NIPAWIN SEWAGE FORCEMAIN
A Directional Drilled Crossing of the Saskatchewan River

Rod Karius, P.Eng., Associated Engineering Edmonton, Alberta
Contact: kariusr@ae.ca

ABSTRACT
From a global perspective, directional drilling is not a new construction technique. It was adapted in the early 1970s from oil well drilling technology. Initially, its use was limited to steel pipeline construction in the petroleum industry for crossing under natural and manmade obstacles such as rivers and highways. In the 1980's, the technology was applied to water transmission lines and sewage forcemains. Today, directional drilling is used not only for the installation of pipelines but also electrical and communication cables.

Installations have been as large as 1200 mm in diameter with distances exceeding several thousand metres. In contrast to the apparent broad usage of directional drilling, the application of this technology to water and wastewater pipeline installations in western Canada is still relatively rare. In researching the use of horizontal directional drilling for the installation of a polyethylene sewage forcemain across the Saskatchewan River at Nipawin, Saskatchewan, no other installations of similar pipe material or diameter were found in western Canada.

This paper has been prepared to document the case history of the directional drilled river crossing at Nipawin. The project is noteworthy in terms of the size of pipe installed (large for polyethylene), length of the crossing, depth of the river valley and variability of the soils encountered. The paper provides a comparison of the costs and environmental impacts for both conventional open cut and directional drilled crossings. Also presented, is a review of the technical considerations that apply to the design of a directional drilled crossing as well as the contractor's proposed and actual methods of dealing with the technical challenges presented by this particular crossing.

THE PROJECT

As a result of changes in provincial regulations governing sewage treatment, the Town of Nipawin was required to upgrade it's sewage treatment facility. Also affected were a number of smaller nearby communities, cottage subdivisions and a canola processing plant. This lead to the development of a new regional sewage treatment facility. Click here to view Figure 1 in a new window.

Construction of the new facility was carried out under a number of contracts, one of which covered the installation of sewage forcemains. The largest component of the forcemains contract was the 400 mm diameter, 3060 m pipeline connecting a new sewage pumping station at the Town of Nipawin to the new treatment facility; consisting of a four cell, 60 ha facultative lagoon. Click here to view Figure 2 in a new window.

THE SASKATCHEWAN RIVER CROSSING
It was recognized early in the design process that the Saskatchewan River would be a major obstacle in the construction of the forcemain. The river valley is 40 m deep and 500 m wide with steep side slopes containing loose deltaic sands overlaying highly variable glacial till deposits. Click here to view Figure 3 in a new window. Water levels fluctuate between two and six metres in depth because of hydroelectric generating stations operating upstream and downstream of the crossing location. Finally, and perhaps most importantly to the Town, the River is a major recreation facility and significant generator of tourism revenue.

Directional drilling was the first construction method to be examined as it had the apparent advantage over conventional open-cut construction of avoiding the problems associated with working in the river valley. However, the initial findings were disappointing. Because of the depth of the river valley and limitations on the entry and exit angles, the total drilling distance was going to be twice the width of the river valley. This would place the entry and exist points too far away from the pipelines proposed right-of-way. In addition, the cost appeared to be about twice that of an open-cut crossing.

Engineering work proceeded into the detailed design stage on the basis of a conventional open-cut crossing. Polyethylene was selected for the pipe material. Details were developed to deal with river bank erosion and concrete ballast was sized for the submerged section of the pipeline.

Protection of the submerged pipeline during flood events proved to be an obstacle that would in the end raise the cost for open-cut construction and bring it into the same order of magnitude as directional drilling. The flood frequency selected for design was a 1:100 year return period. This yielded a flow of 6400 m³/s and a velocity of 2.2 m/s. Scour at this velocity would extend through the sandy river alluvium to the till formation below, requiring the pipe to be placed on the surface of the till layer and covered with a scour protection apron, or to be placed into the till layer with a minimum cover depth of one metre. The latter option was carried through into final design.

The necessity to excavate into the till layer was likely going to require unconventional methods and/or heavy marine excavating equipment. Recognizing this and its cost implications, it was decided to revisit the directional drilling alternative. However there was insufficient time remaining in the schedule to complete a detailed design for this approach. The project went to tender on the basis of a conventional open-cut river crossing with provision for directional drilling to be submitted as an alternative bid item.

Five bids were received; three were based on an open-cut crossing while two of the bidders provided prices for the directional drilling alternative. A comparison of the pricing for the bid items pertaining to the two crossing methods is provided in Table 1.

