This is an excerpt from a technical paper presented at NASTT’s 2016 No-Dig Show in Dallas, Texas.
ABSTRACT
Culverts are very critical to drainage and transportation of fluids under highways. State Departments of Transportation maintain thousands of these culverts under highways, road and freeways. The Ohio Department of Transportation alone maintains over 85,000 culverts under Ohio’s priority and general highways. Through regular inspections and condition assessment of these culverts, a course of action ranging from routine maintenance to replacement is recommended. Pipe bursting is a viable alternative to replace deteriorated culverts. However, a high percentage of these culverts are made of corrugated metal pipes which are challenging to burst because the ridges tend to fold under the compression stress making it difficult, and often times, impossible to burst. The research team at Bowling Green State University (BGSU) in collaboration with two pipe bursting manufacturers (TT Technologies and Hammerhead) conducted pipe bursting research tests aimed at finding solutions to bursting corrugated metal pipes. This paper provides an overview of the pipe bursting operations through which four corrugated metal pipe culverts (12”, 18”, and 24” in diameter) were successfully replaced through this collaborative effort.
INTRODUCTION
The State Departments of Transportation (DOTs) are responsible for a large number of highway assets including culverts, which are important drainage structures under roads. The main purpose of these culverts is to transport water or fluid from one side of the highway to the other. During the industrial growth in the 1950s, culvert construction became necessary as a result of the freeway construction projects initiated in United States through the Federal-Aid Highway Act of 1956 (Camp, Boyce, & Tenbusch, 2010). Corrugated pipe, and in particular, corrugated metal pipe (CMP), was generally the material of choice on these low bid projects because of the relative low cost for a given strength of the pipe. The corrugations add strength to the pipe while permitting a reduction in wall metal thickness resulting in lower pipe material cost per foot of pipe (Tenbusch, Dorwart, & Tenbusch, 2009). Many of these culverts were designed for a 50-year life cycle, which is now ending (Camp, Boyce, & Tenbusch, 2010). For these assets to continue to perform their intended function and meet future demands, they have to be replaced or rehabilitated.
As underground structures, culverts are less noticeable and are often ignored until a catastrophic failure occurs (Gee, 2007). These failures lead to temporarily roadway closure, disruption of traffic flow, and considerable re-installation costs. A complete collapse of the culvert may result in the collapse of the roadway posing a major safety risk or hazard to motorists. With factors such as aging and deteriorating national infrastructure, increasing congestion, highway safety challenges, and limited funds, state departments of transportation are looking for innovative ways to manage their transportation assets (Gee, 2007). Consequently, the selection of economic alternatives to replace deteriorated culverts has become an important aspect of managing these assets.
Open-cut, which is the traditional method for culvert rehabilitation, is an expensive alternative for deep installations due to the massive excavation and need for shoring. Apart from the direct cost, there are social costs such as traffic disruption, road closures, business interruptions, noise pollution, environmental impact, and reduced safety for both workers and road users associated with open-cut. Trenchless rehabilitation methods such as cured-in-place pipe, slip lining, fold and form and other relining techniques have the disadvantage of reducing the internal diameter of the existing pipe and hence not applicable where there is the need to increase the diameter and flow of the existing pipe.
Pipe bursting provides an innovative and practical alternative to open cut without the disturbance and the cost of excavating a trench (Atalah, 2008). Pipe bursting has several advantages over the traditional open-cut method; it is much faster, more efficient, and less expensive especially in gravity applications due to their deeper depths. Pipe bursting is the only trenchless rehabilitation method that can replace an existing pipe with an entirely new pipe resulting in total replacement of the existing deteriorated pipe (Lueke, 1999). Pipe bursting also has the advantage of maintaining or increasing the flow capacity of the existing deteriorated pipeline by increasing the diameter of the replacement pipe. Pipe bursting has been used to replace almost all types of pipes including lightly reinforced concrete pipes, ductile iron pipes, clay pipes, steel pipes, vitrified clay pipes (VCP), cast iron, plain concrete, asbestos and some plastics. However, corrugated metal pipe (CMP) is not considered a good candidate for pipe bursting because the ridges of CMP fold like an accordion under compression thickening the wall and making it almost impossible to burst or slit or split.
The Ohio Department of Transportation (ODOT), alone maintains over 85,000 culverts and about 20% (17,500) of these culverts are corrugated metal pipes (ODOT Culvert Database, 2014). Considering the large number of existing CMP culverts and the continual use of CMP for culverts, it is essential to expand the pipe bursting applications to these culverts, which will in turn provide an alternative rehabilitation method for municipalities and transportation agencies.
To determine the system and tools for successful bursting of corrugated metal pipes, field tests were conducted that involved the replacement of actual culverts under existing roads. The two pipe bursting manufacturers, TT Technologies and Hammerhead, contributed their bursting equipment and technicians. These tests provided the opportunity for the manufacturers to investigate different accessories, designs, and system configurations to successfully burst corrugated metal pipes.
Through the collaboration of ODOT, the manufacturers, and the research team from BGSU, four CMP culverts were successfully replaced using pipe bursting. The pipe bursting tests were done in ODOT’s Districts 2, 5, and 10. All the pipes were replaced with high density polyethylene (HDPE) DR 17 pipes which were delivered and fused on site. The District 10 test was done with a pneumatic bursting system, while the District 5 and 2 tests were done with a static bursting system.
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