SCOPE

This document was prepared for the purpose of establishing a degree of uniformity of installation that will result in a quality product for the owner as well as an efficient and profitable installation for the contractor. Although prepared primarily for the installer, the owner and engineer's interests are equally considered to the best of our ability.

GENERAL

Procedural adjustments may be made by a knowledgeable contractor and/or engineer but should be carefully considered. In case of conflict with the project specifications, the user is advised to resolve all issue(s) before attempting the installation. Interruptions during installation can have serious consequences.


PROJECT PRE-PLANNING

Safety

Consult drill manufacturers' recommendations, OSHA, local codes and regulations regarding the safe operation of Horizontal Directional Drills (HDD). Some government entities have established rules and regulations governing the use of directional drills within their jurisdiction that require certain permits and licenses and carry severe penalties for violations.

Traffic Control

Refer to local ordinances and the "Manual on Uniform Traffic Control Devices, available for purchase at www.AASHTO.org and draft a workable traffic control plan.

Inspection Tape Review

If available, review tapes and logs to determine the location of all active service connections as well as sags. If the system to be replaced has not been televised, conduct the necessary inspection and review as above. In the event that a "plug" exists and the line cannot be fully televised, determine the existence and location of services lines by using dye, smoke or electronic methods.

Installation Sections

Review Plan & Profile sheets as available to determine the most efficient installation sections to maximize installation lengths and minimize surface disturbance, homeowner/business inconvenience and traffic disruption.

Space for "Stringing" and fusion of HDPE or Assembling PVC

Ascertain that the space used for "stringing" the full length of pipe will be available for the time needed to fuse the pipe and complete the installation. Fusing half of the section "on the fly" can be accomplished under favorable conditions but an excess of fusion sections can be troublesome.

Insertion Pit and Service Line Excavations

Determine the most advantageous location(s) for the insertion pit(s)., using pits common to more than one installation section or a Manhole removal/replacement excavation. When using HDPE, excavate insertion pit(s) to allow pipe to conform to not less than the manufacturer's minimum radius (Pipe Bend Radius below) although the manufacturer's minimum radius is generally less than that needed for a smooth installation. An insertion pit with a steep slope will cause the pipe to "ride up" at the entry point raising the flowline at that point. Cold weather installations will require a larger radius allowance. When using restrained joint pipe, excavate the insertion pit sufficiently long and deep to allow handling and assembly of the pipe on grade, without interruption as the installation progresses. Note service excavations that will need additional safety considerations and those that may be beneficial as mud retrieval points.

By-Pass System

The by-pass system should be installed with a degree of permanence that will exceed the installation period, in case of unforeseen interruptions.

Slurry Removal Method and Disposal Location

Decide the removal method, calculate the anticipated removal volume, haul cycle and number of transport vehicles needed to maintain installation without interruption. Because disposal regulations differ so widely, provisions for a reclaiming unit, stabilization pit, or other treatment facility may be necessary.

Materials Review

Ascertain that all materials will meet or exceed the specification requirements and all material submittals or samples can be readily obtained. Assure that additional electrofusion pieces are readily available or are part of the project inventory.

Invert Removal/Replacement Procedure

Invert (Manhole Base) removal may be more difficult than anticipated. (See PROCEDURE section for details on Invert Removal) Allocate sufficient resources to prevent delays. Note specifications regarding cut-outs, shaping, manhole adapters and electrofused restraints.

Reamer and Pulling Head Selection

Select and obtain a reamer most suitable for the task, with an appropriate mandrel length. See below.

Locate Existing Underground Utilities

Locate existing underground utilities at points of excavation and along any projected drill path by "pot holing" or other non-destuctive methods.

Procedure

Traffic Control

In the event the HDD is set up in traffic, follow established traffic control procedures contained in the "Manual on Uniform Traffic Control Devices" and in accordance with the project traffic control plan. Protecting the driller and the HDD is vitally important to the project. Any injury to the driller or damage to he drill can have serious consequences to the project beyond the obvious.

Establish the By-pass System

The by-pass system should be capable of controlling peak flows without interruption for an extended period should the unexpected occur. The liability that can be incurred by a poor by-pass system can be dramatic, making this an unwise area to trim costs.

Break and Remove Manhole Inverts

Breakout the Manhole invert through which the reamer will pass. UnIess it is determined that the installer can, by the use of a special reamer, practice, and skill of the drill operator, ream through the invert, it is absolutely necessary that the invert be removed sufficiently to allow the reamer to passthrough without deflection. Occasionally, this operation can be more difficult than it appears and therefore needs early attention.

