Download Lifting earthquake-affected buildings in Christchurch

FACTSHEET
CHRISTCHURCH RECOVERY
LIFTING EARTHQUAKE-AFFECTED BUILDINGS IN CHRISTCHURCH
A significant number of buildings will need to be lifted to allow
their foundations to be replaced following the earthquakes
in Christchurch.
The on-going seismic activity in Christchurch has created hazards
that would not normally be expected by contractors undertaking
foundation replacement in other parts of
New Zealand.
The New Zealand Heavy Haulage Association’s Best Practice
Guide to Building Relocation in New Zealand details industry best
practice when lifting buildings.
This fact sheet has been written as a supplement to the
guide. It aims to improve awareness of the hazards involved
in lifting buildings in Christchurch. It also provides industry
recommendations for controlling these hazards.
b. Stability – jacks must be set up in such a way that they are
stable throughout the entire lifting operation.
c. Number of jacks – operators must install sufficient jacks
to ensure the structure is supported without excess
deflection.
d. Lifting points – the integrity of the lifting points must
be determined to avoid collapse. Many buildings will have
sustained structural damage as a consequence of the
earthquakes. Consideration should be given to installing a
greater number of jacks than may normally be required to
lessen point loads on the structure.
e. Bracing – jacking systems must have bracing to avoid
slippage and toppling. High-lift jacking systems rely on
their base plate size and mast contact area against the
building to provide bracing. It is crucial that the mast is in
contact with the wall of the building to provide bracing.
What hazards could be encountered when lifting
earthquake-affected buildings?
Ground instability
The Christchurch earthquakes have caused varying degrees of
ground uplift, slumping and liquefaction. A geotechnical engineer’s
advice should be sought prior to work commencing on unstable
ground. Operators need to make site specific assessments of
ground conditions to ensure that buildings can be jacked and
temporarily supported safely without their supports sinking.
Where necessary, additional dunnage should be placed under jacks
or supports to ensure safe bearing.
Structure instability
Buildings to be lifted for foundation replacement will have
suffered varying degrees of structural movement during the
earthquakes. Operators need to carry out a thorough visual
inspection of each structure to assess what additional bracing,
propping, and repairs may be required before lifting.
The earthquakes may have caused significant damage to the
foundations of a building, and in some instances the building
may not be entirely supported by the foundations. There is
an increased risk to workers while they are disconnecting the
building from the foundations, particularly with the likelihood of
aftershocks. Therefore, jacks and/or temporary supports should
be installed to stabilise the building before it is disconnected
from the foundations.
Building collapse from aftershock
Aftershocks are a significant hazard for all buildings that are
being lifted, or have been lifted for foundation remediation.
This hazard must be controlled through the use of safe working
practices to ensure the safety of the building and the people
working under or in close proximity to it.
Reinforcing the basics of good jacking procedure is essential:
a. Ground Bearing – jacks must be placed on suitable bearing
ground. Additional dunnage should be placed under jacks to
ensure safe bearing.
f. Levelling – jacks must be installed on level bases to ensure
the jack remains level and plumb throughout the lifting and
lowering procedures. Placing the jack on a level base and
plumbing it against the wall of a building will mitigate the
risk of slippage or lateral movement.
g. Lifting – a competent person with sufficient training
and/ or experience must supervise a jacking operation.
Personnel should not be under the building while it is being
lifted. Once a building is lifted, it is best practice to install
temporary supports under the perimeter walls of the
building before packing off the middle.
Contaminated silt and soil
The earthquakes have caused widespread deposits of liquefied
silts which may be contaminated with sewage and storm water
from ruptured pipelines. Contaminated soils can be a breeding
ground for bacteria, viruses, and parasites. Personnel working
under buildings can be at risk of infection and should be provided
with protective clothing and equipment to minimise this hazard.
Good personal hygiene standards are important when conducting
work with contaminated silt and soil. Workers should clean their
hands with soap and water, and dry their hands prior to eating or
smoking, and when leaving the worksite. Smoking while working is
not recommended, as this is a common source of infection.
Further information on how to manage this hazard can be
obtained from the Department of Labour factsheet – Advice for
working with sewage contaminated silt and soil.
Demolition
Some buildings being lifted for foundation replacement or
removal will have attached structures requiring demolition.
These structures may have sustained damage in the earthquakes
and demolition by hand may not be able to be performed safely.
