Views:11 Author:Site Editor Publish Time: 2020-03-24 Origin:Site
Introduction of Horizontal Directional Drilling
Horizontal Directional Drilling (HDD machine) has revolutionized the underground utility installation industry. Today, HDD is a recognized and often preferred method for installing all types of underground utilities such as water, sewer, gas, electric, and telephone. HDD is also well-suited for installing environmental remediation wells. The purpose of this chapter is to familiarize you with what HDD is and how HDD works.
What Is HDD?
HDD is a process by which it is possible to install utilities underground with minimal disruption to the ground surface. This is accomplished by making a pilot bore into the ground at an angle and then leveling out at a specified depth. Once the proper depth has been reached, it is then possible to advance the pilot bore horizontally to a destination point where the drill is redirected so it exits the ground.
Once it exits the ground, the drill head is removed and a back reamer or expander is attached along with a swivel and the product (i.e. conduit, cable, water or gas pipe, etc.) that is to be installed. It is then pulled back through the pilot bore to the drilling unit. To better understand it, let's take a look at the individual pieces of the process.
Directional Drilling Machines
Directional drilling machines (also referred to as drill rigs, boring machines, or drills) are available in many sizes. Regardless of the size, they all have three main functions: rotation, forward thrust, and pullback. The industry-wide standard for rating the size of a machine is the total pounds of pullback capability. However, more emphasis is being placed on the rotational torque rating of machines. Directional drilling machines can also be split into two other categories: self-contained or remote units.
A self-contained unit refers to a machine that has the power unit, drill pipe, and rack on board. A remote unit consists of a power unit that is attached permanently to a truck bed, trailer, or is skid-mounted and has hydraulic hoses running to the drill rack. Self-contained machines are quite popular because of the reduced setup time and because the extra weight helps to hold the machine in place. However, the reduced weight of remote units coupled with a smaller physical footprint makes them a good choice for residential areas or areas with limited access for machine placement. Regardless of the size or style of the machine, they all have the same basic nomenclature. As you can see, the difference between the two styles is only in the configuration of the units.
Drill pipe, also known as drill stem, drill rod or drill string, is available in numerous diameters and lengths,depending on the size of the drill rig that it is to be used on. Diameters of drill pipe can range in size from just over one inch up to six inches or larger. The length of each drill pipe can range from six feet up to 30 feet or longer.
Drill pipe are hollow to allow drilling fluids to pass from the drill rig to the drill head. Some drill pipe is nothing more than a steel pipe with threaded couplings welded on. This type of drill pipe is inferior and often fails down hole because it cannot withstand the rotational torque or the bend radii that it is subjected to.
Drill heads come in many sizes, shapes, and styles, with the most common being design that utilizes a replaceable duckbill bit for cutting and steering. This style of head has a cavity in the center to house the necessary electronic locating equipment Passages for drilling fluid are routed around the center cavity to help keep the locating electronics in the head cool. The duckbill or cutting bit attaches to the front of the drill head at a tapered angle. It is this angle that causes the drill head to change direction of travel when thrusting forward with no rotation.
Three-piece drill heads, as the name implies, actually come in three pieces The body section has a cavity to house the locating electronics. The front of the body section is threaded so the front section can be attached. The front section can accept a duckbill for cutting and steering. Sometimes special cutting bits designed for cutting harder geological formations are attached directly to the body section in lieu of the front section and duckbill configuration. The back end of the body section is also threaded. This allows the rear section of the head to be attached to the body. The back section is merely a transition from the body section to the drill pipe.
Once the pilot bore is completed, the drill head is removed and a back reamer is attached to the drill string. Back reamers, also known as expanders or hole openers, have two major functions. The first and most obvious is to enlarge the hole to a size large enough to allow room for the product to be installed The other function is to mix the cuttings with the drilling fluids to create a slurry down hole, thus creating a better environment for installing the product line.
There are numerous styles and sizes of back reamers. Choosing the proper back reamer is dependent on the size of the product being installed and the type of soil conditions being encountered.