Today a front page item in the Nation was about houses collapsing :

Residents hurriedly moved belongings out with helps from Muang Bang Bua Thong Municipality officials, who also put up a sign "no entry" to prevent people from getting hurt from further subsiding.

A homeowner Wasin Ubolrassamee, 41, said his family lived there for 10 years and they heard a loud crack Monday morning, as if there was a construction going on in the Soi 4 neighbourhood.

Tuesday morning they heard the noise again three times and saw cracks rapidly appeared on ceilings and walls so they ran out and saw neighbours stood shaken up outside their homes too, Wasin said.

The estate headman Wichian Amatasatja, 65, discussed with the affected residents about demanding compensations from the estate developer. He said that 13 townhouses in Soi 1 in this estate had also subsided in 2004and the developer then paid the affected at Bt300,000 per home.

Wichian said the estate engineer had once told him that connected townhouses laid heavy on the soil, which is soft being old rice fields, so the houses slowly sank each year until the soil could no longer contain causing the subsiding. Wichian also suspected the estate contractor' foundation pillar laying method might also be a factor.

The estate was passed on from the original owner, a bankrupt businessman, to Sin Asia Co and later Bangkok Commercial Asset Management Co Ltd.

This is something I have been expecting to happen ever since I moved into the area. There is rapid development going on in this area and as mentioned above this is on former paddy fields. I have been able not only to witness this in my own house and village, but have also been able to watch the problem being perpetuated in the news buildings mushrooming in this area.

The cause of the problem is simple, the paddy fields were about 2 to 3 metres lower than the surroundings in order for the crops to be flooded.

When used as building land the fields are built up to road level by adding tonnes of alluvial soil and clay, basically dried mud!

Piles are then sunk and buildings constructed on these piles. This is a futile endeavour, piles need to reach bedrock or consolidated strata. In a flood plain basin the piles and footings I have seen being used are totally inadequate.

Alluvial soils, particularly if they have a high clay content will have a seasonal movement, the clay shrinks and expands with changes in water content. This is known in the trade as 'soil heave', and is a very common feature in the London area which is a clay basin.

The best solution is not to use piles for single homes, instead we cast a large reinforced concrete 'raft'. This raft supports the entire house which is built on it. If there is any soil movement then the entire raft will sink, rise, or in the worse case tilt slightly. The house as it sits on this raft is unaffected. In the worst case scenario, where the tilt is severe hydraulic rams are used to jack up the raft and concrete is injected into the space.

 This is all well established technology, any civil engineer should be aware of it.  So why not use it in Bang bua thong? It takes longer to sink piles, but a raft uses more concrete, concretes is slightly more expensive than piles, costing both materials and labour.

So as far as I can see these houses collapsed for the simple reason someone wanted to save a few Baht.