It was a pleasure to be invited by Petroleum Engineering Department of University of North Dakota to present a short course on computational geomechanics. The course was held on April 2018 in Grand Forks, ND. The main objective of this short course is the implementation of numerical modeling and geomechanical simulation in petroleum engineering. The course focuses on practical application of numerical modeling on simulation and prediction of geomechanical problems such as wellbore stability analysis, hydraulic fracturing and injection into a porous media. Several topics including elasticity and plasticity of the rock medium, constitutive models, stress distribution, and permeability considerations will be discussed. Simulation procedure of isotropic and transversely isotropic medium and faults and discontinuities will be presented. Commercial programs for geomechanical modeling will be introduced, and finite difference and finite element methods for numerical modeling will be described. The finite difference program, FLAC developed by Itasca Consulting Group Inc. will be considered for conducting practical simulations. 

Course topics were including:

• Introduction to numerical modeling in geomechanical medium
• Introduction to FLAC
• Example application of wellbore stability analysis
• Example application of hydraulic fracturing and fluid injection into porous medium
• Constitutive models used in geomechanical medium
• Permeability considerations
• Discontinuity and faults modeling in geomechanical medium

https://dspace.lboro.ac.uk/dspace-jspui/bitstream/2134/24176/4/GIBBINS2016DEV.pdf

It was an honor to be the head of judges for GeoWall competition at ASCE Mid-Continent Student Conference. The ASCE Mid-Continent Student Conference was held in April 2018 and several Midwestern schools joined the conference for GeoWall, Bridge, and Canoe competitions. The GeoWall competition was held among four schools including Southern Illinois University Carbondale, University of Missouri Columbia, Kansas State University, and University of Arkansas. 
Photos from left to right: Megan Hart from UMKC, Pravin Jha from Helitech, Eric Glazier from Gonzalez, Siavash Zamiran , and Lyle Simonton from Subsurface Constructors and president of ASCE St. Louis Section

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The article "Seismic motion response and fragility analyses of cantilever retaining walls with cohesive backfill" has been published in Journal of Soils and Foundations in February 2018. In this article, the seismic motion response of a cantilever retaining wall with cohesive and cohesionless backfill materials was evaluated using fully dynamic analysis based on finite difference method. The dynamic analysis was validated based on experimental test results and then compared to analytical and empirical correlations based on Newmark sliding block method. Seven different earthquake events and the backfills with low to high levels of cohesion were considered. Nonlinear regression analyses were carried out to provide correlations between free-field peak ground acceleration (PGA) and maximum relative displacement of the retaining wall. These results were compared to results from empirical and analytical methods. Furthermore, fragility analyses were conducted to determine the probability of damage to the retaining wall for different free-field PGAs and backfill cohesions. It is demonstrated to what extent a small amount of cohesion in backfill material can influence displacement of the retaining wall and probability of damage in seismic conditions.
For reading the full article please visit here. 

Siavash Zamiran was interviewed by The Riverfront Times, a weekly magazine in St. Louis Metro area. The following is the article by Ms. Katie Hayes, The Riverfront Times journalist.
Link of the article
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"While most people associate earthquakes with the West Coast — a price residents pay for sunny beaches and L.A. glamour — here's a sobering fact: Missouri is also at risk for a major earthquake.

"Although the earthquakes in the Midwest are less frequent, their effects are wider," says Siavash Zamiran, a civil/geotechnical engineer at Marino Engineering Associates in St. Louis. "There is a lot of probability of another earthquake happening, but not much public awareness of that."

In the next 50 years, there is a 25 to 40 percent chance of an earthquake magnitude six or higher hitting the region. There is a 7 to 10 percent chance of a magnitude seven or higher, as found by the United States Geological Survey. 

How big is that? The Loma Prieta earthquake, which famously interrupted the 1989 World Series in San Francisco, crumpling the upper level of the Bay Bridge, collapsing a freeway and causing 67 deaths, reached a magnitude of 6.9.

In other words: It's big.

