Download Stress-Strain Relationship in Soil

Adam Stock, Civil Engineering, 2012, STEP scholar
Mentor: Professor Huabei Liu, Civil Engineering, The City College of New York
Education
 My first year of college I traveled abroad to Israel where I spent the year studying Jewish law, scholarly works and culture
 My formal college education began at Yeshiva University where I spent 2 years studying math and science
 I transferred to City College in Fall 2009 to begin my Civil Engineering studies
Experience
 This has been my first experience in the research world, and it has taught me several important lessons already. But mainly I am using it to help me determine the path I want to take once I graduate from college.
 I am hoping next to become involved in a large scale construction project to really learn how engineering is applied during the construction period.
 During the Summer 2009 I interned for a small scale engineer/contractor in Los Angeles, California.
Abstract
For every material there a maximum amount of stress or pressure
that can be withstood until failure occurs, this is called the ductility
of the material. Each type of soil would have a different ductility
value. Currently there is no formula to determine the ductility of a
soil, sample soil must be tested in a laboratory to determine its
strength.
Therefore we have been analyzing test results on the stress-strain
relationship in soil in order to see if we can determine an equation
that would simplify the process of determining the ductility of a soil.
Project Description
Goals
• To determine if there is a correlation between the stress‐strain relationship, soil type and the point of failure of a material
• If there is a relationship: to create an algorithm that would make it possible to determine the ductility of a soil using pure mathematics
Procedure
 Search Engineering databases for relevant data. We were looking for either dry or saturated and drained Triaxial tests.
 Extract the relevant data and convert it into the form required for proper analysis
 Compare the data to determine if there is indeed a correlation
Background
 What is a Triaxial test?
 A triaxial test tests the shear strength of material. The principal behind the test is that axial load can be different from the shear load, allowing one to measure the stress‐strain relationship
 There are three types of triaxial test: Unsaturated; Saturated drained; and Saturated undrained. For this project we were only
searching for the unsaturated and the saturated drained results.
The figure to the left depicts the loading applied during a triaxial test.
Research
 In this project there were no experiments performed to compile the data. Rather the data was extracted from published articles contained in the American Society for Civil Engineers database.
 The searches focused on finding any articles that contained stress‐
strain relationship data that was compiled using the accepted triaxial tests.
 Any relevant graphs or charts were filed away to be analyzed later.
Data
 The graph to the left exemplifies the stress‐strain relationship graph.
 The table shows how stress‐strain data can be broken down into several categories.
 Both Images were taken from Prakasha and Chandrasekaran’s paper entitled “Behavior of Marine Sand‐Clay Mixtures under Static and Cyclic Triaxial Shear.”
Analysis
• Once the data is collected the relevant data needs to be extracted:
–
Type of Soil
–
Void Ration (e0)
–
Confining Stress (σ0/σ3)
–
Max Stress (q)
–
Corresponding Axial Strain
• Next half the value of the max stress and the corresponding axial strain need to determined.
• The max modulus is then computed as the max stress divided by its corresponding strain. Likewise the midpoint modulus is computed the same way.
• Many times since the data is not easily accessible from the papers, the graphs need to be digitized using special software that turns the graphs into easy to use Microsoft Excel data.
Interpretation
 Once all the required data has been extracted and analyzed it must also be interpreted.  We will be looking to see if there is any correlation between soil type, density and the rupture point.
 The first step would be to plot the data
 Next we would check to see if there is an equation that could be used to it the data
 Lastly, we would have to check to see how strong the correlation is to that equation
Results
 This research is still on going and results have not yet been obtained
 So far we have a lot of data stored away, however we would ideally like to have more data before analyzing the data we have
and making a conclusion
 Hopefully very soon we will be able to create an algorithm that will allow us to easily compute the failure point of soil materials
Acknowledgements
I would like to thank Professor Huabei Liu for his help and guidance throughout the project