Laboratory Report on California Bearing Ratio Test

Laboratory Report on California Bearing Ratio Test Summary California Bearing Ratio Test (CBR Test) is conducted in this laboratory. The test is to measure of soil shear strength relative to standard crushed stone material and performed for unbounded layers. Our group had done some safety precautions during laboratory, for example, reading the Lab Safety Regulation carefully and wearing gloves. After the test, moisture content (8.806%) of soil sample is determined and the data is used to plot the graph (Force against Penetration). As the curve is uniformly convex upwards, no correction is required. By comparing the CBR at 2.5mm (22.34%) and 5.0mm (21.14%) deformation, the design CBR is obtained, which is 22% (nearest to 1%) and we find that the type of soil is sandy gravel. Introduction This test is carried out to measure the pressure required to penetrate the soil sample with standard area plunger. Then we can determine the California Bearing Ratio (CBR) of a soil, which is obtained by measuring the force and penetration with a cylindrical plunger of cross-sectional area 1935mm2. The CBR rating is used to measure the load bearing capacity of soil, which is used for constructing the road. It can also be used to measure the load bearing capacity of unimproved airstrips or for soils under paved airstrips. The harder the surface is, the higher the CBR rating. The test should carry out on material by passing the 20mm BS test sieve. The test needs to choose the moisture content of the soil to indicate the design conditions for the test results. However, the moisture range has been investigated, water should be added as required to previously air dried soil in which soil aggregations greater than the 5mm BS test sieve have been broken down. Hence, mixing is important. The test uses the plunger to penetrate the soil sample at a rate of 1mm/min to a maximum depth of 7.5mm. The method of test is set out in B.S. 1377. The test applied an initial seating force to the plunger. Ignoring the seating force, the force at following penetrations are recorded and plotted on a curve. There are a standard curve was produced by the California originators of the tests which is testing on crushed limestone. The loads required producing penetration of 2.5mm and 5.0mm are expressed as percentages of standard loads of 13.24KN and 19.96KN respectively. Objective The test is to characterize the resistance of a given material to uniaxial penetration, and to measure the soil shear strength relative to standard crushed stone material. Procedure To perform this laboratory, the procedures are as follows: 1. Weight the mould body and the base plate 2. Divide the prepared soil into three portions approximately 3. Attach the extension collar to the mould to prevent the leakage of the soil during compacting it 4. Stand the mould assembly on the solid base 5. Place the first portion into the mould and compact it with 2.5kg rammer for 62 blows. The blows should be evenly distributed over the surface 6. Repeat step 5 with the left two portions of soil one by one 7. Remove the extension collar by C- spanner and trim the soil level to the top of the mould 8. Weight the mould with soil and base plate 9. Place the mould with soil at the central of the testing machine 10. Place the appropriate surcharge discs on top of the sample CBR Test Machine 11. Set zero to the reading of the force measurement device 12. Start the machine and record the readings of force measurement device for every 0.25mm penetration. The total penetration should not be larger than 7.5mm 13. Take out the soil by the Extruder 14. Weight the tin 15. Put soil sample into the tin and weight it 16. Put the tin into oven 17. Weight the dried sample with tin Results Curve of Penetration vs Load 6 5 Load(KN) 4 3 2 1 0 0.00 1.00 2.00 3.00 4.00 5.00 Penetration(mm) The graph is not required to make correction. Load at 2.5 mm penetration = 2.958kN Standard CBR at 2.5 mm = 13.24kN Load at 5.0 mm penetration = 4.2195kN Standard CBR at 5.0 mm = 19.96kN Final CBR = max (22.34%, 21.14%) = 22.34% = 22% (nearest 1%) The type of soil is sandy gravel. 6.00 7.00 8.00 9.00 Discussion Discussion of Result Comparision of Penetration/Force on Plunger among Different Groups 8 7 Force (kN) 6 5 4 our group Group A 3 Group B 2 1 0 0.00 2.00 4.00 6.00 8.00 10.00 Penetration (mm) The result is affected by the soil density, moisture content and human error. Low value of moisture content will decrease the workability of soil so that it is difficult to be compacted. If the soil becomes more workable and compactable, it will produce the higher density. Then, soil shear strength and resistance will be affected. Hence the CBR will be higher. At high moisture contents, dry density and resistance decrease with increasing water content. Hence, it will produce a low CBR value. In our case, the moisture content of our group’s soil is 8.806% and CBR value is 22%. Comparing with other group’s result, the moisture content of group A’s soil is 11.21% which is higher than ours. The strength of compaction in their soil is relative low, so the CBR value is 12%, which is lower than ours. This result may show that the higher the moisture content, the lower the CBR value. However, the result may also be affected by other aspect. For instance, soil density of two groups may be difference or rammer compaction may be uneven so the result may have a large difference. We have also compared with the result of Group B, their CBR value is 28%, and the moisture content is 6.46%. Due to the fact that the compaction strength and quality of soil is different, their CBR value is higher than ours, but the moisture content is lower than ours. Based on the aforementioned, we can draw a short conclusion that the higher the CBR value, the lower the moisture content of the soil. Moreover, the shape of curves is different from each other because of the difference in hardness of soil in the certain extent. The steeper the slope means the plunger needs to use greater force to penetrate the soil at the beginning. The slope will then become flatter because the plunger uses constant force to penetrate the soil. While soil with higher moisture content needs relatively less force to be penetrated by the plunger, as a result of a flatter slope of the CBR curve. On the other hand, from the result of experiment, we found that the CBR value of the sample is 22%. From the typical laboratory CBR values, the range of CBR value of sandy gravel is 20 to 60. The sample meets the range. Therefore, the sample can be determined as sandy gravel. Discussion on Laboratory Safety 1. Read Material Safety Data Sheet (MSDS) carefully before handing chemicals. - As some chemicals are harmful, toxic, inflammable, we need to read the instruction of MSDS before using the chemicals to prevent the accident. 