Versie 5.1

Design of Horizontal Directional Drilling

Horizontal directional drilling (HDD) is one of the fastest growing techniques for trenchless installation of pipelines. On one hand, they provide a logical alternative when cables, pipelines or small tunnels need to cross dikes, wetlands, rivers and other structures that have to remain intact. On the other hand, HDD techniques minimize the impact of construction activities in densely populated and economical sensitive areas. In the Netherlands HDD has been used on a large scale since the eighties. Since the seventies GeoDelft has been involved in the development and execution of trenchless technologies. Years of research have resulted in one of the first design codes for HDD, as well as a computer program. Since the release of the first version in 1995, MDrill provides users with the minimum and maximum drilling fluid pressure during the different phases of construction. MDrill can also analyse the stresses in the pipeline during and after construction for different pipeline materials.

MDrill enables the fast design of a pipeline configuration installed by the Horizontal Directional Drilling technique (HDD). In HDD three installation stages are considered:

• Pilot drilling
• Reaming the initial pilot borehole
• Pulling back the pipeline

The initial borehole is called a pilot hole. The diameter of the pilot hole is enlarged using a reamer. Depending on the required final borehole diameter, the borehole can be enlarged in several steps using reamers of increasing diameters. Finally, the pipeline is pulled into the borehole.

Barrel reamer and flycutter

During all drilling stages, drilling fluid is pumped under pressure into the borehole. The main function of drilling fluid is to transport cuttings from the drilling head through the borehole to the ground surface. A specific minimum pressure is required for the transport function of the drilling fluid. The fluid pressure in the borehole, however, should not exceed a specific maximum value. The maximum value is related to the strength of the soil around the borehole. If the maximum fluid pressure is exceeded, a ‘blow-out’ may occur. Besides the pressure of the drilling fluid, other factors play a role in the design process. Both the strength of the pipeline during the pull back operation and the strength of the pipeline in operation need to be sufficient to withstand the forces acting on the pipeline. 

2D cross section

MDrill comes as a standard module, which can be extended further with other modules to fit two other applications related to pipeline installation:

DGS.05.00 Horizontal Directional Drilling
DGS.05.01 Micro Tunneling module*
DGS.05.02 Trench module*

*) modules are available in version 6.