Determination of Compressive Strength by the Immediate Untrained Tori Axial Test - Lab Report Example

Name Course Date Tutor Determination of compressive strength by the immediate undrained triaxial test The triaxial test is done in a cell and it allows water to flow in or out of the sample in a controlled manner (Fang, 1997). Therefore, it can used to measure the undrained and drained shear strength of test samples. The angle of shearing resistance of the soil and the apparent cohesion are obtained by measuring the minimum and maximum stresses at failure. This is done by increasing the axial and vertical stress until the sample fails depending on different axial and lateral stress. The drainage condition of a sample will affect the results. The drainage is prevented in undrained test (Fang, 1997; Preene, 2012). Aparatus (a) Constant rate of strain compression testing machine (set at 1.5mm per minute) (b) Triaxial cell for 38mm diameter samples complete with solid end caps, rubber sheaths and O-rings (c) Extruding apparatus, sample former and sheath expander (d) Moisture content tins Triaxial cell and the arrangement of triaxial cell in load frame Method The experiment began with preparation of three 38 mm diameter samples. The rubber sheath was then fitted over the sample using sheath expander. The rubber sheath was secured by placing O-rings in the required position. The cell cover was then placed, before adjusting the machine until cell plunge id closed to the top platen and the cell was filled with water until it escape through the cell bleed valve, which is also closed and the cell pressure was increased to 138kN/m2. The motor drive was engaged and the machine was run until the proving ring dial starts to move. The machine was stopped, the strain dial gauge set to zero, and the stress dial gauge se to 2 divisions. The motor was started and the stress dial gauge was recorded at an interval of 0.50 mm strain until it fails. It is assumed that failure has occurred if there is no decrease for three consecutive reading. Before winding up the experiment, motor was stopped, the cell pressure released, bleed valve opened, and water was allowed to drained from the cell and finally emptying the cell. Also, the sample was removed, the failure sketched, and moisture content determined. The test was also done on the other two samples with lateral pressure of 276 and 414 kN/m2. Calculations and results Undrained triaxial test on soil Test 1 Test 2 Test 3 Rate of strain (mm/min) 1.5 1.5 1.5 Cell pressure (kN/m2) 138 276 414 Proving ring factor (kN/div) 0.00121 0.000719 0.00121 1. The moisture content for the samples Test Number Tin Number Tin weight Wet +Tin Dry + Tin 1 39 15.47 199.15 173.64 2 49 10.19 190.26 165.08 3 98 25.88 208.43 183.94 Container number 39 49 98 Mass of wet soil +container (m2) g 199.15g 190.26g 208.43g Mass of dry soil +container (m3) g 173.64g 165.08 183.94g Mass of the container (m1) 15.47g 10.19g 25.88g Mass of moisture (m2-m3) g 25.51g 25.18g 24.49g Mass of dry soil (m3-m1) g 158.17g 154.89g 158.06g Moisture content, 16.13% 16.26% 15.49% 2. Deviator stress = 1st Deviator stress = 2nd Deviator stress =etc The table showing the deviator stress is shown below Test 1 Strain (%) Strain (dia. 0.002mm) Stress (dia. 0.002mm) Load (kN) Area (mm2) Deviator stress (kN/m2) 0 0 0 0 1133 0 50 25 7.8571E-11 1141 26.5118317 100 35 1.1E-10 1149 36.8581375 150 40 1.2571E-10 1157 41.832325 4 200 52 1.6343E-10 1164 54.0549828 250 57 1.7914E-10 1172 58.8481229 300 62 1.9486E-10 1181 63.5224386 6 350 65 2.0429E-10 1189 66.1480235 400 69 2.1686E-10 1197 69.7493734 450 72 2.2629E-10 1206 72.238806 8 500 75 2.3571E-10 1214 74.752883 550 78 2.4514E-10 1223 77.1708913 600 80 2.5143E-10 1232 78.5714286 10 650 82 2.5771E-10 1241 79.9516519 700 85 2.6714E-10 1250 82.28 750 88 2.7657E-10 1259 84.5750596 12 800 88 2.7657E-10 1269 83.9085894 850 90 2.8286E-10 1278 85.2112676 900 92 2.8914E-10 1288 86.4285714 14 950 95 2.9857E-10 1298 88.559322 1000 96 3.0171E-10 1308 88.8073394 1050 97 3.0486E-10 1318 89.0515933 16 1100 98 3.08E-10 1328 89.2921687 1150 100 3.1429E-10 1339 90.3659447 1200 103 3.2371E-10 1350 92.3185185 18 1250 105 3.3E-10 1360 93.4191176 1300 107 3.3629E-10 1371 94.4347192 1350 108 3.3943E-10 1382 94.5586107 20 1400 110 3.4571E-10 1394 95.4806313 1450 111 3.4886E-10 1405 95.594306 1500 113 3.5514E-10 1417 96.49259 Test 2 Strain (%) Strain (dia. 0.002mm) Stress (dia. 0.002mm) Load (kN) Area (mm2) Deviator stress (kN/m2) 0 0 0 0 1133 0 50 82 2.5771E-10 1141 51.6722174 