Leadership Alliance National Symposium Presentation
1. Centrifuge Testing to
Evaluate Seismic Soil
Structure Interaction and
Lateral Earth Pressures
Near Buried Water
Reservoir Structures in
Southern California
Miguel Frias
Dr. Shideh Dashti, Ph.D.
Department of Geological Engineering
University of Wisconsin-Madison
2. What do you think of when you hear the following three
places: San Francisco, Tokyo, Istanbul?
?
Big
Large
Cities
Engineeri
ng
Very
Populat
ed
Lots of
People
Modern
3. Why care?
“You have to build in a way that allows the earthquake energy to be
absorbed. Our objective as engineers is to increase the absorption”
Professor Oral, PhD Civil and Environmental Engineering, MIT
5. Objective
Evaluate the reliability of
different types of pressure
sensing technologies in
capturing lateral earth
pressures imposed by the
backfill of Nevada Sand.
10. Specific Gravity Test
Object Mass (g)
Filter .5
Filter + Sand 60.5
Empty dry 500 mL volumetric flask 180.2
Flask + Sand from filter 240.3
Flask with water + sand after de-airing process 715.3
Flask with water up calibration mark (water only) 677.9
Calculation: Gs= Ws/Ws+Wfw-Wfws
Where…
Weight of the soil (Ws)
Weight of the flask + water (Wfw)
Weight of flask + water+ soil (Wfws)
*Gs=60g/60g+677.9g-715.3g = 2.65 %
Specific Gravity, Gs, of
various soil types
Sand 2.63-2.67
Silt 2.65-2.7
Clay & Silty
Clay
2.67-2.9
Organic Soils <2.0
13. Acknowledgements
Shideh Dashti, PhD
Min Zang, PhD
SMART Program
University of Colorado
University of Wisconsin-Madison
Thank You
Editor's Notes
Have you ever asked yourself, what a world without engineers would be like? Heres a better question, how important will engineers be in the future? Being an engeinering student, I vision myself one day being a leader of a big project and intergrating the newest green technology out there. Most importantly, desigining buidlings that ill put socity out of harms way. Good afternoon everyone and welcome. For those who don’t know me, My name is miguel frias. I’m a rising junior at the Univerostu of wisconsin madiosn pursing a degree in geological engineering. I’m also part of the SMART Program , a summer research program at the Unversity of Colorado. Today I’m going to take you on a journey on my summer project called centrifuge testing to evaluate Seismic Soil Structure Interaction and Lateral Earth Pressures Near Buried Water Reservoir Structures in Southern California. I hope that By the end of this presentation , everyone will leave with a better understanding of my research project.
Before we move on any further. I have a quick question for everyone to keep in mind. What do you think of when you hear the following three places: San Fransico, Tokyo, and istanbul? Take a second or two to think it over. This is the same exact question I asked in a recent survey I did a week ago. Here are some of the most popular responses I received. For the most part, they all seem to relate to one another. However, no one was able figure out the bigger picture.
Earthquakes. The three 3 cities you just saw the are the 3 most densely populated cities where seismologist expect major earthquakes to hit. Your probably asking yourself, why should I care? As a n engineer, its my responsibly to prevent this from happening. I know its impossible to stop mother nature, but With the correct research and technology, I know we can definitely construct buildings that can withstand earthquakes. However, my lab doesn’t focus much on what happens above the earth. Instead, we focus on working with underground structiures such as underground reservoirs which is how this project came to be about.
In order to comply with new water quality regulations in California, the Los Angeles Department of Water and Power
(LADWP) is planning to bypass each of its open reservoirs and replace them with buried reinforced concrete
reservoirs. Open reservoirs in Los Angeles store drinking water from the Metropolitan Water District, and groundwater sources. The treated water that enters the open reservoirs is exposed to contamination from surface runoff, animals, and even humans. These problems can be eliminated by bypassing these reservoirs and construcsting a new reservoir called Headworks reservoir. The proposed project incldued includes 35 to 40-foot high walls that will be buried and restrained against rotational movement.
Construction of the Headworks Reservoir has been divided into separate construction phases.
