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