Usually, it is necessary to assess the safety against buoyancy in connection with approval planning in order to prove the safe position of the pipeline when used in groundwater [HDD-136].

Whereas in the calculation of buoyancy for the pipe string in the construction condition (see (Calculation of buoyancy and ballasting)) the cover must not be included, the safety against buoyancy in the operating condition is to be verified by the superimposing, …

The pipelines installed by using HDD have to be calculated for the different kinds of impacts during later operation.

When calculating the structure of pipes which are to be installed by means of HDD, it is differentiated between calculations for the

• state of construction and the
• state of operation [HDD-17].

In horizontal directional bores in aquiferous subsoil or under bodies of water, annular space grouting with long-term hardening suspensions can become necessary to prevent buoyancy (see (Calculation of buoyancy and ballasting)) [HDD-15] and to prevent a hydraulic connection between the body of water and the groundwater or groundwater and borehole (see (Layout of the line)).

Grouting the annular space can also be demanded by the client to prevent settling …

In this variant, during pulling-in, a hardening suspension based on hydraulic binders (e.g. cement suspensions, cf. Volume 1, Section 2.1.4 [HDD-1]) is pumped inside the borehole instead of a drilling fluid. Due to the higher density of the grouting material the available drilling fluid is displaced and leaks from the borehole in the starting- and target shaft. Here, there is the risk of jamming of the pipe string if the hardening process of the …

When grouting after pulling-in, the grouting material can be injected through an additional grouting line, which is also pulled-in outside of the pipe string, inside the remaining annular space. The grouting line must not be connected mechanically with the pipe string (e.g. via adhesive tape, cable clips). In addition, the outer diameter of the grouting line is to be taken into account during reaming. If the pipe string has reached its final position …

In horizontal directional bores in aquiferous subsoil or under bodies of water, annular space grouting with long-term hardening suspensions can become necessary to prevent buoyancy (see (Calculation of buoyancy and ballasting)) [HDD-15] and to prevent a hydraulic connection between the body of water and the groundwater or groundwater and borehole (see (Layout of the line)).

Grouting the annular space can also be demanded by the client to prevent settling …

During drilling work, all the measurement values shown in Table 33 must be acquired and documented in accordance with DVGW-GW 321 [HDD-15].

(Table: Table 33: Measurement values to be acquired and documented in accordance with DVGW-Working sheet GW 321)

According to the DVGW Working Sheet GW 321 [HDD-15], the following controls and measurements must be carried out at the pipe string prepared for pulling-in:

• Before pulling-in:
  • Visual checking of the …

Contractors who are assigned to execute the drilling work must possess the required qualification according to DVGW-GW 321 [HDD-15], which they have to present to the client. This evidence is regarded as provided if the drilling contractor possesses a DVGW certificate according to DVGW-GW 301 [HDD-166] and/or GW 302 [HDD-167]in the corresponding group GN 2.

The contractor needs to employ qualified expert staff. As the supervisor in charge for HDD, …

A complete and consistent documentation of all relevant process steps of the HDD project must be kept by the personnel who must be named to the client. The type and scope of the data to be acquired must be clarified between the client and contractor before the start of the work [HDD-15] [HDD-67].

Unless other periods are agreed upon with the client, this documentation must be retained for a period of 10 years by the contractor; so that even after …

The pipe string installed by means of HDD must be linked to the ongoing pipeline in a stress-free and, for pipes, in a restrained jointed manner in accordance with the respective technical regulations [HDD-15].

HDD requires a relatively large starting pit because of the necessary bending radius and depending on the diameter of the pipes, on the depth from the pipe invert of the pipe to be replaced, on the height of the pipe string above the ground …

During drilling work, all the measurement values shown in Table 33 must be acquired and documented in accordance with DVGW-GW 321 [HDD-15].

(Table: Table 33: Measurement values to be acquired and documented in accordance with DVGW-Working sheet GW 321)

According to the DVGW Working Sheet GW 321 [HDD-15], the following controls and measurements must be carried out at the pipe string prepared for pulling-in:

• Before pulling-in:
  • Visual checking of the …

In the last decade, there have been further developments
based on the conventional HDD method in
construction technology and/or machine technology
in order to broaden this method’s application. In the
following, several examples will be presented.

(Image: Working process in the "Meeting-in-the-Middle" method)An emphasis of the present technical developments concerns the extension of the drilling to more than 2,500 m (≈ 1.5 miles). Under ideal conditions, in the future, even 4,000 m (≈ 2.5 miles) long drillings are considered possible by contractors [HDD-173].

