According to [HDD-103], soil classification is the classification of soils for structural purposes. Classification refers to the categorizing of soil samples into soil groups according to fixed characteristics and criteria.

The purpose of a classification is the establishment of unified evaluation properties that allow a preliminary estimation of the suitability of subsoil for certain civil engineering purposes. In addition, by determining the properties …

In trenchless construction, despite their importance to construction procedures, the structure and properties of the subsoil can only economically be explored in a very intermittent fashion over the length of the utility lines installed (see Volume 1, Section 4.5 [HDD-1]).

According to DVGW-GW 312 [HDD-15], for HDD a bore spacing of 50 m (≈ 164 ft.) is to be aimed at. If two neighbouring drill profiles show significant differences in their condition …

The exploration depth must include all layers that are to be drilled through in the HDD project. Furthermore, in drillings through subsoil with groundwater, additionally the exploration depth must be determined according to the hydrogeological conditions.

For HDD, the DCA [HDD-17] recommends to sink exploratory boreholes 2 m to 5 m (≈ 6.5 ft. to 16.4 ft.) below the planned line axis. This provides an additional explored area in case a change of borehole …

(Image: Influence of the subsoil on HDD)For using HDD methods, accurate and comprehensive information on the subsoil, based on qualified and targeted subsoil investigations carried out by the client, is a necessity in order to be able to ensure its feasibility and to reduce the subsoil risk to a minimum [HDD-17]. The building owner as the client is basically responsible for the subsoil and its associated characteristics. Also, in line construction, …

HDD is to be used in such way that structures owned by third parties are not endangered. The corresponding requirements by DVGW-GW 315 [HDD-114], DVGWGW 316 [HDD-78] and DVGW Data Sheet W 380 [HDD-115] must be taken into account and adhered to [HDD-15].

According to DIN 18319 [HDD-62] [HDD-108], in the interest of an interruption-free construction process and for the protection of possibly endangered persons, it is necessary to also gain knowledge …

(Image: Schematic view of the georadar measuring principle)In the geo- and ground radar (GPR - Ground Penetrating or Probing Radar), which is one of a number of geophysical methods (see Volume 1 Section 4.5.2.2 [HDD-1]), a high-frequency electromagnetic radiation pulse is transmitted into the subsoil by means of an antenna. The signal is partially reflected at the contact borders between strata and other interference bodies and is recorded by a receiver. …

(Image: Principle of locating electromagnetic alternating fields – magnetic field locating)In this method of line locating, Ampère’s as well as Faraday’s law of magnetic inductions are applied. Here, a measurable electromagnetic field is generated around a line that is to be located (metallic conductor) by means of alternating current (AC). The streamlines of the field penetrate the subsoil unresistantly and enclose the current centre in the form …

(Image: PE 100-pipe with dimensionally added protective coating of minerally reinforced PP and integrated, spirally wound conductor tape of the type egeplast SLM® 2.0 DCT (DCT – Detection and Checking Technology) – View and design)To locate non-metallic lines that are not equipped with integrated metal locating tapes or tracers (Figure 246a) and thus cannot be located with the above mentioned active or passive methods, the following methods are available:

HDD is to be used in such way that structures owned by third parties are not endangered. The corresponding requirements by DVGW-GW 315 [HDD-114], DVGWGW 316 [HDD-78] and DVGW Data Sheet W 380 [HDD-115] must be taken into account and adhered to [HDD-15].

According to DIN 18319 [HDD-62] [HDD-108], in the interest of an interruption-free construction process and for the protection of possibly endangered persons, it is necessary to also gain knowledge …

If supply or discharge lines are drilled into in spite of thorough preliminary exploration measures, various rules of conduct are to be observed by the drill operator and the personnel at the construction site depending on the line type concerned [HDD-65] [HDD-128].

Due to the particularly serious effects of this type of damage on the drill operator and the personnel at the construction site, both prophylactic (additional) and acute protective measures against completing a dangerous circuit from the conductor to another object should be employed when boring close to current- carrying cables.

Prophylactic protective measures

For HDD methods, additional protection measures for the personnel operating the drill are …

When boring into other supply and discharge lines the following precautions should be taken [HDD-65] [HDD-128].

Gas strike

• Evacuate area immediately.
• The drill operator should shut down all engines, and under no circumstance should the operator attempt to reverse the bore to break contact as further movement may cause a spark.
• Emergency services and the gas utility company should be contacted immediately.

