The article discussed that the lack of rainfall around Australia generally is causing the soil under and around many houses to dry and shrink, leading to cracking of the houses. The article is mostly informative and correct, but it doesn’t actually give you much information on when you should start to worry.
Any cracking is a concern, but the rapidity with which it appears and develops is a larger cause for worry. Some cracking is slight and only shows minor seasonal change (getting wider over summer and then closing up over winter). It tends to remain generally constant over the years. Other cracking however may be rapid and severe, going from no cracking to cracks 10mm and wider in the order of 3 months. This may indicate a severe and worsening problem with the underfloor plumbing, or another cause. This type of rapid appearance of cracking should be investigated urgently.
With any cracking, investigation to find the cause and remedial works undertaken in a timely manner are likely to result in a cheaper overall cost, rather than putting the problem off by ignoring the issue for several years.
It’s cheaper to fix a smaller problem…
It is always cheaper to resolve a smaller problem earlier rather than wait until the problem is larger, requiring more extensive and expensive works to remediate it.
Hence,
if cracking:
has suddenly appeared
is worsening slowly over time
is causing you to worry or stress
Magryn strongly recommends that you seek professional advice from a suitably qualified and experienced engineer.
We are here to help. Just give us a call on 8295 8677, or email admin@magryn.com.au.
Retaining wall engineering involves the assessment and design to create a wall to retain a height of material. In some situations, an engineering design is legally required to satisfy local council requirements.
Retaining walls come in all sizes from 0.2m to 10m high and many different styles. There are moss rock walls, steel post/concrete sleeper walls, stacked block walls, steel-reinforced concrete-filled block walls and many more.
And of course, retaining walls come with many different prices. They are generally expensive, and the longer and taller they are, the more costly the total price.
Image courtesy Outback Sleepers
But what type of retaining wall is best for you?
What are the main types of retaining walls?
Post and Sleeper Retaining Wall
The most common type of wall used in residential cases is the post and sleeper wall. This can either be:
Timber post and sleeper, with the posts set in a concrete fill bored pier. These are not recommended as the timber rots or is eaten by termites, reducing the lifespan of the wall. If you get 15 years out of a wall like this, you are doing well.
A steel post/concrete sleeper wall with the posts set in concrete-filled bored piers. These walls should last at least 40 to 50 years and are a similar price to the timber version above.
These
walls can have metal sheet fences installed over.
The timber sleepers come in many different colours and textures and don’t have to be concrete grey and flat.
These
tend to be the cheapest type of retaining wall and are very versatile.
As the wall is supported by a concrete pier in the ground, these walls may not be suitable for sites with shallow rock, as the cost of boring into rock is high. If rock is suspected or known to be shallow in the area, it is best to take some soil logs to determine upfront if this type of wall is the best option or not.
This
type of wall is suitable for wall heights of 200mm to 5m. Obviously, the
greater the level change, the greater the cost of the wall.
This type of wall is suited to placing a retaining wall across an easement, where it may be necessary to excavate and replace a pipe sometime in the future. In this case, the sleepers in one bay can be removed, giving easier access to the pipe under that area. The general requirements are for the in-ground concrete piers to be at least 1m away from the pipe.
Moss Rock Retaining Wall
This
type of wall is basically a battered earth slope with large rocks stacked over
it, in an engineered layout.
This type of wall does not extend far below ground level and hence is suitable for sites with shallow rock, but it has a very wide footprint due to the batter slope and the size of the rocks. This width is typically as wide as the wall is high, or wider.
These walls have a very natural look compared to other types of retaining walls.
Steel reinforced, concrete fill block walls
These retaining walls are made from concrete besser block (or similar) and contain steel reinforcement. Cavities in the blocks are concrete filled. They are narrow (about 200mm wide generally) and can be several metres high.
They
must be founded on either:
a concrete strip beam with reinforced concrete piers under,
a concrete slab footing.
The
concrete slab footing makes these walls suitable for sites with shallow rock.
However, the concrete slab will extend out some distance in front of the wall.
If the wall is to be installed on a site which is to be filled, the slab footing can extend back under the fill, which makes the wall more efficient and the slab footing narrower.
