CVE20004

UNCONSOLIDATED UNDRAINED TRIAXIAL TEST

ASSIGNMENT NUMBER :4

CREATED BY : HARINDER SINGH REHAL

STUDENT ID NO :

Due date : 16/10/2015

Introduction

CVE20004

In unconsolidated undrained test sample is not to drain . The sample is compressed at a different rate . the UU test is applicable to undisturbed sample in which no change in moisture content from out site can be permitted . test can be carried out over a range of moisture content to enable Mohr envelopes for the required to be interpolated . UU test procedure is useful for determining the total strength parameter for soils that have suffered disturbances or moisture change during sampling .

Aim To study the shear strength behaviour of a clay type soil using the triaxial apparatus under undrained conditions using a multi-stage testing approach.

Procedure Familiarise yourself with the mechanics of the triaxial testing apparatus. Record the details of the clay sample – (dimensions and wet mass in order to

determine the wet density). Set up the sample for testing: Place the cylindrical clay sample on the bottom plate

of the triaxial apparatus and cover with the top loading plate. Then fit the rubber membrane over the sample (and top loading plate). Use o-rings to seal each end of the sample and then position the triaxial cell and loading ram over the sample. Flood the cell with water, maintaining a small amount of air in the top of the cell to enable pressurisation.

Apply the cell pressure (σ3): Once the triaxial cell is near full of water, apply the cell pressure (or confining stress) by simply releasing pressurised air into triaxial cell – 100 kPa for the first stage of the test.

Apply the deviator stress (σ1 – σ3): Start the axial loading motor and record the load ring readings for each 0.75 mm of vertical displacement, or for every 1% strain of the sample. Continue the test until the sample fails (the corrected deviator stress reaches a maximum value).

Increase the cell pressure to 200 kPa to allow the sample to fail again (i.e. multi-stage testing). Once the sample fails under the increased cell pressure.

Repeat step 6 for a further increase in cell pressure to 400 kPa. Remove the sample at the end of the test and observe the failure mechanism of the

soil sample. Sketch the failed sample – noting any shear planes or bulging present. Try to measure / estimate the angle of the shear plane at failure.

Determine the moisture content, wet density and dry density of the soil sample.

CVE20004

A description of the sample – in accordance with the terminology used in AS1726

Based on AS1726 sample is Dark brown , moist , firm , med high with plasticity clay .

Data Table

Longitudinal Strain vs. Corrected Deviator Stress for Multi-Stage Testing

Cell Pressure

(kPa)

Longitudinal Deformation

( x 0.01 mm) and

Longitudinal Strain (%) of

sample

Deviator Stress

Calibration and

Correction Factor

Stage No. 1(Cell Pressure = 100

kPa)

Stage No. 2(Cell Pressure = 200

kPa)

Stage No. 3(Cell Pressure = 400

kPa)

Load Ring Readings (Divisions)

Corrected Deviator Stress (kPa)

Load Ring Readings (Divisions)

Corrected Deviator Stress (kPa)

Load Ring Readings (Divisions)

Corrected Deviator Stress (kPa)

100 0 0 4.40 0 0 0 0 0 075 1% 4.385 10 38.67150 2% 4.370 16 61.66225 3% 4.356 18 69.14300 4% 4.341 17 65.07375 5% .4.326 20 76.3450 6% 4.311 23 87.43525 7% 4.296 24 90.92600 8% 4.281 25 94.4675 9% 4.267 26 97.83750 10% 4.252 32 119.99825 11% 4.237 34 127.35900 12% 4.222 36 134.03975 13% 4.207 36 133.561050 14% 4.193 37 136.811125 15% 4.178 37 136.321200 16% 4.163 37.5 137.661275 17% 4.148 38 1391350 18% 4.133 38 138.491425 19% 4.119 39 141.651500 20% 4.104 39 141.141575 21% 4.089 39 140.621650 22% 4.074 39 140.111725 23% 4.0601800 24% 4.004

Graph shows the relationship between corrected deviator stress vs longitudinal stress .

CVE20004

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

stage 1- 100Kpa

38.67

61.66

69.14

65.07

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

stage 2- 200 KPa

NaN

NaN

NaN

NaN

76.3

87.43

90.92

94.4

97.83

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

stage 3- 440 KPa

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

NaN

119.99

127.35

134.03

133.56

136.81

137.66

139 138.49

141.65

141.14

140.62

140.11

NaN

NaN

NaN

1030507090

110130150

Corrected Deviator Stress Vs. Logitudinal StressCo

rre

cte

d D

ev

iato

r s

tre

ss (

KP

a)

CVE20004

Result

Sample NO : Stress 3^1 Stress 1-Stress 3 Stress 1^11 100 69.14 169.142 200 97.83 297.833 300 141.66 541.66

Discussion / conclusion

Value for C = 20 kpa, Value for Ø = 7.5 degree following equation been produced to check the result of Mohr circles of each stage f = 20 + Stress (n) tan7.5°.ꭍ

The experiment reaches the aim which was to study the shear strength behaviour of a clay using unconsolidated undrained triaxle test.

Hand plotting of cell pressure and deviator stress shows the failure point of all 3 stress and result being calculated as Value for C = 20 kpa. Three different test been conducted to find failure stress using different normal stress. After all plotting line of best been drawn tangent to circle to find out the failure stress and result represents that failure stress occurred only at 400 Kpa and 200 kpa .

From the graph can be seen that corrected deviator stress vs longitudinal stress are both linear and nonlinear however as longitudinal stress increases so does corrected deviator stress increases too .

Mohr circle failure graph been drawn on the 2 different scales Horizontal scale is 1:50 and vertical scale is : 1:10.