Soil Mechanics (Report; Shear Box) PDF

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Soil MechanicsPractical (Shear Box Test)ReportStudent: Fredy Sabu (18968721)Practical Day: Monday at 3pmTable of contents1. Objectives of lab2. Procedures3. Completed data sheets 10 and 114. Results from Tasks 2 to 55. Conclusion2. Procedures: We performed six tests in total which was split into 3 t...

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Soil Mechanics Practical (Shear Box Test) Report Student: Fredy Sabu (18968721) Practical Day: Monday at 3pm

Table of contents

1. Objectives of lab 2. Procedures 3. Completed data sheets 10 and 11 4. Results from Tasks 2 to 5

5. Conclusion

1. Objectives of Lab: We are required to determine the ultimate shear strength parameters of a sand using the shear box test. The test configuration forces the soil to fail on the horizontal plane between the two halves of the shear box.

If the sand is initially dense and the normal stress is low, the shear resistance rises to a peak and then drops to an ultimate value accompanied by an upwards vertical movement (i.e. volume increases). For an initially loose sand the shear resistance rises and asymptotes to the ultimate strength, and shearing is accompanied by a downward vertical movement (i.e. volume decreases). Thus, sands in different initial states, but at the same normal stress, tend towards the same ultimate value of shearing resistance. At the ultimate state no further volume change occurs and the samples have the same void ratio, called the critical void ratio. In the course of shearing a loose sample becomes more dense as it reaches the critical void ratio, and a dense sample becomes less dense as it approached the critical value The shear strength,  of a soil is often expressed by the empirical Mohr-Coulomb relation which may be written as:

  c  tan where,  = normal stress on failure plane c = cohesion of the soil  = angle of shearing resistance For the dry sand used in this experiment the values of c and  are the effective stress parameters c and  since the effective stresses are equal to the applied stresses as no pore water pressures are developed.

2. Procedures: 1. We performed six tests in total which was split into 3 test by each group. The three tests were assigned as loose and dense specimens at normal loads of 5, 25, and 50 kg. 2. Measured the mas and internal dimensions of the empty shear box. 3. For the initially dense sample, the sand was placed in the shear and was then compacted using 25 blows of the hammer provided. 4. Measured the depth of the sand in the shear box to calculate the volume of the sand. The cap was placed on the shear box to get an total weight with sand to determine the density of the compacted dense sand. 5. For the initially loose sample, the sand was carefully poured evenly and gently. By levelling the sand we then measured the depth of the sand in the shear box. Once measured the cap was placed to measure the weight and determine the density of the loose sand. 6. Once both loose and dense sand was weighted, they were transferred onto the loading frame at the appropriate loads of 5, 25, and 50 kg applied. 7. After switching on the motor, the shearing of the sample commenced. The readings were recorded for the vertical dial gauge and proving ring for every 0.25mm of the horizontal displacement in the datasheet 10. 8. Test was continued until a total displacement of 6mm was reached. These steps were repeated from steps 3-7 for the each normal loads.

3. Datasheets 10 and 11 Table 1: Datasheet 10 - Loose sample Test No. 1 Normal load, kg 5 Density of sample 0.0010836 (t/m3) Horizonta Prov. Vertical l Ring Displace Displace reading ment ment division (mm) (mm) 0.00 0 0 0.25 19 1 0.50 19 4.5 0.75 19 21 1.00 19 28 1.25 19 29 1.50 19 37 1.75 19 44.5 2.00 19 44.5 2.25 19 53 2.50 19 63 2.75 19 69 3.00 19 70 3.25 19 70 3.50 19 70 3.75 4.00 4.25 4.50

2 25 0.0011559

3 50 0.0010837

Prov. Ring reading division

Vertical Displace ment (mm)

Prov. Ring reading division

Vertical Displace ment (mm)