2. Do not smoke, eat or drink in the laboratories. 3. Do not use audio headphones while carrying out experiments. 4. Do not leave things lying around and keep work areas tidy and clear. - While we do the soil mixing or pouring the soil into the mould, the soil may be fall and lie around. It is easy to slip so the work areas should be tidy. 5. Do not run or play games in the laboratory as we should concentrate on study in the lesson. 6. For an un-conventional testing, the risk assessment should be performed by the lecturer concerned, and the arrangement and advice should be sought from the Senior Technician or the Lecturer In-charge of the laboratory. 7. Student can operate the equipment in the laboratory after receiving proper training and permission from the laboratory technician. 8. Follow exactly the safe way of using the equipment. Do not take short cuts to save time. - If the test is too bright and it produces high temperature, operator should wear the gloves and goggle during experiment. 9. When using any equipment, know how to stop it in an emergency to prevent it out of control. 10. Do not attempt to try out equipment alone. 11. Do not leave tests or experiment unattended. 12. Inform the technician at once if you think an equipment/instrument is not working properly or is unsafe. 13. Do not wear dangling chains of loose clothing which could get caught in moving parts. Keep long hair tucked under a cap or tied back. 14. Mind the fingers using rotary machines or compacting equipment. 15. Beware of leaking coal gas. 16. Protective gloves must be worn when handling heated bitumen or solvent. 17. When heating bitumen, make sure it is free of water. - It is because water’s boiling point is lower than the kind of bitumen. Hence, the water will be stream and be damaged. 18. Organic solvents are potentially toxic, it should be used only under the exhaust hood. 19. All solvents containing vessels should always be covered 20. Keep solvents away from heat, sparks or open flames (Exposure of the vapor to naked flames or red-hot surface may produce “TOXIC GASES”.) 21. Ask technician if you do not clearly understand how to use the equipment. 22. Wear the safety equipment. For example, we need to wear gloves while using rammer which is heavy and easily damage hand. Conclusion To conclude, California Bearing Ratio Test is an important indicator to the performance of the unbounded layer of pavement. The test is to characterize the resistance of a material to uniaxial penetration and to measure of soil shear strength relative to standard crushed stone material for unbounded layers, including sub-base and subgrade. These two layers contribute to the main function, load distributing and load carrying, of the pavement to support vehicles. In our case, the experiment result of our group’s soil sample performs well to have a low moisture content (8.806%) and high CBR (22%). The soil sample of our group can also be proved as sandy gravel. Although such a result is not the best comparing with other groups, it is still acceptable to be used in pavement layers, such as sub-base and subgrade, as the CBR shows a high resistant to uniaxial penetration, which infers a high load bearing capacity. From this laboratory, the influence of moisture upon CBR has been clearly recognized, shown and justified by the results of different groups of soil sample. The higher the CBR, the lower the moisture content. Although the result is clearly deduced, we believe that there are some human-made errors during the test, such as uneven impact distribution of the plunger, wrong reading recorded. According to the result from other groups, the error seems to have a small effect. However, it is still better to perform the test with machinery to obtain a highly accurate result. Also, this can prevent some potential risks by human’s operation of the test. Lastly, we are here to thank for the support by the laboratory technician when performing the test. Appendix Table 1 Mass of mould + base plate + soil (g) Mass of mould + base plate (g) Mass of soil (g) Moisture content (%) (From table 2) 9480.8 4824.6 4656.2 8.806 Bulk density (Mg/m3) (p=m/2305) 2.02 Dry density (Mg/m3) (100p/100+w) 1.857 26.61 Maximum CBR (%) Table 2 Tin number 132 Mass of tin + wet soil (g) 209.78 Mass of tin + dry soil (g) Mass of tin (g) 195.19 29.51 Mass of moisture (g) Mass of dry soil (g) Moisture content of sample (%) 14.59 165.68 8.806 Test Data Penetration of Force on Plunger Gauge Reading Plunger (mm) (kN) Force on Plunger (kN) (cut 50N and adjusted) 0.00 0.25 0 17 0 0.7395 0 0.609 0.50 0.75 31 41 1.3485 1.7835 1.044 1.392 1.00 1.25 49 55 2.1315 2.3925 1.653 1.9575 1.50 1.75 62 67 2.697 2.9145 2.175 2.3925 2.00 2.25 72 76 3.132 3.306 2.5665 2.784 2.50 2.75 81 85 3.5235 3.6975 2.958 3.132 3.00 3.25 89 92 3.8715 4.002 3.2625 3.4365 3.50 3.75 96 99 4.176 4.3065 3.567 3.6975 4.00 4.25 102 105 4.437 4.5675 3.828 3.9585 4.50 4.75 108 110 4.698 4.785 4.0455 4.1325 5.00 5.25 112 114 4.872 4.959 4.2195 4.35 5.50 5.75 117 118 5.0895 5.133 4.3935 4.524 6.00 6.25 121 123 5.2635 5.3505 4.611 4.6545 6.50 6.75 124 126 5.394 5.481 4.7415 4.8285 7.00 7.25 128 130 5.568 5.655 4.9155 5.0025 7.50 7.75 132 134 5.742 5.829 5.0895 5.133 8.00 8.25 135 137 5.8725 5.9595 5.22