This demand is made especially in geographical regions where the existing natural barriers to be crossed under, such as river deltas …

PTT “Push and Pull Technology“ [HDD-174] combines the process technology of two-phase HDD and microtunnelling with hydraulic conveying (Figure 125 a1 and Figure 125 a2) (see Volume 1, Section 8.3 [HDD-1]). Here, transport of the spoil is achieved by means of a liquid drilling fluid inside a pipe that is installed in the pipe string (indirect HDD, cf. (Introduction)) [HDD-7] [HDD-175].

(Image: Two-phase PTT (PTT: Push & Pull-Technique) – Procedure #…

The COMBI-DRILLING method [HDD-176] corresponds in principle to that of PTT described in (PTT “Push and Pull Technology“) (Figure 126a) [HDD-177] and represents a combination of HDD and microtunnelling.

In trenchless installation, the steel pipe string is pulled in directly with the reaming; the drill rig is situated at the entry point as during pilot boring. A modified jacking machine with hydraulic conveying which is arranged at the front of the …

The “Bore-and-Ream Hard-Rock Microtunnelling Method“ [HDD-181] is based on a combination of HDD and the Raise Boring method known from shaft construction [HDD-182].

For the pilot bore with a diameter that is usually 311 mm (≈ 12.2 in.) from a starting shaft, a so-called raise drill rig is used for jacking a pilot drill rod string (8 inch = 203.2 mm) with a jet roller drill head that is driven by a downhole motor using water as a drilling fluid. After …

The GRUNDOPIT method of the German manufacturer Tracto-Technik [HDD-23] represents the increased development of steerable small-sized drill rigs based on HDD especially for laterals in the past years.

These Mini rigs with a maximum pullback of 40 kN or 45 kN are designed according to a modular system (drilling frame, hydraulic station, drill rod box, mixing plant) and are preferably used if

• the space conditions are extremely limited,
• complicated …

The term of hybrid systems describes the possibility of converting drilling devices of other trenchless construction techniques, especially pilot pipe jacking systems [HDD-184] and auger boring machines (see Volume 1, Chapter 7 and Section 5.2.3 [HDD-1]) to suit the technique of HDD. That means, depending on the local and subsoil conditions, these machines can be employed as dry boring techniques as well as HDD methods [HDD-31] [HDD-185]. The base …

(Image: "Over-drilling" method for replacing cables – Longitudinal section and procedure)HDD is also used to replace already existing pipelines or cables. With reference to DIN EN 752 [HDD-186] and/or DIN EN 12889 [HDD-9] replacement is understood to refer to the “construction of a new drain or sewer, on or off the line of an existing drain or sewer, the function of the new drain or sewer incorporating that of the old.“

In the following, a representative …

In the last decade, there have been further developments
based on the conventional HDD method in
construction technology and/or machine technology
in order to broaden this method’s application. In the
following, several examples will be presented.

In the following, several projects that were carried out in practice and reflect the broad range of application of HDD are presented. In some construction measures problems occurred during construction work. They could be solved, however, due to arrangements already made in the planning stage and by introducing ad hoc emergency measures.

(Image: Project "Pipeline-connection Mittelplate“ – Geographic position)The connection of the oil rig “Mittelplate“, situated in the North Sea, to the mainland in Friedrichskoog- Spitze by means of two drillings, each 7.5 km long, through the foreshore of Schleswig-Holstein can be considered a special HDD project of extraordinary dimensions (Figure 132 a). The project was completed in June 2005. The installation depth was down to 25 m (≈ 82 ft.) …

To connect two chemical plants in the cities of Brunsbüttel and Stade situated in northern Germany, the construction of an altogether approx. 55 km (≈ 34 miles) long 6“-pipeline for the transport of ethylene – a flammable gas, which is used for producing polyethylene and manufacturing other chemical elements – became necessary. In connection with this construction project, the Elbe River had to be crossed between St. Margarethen in the north and …

(Image: Crossing the Elbe River for installing a 6“ pipeline by HDD – Procedure of drilling #1)With the first pilot bore (2.7/8“) with a 6.5/8“ washover pipe it was started from the northern location near St. Margarethen and, corresponding to the plan, it was stopped after around 300 m (Figure 133 a, 1st phase). After pulling-back the pilot drill string, subsequently the 20“ steel casing pipe was pressed in with a 28“ drill bit via the drill rod …