As
the walls are blockwork, they are often finished by render and/or paint to
improve their appearance.
These
walls tend to be more expensive than post and sleeper walls, as they require
several trades:
an excavator
a concreter for the slab footing
a bricklayer for the blockwork
Stacked Block Walls
These
are walls constructed of special proprietary engineered blocks, such as
keystone or AB blocks.
They
are suitable for lower height garden walls (up to 1m, depending on the type of
block) and they are:
founded on a rubble base
consist of stacked blocks, which may be unfilled, filled with screenings or concrete
may be hand-
assembled by owners.
Walls higher than 800mm (depending on the block type) may be engineered by including geotechnical tie backs to tie the wall to the soil mass behind.
Engineering Requirements for Walls
All
the different types of retaining walls discussed above require structural
engineering design to ensure they are suitable for their intended application.
An
engineer should be engaged to design your wall for your particular situation.
We would be happy to assist with your selection of retaining wall type and the design of it to ensure your wall is cost-efficient and long-lasting.
Underpinning
is the process of lifting or supporting the footing of a building or structure,
so as to provide a more stable foundation.
Underpinning
is commonly used to stabilise houses when they experience severe cracking.
There
are several different types and methods of underpinning. Two of the most common
are:
Traditional concrete underpinning, which involves piering or excavating under a footing to install a concrete support for the footing.
Chemical underpinning, using an expanding urethane foam or similar to create piers in the soil under a footing, to provide lift to it.
These
methods are quite different and are best used in different situations, the
choice dependent on the cause of the cracking.
Traditional concrete underpins
Traditional concrete underpins used to be dug by hand and were typically 1m cubes of concrete placed under a footing beam. The footing beam could then be jacked up, using the concrete underpin as a stable base.
However,
the cracking in some houses is related to seasonal moisture variation in the
soil which can extend down to over 3m in depth. This seasonal moisture
variation is the drying/shrinkage of the clay soils over summer and the
wetting/expanding of the clay soils over winter. Hence, due to the depth of
soil moisture variation, the 1m cube concrete block also experiences some lift
and settlement over the seasons. Hence, a 1m cube underpin may not be a stable
foundation.
It is better practice to install a concrete underpin as a concrete-filled bored pier to a depth of at least 4m, founding the pier in soils which are stable over the seasons. Please note that this depth may vary due to other considerations, such as the permanent water table depth, soil conditions or shallow rock, proximity of trees, etc.
The footing under the building may then be jacked off the underpin if jacking is viable.
The
location of underpins will affect the decision to use traditional concrete
underpins or another method, as it is preferable to use a machine such as a
small excavator to auger or dig the underpin. It may not always be possible or
practical to position an excavator where required to dig the underpin – you
don’t want an excavator in your hallway!
Jacking over underpins
Underpins are often installed as a stable base so that the footings of the building can be jacked up and re-levelled. This can only be done using traditional concrete underpins.
However,
there are many limitations to this jacking, which include:
The
concrete strength of the footing. If this is too soft, the footing concrete may
crush rather than lift.
If
the footing is bluestone rather than concrete, it may not be recommended to
jack as it is not structurally continuous, or strong
The
footing may crack if lifted too far, which in turn may cause additional
cracking to the building over
Soil
suction on the footing may prevent lift.
Chemical Underpinning
Chemical underpinning is undertaken by injecting an expanding urethane foam (or similar) into the soil at selected locations under the footing. This creates a pier of foam in the soil to lift and support the footing over. This type of underpinning incorporates jacking.
Chemical underpinning has some advantages and some disadvantages when compared to traditional concrete underpins. These are discussed below.
The advantages of Chemical Under-pinning are:
It can be done relatively quickly – only one day is required for a normal house, whereas a week may be required using traditional concrete underpins.
The method provides a large degree of control over the lift undertaken to the footing.
The injection can be undertaken at numerous points close together.
The injection can be undertaken under internal walls more easily than the installation of traditional concrete underpins.
The disadvantages of chemical underpinning are:
The chemical is injected using a wand or tube inserted into the soil under the footing. This limits the founding depth of the pier and the resultant pier is likely to be founded in soil which may show seasonal lift and settlement. This is undesirable (see above).
