TITLE: Unconsolidated Undrained Triaxial Test

OBJECTIVE To determine the shear strength parameters for clayey soil.

THEORETICAL BACKGROUND Triaxial test is more reliable because we can measure both drained and undrained shear strength. Generally 1.4 diameter (3 tall) or 2.8 diameter (6 tall) specimen is used. Specimen is encased by a thin rubber membrane and set into a plastic cylindrical chamber. Cell pressure is applied in the chamber (which represent) by pressurizing the cell fluid (generally water). Vertical stress is increased by loading the specimen (by raising the platen in strain controlled test and by adding load directly in stress controlled test, but strain controlled test is more common) until shear failure occurs. Total vertical stress, which is is equal to the sum and deviator stress (). Measurement of () axial deformation, pore pressure, and sample volume changed are recorded. Depending on the nature of loading and drainage condition, triaxial tests are conducted in three different ways. UU Triaxial test CU Triaxial test CD Triaxial test

UU test measures the undrained shear strength of soils by means of axial compression test on cylindrical specimens in which no drainage is permitted during the test.

APPARATUS a) Strain controlled triaxial load frameb) Triaxial cell assemblyc) Cell pressure supply paneld) Scale e) Balance sensitive 0.1 gf) Moisture cansg) OvenPROCEDURE 1. The diameter, length, and initial mass of the specimen measured.2. The thickness of the rubber membrane measured.3. Soil specimen is set in a triaxial chamber.4. The cell pressure increased to a desired value (70 kPa for the first case and 140 kPa in the second case).5. The specimen sheared at the rate of 1%/min or 0.7%/min (for 70 mm sample height). In automated device, the software calculates it automatically based on the soil type.6. The L , and recorded in every 10 seconds (computer does it automatically).7. The test continued until the deviator stress shows ultimate value or 20% axial strain.8. After the test complete, the cell pressure release to 0, the pressure vent and the cell bring down by bring the the lower platen down, the cell drained and the porous stone clean and assembly.9. The mode of failure then sketch.10. The weight of specimen measured again, and the specimen put into the oven.11. The weight measured again after 24 hour.12. The test repeated using second specimen(140 kPa of cell pressure and third specimen 210 kPa of cell pressure).

USERS GUIDELINE FOR THE ELE TRIAXIAL DEVICE (UU TRIAXIAL TEST)A. POWER AND MAIN SUPPLY SETTINGS ( This step is already done)1. Press the Power Display power button to the ON position. After Stabilization (approx. 15 min.), push the Tare button to zero the display.2. Turn on the laboratory vacuum supply. The associated amount of vacuum available to your system will be displayed on the Vacuum Supply Gauge.3. Turn on the laboratory compressed air supply. Viewing the Pressure Supply gauge, adjust the Master Regulator until the desired maximum supply pressure is reached. The display pressure should be about 10 psi more than the required cell pressure. Do Not exceed 150 psi (1034 KPa) pressure.4. Turn on the laboratory water supply.

B. FILLING OF THE DE-AIRED WATER TANK SYSTEM (This step is already done)1. Turn the De-Airing Water Control valve to he Fill position.2. When the tank water level is about 1 from top, turn the De-Airing Water Control valve to the vent position ( Very Slowly to allow water to drain).

C. DE-AIRING THE WATER TANK (This step is already done)1. Turn the De-Airing Water Control valve to the Vacuum position.2. Apply vacuum form 10-15 minutes and, at the same time, gently shake the tankOcciasionally to enhance the removal or air from water.3. Turn the De-Airing Water Control valve to the vent position.

D. FILLING THE BURETTE CHANNELS ( This step already done).1. Set all five valves on the test cell to he closed position.2. Set the De-Airing Water Control valve to the Pressure position.3. Set the Burette/Annulus Input Control valve to the vent position.4. Set the Annulus Control Switch to the open position (Normal).5. Slowly turn the Burette/Annulus Input Control valve to the Fill position.When the water reaches the desired level, turn the Burette/Annulus Flow Control valve to the Cell Operate position. Do not overfill. Water should not be allowed to flow into the cell pressure tube at the top.6. Repeat the above steps until two burette channels being used are fiiled to the desired level.Note : If the water level in the De-Aired Water Tank System drops to about 1 from the bottom, repeat the filling and de-airing procedures described above.E. DE-AIRING THE BURETTE CHANNELS (This is already done).1. Set the Burette/Annulus Input Control valve for each channel to the vacuum position. Under normal operating conditions, the de-airing process should be complete in about 5-10 minutes.2. After completion, set all Input Control valves back to the vent position.

F. PREPARATION OF THE SAMPLE1. Trim the sample to be tested using a Miter Box.2. Measure the height and diameter of the sample at various location to get an average value.3. Measure the weight of the trimmed sample before test.4. Wrap the sample in a plastic sheeting to prevent any moisture loss.5. Use trimmings to get the moisture content of the sample before test.

