Engineering and Construction: Shear Box - Lab Report Example

Lab Report, Engineering and Construction: Shear box The aim of this experiment was to ascertain the maximum shear stress, which can be applied to any given soil sample in a given direction. The shear stress defines the soils shear strength. We plotted shear stress against normal effective stress and the horizontal displacement separately. Then the vertical displacement was plotted against a horizontal displacement. In this study, the major findings were that a soil sample has its associated soil an apparent cohesion of 15, and a shearing resistance of 34 degrees. Introduction In soil mechanics, the term shear strength describes the magnitude of a shear stress that the soil can sustain (Roscoe 34). On the other hand, shear resistance of a soil occurs as a result of interlocking of particles and particle friction and possibly the bonding or cementation at particle contacts (Roscoe 45). Particle interlocking may cause a material to contact or expand in volume because of being subjected to shear strain (Poulos 560). As soil expands in volume, the density of its particles decreases causing its strength to decrease. This way, the peak strength is followed by the reduction in shear stress. It is always important to understand different values of Shear Strength of a soil sample (Schofield 20). This is because materials differ in their characteristics and tend respond differently when subjected to similar or different load conditions. This means that for one to design a project, he/she must understand the type of soil considering their variations in Shear Strength.In soil mechanics, Shear Strength is given by the formula ?f = c + ?n tan?----------------------------------------------------------------------------(1) c stands for cohesion, ? as an effective normal stress, ? as the angle of friction, ?f as the shear strength, and the shear box test, is defined by BS 1337: This experiment deals with shear resistance of a soil sample. The aim was to use a direct shear box test and a granular soil sample to determine its volumetric displacement and its shear resistance. In this case, a square prism of soil was laterally restrained and sheared along a mechanically induced horizontal plane while subjected to a pressure applied normal to that plane. The shearing resistance offered by the soil as one portion was made to slide on the other and measured at regular intervals of displacement. It was noted that failure occurred whenever the shearing resistance reached the maximum value that the soil could sustain. After obtaining the Shear strength it was plotted against horizontal displacement and on a separate graph, it was plotted against normal effective stress. The vertical displacement was also plotted against the horizontal displacement. Relevant calculation and interpretation were made and compared for purposes of making inference. Procedure In this experimental set up the first step entailed assembling the empty shear box without an upper and loading platens. In doing this, the two halves had to be screwed together. Screws marked “L” were in position as this was done. While ensuring that the apparatus move freely on the runners of the shear box, the box was filled with sand, which was then leveled off approximately 1 mm below the top of this box. The top platen was then placed on the sand. The platen was loaded on the top platen. The ball bearing was put in place. The hanger was then placed on the ball bearing and the weight was added on this hanger. The apparatus were adjusted to take up slack followed by reducing the proving ring dial gauge to zero. The two screws that held the lower and upper halves of the bow together were removed and screwed in those screws, which were marked “L”. After resistance was felt, each was adjusted further in ensuring the two halves get slightly separated. The motor was switched on and the maximum reading recorded on a proving ring dial gauge. The hallmark of the experiment when the circuit was switched off followed