TABLE 1

The lowest directional drilling bid came in at a relatively small premium of only 10% over the lowest open-cut bid. This was considered to be a reasonable price to pay for the environmental benefits gained in not having to disrupt aquatic and recreational activities on the River. It also eliminated disturbance of the River valley's steep side slopes. Based on these benefits, the project was awarded to Bidder #2 for construction of the river crossing by directional drilling.

 
DIRECTIONAL DRILLING: TECHNICAL CONSIDERATIONS
If time would have permitted detailed design of the directional drilling alternate to be carried out, a series of technical considerations would have been addressed to establish performance specifications for the pipe and its installation. However the situation was now reversed. The pipe was already specified and the contractor was in control of the construction details. In order to deal with this situation, the contract award was made conditional on certain technical considerations being satisfactorily addressed by the contractor.

The contractor was requested to provide information on the entire directional drilling concept and to specifically address the following seven components:

- Drilling and pipe installation process

- Right-of-way requirements

- Geotechnical considerations

- Impact on specified product pipe

- Pulling head design

- Testing and commissioning procedure

- Contractual issues.

Excerpts from the contractor's submissions are outlined below to highlight the unique aspects of this project and to contrast with some of the actual events and difficulties that occurred during construction.

Drilling and Pipe Installation Process (Contractor's Plan)
The contractor proposed to set up the drilling rig on the east bank of the River and increase the 12_ optimum entry angle into the 17_ to 20_ range. The rig could then be placed as close as possible to the River to minimize the drilling distance. However, this steep angle would be at the rig's upper limit, increasing the risk of mechanical and safety problems. The borehole would then follow the contour of the river bottom with a minimum cover of 6 m at its shallowest point and exit at an 8_ angle onto the west bank resulting in a total crossing distance of 568 m.

The drilling operation would take place in several stages (Click here to view Figure 4 in a new window), the first being the pilot hole. The contractor proposed to drill the pilot hole with a 250 mm diameter bit attached to a 165 mm mud motor. The pilot drilling would be followed by two reaming operations at diameters of 450 mm and 600 mm. The reaming tools would be the tri-cone type in order to cut through any rocks and boulders that might be encountered. Concurrent with the drilling operation, the poly pipe would be assembled on the west side of the River. The entire length of the crossing pipe had to be fused into a continuous section and tested. Immediately following the final reaming operation, the entire length of the polyethylene pipe for the crossing would be pulled into the borehole on the west bank and under the river, exiting at the drilling rig on the east bank.

The total directional drilling operation from mobilization through to installation of the pipe was to take no more than four weeks during the period between mid April and mid May, 1995. The duration of specific activities was anticipated to be as follows:

- pilot borehole: 4 to 5 days

- first reaming operation: 3 to 4 days

- second reaming operation: 3 to 4 days

- pipe pull operation: 8 to 20 hours

Right-of-Way Requirements
On the east side of the River, the contractor identified the need for a 20 m x 40 m working area for the drilling rig and support equipment. The working area had to accommodate a large drilling fluid tank, skid mounted power plant, control cab, two flatbed trailers containing the drilling pipes plus laydown areas for bagged bentonite, drilling head assemblies and other accessories. The drilling rig also needed access to a continuous supply of water.

At the exist end on the west bank, a smaller working area was needed immediately adjacent to the borehole for a backhoe and loader to assist in the movement of the pipe during installation. Of more significance was the area needed to string, fuse and test the pipe. Ideally, in order to minimize drag forces, the alignment for this area should be a straight line continuation of the borehole. In addition, the ground should be vegetated or if stripped, the soil should be free of stones.

Geotechnical Considerations
The contractor's knowledge of the subsurface soil conditions and the tools employed to deal with these conditions are the most important factors in how successful the directional drilling operation will be. Ideally, test holes should be drilled along the crossing alignment to establish a profile of the soils and their properties.

On this project, the contractor elected to make use of existing geotechnical information without doing any exploratory testing of his own. The information made available to the contractor was compiled previously during studies of proposed locations for a hydroelectric generating station that was eventually constructed approximately 4 kms upstream of the crossing location. The information was in the form of drill hole logs and interpretive geologic profiles. However, none of this information was specific to the crossing site and it gave no indication of the extent to which rocks and boulders could be encountered in the till formations.