G. PREPARATION FOR THE TRIAXIAL LOADING1. Double click on software icon DS7 on the desktop.2. Click on the button New Test.3. Select UU1 Triaxial Quick undrained Test-AS.4. Click on the button Select a Machine for the test.5. Fill in the spaces in this window and click on the button ok to the right sight of the screen. The fields marked * by their side can not be left blank and characters /*.,:;@#? can not be used while filling up the spaces.6. In the window Test in Progress make sure that you select the test that you want to run and then click on the button ok at the bottom of the screen.7. Switch on the Load Cell machine using the button at the back.

A. B. C. D. E. F. G. H. MONITORING THE TEST1. In the Test Monitoring, window, make sure that all the test data shown in the upper box is correct.2. Click on the button Start Test Stage located to the upper right side of the screen.3. In the next window select Test Initialization and click on button OK in the bottom.4. In the Test Initialization window, enter the previously measured sample Diameter, Weight and Height.5. The bulk density of the sample will be calculated automatically by the software.6. The information regarding the Membrane Thickness and Youngs Modulus are default value and may not be changed, unless using a different kind of membrane around the sample.7. After entering all data click on the green button Confirm Setup Data.8. This will bring you back to the Test Monitoring Window.9. Again click on button Start Test Stage located to the upper right side of the screen.10. This time select Compression from the menu and then click on button OK at the bottom of the window.

I. COMPRESSION STAGEFrom the previous stage you will be directed to the screen titled Compression Stage for Undrained Test.I. Vent Cell Pressure Transducer to Atmosphere and Reset:a) Set the Burette/Annulus Input Control valve to the Pressure Position.b) Set the Annulus Control Switch valve to the on position.c) Set the Burette/Annulus Flow Control valve to the Cell Operate position.d) Make sure all the cell pressure transducer is open to atmosphere and wait for 10 secondse) In the DS-7 software window, click on the red button Reset Cell Pressure.

II. Fill and Pressurise the Cell. Select Material Type and Press Button to Calculate Suggested Rate of Strain on Enter Directly:a) Close the valve on the test Marked CP.b) Carefully place the sample on the Triaxial cell base pedestal.c) Place the top pressure pad and use black O-rings to secure the membrane around the base pedestal and top pressure pad.d) Place the Triaxial cell cover over the sample and use the three rods to secure it in place.e) Open the knob at the top of cylinder and attach the tube marked CP to the knob knob marked Water located at the bottom left of the panel. Open the valve on the test cell marked CP. This will gradually fill the cell. Control the flow using the valve marked CP.f) Close the knob at the top of the glass cylinder when the cell is filled with water.g) Detach the tube marked CP from the knob marked Water and attach it back to the knob marked CP on the panel.h) Close the valve on the test cell marked CP.i) Use the knob in the Set Pressure Control panel to increase the pressure to the desired cell pressure level. Monitor the cell pressure box in the DS-7 software window to get the accurate reading.j) Set the Burette/Annulus Input Control valve to Pressure position.k) Slowly open the valve on the test cell marked CP. This will transfer the cell pressure to the water inside the glass cylinder.l) In the DS-7 software window, select the right Material Type to the right side of the window and click on the button calculate Rate of Strain.m) Input the Calculated rate of displacement value from the computer screen to display window at the bottom of the test cell and press Enter .

III. Calculate Logger Sampling Rates (based on percentage of length of specimen at failure):a) On the DS-7 software window, fill up the boxes marked first increments, upto, and second increments. This is the increment at which the result will be captured by the transducer. The default values are from the ASTM Standard. Set both for 0.01%.

IV. Reset Force Transducer & Bring Piston just into contact with top cap:a) Raise the sample using the key on the keypad on the loading frame until the load piston just touches the top notch of the top plate above the soil sample.b) On the DS-7 software window, click on the red button marked Reset Force Transducer.c) This should reset the lower right window on the Test Monitoring Window in the DS-7 software to 0.0 lbf

V. Reset Axial Displacement & Start Compression at End of Count Down:a) Place the axial displacement transducer bottom touching the horizontal rod and click on the button Reset Axial Displacement Transducer on the DS-7 software window.b) This should reset lower left window on the Test Monitoring window of the DS-7 software to 0.0 inches.

VI. Click on the green continue button at the bottom of the page of the software window.VII. A window will appear that will instruct you to press enter (Green Button) to start the Test Countdown. If everything is ready, click on the green button Start Test Countdown.VIII. Once the two whistles go, press the green button Run on the keypad at the bottom of the test cell.

J. TO STOP THE TEST1. To stop the loading at any time press red button Stop on the keypad of the load frame.2. In the DS-7 software, on Test Monitoring window click on button End Test stage3. Click on button Start Test Stage button.4. Select Final Measurements and click on OK5. Enter all parameters that are available at this timeFinal Specimen weight (wet)Final Specimen Weight (Dry)Initial Moisture Content from TrimmingsLab Temperature during testParticle Specific Gravity6. Click on green button Confirm Data.7. Click OK on the window stating FINAL STAGE IS NOW COMPLETE. PRESS OK TO STORE THE TEST DATA READY FOR ANALYSIS OR PRESSS CANCEL TO PERFROM FURTHER STAGES8. Save the Raw data obtained from the test to a directory of your choice. The software will prompt to a default directory.9. Click on button exit to exit from the software.

