UNCONSOLIDATED UNDRAINED TEST 1.0
INTRODUCTION In an unconsolidated undrained test the sample is not allowed to drain. The sample is compressed at a constant rate (strain-controlled). The UU test is applicable to undisturbed sample in which no change in moisture content from the in-situ value can be permitted. Test can be carried out over a range of moisture content to enable Mohr envelopes for the required to be interpolated. The UU test procedure is useful for determining the total strength parameters for soils that have suffered disturbances or moisture change during sampling.
2.0
PRINCIPLES This method can be used for determining the undrained shear strength of cohesive soil when it is subjected to a constant confining pressure and to strain controlled axial loading, when no change in total moisture content is allowed.
3.0
OBJECTIVES To establish a procedure for determining the Unconsolidated Undrained Test by Triaxial Compression without measurement of pore pressure, which gives the shear strength of cohesive soil.
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4.0
APPARATUS
Soil sampling NO ITEMS 1
Sampling tube
2
Sample extruder
3
Wire saw
4
Automatic balance
5
Callipers
2
Soil testing NO ITEMS 1
Rubber membrane
2
Membrane stretcher
3
o-ring seal
FIGURE
3
5.0
PROCEDURES SAMPLE PREPARATION
Bulk sample is prepared in size of 38mm in diameter and 76mm in height. In any case, the height-to-ratio should be 1:2.
The height, Lo, diameter, Do and mass with sufficient accuracy is determine to calculate the soil’s bulk density.
The sample is carefully put inside the rubber membrane. Porous disks at both top and bottom of the soil sample are put and seal with O-ring. All together are assembled so that the specimen can stand inside the cell chamber.
SAMPLE TESTING The triaxial cell chamber (with the specimen inside) is place on the platform of the compression machine.
The proper adjustment is making so that the piston of the triaxial cell just rest on the top platen of the specimen.
The chamber of the triaxial cell is filled with the water by opening valve mark with (a), (b), and (c) and all the air must be displaced through the air vent. Those valves immediately closed when the chamber full with water. The cell pressure is applied to the specimen through the chamber fluid. It done by opening valves mark with (b), (c), (d), and (e) and the required pressure is set. All drainage to and from the specimen are closed so the drainage from the specimen does not occur.
Inside the Local Disk (c), the Winsclip program is selected and new folder is created. Then, from the Winsclip program, the Files is pressed and New job file is choose. Folder and input file name is selected and press Ok. Job file name, borehole name and sample name are input before press Ok and Close.
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Configuration menu is pressed and new test (total triaxial) is selected by name. The total UU S, Stage M and Specimen are choosing before click Ok. Then, Total triaxial configuration is selected and the proper load and strain source are identified. The loadcell for load is selected while the displacement for strain and the correct number of the specimen and machine also selected. When to stop the test is decided by selecting the appropriate box.
The test is proceeding and the control menu pressed to overview the data. Then, shear stage menu is selected and go to the initial condition. The specimen detail and condition are filled before press Ok. It proceed to control menu and Run is selected. The specimen of application is clicked and press Ok. The data is double checked and confirmed by pressing Ok. Then, button Up at the compression machine is pressed immediately. Shear stage menu is selected to view the data and either data entry are choosing to view tabulated data, stress-strain to monitor, the stress-strain curve or Mohr Circle to view the Mohr Circle. Then, select stop at the control menu when the specimen showing sign of failure. The button Stop at the compression machine is immediately pressed. The Mohr circle is viewed and keyboard control button is pressed simultaneously with the right click to generate the Mohr-Coulumb envelope. The envelope then adjusted so that the shear strength parameter is determined.
Then, the chamber pressure is released, the water inside the triaxial chamber is drained, the compression machine is reversed, the triaxial cell is lowered and the machine shut off. The specimen is carefully removed and all apparatus are disassembled. The specimen condition is examined and the final weight is determined.
