Description
Horizontal Directional Drilling (HHD), is an innovative technique adapted from the drilling technology used usually in the petrochemical industry, for the installation of underground utilities where conventional open-trenching solutions are inappropriate or not permitted, such as under rivers, railways, highways, in protected areas (national parks, urban areas of historical importance) or in densely populated residential areas (Figure 1).
This technology is currently also used for slope stabilization, to lay the drain pipes instead of the conventional drilling; it can be used in geological conditions ranging from soft to very hard formations.
The process starts with the construction of the receiving hole and the entrance pits. These pits will allow the drilling fluid to be collected and reclaimed to minimize cost and to prevent excessive waste. The first stage drills a pilot hole on the designed path (Fig. 2a) and the second stage enlarges the hole by passing a larger cutting tool known as the back reamer (Figs. 2b, 3b). The reamer's diameter depends on the size of the pipe. Throughout the drilling and reaming process the drilling is done with the help of a viscous drilling fluid. It is a mixture of water and, usually, polymer continuously pumped to the cutting head or drill bit to facilitate the removal of cuttings, stabilize the bore hole, cool the cutting head, and lubricate the passage of the product pipe. The third stage places the drain in the enlarged hole by means of the drill steel and is pulled behind the reamer (Fig. 3c) to allow centering of the pipe in the newly reamed path (Fig. 2c).
The equipment used in a directional drill operation (Figs. 3, 4, 5, and 6) depends on the size of the pipe, length of the run, and surrounding locations. For the large bores, a 100,000 pound pulling power drill is used with a reclaimer, excavator, and multiple pumps and hoses to move the fluid. The drilling steel is a 3-in. diameter pipe with male and female threads (Fig. 4). The head of the operation comes in multiple designs and depends on the rock or soil being penetrated. The drilling head (Fig. 6) has multiple water ports to allow removal of material. A talon bit involves the diamond tipped cutters. These allow for steering and cutting the material. Another head type is a mud-motor which is used in rocky landscapes (Fig. 6).
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Typically a small two-person crew is required including a drill operator and a tracker. The tracker directs the progress of the drill by using a hand held device that gathers data from a sonde located in the drill head just behind the bit. The advantages of this system are:
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the size of the worksite consists of two small entry and exit pits;
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the drain may be laid at the desired depth with no risk to the operator;
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the bore path can be directed to avoid buried obstacles or other utilities, or to follow an angled trajectory according to the particular requirements of the bore design;
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the installation is faster and safer with no need to back-fill the excavation.
An experimental application at Barton-on-Sea, UK, proved very successful. The drains were drilled from a starter pit in very stiff clay some distance away from the toe of the unstable seacliff. Once drilling had penetrated sufficiently below the toe of the cliff, the directional drilling was made to turn upwards to come out onto the main plateau at the top of the cliff, where the reamer and the perforated pipe werea fixed to the drillstring and pulled back to the starter pit. This arrangement allowed the drains to intercept several perched water tables in the stratified soil profile and to discharge by gravity. The minimal intrusiveness of the technquie is an added bonus, allowing installation in envioronmentally sensiive locations with minimal disruption.
Design methods
The design of horizontal drains can be carried out by using numerical analyses or easily by adopting design charts available in literature (Di Maio et al.1988, Desideri et al. 1997, Pun & Urciuoli 2008). See the section 4.3.
However when this technology is used apart from the design of drains (length, diameter, number, and interspace), it is important that the work area at entry and exit is adequate and safe and to plan bore path with adequate separation from utilities and obstacles.