The system requires the use of a very high-pressure pump.
Which underpinning method to choose? Chemical or Traditional?
The
decision whether to use traditional concrete underpins or chemical underpins
should depend on the reason for the movement and cracking occurring, and
location of the cracking.
If
the movement is due to seasonal wetting and drying of soils around the exterior
of a house, traditional concrete underpins are better as they are founded at a
deeper depth.
If the movement is in the centre of a house and is not related to seasonal wetting and drying of the soils, chemical underpins may be a better option.
Magryn recommends both types of underpinning, with the choice depending on the details and requirements of the individual project.
We recommend that you engage a structural engineer to review any project which may require underpinning, to ensure that:
You receive an unbiased and professional opinion on the need for underpinning.
You receive a report documenting the scope of underpinning you require. You can then take this scope to several underpinners to obtain easily comparable quotes. The report should detail the number and location of underpins required, as well as the details of these underpins (depth, size, reinforcement, etc).
Magryn would be pleased to assist you by providing an underpin report and design for your house. We can even recommend quality, reliable contractors to undertake the work. Our preferred underpinner is Complete Underpinning (contact Grant on 0423 305 078)
Give us a call on 8295 8677 and discuss your problem and requirements with us.
Underpinning Costs
The
relative cost of chemical underpinning vs traditional concrete underpins is
variable and depends on many factors, but the order of magnitude of both
options is similar. The exact relative costs are best explored with individual
contractors.
Boring for an underpinning
Jacks positioned for underpinning lift
Magryn
recommends both types of underpinning, with the choice depending on the details
and requirements of the individual project. We recommend that you engage a
structural engineer to review any project which may require underpinning, to
ensure that:
You
receive an unbiased and professional opinion on the need for underpinning.
You
receive a report documenting the scope of underpinning you require. You can
then take this scope to several underpinners to obtain easily comparable
quotes. The report should detail the number and location of underpins required,
as well as the details of these underpins (depth, size, reinforcement, etc).
Magryn would be pleased to assist you by providing an underpin report and design for your house. We can even recommend quality, reliable contractors to undertake the work.
Give us a call on 8295 8677 and discuss your problem and requirements with us.
Houses
are a rigid structure, built on top of a footing, which in turn rests on the
soil under the house.
When
the soil moves, the footing over can bend and this causes the house structure
over to move and crack.
What causes soil to move?
Many things can cause the soil to move. For clay type soils this generally involves a change in moisture content. As clay soils dry, and shrink, or when they get wetter and swell. This change in moisture content can be due to many different reasons, including:
Seasonal
change – soils get wetter from winter rains and dryer in summer.
The
effects of trees drawing water from the soil.
Leaking
pipes under the house. This can include sewer pipes, stormwater pipes, and
water supply pipes.
Poor
stormwater management around the house, allowing roof stormwater to pool around
the house.
A
change in the water table level in the ground.
Some
clay soils are more “reactive” than others, meaning they shrink and swell more
for the same moisture content change.
Sand Soils
Sand
soils on the other hand, are not reactive, and don’t change volume with a
change in moisture content. However, sandy soils have other problems. Sandy
soils, particularly in Adelaide are along a coastal strip and are generally old
sand dunes. These dunes were placed by wind action and the sand is poorly
compacted. Hence when you build a house on top of them, they can compact and
settle, which may cause the house to crack.
What impacts the amount of cracking?
The
extent a house may crack will depend to some extent on three factors:
The soils under the house. Very reactive (or heavy) clay soils will move more with a change in moisture content, starting the cracking process.
The footings of the house are very important, as the stiffer the footings, the less movement and cracking of the house over. Generally, there are several different categories of footings, which work (or don’t work) to different degrees:
Bluestone footings on houses built before around 1910. These are just large rocks in the ground and are very flexible with very little structural integrity. These footings are very flexible.
Concrete strip footings, which are reinforced concrete beams, generally just under the walls of the house. These are in houses with timber floors. They are better than bluestone footings, but still very flexible in comparison to modern footings.
Modern footing systems (generally on houses built after around 1980). These can be concrete raft, waffle pod or grillage raft. These all incorporate a concrete slab with concrete beams built integral with the slab. They are quite stiff and perform the best.
