Warren Boys and Ian Roebuck, of Ian Roebuck Crane Hire, remove the northen gable cross at Taranaki Cathedral. Having sat... read more
Well, that’s what we are working to find out.
Dr Dmytro Dizhur and assistant Dr Marta Giaretton were on site for three days in January investigating the makeup of our stone walls. Using a combination of techniques, the aim was to gain a lot more information on the properties of our unreinforced masonry walls. This is no simple matter as Taranaki Cathedral has walls of many different ages. The oldest wall erected in 1846 is to the left of the old entry facing Vivian Street. The eastern walls behind the organ were built in 1893. The stone masons who worked on each were a generation apart, so differences should be expected.
Dr Dizhur is a Research Fellow at QuakeCORE (Centre of Research Excellence) at Auckland University. His specialty is seismic assessment, investigation and retrofit of masonry buildings so when our Peer Review engineer Win Clarke recommended further site works be undertaken, Dr Dizhur was an obvious choice.
Dr Dmytro Dizhur and Dr Marta Giaretton about to start work at the eastern end of the church
Using a combination of very high tech equipment he and Marta worked from dawn to dusk off scaffolds and a cherry picker inside and outside the church recording huge amounts of information. Gaining access at the eastern end of the church was especially tricky. Careful measurement indicated it was possible to get the cherry picker in to place but theory and practice are sometimes not the same. Backing the trailer unit between trees and gravestones required millimetre precision and a team of helpers as well as John Pickering’s labrador barking orders!
Dr Marta Giaretton using the GPR unit to record information on the internal makeup of the stone walls.
Walls of different ages were selected to provide the fullest picture possible. A GPR unit (Ground Penetrating Radar) was used to indicate where voids in the walls might be. This was followed by the drilling of holes through mortar sections so that a tiny camera could be inserted in to the walls. Called a boroscope the camera recorded what it was seeing directly to a screen. We have not known if the huge corbel stones that stick out in to the church supporting the roof trusses extend to the outer wall or just how many stones cross over the inner and outer wall cavity providing extra strength. These camera shots will help fill in many gaps in our knowledge. Understanding the amount of space or voids in the walls improves our estimates on the amount and impact of grouting the cavity – a likely technique to be used in the strengthening.
We look forward to the results being with our Peer Review Engineer at the end of February.
And in case you are wondering – all the holes were refilled with mortar that will eventually fade to be indistinguishable.
Evening sets and Dr Dizhur drills the last of the exploratory holes on the western gable.