Necessary preconditions for the service capability of a community and urban development are efficient networks of pipelines and cables that provide a secure supply of water, gas, district heating, electricity and telecommunication as well as an ecologically friendly and secure drain and sewer system, i.e. collection and discharge of waste water.

However, depending on their degree of connectivity and their actual condition, they must be expanded today …

(Image: Overview of the techniques of trenchless installation of pipelines)

Horizontal Directional Drilling methods, in short HDD-methods, form a special group of methods among the steerable methods of trenchless construction (Figure 1) [HDD-1]. This is why they are dealt with separately in this volume [HDD-2] [HDD-3].

Horizontal Directional Drilling was developed for the trenchless installation of cables and pipelines out of the directional techniques …

Among the methods covered in this volume, HDD involving the use of drilling fluid is the most common method for the trenchless installation of pipelines. In all cases a fluid serves for removing spoil.

In (Drilling fluid) the tasks of drilling fluid are described in detail [HDD-14] [HDD-15] [HDD-16].

The following working steps are necessary for carrying out the method (Figure 3a, Figure 3b, Figure 3c) [HDD-12] [HDD-17] [HDD-18]:

1. pilot bore,
2. reaming(s) and
3. pulling-in.

(Image: Working steps in HDD – Pilot bore) (Image: Working steps in HDD – Reaming) (Image: Working steps in HDD – Pulling-in)

Phase 1: Pilot bore

After determining the line and gradient for the pipe(s) to be installed, which – because of the steerable drill head – can occupy a wide …

When space is scarce, flexible pipes such as district heating pipes (see Volume 1, Section 1.1.3 [HDD-1]) and cables as well as plastic pipes supplied in coils (PE pipes) (see (PE-pipes)) are pulled directly behind the reamer and the swivel joint in one piece from the drum or a special pipe coil transport trailer. However, limitations on the pipe diameter that is practical for coiling arise from the permissible bending radius of a particular pipe …

(Image: Installation and layout of a pipe string – consisting of ductile cast iron pipes on a sliding track of steel sheets that are welded together)The pipe string, prepared for pulling-in with regard to the installation instructions of the pipe manufacturer, is pulled-in, in one piece. Roller or slide tracks are used in order to minimize friction of the pipe string on the ground surface and thus to reduce the pulling-in forces exerted by the drill …

This variant of the pulling-in process is used where only limited space is available such as in inner-urban regions and river culverts or inverted siphons with steep banks (see (Drinking water supply line DN 400 in the moorlands between De Meern und Harmelen)). In this case, pipes or pipe strings with restrained plug-in joints (see Volume 1, Chapter 13 [HDD-1]), for instance, ductile cast iron pipes (see (Ductile cast iron pipes)), are connected …

The following working steps are necessary for carrying out the method (Figure 3a, Figure 3b, Figure 3c) [HDD-12] [HDD-17] [HDD-18]:

1. pilot bore,
2. reaming(s) and
3. pulling-in.

(Image: Working steps in HDD – Pilot bore) (Image: Working steps in HDD – Reaming) (Image: Working steps in HDD – Pulling-in)

Phase 1: Pilot bore

After determining the line and gradient for the pipe(s) to be installed, which – because of the steerable drill head – can occupy a wide …

The boring plants used in HDD technology consist of the drill rig, and additional equipment depending on the drilling method.

In drilling technology, the drill rig is understood to be the machine equipment for the drilling of boreholes. Drill rigs are usually mounted as a unit on a base frame, a truck, a trailer or a tracked vehicle. Thus, they are easily transported, and besides exceptional cases, are operational in a short space of time without …

Because of the relatively short drilling times per pipe installation project and because of operation also under complicated site conditions, trenchless installation makes higher demands on transportability or self-movement of the drill rigs on site. This can involve many forms of transport bases [HDD-17]:

• Without transport base: For very light Mini drill rigs especially designed for lateral or service pipe connections, a special transport base is …

Transport bases have to be sufficiently stable in order to introduce the thrust or pullback force into the drill or pipe string. In most cases in which the friction forces between the positioning surface of the transport base and the ground surface are insufficient, the stability of the drill rig must be ensured by means of a corresponding front and rear support (Figure 13 a and 13b) and, if required, additional anchoring.

(Image: Equipment of a Midi …

Because of the relatively short drilling times per pipe installation project and because of operation also under complicated site conditions, trenchless installation makes higher demands on transportability or self-movement of the drill rigs on site. This can involve many forms of transport bases [HDD-17]:

• Without transport base: For very light Mini drill rigs especially designed for lateral or service pipe connections, a special transport base is …

The components of the drive assembly, i.e.

• thrust drive,
• rotary power head, 
• adjustment of the drilling frame’s inclination,
• crushers,
• movement of the crushers,
• crane,
• drill rod change system,
• introduction of the anchor for fixing the soil plate,
• chassis and
• flushing pumps

are operated via hydraulic power packs in the form of hydraulic cylinders and hydraulic motors (axial piston- , radial piston- or gear wheel motors). They are energized …

(Image: Specially designed drill rod for rotary-percussive drilling (TwinDrive-impact drill rod for diameters 48 mm to 82 mm))The drill string comprises the drill rod string, the drilling tool and, if required, the completing elements. It is connected to the rotation or rotating impact drilling mechanism and must be designed in such way that the maximum loading to be expected can be absorbed taking due account of safety factors as discussed below […

Concerning the drilling tools, the following are differentiated in HDD depending on the working steps:

• drilling tools for pilot boring,
• drilling tools for reaming(s),
• drilling tools for borehole calibration,
• drilling tools for smoothing the borehole.

(Image: In-Line-jet head (left) and angled jet head (right) with bent sub)Depending on the in-situ subsoil, the following drill heads are used for pilot boring:

• jet head,
• drill bit with slanted steering surface or with steering plate,
• rock bit.

Jet head

Jet heads possess exchangeable jets that can be arranged either straight (In-Line jet head) or eccentrically (angled jet head) to the drilling axis [HDD-513]. It is preferably used in very soft soil …

(Image: Helical gear motors according to the Moineau principle)Downhole mud motors are used in geological formations that cannot be handled with the common drilling tools for pilot boring in loose soil.

They are installed directly behind the drilling tool or are built into the drill string by intermediate switching of drill string elements. The drill string above the downhole mud motor must take up the return moment and in this case does not need …

(Image: Thrust/push head for borehole diameters 135 mm and 190 mm)Borehole calibration tools are used after expansion bores (intermediate reamings) in cohesive soil if it is found out or assumed that the borehole wall is torn and/or material has loosened from the borehole wall. Furthermore, these drilling tools are used after breaking of the drill string and after the recovery of the single components from the borehole [HDD-23].

To simplify the entry …