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6.0
RESULTS
Length of specimen
: 76 mm
Diameter of specimen
: 38 mm
Area specimen
: 0.001134m2
Volume specimen
: 8.619 x 10-5 m3
STAGE 1 No
Strain (mm)
Strain1 (%)
Area(mm)
Load(N)
Dev stress(kPa)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
8.86 8.94 9.07 9.2 9.33 9.46 9.6 9.73 9.87 10.01 10.14 10.28 10.42 10.56 10.7 10.84 10.98 11.12 11.26 11.4 11.54 11.68 11.82 11.95 12.09 12.23 12.36 12.49 12.63 12.76 12.76
0 0.11 0.28 0.45 0.62 0.79 0.97 1.14 1.33 1.51 1.68 1.87 2.05 2.24 2.42 2.61
0.001134 0.001135249 0.001137184 0.001139126 0.001141075 0.00114303 0.001145108 0.001147077 0.001149285 0.001151386 0.001153377 0.00115561 0.001157734 0.001159984 0.001162123 0.001164391 0.001166547 0.001168711 0.001171004 0.001173184 0.001175495 0.001177692 0.001179898 0.001182112 0.001184334 0.001186565 0.001188804 0.001190926 0.001193182 0.00119532 0.001195824
25.5 54 68 77.5 84.5 91.5 96 101
0 25.1 37.37 45.65 51.2 57.24
2.79 2.97 3.16 3.34 3.53 3.71 3.89 4.07 4.25 4.43 4.61 4.78 4.96 5.13 5.17
103 105.5 110 112.5 112.5 115 117 119.5 122 124
61.06 65.31 66.93 68.6 72.38 74.4 74.26 76.28 77.85 79.6 81.59 83.14
126 129 133.5 136 138.5 140.5 143 147.5 150
85.12 87.09 90.37 92.32 94.26 95.78 97.7 101.3 102.93
152.5 152.5 152.5 154.5
104.88 104.68 104.48 106.11
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STAGE 2 No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Strain (mm) 12.83 12.94 13.07 13.21 13.33 13.47 13.6 13.73 13.86 13.99 14.12 14.25 14.38 14.52 14.65 14.78 14.91 15.04 15.18 15.31 15.45 15.58 15.72 15.86 16 16.13 16.27 16.41 16.55 16.69 16.72
Strain (%) 0 0.14 0.32 0.5 0.66 0.84 1.01 1.18 1.36 1.53 1.7 1.87 2.04 2.22 2.39 2.57 2.74 2.91 3.09 3.26 3.45 3.62 3.8 3.99 4.17 4.34 4.53 4.71 4.89 5.08 5.12
Area (mm) 0.001134 0.00113559 0.00113764 0.001139698 0.001141534 0.001143606 0.00114557 0.001147541 0.001149635 0.00115162 0.001153611 0.00115561 0.001157615 0.001159746 0.001161766 0.001163913 0.001165947 0.001167988 0.001170158 0.001172214 0.001174521 0.001176593 0.001178794 0.001181127 0.001183346 0.001185448 0.001187808 0.001190051 0.001192304 0.00119469 0.001195194
Load (N) 131.5 161.5 166.5 169 171 173.5 176 178 178 180.2 183 185 187.5 187.5 187.5 187.5 187.5 190 187.5 190 187.5 190 187.5 187.5 190 187.5 190 190 194.5 199 199
Dev stress (kPa) 0 26.41 30.76 32.4 34.1 36.22 38.34 40.02 39.95 41.67 43.76 43.69 45.34 47.4 47.32 46.99 46.9 48.96 46.73 48.77 46.55 48.22 46 45.91 47.93 45.73 47.5 47.4 51.08 54.74 54.72
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STAGE 3 No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38
Strain (mm) 16.76 16.85 16.99 17.12 17.26 17.39 17.53 17.66 17.8 17.93 18.06 18.19 18.33 18.46 18.59 18.72 18.86 18.99 19.12 19.25 19.38 19.51 19.65 19.78 19.91 20.04 20.17 20.31 20.44 20.58 20.71 20.84 20.98 21.12 21.25 21.39 21.53 21.67
Strain (%) 0 0.12 0.3 0.47 0.66 0.83 1.01 1.18 1.37 1.54 1.71 1.88 2.07 2.24 2.41 2.58 2.76 2.93 3.11 3.28 3.45 3.62 3.8 3.97 4.14 4.32 4.49 4.67 4.84 5.03 5.2 5.37 5.55 5.74 5.91 6.09 6.28 6.46
Area (mm) 0.001134 0.001135362 0.001137412 0.001139355 0.001141534 0.001143491 0.00114557 0.001147541 0.001149752 0.001151737 0.001153729 0.001155728 0.00115797 0.001159984 0.001162004 0.001164032 0.001166187 0.001168229 0.001170399 0.001172457 0.001174521 0.001176593 0.001178794 0.001180881 0.001182975 0.001185201 0.00118731 0.001189552 0.001191677 0.001194061 0.001196203 0.001198351 0.001200635 0.001203055 0.001205229 0.001207539 0.001209987 0.001212316
Load (N) 171 208.5 211 215.5 220.5 222.5 227.5 229.5 232 234.5 234.5 237 237 239 239 241.5 244 244 239 241.5 246 246 246 248.5 248.5 246 246 244 246 244 241.5 241.5 241.5 239 239 237 237 237
Dev stress (kPa) 0 33.03 35.16 39.05 42.86 44.53 48.81 50.47 52.55 54.25 54.16 56.23 56.12 57.74 57.64 59.43 61.46 61.35 56.97 59 62.73 62.24 62.12 64.12 64 61.78 61.66 59.61 61.18 59.38 57.18 57.08 56.71 54.52 54.42 52.65 52.54 52.44
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39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
21.81 21.95 22.08 22.23 22.37 22.5 22.64 22.78 22.91 23.05 23.18 23.13 23.45 23.58 23.71 23.85 23.98 24.11 24.25 24.38 24.41
Initial Condition
6.64 6.83 7 7.2 7.38 7.55 7.74 7.92 8.09 8.28 8.45 8.62 8.8 8.97 9.14 9.33 9.5 9.67 9.86 10.03 10.07
0.001214653 0.00121713 0.001219355 0.001221983 0.001224358 0.001226609 0.001229135 0.001231538 0.001233816 0.001236372 0.001238667 0.001240972 0.001243421 0.001245743 0.001248074 0.001250689 0.001253039 0.001255397 0.001258043 0.00126042 0.001260981
