1. SHEARBOX TEST ON SAND
1.1 OBJECTIVE
To determine the ultimate shear strength parameters of a sand using the shearbox test.
1.2 INTRODUCTION
The main features of the shearbox apparatus are shown in Figure 1. In a standard test a
constant vertical stress is applied to the sample and then one half of the shearbox is
displaced horizontally. The test configuration forces the soil to fail on the horizontal
plane between the two halves of the shearbox.

Typical results from shearbox tests on a sand prepared in its loosest and densest states
and with the same normal stress are shown in Figures 2 and 3. Figure 2 shows the relation
between the shear stress and the horizontal displacement, and Figure 3 the relationship
between the vertical movement of the top platen and the horizontal displacement. The
shape of both of these relations depends on the initial density of the sand. If the sample is
initially dense and the normal stress is low, the shear resistance rises to a peak and then
drops to an ultimate value (Figure 2) accompanied by an upward vertical movement (i.e.
volume increase) (Figure 3). For an initially loose sample the shear resistance rises and
asymptotes to the ultimate strength (Figure 2), and shearing is accompanied by a
downward vertical movement (i.e. volume decrease) (Figure 3).

Thus, sands in different initial states, but at the same normal stress, tend towards the same
ultimate value of shearing resistance. At the ultimate state no further volume change
occurs and the samples have the same void ratio, called the critical void ratio. In the
course of shearing a loose sample becomes more dense as it reaches the critical void
ratio, and a dense sample becomes less dense as it approached the critical value.

1.3 PROCEDURE
A total of six tests are to be performed, three by each group. Three tests are to be
performed on loose specimens at normal loads of 5, 25, and 50 kg, and three tests on
dense specimens at the same normal loads.
1. Measure the mass and the internal dimensions of the empty shearbox.
2. For each initially dense specimen, the sand should be placed in the shear box and
then compacted using 25 blows of the hammer provided. Measure the depth of sand
in the box and compute the volume of the sand. Place the cap on top of the specimen.
Weigh the box with sand and determine the density of the compacted dense sand.
3. For each initially loose specimen, the sand is poured in evenly and gently. Level the
sand surface, and measure the depth of sand in the shearbox. Any vibration should be
avoided as it may cause compaction of the loose sand. The test procedure is otherwise
identical to that used for the dense samples. Place the cap on top of the specimen.
Weigh the box with sand and determine the density of the loose sand.
4. The shearbox should then be transferred to the loading frame and the appropriate
normal loads (5, 25 or 50 kg) applied. At this stage, the screws holding the upper and
lower parts of the shearbox MUST BE REMOVED.
5. After engaging the clutch for each box the motor may be switched on, and the
shearing of the specimens commenced.
6. Record readings of the vertical dial gauge and proving ring (reading of the shear
force) for every 0.25 mm of horizontal displacement in Datasheet 10. The test should
be continued until a total displacement of 6 mm is reached.
7. Repeat steps 2 to 6 for the different normal loads.

1.4 REPORTING OF RESULTS
1. Complete the results of testing in Datasheet No 10 and Datasheet No 11.
2. A summary plot showing the stress ratio (/) versus horizontal displacement for all
the tests (i.e. for both dense and loose samples). You can plot it in an Excel
spreadsheet. From the plot, determine the ultimate shear stress for each test.
3. A summary plot showing the vertical displacement versus horizontal displacement for
all tests.
4. Using the results from the summary plot in (2), complete Table 1 showing for each
test of both loose and dense sand: the normal stress () and ultimate shear stress (ult)
.
5. A plot of ultimate shear strength (stress) versus normal stress. Show the data from all
the tests on a single plot. Determine the ultimate shear strength parameters (c, ult)
for the sand.
6. Students MUST complete Task 1 and present the results to the demonstrator before
leaving the lab class.
7. A type-written report is to be submitted within one week of the practical class. The
report should be concise consisting of the following:
a) State clearly the objectives of experiment
b) A brief outline of the experimental procedures
c) Completed data sheets 10 and 11
d) The results from Tasks 2 to 5 above
e) Comments, if any, on any trends, particularly with respect to the effects of normal
load and density (loose or dense), apparent in the summary plots