SEPTA and HNTB were recognized for their work on the area along the NHSL between Roberts Road and Garrett Hill Stations that shifted as a result of the Philadelphia region being deluged with almost 30 inches of rain during a 45-day period in August and September 2011. In this section of the NHSL, a layer of saturated soil lost its strength, resulting in about 150-feet of the 40-foot tall embankment supporting the tracks to drop vertically and push out the side of the slope. The inbound track in this area dropped approximately 12 inches and moved horizontally by about 16 inches.
SEPTA hired HNTB to inspect and survey the entire slope before performing a subsurface investigation at the affected area. After performing soil borings, HNTB installed inclinometer casings, steel tubes that allow for the lowering of a probe to a depth of 65-feet below the ground surface to measure movement in the embankment, at the top and toe of the slope. A daily track and embankment monitoring program was also instituted.
HNTB designed the permanent slope repair and provided construction support throughout the project. Because of the location of the slope failure, a temporary access road had to be built before the project commenced. Thirty-three days after the slope failed, design was completed and a construction contract for the permanent repairs was awarded. The site repairs included protecting adjacent properties and stream from erosion and runoff; constructing a 245-foot-long post and plank retaining wall to support the new embankment; removing portions of the saturated soil from the slope; installing drainage features to allow water to infiltrate out of the slope; rebuilding the slope at a less steep, more stable angle and planting native grasses to protect the surface of the new embankment from erosion. Construction was completed in March 2012.
FEMA awarded SEPTA $2,943,479 for the project.
"Receiving this award along with our partner, HNTB, recognizes our collaborative efforts in an emergency situation," said SEPTA General Manager Joseph Casey. "Thousands of our customers use the Norristown High Speed Line every day and our work with HNTB established a plan that allowed us to maintain service while the repairs were being made."