Building on sand (Fern Bay)

[gg1965]

Hi all,

Not that i would buy anyway, but there is an area just north of Newcastle called Fern Bay which has new house and land packages. They look good and are typical of new house and land packages but are well priced (when compared to the Canberra market).

But one thing that puzzles me is that they are built on sand. looking at the gardens and green spaces in this area, the land is all sand - white and fine sand.

Now i know they build on sand in areas in Dubai but they put in massive foundations but these places in fern bay are on concrete slabs and no obvious signs of any deep setting foundations that i have seen in Dubai. Plus they have cleared a lot of the vegeation in this area away and have planted lawns which may not really hold the sand in place over time.

Am i wrong in questioning this? Has building and slab concreting technology reached a stage where they can safely build on sand blocks now?

As i said, i am not interested in buying into this area as it isn't the type of thing i am normally interested - ie it isn't an old house in the inner suburbs or a federation style home in regional nsw, but i am just curious anyway.

FWIW there does not seem to be any new schools or shops or services planned for this area - just new homes on sand. maybe i'm wrong?


thanks



g

 

[nww]

I think you will find the area is similar to the Tomaree peninsula (Nelsons bay)
Walk around the bay and you will will find new develpment sites that have
exposed dark gray looking sand. They have been building homes up there
for probably 100 years if not more without much drama.
But you could take a leaf out of a book I know "build your house upon a rock not upon the sand"

 

[gg1965]

I know of many houses that have been built on sand with poles and then the floor is raised up over and above the sand. however these homes in fern bay are on concrete slabs which sit directly on the sand - to me, this is is very different.

i am guessing that concrete slab technology must've have got better to allow this (and to prevent the slab from shifting), but i don't really know. can anyone confirm?

 

[battler]

i am guessing that concrete slab technology must've have got better to allow this (and to prevent the slab from shifting), but i don't really know. can anyone confirm?

I'm not exactly sure, but I think they use a raft or floating slab to allow it to move a bit.

 

[vbplease]

I'm not exactly sure, but I think they use a raft or floating slab to allow it to move a bit.

That's correct. There's actually no problem building a raft slab on dry loose sand. At least you know its all homogeneous i.e. won't shrink or swell with changes of moisture content.

The old saying "never build you house on sand" refers to tidal areas.. foundations will erode away.

The reason they use pile foundations in Dubai is because the load from high rise buildings - self weight, live loads, and overturning loads from wind/earthquake require foundations say 2MPa or 2000kPa. But for a residential slab 75-100kPa is fine and sand can achieve this.

 

[Zeddy]

vbplease is generally correct, but I would beg to differ on:

There's actually no problem building a raft slab on dry loose sand.

Building on sand soils is ok provided that the foundation is still effectively compacted. Whilst it's true that the footing will not be subject to reactive soil movements, bearing capacity is still very much an issue.

Also be aware of any larger developments going on around you, especially large buildings requiring piled footings. If these piles are driven in a dynamic fashion (bashing them in instead of boring), the vibrations can cause settlement and distress to adjacent buildings.

gg bottom line is provided your foundation is well compacted and your raft footing properly designed, there shouldn't be any issues. If however that building is simply a slab on ground, then you may have movement problems.

 

[Aaron Sice]

are you for freakin' real?

sand is more stable than clay can dream of! hell - even sand on shale rock is better than clay.

here in WA about 80% of all new development is sand down to at least 2.0m - those that are on clay or mud end up being backfilled with - wait for it - SAND!

in fact - clay in the metro area is near-on unheard of except for near the river and low lying foothills basins like Armadale.

you guys over east crack me up!!

