Joint CAGE / ASCE March Lunch Meeting
Please join us for thought provoking presentations on contemporary geotechnical engineering research being conducted at the University of Colorado
 

Our Speakers:

Title: Considerations for the Mitigation of Earthquake-Induced Soil Liquefaction in Urban Environments
 

Bio: Dr. Shideh Dashti is an Associate Professor in Geotechnical Engineering and Geomechanics at the University of Colorado Boulder (CU) and the Acting Associate Dean for Research in the College of Engineering and Applied Science. She also directs a college-funded interdisciplinary research theme titled RISE: Resilient Infrastructure with Sustainability and Equity. Shideh obtained her undergraduate degree at Cornell University and graduate degrees at the University of California, Berkeley. She worked briefly with ARUP and Bechtel on several engineering projects in the US and around the world. Her research team at CU studies: the interactions and interdependencies among infrastructure systems during earthquakes and other disasters; seismic performance of underground structures; consequences and mitigation of the liquefaction hazard facing structures in urban settings; and the intersection of resilience, sustainability, and social justice. She is the recipient of the 2018 Arthur Casagrande Award and the 2021 Walter Huber Civil Engineering Research Prize from ASCE, among other honors and recognitions.

Title:  Centrifuge Modeling of Impoundment Failures and Practical Risk Assessment for Run-outs
 

Bio: Dr. Srikanth S. C. Madabhushi is currently an Assistant Professor in the Geotechnical Engineering and Geomechanics Group and co-director for the Center of Infrastructure, Energy and Space Testing at the University of Colorado Boulder. He obtained his MEng and PhD at the University of Cambridge in 2014 and 2018 and was a post-doctoral research associate at the University of California Davis between 2018 and 2020. His research focus is on Geomechanics and Geohazards using physical and numerical modeling, and he has a particular interest in soil retaining systems, dynamic soil-structure interaction and coastal engineering.


 

Title: Water-weakening effect on drilled caissons socketed in claystone bedrock
 

Bio: Dr. Yida Zhang is currently an assistant professor in the geotechnical engineering and geomechanics group at the University of Colorado Boulder. He obtained his PhD degree from Northwestern university in 2016, MS degree from Louisiana State University in 2012, and BS degree from Zhejiang University in 2010, all in civil engineering department. His specialty and research interests are constitutive modeling of geomaterials interacting with environmental factors, granular mechanics, poromechanics, thermodynamics, and energy geotechnics.


 

Title:  Soil-structure interaction of buried infrastructure: centrifuge testing of jointed pipelines​
 

Bio:  Dr. Brad Wham serves as Research Assistant Professor at the University of Colorado Boulder and the Center for Infrastructure, Energy, and Space Testing where he directs unique campus laboratories and diverse collaborations to conduct a range of research activities targeting resilient critical infrastructure systems, including water and energy distribution. He holds various degrees in geotechnical and structural engineer from Cornell University and Virginia Tech.



Pricing:
CAGE and ASCE Member $10
Nonmember $40
Students/University Professors  $0

Click Here to Register
 
PDHs = 1.5 hours - provided upon request
 
Parking:
There are a number of short-term visitor parking lots on the Boulder Campus.
Our “insider’s” suggestions for parking are Lots 436 and 308
Parking permits can be purchased in advance at: 
https://cuboulder.aimsparking.com/permits/?cmd=new
Parking is also available through the ParkMobile app
 
Area Map:
See below for parking lot numbers.  Koelbel 352 is in the North end of the building as highlighted.
































Presentation Abstracts:
 
