LEEDS BECKETT UNIVERSITY

CIVIL ENGINEERING

GEOTECHNICAL ENGINEERING A (BSc)

Laboratory Experiment:

The direct shear box test BS 1377; Part 7 1990: 4 and 5

Object of Experiment:

To determine the angle of shear resistance and volumetric displacement of a sand using the direct shear box test.

Method:

Assemble the empty shear box as shown, without the upper and loading platens. The two halves of the box should be screwed together with the screws marked by a cross cut into the heads; the two screws marked ‘L' should be in position but clear of the joint between the two halves. Ensure that the apparatus is moving freely on its runners. Fill the box with loose sand and level it off about 1mm below the top of the box. Place the top platen, on the sand and the loading platen on the top platen. Put the ball bearing in place and the hanger on the ball bearing. Place a weight on the hanger.

Adjust the apparatus to take up any slack, and then zero the proving ring dial gauge.

REMOVE THE TWO SCREWS HOLDING THE UPPER AND LOWER HALVES OF THE BOX TOGETHER, then screw in those marked ‘L' until resistance is just felt: give each one a further half turn to ensure that the two halves are slightly separated so that the normal stress is being applied to the sand only, then remove them.

Switch on the motor. Record the maximum reading on the proving ring dial gauge, then switch off and slacken off the apparatus.
Dismantle the box entirely and pour all the sand back into the container.Repeat the test three more times, increasing the mass on the hanger. Record the results on the attached sheet.

Results and Calculations:

• Calculate the values of effective normal stress (σ') for each loading condition.

• Plot τ against horizontal movement for each loading condition.

• Determine values for shear stress at failure (τf)

• Plot a graph of τf against σ'. Draw the straight line of best fit through the origin and the points, and calculate the value of the angle of shearing resistance of the soil from the co-ordinates of any convenient point on the line.

• Plot vertical displacement against horizontal displacement.

Conclusion:

• Comment on the value of φ for the sand you tested.

• Explain the main points to the vertical vs horizontal displacement plot.

• Comment on the use of this test and your findings.

Indicative Reading:

Manual of Soil Laboratory Testing Vol.1 - K.H. Head

Basic Soil Mechanics - Whitlow, R.

Laboratory Work in Soil Mechanics - B. Vickers (Chapter 4: Shear-strength test is available to download from My-Beckett).

https://www.dropbox.com/s/kp17e9w8xp79mbv/expected.rar?dl=0