hdd applications and process

8/10/2019 HDD APPLICATIONS AND PROCESS

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CHAPTER 2 - HDD APPLICATIONS AND PROCESS

A wide range of directional drilling units exist in the market place. The smallest drilling rigs aretypically used for the installation of telecommunication residential service cables. Larger rigsare capable of installing pipelines up to 1200mm (48 inches). Installation range is determined bymany parameters including rig size, soil conditions, and product diameter. Installationsexceeding 1,800m (6,000 ft.) have been completed successfully. This chapter will describe thedirectional drilling process, from mobilization to demobilization.

2.1 Equipment Set-up, Pre-construction Walkover, and Inspection

The drill rig is off-loaded and positioned over the bore centerline a sufficient distance behind theentry point to allow for the carriage height and entry angle, such that the drill bit will enter the

ground at the correct location and angle. Depending on rig size and entry angle, this distancemay be 1 to 6m (3 to 20 ft.) behind the entry point. The entry angle is usually between 8 and16 degrees, although entry angles of up to 20 degrees have been used on some large diameter

projects. A small pit is usually excavated over the entry point, using a backhoe or shovel. If theentry point is within a paved area, the pavement must first be removed using a jackhammer orconcrete saw, depending on the Owner/Engineers requirements. Machines are often stakeddown, using the powered rotating augers located either side of the spindle at the front. Care must

be exercised to avoid contact with underground utilities during stake-down, and to ensuresufficient reaction can be developed for thrust and pullback.

While the equipment is being set up, the entry and exit areas should be delineated using traffic

cones and construction tape or flagging. The work areas should be laid out in accordance withthe specifications and traffic control plans. Fencing should be installed to restrict access andensure public and worker safety. If the equipment cannot fit into the allowable entry area, theOwner/Engineer should be contacted to resolve the problem. Likewise, the exit area mustaccommodate the product reel and trailer, or the pipe laid out for welding or fusing. If thespecified exit area is insufficient, the Contractor should notify the Owner/Engineer to resolve the

problem. Thorough planning and a pre-bid or pre-construction walkover site inspection shouldavoid potential conflicts such as insufficient work areas. Planning, including the walkoverinspection is discussed in Chapter 4.

2.2 Equipment and Materials or Project Preparation

A list of equipment and materials necessary for the job should be prepared in advance. Beforeequipment is dispatched to the job site, it should be serviced, inspected for damage, and repairedas necessary. This includes bits, reamers, swivels, hoses, gauges, etc. Drill pipe should beinspected for damage to the pipe and threads and replaced if necessary. The electrical strikesensing system should be checked to ensure it is in good working condition. Anchoringrequirements should be determined. Appropriate types and quantities of drilling fluid additivesshould be on hand, including any special additives or components for dealing with excessivewater hardness, high or low pH, or brackish conditions. Simple tests should be conducted toensure the water supply is suitable. (See sections 3.8 and 4.2.11 and Appendix A for additionalguidance on drilling fluids.) Where possible, procure a secured area near the job site for staging

HDD GP Guidelines 2-1 Chapter 2: HDD Applications and Process


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all equipment and materials. Ensure that everything needed is on hand before beginning thebore. As it is unloaded on-site, the equipment and materials should be checked off against thechecklist prepared for the job.

2.3 Pilot Bore and Tracking

Prior to drilling, the drilling fluids should be mixed and sufficient quantities should be availableto complete the pilot bore, pre-reaming, and reaming passes. The actual quantity of drillingfluids that must be pumped to remove cuttings and maintain a stable open bore will usuallyexceed the bore volume, sometimes by substantial amounts, depending on ground conditions andother factors.

When the drill rig is properly set up and anchored and drilling fluids mixed, the pilot bore can beinitiated. To make entry of the drill string easier, a small entry pit is usually excavated. The pit

facilitates entry of the bit at the proper angle and helps contain drilling fluids. The pilot boreshould begin with the slanted head at 6 oclock to facilitate entry without deflection upward or toone side. It may be necessary at times to position a backhoe bucket on top of the drill head as itenters the ground to facilitate proper entry.

