In March, Andy Pomfret and his team from Initia (geotechnical specialists) spent time at the pool testing the ground to gain an understanding of the types of soil that make up the foundations under and around the 50m outdoor pool.
Mr Pomfret, who has been involved in geotech testing at pools around the country, says the report will help plans for pool refurbishment to be developed that mitigate issues from subsequent movement due to poor ground conditions.
“A geotech report is an understanding of the ground water conditions and it’s needed to enable a full design of the pool to go ahead without any issues like settlement, cracking of the pool, the load of the structure."
“So really you need a really good understanding of what’s beneath the pool and surrounding areas so when a new facility is constructed it won’t have any issues.”
The preliminary testing includes taking samples from various depths around the facility to get a visual understanding of the water content in the soil.
“In an ideal world we would find something hard so when the pool is revamped or reconstructed then the founding layer is hard enough and it won’t settle. Unfortunately given it’s Rotorua and we have lake deposits here it’s quite soft so we may have to come up with some alternative foundation solutions,” Mr Pomfret says.
In order to get a complete picture of the ground condition geologists from Southern Geophysical have also carried out resistivity and ground-penetrating radar testing as a non-invasive way to determine the layers of material under the ground.
Southern Geophysical geologist Richard Mellis says that coupled with the data from the bore hole tests, the survey results will give designers a really good picture of any issues they need to take into consideration when planning for the pool upgrades.
"One method of testing is using a resistivity line to measure what's under the ground. The different layers. For instance a gravel layer will be highly resistive and a clay layer that's saturated will have very low resistance."
Mr Mellis explains that the cables and the electrodes in the ground use a current emitted from the computer to test the electrical resistance of the ground at any particular location.
"We step those electrodes wider and we measure deeper and by measuring the resistance in the ground we can tell you what type of material is in the ground by combining this data with bore hole logs."
"We can tell you where those layers are in the ground and whether or not they're dipping whether there is a channel...and from that people can determine what we do from here."