Shideh Dashti:
Title: Considerations for the Mitigation of Earthquake-Induced Soil Liquefaction in Urban Environments
Abstract: In cities, seismic coupling among structures through soil (structure-soil-structure interaction, SSSI) is known to influence ground motions, settlement patterns, and demand on superstructures. Yet the effects of interactions between soil and building clusters on structural performance are poorly understood, particularly on ground susceptible to cyclic softening and liquefaction. Existing analytical methods cannot capture the nonlinearity and complexity of seismic coupling on softened soil, while advanced numerical tools that can capture such complexities have not been validated. The empirical liquefaction database is also limited near building structures, particularly for cases with mitigation. Consequently, liquefaction mitigation measures designed ignoring SSSI may perform poorly when evaluated at a systems level. In this presentation, experimental (centrifuge) and numerical models are used to evaluate the mechanistic consequences of seismic coupling on the effectiveness of common mitigation approaches (e.g., ground densification and prefabricated vertical drains). The performance of mitigation is shown to depend strongly on the geometry of improvement, dynamic properties of the neighboring structures, and building spacing. Although settlements are generally reduced satisfactorily, the combination of SSSI and mitigation typically notably amplify asymmetrical deformations below the foundations (hence, permanent tilt) as well as column strains, particularly for an unmitigated neighbor. The results indicate that ground improvement properties and geometry must be designed with extreme care in urban settings, particularly when near a taller and weaker neighboring structure at the corner of a cluster. 
 
Srikanth Madabhushi:
Title:  Centrifuge Modeling of Impoundment Failures and Practical Risk Assessment for Run-outs
Abstract: Numerous industries are concerned by the humanitarian, environmental, and economic consequences of debris flows, landslides and material run-outs. Historic and recent failures of tailings dams (e.g., Fundão or Brumadinho) and fly ash impoundments (e.g., Kingston) highlight the need the for improved risk assessment. However, the run-out behavior of these materials following a loss of confinement such as from dam failure is not well understood. These material's complex constitutive behavior means multiple mechanisms can contribute to their failure, including slope instability, seepage forces, erosion or static liquefaction. In this presentation results from centrifuge testing of fly ash deposits, with varying initial deposit density and water table height and subjected to a rapid loss of lateral confinement, are presented. Deformation, pore pressure and water content measurements are used to investigate and separate the mechanisms governing the run-out. Static liquefaction is observed in deposits initially looser than the critical state and lead to a rapid material outflow. Slope instability is the initial failure mechanism for denser deposits or those with reduced water tables, with transient stability due to dilation-induced negative excess pore pressures followed by progressive failures caused by seepage pressures from drainage and pore pressure dissipation. Cone penetration tests, performed before the loss of confinement and at different penetration rates, are used to characterize the material run-out and volume change tendencies. The results from CPT soundings at different rates demonstrates a novel, practical and effective method for assessing the run-out risk of a variety of contained material deposits in the field.


Yida Zhang:
Title:  Water-weakening effect on drilled caissons socketed in claystone bedrock
Abstract: A large number of bridges and structures in Colorado are supported by drilled caissons and shafts socketed in weak clay-bearing rocks (e.g., Denver blue claystone and Pierre shale). During the construction of caissons using the wet drilling technique, drilling fluid gets in direct contact with the bedrock, potentially causing their slaking and degradation and, thus, undermining the foundation capacity. This talk evaluates the effect of water infiltration on the axial capacity of caissons embedded in claystone. The methodology of this research combines laboratory testing and coupled finite-element analysis for unsaturated porous materials. A series of experiments were conducted to determine the hydraulic characteristics and the strength-suction relations of the claystone samples obtained from three sites near Denver, Colorado. These parameters were then used in numerical studies of wet drilled caissons subjected to different wetting times (i.e., the time interval between the completion of drilling and the placement of concrete). The results showed that the immediate caisson capacity reduction is higher for more permeable, initially less saturated, and more water-sensitive claystone formations. On the other hand, the capacity reduction was found to be negligible if the rock was relatively intact with low permeability, regardless of its strength-suction characteristics. These results provide the basis to establish practical guidance to evaluate and minimize the impact of wetting time on caisson constructions.
 
Brad Wham
Title:  Soil-structure interaction of buried infrastructure: centrifuge testing of jointed pipelines
Abstract: As utility owners and engineers seek improved resiliency across their buried pipeline networks, manufacturers have responded with novel components and improved products to accommodate the demands that various natural hazards can impose. These systems include enlarged joints, restraints, or other components along pipelines that increase frictional interaction during relative ground movement. This talk will present a subset of centrifuge experiments designed to quantify the axial frictional resistance along buried pipes with enlarged connections. The results of this ongoing study are intended to inform developing standards for water and wastewater pipeline design.