Procedure for Consolidated Undrained Testing of Soil. 1. Pre-soak the porous stone for the upper and lower platten.

Transcription

1 Procedure for Consolidated Undrained Testing of Soil 1. Pre-soak the porous stone for the upper and lower platten. 2. Trim or prepare a specimen such that the length to diameter ratio is between 2 to Obtain four height measurements approximately 90 degrees apart and use the average of these four measurements as the height of the sample 4. Using calipers, take two diameter readings 90 degrees apart at the top, at the mid height, and at the base (6 readings total). Record these readings. Use these measurements to calculate the average diameter of the sample as follows. Diameter (avg.) = (diameter top + 2 diameter mid height + diameter base) / 4 5. Compute the initial area of the sample from the avg. height and diameter measurements 6. Weigh the sample and record the results. 7. Prepare the membrane for insertion of the sample. To do this, you must use a plastic mold with the membrane inserted into the interior of the mold. Stretch the membrane against the side of the mold and lap the excess ends of the membrane on the outside of the mold. Place the membrane O-rings onto the mold and position them so they are not touching the overlapped membrane. 8. Apply a vacuum to the mold to draw the membrane tightly against the mold. 9. Carefully insert the sample into the membrane and center the sample. 10. Remove the vacuum. 11. Insert the bottom porous stone into the membrane. 12. Attach the membrane, porous stone and sample to the lower platten using an O-ring to seal the membrane against the platten. (A better seal may be possible if the platten perimeter is slightly lubricated with silicone grease.) 13. Insert the top porous stone into the membrane. 14. Attach the membrane to the upper platten with O-rings. Do not damage or disturbed the sample. 15. Center the plattens to ensure the concentric loading and make sure the ram rod is seated in the top of the top platten. Once seated tighten the knurled nut that holds the ram rod in

2 place so as not to preload the sample. 16. Connect the top platten tubes. Ensure that there are small O-rings where the tubes connect with the top platten. 17. Check the O-rings for the cell (base and top). Seal the cell with the knurled nuts and bolts. 18. Flood the cell and remove all air for the cell. While flooding the cell, make sure that water can escape from the top of the cell by using a drain line. 19. After flooding the cell, flood the line to the bottom platten, until all air is removed both the top and bottom platten lines. To do this you should attach the back-pressure line to the inlet line to the bottom platten and apply a slight driving pressure. Also, the cell pressure should be applied that is slightly higher (1 to 2 psi) than the inlet driving pressure, so as not to expand the membrane with water. 20. Saturate the sample by allowing flow into the bottom platten, through the sample and out the upper platten. Use a drain line to allow flow out the upper platten. 21. After saturation and to begin consolidation, you should close the bottom platten so that flow of water into to the bottom platten is stopped. Decrease the driving pressure on the bottom platten inlet to zero. 22. Leave the drain line to the top platten open during consolidation. 23. Apply a predetermined confining stress. 24. Allow the sample to consolidate until there is no longer a change in height of the sample 25. Remeasure the sample after consolidation by draining the cell. Repeat the measurements made in steps 3 and Reflood the chamber. Ensure that no air is in the lines and in the cell. 27. Reapply the confining (i.e., cell) stress. Use the same confining stress that was used during consolidation. 28. Prepare the sample for shear. Ensure that there is enough travel on the dial gages and that no interference with holding brackets, clamps, etc. 29. Pre-determine the strain rate and set the travel rate of the loading table to the predetermined strain rate. 30. Take initial load and dial gage readings without any load on the sample.

3 31. Loosen the knurled nut that holds the ram rod in place. 32. Slowly lower the piston to the sample until the dial gage registers movement. 33. Retake the load and dial gage readings (seating load). 34. Begin testing and take readings at pre-chosen strain rate. 35. Continue readings until the load peaks (sample fails) or until 20 percent strain is reached. 36. Disassemble the triaxial device. 37. Weigh the sample wet immediately after shearing. 38. Oven dry the sample. 39. Weigh the dry sample.

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