Reference no: EM132897465
1. SHEARBOX TEST ON SAND
1 OBJECTIVE
To determine the ultimate shear strength parameters of a sand using the shearbox test.
2 INTRODUCTION
The main features of the shearbox apparatus arc shown in Figure 1. In a standard test a constant vertical stress is applied to the sample and then one tialf of the shearbox is displaced horizontally. The test configuration forces the soil to fail on the horizontal plane between the two halves (lithe shearbox.
Typical results from shcarbox tests on a sand prepared in its loosest and densest states and with the same normal stress arc shown in Figures 2 and 3. Figure 2 shows the relation between the shear stress and the horizontal displacement, and Figure 3 shows 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 approaches the critical value.
3 TESTING 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, 2& 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) are 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.
4. REPORTING OF RESULTS
1. Complete the results of testing in natasheet No 10 and Datasheet NO 11.
2. A summary plot showing Inc the ultimate shear stress for each tefsor all the tests (i.e. for both dense and loose samples). You can plot it in an MS Excel spreadsheet. From the plot, the stress ratio (r/σ) versus horizontal displacement MS versus horizontal displacement for
3. A summary plot showing the vertical displacementh
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 (σ) and ultimate shear stress (τult)
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' Φ, 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 datasheets 10 and 11;
d) The results from Tasks 2 to S 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.
1.5 PERFORMANCE CRITERIA AND ASSESSMENT
STANDARDS
The following criteria will be used in assessing the submitted lab report:
(1) Active participation and completion of the required lab tasks during the lab class. It will include punctuality, dress code and compliance with OH&S requirements.
(2) Adequate elaboration of objectives of the experiment, and accurate, concise description of experimental procedures.
(3) Clear and concise reporting and presentation of experimental results .(including clarity, neatness and correctness). Keep in mind that this is to be a type although the recorded raw data can be hand-written. Use MS Excel spreadsheet and is required. the equation editor in MS Word in preparing the report, if this type-written report
(4) Addressing the objectives of the experiment adequately. If there were unexpected errors in the experimental results, clear and rational explanations should be provided.
(5) Addressing questions in the handout (if any) and the conclusions of the experiment adequately.
Attachment:- Soil mechanics practical report.rar