100 95 2.9857E-10 1149 59.4473455 150 103 3.2371E-10 1157 64.0077787 4 200 110 3.4571E-10 1164 67.9467354 250 115 3.6143E-10 1172 70.5503413 300 121 3.8029E-10 1181 73.6655377 6 350 126 3.96E-10 1189 76.1934399 400 131 4.1171E-10 1197 78.6875522 450 136 4.2743E-10 1206 81.0812604 8 500 140 4.4E-10 1214 82.9159802 550 144 4.5257E-10 1223 84.6573998 600 147 4.62E-10 1232 85.7897727 10 650 150 4.7143E-10 1241 86.9057212 700 153 4.8086E-10 1250 88.0056 750 156 4.9029E-10 1259 89.0897538 12 800 159 4.9971E-10 1269 90.0874704 850 161 5.06E-10 1278 90.5782473 900 163 5.1229E-10 1288 90.9914596 14 950 166 5.2171E-10 1298 91.9522342 1000 169 5.3114E-10 1308 92.898318 1050 172 5.4057E-10 1318 93.8300455 16 1100 174 5.4686E-10 1328 94.2063253 1150 176 5.5314E-10 1339 94.506348 1200 177 5.5629E-10 1350 94.2688889 18 1250 178 5.5943E-10 1360 94.1044118 1300 182 5.72E-10 1371 95.4471189 1350 186 5.8457E-10 1382 96.7684515 20 1400 191 6.0029E-10 1394 98.5143472 1450 192 6.0343E-10 1405 98.2548043 1500 193 6.0657E-10 1417 97.9301341 A graph of deviator stress against the strain Test 3 Strain (%) Strain (dia. 0.002mm) Stress (dia. 0.002mm) Load (kN) Area (mm2) Deviator stress (kN/m2) 0 0 0 0 1133 0 50 37 1.1629E-10 1141 39.237511 100 45 1.4143E-10 1149 47.3890339 150 52 1.6343E-10 1157 54.3820225 4 200 56 1.76E-10 1164 58.2130584 250 60 1.8857E-10 1172 61.9453925 300 63 1.98E-10 1181 64.5469941 6 350 67 2.1057E-10 1189 68.1833474 400 70 2.2E-10 1197 70.7602339 450 72 2.2629E-10 1206 72.238806 8 500 74 2.3257E-10 1214 73.7561779 550 76 2.3886E-10 1223 75.1921504 600 79 2.4829E-10 1232 77.5892857 10 650 81 2.5457E-10 1241 78.9766317 700 83 2.6086E-10 1250 80.344 750 86 2.7029E-10 1259 82.6528991 12 800 87 2.7343E-10 1269 82.9550827 850 90 2.8286E-10 1278 85.2112676 900 92 2.8914E-10 1288 86.4285714 14 950 95 2.9857E-10 1298 88.559322 1000 99 3.1114E-10 1308 91.5825688 1050 102 3.2057E-10 1318 93.6418816 16 1100 104 3.2686E-10 1328 94.7590361 1150 106 3.3314E-10 1339 95.7879014 1200 107 3.3629E-10 1350 95.9037037 18 1250   0 1360 0 1300 110 3.4571E-10 1371 97.0824216 1350 111 3.4886E-10 1382 97.1852388 20 1400 112 3.52E-10 1394 97.2166428 1450 114 3.5829E-10 1405 98.1779359 1500 115 3.6143E-10 1417 98.2004234 Discusion Compared to shear box test that provides stresses failure plane, triaxial test provides the strength in terms of the principal stresses. Mohr envelope for the soil sample comprises of a shear diagram and is determined from triaxial compression test. Mohr cycle rupture is Mohr cycle that is tangential to the shear strength line (Fang, 1997; Preene, 2012). The results from Mohr circle stress transformation is used to relate the strengths from the tests. The construction of morh circle is important in soil mechanics beacuse enables approximation of different practical situations as plane starin problems. Mohr circle also enables determination of stresses acting on a plane and a given point, given the stresses are acting normally on the plane ar principal stresses. The cohesionless soil sample produces a Mohr envelope that passes through the origin (Preene, 2012). The undrained strength on confining stress is independent because an increase in pressure in the cell without allowing drainage affects the rising pore pressure by the same amount. Therefore, the effective stress remains unchanged and the subsequent strength remains unaffected because the effective stresses determine the behavior of the soil. The change in pore pressure during the shearing is due to the moisture content and the initial effective stress. In the experiment the change in pressure is similar for the samples. Constant moisture content produces constant strength. Other factors that can affect the shear strength of the geological sample are the strata continuity, spatial variability and error in estimation (Preene, 2012). Conclusion The main objective of a triaxial test was to determine the Mohr envelope for the soil sample, from which the cohesion and angle shearing resistance can be established from the envelope. Soil sample with zero cohesion the Mohr envelope passes through the origin. Mohr envelope comprises of a shear diagram and which in most case is a straight line. Mohr cycle rupture is Mohr cycle that is tangential to the shear strength line. References Fang, H. -Y., 1997. Foundation engineering handbook. New Delhi: CBS Publishers & Distributors. Preene M., 2012. Groundwater Lowering in Construction: A Practical Guide to Dewatering, Volume 6 of Applied geotechnics, 2nd ed, CRC Press, Read More