Chicago Department of Water Management constructed a relief sewer, including a series of drop shafts, drain connections, catch basins and inlets along North Lavergne Avenue. This $20 million project replaced a 100-year-old sewer, preventing flooding in neighborhood homes. Jay Dee Contractors performed this work, which included installation of over 2,600 feet of reinforced concrete pipe sewer in a shallow tunnel (about 60 feet below the ground), five drop shafts connecting to the shallow sewer tunnel or to the existing deep tunnel (over 200 feet below grade), and connection structures to join the two tunnels. G2 Consulting Group assisted Jay Dee by evaluating subsurface conditions to guide construction techniques.
Chicago Department of Water Management
G2 identified dewatering requirements for construction of the drop shafts, providing shaft designs through both soft ground and underlying rock leading to the deep tunnel, and evaluating design alternatives to meet requirements for constructing the shallow tunnel under an existing railroad line. In addition, G2 assisted Jay Dee Contractors during tunnel construction when the tunnel boring machine unexpectedly encountered saturated soils.
G2 Services Provided
Geotechnical Investigation and Design
Tunnel shafts were drilled through soft soils which overlay a deeper rock layer. Limited data was available to define the interface of these two layers. G2 conducted a geotechnical investigation to characterize existing conditions and evaluate dewatering techniques for construction of the shafts.
One of the shafts extends over 230 feet, connecting the new shallow collector tunnel to the existing deep tunnel. G2 developed shaft construction designs to provide stability in the soft soil conditions and in the rock.
As the tunnel was being constructed, saturated soils halted work. G2 assisted Jay Dee by designing an approach using grouting and dewatering techniques to enable work to continue.
An existing railroad line crosses over the alignment of the new tunnel. G2 assisted Jay Dee Contractors as they analyzed design alternatives to meet the railroad’s requirements.
Smart. Results. Fast. G2’s geotechnical solutions facilitated an expedited construction schedule for this highly visible project by simplifying excavation of the tunnel drop shafts and addressing construction challenges during tunnel boring.
Part of Cleveland’s long term plan to control sewage discharges into Lake Erie, the $179 million Dugway Storage Tunnel intercepts high water flow and directs it to proper treatment before discharge to Lake Erie. This project included the installation of a 24-foot diameter, 15,000-foot long storage tunnel at depths approaching 200 feet below ground level. Several consolidation sewers, diversion structures, and drop shafts were constructed to capture and store combined sewer overflow from the service area.
Northeast Ohio Regional Sewer District
G2 Consulting Group designed shafts ranging in configuration from circular with concrete ring beams to trapezoidal with steel bracing to facilitate construction of both tunnels and junction chambers.
Work was performed in populated areas, and the construction approach minimized impact on this population. G2 designed remote geotechnical instrumentation to monitor construction activities, including vibration, providing the team access to this important data on a real time basis.
This project was on a fast-paced schedule. In cooperation with Walsh, G2 submitted plans and specifications for all 6 Phase I shafts within 30 days of Notice to Proceed.
Smart. Results. Fast. G2 completed design of 6 shafts within 30 days to meet critical project milestones.
Rehabilitation of the Ann Arbor Wastewater Treatment Plant was the largest capital project undertaken in the city’s recent history. The project included rebuilding half of the wastewater treatment plant and renovating the other half while remaining in continuous service. The City hired Walsh Construction Company to lead the work, and Walsh in turn tapped G2 Consulting Group to oversee the challenging underground work portion of the project.
City of Ann Arbor
Because most of the work occurred underground, several geotechnical engineering firms were retained by subcontractors to perform work. G2 coordinated these technical efforts for consistency among the various disciplines on site and managed Walsh’s geotechnical risk.
One of the great challenges at this project site was the hydrogeological characteristics. The complicated artesian conditions coupled with the depths of required excavations and the presence of the Huron River along the perimeter of the project site required careful consideration and coordination among all the trades involved. G2 provided an independent evaluation of site dewatering to help expedite the subcontractor submittal approval process and to evaluate the proposed phased dewatering across the site.
G2 constructed a mathematical model of the hydrogeological conditions and calibrated the model based on actual pumping and drawdown response on the project site. G2 used existing geotechnical data along with the geotechnical instrumentation data being collected during the course of the project to evaluate how much dewatering to perform during specific underground tasks across the site. This reduced the amount of energy consumed during construction by only pumping the amount required at specific locations.
Several small braced excavations were required during construction. G2 designed earth support systems using the materials and equipment available on site allowing Walsh to self-perform work and expedite the schedule.
Smart. Results. Fast. G2 provided geotechnical solutions to address challenging conditions for this highly visible project, expediting the schedule, reducing costs and managing risk.
After nearly four decades of service, the Clintondale Pump Station was experiencing serious problems: its three, 500 horse power pumps had outlived their life, its operations were outdated, maintenance had to be done in confined space, and the lines leading to the facility were severely inadequate to feed the pumps. The Macomb County Public Works Office retained a construction team led by Walsh Construction to construct a facility to meet current and future needs. Walsh turned to G2 Consulting Group to solve the challenging geotechnical conditions that were threatening construction.
Macomb County Public Works Office
G2 Consulting Group provided geotechnical engineering consulting to the construction team to address artesian conditions on the project site.
G2 Services Provided
Remote Geotechnical Instrumentation
Extensive underground construction was required to construct the new pump station design, and the team knew that artesian groundwater conditions existed on site.
Instead of proceeding with the expensive jet grouting originally recommended to address this, G2 designed a depressurization plan to manage artesian groundwater conditions that included temporary earth retention systems and a geotechnical instrumentation monitoring plan to proceed with construction safely.
Key to this approach was a remote geotechnical instrumentation plan to continuously monitor groundwater pressures within the aquifer around the shafts and settlement within the cohesive soils at different depths to verify anticipated conditions. The use of continuous monitoring proved to be especially beneficial when structural questions arose during demolition and when the site lost power during dewatering.
Smart. Results. Fast. G2 developed a more conventional construction approach that ultimately saved the owner nearly $2 million, while enabling the construction team to better manage owner risk while maintaining the project schedule.