237 239 239 241.5 241.5 244 246 248.5 253 255.5 258 260 260 262.5 262.5 267 267 267 269.5 269.5 269.5
52.08 53.61 53.51 55.44 55.32 57.01 58.51 60.42 63.95 65.84 67.73 68.96 68.82 70.69 70.55 74 73.86 73.46 75.29 75.14 75.11
Sample 1
Sample2
Sample 3
Dry unit weight kg/m3
623.72
678.36
646.49
Moisture content
29.56
23.49
27.46
50
100
150
Deviator stress kN/m2
104.68
54.72
73.86
Axial Stress kN/m2
154.68
154.72
223.86
Failure Conditions: Cell pressure kN/m2
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Samples
1
2
3
Weight of evaporation dish (g)
20.20
20.01
20.10
Weight of evaporation dish + wet soil (g)
27.30
27.37
27.34
Weight of evaporation dish + dry soil (g)
25.68
25.97
25.78
Weight of dry soil (g)
5.48
5.96
5.68
Moisture loss (g)
1.62
1.4
1.56
Moisture content %
29.56
23.49
27.46
6.1
CALCULATION
Initial Area of the sample
= d2/4 =π (38)2/4 =0.001134m2 = Ao / (1- ε)
Area
= (0.001134)/ (1-0.66%) =0.001141534 mm Axial stress
= cell pressure + deviator stress = 50 + 74.60 = 124.26 kN/m2
For Sample 1: Moisture loss= (Weight of evaporation dish + wet soil)– (Weight of evaporation dish + dry soil) = 27.30 g - 25.68 g = 1.62 g Weight of dry soil = (Weight of evaporation dish + dry soil) - Weight of evaporation dish = 25.68 g - 20.20 g
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= 5.48 g Moisture content = Moisture loss / Weight of dry soil × 100% = 1.62 g / 5.48 g × 100% = 29.56 %
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TOTAL TRIAXIAL STRESS-STRAIN 120
100
Deviator Stress (kPa)
80
STAGE 1
60
STAGE 2 STAGE 3
40
20
0 0
1
2
3
4
5
6
7
Strain (%)
12
MOHR CIRCLE GRAPH
13
7.0
DISCUSSION
The triaxial test is one of the most reliable methods available for determining shear strength parameters. It is widely used for research and conventional testing. When conducting site investigations for buildings, in most circumstances short term stability will be the most critical. Therefore the Unconsolidated Undrained Tests will be use in the determination of total shear strength parameters of cohesive soil. The specimen is subjected to a confining pressure by compression of the fluid in the chamber. (Air is sometimes used as a compression medium). To cause shear failure in the specimen, one must apply axial stress through a vertical loading ram (sometimes called deviator stress). This stress can be applied in one or two ways: 1. Application of dead weights or hydraulic pressure is equal increments until the specimen fails. (Axial deformation of the specimen resulting from the load applied through the ram is measured by a dial gauge.) 2. Application of axial deformation at a constant rate by means of a geared or hydraulic loading press. This is strain-controlled test. The axial load applied by the loading ram corresponding to a given axial deformation is measured by a proving ring or load cell attached to the ram.
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The undrained tests can also be used to determine the total (or undrained) strength parameters cu, fu. In this method ,compressive strength of soil are determined in term of total stress which resulting of the strength is depends on the pressure in the fluid during the loading. If the specimen 100% saturated,consolidation will not occur when the confining pressure applied during the shear portion because drainage is not permitted. The unconsolidated undrained traixial strength is applicable when the load are asssumed to take rapidly in sufficient time for the induced pore pressure to dissipate and consolidation occur during loading period. The error occurs during the experiment are: The specimen prepared not perfectly straight from the site (disturbed) which this can affect the shear strength and moisture content. Some mistakes in handling the load and setting up the specimen.
There are three different cell pressure applied in our experiment which are 50 KN/m2, 100 KN/m2 and 150 KN/m2.
The Mohr’s circle envelope is obtained throughout the graph of stress (kPa) against strain (%). For cohesive soil, the value of C which is the y-intercept of the graph cannot be equal to 0; as 0 is for non-cohesive soil. Non-Cohesive
Cohesive
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8.0
CONCLUSION As a conclusion, the value of shear strength parameter is obtained from this experiment. So the objective, which is to establish a procedure for determining the Unconsolidated Undrained Test by Triaxial Compression without measurement of pore pressure, which gives the shear strength of cohesive soil, is achieved. The value that we get is
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