Demolition by excavator may be a
safer option.
www.dol.govt.nz
0800 20 90 20
FACTSHEET
Other hazards
The Department of Labour factsheet Working in earthquakeaffected buildings identifies a number of hazards specific to
Christchurch and provides useful information on how to control
them.
Methods to support and stabilise lifted buildings
There are a number of methods that house movers use to
support buildings once they have been lifted. The method they
use depends on a range of factors including: size of building,
topography of site, exposure to wind, and complexity of the new
foundations.
Note: lifting and stabilising work conducted on TC21 and TC32
land should be informed by geological advice. Contact the
engineer responsible for the foundation repair/rebuild proposals
to see if there are any particular concerns that need to be
accounted for.
For this reason, the industry believes it is essential in terms
of safety to provide a supplementary bracing system for all
lifted buildings that are being worked under for foundation
replacement, or have the potential to injure should they fall off
their supports in an aftershock.
The following systems – reviewed by consulting engineers – are
satisfactory for reducing the amount of lateral movement in an
aftershock.
Buried concrete block method
This system involves burying a number of 1000kg concrete blocks
around the perimeter of a lifted building and fixing them to the
building using acrow-props.
Screw pile method
This system involves winding in a number of double-helix screw
piles around the perimeter of a lifted building and securing them
to the building using chains and shackles.
Details of each method and industry recommendations on
how they should be used to minimise the risk to a building in an
aftershock are as follows:
For full technical information and engineering calculations for
each method, please contact the New Zealand Heavy Haulage
Association.
Timber cribbing or stys
Note: lifting and stabilising work should be co-ordinated with the
foundation repair work so that houses are not left on temporary
supports for any longer than is necessary (bearing in mind
resource and labour constraints).
Timber stys are typically made from stacked layers of 150mm
x 125mm x 900mm pinus radiata timber. Timber house piles
may be used, but a minimum length of 900mm is recommended.
A number of stacks or stys will be used to support each
building, and it is best practice to install them underneath the
external and internal load-bearing walls of a building. If this
is not possible, steel cross beams should be placed on top
of the stys to transfer the load off the floor. Typically stys
will be constructed level and true with two blocks of timber
per course. Due to the risk of aftershocks in Christchurch,
it is recommended that the number of blocks per course be
increased to three or four as is normal practice for buildings of
heavy construction.
Tripod pipe stands
Tripod stands are manufactured from welded steel pipe with a
one metre-square base and height adjustable. They have a safe
working load of three tonnes and can be clamp-fixed to the
bearers of a building. It is recommended that they are placed on
level timber dunnage so they do not sink in
soft soils.
References
Revised Guidance on Repairing and Rebuilding Houses Affected
by the Canterbury Earthquake Sequence – Department of
Building and Housing (now the Ministry of Business, Innovation
and Employment – Building and Housing Group)
Best Practice Guide to Building Relocation in New Zealand:
available from the New Zealand Heavy Haulage Association
(www.hha.org.nz)
Working in earthquake-affected buildings – Department of
Labour
Advice for working with sewage-contaminated silt and soil –
Department of Labour
Acknowledgements
The New Zealand Heavy Haulage Association wishes to thank
the following member companies for their contribution to this
document:
Jacks
Laing Properties Ltd
High-lift jacks are the most common means of support used by
house movers when re-piling buildings or placing new foundations
for relocated buildings. They provide stable support, even in
strong wind conditions. However it is best practice to provide
additional support using either timber stys or tripod stands
when personnel are working with machinery under a building or
on exposed sites. Additional supports are now recommended
when working
in Christchurch.
King House Removals Ltd
Supplementary methods to brace lifted buildings
The violent horizontal and vertical shaking experienced in a
significant earthquake or aftershock has the potential to
dislodge lifted buildings off their temporary supports.
Perriam Enterprises Ltd
Coffey House Removals (2007) Ltd
NZ Building Removals Ltd
Smith Crane & Construction Ltd
AV Martyn & Co (1968) Ltd
Fulton Hogan Heavy Haulage Ltd
Patterson Contracting Otago Ltd
Transit Homes Ltd
Special acknowledgement must be made to Carl Baker of
Hastings House Removals Ltd for compiling this document.
1. Technical Category Two land – minor to moderate land damage from liquefaction is possible in future large earthquakes.
2. Technical Category Three land – moderate to significant land damage from liquefaction is possible in future large earthquakes.
The Department of Labour takes no responsibility
for the results of any actions taken on the basis of
this information, or for any errors or omissions.
www.dol.govt.nz
0800 20 90 20