by slackening off the apparatus. The box was dismantled entirely and all the sand poured back into the container. The test was repeated three times while increasing the mass on a hanger. Results were recorded on the attached sheet. Results of the experiment This experimental sets four test were conducted. The first part involved measuring the normal load. Next was to conduct the first test. Appendix A: Tables 01, 02, 03, and 04 shows the experimental results obtained in this experiment. Results obtained in this experiment were plotted in Graph 1, 2 and 3 as shown in figure 01, figure 02, and figure 03 Figure 01: Shear Stress (KN/m) against horizontal displacement (mm). Figure 02: Vertical Disp. (mm) against horizontal displacement (mm). Figure 03 Calculations Graph: y=mx+c y=0.9x+15 Gradient = 1.0 Intercept (apparent cohesion, c) = 15 ? (angle of shearing resistance)= 34o Test 1: Shear Stress: ?f = c + ?n tan? = 13 + 40.88 x tan34o = 37.54 Test 2: Shear Stress: ?f = c + ?n tan? = 15 + 68.15 x tan34o = 57.25 Test 3: Shear Stress: ?f = c + ?n tan? = 15 + 95.38 x tan34o = 74.97 Test 4: Shear Stress: ?f = c + ?n tan? = 15 + 122.63 x tan34o = 92.66 Discussion Results obtained in this experiment show that that soil that was tested has the ability to withstand shear stress. This is because of having interlocking particles which are responsible for friction. The soil composition was the key property of soil which was involved in interlocking and maximizing friction. This contributed towards increased property of the soil sample to with stand shear stress. In the soil sample, parameters that played a vital role include the shape of the particles, and the size of the grain. Graph 01 clearly shows that as far as this experiment is concerned, the tests’ highest shear strength high. Figure 02 show that at the beginning of this experiment, the horizontal displacement increases. However, this is not the case with vertical displacement as it remained unchanged. But after the soil sample displaced 1mm along the horizontal displacement, there was change in the vertical displacement. Both the vertical and horizontal displacement started increasing steadily in tests 1, 2 and 4. Worth noting is the fact that the rate of displacement was not constant. This may have been caused by varying soil composition and the increasingly changing density of the soil particles. This rate may be faster than for the rest of the sample. In effect, this may have led to fluctuation in the rate of displacement. This experiment indicated that granular soils have a high shear stress. From this experiment, it became clear that shear stress can be increased or reduced to suite any circumstances. Conclusion In conclusion, the aim of the experiment which was to test the granular soil sample with a view to determine its volumetric displacement and shear resistance with the use of a shear box was achieved. The experiment showed that the angle of shear was equal to 34 degrees, the apparent cohesion for the soil was 15 the values for shear stress for tests1, 2, 3 and 4 were 37.54, 57.25, 74.97, and 92.66 It was important for me as an engineer to understand how to find shear strength of a soil sample. However, further tests need to be carried out in order to ascertain the strength of soil as stated in BS 1377-7.They are determination of residual strength using the small ring, determination of the unconfined compressive strength and determination of the undrained shear strength in triaxial compression without measurement of pore pressure. Work Cited Poulos, Sophie. "The Steady State of Deformation", Journal of Geotechnical Engineering 107 (GT5): 2001: 554–562 Roscoe, Schofield, "On the Yielding of Soils", Geotechnique; 1999; 8: 22–53  Schofield, Hump, "The Mohr-Coulomb Error", in Luong, Mechanics and Geotechnique (LMS Ecole Polytechnique): 1998: 19–27 Appendix A Table 1: Test1 Normal Load (kg) = 15, Normal Load (N)= 150 Effective Normal stress (kN/m2) = Horizontal Disp. (mm) Vertical Disp. (mm) Proving Ring Reading Load = Proving Ring Reading x