Impact on Specified Product Pipe
Under normal circumstances, the specifications for pipe material to be installed by directional drilling would be determined through an analysis of the following operational and installation conditions:

Theoretical analysis of the anticipated pressures and stresses, as well as input from the pipe manufacturer, resolved all concerns except two: differential pressure during installation and tension stresses. Differential pressure posed a problem because of the 500 to 550 kPa hydrostatic pressure that would be exerted externally by the drilling fluid and the absence of any compensating internal pressure based on the contractor's proposed "dry" installation. The calculated differential pressure exceeded the pipes critical external collapse pressure based on the estimated 8 to 20 hours it would take to complete the pull, open the head end and pump water into the pipe to equalize the pressure. The other concern, tension stresses, resulted from the 75,000 kg pulling capacity of the drilling rig as compared to the 40,000 kg maximum permissable pulling force on the DR11 pipe. The potential existed for the rig operator to tear the pipe apart during the pulling operation.

Of the two outstanding concerns, the pipe collapse possibility was the most serious and difficult to deal with. The pipe separation issue could easily be addressed through close observation of the rig's pulling forces by monitoring instrumentation located on the rig operator's control console. The pipe collapse issue required a major change in the contractor's installation procedure. The pipe pulling process would have to change from a "dry" to a "wet" installation.

Three "wet" installation options were considered. The first was to have the pipe filled with water prior to the pulling operation. This was rejected on the basis of the additional weight the rig would have to pull which would increase the risk of the pipe being pulled apart.

The second option was to add water during the pulling operation only in sufficient quantity to fill the section of pipe at the low elevation in the river channel. This option had a complication however. A vacuum condition in the head end of the pipe would occur when the pipe started its climb up the east bank. This could have been overcome by stringing a small diameter, thick walled pipe through the entire length of the product line to allow air to enter the head end of the forcemain. The contractor rejected this approach on the basis of cost and complexity.

The third option was to use a perforated pulling head that would permit drilling fluid to enter the product pipe as it was being pulled through the borehole. This option was the simplest and least costly but it did have a margin of risk in that the perforations could become plugged with borehole cuttings. However, the contractor assessed this option as having the least risk and selected the perforated pulling head as the preferred means to facilitate a "wet" installation.

Pulling Head Design
The pulling head is the tail end piece of a connection that couples the drill stem to the product pipe. Other components in this assembly include a barrel reamer, swivel and shackles.

The pulling head is generally custom built for each crossing to suit the diameter and DR of the product pipe as well as the anticipated pulling stresses. The pulling head is fabricated out of steel and is cylindrical in shape for insertion into the product pipe. Bolts connect the pulling head to the pipe.

The number of bolts and their spacing is critical. An insufficient number of bolts will result in shear failure under the load imposed during the pipe pull. Too many bolts or too close of a spacing and the product pipe will tear apart under load.

A further consideration was introduced with the need to have openings in the pulling head for the "wet" installation. This would require reinforcing to be added between the openings to strengthen the pulling head.

Testing and Commissioning Procedure
Before the drilling rig would be permitted to leave the site, the contractor would have to demonstrate through testing that the pipe had been installed satisfactorily. Three tests were agreed to. The first being a leakage test of the fused pipeline prior to installation. The second being a leakage test after installation, and the third being a flow test to confirm that collapse of the pipe had not occurred. In addition, the forcemain would have to be pigged to remove the drilling fluid and borehole cuttings that would enter the pipeline as a result of the "wet" installation.

Contractual Issues
A significant concern to the Town of Nipawin was the level of contractual risk they were taking in awarding the contract on the basis of what was little more than a "proposal" for the river crossing component of the project. This was addressed in a number of ways. Firstly, all of the technical issues had to be dealt with. Secondly, the contractor had to provide confirmation that the directional drilling sub-contractor's work was covered under his Performance Bond and his Labour and Material Payment Bond. Last of all, the contractor had to agree to lock in the quoted drilling price as a lump sum rather than a unit price to eliminate any possibility of the cost increasing due to a longer than anticipated borehole distance.

CONSTRUCTION
Site Preparation and Setup
The drilling subcontractor mobilized to the site in mid April, about two weeks later than initially proposed because of the late spring thaw. Equipment setup and stockpiling of materials took place between April 16 and 25.

Site preparation work on the rig (east) side of the crossing included stringing fire hose overland to the closest hydrant, excavation and concrete placement for an 11 m³ anchor to hold the rig in place and erection of temporary fencing to secure the working area. On the pipe assembly (west) side of the crossing, the working right-of-way limits were established for stringing and fusing the pipeline.

