Testing the HBA Anchors

On 8th April 2010, Chilbolton received a visit from Autonational, the Dutch company who will be doing the installation of the HBA (High Band Array). The HBA tiles need to be anchored to the ground to prevent any movement. This is done by driving a metal peg vertically down into the ground using an electric or hydraulic hammer. When tension is then put on the peg, it tumbles into a horizontal position to lock into the ground base. Each anchor can take a load of over 200kg. Because the different LOFAR sites vary considerably, it is necessary to test each one before the installation commences, to ascertain whether pilot drilling is required, what type of mechanical hammer is needed and what the best target depth is. The Chilbolton site is on a chalk base and it seems that it will be heavily affected by the ground water content at the time of the HBA anchoring. We will be using hydraulic hammers and driving the pegs 600mm below the surface.

In the below photo, Henk Paarhuis drives in a test anchor on the northwest edge of the HBA field. Eric Petrusma assists by keeping the anchor cable clear of the hammer bit.