The type of house construction over the footings. The more flexible the house structure, the better it will accommodate some slight movement without cracking. Typically, the following applies:
the most flexible type of house structure is timber-framed and clad, as in a weatherboard type of house.
a brick veneer house with internal timber framing and plasterboard lining, with a single external skin of brickwork is generally good, if the external brickwork has movement control joints (ie is articulated) to absorb some movement.
a full brick house which has double-leaf external brick walls and single leaf internal brick walls, and has brickwork movement control joints (internally and externally) is more rigid. This type of house construction with the movement control joints is rare.
the most rigid type of house construction is a full brick house with double-leaf external brick walls, and single leaf internal walls without any brickwork movement control joints included. This type of house construction was very common before the 1960’s.
The more rigid the house structure, the more it
will tend to crack.
That’s not a crack!
It
is better to have a house that has no cracks rather than a cracked house.
However, most houses (particularly in Adelaide) show some cracking.
Cracking
can be divided based on its severity:
slight cracking, which are cracks less than 1mm wide. These are generally not of a structural concern.
moderate cracking, which are 1 to 5mm wide.
severe cracking, showing cracks wider than 5mm. These may be a structural concern.
If
a crack is causing you concern, then it should be looked at and
reviewed by an experienced structural engineer.
Are cracks dangerous?
Generally,
cracks in houses are not dangerous, but there are exceptions in severe cases.
If cracks are extensive, this can loosen brickwork or individual bricks, which may fall.
If the cracking causes walls to lean, the walls may become unstable and fall.
If the movement in the house is excessive, this may loosen the ceiling panel, causing it to fall.
If the cracks are very wide (greater than 20 or 30mm) this indicates severe movement and instability in the house.
Of
course, the appearance of cracks in your house can reduce its potential sale
value, should you wish to sell it.
If
you are concerned, you should get your house reviewed by an experienced
structural engineer.
What will happen if I do nothing?
Most cracks have some seasonal influence, meaning that they change with the seasons. Generally, they get wider over winter and tend to close up over summer.
Hence
they open and close over the year, and tend to grow in width and length over
the years, getting worse.
If
you do nothing, they will tend to grow until they become a structural problem,
and ultimately compromise the structural integrity of the house.
So
the sooner you do something to control them the better.
The
exception to the above is cracks which appear suddenly and grow very quickly (eg
they appear and grow to 20mm wide over six months). These are often due to
another external cause and require urgent attention.
What can I do to repair a house that’s cracking?
There
are many things that you can do to repair a house that is showing movement and
cracking – some are expensive and some are not.
It
is important that any action you take is targeted towards what is causing the
cracking, so that you reduce the cracking and don’t waste your money.
It
is important to realise that it is unlikely that you will eliminate all future
cracking and your aim should be to reduce it to a maintenance level, where
regular patching and painting is all that is required.
Some
of the work that can be done to control cracking in a house can include:
collect and dispose of stormwater properly, so that it does not soak into the soil around your house
ensure that there is perimeter waterproof paving all-around your house
remove large trees that are too close to the house. This may require approval from council for significant or regulated trees, or co-operation from your neighbours
check sewer, stormwater and water supply pipes for leaks and repair as necessary
underpinning. This is often used as a last resort, as it is expensive and invasive. Also, underpinning will not prevent all future cracking and may cause cracking in some areas not currently showing cracking. Please refer to our (future) blog on underpinning methods and recommendations.
install articulation joints in brickwork and timber framed walls/ceilings, to provide movement locations
installation of reinforcement into brick and stone walls across existing cracks
general crack repair in walls.
We
recommend that you seek and receive professional advice in regards what is
required in your particular case in regards remedial work to reduce and limit
future cracking.
What can Magryn do to assist you?
We
have years of experience in building movement assessment and recommending
appropriate remedial works.
We
will get one of our experienced engineers to visit and inspect your house
internally and externally. We may also:
take
a level survey of the floor of the house to determine the extent of vertical
variation
take
a borelog of the soils on site to determine how reactive the clays are (how
much they shrink and swell with changing moisture content) and how dry they are
at depth
review
previous work undertaken on the house and the history of the cracking.