Constant (N) Shear Stress = Load x 10-3 / Area (kN/m2) 0 0 0 0 -11.33333333 0.2 0 126 73.71 725.7666667 0.4 0.01 180 105.3 1041.666667 0.6 0.04 222 129.87 1287.366667 0.8 0.1 238 139.23 1380.966667 1 0.16 225 131.625 1304.916667 1.2 0.23 259 151.515 1503.816667 1.4 0.3 265 155.025 1538.916667 1.6 0.38 247 144.495 1433.616667 1.8 0.44 246 143.91 1427.766667 2 0.51 243 142.155 1410.216667 2.2 0.58 247 144.495 1433.616667 2.4 0.64 245 143.325 1421.916667 2.6 0.74 244 142.74 1416.066667 2.8 0.76 227 132.795 1316.616667 3 0.81 228 133.38 1322.466667 3.2 0.85 224 131.04 1299.066667 3.4 0.9 217 126.945 1258.116667 3.6 0.94 220 128.7 1275.666667 3.8 0.97 221 129.285 1281.516667 4 1.01 209 122.265 1211.316667 4.2 1.05 203 118.755 1176.216667 4.4 1.08 200 117 1158.666667 4.6 1.1 197 115.245 1141.116667 4.8 1.13 195 114.075 1129.416667 5 1.16 195 114.075 1129.416667 Appendix A Table 2: Test1 Normal Load (kg) = 25, Normal Load (N)= 250 Effective Normal stress (kN/m2) = Horizontal Disp. (mm) Vertical Disp. (mm) Proving Ring Reading Load = Proving Ring Reading x Constant (N) Shear Stress = Load x 10-3 / Area (kN/m2) 0 0 0 0 -11.33333333 0.2 0.01 122 71.37 702.3666667 0.4 0 218 127.53 1263.966667 0.6 0.01 288 168.48 1673.466667 0.8 0.03 345 201.825 2006.916667 1 0.08 289 169.065 1679.316667 1.2 0.12 415 242.775 2416.416667 1.4 0.19 435 254.475 2533.416667 1.6 0.25 445 260.325 2591.916667 1.8 0.32 443 259.155 2580.216667 2 0.39 447 261.495 2603.616667 2.2 0.47 444 259.74 2586.066667 2.4 0.54 440 257.4 2562.666667 2.6 0.61 435 254.475 2533.416667 2.8 0.68 432 252.72 2515.866667 3 0.74 427 249.795 2486.616667 3.2 0.8 429 250.965 2498.316667 3.4 0.86 410 239.85 2387.166667 3.6 0.92 407 238.095 2369.616667 3.8 0.97 394 230.49 2293.566667 4 1.02 398 232.83 2316.966667 4.2 1.08 388 226.98 2258.466667 4.4 1.12 374 218.79 2176.566667 4.6 1.17 369 215.865 2147.316667 4.8 1.21 355 207.675 2065.416667 5 1.25 338 197.73 1965.966667 Appendix A Table 1: Test3 Normal Load (kg) = 35, Normal Load (N)= 350 Effective Normal stress (kN/m2) = Horizontal Disp. (mm) Vertical Disp. (mm) Proving Ring Reading Load = Proving Ring Reading x Constant (N) Shear Stress = Load x 10-3 / Area (kN/m2) 0 0 0 0 -11.33333333 0.2 0 140 81.9 807.6666667 0.4 0 299 174.915 1737.816667 0.6 0.02 420 245.7 2445.666667 0.8 0.05 488 285.48 2843.466667 1 0.1 526 307.71 3065.766667 1.2 0.14 547 319.995 3188.616667 1.4 0.2 559 327.015 3258.816667 1.6 0.26 572 334.62 3334.866667 1.8 0.32 590 345.15 3440.166667 2 0.39 588 343.98 3428.466667 2.2 0.46 531 310.635 3095.016667 2.4 0.51 561 328.185 3270.516667 2.6 0.57 564 329.94 3288.066667 2.8 0.64 557 325.845 3247.116667 3 0.69 567 331.695 3305.616667 3.2 0.75 570 333.45 3323.166667 3.4 0.82 560 327.6 3264.666667 3.6 0.88 551 322.335 3212.016667 3.8 0.93 527 308.295 3071.616667 4 0.97 514 300.69 2995.566667 4.2 1.02 488 285.48 2843.466667 4.4 1.05 481 281.385 2802.516667 4.6 1.09 478 279.63 2784.966667 4.8 1.12 468 273.78 2726.466667 5 1.15 470 274.95 2738.166667 Appendix A Table 1: Test4 Normal Load (kg) = 45, Normal Load (N)= 450 Effective Normal stress (kN/m2) = Horizontal Disp. (mm) Vertical Disp. (mm) Proving Ring Reading Load = Proving Ring Reading x Constant (N) Shear Stress = Load x 10-3 / Area (kN/m2) 0 0 0 0 -11.33333333 0.2 0 179 104.715 1035.816667 0.4 0 312 182.52 1813.866667 0.6 0 381 222.885 2217.516667 0.8 0.01 445 260.325 2591.916667 1 0.04 523 305.955 3048.216667 1.2 0.08 608 355.68 3545.466667 1.4 0.13 658 384.93 3837.966667 1.6 0.2 689 403.065 4019.316667 1.8 0.26 710 415.35 4142.166667 2 0.32 714 417.69 4165.566667 2.2 0.39 733 428.805 4276.716667 2.4 0.47 739 432.315 4311.816667 2.6 0.53 729 426.465 4253.316667 2.8 0.59 732 428.22 4270.866667 3 0.66 749 438.165 4370.316667 3.2 0.74 750 438.75 4376.166667 3.4 0.8 740 432.9 4317.666667 3.6 0.85 700 409.5 4083.666667 3.8 0.91 690 403.65 4025.166667 4 0.96 698 408.33 4071.966667 4.2 1.02 691 404.235 4031.016667 4.4 1.07 676 395.46 3943.266667 4.6 1.12 661 386.685 3855.516667 4.8 1.16 636 372.06 3709.266667 5 1.2 592 346.32 3451.866667 Read More