0 32 36 40 40 45 60 72 80 80 80 87 87 87 89 89 89 87 81

0 53.5 52.5 53.5 53.5 53.5 53.5 53.5 53.5 55 63 68 70 84 95 112 120.5 129.5 135

0 65 80 100 120 130 135 140 142 146 148 150 151 151 151 151 151

0 1 1 1 1 1 1.5 4.5 4.5 12 18 20.5 20.5 20.5 20.5 20.5 20.5

Calculations: Test No. 1- calculating density Mass of empty shear box = 2.14kg Mass of shear box + soil = 2.29kg Mass of soil = 2.29-2.14 = 0.15kg Volume of sample = (3600*38.45)10E-6 m 3 = 0.13842 m3 Density = Mass/ Volume = 0.15/ 0.13842 = 1.0837 kg/m3 Test No. 2- calculating density Mass of empty shear box = 2.14kg Mass of shear box + soil = 2.30kg Mass of soil = 2.30-2.14 = 0.16kg Volume of sample = (3600*38.45)10E-6 m 3 = 0.13842 m3 Density = Mass/ Volume = 0.16/ 0.13842 = 1.1559 kg/m3 Test No. 3- calculating density Mass of empty shear box = 2.14kg Mass of shear box + soil = 2.29kg Mass of soil = 2.29-2.14 = 0.15kg Volume of sample = (3600*38.45)10E-6 m 3 = 0.13842 m3 Density = Mass/ Volume = 0.15/ 0.13842 = 1.0837 kg/m3

Table 2: Datasheet 10 - Dense Sample Test No. 1 Normal load, kg 5 Density of sample 0.0010837 (t/m3) Vertical Horizonta Prov. l Ring Displace Displace reading ment ment division (mm) (mm) 0.00 0 0 0.25 9 1 0.50 9 1 0.75 11 1 1.00 11 1 1.25 11 1 1.50 15 2.95 1.75 20 2.9 2.00 22 1.5 2.25 23 1.5 2.50 28 1 2.75 29 4 3.00 29 11.5 3.25 29 21.5 3.50 29 37.0 3.75 29 53.0 4.00 29 59.0 4.25 29 66.0 4.50 29 69.2 4.75 29 61.5 5.00 28 79.0 5.25 28 79.0 5.50 28 85.0 5.75 28 86.0 6.00 28 86.0

2 25 0.0011559

3 50 0.0010837

Prov. Ring reading division

Vertical Displace ment (mm)

Prov. Ring reading division

Vertical Displace ment (mm)

0 38 41 43 42 45 60 70 72 81 83 85 86 85 85 85 84 84 83 82 81 81 81 81 80

0 1 1 1 1 0 1.5 6.5 7.0 7.0 7.0 7.0 6.0 0.5 2.0 8.0 15.0 16.5 18.6 20.0 32.0 36.0 36.0 41.5 43.0

0 57 64 65 70 70 91 118 138 141 145 149 150 151 152 152 152 151 150 150 149 149 149 148 149

0 1 1 0.5 0.5 0.5 0.7 0.5 0.8 0.6 0.7 0.7 6.0 11.0 23.0 29.0 34.5 39.5 44.0 45.0 50.0 52.5 52.5 53.0 55.0

Table 3: Datasheet 11 - Loose sample Test No 1 Normal stress ,σ 13.625 (kPa) Horizonta τ, shear Stress l stress ratio Displace (kPa) τ/ σ ment (mm) 0.00 0 0 0.25 13.19 0.968 0.50 13.19 0.968 0.75 13.19 0.968 1.00 13.19 0.968 1.25 13.19 0.968 1.50 13.19 0.968 1.75 13.19 0.968 2.00 13.19 0.968 2.25 13.19 0.968 2.50 13.19 0.968 2.75 13.19 0.968 3.00 13.19 0.968 3.25 3.50 3.75 4.00 4.25 4.50

2 68.125

3 136.25

τ, shear stress (kPa)

Stress ratio τ/ σ

τ, shear stress (kPa)

Stress ratio τ/ σ

0 22.22 25 27.77 27.77 31.25 41.67 50 55.56 55.56 55.56 60.42 60.42 60.42 61.80 61.80 61.11 60.42 56.42

0 0.326 0.368 0.408 0.408 0.460 0.613 0.735 0.817 0.817 0.817 0.888 0.888 0.888 0.908 0.908 0.898 0.888 0.827

0 45.13 55.56 69.44 83.33 90.28 93.75 97.22 98.61 101.38 102.78 104.17 104.86 104.86 104.86

0 0.332 0.409 0.511 0.613 0.664 0.689 0.715 0.725 0.745 0.756 0.766 0.771 0.771 0.771

