Drilled drainpipe dewatering system

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Drilled drains for dewatering

The last few years’ high precipitation has caused various slope movements like landslides and riverside cliff topples throughout our country. The main cause of these – sometimes catastrophic – events is the elevation of groundwater level. As rainwater seeps underground, and reaches the slanting, water-susceptible soil layers, they slowly become saturated. After a certain level of saturation their shear strength degrades to a point, where slope stability cannot be maintained any more.

Surface water management and subsurface drainage are good  solutions to prevent further damage and mass movements ( landslides )  and to restore slope stability preventing the further landslides .

Well-known, well-proven, ordinary drainage systems can be very costly and difficult to construct in greater depths (below 7 meters) – although, in the end, if planned and installed properly, they usually provide a reassuring solution.

In ground masses, that are subject to past and ongoing movements ( landslides ) the construction of these ordinary drains are extremely dangerous, sometimes even impossible.

To solve this problem, SYCONS – having many years of experience in the field – developed a new method for drain construction, a technology based on directional drilling. This method had been tested and proved effective on multiple occasions.

The construction of drilled-jacked drains can be started from:

  • shallow trenches at the foot of the slope, in the case that failure hasn’t yet occured
  • deep drive shafts, positioned behind the rupture ( sliding ) surface, in the intact, undamaged soil mass.

  • A thorough geotechnical investigation (Geotechnical Report) precedes the building process, providing detailed information on the position of saturated, permeable soil layers and soil masses. With the evaluation of these data we can determine the orientation, inclination and starting point of the special drain pipes, and start the construction.

    The drilled drain technology is suitable for the construction of special drain lines without a separate filter body – primarily in coarse-grained soils (having max. 3-5% clay content) with an achievable length of 40-50 meters in case of pipe jacking with reusable steel casing and 150-200 m in case of HDD drilling as laying method. We are able to lay these deep drilled drainage lines till a depth of 20-25 m.

    Higher silt and clay content results in decreased permeability, so in finer grained soils it may be needed to increase the filter surface area of the drainage pipe with the construction of an additional vertical filter body above the drainage pipe (gravel filter well) to reach adequate dewatering performance.

    If there are multiple soil layers situated above each other that need to be dewatered, and the most important one lies deep underground, their water content can easily be collected by vertically drilled shafts filled with filter gravel. Water from the bottom of the filter shafts can be led by the deep drilled crosiing drainage pipes to a central monitoring shaft, from which it can be conducted to a natural or pre-built receiver (a lake, a river, a trench or a rainwater collector system).

    Download landslide prevention brochure