I-476



Pennsylvania Turnpike Commission | Carbon County, PA

This project consisted of the rehabilitation and/or reconstruction of two miles of I-476, including the major Lehigh River bridge and Pohopoco Creek bridge crossings. AEG provided geotechnical, survey, and environmental services for this project on the Turnpike’s Northeast Extension. Components included preparation and review of portions of the roadway GERs; performing and reviewing computations for drilled shaft design, steel H-pile design, and retaining wall design; investigation and design of anchored rock cut and spread footing design; and preparation and review of structure foundation reports. Geotechnical challenges included design of 20-foot or higher (exposed) retaining wall system along an existing:embankment slope and concurrent design of a 100-foot-deep rock cut, including geologic analysis, stereonet analysis, RockPack III computer analysis, design of rock anchor retaining system and architectural facing for the near-vertical rock cut to accommodate roadway widening. AEG was also involved in the construction-phase project oversight, including instrumentation and survey monitoring of the North Wall (T-Wall® system).

AEG preformed Phase I/II/II Environmental Site Assessments (ESAs). AEG prepared a Phase I ESA and recommended further investigation for the Thruway Used Auto Parts Site. A Phase II ESA characterized shallow soil conditions. Prior to Phase III activities, AEG performed terrain conductivity studies using a Geonics® EM-31 Terrain Resistivity/ Conductivity Meter. A Phase III ESA was performed through a joint geotechnical and environmental boring program.

Survey work tasks consisted of the monitoring a retaining wall approximately 800 feet long and approximately 30 feet tall at its tallest point. Anomalies in the readings from the inclinometers set along the base of the new retaining wall prompted an investigation to determine if the wall was settling or deforming beyond acceptable limits. AEG installed permanent survey targets at key points along base and top of the retaining wall and a network of permanent survey control stations located outside the area of construction. The positions of the wall targets were monitored periodically with measurements from the control stations to detect any movement over time. The system was designed to detect horizontal movement of 0.02 foot or greater and vertical movement of 0.01 foot or greater. Our survey crew also surveyed the top of the retaining wall.