Geotechnical Investigations for Realignment of I-76 Across The New Baltimore Landslide, SW Pennsylvania

摘要

The Pennsylvania Turnpike Commission (PTC) plans to widen 1-76 due to increased traffic in Somerset County. The New Baltimore landslide, which has caused serious problems for the turnpike since its construction in 1939, is located near mile marker 128 in Somerset County. The landslide extends 2000 feet (610 m) upslope and 1000 feet (305 m) laterally, and moves 5 to 10 inches (13 to 25 cm) per year. The design plan for widening the turnpike may require cutting into the slope between mile markers 128 and 129 on the east-bound side of the turnpike, thereby passing through the New Baltimore landslide. A matter of significant concern is reactivation of the landslide upon realignment, adding to the existing instability. This research project is being conducted to determine the engineering properties of rocks and stability of slopes located between the mile markers mentioned above. Field work is currently being conducted to find the upper limit of the landslide. Preliminary discontinuity data are being analyzed to evaluate various modes of slope failure. A subsurface investigation, consisting of 12 borings and installation of 6 slope inclinometers and 1 piezometer, was conducted by American Geotechnical and Environmental Services, Inc. of Pennsylvania. Laboratory tests were conducted on the core samples to determine slake durability and unconfined compressive strength. The results of the study completed so far show that the bedrock geology of the New Baltimore landslide site consists of the Upper Devonian Catskill Formation which contains inter-bedded sequences of claystone, siltstone, and sandstone units. The slake durability index of claystone ranges from 72% to 99% whereas the unconfined compressive strength of the sandstone/siltstone units ranges from 8900 psi (61 MPa) to 25600 (177 MPa) psi. The inclinometer data show that there is small movement along the weaker claystone/clayey siltstone units (where gouge was encountered during drilling) and this is being closely monitored. This study is still in progress. The results of the study will be used to develop remedial measures for the New Baltimore landslide so that the interstate highway can be realigned safely.