Sinking front yard

[aoneseller]

Hi,

I would like to ask if anybody got any idea how to fix the following.

Our house with yard in Bangkok built on stilts near river area 6 years ago. Well, the front yard corner in one side is sinking down year by year. It looks like not going to stop. A "stonrmason" from our village suggested the front yard has to knock down and rebuild on more barrels with stilts. It would cost 300k baht. If someone has less costly idea I would appreciate.

Thank you

[Crossy]

I assume that the yard is on smaller / no piles and the house itself isn't moving (we are in a similar situation and have 16m driven piles under the house).

How fast is it actually sinking (mm or inches per year)?

We had a similar issue with the concrete pad our water tanks sit on (only on 2m piles), during high river levels a couple of years back the whole lot started to tilt. Once the river went down and the movement stopped I removed the tanks and just levelled up the top with more concrete and mesh. It hasn't moved since but the river hasn't been as high either.

If it's cosmetic and not affecting the house structure you could do something similar perhaps.

[Morakot]

Here's a radical suggestion: Remove the entire concrete cover from your yard! Stabilise any clay by adding sand and level out with a substantial layer of compacted gravel. If you like, finish with grass pavers or similar.

Subsidence can be aggravated by a reduction of surface permeability. Concrete surface covers will almost always merely mask existing ground problems and contribute to exiting structural and environmental damage. There is a widespread misconception amongst Thai builders that a concrete surface cover is the solution to soil shrinking problems; in fact---as a whole raft of established scientific literature shows---a reduction in surface permeability is useless at best and often harmful to structures and surroundings. It is disheartening to see how in the name of "progress" and almost mythical disbelieve, resources are wasted and quality of life is reduced.

Edited July 4, 2016 by Morakot

[Morakot]

[thailand49]

I am not expert but in a situation like this obtaining more than one opinion is necessary instead of a stonemason, maybe a soil engineer? The problem isn't to fix the resulting problem but also to find out what is causing the problem?

[aoneseller]

Crossy: the house is not moving, just the yard in the front corner. Few centimeters per year. I leveled up already and installed tiles. If level up again it would have more weight on it and sink faster.

Baguette: u mean put more mud under the yard?

[Sean87s]

I wouldnt even remove the concrete surface. Just drill huge holes, drive huge concrete piles down in the holes and then reinforce with steel bars and fill it up with concrete again.

[Morakot]

Crossy: the house is not moving, just the yard in the front corner. Few centimeters per year. I leveled up already and installed tiles. If level up again it would have more weight on it and sink faster.

Baguette: u mean put more mud under the yard?

[Am I understanding this correctly there is actually a gap between the concrete slab on piles and the ground? Why? Is this built on top of some canal? Are you not worried what creatures live underneath? I'm curious about the rational of this design.]

You are correct; adding concrete on top of the "dent" may increase the sinking. Putting mud or rubble under the slab may stop the sinking, but would defeat the purpose of your current design.

If you want to retain this structure, additional piles will be needed within the vicinity of the damage. Sean's suggestion is spot on! Drive in piles and have rebar horizontally interconnecting the piles where it sunk. Once properly supported level out the top with concrete.

Edited July 5, 2016 by Morakot

[metisdead]

A non helpful post has been removed.

[aoneseller]

Morakot:

Yes, there is a gap (around 1 meter). This area this is the only way to build house.Near river, swamp area.Yes, there are some iguana under, but they are ok.Anyway, I think I will try to put rubble under, if still sinking,than drill hole and drive more pile. I guess..

[warrimurf]

If you look at the geo survey of the BKK area you will see the layer of unstable clay runs deep.

You need to pile down to the stable layer of hard clay it's a tan colour quite hard with gravel in it not black or dark grey, depth varies from roughly 15m to 25m.

If you look at housing developments you will see the piles being driven that is what you need, nothing else will be stable.

Boring and filling with reinforcing bars and concrete is also the same anything else really is temporary and a waste of time.

Bite the bullet or live with it.