Excavate Service Connections and Install Wye

After excavation of service connection, cut the existing service line a convenient distance from the main and install a wye with a riser to the surface (Figure I below). It may be a necessary safety precaution to install a riser and backfill to the surface if the excavation constitutes an attractive nuisance.

The service line may in most instances remain active until the installation process begins. Prior to the installation, all connections must be isolated from the main. Although not absolutely necessary, the wye serves the purpose of allowing continuous monitoring of the service during installation. Cutting and plugging the line without a wye will serve the purpose of protecting the home or business owner from invasive fluids but prevents monitoring for possible backups. Un-backfilled service excavations may also be used as mud retrieval points. Reconnections may be made immediately after installation if PVC RJ, fusible PVC or restrained joint ductile iron is used but reconnections to HDPE should be made after the prescribed waiting period, usually determined by the engineer. If no requirement for the "relaxation" period is specified, wait at least 4 hours before making the connection or if conditions allow, make connections and wait the prescribed period before backfilling.

"String" and Fuse HDPE or Stockpile PVC RJ for Assembly

String the HDPE or fusible PVCalong the pre-determined route and fuse into the proper length(s). Although not normally required, exterior de-beading is a definite asset to ease of installation, reducing possible degradation of the wall cake.

OR:

Stockpile Restrained Joint PVC or ductile iron with sufficient restraint assemblies at the insertion point. When assembled, clip splines on PVCRJ as close to the coupling as possible.

Set up the Directional Drill and Mud Unit Pull "down grade" whenever possible.

Calculate the horizontal distance from the actual terminal point of the pipe where the new pipe ends, nearest the drill, (point "b", figure 2) to the point of entry using a combination of available entry angles and radii well within the radius constraints of the drill stem manufacturer plus 10 feet.

Remember that the pipe will be on grade at point "b", figure 2, but will steadily rise above point "a", figure 2, caused by the resultant upward force of the drill stem. For this reason, it is highly recommended that the "on grade" section (ab, figure 2), be maintained. The amount of rise depends on soil type, compaction, and pull back force among others and may be negligible or severe but will always be a problem to be reckoned with especially when grades are flat.

Drill into point "a" and extend the drill stem through the existing pipe into the insertion pit. Ascertain that the swivel is adequate for the work, in good condition and well lubricated. Connect the selected reamer and pipe. Activate the mud pump and be certain that all mud ports are open on the front and back of the reamer. Begin the operation slowly using near maximum RPM with steady pull back force to avoid stalling the reamer. Adjust RPM for a smooth, uniform cut.

On first use, use ample mud flow until comfortable with the results. Also on first use it is helpful if an inspection hole can be drilled or dug 30' to 50' from the entry point of the pipe to check mud/debris flow and viscosity.

Select Reamer and Attach to Pulling Head

It is important that the selected reamer be in good condition with sharp bits and/or cutting edges. Reamers are in general multi-purpose as shown in figure 3 below, however very hard vitrified clay pipe (VCP), concrete, concrete encased pipe, or upsizing in rock, will make a reamer of the style shown in figure 4 below a wiser choice. A variety of reamers for various piping and conditions are available from the various HDD tool suppliers. Connect the reamer to the pulling head as close as possible without rubbing, usually a 1" to 2" space is easily obtainable but may require a window in the mandrel to access the connecting pins. It is imperative that the space between the reamer and pulling head not exceed 3". The ever present granular bedding material surrounding the existing pipe, gravel deposits, or cobbles can cause grade irregularities if the space is too large.

Ascertain that the selected reamer is compatible with the replacement pipe, the mandrel diameter ("D" dimension, figure 5) 0" to 1" larger than the OD of the replacement pipe, the length ("L" dimension, figure 5) nominally 18" but may be extended to assist in the vertical realignment of sags and deflections in the existing pipe, and the overcut ("0" dimension, figure 5) not exceed 1.5".

Maintain Continuous Debris Removal

As the debris flow is being properly established, vacuum material as it flows into the first available retrieval point. Continuous removal will assist in preventing inadvertent return ("fracing out") as well as improving mud economics if a cleaner is used.

Inspection

Upon completion, inspect line visually for acceptance. Because mistakes occur more often in first use, inspection for owner acceptance is advised before proceeding to other sections of work.