If you asked residents and business owners along Delaware Avenue in the Town of Bethlehem, NY, last spring if they thought a landslide could occur in their neighborhood they would have said, “No way — no how — not here!”
But, on the afternoon of May 16, 2000, that’s exactly what happened.
As a result of heavy rains that significantly increased the water levels and velocity of the Normans Kill, a landslide occurred along Delaware Avenue. While there were no personal injuries, the slide claimed a produce stand on the edge of the hill and threatened a neighboring car wash and medical office parking lot. The portion of the road affected was a vital link between the City of Albany and the Town of Bethlehem; one that serves 19,000 vehicles daily.
Bob Burnett, assistant director of New York State’s Department of Transportation’s (NYDOT) geotechnical engineering bureau, remembers that day well.
“We were called in the next morning because people were getting concerned. There was a tall failure scarf behind the building, which wasn’t far from the road. It was approximately 100 ft. high and about that same distance off the edge of the pavement. That’s when we decided to close the curb-line lane of Delaware Avenue and observe the site all that night,” Burnett recalled.
It didn’t stop there. The following morning another significant portion fell off the side of the failure scarf, the vertical portion near the top. There were two or three other drop-offs and such falling off during the day. This caused NYDOT to close all four lanes of Delaware Avenue right before the onset of rush hour traffic on May 18: an act frowned upon by nearby residents and businesses.
The soil failure was attributed to the natural process of streams eroding the bottoms of valleys, the valley walls falling into the stream, and then the whole process starting over again. “It was hundreds, probably thousands, of years in the making,” Burnett explained. “In this instance we had some very high flows in the past year or so. We had Hurricane Floyd move through the area last fall and we had an extremely wet spring.
“This particular location was situated on the outside bend in the stream. It became undermined to a point where a portion of the stream bank was lost back into the stream,” he continued. “Once the stream bank was lost into the stream, the chunk above it was undermined and it progressed quickly up the hillside.”
For Burnett and his crew, the early hours of this disaster were the most challenging because of how quickly things were moving. “We had one large drop on Tuesday but then four separate chunks fell off two days later. We didn’t know how far or how fast it was going to go so the safe thing to do was close the road,” Burnett claimed.
No Simple Fix
In order to stabilize the situation and prevent future landslides from occurring, the Normans Kill had to be relocated away from the roadway and the existing channel needed to be drained. Additionally, the Albany City water line and a Niagara Mohawk gas line needed to be relocated. To ensure the uninterrupted delivery of essential services to Niagara Mohawk customers during the winter heating season, the gas line needed to be relocated by Oct. 31. To maintain an adequate supply of water to the City of Albany, the three required water line shutdowns had to be completed in less than 96 hours.
“Since the stream had caused the undermining, the soil had moved and, consequently, was not as strong as it originally had been,” reported Burnett. “The soil was mixed up and tossed around and the water was moving. We knew we couldn’t put the stream back in its original location. Instead, we were looking at how we were going to move the stream without changing it upstream or downstream.”
To get the water flowing, a temporary opening was cut some distance farther away from the original stream. Initial assessments indicated that stabilizing the upper portion of the slope would help, so a fair amount of stone was placed on the top. However, another large rainstorm in early June, which brought with it 5 in. of rain, once again washed out the bottom of the stream.
By now, the bottom contained loose, broken up material that the stream was easily able to carry away. “We also had a narrow stream channel that had just been cut as a temporary measure. So, we lost the bottom and the slide again. We knew if we were going to keep facing natural events like that, we needed to do a better job, even with a temporary solution,” Burnett said.
Second Time Is The Charm
The second time around a wider stream channel was cut. This one was armored with stone on both sides and on the bottom. By August, a decent channel had been created, a 30-ft. (9 m) high interim buttress of the landslide surface was in place and two lanes of traffic were reopened.
As for the water line, there were several hundred feet that had to be relocated. With the new stream alignment, the water line was now buried in a shallow location and was completely unprotected.
“We had to turn the water line, make a crossing for it underneath the new stream location and then bring it back to the surface and across the old stream location,” explained Burnett. The millions of dollars of water line work will be paid for by the federal government under its Disaster Relief Fund.
On Nov. 8, 2000, Delaware Avenue fully opened, nearly six months after the massive landslide. While workers finished stabilizing the slope the day before with the final buttress — a 30,000-ton (27,000 t) rock blanket — NYDOT engineers wanted to wait 24 hours before opening the road in order to verify that the pressure and water levels on the slope remained stable.
“We still continue to monitor the site,” Burnett asserted. “We have 10 instruments monitoring movement and 20 monitoring the ground water. The ground water monitors are the most volatile. They react at ground water movement but everything has settled down and it’s been quiet since we filled in the stream channel at the bottom.”
The nearly $1.5 million in work was performed by the Reale Construction Company of Ticonderoga, NY, who served as the emergency contractor. Their work included 10,000 tons (9,000 t) of gravel for an access road to the landslide, 4,500 tons (4,050 t) of large stone to armor the temporary channel and 20,000 tons (18,000 t) of light stone to shore up the failed slope adjacent to Delaware Avenue.
The permanent solutions of relocating the Normans Kill, providing new Normans Kill crossings for the Albany City waterline and a Niagara Mohawk gas line and restoring all four lanes of traffic on Delaware Avenue was completed by James H. Maloy Construction Company of Loudonville, NY. That work carried a price tag of $9.3 million.
To ensure expedited completion of the work, the contract included an incentive/distinctive clause stipulating that the diversion of the Normans Kill to its new channel had to be completed before Nov. 24, 2000. If the work was completed prior to that date, the contractor would receive a $10,000-per-day incentive; if the deadline was missed, the contractor would be assessed a $10,000-per-day penalty. All work was completed on schedule.
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