I asked a Thai lawyer the following but she could not give a definitive answer but seemed to believe that the neighbor was within his rights because they own that land . 

 

The back of our property outer wall appears to be the extent of the plot . What has happened is that the owner of the adjacent land has built some properties about 2-3 meters from our back wall . They have dug out the foundations and the soil has been piled up within the space between their new houses and our house and the dug out foundation soil is banked up against our wall to about 1 meter high and 8 meters long . I am concerned that this will cause damp to penetrate through our single skin wall and damage our interior decor . Does anyone have knowledge about whether this is allowed under Thai planning laws ?

You need to determine where your property boundary is. Usually walls are built or should be built within your property leaving some distance from the exterior if your wall and your boundary line. If that's thats case you can ask the neighbor to remove the soil off your property\wall. If the wall is on the boundary your stuck as the neighbors land ends at your wall. You may need to be very diplomatic about it and involved the village headman with your concerns. Don't expect much cooperation though as thais never think ahead or act proactively to avoid problems.