I-495 Emergency Bridge Repairs, Wilmington, DE

GTA provided emergency response and corrective action services including subsurface exploration and geotechnical engineering services to repair BR1-183 on I-495 over Christina River in June 2014 through its open-ended contract with Walton Corporation. GTA’s engineers and scientists worked diligently 24/7 for 12 days in order to obtain the necessary subsurface exploration for the design team. Working conditions were tight as contractors worked to remove a soil stockpile thought to cause the bridge’s foundation to tilt and rotate, subsequently closing the bridge for almost four months. Given the limited access underneath the bridge, it was imperative that the subsurface exploration and instrumentation be installed prior to the foundation contractor mobilizing to the site. Staff engineers performed borehole logging for six Standard Penetration Test borings and approximately 120 feet of rock coring performed by Walton Corporation. The elevated pore pressures at the project site made for difficult drilling conditions. GTA performed 12 Cone Penetrometer Test soundings along with pore pressure dissipation tests, and GTA also monitored pore pressure through monitoring wells, pressure transducers and vibrating wire piezometers installed during those days. GTA oversaw the installation of that instrumentation, as well as two in-place inclinometers with automated readings. The instrumentation was monitored remotely using a data acquisition system. The instruments were monitored for approximately 12 months by GTA, who performed data reduction and provided Delaware Department of Transportation (DelDOT) with a monthly summary. GTA supplemented consolidation testing performed by DelDOT’s in-house laboratory by performing unit weights and loss on ignition tests of undisturbed samples, 14 Unconsolidated Undrained Tests and 14 compression tests on rock.