Practical Reports 2 Geotechnics

Geotechnical Engineering Laboratory Coursework

Answer ALL questions showing ALL calculation steps clearly. Where graphs are required you MUST use either actual graph papers (not plain paper) or Excel plotting. Make sure the plotted data points and connecting curves/lines are clear and tidy. Label the axes of graphs and indicate the measurement units.
10% of the module mark

QUESTION 1

The following results were obtained from a series of consolidated undrained triaxial tests carried out on undisturbed samples of a compacted soil.

Test No. Cell pressure (kPa) Additional axial load at failure (N)
1 200 342
2 400 388
3 600 465

Each sample originally 76 mm long and 38 mm in diameter, experienced a vertical deformation of 5.1 mm. Draw the failure envelope and determine the Coulomb equation for the shear strength of the soil.

QUESTION 2

An undisturbed soil sample was tested in a falling head permeameter. The results were:

Initial head of water in stand-pipe 1500 mm
Final head of water in stand-pipe 605 mm
Duration of test 281 s
Sample length 150 mm
Sample diameter 100 mm
Stand-pipe diameter 5 mm

Calculate the coefficient of permeability of the soil in m s–1.

QUESTION 3

The following results were obtained from a compaction test using the 2.5 kg rammer:

Test No. Mass of mould + wet soil (g) Moisture content (%)
1 2783 8.1
2 3057 9.9
3 3224 12.0
4 3281 14.3
5 3250 16.1
6 3196 18.2

The mass of the compaction mould excluding collar and base was 1130 g and the soil had a particle specific gravity of 2.70. Plot the curve of dry density versus moisture content. On the same graph plot the curves representing 5% and 0% air voids. Determine the optimum moisture content for the soil.