The pilot bore is drilled along the planned alignment from entry to exit. The planned path shouldhave the fewest bends possible. This prolongs drill string life and minimizes pullback problems.The ideal bore begins with a straight, tangent section inclined at the angle of entry to the groundsurface. The straight tangent section is needed to gain sufficient depth to provide steeringreaction and depth of cover. The drill head is then steered in an upward sweeping curvetransitioning into a horizontal segment before turning another upward sweeping curve, and

continuing to the exit point along a straight tangent segment inclined at the angle of exit (5 to 10deg) with the ground surface. Another pit is usually excavated at the exit point to facilitatecontainment of drilling fluids and entry of the pipe or cable during pullback operations. Figure2-1a illustrates the pilot boring process.

FIG 2-1a. Pilot Bore Process



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The type of drill bit used will vary depending on ground conditions and Contractor preferences.Selection of drill bits is discussed in Section 3.8. The method of steering the pilot drill bit mayalso vary, depending on whether the ground is relatively soft soils or rock.

As discussed in Chapter 3, the drill head is tracked by monitoring an electromagnetic signaltransmitted from the transmitter mounted in the drill head to the receiver at the surface.Alternatively, it may be tracked with a wireline or wireless non-walkover system. The drilllocator determines drill head location and calculated depth, drill head inclination, or tool faceangle, and orientation of the slanted face. The drill locator provides the tracking information tothe driller or provides instructions to the drill rig operator for steering.

Whether a walkover or non-walkover system is used, the objective is to calculate the actuallocation of the drill head as the bore progresses. Appropriate steering inputs can then be made tokeep the bore along the design drill path. Steering corrections should begin promptly when

deflections are detected or changes in the bore paths direction are needed. The correctionsshould be gradual and remain within the allowable bend radius. To avoid over-steering andundulations in the bore path, steering corrections should end just before the correction iscompleted.

It is sometimes necessary to pull the drill head back one or more drill pipe lengths to increasesteering response and achieve desired corrections. The drill head may also be retracted whencirculation is lost to try to re-establish circulation. This issue is discussed in more detail inChapter 6.

During the pilot bore, the surface should be closely monitored for inadvertent drilling fluid

returns. Any fluids should be promptly cleaned up. Drilling practices may require modificationto reduce the risk of continued returns, as discussed in Chapter 6.

At the completion of the pilot bore, the drill bit and transmitter or steering tool are usuallyremoved in preparation for reaming. Any excess drilling fluids or cuttings around the exit should

be cleaned up to enhance safety and avoid runoff to storm drains or streets.

2.4 Reaming/Hole Enlargement

The back-reaming process is illustrated in Figure 2-1b. If the pilot bore is to be enlarged, areamer hole opener is attached to the drill pipe and the drill pipe is pressurized to ensure the jets

are open. The reamer is then rotated and pulled (or pushed in some cases) back through the pilotbore to enlarge the bore in one or more reaming passes. The number of reaming passes dependson the diameter of the product compared to the diameter of the pilot bore, ground conditions, anddriller preferences. The number of reaming passes commonly varies from zero to three; howevermore passes may be necessary. For example, if durable product is being pulled, reaming may beunnecessary. If 1200 mm (48) diameter pipe is being pulled, several reaming passes may berequired.



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FIG 2-1b. Backreaming Process

In loose or soft soils, the number of required reaming passes will typically be less than if hardsoils or rock are encountered. This is primarily due to torque limitations, cleaning plant capacity,and pump capacity. Reaming may be accomplished by pulling or pushing the reaming toolthrough the hole. The final bore diameter must be larger than the product diameter to reducefrictional pullback loads and to facilitate flow of the drilling fluids around the product. As a ruleof thumb, the final bore diameter should be the lesser of the product diameter plus 300mm (12

inches) or 1.5 times the diameter of the product. For small diameter products ( ), the reamershould provide a minimum 2-inch annular space, i.e. the reamed diameter should be 4-incheslarger than product diameter. However, different contractors will have their own preferences,

based on their experiences under various conditions. Table 2-1 provides recommendations forreamed diameter, keyed to product diameter. In most cases, the Contractor should be allowed to

select the final reaming diameter, consistent with their experiences. However, in rare instances,it may be necessary to establish lower and/or upper bound limits.