The cause for concern stems from the New Madrid Seismic Zone — a major seismic zone between the Missouri Bootheel and Memphis, Tennessee.

But that doesn't mean you need to start packing for a safe space. Not yet.

Greg Hempen is a geophysicist who retired from the United States Army Corps of Engineers and now serves as a consultant for the Missouri Seismic Safety Commission. The commission is part of the Missouri State Emergency Management Agency, or SEMA.
"The greatest hazard is from the New Madrid in our area, but that doesn't mean every place in St. Louis will be equally devastated," Hempen says. "The principle threat to structures and residences is in the floodplains. Most people in the uplands should not be too adversely affected."

More than 200 years ago, New Madrid suffered through an earthquake from this seismic zone. The New Madrid Historical Museum, located in the Missouri Bootheel, has testimonies from people who experienced a series of three magnitude 7 earthquakes between 1811 and 1812.
One testimony is a letter sent by William Leigh Pierce to the editor of the New York Evening Post in 1811. It reads, "At New Madrid, 70 miles from the confluence of the Ohio, and on the right hand, the utmost consternation prevailed among the inhabitants; confusion, terror and uproar presided; those in the town were seen running for refuge to the country, whilst those in the country fled with like purpose towards the town. I am happy, however, to observe, that no material injury has been sustained."

Should another earthquake of that magnitude hit, however, the damage would be considerably worse than it was 200 years ago.

"People in 1811 and 1812 were mostly self-sufficient," Hempen says. "They built their own structures. If the structure was only damaged a little, they could repair it. If it was damaged a lot, they could stay with a neighbor until the community repaired it." Today, of course, our lives are more complicated — and our edifices more elaborate.

Masonry buildings, those made with brick and mortar, are the most susceptible to earthquake damage. 

"We have some specific issues in St. Louis," Zamiran says. "One is that our buildings are more masonry buildings. So they are built with bricks, without any structural frames, without steel or concrete. They are very vulnerable."

Hempen, however, notes that he lives in a masonry structure that was built in the 1950s and has accepted the risk. While earthquakes are a concern in the region, Hempen says they are not the only hazard people should prepare for.

"I think there is a variety of things people should do short of preparing structures and preparing renovations," Hempen says. "There are many programs for all hazards. I think people should consider a variety of things. One is, do they have a hazard plan, an emergency disaster plan? If there is an evacuation, do they have an emergency list of what they should have?"

Two of the programs Hempen discusses are the Great Central U.S. ShakeOut and Map Your Neighborhood — both meant to educate people in the region about disaster preparedness.

Eight states would be directly affected by an earthquake from the New Madrid Seismic Zone. James Wilkinson, executive director of Central U.S. Earthquake Consortium, brings together emergency managers from each of those states. He says Missouri and the eight states he represents are fully engaged in earthquake emergency update with FEMA.

"Folks need to understand the earthquake is not a West Coast thing exclusively," Wilkinson says. "We have active faults, manmade and naturally occurring. It's important people take time to do research about where they live and the susceptibility they have to earthquakes. Just because there is a threat doesn't mean it has to be all encompassing."​"

Current seismic design criteria for retaining wall structures suggested by different organizations are based on estimating seismic earth pressure of the wall using analytical solutions (e.g. AASHTO 2012; Campos 2008). Different guidelines including AASHTO and Caltrans consider pseudo-static analytical solutions to identify seismic earth pressure (AASHTO 2012; Campos 2008). The first analytical attempt as a pseudo-static method to evaluate seismic earth pressure of retaining walls was suggested by Okabe (1926) and the method was verified in retaining walls with unsaturated and cohesionless soil material by Mononobe and Matsuo (1929) using shake table test results. The method developed by these investigators is known as Mononobe-Okabe (MO) method and is still widely used to determine seismic earth pressure of retaining walls. MO procedure is an extension of Coulomb theory and is based on limit equilibrium method and assumes an occurrence of a failure wedge in the backfill. MO method considers the earthquake acceleration is uniform in the backfill and is applied to the center of gravity of the failure wedge.
 