Cracking Report
We then write you an engineering report which notes:
What
the current extent of damage and cracking was at the time of the inspection.
Any
site factors which may be influencing the house and cracking.
A
discussion of what is causing the movement and cracking of your house.
A
list of recommended remedial work which should be undertaken. This may or may
not include underpinning – if it does, we will include an underpin plan and
design, which you can take to different underpinners to obtain quotes on the
work.
Our fees for the above are time-based, and dependent on how much time we spend on your job.
If you would like to book in for an engineer to attend and inspect your house, or just talk to us regarding your house, please give us a call on 8295 8677 or contact us here.
“Concrete Cancer” a generic term often used to describe cracking and spalling concrete in buildings. Concrete cancer indicates a severe problem which requires remediation.
Concrete in buildings is often concrete with steel bars inside it to act as reinforcement in the tension zones of the concrete.
The “cancer” term is often used as this is a problem which once it starts, tends to grow and spread until eventually, it will affect the structural integrity of the building. This type of deterioration is a problem best attended to in the early stages when it has not spread. Addressing this issue as soon as possible is likely to minimize the extent of damage, which in turn reduces the remediation costs.
The problem occurs in steel-reinforced concrete elements, such as balconies, edges of floor slabs and concrete wall panels.
What causes concrete cancer?
Over time moisture and salts permeate into and move through the concrete. This moisture will eventually encounter the steel reinforcement bars, causing the steel to rust. As the steel bars rust, they expand causing the concrete around them to crack and spall.
This cracking, along with the associated rust staining on the concrete, are the typical telltale signs of concrete cancer.
As the concrete cracks, it then allows easier water penetration to the steel bars, accelerating the process.
There are several important factors which will determine how quickly concrete cancer is likely to occur. These are:
the proximity of the building to the sea or an industrial area. Airborne salts will cause a problem much faster.
is the concrete sealed or painted, thus reducing moisture and salt penetration?
is it good quality concrete (ie strong and impervious) or is it poor quality concrete which allows more moisture and salt intrusion?
how much concrete is there around the steel bars? The greater the concrete cover, the longer it will take for the salts to get to the steel and hence the longer to start rusting.
how old is the building? The older the building, the more time the moisture and salts have had to penetrate the concrete.
How important is it to treat concrete cancer?
The steel reinforcement bars in the concrete act as tension tie rods and are vital for the performance of the concrete element.
If concrete cancer occurs, it will:
reduce the cross-section of steel reinforcing bar able to act as a tension tie
spall concrete off the outside of the element, breaking it apart.
Hence, the concrete element becomes more and more ineffective and unable to do its job.
It should be noted that concrete cancer deterioration in one part of a concrete element may render the entire member ineffective.
When should concrete cancer be treated?
It is important to treat the concrete cancer as early as possible. Leaving it untreated may lead to the spreading of the rusting along the steel bars, or extensive loss of cross-section of the steel bar, which affects its ability to perform.
If the rusting of the reinforcement is allowed to spread along the reinforcement bars it means that a much greater area needs to be treated, rather than a small area. This increases the cost of the remedial work.
If the rusting of the steel reinforcement is allowed to continue unabated, the cross-sectional area of the bar may reduce or the bar may break. This then means that the remedial work will need to include replacement of the steel reinforcing bar, at a much higher cost than treating the bar when only slightly rusted.
We have had several cases where steel-reinforced concrete balconies have had to be cut off the building and completely rebuilt, as the concrete cancer was so severe that they could not be saved. Don’t leave your concrete cancer untreated until it is too late!
What can be done to treat concrete cancer?
We can specify many ways to treat and remediate the concrete cancer.
In the early stages, treatment can be as simple as cleaning and painting with specialised products. However this may still be expensive, depending on the extent of damage and ease of access to the affected areas.
In later stages of concrete cancer, the repair work is much more involved and may include replacement of steel reinforcement and extensive patching.
Other remedial work may be specified, depending on site conditions, such as the installation of galvanic anodes to slow future corrosion.
The above advice is generic only and cannot be taken as site-specific for a particular case.
Each case needs to be assessed and reported on individually by an experienced structural engineer, who will specify particular remedial work for that building and site.