During the process of establishing the west side right-of-way, the contractor requested a change in the location of the exit point for the borehole. The contractor preferred to exit on higher ground to eliminate difficult trenching conditions up a ravine. However, this would lengthen the river crossing. The change was agreed to on the basis that the drilling component of the river crossing would be done for the same total price tendered for the original crossing location. In other words, payment for the drilling component became a lump sum price.

The entry and exit points were established on the ground. A ground profile was surveyed between these two points and the water's edge on each bank. Sensing cable for the guidance system was then strung along the ground, offset on both sides of the profile alignment, between the exit/entry points and the river bank.

The surveyed ground profile was entered into a computer program employed by a specialist firm the drilling contractor retained to provide steering and tracking for the drilling of the borehole. The software generated a profile of both the ground/river bed surface and the proposed borehole path. The resulting crossing distance of approximately 680 m was, as anticipated, significantly longer than the 568 m estimated earlier by the contractor. This necessitated an increase in the quantity of DR11 pipe and a corresponding marginal increase in the project's cost. Fortunately, the drilling cost did not increase as the contractor had already agreed to a lump sum price.

The borehole trajectory was fine tuned to meet minimum clearance requirements between the pipe and the river bed. The entry and exit angles were set at 17_ and 13_ respectively.

On April 26 the drilling head components were assembled and placed into position on the rig. The assembly included a 250 mm diameter drill bit, mud motor, the steering section known as a bent housing, and a downhole probe that relays inclination, drill head orientation and positioning data back to the guidance computer.

The subsequent sequence of events involved in the drilling of the borehole and installation of the pipe are depicted in a series of diagrams on Figures 5 and 6 followed by a chronologic summary on Figure 7. These events are elaborated on in the text that follows.

Borehole
Drilling commenced early on April 27. By the end of the first day a distance of 150 m had been covered. Drilling commenced the next morning and had progressed for several hours when the guidance system started to indicate the borehole was moving off the design trajectory. The entire drill stem (20 pipe lengths) was pulled out and the borehole restarted.

The second attempt was more successful as the borehole maintained the desired trajectory down the east bank and across the river bottom. By late in the day on April 29, the borehole was well on its way up the west bank when the rate of progress started to decrease rapidly to the point of no forward progress at all. Furthermore, reversing the progress made to this point was found to be impossible as the drill stem could not be pulled back out of the borehole despite maximum pulling forces being applied by the rig. This served only to dislodge the 11 m³ concrete block anchoring the rig. The drill bit and stem were stuck!

The problem was attributed to rounded rocks and boulders in the till that the drill bit was not cutting into. Instead, the bit was being deflected sideways in various directions as it travelled through the till causing the drill stem to bend and bind on the rocks. The friction pressure generated exceeded the safe torque capacity of the drill rig.

A number of options were considered by the drilling contractor to get "unstuck". Explosive charges could be sent down the hole, inside the drill stem to perforate the pipe, allowing drilling fluid to lubricate the pipe behind the drill bid assembly. Or, a smaller rig could be brought in and set up on the west bank to drill along the exit trajectory down to the bit and along side some length of the drill stem.

Both of the above options were fairly risky in comparison to the preferred choice of excavating down to the drill bit. This option was favoured because the drill bit was thought to be relatively close to the exit point. The computerized guidance system placed the drill bit approximately 50 m from the exit point and only 11 m below ground.

On May 1 the general contractor's largest backhoe on the project was moved to the calculated location of the drill bit. The operation was successful in exposing the drill bit at the 11 m depth but it did not help the efforts to free the drill stem. It was therefore decided to enlarge the excavation and slope it back to the exit point so that the drill stem could be pulled from the exit end at the same time that the rig was applying force to move it forward. It was hoped that the added pulling power would be sufficient to overcome the friction pressure.

Over the next several days the excavation was enlarged, the drill bit removed and replaced with a pulling head and a large crawler tractor and heavy cable brought in. On May 5 the drill stem was successfully dislodged and moved forward in the open excavation to ground surface at the exit point.

