1

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.

2

4.0 APPARATUS

Soil sampling

NO

ITEMS

1 Sampling tube

2 Sample extruder

3 Wire saw

4 Automatic balance

5 Callipers

3

Soil testing

NO

ITEMS FIGURE

1 Rubber membrane

2 Membrane stretcher

3 o-ring seal

5.0 PROCEDURES

SAMPLE PREPARATION

4

SAMPLE TESTING

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.

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.

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.

The triaxial cell chamber (with the specimen inside) is place on the platform of the compression machine.

5

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.

6

The specimen is carefully removed and all apparatus are disassembled. The specimen condition is examined and the final weight is determined.

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 8.86 0 0.001134 25.5 02 8.94 0.11 0.001135249 54 25.13 9.07 0.28 0.001137184 68 37.374 9.2 0.45 0.001139126 77.5 45.655 9.33 0.62 0.001141075 84.5 51.26 9.46 0.79 0.00114303 91.5 57.247 9.6 0.97 0.001145108 96 61.068 9.73 1.14 0.001147077 101 65.319 9.87 1.33 0.001149285 103 66.93

10 10.01 1.51 0.001151386 105.5 68.611 10.14 1.68 0.001153377 110 72.3812 10.28 1.87 0.00115561 112.5 74.413 10.42 2.05 0.001157734 112.5 74.2614 10.56 2.24 0.001159984 115 76.2815 10.7 2.42 0.001162123 117 77.8516 10.84 2.61 0.001164391 119.5 79.617 10.98 2.79 0.001166547 122 81.5918 11.12 2.97 0.001168711 124 83.1419 11.26 3.16 0.001171004 126 85.1220 11.4 3.34 0.001173184 129 87.0921 11.54 3.53 0.001175495 133.5 90.3722 11.68 3.71 0.001177692 136 92.3223 11.82 3.89 0.001179898 138.5 94.2624 11.95 4.07 0.001182112 140.5 95.7825 12.09 4.25 0.001184334 143 97.726 12.23 4.43 0.001186565 147.5 101.327 12.36 4.61 0.001188804 150 102.93

7

28 12.49 4.78 0.001190926 152.5 104.8829 12.63 4.96 0.001193182 152.5 104.6830 12.76 5.13 0.00119532 152.5 104.4831 12.76 5.17 0.001195824 154.5 106.11

STAGE 2

No Strain(mm)

Strain (%)

Area(mm)

Load(N)

Dev stress(kPa)

1 12.83 0 0.001134 131.5 02 12.94 0.14 0.00113559 161.5 26.413 13.07 0.32 0.00113764 166.5 30.764 13.21 0.5 0.001139698 169 32.45 13.33 0.66 0.001141534 171 34.16 13.47 0.84 0.001143606 173.5 36.227 13.6 1.01 0.00114557 176 38.348 13.73 1.18 0.001147541 178 40.029 13.86 1.36 0.001149635 178 39.95

10 13.99 1.53 0.00115162 180.2 41.6711 14.12 1.7 0.001153611 183 43.7612 14.25 1.87 0.00115561 185 43.6913 14.38 2.04 0.001157615 187.5 45.3414 14.52 2.22 0.001159746 187.5 47.415 14.65 2.39 0.001161766 187.5 47.3216 14.78 2.57 0.001163913 187.5 46.9917 14.91 2.74 0.001165947 187.5 46.918 15.04 2.91 0.001167988 190 48.9619 15.18 3.09 0.001170158 187.5 46.7320 15.31 3.26 0.001172214 190 48.7721 15.45 3.45 0.001174521 187.5 46.5522 15.58 3.62 0.001176593 190 48.2223 15.72 3.8 0.001178794 187.5 4624 15.86 3.99 0.001181127 187.5 45.9125 16 4.17 0.001183346 190 47.9326 16.13 4.34 0.001185448 187.5 45.7327 16.27 4.53 0.001187808 190 47.528 16.41 4.71 0.001190051 190 47.429 16.55 4.89 0.001192304 194.5 51.0830 16.69 5.08 0.00119469 199 54.7431 16.72 5.12 0.001195194 199 54.72

