​Client:
The Corradino Group/Michigan Department of Transportation

Location:
Detroit, Michigan

Prime Consultant:
The Corradino Group

Sub Consultant:
NTH Consultants, Ltd.

Total Project Budget:
$33 Million

Total NTH Budget:
$9.9 Million

Project Start:
May 2005

Project Completion:
​November 2008

NTH’s Value Added
Because of the very complex nature of the investigation, the depth of drilling involved, and the client’s schedule needs, the field investigation was conducted 24-hours per day, seven days per week, for six months; and was completed ahead of schedule.

Detroit River International Crossing

Geotechnical Investigation

Project Overview
NTH Consultants, Ltd. (NTH) was retained by The Corradino Group (who was the prime consultant to the Michigan Department of Transportation) to collect relevant geotechnical data and evaluate conceptual designs for a cable-stayed bridge, suspension bridge, or tunnel. Following an initial research effort of historical land use comprising several of the potential river crossings, NTH determined that there was a high risk that historical brine wells (and associated cavities) were present in the vicinity of the proposed bridge.  A unique and precedent setting Brine Well Cavity Investigation program was developed by NTH, which brought together a team of world-renowned experts in the fields of deep rock drilling, down-hole geophysical methods, cross-well seismic imaging, and rock mechanics.

Project Scope
Brine Well Investigation: 
The program was initiated with a computer modeling effort that determined the size and extent of cavity that may be subject to collapse through complex three-dimensional finite difference analysis.  An extensive geophysical forward modeling program then followed.  Ultimately, a cutting edge program of cross-well seismic imaging was selected, supplemented by vertical seismic profiling, and down-hole geophysical logging.  
​    
Cross-well seismic imaging was used to delineate the size, locations, and shape of potential brine well cavities in two proposed crossing corridors on the U.S. side of the river.  The investigation plan included thirteen deep (1,750 feet) rock cores and borings, in combination with cross-well seismic imaging techniques that involved simultaneous and integrated data collection from multiple boreholes spread across the Delray neighborhood in Southwest Detroit.  The cross-well seismic imaging was supplemented by an array of down hole geophysical testing including sonic profiling, circumferential acoustic imaging (side-wall imaging of the boreholes), natural gamma surveys, compensated density, photo-electric logging, borehole gravity, and vertical seismic profiling.

Foundation Investigation:  
Once the final bridge corridor could be confirmed based on the brine well investigation and other factors, a separate geotechnical investigation was performed to determine the design and construction requirements for the foundations of the proposed bridge.  

The geotechnical investigation included 8 test borings that extended to approximately 150 feet deep, and included an array of soil and rock testing to determine the geotechnical characteristics of the ground.  Based on the information gathered, various deep and shallow foundation alternatives were developed for the proposed bridge concepts, and Load Factored Resistance Design (LRFD) methods were used to determine foundation design capacities. NTH developed final reports for the brine well and geotechnical investigations, which detailed all aspects of the investigations, analysis, conclusions, and recommendations. These reports became part of the final submittal to the Federal authorities, necessary for this project to proceed.