Hortizonal Directional Drilling in rock

Selborne situated in the South Downs National Park required a new 125 SDR11 rising main from the village pumping station to the refurbished STW.

Client Thames Water explored various installation technique’s ranging from micro-tunnelling to open – cut but main contractor Cappagh Construction with engineering assistance provided by AWL designed an installation which could be under taken by Horizontal Directional Drilling.

The direct route required the drill to run from one shallow valley, beneath a plateau covered by fields and woodland and exit in a steep sided valley at depths of up to 25m to 30m deep for the majority of the drill.

Boreholes were carried out in advance to depths up to 40m, confirming that the ground was Upper Greensand Formation comprising weak to strong sandstones and siltstones.

AWL utilised their 64te Midi Horizontal Directional Drill Rig complete with a 5 ½” mud motor and a PDC 7 7/8″ bit with a Tensor MGS probe. Due to lose ground the first 20 metres required the installation of a steel casing to support the drilling fluid. No reaming was required and the SDR11 125 diameter pipe was pulled directly into the drill hole.

Directional Drilling