Click to enlarge Geological engineer Ian McCahon

Initial sub-soil testing of Maori Park where Timaru’s new $23.5 million aquatic and leisure centre is to be built has shown a stable base that geological engineer Ian McCahon describes as being very suitable for the project to go ahead as conceived.

Mr McCahon, of Geotech Consulting Ltd, Christchurch, spent yesterday ( Thursday October 15) punching a sample cone down up to eight metres into the ground in six locations around the proposed pool site to measure sub-strata stability and suitability for the proposed buildings and pools.

He said the computer-analysed findings supported his expectations that like most of Timaru, loess, or windblown soil from the glacial period, had covered the site at a depth of up to 12 metres.

“Loess is the yellow-coloured sandy silt common around South Canterbury cliffs. It makes a suitable foundation for the structure envisaged here,” Mr McCahon said.

Below 12 metres the geology usually turns to basalt rock, he said.

The sub-strata testing process known as CPT (cone penetration tests) involved a truck-mounted hydraulic ram slowly pushing sections of 50mm diameter hollow stainless steel rods vertically into the ground, piece by piece.

Inside the rod a cable transmits wall friction measurements to a computer above and sophisticated resistance-measuring sensors on the truck plot penetration resistance as the ram forces the rods into the ground at a gradual pace. The higher the resistance, the firmer the ground. A match-up between the two sets of data enables the computer to draw a subterranean graph.

“What we have been looking at are typical and expected readings, if anything showing a slightly stiffer base than we thought four metres down. That’s great from an engineer’s point of view,” Mr McCahon said.

The test rig was provided by McMillan Drilling Ltd.

The specialist truck features a 300mm thick concrete deck that weighs 15 tonnes to prevent the plunging rods from lifting the truck.

“If the back wheels of the truck lift by even a small degree, the rods can be subject to sideways stresses and bending that could damage them,” Mr McCahon said.

Mr McCahon, who lives in Christchurch and graduated from Canterbury University with a civil engineering degree, also has a family connection with Timaru.

His great grandfather was noted historical photographer William Ferrier, who was famous for a series of photographs of Caroline Bay and the surrounding district and its buildings around 1914. Mr Ferrier’s work hangs in many galleries and buildings around the district.

ENDS

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