Goodbye open trenching28 September 2016
Modern engineering has developed sophisticated subsurface construction methods that eliminate open trenching. These trenchless piping methods are currently enjoying a rapid rise in popularity throughout the construction and civil engineering sectors. They reduce costs and disruption to existing built environments during construction.
The two most popular trenchless methods for pipe installation today are horizontal directional drilling (HDD) and microtunnelling. Surprisingly, each of these methods evolved along completely independent lines of development.
HDD’s roots are in the oil industry and date back to the early part of last century. The method uses techniques and processes common to vertical well drilling, but today HDD equipment is tailor-made for horizontal, or near horizontal, installations. It is frequently employed for telecommunications or power projects due to its suitability for long-distance installation lines.
HDD typically involves a surface launched and retrieved drilling process that is ideal for the installation of long continuous lengths. While it is best suited to the installation of pressure pipelines more than 1.2 metres for oil, gas and water transmission, it is also used for the direct installation of telecommunication and electrical cables.
On the other hand, microtunnelling has been around for just a few decades, and originally focused on sewerage pipe installation. It originated in Japan in the 1970s and was a development of conventional pipe jacking to enable smaller pipes to be installed mechanically. It was specifically designed for excellent installation accuracy, and is used primarily for the installation of gravity pipelines, in particular sewers.
Unlike HDD and like other methods of tunnelling, microtunnelling is undertaken from and to below ground shafts or pits. A key difference between HDD and microtunnelling lies in the way it deals with the surrounding earth or soil in which the pipes are installed, and thus the pipes’ suitability for different ground conditions.
There is crossover between the two methods. Some small diameter gravity sewers are installed by HDD, especially when plenty of pipe gradient is available. Similarly, some pressure pipelines are directly installed by the microtunnelling method. However, the different attributes of the two methodologies mean they rarely compete for the same work.