The City of Bowling Green, Ohio, operates a water distribution system that delivers high-quality water. The system operates optimally in a grid system; larger, “trunk water mains,” are installed in a grid pattern on the outer limits of the system with smaller lines branching of the larger lines.

Almost all the residential, industrial and commercial areas in Bowling Green were limited to the west side of I-75. However over the past few decades, these areas grow on the east side of I-75. Two 24-in. water mains crossed underneath I-75 at the central and south part of the city to provide water to the east side. These limit development in the north eastern section and subject the WWTP (located in that part) to an undue risk if any damage occurs in the central trunk. The installation of a 16-in. waterline underneath I-75 at the northern end will ensure fire protection for the existing industry and supply a second water source to the WWTP.

Four construction methods are examined to cross the interstate with a new waterline: open-cut with detouring traffic, postponing the installation until resurfacing the interstate to install the line by open-cut, horizontal directional drilling (HDD) and auger boring. This article examines the design and construction cost of the four potential methods of construction to install a 16-in. waterline underneath I-75.

The City of Bowling Green located in Wood County in Northwest Ohio has a current population of approximately 29,000. The City owns and operates its public utilities systems including a water treatment plant and water distribution system, as well as a wastewater collection system and wastewater treatment facility. The City treats, distributes and releases an average of 7 million gals of wastewater a day and has a maximum capacity of producing 10 million gals of potable water a day (City of Bowling Green, 2010).

This article examines a portion of the water distribution system that was constructed in less than an optimal format. Ideally, a water distribution system is set up in a grid format, which allows for optimized flow throughout the system (Alperovits & Shamir, 1977). However, dead end lines occur; dead end lines have only one end connected to the grid. The City’s wastewater treatment plant (WWTP) uses city water in its treatment process; however, the wastewater plant receives water from a dead end water line. There is also a large industrial park that is served by the same dead end water line. This is a weak point in the water distribution system. If the current water line that serves the WWTP or industrial park fails, the WWTP and several large factories will be without water service. This could cause an overflow of raw wastewater into the environment, which is illegal and could cause flooding in residences homes.

The proposed water line connects the dead end line on Dunbridge Road to the water line on Mercer Road creating a loop and a second feed to the wastewater treatment plant and industrial park. The line is needed to meet increasing demands in the north east area.

This study attempts to evaluate the installation alternatives to the proposed line that close the loop and eliminate the dead end in the distribution system. Creating this loop significantly reduces the risk of interruption to water supply to the WWTP and Industrial Park, enhances the fire protection to areas currently lacking fire protection and encourages future development in the area.

Four potential methods of pipeline installation were examined: open-cut a trench to cross the Interstate by diverting traffic, HDD or auger boring and jacking and open-cut during the interstate reconstruction. Using water-modeling software the City of Bowling Green’s Engineering Division determined that the desired pipe size is 16 in. (T. Sonner, Personal Communication, March 21, 2012).

According to the ODOT’s Policy for Accommodation of Utilities, which gives detailed guidance for the procedure of crossing state-owned right of ways, HDD or auger boring are acceptable methods for crossing the interstate (Ohio Department of Transportation, 2007). The final method to be approved will be a negotiated between ODOT and the City of Bowling Green.

Installation Methods
The following four installation methods were considered for the project:

  • Open-cut a trench and cross the Interstate by diverting traffic.
  • Construct and install the pipeline using trenchless technologies and cross the Interstate by means of directional drilling.
  • Construct the pipeline using trenchless technologies and cross the Interstate by jacking and auger boring.
  • Postpone the project and install the pipeline when road reconstruction is occurring allowing for an open-cut installation while traffic is already diverted.

Traditional Open-Cut Method
The first potential pipeline method of installation is traditional open-cut. The advantage of traditional open-cut construction is allowing the project to progress in a continuous fashion; the laying and backfilling of pipe allows the project to progress at a steady pace. The traditional open-cut method is suitable for nearly all soil conditions. Finally, the traditional open-cut method is often the most economical choice due to the lack of additional support operations and systems required with trenchless methods (Trench and Excavation Support Options). It is well documented that cutting the asphalt and subsequent repairing of cut asphalt significantly reduces the lifespan of the asphalt paving.

Horizontal Directional Drilling
The second examined pipeline installation method was HDD. The entire project or portions of the project, such as the interstate crossing could be installed using the HDD method. HDD was initially used in the installation of telecommunication lines but is now used to install pipelines of up to 48 in. in diameter (Abraham, Baik, & Gokhale, 2007). The advantages of HDD are many such as: no interruption of traffic flow, minimal surface and subsurface disturbance, and little if any surface restoration after project completion. HDD is a surface launched process not requiring drive pits or reception pits, which can significantly reduce project costs. However, pits may be required to connect existing utilities to newly installed utilities (Abraham, Baik, & Gokhale, 2007).

