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1. Objective:
To determine the unconfined compressive strength of soil
2. Apparatus Used:
(a) Load frame to apply compressive load at constant rate of strain
(b) Proving Ring
(c) Dial gauge
(d) Vernier calipers
(e) Bearing plates
(f) Trimmer, sample extractor, constant volume mould with plungers
Specimen Size:
Minimum diameter: 35 mm
Height to diameter ratio = 2
3. Theory:
In this test, a cylinder of soil, without lateral support, is tested to failure in simple compression, at constant rate of strain. The compressive load per unit area required to fail the soil cylinder is called the " unconfined compressive strength " of the soil. Half of this is taken as the shear strength of the soil. The test is applicable for cohesive soil.
4. Preparation of Specimens:
A. Undisturbed Specimen
(i) Remove the protective cover (paraffin wax) from the sample.
(ii) Place the sampling tube in the sample extractor and push the plunger till a small length of sample comes out.
(iii) Cut out this projected sample using a wire saw.
(iv) Again push the plunger of the extractor till a 7.6 cm long sample comes out.
(v) Cut out this sample carefully and hold it so that it does not fall.
(vi) Measure the diameter at the top, middle and bottom of the sample and find the average and record.
(vii) Measure the height accurately and record.
(viii) Find the weight and record.
5. Procedure:
(i) Place the specimen on the base plate of the load frame.
(ii) Keep a bearing plate with a ball seating groove on the top of the specimen.
(iii) Place a hardened steel ball on the bearing plate.
(iv) Fix the proving ring to the load frame such that it transfer the load from the frame to the ball and it turn to the specimen.
(v) Make final adjustments to ensure that the load is applied axially to the specimen.
(vi) Fix a dial gauge to measure the vertical compression of the specimen.
(vii) Adjust the gear position on the load frame to give a strain rate of 1.25 mm/minute.
(viii) Start applying the load and record the readings on the proving ring dial and compression dial every 30 seconds.
(ix) Continue loading till cracks have developed on the specimen or till the specimen has compressed by 1.5 cm.
(x) Stop loading and take the specimen out of the load frame.
(xi) Sketch the failure pattern.
(xii) Measure the angle between the horizontal and the cracks
6. Observation Table:
Initial Diameter (Do) : --------------------
Initial Length (Lo) : ----------------------
Area of cross section (Ao): π/4 . Do^2
Observation Table:
Time Compression Dial Reading Strain(∈) Corrected Area Proving Ring reading Axial load
(minutes) (mm) ∆L/L Ac = Ao/(1- ∈) (Div.) P (kg)
0 ------- ------- ------- ------- -------
0.5 ------- ------- ------- ------- -------
1.0 ------- ------- ------- ------- -------
1.5 ------- ------- ------- ------- -------
2.0 ------- ------- ------- ------- -------
2.5 ------- ------- ------- ------- -------
3.0 ------- ------- ------- ------- -------
3.5 ------- ------- ------- ------- -------
4.0 ------- ------- ------- ------- -------
4.5 ------- ------- ------- ------- -------
5.0 ------- ------- ------- ------- -------
5.5 ------- ------- ------- ------- -------
6.0 ------- ------- ------- ------- -------
Compressive stress = P/Ac
Unconfined compressive strength: --------------------
Shear strength of soil : -------------------
Consistency of the soil : ------------------
7. Standard Value:
Thanku sir
ReplyDeleteVery well explained, thank you sir.
ReplyDeleteThank you soo much sir
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