Table 4: Datasheet 11 - Dense Sample Test No 1 Normal stress ,σ 13.625 (kPa) Horizonta τ, shear Stress l stress ratio Displace (kPa) τ/ σ ment (mm) 0.00 0 0 0.25 6.25 0.46 0.50 6.25 0.46 0.75 7.64 0.56 1.00 7.64 0.56 1.25 7.64 0.56 1.50 10.42 0.77 1.75 13.90 1.02 2.00 15.28 1.12 2.25 15.97 1.17 2.50 19.44 1.43 2.75 20.14 1.48 3.00 20.14 1.48 3.25 20.14 1.48 3.50 20.14 1.48 3.75 20.14 1.48 4.00 20.14 1.48 4.25 20.14 1.48 4.50 20.14 1.48 4.75 20.14 1.48 5.00 19.44 1.43 5.25 19.44 1.43 5.50 19.44 1.43 5.75 19.44 1.43 6.00 19.44 1.43

2 68.125

3 136.25

τ, shear stress (kPa)

Stress ratio τ/ σ

τ, shear stress (kPa)

Stress ratio τ/ σ

0 26.39 28.47 29.86 29.17 31.25 41.67 48.61 50.0 56.25 57.64 59.03 59.72 59.03 59.03 59.03 58.33 58.33 57.64 56.94 56.25 56.25 56.25 56.25 56.55

0 0.39 0.42 0.44 0.43 0.46 0.61 0.72 0.74 0.83 0.85 0.87 0.89 0.87 0.87 0.87 0.86 0.86 0.85 0.84 0.83 0.83 0.83 0.83 0.82

0 39.58 44.44 45.14 48.61 48.61 63.19 81.94 95.83 97.92 100.69 104.17 104.86 105.56 105.56 105.56 105.56 104.86 104.17 104.17 103.47 103.47 103.47 102.78 103.47

0 0.29 0.33 0.33 0.36 0.36 0.46 0.60 0.70 0.72 0.74 0.76 0.77 0.78 0.78 0.78 0.78 0.77 0.76 0.76 0.76 0.76 0.76 0.75 0.76

Stress ratio vs Horizontal Displacement (Dense Sample) 1.6 1.4 1.2

Stress Ratio

1 Test No.1 Test No.2 Test No.3

0.8 0.6 0.4 0.2 0 5 0.

0

1

5 1.

2

5 2.

3

5 3.

4

5 4.

5

5 5.

6

Horizontal Displacement (mm)

Results from tasks 2-5 (Graphs): Stress ratio vs Horizontal Displacement (Loose Sample) 1.2 1

Stress ratio

0.8 Test No.1 Test No.2 Test No.3

0.6 0.4 0.2 0

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 Horizontal Displacement (mm)

Graph 1: Loose Sample (Stress Ratio)

Graph 2: Dense Sample (Stress Ratio)

4. 4. 4. 4. 4. 4. 4. 4. 4. 4. 4. 4. 4. 4.

Horizontal Displacement vs Vertical Displacement - Loose Sample 160 140

Vertical displacement (mm)

120 100 Test No.1 Test No.2 Test No.3

80 60 40 20 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 Horizontal Displacement (mm)

Graph 3: Displacements (Loose Sample)

Horizontal Displacement vs Vertical Displacement - Dense Sample 100 90

Vertical Displacement (mm)

80 70 60 Test No.1 Test No.2 Test No.3

50 40 30 20 10 0

Horizontal Displacement (MM)

Graph 4: Displacements (Dense Sample)

Table 5:Normal Stress vs Ultimate Shear Stress Normal Stress, σ (kPa) 0 13.625 68.125 136.23

τult, ultimate shear stress (loose sand) (kPa) 0 13.19 60.42 104.86

τult, ultimate shear stress (dense sand) (kPa) 0 20.14 56.25 105.56

Ultimate Shear Stress vs Normal Stress 120 100

Normal Stress

80 Ultimate Shear Stress (Loose) Ultmate Shear Stress (Dense)

60 40 20 0 0

13.63

68.13

136.23

Ultimate Shear Stress (kPA)

Graph 5: Ultimate Shear Stress vs Normal Stress Ultimate shear strength parameters for sand: For loose soil sample; ɸ = tan-1 (104.85/136.25) = 37.5798 For dense soil sample; ɸ = tan-1 (105.56/136.26) = 37.7648

5. Conclusion: The experiment conducted determines the shear strength of the sand and its effects of density in soil on its strength. This was to prove that the failure strength on a surface that already been set. When conducting the experiment, came to the conclusion that the loose samples took an ample amount of time to settle before we finally got the readings. However, it was the opposite for the dense sample. To conclude all of this by doing the experiment we were able to say that theory is valid and this was proved by the results obtained which were really close....