The cost of HDD is quite competitive when compared to traditional open-cut installation. Consideration must be given to the depth of installation when using HDD. As the depth increases the cost of HDD becomes more competitive when compared to the cost of open-cut trenching. When there is limited accessibility to the installation site, HDD can be used where traditional methods are prohibited or impractical.

HDD is not without its limitations, intersecting utilities pose problems for HDD placing constraints on the depth of installation. If other utilities cross the path of the HDD machine, the new installation may have to be placed at an undesirable depth. There is also the possibility of surface heaving and subsidence. The installation requires high-pressure slurry to assist in constructing the borehole for pipe pullback. If the soil is of insufficient strength to withstand the pressure, surface heaving can occur. Furthermore, the pressure and high flow rates of the slurry can also cause soil to erode causing voids resulting in subsidence (Baik, 2003).

Horizontal Auger Boring
The third examined method is to install the pipeline by traditional open-cut and auger bore under the interstate. The operation requires the excavation of a jacking pit and a receiving pit. Vertical alignment is controlled by a water level and horizontal alignment control can be somewhat limited (Abraham, Baik, & Gokhale, 2007).

Auger boring has its advantages. Auger boring casings can range in size from 4 to 60 in. Typical drive lengths range between 40 to 300 ft. Site restoration is only required at the boring and receiving pits. Auger boring is particularly useful in unsuitable soils, cobbles and boulders as large as one-third the size of the casing can easily be handled and removed from the casing. A major advantage of auger boring over other trenchless methods is the casing acts as the borehole eliminating the possibility of cave-ins during the boring process.

Auger boring may not be the most practical method when line and grade are important. Auger boring requires a substantial investment due to the variety of casing sizes, which require many different size cutting heads and augers; therefore, increase costs. Setup and bore pit excavation can also be more costly than other trenchless methods due to the forces required to drive the cutting head, casing, and auger (Abraham, Baik, & Gokhale, 2007).

Postpone and Install During Road Reconstruction
Postponing the project and installing the pipeline during road reconstruction is a viable method of installation worth exploring. There is a high possibility that ODOT will reconstruct the Interstate in the near future and add a third lane in both northbound and southbound lanes of travel. The pipeline could be installed by means of open-cut while the road is being rebuilt and traffic is already diverted. This may save a substantial amount of fund in the initial project.

Estimated Quantities and Costs for the Project
Quantities were estimated for the project by obtaining historical bid data from the City of Bowling Green’s engineering division. Two bid tabulations were used to obtain estimates, Gypsy Lane Water Line Extensions Phases One and Two. These two bids were used due to their similarity to the proposed project. There are few connection points and there is no asphalt cutting required. The project also has an auger-boring estimate contained in the bid. Hydrant assemblies were obtained from the Gypsy Lane Water Line Extension Phase Two.

Prices — not available from historical data — were estimated using RS Means, a construction estimating software program that allows the user to estimate a variety of construction projects using current pricing. Projects are broken down into material, equipment and labor. Data was also acquired by obtaining estimates from contractors.

This project requires the installation of approximately 5,700 ft of 16-in. water line; 16–in. DR18 PVC pipe was the selected pipe for installation. The Interstate crossing consists of a total of 300 lf with 80 lf of asphalt. There are also two connection points at each end of the project requiring a transition fitting to connect two differing pipe materials. A separate estimate was used to price the transition couplings and their installation.

The cost of the project is divided into two phases: the open-cut portion of the project and the crossing at the interstate. The most practical way to complete the project would be to install the pipeline by means of open-cut and then perform one of the four methods discussed to cross the interstate.

Project Estimate Traditional Open-cut Installation

Since the project is in a relatively remote area, the material removed from the trench can be stored near the project and placed back in the trench. Below is an estimated cost of installing the 16-in. water line by traditional open-cut. Table 1 shows the open-cut portion of the project minus the open-cut, backfilling and compaction of the interstate, which was calculated using RS Means.
Table 1
Table 2 shows the estimated cost of removing and re-installment of the asphalt pavement and sub-grade of the Interstate. This estimate was obtained by using RS Means.

Table 2

Finally, a cost estimate was developed to accommodate traffic diversion. Required distances for delineation devices and signage for single lane closures on interstate highways was determined using, “ODOT’s Manual for Uniform Traffic Control Devices” (Ohio Bureau of Traffic Engineering 1999). The unit costs in Table 3 below were acquired from Safeway of Perrysburg Ohio, who specialize in renting traffic control devices.

