## Design Radius of Curvature

Determining the entry and exit points, the depths that must be achieved, and direction changes for the drill path are all major parts of the planning process. One of the keys to these calculations is the bend radius of the drill rod and or the product pipe. Bend radius is often misunderstood. It is often confused with the number of feet needed to make a 90-degree turn. Bend radius is defined as the forward distance required for a drill string to make a 90-degree turn see Figure 4-2 ....

## HDD Risk Identification

Potential risks that are a part of all HDD projects include a failure to complete the bore, safety of the public and workers, environmental issues, damage to surface structures, and striking other underground structures. Risk reduction is the attempt to identify potential risks during the planning and design phase so that they may be eliminated or reduced. A risk contingency plan is often used by the engineer and or contractor to help identify the major risks and develop general plans and...

## Calculating the Pull Loads

The first step in calculating the estimated pulling loads is to develop the input data that will be used in the calculations. This data includes the product-pipe material properties, the drilling-fluid properties, and any code or design factors that are applicable. An example of the input data required for calculating estimated pulling loads is provided in Example 6-1 later in this chapter. Defining the Bore Path The next step is to define the bore path for the crossing. Figure 6-1 defines a...

## Identification of Risks

An important part of the planning and design phase of a HDD project is to identify and avoid or at least reduce possible risks. If potential risks cannot be avoided or reduced, the crossing alternative should be closely evaluated and other alternatives considered. A decision has to be made as to whether to accept the risks or select another crossing option. Even with the best planning and design efforts unexpected risks can occur. Experienced and qualified contractors are well equipped to solve...

## Geotechnical Investigation

The information from the geotechnical survey is used to select the crossing route, drilling tools, procedures, and the drill-path design. The level of effort required for the geotechnical investigation depends on several factors, such as the pipe diameter, bore length, and the nature of the HDD crossing. For many HDD projects, especially in municipal areas, the subsurface investigation consists primarily of research of existing geotechnical data. Due to the costs and the congested nature of...

## Drilling and Steering

Drilling curved and horizontal bore holes requires specialized drilling equipment. This equipment is contained in a bottom-hole assembly BHA that consists of a drilling tool, a bent subassembly, and a steering tracking tool. Pilot-hole directional control is achieved by using a nonrotating drill string with an asymmetrical leading edge. The asymmetry of the leading edge results in a steering bias. When a change of direction is required, the drill string is rotated so that the direction of the...

## Frictional Resistance

Pipe resistance to pullback in the bore hole depends primarily on the frictional force created between the pipe and the hole or the pipe and the ground surface in the entry area, the frictional drag between pipe and drilling slurry, the capstan effect at bends, and the weight of the pipe. Equation 7-4 gives the frictional resistance or required pulling force for pipe pulled in straight, level bores or across level ground Figure 7-2 . FP pulling force in pounds coefficient of friction between...

## Entry and Exit Angles

Generally the entry angles should be held between 8 and 16 degrees from horizontal, although entry angles up to 24 degrees have been used on some projects. These boundaries are due chiefly to equipment limitations. The preferred drill path is made up of straight tangent sections before the introduction of any curves. The radius of the curve is determined by the bending characteristic of the product pipeline or in some cases the drill-rod pipe. The curve usually brings the drill-path profile to...

## Chart Hdd Applications

Stricter placement tolerances, as is the case in many municipal applications. Chart 1-1 lists the distribution by industry of HDD applications. As a result of the growth of HDD, the marketplace is providing a wide range of HDD units and support equipment. HDD rigs range from mini-rigs that are usually used for the installation of smaller pipe and conduits 2 inches to maxi-rigs that are capable of installing 48-inch pipelines. The length of pipe that can be installed by HDD is determined by many...

## Drilling Fluid System

For HDD construction the primary impact on the environment revolves around the use of drilling fluids. Many regulatory problems result from a misunderstanding of the effects of drilling fluids. Informing the regulatory agencies about the purpose and composition of HDD drilling fluids is important for many successful HDD projects1. For many HDD projects the drilling fluid system comprises a substantial portion of the HDD equipment and cost. The system is composed of both the equipment and the...

## Figure Typical HDD Drill

Must be anchored to provide a reaction against which the mechanical system can operate. Anchoring is typically done by driving stakes through openings at the front of the rig, attaching the rig to a buried weight, or simply attaching the rig to a large, heavy piece of equipment on the surface. The drill rig must provide sufficient thrust and the drill pipe sufficient strength to advance the drill string the full length of the proposed bore hole and sufficient pulling force to retract casing...