Pipe Ramming Replaces Drainage Culverts in Municipal and Railway Applications
Railroad and state highway officials alike are becoming keenly aware of the need for the replacement of drainage culverts. Many corrugated metal culverts inserted thirty years ago or more are rusting and deteriorating.
Some blame the chemicals used on roadways or the increased use of chemicals on farm fields. Yet others blame nature herself for her seasonally damaging frost. In any case, the result is the same – rotted pipe and diminished drainage capability.
Many drainage culverts are in need of replacement. Depending on the culvert's condition, relining is the least costly option.
Bowed, collapsed or undersized culverts present a unique challenge. Eighty-foot-long galvanized metal drainage pipes under roads experiencing significant ground-frost conditions, are subjected to the heaving of the ground every winter. Then every spring, as the frost leaves the ground, the ends of the culvert push up because the frost is a lot heavier underneath the road. This eventually leaves the culvert in the shape of a bow, six inches deeper in the middle than it is at the ends. The center section of the pipe eventually rots away and leaving a capacity flow problem. In addition, the subsurface roadbeds must be protected. There is too much traffic, both on the rails and on the roads, to allow water-damaged voids to lead to a collapse of the subsurface. Yet, even if replacement of the drainage conduit is the desired course of action, the question still remains as to how to replace the drainage pipe cost effectively. Open cutting is just not an option in most of these situations.
In High Prairie, Alberta, 500 km north of Edmonton, increased logging and farming operations have led to the increased need for water drainage, boosting the need for effective drainage culverts and even up-sized-diameter culverts. In the spring when the snow melts, the ditches become small rivers, with water flowing everywhere, threatening highway roadbeds and road surfaces alike.
At a recent demonstration project under Highway 2, attended by more than 30 transportation and railroad officials, a rotted 91 cm diameter corrugated metal drainage pipe was replaced by pipe ramming in a 107 cm by 14 mm thick steel wall carrier pipe with a 58 cm diameter HammerHead Mole by Wayne Sharris Construction of Edmonton, Alberta. The options for replacement were limited.
Open cutting and excavating a larger trench for the upsized replacement pipe would have meant the troublesome hutting down of the highway. Traditional auger boring was ruled out for a number of reasons. They wanted to keep the location of the drainage flow the same, maintaining the identical topography, grade and flow, and auger boring would not be able to bore over and concentrically swallow an existing pipe.
The old metal culvert would get caught up in the auger flighting, locking it up permanently. With auger boring, there would also be the possibility of hitting a sand pocket and the threat of creating voids in the subsurface roadbed. The pipe-ramming method was deemed to be the most effective and efficient way of getting the new pipe in by ramming in the larger-diameter pipe, concentrically swallowing the existing pipe and maintaining the existing location and grade of the drainage flow. With pipe ramming, there is no concern about creating voids since there is no soil displacement.
On this project, the grade of the pipe ram for the new 24 m steel pipe was set so that the low end of the pipe was between 10 and 15 cm below the high end. The launch pit was dug and graded to meet this requirement in one afternoon.
The pipe and tool were lowered into position with the top of the new pipe set two inches above the top of the existing culvert. The next day in a short 2-hour period, the new steel pipe was rammed in place by the HammerHead Mole Pneumatic Tool, with the new steel pipe cutting through the old rotted conduit and actually pushing some of the tail end of it out the exit end. The final grade was measured at 13 cm over the 24 m run, between the required grade parameters. To complete the clean-out, the remains of the old culvert were completely extracted, using a plug cone hooked onto a heavy-gauge cable and pulled by a backhoe through the new pipe.
Drainage culvert replacement by pipe ramming is also gaining acceptance under railroad tracks. The railroads have the same problem with ancient culverts and the same concerns about older technologies; the pipe-ramming method solves these.
Such a situation existed near New Albany, Indiana, just across the Ohio River from Louisville, Kentucky, CSX Transportation trains operate daily, hauling freight through the southern Indiana countryside. Six times a day, 365 days a year, they haul. The rail bed must not erode, and the embankments must remain rock-solid.
Over a 8 km stretch of this railroad, as it runs north from New Albany to Salem, Indiana, there are stone box culverts created 100 years ago and updated corrugated pipe brethren that followed them 70 years later. Time took its toll, and the rusted corrugated pipe and deteriorated stone culverts had begun to collapse. They needed to be replaced so that there would be no threat of erosion to the embankment or to the rail bed.
CSX Transportation had many concerns when planning this drainage replacement project. Safety concerns with settlement, quality concerns over the track and its rail bed, and concerns of disruptions to train traffic were high on their list.
There were 5 drainage culverts scheduled for replacement out of the 350 in the 130 km that separate Louisville, Kentucky, and Bedford, Indiana. Originally, the railroad planners thought that they would be forced to bid the job on an open-cut basis, and demand from the contractor that any one of the new pipes would have to be installed in a single day, with the trench backfilled and compacted, and the track replaced by nightfall so that trains could be routed to run the track the same evening.
This original plan faced potential scheduling nightmares. So, when Midwest Mole, Inc. suggested using pipe ramming with a large HammerHead Mole to push in the new casing and install the new drainage pipe without disrupting train traffic, the railroad officials were all ears.
With pipe ramming, the railroad was able to keep train traffic moving without any disruption, and by swallowing the old culvert when ramming in the new steel pipe, they did not have to change the drainage flow patterns. Also, there was never any fear of loss of integrity to the rail bed and embankment. They never had to worry about creating any voids during the installation since they were driving a solid steel pipe. Nor did they have to be concerned about any post-project settlement with pipe ramming.
Pipe ramming easily handled the tough soil conditions underneath the rail beds, like boulders, rock floaters, sand, gravel, rip rap and rail ties. When pipe ramming, the lead reinforced pipe edge shears the ties, and cuts and breaks up the rocks. One of the casings rammed in was 107 cm in diameter in order to concentrically swallow up a deteriorated 91 cm corrugated pipe, through which a small creek ran.
Pounding through layers of Indiana limestone, Midwest Mole brought in the HammerHead Mole to get the pipe hammered in the 15,2 m needed over the existing culvert.
With its 107 cm adapter ring and 61 cm collets to accommodate the tool, the HammerHead was lowered into the launch pit some 3 m below the track surface. The tool was started up, it taperlocked itself into the collets and the push was on.
The HammerHead pounded the pipe in under 90 minutes, through limestone floaters, boulders cobble, and railroad ties. When the crews cleaned out the limestone spoil, they saw the aggressive chipping that the tool had accomplished.
Pipe ramming dramatically improves the ability to escalate any culvert replacement program. This method is superior to any other in putting in new drainage pipe. With pipe ramming, there is no interruption of service, no appearance of settlement, and no concern about rail bed or roadbed integrity.
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