East 2014, west 2017
So our main objective results in evaluating the reliability of different types of pressure sensing technologies in capturing static lateral earth pressures imposed by the backfill of nevada sand. Speaking of nevada sand, I’ve brought along a few bags of nevada sand so you have an idea of what we are working with. Let me know what you think. My grad student is from michigan. Any michigan people out here? Well anyways, she says this feels like lake michigan sand? I’m from wisconsin. If you know your geopgraphy, you should know that wiscosnin is on the other side of lake michigan. Trust me, lake michigan sand does not look like this at all. I wish but it doesn’t. The data from these tests help better understand seismic soil-structure-interaction (SSI) and the distribution of lateral seismic earth pressures on the walls
Before we could do any sensor installation, we first had to modify our centrifuge box which was a big challenge. The reason I say that is because out retaining wall measures 12 inches where as the cubed box in which we are placing the wall measures 16 inches. As you can tell, theres a 4 inch gap where sand can easily escape. SO our goal was to constuct an extension wall/ supportive wall to make up for those 4 inchs. We used a computer design software called AutoCAD to design the images seen on left. Once all drawing were completed, we took them to a our local machine shop and within a few days, the had bolted down all of the pieces. Together. The pictures on your right are the fianl project.
Preparing our retaining wall and installing our sensors was probably the most stressful and tidious part of this whole lab. The reason I say this is because our sensors have not been used in over 20 years. That being said, rusting in the wires becomes common but lucky us, all sensors were in pretty good codnsns. The red cables you see here are the actual strain gages. Straing gages will allow us to measure bending moment distributions acting on the structure wall under increased gravity caused from the centrigure which will be discussed later. We had to Tested/ Checked the resistance of the each strain gauge using a volt meter. The resistance of each strain gauge on both the back-fill side and excavated side were found to be between 118-123 ohms. Once we determined their resistnace, we had to solder the cables to data cords. Soldering is like welding where you sitck two pieces of wires together but sill, the eletcical current can still flow throguh. The end of the data cables were placed in Ethernet cap which willl than be connected inside our centrifue. As you can see, a total of 15 sg were installed on both the sand and no sand side
Another type of sensor we used are pressure sensors. These will determine the total amount of pressure that is distribtion along the sand face of the wall. A Total of 13 strain gages were installed on the sand side and the reason for the uneven balance betweeen SG and PS is that that on the side where the pressure sensors were installed, there was no more room to install 12 14 or 16. The resistance for each pressure sensor was also checked using the volt. All pressure sensors measured a resistance higher for both input and output than the expected resistance. This may be due to the older wires having rust within the whole wire. Nevertheless, the tested measurements are still fairly close to the original expected values
Here is a table with the resistance of each pressure sensor just showing you that.
Before we can do work with our centufyger, we must first understand the properpiest of the sand we are working with. One of the test we did is a shieve analysis test. A shieve analysis consst of shaking a soil (Nevada Sand ) in our cases throug a set of sieves that have preogessivly smaller openings as you go downwards. So the reason for this is that at somepoint on its way down, the sand will eventually come to a halt on a certain sieve because its sand grains particles are a bit bigger than the openings on the sieves. This tells us the grain size of our soil. Heres a grapgy plotting % passigns vs grain size. As you can see, our test in black pretty much are similare to past experients. This curve tells us that most of the sand was captured between the .05 and .1mm which makes sense since our sand is very fine.
Another test that was done was a specific grabity test. SG is defined as the ration of the unit weight of a given material to the unit weight of water. In dealing with soils testing, the value of specific gravity is necessary to compute the soil’s void ratio and for determining the grain-size distribution in other tests such as a hydrometer analysis. So, as you can see, the formula need to obtain a specific grabbity is the weight of soil over the weight of the soil + wight of flask/water – weight of flask/water/soil. Once obtained, we obtained a sg of 2.65. if we look at the table, the average range for sand lies between 2.63-2.67. we were spot on.
Last but not least, pluviation testing. Pluvating sand is used to make the sand as uniformed and evenly spaced out as possible. All we do here is rock the drop bucket which is filled with sand back and forth twice and we have to remeasure the height everything. So really, we want a consitent height from the bottom until the sand reached the very top. We need to know the height to obtain certain relative density's for calibration. We will drop at this certain height onto the retaining wall to calibrate the sensors.
So whats next. Spinning using our medium size centrifuge. We use a centrifuge to increase the amount of g force acting on our wall. We do this to stimulate seismic like behavior. Only then will we be able to analyze and get our final results.
Thank you for your time. I hope I have been able to explain all aspects of our project. If there are any questions left, I’ll be more than happy to answer them
