Bridge Abutment Soil Compaction Test. Ashford Kneitel East Los Angeles College University of California, San Diego Scott Ashford

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1 Bridge Abutment Soil Compaction Test Ashford Kneitel East Los Angeles College University of California, San Diego Scott Ashford

2 Abstract A new bridge is about to be erected in San Diego's Camp Elliot army base. Azadeh Bozorgzadeh headed the design of the bridge. We tested the soil of the site location in order to determine the optimum level of water to add in order for the soil to have the best characteristics to support the bridge abutments. The preferred properties to be improved are strength, compressibility, volume stability, erodibility, and hydraulic conductivity. Our modified soil compaction test required soil to be compacted into 5 layers in a 6'' mold. Each layer was given 56 blows from a 10-lbf hammer dropped from 18'' high, exerting a total effort of 56,000 ft-lbf/ft 3. The test was repeated 5 times until a relationship between water content and dry unit weight of the soil was established. For bridges, it is best to use 95% or more of the optimum recorded water content.

3 During my PEER Summer Internship at UCSD, I worked on two projects. The first project consisted of setting up a laminar box on top of a shake table. I worked 8 hours a day on jobs such as reparing holes in the laminar box bladder, assembling the strain gauges on the aluminum pile, and cleaning the actuators. We completed the set up on time, and were able to do the testing of the pile in sand and water. For the second project, I worked with doctoral candidate Azadeh Bozorgzadeh. Ms. Bozorgzadeh has designed a bridge that is being built in Camp Elliot army base in San Diego, California. The construction of a bridge abutment will be the first step. The conduction of a soil compaction test was necessary in order to determine the optimum level of water to add to the soil. Our objective was to discover how to allow the soil to have the best characteristics in order to maximize support of the abutment. The properties of the soil that we were looking to optimize were its strength, compressibility, volume stability, erodibility, and hydraulic conductivity. Specifically, we were looking at an increase in shear strength, an increase in swell potential, an increase in density, a decrease in shrinkage, a decrease in permeability, and a decrease in compressibility. Optimized soil comes from a compaction process which will give a maximum weight of soil per volume. Our approach consisted of a carefully performed soil compaction test. We decided to use the modified version of the standard test. We considered this test to be very reliable. The very same data collected from this test was to be used in the construction of an actual bridge. The modified soil compaction test has been proven to be the most effective method of discerning the optimum attributes. The first step began with Camp Elliott sending us buckets of the real soil that the abutments would be built on. This was the soil we would be using for the test. The soil wad first air-dried to remove the minute amount of moisture in the soil. It was then screened through a No. 4 sieve. Compaction tests were conducted on 5 soil samples. Five measurements of tap water were added to different soil samples. Thus, each soil sample had a different water content. The water was thoroughly mixed in a large bowl until it was evenly mixed in the soil. The soil was then placed into 5 layers in a 6'' mold. After each layer was completed, the soil was given 56 blows from a 10-lbf hammer dropped from 18'' high. This exerted a total effort of 56,000 ft-lbf/ft 3. Soil samples were removed from the molds and broken up into smaller chunks. Chunks were weighed and recorded. They were than placed into a drying oven overnight. The next day, the dried soil was weighed again. The dry unit weight was recorded for each water level. The optimum average water content occurred at 10.21% which produced a dry unit weight of Kn/m 3. For bridge building, it is best to use 95% or more of the optimum recorded water content. This means that anywhere from % water content will yield optimum results.

4 I would have liked to stay in San Diego longer to continue work on the new bridge at Camp Elliot. There are lots of new ideas and concepts to be tested out. I am very grateful to have been given the opportunity to get so much hands on experience. I was able to see how hard it is to stage an experiment such as a laminar box test. The test itself runs around 20 seconds, yet it takes several months of hard, laborious work go into those 20 seconds. Knowing that the data collected from a soil compaction test will be used in a major structure puts a lot more pressure on yourself. People's lives can be at stake if wrong data is being used for the bridge. We really had to be extra careful in the soil testing. I gained so much information in this internship. I learned more in these 10 weeks than I have in years of previous schooling. Hands-on really is the best experience to learn about engineering from all angles (literally)! Graduate work is so important to the field of Structural Engineering. Earthquake engineering has so many unopened doors. It is a subject that has relatively little information compared to other engineering areas. I will be continuing my studies beyond undergraduate work.

5 Acknowledgments I wish to thank the following for all their help and generosity during my internship: Scott Ashford Linda Nelson Azadeh Bozorgzadeh Liang PEER REU UCSD

6 Table 1. Compaction Test Results Run Number Units Test #1 Test #2 Test #3 Test #4 Test #5 Wet Unit Weight Kn/m Tare Number Pt 1,1 Pt 2,2 Pt 3,3 Pt 4,4 Pt 5,5 Water Content % Ave Water Content % Dry Unit Weight Kn/m Figure 1. Soil Compaction Dot Plot Dry 20.. Unit. 19. Weight. Kn/m Average Water Content %

7 Soil Compaction Hammers Drying Oven Soil Compaction Molds

8 References Day, R.W., Soil Testing Manual: Procedures, Classification Data, and Sampling Practices, New York, NY, USA, 2000 Head, K.H., Manual of Soil Laboratory Testing, New York, NY, USA, Smoltczyk, U., Geotechnical Engineering Handbook Vol 2: procedures, Washington, D.C., USA, 2003