Assessment of the Cyclic Strain Approach for the Evaluation of Initial Liquefaction

Rodriguez Arriaga, Eduardo

Assessment of the Cyclic Strain Approach for the Evaluation of Initial Liquefaction

dc.contributor.author	Rodriguez Arriaga, Eduardo	en
dc.contributor.committeechair	Green, Russell A.	en
dc.contributor.committeemember	Dove, Joseph E.	en
dc.contributor.committeemember	Rodriguez-Marek, Adrian	en
dc.contributor.department	Civil and Environmental Engineering	en
dc.date.accessioned	2018-12-23T07:00:44Z	en
dc.date.available	2018-12-23T07:00:44Z	en
dc.date.issued	2017-06-30	en
dc.description.abstract	Field-based liquefaction evaluation procedures include the stress-based, strain-based, and energybased based approaches. The existence of a volumetric threshold shear strain, γtv, under which there is no development of excess pore pressures, and the unique relationship between pore pressure ratio and cyclic shear strain, γc, make a compelling argument for using a strain-based approach. However, the cyclic strain approach has not yet been standardized for field evaluations. The primary objective of this thesis is to use published databases of 415 shear-wave velocity and 230 Standard Penetration Test liquefaction field case histories to investigate the performance of the cyclic strain approach for the evaluation of initial liquefaction relative to the cyclic stress approach. Additionally, the concept of the γtv is expressed in terms of the peak ground surface acceleration and defined as the threshold amax. Computing (amax)t could provide a fast and simple evaluation for initial liquefaction, where no liquefaction is expected for a minimum computed (amax)t determined from the case histories. The variant of the strain-based procedure proposed herein avoids the direct need for laboratory cyclic testing by employing pore pressure generation models that are functions of cyclic shear strain, number of equivalent cycles, and relative density to predict initial liquefaction. The results from the proposed procedure are compared with those of the stress-based approach to determine which better matches the field observations of the case histories. It was found that the cyclic strain approach resulted in 70% to 77% correct predictions. In contrast, the cyclic stress approach yielded 87% to 90% correct predictions. The reasons why the predictions were not always correct with the cyclic strain approach are due to inherent limitations of the cyclic strain approach. Most significantly, an inherent and potentially fatal limitation of the strain-based procedure is it ignoring the softening of the soil stiffness due to excess pore pressure in representing the earthquake loading in terms of γc and neqγ.	en
dc.description.abstractgeneral	Earthquakes can cause heavy damage when they occur. One of the ways in which this happens is when the earthquake shaking causes the soil to behave like a liquid. This is the phenomenon known as liquefaction. An example of liquefaction is a person sinking in quicksand. Relating this to earthquakes, liquefaction can be thought of as a building sinking in quicksand that formed as a consequence of earthquake shaking. Destructive cases of liquefaction have been reported in almost all major earthquakes. When cases of liquefaction are properly documented, they can provide information that will help engineers and scientists assess the efficacy of existing liquefaction evaluation procedures and/or to develop new procedures. There are different methods to evaluate the occurrence of liquefaction, with the cyclic stress approach being the most widely used. This study assesses the efficacy of an alternative approach to see if it yields better predictions of liquefaction triggering than the cyclic stress approach. The approach under consideration is called the cyclic strain approach. To examine the effectiveness of the cyclic strain approach, sites that experienced liquefaction in the past were analyzed to see if the predictions made with the approach matched the past field observations. Due to potential shortcomings in implementing the strain based procedure, as well as inherent limitations of the procedure, the strain-based procedure yielded predictions that were inferior to the more widely used stress-based procedure.	en
dc.description.degree	Master of Science	en
dc.format.medium	ETD	en
dc.identifier.other	vt_gsexam:11234	en
dc.identifier.uri	http://hdl.handle.net/10919/86523	en
dc.publisher	Virginia Tech	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	liquefaction	en
dc.subject	cyclic strain approach	en
dc.subject	threshold strain	en
dc.subject	pore pressure generation	en
dc.title	Assessment of the Cyclic Strain Approach for the Evaluation of Initial Liquefaction	en
dc.type	Thesis	en
thesis.degree.discipline	Civil Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	masters	en
thesis.degree.name	Master of Science	en