For more information on Concrete Cancer Treatment please contact Magryn.
The historical timber main wharf at Pt Augusta was built in 1870 and has seen irregular and adhoc maintenance over the years.
In 2018, Magryn undertook a comprehensive assessment of the whole of the wharf, including timber decking, wharf substructure and timber support piles, both above and below water level.
This assessment showed that the wharf is in poor condition and urgently in need of maintenance and structural repair. A plan was formulated by Magryn to allow this project to be tackled over several years, with the most urgent areas of concern address first.
If these works are carried out it is anticipated that the historical wharf can be retained and used for recreational purposes of the community into the future.
Magryn celebrated 25 years in business this year, growing slowly but steadily over that time to a current staff of 14.
Celebrations were recently held at Jolly’s Boathouse on the Torrens River, with staff and partners, clients, past staff members, service providers and friends enjoying a cocktail party.
The food, wine and night was enjoyed by all.
Terry Magryn
Ian Willsmore and Andrew Pawlowski
Kirsty and Peter Vial, and Robyn Magryn
Nick & Jess Pedler, Felicity Huggins & Chris Magryn
When it comes to Civil Engineering Companies Adelaide, Magryn & Associates are world class!
Actively consulting in Civil, Structural and Mining Engineering and specialists in Coastal and Marine work.
Magryn and Associates is a medium sized engineering consultancy firm. With a focus on exceptional engineering designs, all carried out in accordance with good practice and the relevant Australian Standards, we have experienced year-on-year, consistent and sustainable growth.
Hardstand area designs like Roadways, Pavement and Elevated Boardwalks.
Stormwater Design
There are many types of designs for stormwater systems and these vary depending on what you are trying to achieve.
Some of our storm water management designs have included:
Water collection and disposal
Water retention tanks for reuse onsite
Detention tanks for ponds and other slow release areas
V-notch flow measurement weirs for rivers and streams
Pipe systems, pump systems and
reatment systems for removal of pollutants.
Hardstand Area Designs
This is about roadway and pavement systems that include factors like type of traffic load, including minimal, high and general roads or highway conditions. Other factors have to be considered too, like stormwater runoff control, the surfaces used and ground conditions on which it is to be constructed, ie poor ground or fill areas.
Designs we have undertaken have included reinforced concrete, rubble, concrete block pavers, asphalt and two coat bitumen spray seal.
Retaining Walls
With height capabilities of up to nine metres, each retaining site has to be engineered according to its particular conditions and needs.
We take into account things like the presence of groundwater, underlying shallow rock, fill or other challenges. We have a number of engineering design options available like:
steel posts
concrete sleepers
crib walls
ground anchors for stabilisation
masonry walls
reinforced concrete and
reinforced masonry walls.
Elevated Boardwalks
Elevated boardwalks are precast concrete pieces that are used for trails, greenways (wetlands), observation piers and pedestrian bridge projects.
Unlike their wooden counterparts, concrete boardwalks require minimal if any maintenance. Using either steel reinforced concrete or glass fibre reinforced plastic (GFRP) reinforced concrete, elevated boardwalks are suitable for either pedestrian or vehicular traffic.
The GFRP sections are lighter due to a reduced concrete cover and do not rust.
Problem Solving
Problems can occur with old and new buildings. These are
often challenging, unusual and sometimes unique. These can happen in just about
any way, shape and form, but are normally found in the following areas…
Flooding, through the roof and/or at ground
level
Dampness in other forms and problems
Ageing balconies, weathered or rotted
Balustrades that have weakened
Broken or deflected roof structures
Structural designs to match or compliment the
architectural style or details
We have extensive engineering knowledge and practical experience and tackle each problem individually. Magryn Engineering will investigate and discover the cause, then engineer a robust and enduring solution tailored to the specific problem.
If the customer requires it, we can also engage the required contractors and oversee their work, thereby ensuring the problem is completely resolved.
Magryn and Associates
Our staff of thirteen are comprised of eight qualified engineers who are supported by technical officers, drafters and administrative officers.
We are small, which allows us to deliver personalised service and yet, able to tackle complex engineering projects both at home and abroad.