Table 3

The total estimated cost to perform the project by means of traditional open-cut would be: $548,733.04.

Project Estimate Using HDD
In an interview with Dustin Schlachter of S & S Directional Boring Ltd., a cost of $95 per linear foot was quoted with an additional emergency contingency charge of $30 per linear foot in case of road heaving or settling. Below in Table 4 is the estimated cost of the project using horizontal directional drilling using HDPE.

Table 4

For comparison purposes, an estimate of the directional drilling portion of the project was developed using RS Means. Below in Table 5 are the unit costs and total costs for horizontal directional drilling. Boring pits are included in the estimate in case the desired angle of drilling cannot be obtained.

Table 5

RS Means will only estimate the cost of directional drilling of a 12-in. pipe. In order to convert the price to 16-in., the cost of the directional drilling is broken down into a cost per inch. Increasing the size by 4 in. increases the cost $331.67 with the total cost being $28,746.67 and a total unit cost of $95.82. If the $30 emergency contingency is added, the total cost to perform the directional drilling is $125.82/lf.

In order to obtain drilling fluid costs, the Baroid company was consulted. In order to accommodate a 16-in. pipe several back reaming processes must be made. Below in Table 6 are the costs calculated for drilling fluid materials.

Table 6

The total estimated cost from bid tabulations, contractors estimate, and drilling fluid equals $514,459.12 + $2.146.86 = $516,605.9

Project Estimate Auger Boring
The project estimate for crossing the interstate by means of auger boring was calculated in the same manner as the previous two methods. Table 7 shows the estimated cost of the interstate crossing performed by the auger-boring using RS Means.

Table 7

Below in Table 8, is the estimated cost of auger boring using RS Means. The estimate includes driving and receiving pits as well as dewatering and sheet piling.

Table 8

The slight difference in the cost per linear foot for the auger bore using RS Means is due to the slightly larger casing. The total cost to install the project by auger boring from bid tabulations equals $658,309.12

Postpone the Project

Postponing the project and having the water line incorporated into the design of the highway reconstruction may lower the overall cost. If ODOT were to pick up the cost of traffic diversion and remove the asphalt and sub-grade, The City may pay the cost to install the water line across the highway. Once the water line was installed, it could be incased in a concrete casing. Below in Table 9 is the open-cut portion of the project including the highway crossing minus the asphalt and road sub-grade estimate.

Table 9

An RS Means estimate was developed to establish the cost of incasing the water line in concrete and filling the trench with a suitable granulated fill. Compaction is also included in the estimate. Below in Table 10 is the estimate to install the concrete and fill the trench with granulated fill.

Table 10

The total cost to postpone the project would be: $512,387.47. Table 11 shows the total costs of all methods and the total cost per linear foot and the cost per foot to cross under the highway.

Table 11

Recommendation
The least expensive method of installing the water line is the open-cut method. However, open-cutting across Interstate 75 does not seem likely. The next least expensive method at $89.89 per linear foot is to postpone the project and install the water line when the highway is being reconstructed. The timing of this method may not coincide with the needs of the community. It has recently been discovered that the construction of a new water tower is being designed near the project area. Therefore, this project may be expedited, which makes the horizontal directional drilling more attractive. HDD across the interstate is the next least expensive method at $90.63 per linear foot. Furthermore, when indirect costs, such as social costs, which this paper does not address, are considered a trenchless method is more desirable. ODOT may be convinced to allow the water line to be constructed without a casing making this the most economical way to complete the project.

Victor C. Goduto is with the City of Bowling Green, Ohio. Dr. Alan Atalah, Ph.D., P.E. is an associate professor working for Bowling Green State University.

References

  • A Decision Support System for Horizontal Directional DrillingTunneling & Underground Space Technology, 200318 (1), 99.
  • Design of optimal water distribution systems.Water Resources Research-1977 Vol 13 (6) 885-900
  • Development of a Decision Support System for Selection of Trenchless Technologies to Minimize Impact of Utility Construction on RoadwaysLafayette, INPurdue University2007
  • Google MapsGoogle Maps2012https://maps.google.com/maps?hl=en&tab=wl.
  • Ohio Bureau of Traffic Engineering Ohio manual of uniform traffic control devices for streets and highwaysColumbus, OhioOhio Bureau of Traffic1999
  • Ohio Department of TransportationPolicy for Accommodation of UtilitiesPolicy for Accommodation of Utilities2007https://www.dot.state.oh.us/districts/D10/Right_of_Way_Permits/Documents/Manuals/Utilities percent-20Manual.pdf
  • Web Soil SurveyWeb Soil Survey2012https://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx

 

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