Functional suitability criteria
Type of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Fall | 2 | Horizontal drains are used to stabilize deep landslides essentially characterized by circular slip surface. |
| Topple | 2 | |
| Slide | 6 | |
| Spread | 4 | |
| Flow | 4 | |
Material type |
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| Descriptor | Rating | Notes |
|---|---|---|
| Earth | 4 | The Horizontal Directional Drilling technology can be applied to several soil types such as clay, sandy and limey soil, and rocky ground. |
| Debris | 8 | |
| Rock | 4 | |
Depth of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Surficial (< 0.5 m) | 0 | These drainage system can reach very deep slip surface through any type of path. |
| Shallow (0.5 to 3 m) | 0 | |
| Medium (3 to 8 m) | 6 | |
| Deep (8 to 15 m) | 8 | |
| Very deep (> 15 m) | 8 | |
Rate of movement |
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| Descriptor | Rating | Notes |
|---|---|---|
| Moderate to fast | 2 | The steady-state condition is attained some time after drainage construction (i.e. at the long term) in fact after drain installation, a transient phenomenon of equalization of pore pressures occurs. Drains are completely effective after such a delay and they represent the suitable mitigation measure for very slow landslides. |
| Slow | 6 | |
| Very slow | 8 | |
| Extremely slow | 8 | |
Ground water conditions |
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| Descriptor | Rating | Notes |
|---|---|---|
| Artesian | 4 | This system is suitable for deep freatic water table. |
| High | 6 | |
| Low | 8 | |
| Absent | 0 | |
Surface water |
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| Descriptor | Rating | Notes |
|---|---|---|
| Rain | 4 | Horizontal drains are not suitable to drain shallow water. |
| Snowmelt | 4 | |
| Localized | 0 | |
| Stream | 0 | |
| Torrent | 0 | |
| River | 0 | |
Reliability and feasibility criteria
| Criteria | Rating | Notes |
|---|---|---|
| Reliability | 6 | It’s necessary flushing the pipes with a high pressure water jet for a good working. |
| Feasibility and Manageability | 6 | Technique and design process are sufficiently established. |
Urgency and consequence suitability
| Criteria | Rating | Notes |
|---|---|---|
| Timeliness of implementation | 7 | Drain alignment can be adapted to avoid obstacles and buildings. Easily implemented with 2 man crew. Faster and safer than other methods, with no need to enter or backfill threnches, but requires specialist equipment. |
| Environmental suitability | 4 | will be updated |
| Economic suitability (cost) | 6 | The cost of this type of drilling is 5-7 times higher than the conventional drilling. |
References
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American Society of Civil Engineers (ASCE). (2005). “Pipeline design for installation by horizontal directional drilling”. ASCE manuals and reports on Engineering Practice No.108.
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BS: 6031 (1981). “Code of Practice for Earthworks”. British Standard Institution.
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Burghignoli A., Desideri A. (1987). “On the effectiveness of tubolar drains”. Proc.IX ECSMFE,Dublin, Vol. 1, 121-124.
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Canadian Association of petroleum producers (2004). “Planning Horizontal Directional Drilling for Pipeline Construction“, Guideline. CAPP Publication, 2004-0022.
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Capaccetta M. (2006). “Applicazioni del directional drilling nei lavori di drenaggio di versanti in frana”. In: I sistemi drenanti nei dissesti del territorio, 7 Aprile 2006 - Grugliasco – Torino.
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Desideri A., Miliziano S., Rampello S. (1997). “Drenaggi a Gravità per la Stabilizzazione dei Pendii”. Hevelius Edizioni, Benevento.
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Di Maio C., Evangelista A., Viggiani C. (1988). “Analisi dell’efficienza di sitemi di dreni tubolari”. Rivista Italiana di Geotecnica, 12 (4), 187-199.
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Grays Harbor Pipeline. nd. Horizontal Directional Drilling (HDD). http://www.graysharbor.twc.com/HDD-fact_sheet.htm.
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HDD Consortium. (2004). “Horizontal Directional Drilling Good Practices Guidelines”. ISBN: 1-928984-13-4. North American Society for Trenchless Technology.
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Highway agency (2007). “Review of the use of horizontal drainage systems”. Final Report. Halcrow Group Limited, January 2007.
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Hutchinson, J.N. (1977). Assessment of the effectiveness of corrective measures in relation to geological conditions and types of slope movement (General Report). Bulletin of the Int. Association of Engineering Geology 16: 131-155.
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Kenney, T. C. & Lau, K. C. (1984). Temporal changes of groundwater pressure in a natural slope of non fissured clay. Can. Geotech. J. 21(1): 138-146.
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Kenney T.C., Pazin M. & Choi W.S. (1977). Design of horizontal drains for soil slopes. ASCE Journal of Geotechnical Engineering Division, 103(GT11): 1311-1323.
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Marino R. (2007). Analisi 3D Dell’efficienza di Aste Drenanti per la Stabilizzazione dei Pendii. Graduate thesis, University of Naples Federico II.
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Nonveiller E.(1981). Efficiency of horizontal drains on slope stability. Proc.X.ICSMFE,Stockholm, 3, 495-500.
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Pun W.K., Urciuoli G. (2008). Keynote paper: Soil nailing and subsurface drainage for slope stabilization,. 10TH INTERNATIONAL SYMPOSIUM ON LANDSLIDES AND ENGINEERED SLOPES June 30 ~ July 4, 2008, Xi’an, China.
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Scandrill Co. L.L.C. (2001). Horizontal Directional Drilling. http://www.scandrill.ca.ae/html/hdd.htm.
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Trenchless Technology British Columbia. nd. Trenchless Technology - A Canadian Perspective Guide. http://trenchless-technology.org/canguide.html.
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Walker B.F. & Mohen F.J. (1987). Ground water prediction and control and negative pore water pressure. In Walker & Fell (eds.), Soil Slope Instability and Stabilisation, 121-181.