Table 2-1. Recommended Relationship between Product Diameter and Reamed Diameter

Product Diameter Reamed Diameter

< 8 Diameter of product + 4

24 Diameter of product x 1.5

> 24 Diameter of product + 12



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2.5 Cable/Pipe Layout, Fabrication, and Testing

The product is prepared for installation while the bore is being reamed. The specific stepsinvolved will depend on project requirements, intended function of the product, and productmaterial. Generally applicable procedures include:

notify Engineer of plan and schedule for layout, fabrication, and testing;

ensure that the layout area is relatively clean, flat and free of debris, sharp rocks or otherobjects that could damage the product;

ensure that the correct product (material, diameter, thickness and length) is on-site, meetsor exceeds specified requirements, and is free of debris and material defects. If not,replace any incorrect or defective materials;

ensure that proper fabrication and handling equipment is on-site for fusing or weldingsections of the product, and that trained, experienced personnel are available for this task.Ensure that manufacturers recommendations are followed during welding or fusingoperations, including temperature control for cold weather butt-fusing operations;

inspect fabricated product for defects in workmanship and repair/replace any defects.

ensure that the proper testing apparatus is on-site and that field personnel understand thetest procedure, timing and sequence of testing, and minimum performance requirementsas stated in the Contract Documents;

perform quality control tests and carefully document results, as required by the ContractDocuments prior to installation;

record any failures, and repair and retest until fabricated product passes all applicabletests.

For specific fabrication and testing guidance, manufacturers recommendations and the ContractDocuments should be consulted.

2.6 Pullback

After fabrication and pre-installation testing have been completed, the product is prepared forpullback. A pulling head is attached to the product. A swivel is installed between the reamerand the pulling head to prevent rotation of the product. The product must be properly positionedand supported to enter the bore. It may be necessary to support the product on rollers or with acrane to prevent damage (scratches or gouges) to the product during pullback. Breakaway

swivels may also be installed between the product and swivel to prevent overstressing of theproduct as it is installed. Breakaway swivels are designed to fail before the pullback loadexceeds the safe capacity of the product. Pullback should be completed without interruption, toreduce risk of becoming stuck in the bore.

2.7 Connections

The General Contractor, Owner, or a party other than the directional drilling Contractor typicallyconstructs connections of the new product to existing cables or pipes. The connections may varyfrom cable splices in a vault to pipe couplings, elbows, or tees. The primary responsibility of thedirectional drilling Contractor is to begin and terminate the HDD installations at the locations



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shown on the plans, and to cap the product as required in the specifications. If the exit differsfrom that called for on the plans, the directional drilling Contractor is responsible for ensuringthat the connection can be made. This may require a short section to be re-drilled prior toinstallation, or a short open-cut section if done after installation.

2.8 As-Builts/Operator Logs

The as-built drawings are typically produced by the Construction Management firm or Owner,using the design drawings. The directional drilling Contractor will mark the plans to indicate anyand all vertical and horizontal deviations between the design and actual bore. The Owner mayrequire submission of complete, as-built plans and the operator logs prior to final payment. It isgood practice to update the as-built drawings on a daily basis, to exercise quality control, and tocheck the as-built revisions prior to submittal. As the underground environment becomesincreasingly crowded, accurate as-built drawings become invaluable for future maintenance and

new construction. Maps or as-builts created by remote mapping systems are also very helpful.

The operator logbook should be maintained and updated daily by the drill rig operator orSuperintendent. The logbook should include the drill locators notes and records for bores usingsteering and tracking systems. An operator logbook should include pipe number, depth, pitch,steering commands, and notes. For large diameter or high risk bores, the log may also includerig performance parameters such as thrust, pullback, torque, drilling fluid circulation, drillingfluid composition, ground conditions, potential obstructions or objects encountered, time theshift started and ended, footage during the shift, and other parameters. The logs should belegible, accurate, and should be submitted to the Inspector, Owner, or Construction Manager, asrequired by the Contract Documents.

2.9 Demobilization, Site Cleanup, and Restoration

After the product is installed, the entry and exit pits are cleaned of drilling fluids and cuttings andbackfilled with native soil or select backfill that is placed and compacted in accordance withContract Documents. Surface debris, trash, worn out or broken tools and equipment must beremoved. Surface grading, seeding, and re-vegetation may be required for undeveloped areas.For developed areas, surface restoration may include replacement and compaction of pavementsub-base and base materials and the paving course. Reconstruction of sidewalks, curbs, andgutters that have been damaged by Contractors operations will be required. The objective is toleave the area in pre-existing or better conditions. Often, payment of final closeout invoices and

retained amounts is contingent on proper site restoration and clean up.
