Step 4 - Making the foundations - Laying the steel for the foundations

Phew our soil passed our plate load tests with flying colours.... onto stage 4.



Once the soil has been compacted and the tests have been done, we cover the bare soil with a thin layer of concrete to stop it getting wet and soggy as this would weaken the soils ability to take the pressure of the building.







The foundation is made up of around  1440 tons of steel reinforcing bar (Rebar) which is twisted and shaped into boxes. (using our earlier elephant analogy that 288 big ones..)

The rebar has different names depending on its diameter. For this foundation we use 7 types of rebar

R6 - 6mm round Bar - mild Steel
T10, 13, 16, 20, 25, 32 - which is t for torsional and the diameter of the bar in MM.

You can see the steel rebar being laid out to form a grid, and if you look closely you can see were we put more rebar at the column positions, to prevent the columns "punching" through the foundation (the punching shear). The punching shear of these these columns positions is around 600 tons of pressure...most of our columns will be around 1m x 1m in diameter.

Laying the first layer of rebar, its a very unpleasant job under the sun all day!

The final project - A complete mesh (not mess) of steel, like a box, ready to have concrete poured into it...

Step 3 - Making the foundations - Testing the soil

well we finished Step 1 and step 2 and now we need to tackle

Step 3.......

Once we have excavated the soil down to the right level, it is time to do some more tests which will help us confirm the design of our raft foundation.

The test we do here is called a plate load test...

For this test we put a plate under load..... (you see its not that hard, is it?)

We choose around 10 areas around the site and then construct a series of pads, we place plates on the ground and then slowly in a series of cycles place the plates under increasing pressure using an hydraulic jack. We test these plates up to a pressure of 800 Kpa  (kilopascal) ... 80 tons to the ordinary man on the street.

This is 3 times the ultimate planned weight of the building on the ground





The plate itself is only 30cm x 30 cm  and this weight is the equivalent of around 16 full grown african elephants balancing on this single point...

I have heard a rumour that in the olden days, before the hydralic jack this service was an important source of revenue for circuses with elephants.

 Almost there,  80 tons of pressure.

For the test to pass we allow only a deflection of a maximum of 2.5 cm into the soil! If the soil fails the test, this area of the site will need to have this soil removed and a better quality of bearing material added in its place.








More detailed information on this process can be found here!

Step 2 - Excavation - Preparing the foundations

Preparing the foundations...Digging a hole....

In the last step we decided to build a raft foundation, a big "raft" of concrete that is going to support the building, the first step to this is to dig out the existing soil...

Part of this building is an extension of the current basement carpark which is semi - underground (at the very front it is a ground level).

The site excavation size is about 67m x 81m with the depth ranges from 2.55m to 5.95m ( at the tent plaza end)

 This means we need to excavate about 16500 m3 of earth to get down to the start of the level of the foundations.

Each big earth moving truck that you see in Singapore can carry between 6 - 9 m3 of earth, depending on how well the earth is compacted when it is dropped in by the excavator.

So this means we need to remove around 2532 individual truck loads of soil from the site.......

Our soil goes to an earth dumping ground at Marina South and might be used for reclaiming more land around Singapore..More information on earth dumping in Singapore




Once the soil is removed and we have got to the final level that will form the foundations, we then compact the ground with 10,000 Kg vibrating roller. You can feel everything shake when this is working...

Step 1 - Making the foundations - Designing foundations.

Foundations, actually one of the most important parts of the building, for I hope obvious reasons..

There are many choices on which foundation system to use in a building like this and in many cases it can be a difficult decision to make...

To make it a little easier we approach it scientifically and to start this process off The first thing we need to do is assess the quality of the soil that is going to be under the building as this will be taking some of the load of the building.



When you see one of these appear in your neighbourhood, it might just be time to leave for a few months :) It means someone is collecting information for an imminent building project!

The pipes on the floor are for the soil samples which collect in the middle of the pipes as they are driven into the earth.

In our case we took around 10 drill holes all over the site and take core samples of the soil. We drill down around 30 metres from the existing level

Our engineer studies these stratas - If you are wondering the use of these physical geography lessons, here it is...

These are copies of some of our soil reports and you can see what the composition of the soil is underneath the building. Unfortunately no gold, diamonds or oil...

The soil is very different all over the island.

There are many idioms out there related to the building of things on sand, you can see from these reports, that in the real world of building you can quite build a house on sand and be perfectly happy that it will be there for a very, very long time..

From analysis of these soil reports we decided to construct the foundations as a "raft". This is as it sounds, it is a big raft of concrete on which the building rests. This has a number of advantages, but one of the reasons for choosing this system was to minimise the disruption on the workings of the school and our residential neighbour...

A more detailed explanation of these different foundation systems can be found here or if you are short of time take a look at this condensed version......



Go to the next step - Preparing the foundations

Does it look like a building site yet?

Our interactions with the kindergarten left us battling against a number of clear expectations from these little but very astute ones. Quite clearly from their perspective a building site in Singapore is not really a building site without a suitably large crane being visible. Bowing to this pressure we have now got on and installed one on the site.

I hope we have gone up just slightly in the eyes of some our most important customers. 

This crane is a called a "Luffing crane" which is different from many of the cranes that you see in Singapore that have a fixed horizontal beam with the hook moving up and down this beam. The main problem with that traditional type of crane is that it would oversail occupied areas of the school. For pretty obvious safety reasons this is unacceptable to us. 

However the choice of crane does influence various elements of construction and planning, when we are lifting loads at the full extension of the crane, we will be  down to a very low capacity, perhaps just a few tonnes (around 2 and a half cars!) . The heavier loads will  have to be lifted close to the tower or broken into smaller pieces. This is influencing the design of the steel for the roof structures for the theater and the exam hall which will now need to be designed into "bite sized chunks" and then welded together once they have been craned onto the roof...

Assembled like a very large lego set..

The finished product at some 40 metres above the ground and positioned in the middle of our new building.

The crane is operated by a man (or women) sitting in the small cab sitting on top of the crane, these individuals need to be very brave and quite tough as there is no air conditioning up in that glass box and the tower itself moves back and forth as it picks up and drops off heavy loads or if the wind is strong.

You also need to be rather patient as you cant just come down if you forget something! Lunch is usually delivered to the crane operator by him dangling a long rope with a hook down to his team on the ground.

K1 have a go on a "digger"

Continuing the K1 unit of inquiry about construction we organised a quick go on the "baby digger"

One for the pedals and one for the controls..

How many students can fit in the bucket...

Progress of Site - early March 2014

Current Progress on site - March 2014

Well the excavation has now started in earnest, we are averaging around 100 truck loads of soil from the site every day and we will need to do this non- stop for at least 60 days to get to the final level of the basement (as this is a school project I will let you work out how many truck loads of soil this will be!) 

You can now see a strange cage of steel in the middle of the site, to correct some misinformation in the Primary School I can confirm this is not for the builders at night, the guard dog or naughty children but it is in fact the foundations for the tower crane which will soon be rising from the ground. This cage will be lowered in the hole in the ground and is support by the 12 pieces of steel that can be seen poking from the ground.

This will be interesting as everyone knows that the building site is not a building site with a big crane but also because it will give all that are watching carefully an idea of the final level of the car park as this huge lump of concrete will eventually be left under the car park floor.

For the sake of future generations that may be reading this blog in 2224, I will be embedding a number of coins from 2014 in this block of concrete so please get digging if the school is now short of funds....