Communication line strike

• Drilling must …

If supply or discharge lines are drilled into in spite of thorough preliminary exploration measures, various rules of conduct are to be observed by the drill operator and the personnel at the construction site depending on the line type concerned [HDD-65] [HDD-128].

In carrying out drillings, difficulties in part are inherent to this type of work repeatedly occur and thus lead to enormous financial losses on the client’s as well as on the contractor’s side. These failed drillings also are frequently caused by insufficient construction preparations as well as insufficient geotechnical investigations or explorations by the client and the contractor. Such investigations are a critical part of the use of this method […

For several years now, numerous programs, so-called Bore Planning Tools, have been available on the international market. They are intended to simplify the software- based planning and realisation of HDD projects.

These software tools (e.g. Atlas Bore Planner™ [HDD-131], Grundo Bore Planner [HDD-23], Phrikolat Bohrlinienplaner [HDD-54], Boretech Holland [HDD-46] [HDD-132]), which are relatively easy to handle and are often offered by the drill manufacturers, …

With the layout of the line, the horizontal position of the drilling within the area is determined. If possible, the line of the drilling should run straight and at right angles with the obstructions that might have to be passed (e.g. river, canal, road). In the layout of the line, the following issues must be addressed [HDD-136]:

• technically required drilling distance,
• conditions for the construction site arrangement (spatial conditions),
• easements,

By means of the gradient, the vertical position of the drilling (positional depth) is determined. To create the gradient, the compulsory aspects for the drilling are to be analysed. They can comprise, for example [HDD-136]:

• the length and the depth of the area to be crossed (e.g. depth and width of rivers and canals),
• the geology of the drilling layout,
• the cover,
• obstructions,
• the minimum permissible elastic bending radius or permissible minimum …

The curve radius of the borehole plays a decisive part when it comes to designing the drill profile. The minimum permissible curve radius is either given by the minimum bending radius of the drill rod, the minimum permissible elastic bending radius or the permissible minimum curve radius of the pipe string to be pulled in [HDD-17].

As a rule, the planning of the relevant minimum permissible curve radius for small drilling projects and PE pipes orients …

In the case that the drill rod string provides the minimum permissible curve radius, it is to be determined according to the manufacturer’s information. As guide values in this regard the minimum bending radii given in Table 31 can be assumed with reference to the size of the drill rig or the diameter of the drill rod.

For drill rod strings by the manufacturer COLLI DRILL [HDD-137], the minimum bending radius R_min, for example, can be calculated with …

If the minimum permissible curve radius of the drilling is controlled by the pipe to be pulled in, then the determination of the minimum permissible elastic bending radius for planning and execution is more complex. Furthermore, a differentiation has to be made between the actual pipe string inside the borehole and the overbend at the surface [HDD-17].

Generally, for welded steel pipe strings, the bending analysis according to Mohr applies when determining …

Besides welded pipe strings, in HDD use is also made of ductile cast iron or steel pipes with restrained, angular sockets and spigot joints such as TIS-K, TKF, BLS or DKM (see (Joints of ductile cast iron pipes) and (Restrained plug and socket joints)) [HDD-140].

(Image: Longitudinal section through a bent drilling path to calculate the permissible minimum curve radius and/or the borehole diameter D when installing ductile cast iron pipes)

With reference …

The curve radius of the borehole plays a decisive part when it comes to designing the drill profile. The minimum permissible curve radius is either given by the minimum bending radius of the drill rod, the minimum permissible elastic bending radius or the permissible minimum curve radius of the pipe string to be pulled in [HDD-17].

As a rule, the planning of the relevant minimum permissible curve radius for small drilling projects and PE pipes orients …

There are as yet no generally binding or standardised calculation models for determining the size of a suitable drill rig, i.e. of the necessary pullback force potential for the individual case of application. However, it should be considered here that during the pulling-in process – e.g. because of longer drilling interruptions or borehole collapses – a substantially higher pullback force may be required than that calculated with the above mentioned …

For several years now, numerous programs, so-called Bore Planning Tools, have been available on the international market. They are intended to simplify the software- based planning and realisation of HDD projects.

These software tools (e.g. Atlas Bore Planner™ [HDD-131], Grundo Bore Planner [HDD-23], Phrikolat Bohrlinienplaner [HDD-54], Boretech Holland [HDD-46] [HDD-132]), which are relatively easy to handle and are often offered by the drill manufacturers, …

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].