Slip threatens buildings

A new report has raised concerns major buildings could be at risk if a central city slip worsens significantly.

Council has already budgeted $680,000 towards the Bryce St riverbank slip but a new engineering assessment says the cost of fixing the "tricky" slip may be more than double that.

An unexpected briefing to Hamilton city councillors meeting yesterday advised them that additional investigations may prove the risk is less, and remediation cheaper than feared.

While engineers believe further slipping would be relatively shallow seated, "any increased slope regression could pose a risk to any existing structures or assets in close proximity".

A gas pipeline and the river walkway itself are considered at high risk, but the further work was needed to quantify the risk to buildings further away - including the Ibis hotel and the IRD building and 2-4 Bryce St.

Council staff have already met with affected land owners, incluing Tainui, to discuss the report.

Remedial options already scoped include soil nailing and retaining walls, at a potential cost of up to $1.5 million. 

However the remedial works themselves could pose a further threat, say geotechnical engineers from Tonkin and Taylor. 

Engineering firm Bloxam Burnett and Oliver have been commissioned to do the further investigations. 

The company has experience strengthening the Narrows Bridge, which had a lengthy closure due to erosion undercutting its foundations, and the Cambridge High Level Bridge.

While there is no indication the Claudelands road and rail bridge is at any immediate risk, intensive monitoring is planned for signs of further movement, and contingency plans include closing the bridge at short notice.

Further geotechnical tests will establish the strength of a critical soil layer along the steep riverbank section. 

The troublesome section of riverbank walkway has been closed since July last year, when a slip prompted a geotechnical assessment of a 600m stretch with a history of instability.

Tonkin and Taylor's hazard assessment has shown the risks could be higher than first thought, warranting further investigation, council staff have told councillors.

Waikato Times