Category Archives: Sesimic and Earthquakes

Ground Improvement, Sesimic and Earthquakes

Hybrid Ground Improvement System for Liquefaction and Settlement Mitigation

Malcolm Drilling, Inc. and Dan Brown and Associates, LLC were the design-build team for a hybrid ground improvement system consisting of vibro-stone columns (VSC) and cutter soil mixing (CSM) panel grids to mitigate liquefaction and achieve target settlement performance criteria for a mixed-use development in Santa Cruz, California.

The development is being done by the Lincoln Property Company and consists of three separate 7-story buildings including 175 apartments and ground floor retail. The separate buildings provide public access from the street to the San Lorenzo River multiuse path. The project is an anchor for the City of Santa Cruz’s plan for revitalizing downtown with enhanced access to the river and increased density of affordable housing.

VSC were used on the interior of the site to densify granular soils while the CSM grids were designed to limit shear demand around the perimeter of the site where existing sensitive buildings and a USACE-controlled levee along the San Lorenzo River prevented the use of vibratory methods. The final project included 125 CSM panels for ground improvement and 558 VSC.

VSC probe and aggregate hopper supported by crane (foreground) with CFA piling rig on standby to predrill through refusal layers. San Lorenzo River levee visible in background
Cutter soil mix rig installing panel adjacent to existing structure at south site perimeter.

The hybrid ground improvement system supported a mat foundation beneath a single-level basement that spanned the entire site, atop which three individual seven-story mixed-use structures were constructed. The grade-level diaphragm resulted in combined seismic participation from the three structures which led to significant mat bearing pressures beneath shear walls and at the site perimeter.

In true design-build fashion, final geotechnical information was not available until after construction began and existing buildings on the site were demolished. This allowed access to install trial patterns of VSC with pre- and post-installation testing as well as additional exploratory CPT to identify the depth transition for the Purisma Formation bearing layer from about 60 ft in the northern portion of the site to about 20 ft in the southern portion of the site. VSC and CSM panel depths through the transition zone finalized while construction of the first production CSM panels was underway at the southern site edge.

Along with the Owner’s geotechnical engineer, Rockridge Geotechnical, DBA and Malcolm implemented multiple quality assurance and control measures. The CSM design and QA/QC program included a bench-scale study using soil samples from the geotechnical investigation, test panel installation using three different binder mixes with variable cement content to investigate soil mix compressive strengths, daily wet-grab sampling of production columns for strength testing, and coring of select columns for visual observation of mix continuity and sampling for strength testing of cured in-situ soil mix. Ground improvement through VSC was verified using post-installation CPT which were analyzed and evaluated on an individual basis against project performance criteria.

CSM core samples.
Pre- and post-VSC installation CPT profiles for liquefaction triggering.

The RiverRow project demonstrates the successful use of the design-build method to optimize site-specific ground improvement technologies to meet multiple project needs while safeguarding the interest of a wide variety of surrounding stakeholders, including sensitive structures and a USACE-controlled levee.

 
Bridge Construction, Bridge Foundations, Drilled Shafts, Foundation Design, Sesimic and Earthquakes

PROJECT HIGHLIGHT: 30 CROSSING DESIGN-BUILD

DBA is pleased to be part of the Kiewit Massman Construction (KMC) design-build team delivering the first transportation design-build project in the State of Arkansas, 30 Crossing. The project will improve traffic patterns and capacity along a 3-mile urban corridor of Interstate 30 from the Interstate 630 interchange south of downtown Little Rock to the Interstate 40 interchange in North Little Rock. The project includes replacing the existing bridge over the Arkansas River with two bridges supporting 12 lanes of traffic. 30 Crossing is the capstone project of the Connecting Arkansas Program (CAP), one of the largest highway improvement programs ever undertaken by the Arkansas Department of Transportation (ArDOT).

Teamed with designers Burns & McDonnell and HDR, DBA is the lead geotechnical and foundation designer for the navigation unit and north approach unit of the new river bridges. The bridge foundations are 10-ft diameter drilled shafts socketed into shale bedrock. Due to the project’s proximity to the New Madrid Seismic zone, design of the bridges included seismic considerations for critical operational class structures. Geotechnical seismic analysis included liquefaction triggering and lateral spreading evaluation. DBA worked closely with the structural designers to consider kinematic loads induced by lateral spreading and the interaction of substructure and superstructure components during lateral spreading events. The north abutment includes a column supported MSE wall embankment (CSE). The CSE ground improvement is included to mitigate performance and stability issues associated with shallow, soft alluvial silts and liquefaction hazards associated with deeper, alluvial sands.

KMC is self-performing the drilled shaft construction and CSE installation. To date, all of the eastbound bridge drilled shafts have been installed in the river and for the north approach. The ground improvement elements as part of the CSE beneath the eastbound embankment has also been completed. Once the eastbound bridge is ready for traffic in 2022, both directions of Interstate 30 will be temporarily shifted to the eastbound bridge, and the existing bridge will be demolished to allow for construction of the westbound bridge in its place.

Senior Engineer, David Graham, P.E., is the geotechnical engineer of record and has been involved in all aspects of the project form pursuit phase to current construction activities with significant contribution and guidance of Senior Principal Engineer and COO, Paul Axtell, P.E., D.GE. Senior Engineer, Ben Turner, Ph.D., P.E., G.E., lead the geotechnical seismic design and analysis effort. Project Engineers, Dan Ding, Ph.D., P.E. and Nathan Glinski, P.E., continue to be heavily involved in construction support and observation.

Eastbound Pier 13

Westbound Pier 13 drilled shafts

Looking north from Pier 13 at Eastbound Piers 14 and 15

Photos Credit: DBA

DBA News, Sesimic and Earthquakes

2018 Tennessee Earthquake GEER Report

Tim Siegel was one of four co-leaders of a Geotechnical Extreme Events  Reconnaissance (GEER) team that investigated the impacts of the 2018 Tennessee Earthquake that occurred near Decatur, Tennessee on December 12, 2018.   Among the team members were Ali Leib and Mark Madget.  The team performed reconnaissance of the area around the epicenter of the quake and prepared a report of their observations.

The quake occurred at 4:14 am EST approximately 12 km north-northeast of Decatur, Tennessee, which is about 240 km southeast of Nashville, TN.  The highest recorded peak ground acceleration (PGA) was 0.0215g approximately 36 km from the epicenter.  At least 21 aftershocks were recorded through December 18, 2018.  The GEER team did not encounter any evidence of earthquake-induced damage in the areas they visited.  Organizations such as the Tennessee Valley Authority (TVA), the Oak Ridge National Laboratory (ORNL) , and the Tennessee Department of Transportation (TDOT) “reported that either there was no damage to their facilities or that their operations were unaffected due to earthquake.”

The team’s report can be downloaded from GEER here.  Click the image below to see the list of the entire team.

GEER is a “volunteer organization of geotechnical engineers, engineering geologists, and earth scientists from academia, industry, government organizations, and non-profit organizations.”  They assemble teams to conduct detailed reconnaissance after extreme events (earthquakes, landslides, floods, hurricanes, etc.) in order “to  obtain valuable perishable information that can be used to advance research and improve engineering practice.”

To find out more about GEER, visit their website.