Experiment No. 1 CALIFORNIA BEARING RATIO
1. Objective(s): The activity aims to introduce to the students the standard method of determining the strength of base, subbase and sub grade material using the California Bearing Ratio. 2. Intended Learning Outcomes (ILOs): The students shall be able to: Connect the CBR value in the determination of the thickness of sub grade soil for a specific wheel load. Determine the California bearing ratio in a given soil sample. describe the methods of how the California bearing test is performed
3. Discussion: The California Bearing Ratio test (CBR) was developed by the California Division of Highways as a method of classifying the soils for suitability for use in highway construction, especially for the classification of base coarse materials for the support of flexible pavements. Shortly after the start of World War II the US Army Engineers adopted the CBR test for use in design and construction of bases for airfield runways. The army engineers greatly improved the test procedure by substituting a dynamic method of compacting the soil and this change is now accepted as the standard procedure. The CBR test is a measure of the shearing resistance of the soil under controlled density and moisture conditions. Therefore the test cannot be considered as a classification test since the results are not constant for given soils but dependent on such factors as density and moisture content as well as size and shape of the grains. The CBR value is expressed as a percentage of the unit load required to force a piston into the soil divided by the unit load required to force the same piston to the same depth into a standard sample of compacted, crushed stone. CBR =
test unit load Standard unit load
x 100
The standard unit load obtained from the average of a large number of tests on different crushed stones and are as follows: Penetration (in) mm
Unit load (psi) MPa
(0.1) 2.5
(1000) 6.895
(0.2) 5.0
(1500) 10.342
(0.3)7.5
(1900) 13.100
(0.4) 10.0
(2300) 15.858
(0.5) 12.5
(2600) 17.926
The CBR usually selected is at 0.1-inch penetration. If the CBR 0.2-inch penetration is greater than at the 0.1 inch penetration, the test should be rerun if the check test gives similar results. The value for the 0.2-inch penetration is used. The CBR test can also be made in place on 4. Resources: 1. CBR Mold 2. Hammer
3. Spacer disk 4. Apparatus for measuring expansions 5. Dial indicators 6. Surcharge weight 7. Penetration piston 8. Loading device 9. Soaking tank 10. Drying oven 11. Miscellaneous tools such as mixing pans 12. Spoons, straight edge, balance, drying oven 13. Desiccator and drying can 5. Procedure: Sample Preparation:
1. Air-dry and pulverize approximately 100 Ib of material, screen through a ¾” inch sieve, weigh the material 2.
3.
4. 5. 6.
retained and discard this material. Replace the wasted material with an equal weight of material passing the ¾” inch sieve and retained on the ¼ inch sieve. Determine the optimum moisture content of the material using the modified AASHO Method (see Compaction Test) with the following exceptions. a. Use ¾ inch maximum size material instead of the ¼ inch material. b. Use the CBR compaction mold (with 2 inch spacer disk in bottom) instead of the 1/30 cu ft mold c. Compact material with 55 blows per layer instead of 25 d. Compact in 5 layers instead of 3 layers. The compacted specimen should consist of 5 one-inch layers e. Use fresh material for each compaction sample instead of pulverizing and recompacting the same material Conduct the control compaction test with a sufficient number of specimens to definitely establish the optimum moisture (water), content for 100 percent of modified AASCO density. At least 4 to 5 specimens should be compacted with water contents within plus or minus 2 percent of the optimum moisture content so that the optimum condition can be rigidly established. Note: Height of fall of the hammer must be carefully controlled and the blows uniformly distributed over the specimen Upon establishing the optimum moisture content, mix about 30Ibs (13.64 kg) of the air-dried material with enough water to bring the moisture content to the optimum value determined in step (2) and (3). Cover the material with a damp cloth to prevent the loss of moisture while preparing the specimens. Number and weigh the three CBR molds and attach extension collars and base plates. Insert one of the 2” (250 mm) spacer disks on the base plate of each mold and place a 6 inches (150 mm) diameter filter paper or wire mesh on top of each disks. Compact the soil- water mixture into the CBR mold in accordance with the pr ocedures stated in step 2 and 3 and Compaction Test of previous experiment Note:
1. Prior to compaction of the soil mass, take a representative sample of 20 to 50 gm of soil samples from the top and bottom layers of each mold for water content determination. 2. Remove the extension collar and carefully trim the compacted soil. Even with the top of the mold by means of a straight edge or knife patch with smaller size material any holes that may have developed in the surface by the removal of coarse material. Remove the weight of the mold and compacted soil.