Reaming Operation
With the pilot hole now completed, the drilling contractor retooled for the reaming operation. Because of the problems encountered in the drilling of the pilot hole, the initial reaming would be carried out with a smaller, 250 mm diameter cutting head instead of the 450 mm size proposed in the contractor's original construction plan. Between May 8 and 17, three reaming operations were successfully completed at progressively larger diameters of 250 mm, 450 mm and 550 mm. On May 19 the final reaming, at 650 mm diameter, commenced but ran into problems only 60 m into the borehole when the centering tool came loose from the drill stem. Attempts to move it to the surface with the drill stem were unsuccessful so the contractor elected to send the 550 mm reaming tool back into the borehole to either bring it out or push it into the surrounding till formation. The latter was assumed to have taken place as the centering tool did not emerge with the cutting head. The final reaming was then able to proceed and was completed without further incident on May 26.

During the reaming operations, the general contractor was busy on the west side of the river fusing the poly pipe and carrying out a leakage test. In addition, the pulling head was modified to incorporate the openings needed to allow drilling fluid to enter the pipe for the "wet" installation that would counteract high differential pressures in the bottom of the river channel.

Pipe Pull
With the pipe successfully tested and the pulling head assembly in place, the pipe pull commenced at 7:00 a.m. on May 27. A backhoe was positioned near the exit point to move the poly pipe into line with the borehole as the pipe was strung out along a right-of-way that was at right angles to the crossing. A crawler loader was also employed to keep the far end of the pipe elevated which helped to reduce tension stress in the pipe.

On the east side, at the control console, the drill rig's carriage force was being carefully monitored to ensure it was kept below the 40,000 Kg maximum set by the pipe manufacturer. The pipe made good progress down the west side of the crossing, moving at an average rate of about 1.8 m/min. This continued until the pipe passed the half way point at about 10:30 am. This is when friction between the pipe and the borehole wall plus the accumulation of borehole cuttings in front of the pulling head started to increase the load on the rig. Progress on the next 100 m slowed to less than one metre per minute and further declined to half a meter per minute as the pipe began its ascent up the east bank. Progress halted entirely at the 520 m mark when a roller broke on the rig's carriage platform. The replacement part had to be flown in, necessitating a shutdown until the following day.

Any shutdown during the pipe installation operation has to be considered as a significant potential problem. Consolidation of borehole cuttings and/or collapse of the borehole wall could result in such high drag forces that the pipe might not be able to be moved again. Compounding this was the apparent build up of sand in front of the pulling head as evidenced by the large sink holes developing at the top of the escarpment on the east bank. Furthermore there was concern about how successful the open pulling head had been in allowing drilling fluid to enter the pipe. If not successful, the pipe could be flattened before the pull is restarted and completed.

The new roller arrived early the next morning, was installed and the drilling rig put back into operation. With some considerable effort the pipe moved forward slowly and progressed 15 m when a second mechanical failure halted the pull. The swivel joint in the pulling head assembly had broken.

The broken swivel was a serious problem in that the drill stem had separated from the pipeline. The pulling head wasn't close enough to the surface to excavate a hole to access it as had been done to solve the earlier problem on the west side. The only recourse was to pull the pipe, approximately 530 m, back out of the borehole!

On May 29 heavy equipment was moved to the west side of the river. Slings were employed as the only practical means to grip the pipe. However, this produced major deformations in the pipe which resulted in pieces having to be cut out and replaced. Removal of the pipe took two days with another two days needed for inspection of the pipe by its supplier and replacement of the deformed sections. During the pipe inspection, no evidence was found of deformation due to excessive external pressure in the borehole.

During this period, the 650 mm reaming tool was sent through the hole to remove sand that had slumped into the borehole on the east bank. Upon completion of the reaming operation, a new swivel joint, along with the remainder of the pulling head assembly, was placed into position at the end of the drill stem for another attempt at the pipe pull. The tools in the pulling head assembly were supplemented by the addition of the 650 mm reamer at the front end. This would assist in dealing with the sand problem on the east side incline.

At 7:00 am on Monday, June 2, 1995 the second attempt to pull the pipe across the Saskatchewan River commenced. The pipe pull progressed much quicker than the first time and reached the incline on the east side by 10:00 am. Once again, the rate of forward progress declined rapidly as the pulling head moved through the toughest part of the pull. Sink holes on the east side between the edge of the escarpment and the rig were becoming quite deep, presenting a hazard to personnel and other utilities in the area including Nipawin's main trunk sewer.

Forward movement of the pipeline continued and increased in speed as it approached the surface. At 1:35 pm the pulling head emerged, caked in heavy mud. The contractor was immediately instructed to clear the mud away from the perforations on the pulling head to allow air to enter the pipe. As the openings in the pulling head were exposed, there was an immediate rush of air into the pipe confirming that the pipe was under a vacuum condition but more importantly, confirming that at least some amount of fluid had entered the pipe.

