Drill Drain® is a solution from Ischebeck Titan that allows hydro-static pressure or poor drainage of water in a structure or embankment to be drained without the need for excavation. In some cases during heavy rainfall, rainwater infiltrates topsoil and builds up on the boundary layer (impermeable stratum), the result is an increase in the weight of the water-saturated topsoil, an increased pore water pressure and a reduction in the skin friction at the boundary layer. The topsoil begins to creep on the boundary layer, and in extreme cases this could result in slope failure.
The Drill Drain® filter nail is installed in one operation. It is inserted with standard rotary percussive drilling rigs fitted with a suitable disposable drill bit, normally with the help of water jetting. As soon as the intended depth has been reached, the filter material is injected. A grout body diameter of 90–150 mm is relatively normal. The filter nail penetrates the water-bearing boundary layer, reduces the excess pore water pressure and at the same time improves the shear bond of the soil like a soil nail.
There are very few methods suitable for draining critical slopes. Well points or relief wells, e.g. 150 mm dia. and 30 m deep at a shallow angle, down to an impermeable stratum, are very costly to install. It is difficult to find a filter pipe with enough filter resistance and filter stability for varying soil strata. In addition, water migration, erosion, liquefaction in fine-grained soils, piping, etc. must be accepted.
The Drill Drain system belongs to a group of slope stabilisation methods and therefore it belongs to the Soil Nail system. The Drill Drain system consists of TITAN 40/27 steel tendon (hollow threaded bar), 40mm O.D, 27mm I.D and a grout body made from a proprietary filter material, which with a permeability coefficient k10 = 10-4 m/s is permeable to both air and water.
The filter nail is a composite product. The steel tendon (reinforcement) provides the filter nail and prevents separation of the grout body in the case of larger ground movements. The grout body complies with BS and EN technical approvals meaning that the steel tendon is sufficiently well protected.
Using a standard clay drill bit, consisting of the components of a soil nail, this system is proven worldwide and will alleviate pore and hydro-static water pressure[s]
Like standard soil nails, the hole for the filter nail is usually drilled at an angle of approx. 10° to the horizontal, at an incline or decline. The pore water is drained away by the Drill Drain® filter material into a drainage mat on the air-side of the TITAN threaded bar.
Forming the drainage borehole at 90–150mm (diameter × d, where d = 40mm dia. of steel tendon) is carried out using the direct drilling technique without a casing.
The aim is to be able to supply the filter material to the projects ready-mixed in sacks (< 20 kg) so that only water needs to be added to the forced-action mixer on site.
- Control of slope seepage water
- Retaining wall without hydro-static pressure
- Retention of positive soil properties
- Reduction of pore water pressure
- No ice pressure during periods of freezing
- Allows the installation of micropiles and tie back anchors without the need for dewatering
- Safe, controlled and efficient installation
- Economical installation, when compared to dewatering
VERSATILE AND EFFECTIVE GROUND ENGINEERING SOLUTION
Drill Drain® used at Bray Head with Triur Construction
Bray Head is situated in County Wicklow, south of Dublin in the Republic of Ireland. The route around the headland was surveyed and engineered by none other than Isambard Kingdom Brunel, who at the time was engaged with the construction of the Dublin & Wicklow Railway’s line from Bray to the county town of Wicklow further south. The section of line around the headland from Bray to Greystones was first opened in 1855.
The works were located at coastal defence asset CDR074D (also known locally as ‘Structure C’) situated at 13 miles, 1,225 yards on the Dublin to Wexford railway line. In more specific terms, this asset is located on Bray Head on the railway line between Bray and Greystones in Co. Wicklow within a SAC area. This project was designed to replace a gabion structure that was installed in 1970, movement had been evident for some time but had accelerated in recent years.