In the utility construction world, road crossings are some of the most common and often challenging projects for any contractor. From traffic control to preserving the integrity of the roadway, contractors face a multitude of challenges anytime they attempt one of these projects.
Recently, trenchless contractor Staggs Environmental Construction, Inc., (Staggs Environmental) Muscle Shoals, Alabama, USA, took on a significant casing installation project under a highly traveled roadway, Memorial Drive, near Atlanta, Georgia.
Staggs Environmental president and owner John Staggs said, “The project was done in Dekalb County, Georgia. That entire area is basically under a consent decree and existing sewer systems need to be upgraded and to be in compliance. They’re also doing work on the water system. This portion is a 36-inch watermain project that’s been going on for about a year. The project has moved forward until it reached this major highway, Memorial Drive, and stopped.”
In order to allow the 36-inch ductile iron watermain under the road, a 54-inch diameter steel casing needed to be installed under the road to act as a sleeve for the new water main. The project was initially slated to be completed by a different pipe installation process, however, with the soil conditions in the area, there were concerns that that type of project could affect the stability of the road. Staggs said, “So, after the project sat for about a year, one of the county officials got in touch with us. I told them, that I thought we could pipe ram it and that would be the safest, most sure way to get across the road. And after about three weeks of deliberation, that’s the route we took.”
Trenchless Specialists Eddie Ward and Rick Melvin from trenchless equipment manufacturer TT Technologies, Aurora, Ill., provided technical and equipment support on the project. Ward said, “Pipe ramming is often the method of choice for road and railway crossings because of its ability to install casings without creating voids or surface slump. That was key on the Memorial Drive project.”
To install the 140 feet of 54-inch casing, Staggs Environmental choose a 24-inch diameter Grundoram Taurus pipe ramming system from TT Technologies.
Staggs Environmental Construction has over 20 years of trenchless experience and was the right contractor to get the Memorial Drive project moving again. Staggs said, “I started and incorporated the business in February of 2003. We originally focused on manhole rehab point repairs and service replacements for the cured-in-place industry. Then we decided to get into the pipe bursting and the pipe ramming business in about 2006. Trenchless utility contracting is all we do. No private or residential work.”
Before Staggs Environmental could get started with pipe ramming, the ramming pit needed to be excavated. Staggs said, “It took the general contractor about two weeks to finish the excavation for the ramming pit. It was kind of in a tight area. So, it took about two weeks of prep to get the launch pit ready for us to come in and put the casing in. The overall pit length was 44 feet, and it was at least 10 or 12 feet to the top of our casing.”
According to Melvin, the pit excavation revealed several key findings. He said, “You might expect the infamous red Georgia clay, but that wasn’t the case here. It was a silty sandy soil. It was actually great soil. Not wet, very conducive for pipe ramming. However, there was the potential for some big boulders and cobbles. Some large diameter boulders were encountered while digging the pit.
Once the pit was excavated and shored, steel road plates were used to create a solid and stable pit floor. The plates were tied into the shore box to keep them in place during ramming. A creative approach was taken to guide the casing during ramming.
Melvin explained, “Staggs Environmental used angle irons to keep the casing centered. They ran 3-inch angle irons on either side of the casing and welded them down to the plates. First, they positioned the first casing in the pit and got it aligned. Then they put down the angle irons and tack welded them to keep them positioned properly. Then removed the casing and fully welded the irons in place. That’s how they guided the casing and kept it aligned throughout the ram. This wasn’t grade critical, but it needed stay on target.”
Crews also installed a cutting shoe overcut band on the outside of the casing. The cutting shoe provides some reinforcement on the lead end of the casing in case it encounters any rocks like the ones removed during excavation and helps reduce friction.
Once the cutting shoe was in place and the pipe aligned, the connection between the 24-inch diameter pipe rammer and the casing was made through standard ramming gear. Ward said, “Standard 54-inch ram gear consists of a 54-inch segmented ram cone that makes direct connection with the casing. Then 48-inch and 31-inch ram cones facilitate the connection with the casing and the 24-inch diameter rammer. For this project, we ran with a single 1800 CFM air compressor to power the rammer.”
According to Melvin, the location of the project added a level of difficulty. He said, “First there was Memorial Drive. This is main traffic artery and definitely a ‘no dig’ highway. It was also a very tight neighborhood and work window. They ended up having to close an adjacent road to stage casings and equipment. It was very congested. Lots of old trees, houses in a concentrated area.”
Once ramming was underway, Staggs Environmental crews were able to reach a high level of productivity. Staggs said, “We were very efficient ramming the 20-foot sections of 54-inch pipe, averaging about 45 minutes per round. It went really well and there was a tremendous amount of sandy soil. So, I do understand why others were not interested in going under Memorial Drive. The welding times on each new segment of casing typically took between four to six hours per joint. We welded most of them in the morning and then we rammed them in that evening. After we got our first two sections in, we started cleaning them out as we went and then dropped one in and welded again.”
The Staggs Environmental crews were on schedule to have all the ramming done in seven days, but the weather had other plans. Staggs said, “Weather was our biggest challenge on this project. It was just terrible out there. We had some rain that caused a two- or three-day delay. But we were going through a rainy period and a hot period here all at the same time. The 100-degree heat was extremely difficult. Keeping everybody cool and hydrated was the big thing. We made sure everybody had water. We had blower fans on site and put tents over the bore pit to keep the sunshine off and provide shade for everyone working in the pit.”
In the end, ramming the 140 feet of casing, seven sections of pipe, took eight days total. Staggs Environmental crews were on the job for three weeks from start to finish. Staggs said, “They said the thing came out right on target. On grade and on point there. Perfect with everything.”
Melvin said, “It was a solid project and John and his crew did an excellent job. They are highly skilled and know what they’re doing.”