Commissioning
The suction head observed at the end of the pipe pull was one of a number of concerns that could only be answered through the process of commissioning the forcemain. Other concerns included evacuation of the drilling fluid from the pipeline and most importantly, whether or not the "wet" installation was successful in keeping external hydrostatic pressure from collapsing the pipe under the River.

Following connection of the west end of the river crossing forcemain with the balance of the pipeline that was already in place, a pig was introduced on the east side. It was moved through the pipeline under pressure from a 50 mm water service connection since the new pumping station was not yet operational. This proved to be futile as there was insufficient flow to move the relatively heavy mass of bentonite and borehole cuttings up the west incline of the River crossing. In fact, this complicated the cleaning operation by effectively creating a mass blockage in the pipe at the base of the west side incline.

Rather than bringing in a large volume portable pump, the contractor elected to use jetting equipment, introduced at an air release structure on the west side, to breakup the mass of bentonite and borehole cuttings. This proved to be unsuccessful and was eventually abandoned in favour of using the pumps in the new sewage pumping station. This resulted in a temporary shutdown of the commissioning operation while work on the pumping station was completed.

When the new pumps were finally brought on line they had little difficulty in opening the pipeline. Subsequent leakage testing of the poly pipe was successful and measured flow from the pumping station, at 108 l/s, exceeded the design output of 98 l/s. With evidence of better than anticipated flow through the pipeline, the directional drilled crossing of the Saskatchewan River could finally be declared finished and operational.

CONCLUSION
The selection of directional drilling over conventional open-cut methods to cross the Saskatchewan River was made primarily on the basis of environmental considerations. A secondary benefit was the added protection of the pipe from river scour damage by virtue of the deeper burial depth. These benefits were obtained at a relatively small (10%) cost premium.

The physical characteristics of the Saskatchewan River valley at Nipawin coupled with the size and type of pipe installed, tested the abilities of an experienced contractor and highlighted the risks associated with directional drilling. These risks can be minimized, but not entirely eliminated, by thoroughly addressing all of the pertinent technical considerations.

Most important of the technical considerations is the pipe material and its wall thickness. This entails a rigorous stress analysis to ensure the pipeline withstands all of the forces exerted on it during installation.

From a cost stand point, the most important technical consideration is the subsurface soil conditions. The type of soils and the thoroughness of site specific geotechnical information are the biggest factors in the contractor's assessment of risk which in turn impacts the project's schedule and cost.

Despite the risks involved and the problems encountered, the Nipawin project has demonstrated that directional drilling can be successfully employed to cross a major waterway at reasonable cost and without any negative environmental impacts.

ACKNOWLEDGEMENTS
The author gratefully acknowledges the contribution of technical literature by Kamloops Augering Ltd. and Perma Engineered Sales (1983) Ltd., with a special thanks to the Town of Nipawin for their foresight and cooperation.

REFERENCES
Associated Engineering (Sask.) Ltd. (1994), Nipawin Regional Sewage Treatment Facility Predesign Report, Regina, Saskatchewan.

Associated Engineering (Sask) Ltd. (1995), Nipawin Regional Sewage Treatment Facility General Operating Manual, Regina, Saskatchewan.

Ensor, W.D., Fortin and Skipper (1993), Drilling with direction, Civil Engineering J., September, pp. 48-51.

Iseley, Dr. T and R. Tanwani (1990), Trenchless Technology - A paper outlining the methodology of directional drilling, Louisiana Tech Engineer J., Vol. 45, No. 1.

Kamloops Augering Ltd. and D.L. Fisher (undated), Trenchless Technology - A paper outlining directional drilling design parameters, Kamploops, British Columbia.

KWH Pipe (Canada) Ltd. (1993), Sclairpipe High Density Polyethylene Pipe Systems Design Manual, Table 4, pp 11.

Phillips Driscopipe, Inc. (undated), Technical Note #20 - Pulling Head Designs

Phillips Driscopipe, Inc. (1993), Technical Note #41 - "Technical Expertise" Application of Driscopipe pipe in directional drilling and river crossings.

Sharewell Directional Guidance Sytems, Inc. (undated), Steering System for Directional Bores, Stafford, Texas.

Svetlik, H.E. (1995), Design considerations for HDPE pipe used in directional drilling, Proceedings of No-Dig Engineering Conference.