Underpinning methods for earthquake damage repair

Many houses and other buildings in Christchurch have suffered structural damage from the recent disastrous earthquakes.  In addition to the buildings damaged beyond repair by the quakes, many others have suffered damage of the kind that can be repaired by underpinning.

Underpinning means raising the footings of the building back to its original, level position.

The New Zealand Government Department of Building and Housing's Guidelines (for Engineers, Builders and Insurance) "Guidance on house repairs and reconstruction follwing the Canterbury earthquake" describes the different types of house footings in Christchurch and then outlines the acceptable options for underpinning, lifting and re-levelling buildings in Christchurch.

Worth noting is that these Guidelines outline an exceptional modern process for doing this work:

"Perimeter foundation jacking using engineered resin ....

This option is a proprietary lifting process where engineered resin is injected into the ground at multiple points along the foundation. The expanding resin lifts the foundation. The process also densifies the surrounding ground which serves as a reaction layer for the lifting operation."

This method is carried out by URETEK Ground Engineering, the company that pioneered the process, and it is the subject of BRANZ Appraisal No 698.

The Department notes: ".... it is important that specialist contractors be used."

Underpinning using structural engineered resin

URETEK Ground Engineering specialises precisely and completely in this exact work, raising, re-levelling and re-supporting of buildings and pavements, roads and bridges, by injection of engineered structural expanding resins.

And the URETEK method has been well proven in dealing with earthquake and tremor-damaged buildings in mahy countries since the URETEK Method was invented and patented 27 years ago.

The problem -  when a building is not level

With the earthquakes, many less severely damaged buildings have partially sunk into the ground. Floors have gone out-of-level, cracks have appeared in walls, and doors and windows have ceased to work properly.

The solution - correct the building with a good procedure

Uretek Ground Engineering is not in the business of reconstruction, but it can provide a very good correction procedure for footings and foundations, even when the damage is more than minor. In many cases such footing correction will correct other problems, such as bringing cracked walls back together and re-aligning doors, windows, skirting boards etc.

The Government Guidelines document refers builders to the Uretek Method as one of the approved repair procedures. (Also see Building Research Association of New Zealand, BRANZ, Appraisal No. 698).

Of course, many consulting engineers and builders are already familiar with Uretek capabilities and can advise building owners on a particular situation. Uretek Project Managers will also assess Uretek applicability for you (call Phil Johnston 03 987 3835).

What kind of repair to expect

Not in every one, but in many cases of earthquake damage Uretek does offer the best solution. Uretek structural resin injection into the foundation ground beneath the building can usually achieve several aims:

• Uretek lifts the building back to level at its original height.
• When that is done usually wall cracks close up – cracks in interior plasterboard or rendered brickwork, and also cracks in exterior brickwork.
• Generally upon re-levelling, windows and doors are able to fit and work properly again…
• And gaps between skirting boards and floors also tend to close right back up.
• In many conditions, Uretek Deep-Injection can also be used to compact the foundation soil. The bearing capacity of the ground has been increased by up to 500% in some cases! Where applicable, this helps to reduce the potential for future severe movement.