8

STAGE 3

No Strain(mm)

Strain (%)

Area(mm)

Load(N)

Dev stress(kPa)

1 16.76 0 0.001134 171 02 16.85 0.12 0.001135362 208.5 33.033 16.99 0.3 0.001137412 211 35.164 17.12 0.47 0.001139355 215.5 39.055 17.26 0.66 0.001141534 220.5 42.866 17.39 0.83 0.001143491 222.5 44.537 17.53 1.01 0.00114557 227.5 48.818 17.66 1.18 0.001147541 229.5 50.479 17.8 1.37 0.001149752 232 52.55

10 17.93 1.54 0.001151737 234.5 54.2511 18.06 1.71 0.001153729 234.5 54.1612 18.19 1.88 0.001155728 237 56.2313 18.33 2.07 0.00115797 237 56.1214 18.46 2.24 0.001159984 239 57.7415 18.59 2.41 0.001162004 239 57.6416 18.72 2.58 0.001164032 241.5 59.4317 18.86 2.76 0.001166187 244 61.4618 18.99 2.93 0.001168229 244 61.3519 19.12 3.11 0.001170399 239 56.9720 19.25 3.28 0.001172457 241.5 5921 19.38 3.45 0.001174521 246 62.7322 19.51 3.62 0.001176593 246 62.2423 19.65 3.8 0.001178794 246 62.1224 19.78 3.97 0.001180881 248.5 64.1225 19.91 4.14 0.001182975 248.5 6426 20.04 4.32 0.001185201 246 61.7827 20.17 4.49 0.00118731 246 61.6628 20.31 4.67 0.001189552 244 59.6129 20.44 4.84 0.001191677 246 61.1830 20.58 5.03 0.001194061 244 59.3831 20.71 5.2 0.001196203 241.5 57.1832 20.84 5.37 0.001198351 241.5 57.0833 20.98 5.55 0.001200635 241.5 56.7134 21.12 5.74 0.001203055 239 54.5235 21.25 5.91 0.001205229 239 54.4236 21.39 6.09 0.001207539 237 52.6537 21.53 6.28 0.001209987 237 52.54

9

38 21.67 6.46 0.001212316 237 52.4439 21.81 6.64 0.001214653 237 52.0840 21.95 6.83 0.00121713 239 53.6141 22.08 7 0.001219355 239 53.5142 22.23 7.2 0.001221983 241.5 55.4443 22.37 7.38 0.001224358 241.5 55.3244 22.5 7.55 0.001226609 244 57.0145 22.64 7.74 0.001229135 246 58.5146 22.78 7.92 0.001231538 248.5 60.4247 22.91 8.09 0.001233816 253 63.9548 23.05 8.28 0.001236372 255.5 65.8449 23.18 8.45 0.001238667 258 67.7350 23.13 8.62 0.001240972 260 68.9651 23.45 8.8 0.001243421 260 68.8252 23.58 8.97 0.001245743 262.5 70.6953 23.71 9.14 0.001248074 262.5 70.5554 23.85 9.33 0.001250689 267 7455 23.98 9.5 0.001253039 267 73.8656 24.11 9.67 0.001255397 267 73.4657 24.25 9.86 0.001258043 269.5 75.2958 24.38 10.03 0.00126042 269.5 75.1459 24.41 10.07 0.001260981 269.5 75.11

Initial Condition Sample 1 Sample2 Sample 3

Dry unit weight kg/m3 623.72 678.36 646.49

Moisture content 29.56 23.49 27.46

Failure Conditions:

Cell pressure kN/m2 50 100 150

Deviator stress kN/m2 104.68 54.72 73.86

Axial Stress kN/m2 154.68 154.72 223.86

10

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 = πd2/4

=π (38)2/4

=0.001134m2

Area = Ao / (1- ε)

= (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

= 5.48 g

11

Moisture content = Moisture loss / Weight of dry soil × 100%

= 1.62 g / 5.48 g × 100%

= 29.56 %

MOHR CIRCLE GRAPH

12

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.

13

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

14

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

Cohesive

15