3. Place a disk of filter paper or wire mesh on the base plate, invert the mold and compacted soil, and clamp the base plate to the mold with the compacted soil in contact with the filter paper. The sample is now ready for soaking. A. Swell Test : To simulate field conditions, the specimen is soaked under a surcharge weight which is equivalent to the weight produced by the soil, base, or pavement, which will overlie the material in the completed structure. Three inches of overlying material is assumed equal to 5 Ib (2.27 kg) surcharge load on the sample, the total surcharge weight shall not be less than 100 Ib (4.54 kg)
1. Place the adjustable stem and perforated plate on the compacted soil specimen in the mold and apply weight to produce a surcharge equal to the weight specified or required. And place the portable tripod with gage (dial extensometer) on the rim of the mold and mark its location. Adjust stem of perforated plate, record the initial dial reading and remove the tripod with gage. 2. Immerse the specimen in the water tank in four days (96 hrs) by maintaining a constant water level during this period. Each day during the soaking period place the tripod clamp on the mold in its marked location and record the dial reading and time. 3. After soaking period, remove the mold from the water, hold the surcharge weight and perforated plate firmly in place, and pour the excess water from the surface and then let the specimen drain in a vertical position for 15 minutes. Remove the surcharge weight, perforated plate and filter paper or wire mesh, and weigh 4. Calculate the percentage of water absorbed by the specimen and the swell in percent of the initial height B. California Bearing Ratio Test:
1. Place the surcharge load (weights) directly on the sample and center it under the penetration piston in the loading apparatus and bring the penetration piston in contact with the soil through the annular surcharge weight. Adjust the diameter gage for measuring the penetration so that its stem bears on the rim of the mold and record the initial reading. 2. Apply the load smoothly so rate of penetration is 0.05 inch (n 1.27 mm) per minute. Check the rate of load application by using a stopwatch. Record the load readings at penetrations 0.025 (0.64 mm), 0.050 (1.27 mm), 0.075 , (1.91 mm), 0.100 (2.54 mm), 0.125 (3.18 mm), 0.150 (3.81 mm), 0.175 (4.45 mm). 0.200 (5.05 mm), 0.300 (7.62 mm), 0.400 (10.16 mm) and 0.500 inch (12.70 mm) Note: For manually operated loading machine, it may be necessary to take load readings at closer intervals to control the rate of penetration. 3. Release the load, remove the mold from the loading machine, and remove surcharge weight and base plate. Take 20-50 grams for moisture content from top and bottom of the specimen and record. Course: CE 510 Group No.: 6 Group Leader: Endaya, Armand Kerrian Group Members: 1. Arquiza, Mary Joyce 2. Barra, Wilrose 3. Batilo, Julius Caesar 4. Bautista, Emerson 5. Cerdena, Alfredo
Experiment No.: 1 Section: CE52FB1 Date Performed: June 19. 2017 Date Submitted: June 28, 2017 Instructor: Engr. Camino 6. Del Mundo, Patrick
6. Data and Results: Description of Sample: Light brown in color, fine aggregate sample, dry Sampled at: Bldg. 7 TIP-QC
CONDITION OF SAMPLE: (
) SOAKED
( . ) UNSOAKED
DAY DENSITY: Before Soaking = 1.346x10^-3 g/cc After Soaking = 3.100x10^-3 g/cc Water Content = 8.696 % (unsoaked sample) Before Compaction: 14.443 % (soaked sample) After Compaction: Top = 17.65 % Bot = 13.64 % Average After Soaking: 15.645 % SURCHARGE WEIGHT =
90g
PENETRATION NUMBER
AREA OF PENETRATION (in 2)
LOAD
UNIT LOAD IN
Inch
mm
Lb
KN
Piston
psi
mpa
0.098
2.5 5.0
0.295
7.5
0.394
10.0
0.492
12.5
28.315 35.807 41.647 49.585 59.172
3
0.197
6350 8030 9340 11120 13270
2116.667 2676.667 3113.333 3706.667 4423.333
14.629 18.500 21.518 25.619 30.572
3 3 3 3
In the tabulated data above, only the corresponding load and unit load for penetration numbers 2.5mm, 5.0mm, 7.5mm, 10.0mm, and 12.5mm are considered due to the limited value of available standard loads for each penetration- from which the CBR value will rely on. Standard loads for each penetration is shown in the discussion of California Bearing Ratio.
7. Conclusion:
Conducting the experiment through California Bearing Ratio Test. We`ve concluded a number of factors that may affect the result values gained from the soil sample. The description of the soil sample is indeed necessary to note. It is moisture content and density before and after compaction are main factors that will greatly determine its strength capacity to hold the loads of penetration at its certain depth. Differing result are expected in this test. Even so for every soil conditions, it`s conspicuous load that required to penetrate the sample increases as higher value is applied. Meaning a strength of soil is directly proportional with how dense it is. On the on other hand, inverse relationship between two strength of soil and the moisture content
8. Assessment (Rubric for Laboratory Performance): Performance
Beginner
Acceptable
Proficient
indicator
1
2
3
Identify the procedures involved in designing the experiment Develop a protocol to conduct an experiment
Score
Designs an experiment Designs an experiment Fails to design an satisfying the minimum exceeding the experiment following requirements of the requirements of the procedures procedures procedures Develops a protocol to Develops a protocol to Fails to develop a conduct an experiment conduct an experiment protocol to conduct an satisfying the minimum exceeding the experiment requirements minimum requirements Total Score Mean score=(Total Score/2) Percentage Score= (Total Score/6) x 100%
9. References Budhu, M. (2008). Foundations and Earth Retaining Structures. New Jersey: John Wiley and Sons American Society for Testing and Materials (1999). Standard Test Method for CBR of Laboratory Compacted Soils (D1883). Pennsylvania: ASTM International
Technological Institute of the Philippines-Quezon City 938 Aurora Boulevard, Cubao, Quezon City COLLEGE OF ENGINEERING AND ARCHITECTURE Civil Engineering Department CE510 Foundation Engineering
Experiment No.1 California Bearing Ratio
Submitted by: Arquiza, Mary Joyce Barra, Wilrose Batilo, Julius Caesar Cerdena, Alfredo Del Mundo, Patrick.
CE52FB1 Submitted to: Engr. Camino
Date: June 28, 2016
