In error the piling company drew up the piling construction plans for a brick and block house and not a timber frame.
Meaning the piles could have taken a much heavier house. So this house is as safe as houses - excuse the pun.
The chimney is positioned in the middle of the house using three piles.
Another pile is used in the corner of the front porch.
...you have under your proposed house and decide what type of foundations to use.
It's carried out by a soil engineer who has access to a web soil survey of the area and is probably already familiar with the local soil conditions.
One early, crisp morning I met up with my soil engineer and a local farmer with his digging machine. The information we got over the next two hours was very helpful.
I discovered I was going to have to build over an old pond and Victorian dump.
The story goes that when the airmen were stationed at the old Hethel Aerodrome - during World War II and after - they would come and have a swim in my pond at the back.
The remnants of another old pond lay to the north of the plot - under the front left hand corner of the proposed house as you look at the plot from the road. We also dug up a lot of old bottles suggesting an old dump, which was still being used as such.
The willow trees gave it away.
Four willow trees on the boundary and close to our discovery of the pond, were a giveaway sign. As you know, willows thrive on water.
Building Over A Pond - Why no one has built here before.
When the surrounding houses were built in the 1940's the technique of piling construction was considered far too expensive for local builders. So this bit of land was just left alone and continued as a dump right up until modern times.
My neighbour next doors assured me that I have at least one mini car under the garden - he put it there himself! Another local took credit for a motorbike buried at the front. Our arrival has certainly spoilt everyone's fun.
So piling construction was the best option?
Yes. There was no doubt. Having considered the results of the soil survey the surveyor recommended piling foundations even though the pond would affect only a small part of the proposed house. For practical reasons the foundations had to be the same type throughout.
Building on shallow foundations?
Many old timber frame houses were built with very shallow foundations and never survived to tell the tale. They vanished without trace.
Where they have survived you often find sloping floors and ceilings, and leaning walls. But there was a lot of "give" in the materials used then, compared with modern materials.
With modern rigid materials you
can't risk using house foundations that might move over the course of time -
even when you use timber frame. Hence the need for deeper, sturdier
foundations that don't move.
The piling construction company used my house plans and assessed
the need for 20 piles – 15cm in diameter – and 6 m deep. Deeper piles of 10m
would be located under the chimney.
Driving a pile into the ground is the same principle as driving a fence post into the ground. In this case you are driving a hollow steel case.
The hammer of the pile driver is lifted to a height of 2 meters and then dropped onto the pile head pushing it into the ground. With each strike the pile travels a little less distance into the ground until there is effectively no more movement.
In my case the pile has enough strength when the distance travelled by the pile - when struck - is not more than 3mm. This is called the Pile Set.
The live and dead weights of the 4-bedroom house are calculated first and the following equation is used to calculate the Pile Set.
290w(1+h)/(s+12.7) = 13.85 tonnes.
And applies only to a maximum hammer drop of 2m. Each pile in the piling house plans is taking up to 13.85 tonnes to support my house.
Remember the Pile Set s=3. In my case the pile has enough strength when the distance travelled by the pile - when struck - is not more than 3mm. Therefore s = 3.
The weight (w) of the hammer is 0.25 tonne so w = 0.25.The hammer (h) drops 1.5m on each drive. The company use h = 2 just to
Let’s see how the equation works.
Which means a small discount on each pile used in the house foundations.
See the the cluster of six piling
depths nos.10 to 15 from depths of 5m - 5.6m.
These are probably in the willow tree area near the front of the house.
As you can see below my piling construction is now reduced to a set of figures on a form.
The three 5.6m depths - Nos. 18, 19, 20 may well relate to the chimney area.
Each pile is now cut down to 10cm above ground level and filled with concrete. It then has to be tied into the ground beam.
To lay the ground beam a trench is made and lined with plastic shuttering to contain the new concrete.
Metal wire cages are laid over the piles and tied in together.
Finally concrete is poured and allowed to set before the next stage of laying the heavy block work.
House Foundations Warning: Please remember that all calculations and measurements relate to a brick and not a timber frame house. Most important, these calculations are unique to my house and may be inappropriate for any other project.