En­gi­neer de­nies fault

Kapi-Mana News - - NEWS - By AN­DREA O’NEIL

Slips in Whitby are most likely due to builders over­load­ing land af­ter engi­neers have signed off sec­tions, ac­cord­ing to the en­gi­neer­ing firm in­volved.

Whitby Coastal Es­tates em­ployed John­sonville- based en­gi­neer Cardno when it built the south-east Whitby de­vel­op­ment over the past decade. The area has suf­fered nu­mer­ous slips.

Many sec­tion own­ers later em­ployed Cardno to as­sess plans for their houses.

But engi­neers could not guar­an­tee builders and home­own­ers would com­ply with engi­neers’ rec­om­men­da­tions, said Cardno man­ager Ray O’Cal­laghan.

Too much soil might be loaded on to a site or walls, and struc- tures might be built larger than plans al­lowed. Builders might fail to in­stall enough sub-soil drains into new fill, he said.

In the case of the Helm Pl properties pic­tured in last week’s Kapi-Mana News, earth­works to build up a flat lawn hap­pened af­ter Cardno signed off the sec­tion, Mr O’Cal­laghan said.

The non-en­gi­neered fill might have over­loaded the un­der­ly­ing nat­u­ral soil.

‘‘The cause of any slip is that the weight of the soil is greater than the in­ter­nal stresses ca­pa­ble of keep­ing soil in place.’’

Wet soil was heavy, and poorly com­pacted soil held lots of wa­ter, which could also cause slip­ping, Mr O’Cal­laghan said.

An­other pos­si­ble cause of slips was builders dump­ing top­soil into gul­lies be­low Whitby properties. Or­ganic mat­ter un­der the soil then rot­ted and be­came slip­pery, he said.

If fail­ures could be ex­plained it was pos­si­ble build­ing codes were fail­ing to meet con­di­tions on the ground, Mr O’Cal­laghan said.

Then of course there were acts of god, which was why engi­neers took out in­sur­ance, he said.

‘‘Some­times it’s an un­ex­pected, un­der­ly­ing fail­ure that noone could have seen, and that’s when EQC comes in.’’

Cardno had as­sessed the ma­jor­ity of de­vel­op­ments in the Welling­ton re­gion for 30 years, and had never had a slip on its sec­tions be­fore fur­ther work was done, Mr O’Cal­laghan said.

‘‘We’ve not had slips or struc­tural fail­ures any­where in Whitby in the 30 years that we have been work­ing there.’’

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