There are also many studies that evaluated the total seismic earth thrust (Pae) experimentally (Agusti and Sitar 2013; Al-Homoud and Whitman 1999; Atik and Sitar 2009; Nazarian and Hadjian 1979; Prakash 1981; Seed and Whitman 1970) and numerically (Atik and Sitar 2009; Bui et al. 2014; Elgamal and Alampalli 1992; Green et al. 2008; Green and Ebeling 2003; Psarropoulos et al. 2005; Scotto di Santolo and Evangelista 2011; Wilson and Elgamal 2010; Woodward and Griffiths 1996). Specifically, Seed and Whitman (1970), hereafter abbreviated as S&W, conducted different centrifuge tests on retaining walls with cohesionless backfill materials and provided a simple equation for determining Pae, which linearly correlates with horizontal earthquake peak ground acceleration (PGA). Their experimental-based estimation has been used in design guidelines for evaluating Pae, e.g., US Army Corps of Engineers (Whitman and Liao 1985). It is worth mentioning that the earthquake acceleration intensities for the mentioned numerical and experimental studies were limited to PGA ground motions of 0.2g to 0.4g. In most of these studies, the cohesion factor of backfills and hysteretic behavior of soil were also neglected.
 
Guidelines by AASHTO and state Departments of Transportations require the use of granular materials as backfill for retaining wall constructions as backfills with fine and cohesive material are sensitive to swell, shrinkage, and degree of saturation (AASHTO 2012; Campos 2008; Murinko 2010). However, according to field observations in several cases, backfill materials have a various amount of cohesion (Kapuskar 2005). Kapuskar (2005) conducted field observations of more than 100 retaining wall and abutment backfills used in 20 different bridge sites in the State of California. It was concluded that out of 20 bridge sites, 15 of them had sandy backfills with low plasticity fines that had cohesion up to 95 kPa.
 
Seismic response of retaining walls considering backfill cohesion has been taken into account analytically (Das and Puri 1996; Prakash and Saran 1966; Shukla et al. 2009; Shukla and Bathurst 2012; Vahedifard et al. 2014). Most of these approaches were developed based on an extension of MO method with consideration of backfill cohesion, wall adhesion, and tension cracks in cohesive backfill materials. The MO-based methods have restrictions to be used for backfills with different soil layers and complex geometries. Therefore, analytical methods based on trial wedge procedure has been proposed for backfills with various layers of soil or complex geometries (Anderson et al. 2008).
 
In addition to analytical solutions, some experimental and numerical investigations have also been conducted to evaluate the effects of backfill cohesion on seismic response of retaining walls there are some limited experimental and numerical studies are available that assessed the effect of cohesion on seismic response of retaining walls (Agusti and Sitar 2013; Mikola et al. 2014; Wilson and Elgamal 2010, 2015, Zamiran and Osouli 2014, 2015). The limitations of these studies are: 1) the wall response with a variation of backfill cohesion was not considered; 2) the Pae, its point of action, and induced moment under full seismic analyses were not considered; 3) the representative hysteretic damping and shear reduction of the backfill materials have not been considered. Also, these studies focused on the effect of either single soil cohesion parameter or single PGA.
 
In this study, seismic response of retaining walls is evaluated for cantilever walls with cohesive sandy backfill materials via fully dynamic analysis (FDA). A constitutive model accounting the hysteretic behavior of soil during dynamic loading excitation is utilized. A validated numerical approach based on centrifuge test results is used to conduct the FDA. The effect of three earthquake ground motions and backfill with various cohesions on seismic earth pressures, total seismic earth thrust coefficient (Kae), incremental seismic earth thrust coefficient (ΔKae), the location point of action of Pae, and wall moment variations during the shaking event are studied. The results of FDA are compared to estimations based on current analytical solutions. Finally, recommendations are provided for considering the effects of backfill cohesion in seismic response of cantilever retaining walls. 

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