial get with 0.01mm
3. Sample ejector
4. Stop watch
5. Balance
6. Oven
7. Sprit moulds 3.5cm dia. & 7cm long
8. Moulding apparatus, sample of moisture soil
Procedure
1. Preparation of test specimen un-disturb sample, un-disturb cylindrical specimen cut from the figure un-disturb sample obtain from the field is used to trim ends parallel to each other trimmer is used to trim it the specimen to circular cross-section. Ulternative field sample is obtain directly in thin sampling screw having the same interval dia as the specimen be tested. The strip mould is leave tightly from inside and the sample is then pushed out into the spilt mould. The split mould is open carfully and sample taken out.
2. compressive test
1. Measure the initial length and diameter of specimen.
2. Put the specimen on bottom edge of load device.
3. Adjust the upper plate to make contact of specimen said to be lade gauge and space dial gauge to zero.
Compress the specimen upto cracks are definitely developed or a stress strain curve in well passed its or until deformation of 20 % is reached. Take the load dial readily to approximately 1 mm deformation of the specimen.
Stretch the radial titerm measure the angles the cracks and the horizontal possible if specimen homogenious.
Observation
1. Initial dia. Of specimen = 58 mm
2. Initial length (L0) = 80 mm
3. Initial axel = 1134 mm2
4. Initial water content = 26.42 %
5. Initial volume = 729 mm3
Observation table
Axial compression (dl)mm | Pouring ring dial get (divi) | Compressive load (N) | Specimen length in (mm) | Specimen area in (mm2) | Compresive strength in N/mm2 | Axial strain in (%) |
01 | 55 | 270 | 79 | 1148 | 0.235 | 1.25 |
02 | 83 | 400 | 78 | 1163 | 0.343 | 2.5 |
03 | 98 | 490 | 77 | 1178 | 0.415 | 3.75 |
04 | 115 | 565 | 76 | 1193 | 0.473 | 5.0 |
05 | 115 | 565 | 75 | 1209 | 0.467 | 6.25 |
06 | 114 | 560 | 74 | 1226 | 0.456 | 7.5 |
07 | 113 | 555 | 73 | 1242 | 0.446 | 8.75 |
08 | 112 | 550 | 72 | 1260 | 0.436 | 10.0 |
09 | 112 | 550 | 71 | 1277 | 0430 | 11.25 |
10 | 111 | 540 | 70 | 1296 | 0.416 | 12.50 |
Diagram
Calculation
Axial length = δɻ / L0 X 100 where δɻ is change in specimen
L0 is initial length of specimen
1. 1/80 X 100 = 1.25 %
2. 2/80 X 100 = 2.50 %
Average cross-section area
A = A0/1-E where A0 = initial area of specime
A = 1134/1-0.0125
= 1148 mm2
Compressive strength 6 = P/A
6 = 270/1.148
= 0.235 N/mm2
Graph
Result
From graph the minimum unconfined compressive test of given soil sample was found to be 0.437 N/mm2
