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.