K. DRAINING THE CELL1. Turn the Set Pressure Control knob in counter-clockwise direction to reduce the cell pressure.2. Turn the Burette/Annulus Input Control valve to Bridge Off position.3. Open the top knob of the glass cylinder in the load cell assembly.4. Set the Burette/Annulus Flow Control to drain position.5. Open the valve on the test marked CP. This will drain the water from the glass cylinder.

L. DISMANTLING THE CELL1. Use the button on the keypad of the load frame to lower the sample away from the load piston.2. Unscrew the three rods from the sides of the glass cylinder and take out the cylinder.3. Dismantle the sample from the test cell and secure the membrane, top and bottom end plates.DATASample Data:Diameter, Do= 33.35 mmVolume, Vo = 62.02 cm3Water content, w= 13.7%Degree of saturation, s = 61.0%Load rate= 12.7 mm/minArea, Ao = 8.735 cm2Length, Lo= 70.9 mmCell pressure, 3 = 98 kPaLoad ring constant, LRC= 5.68 N/div

CycleDeform, dial0.01(units)L(mm)Load dial unitsSample load, P(kN)L/Lo

1-Corr AreaA1(cm2)Deviator stress1=P/A1(kPa)Normal stress1/3

1st00.0000.0000.00001.00008.7350.000.000

250.2530.0170.00350.99658.76619.390.198

500.5090.0510.00710.99298.79757.970.592

750.75160.0910.01050.98958.828103.081.052

850.85170.0970.01200.98808.841109.721.120

2nd780.7800.0000.01100.98908.7350.000.000

1001.00170.0970.01410.98598.860109.481.117

1251.25260.1480.01760.98248.891166.461.699

1501.50290.1650.02120.97888.924184.891.890

1751.75320.1820.02470.97538.956203.222.074

2002.00340.1930.02820.97188.988214.732.191

3rd1771.7700.0000.02500.97508.9590.000.000

1801.80100.0570.02560.97448.96463.590.649

4th5405.4000.0000.07620.92389.4560.000.000

5505.50150.0850.07760.92249.47089.760.916

6506.50460.2610.09170.90839.617271.392.770

7507.50550.3120.10580.89429.769319.383.259

120012.00660.3750.16930.830710.52356.463.637

130013.00670.3810.18340.816610.70350.473.576

20%1418--------

Maximum deviator stress (from stress-strain curve) 1= 360 kPaMaximum value of vertical stress1=3 + 1= 458 kPa

DISCUSSIONIn this experiment, there are 4 cycles done on the same sample, which is the blue clay cohesive soil. In theory, the sample will fail either at the maximum deviator stress value or at 20% of the axial strain. In this experiment, the soil sample fails fully at the 4th cycle, with the value of deviator stress at 350.47 kPa and at a strain of 0.1834.Since this test only use one value of cell pressure 3, which is at 98 kPa, only one Mohrs circle can be plotted at the graph of shear strength against normal stress . The values of 1 can be obtained from the stress-strain curve; and in this experiment, we have taken the value of 1 from the maximum deviator stress at the 4th cycle, which is where the soil sample fails. Next, to get the value of 1, we have used the formula 1=3 + 1 and we have determined the value of 1 as 458 kPa. Meanwhile, the value of 3 is taken directly from the cell pressure, which is at 98kPa.The horizontal value of the graph is determined as 180 kPa, and this value indicates the Cu, shear strength of the soil sample. However, some precautions also should be taken to make sure to increased the probability that our group can get the exact values and avoided more an errors such as the eyes must be perpendicular to the reading, do not exceeded 150 psi (1034 KPa), and there are a number of major error sources in this experiment - in fact this experiment uses some instrumentation which is not highly accurate and that why sometimes the difference between calculated results and graphical results are due to inaccurate measuring is occurred.

CONCLUSIONAfter finishing the experiment and calculations, we can conclude that from the experiment, the objective are achieved which is to determine the shear strength of the sample.

REFERENCES1. Mdm. Farah Hafifee, Chapter 2 (Soil Strength Behaviour) Note, Faculty of Civil Engineering, UiTM Kota Samarahan.2. Budhu, M. Soil Mechanics and Foundations 3rd Edition., John Wiley & Sons, Inc., 2011.3. Sir Embam Ak Daud, Soil Mechanics Laboratory Manual, Faculty of Civil Engineering, UiTM Kota Samarahan.4. UU Triaxial Test, http://faculty.fullerton.edu/btiwari/geotech_Lab/mainpage_files/other/UU. Retrieved on 8th March 2015.5. Unconsolidated Undrained Test, http://www.uta.edu/ce/geotech/lab/Main/Soil%20Lab/10_UU%20test/UU.pdf. Retrieved on 8th March 2015.