 

[Ajax]

Had a builder tell me sand is great to build on. I always thought rock was better. The gross sum of my knowledge being based on a song I used to sing at Sunday school too long ago...which was in turn based on the following biblical text (Matthew 7:24):-

"Build on the Rock
24 "Therefore whoever hears these sayings of Mine, and does them, I will liken him to a wise man who built his house on the rock: 25and the rain descended, the floods came, and the winds blew and beat on that house; and it did not fall, for it was founded on the rock.
26"But everyone who hears these sayings of Mine, and does not do them, will be like a foolish man who built his house on the sand: 27and the rain descended, the floods came, and the winds blew and beat on that house; and it fell. And great was its fall."
28And so it was, when Jesus had ended these sayings, that the people were astonished at His teaching, 29for He taught them as one having authority, and not as the scribes.

 

[vbplease]

Zeddy, for a location like Fern Bay - I'm guessing it's pure sand? Pure sand I wouldn't have thought is able to be compacted.. Similarly dynamic loads aren't transmitted laterally..

 

[Aaron Sice]

this thread is hilarious.

 

[yadreamin]

I dont think l have ever come up with a shovel full of anything else but sand here in the wild west.
The only time l have heard builders/tradies go off is when they have hit rock or limestone here..
Sand sand glorious sand
cheers yadreamin

 

[Ajax]

Bluecard,

Maybe the ignorance of some of us over East is that many of us are buying established houses and don't get to build new ones. Also that Sydney basin has a lot of sandstone...not so much sand (except for a few bayside or beachside suburbs).

 

[gg1965]

I dont think l have ever come up with a shovel full of anything else but sand here in the wild west.

Sand sand glorious sand
cheers yadreamin

I guess that's why we call you westies Sandgropers

I don't know know what it is with sand but it scares me. Years of building sand castles and watching how "brittle" it can be is worrying. Especially with regular winds and heavy rains.

Reading about the raft style slabs is interesting. So i guess if your block moves, then you just "ride out the movement of it". (I have images of these houses in Fern Bay all moving and collliding with each other).


Thanks

g

 

[The Fence]

So long as the sand can't be eroded away, it's the best to build on....like BC said....have a look at WA...

 

[Aaron Sice]

why would you build on clay?

its agroscopic, it shifts and swells and moves and slides all over the place

i understand the whole east cost is pretty much clay but i wouldn't touch the stuff.

sand can be compacted infinitely better and more precisely than clay.

compact foundations = good foundations.

 

[quoll]

why would you build on clay?

its agroscopic, it shifts and swells and moves and slides all over the place

i understand the whole east cost is pretty much clay but i wouldn't touch the stuff.

sand can be compacted infinitely better and more precisely than clay.

compact foundations = good foundations.

Poor old Adelaide (greater), most of it's sitting on clay, lots of cracking and movement.

Some of the coastal suburbs are on sand, nice and easy, truck in a bit of dirt of the garden.

The only concern you might (very small chance) have is proximity to the ocean, if a king tide / storm is going to cause erosion? So make sure your place is behind 1 or 2 others, they you should be fine. Your building would get more damage from salt than from erosion anyway.

Cheers
Graeme

 

[AJG]

Have had to dig footings in sand with a pick axe more than once because it had been so heavily compacted. Sand is good

 

[craigb]

YES! BC knows his stuff! sand is a good place to have a home, it compacts fairly well and is no reactive, BUT! house construction on sand deffers in the slab construction, piers are placed via tubes, to about 1 meter (depending on the engineers specs) and incorperated starter bars through to the slab , Think of it like floating a gazzilion tone ship on the water, this is how property on sand is ment to work , and i suppose it does???

 

[jimbo_jones]

I agree with the BlueCard and Craig. I have designed and documented several buildings on sandy sites and it is certainly fine to construct on.

A rather large nursing home has just been completed a little north-east of Fern Bay, and is on a sandy site. The floor slabs (we used a waffle pod system in this instance) were piered to depths of 1-3m. Not particularly difficult or costly.

JJ

 

[battler]

A rather large nursing home has just been completed a little north-east of Fern Bay, and is on a sandy site. The floor slabs (we used a waffle pod system in this instance) were piered to depths of 1-3m. Not particularly difficult or costly.JJ

Why did you have to pier to this depth?