Posted: Mon Jan 29, 2007 10:18 pm
Tony,
I have used your “expert� advice to help resolve a number of drainage problems with excellent results and I am hoping that you will be able to help with my current problem.
I am having my garage extended (rebuilt) to include a workshop and an inspection pit (to inspect the undersides of vehicles not drains!). The excavation of the pit (on 28th Nov.) revealed a very heavy clay soil all the way to the bottom (1,800mm) which was excellent for retaining a clean excavation but had other issues. The pit remained dry for a couple of days and was then covered while other building work went on. The weather during December was extremely wet and when the covers came off the excavation it was no surprise to find about 300 – 400mm of water in the bottom. The water was pumped out and the substrate for the concrete floor was laid. The next day the water appeared to have returned to the level of the top of the substrate, approx. 300mm above the clay bottom of the excavation. A hole was drilled in the centre of the pit in an attempt to break through the clay into a permeable layer to act as a drain for the excavation. The hole was abandoned after drilling through approx. 1,500mm of very heavy clay (total depth approx. 3,200mm) and the hole has now filled with water to a level about 10 – 20mm below the top of the substrate.
My belief is that when the pit was originally excavated (Nov’06) the water table was below the bottom of the pit but owing to the severe weather, during December and early January, has now risen to be approx. 300mm above the original excavated depth. Is this feasible / realistic?
Have you any suggestions as to how we might proceed with establishing a solid floor on which to lay the dense concrete blocks to form the pit. We are obviously unhappy with attempting to lay concrete on what is a flooded and potentially unstable sub base.
Any help or advice would be most welcome.
Thank you again for the invaluable help to date.
I have used your “expert� advice to help resolve a number of drainage problems with excellent results and I am hoping that you will be able to help with my current problem.
I am having my garage extended (rebuilt) to include a workshop and an inspection pit (to inspect the undersides of vehicles not drains!). The excavation of the pit (on 28th Nov.) revealed a very heavy clay soil all the way to the bottom (1,800mm) which was excellent for retaining a clean excavation but had other issues. The pit remained dry for a couple of days and was then covered while other building work went on. The weather during December was extremely wet and when the covers came off the excavation it was no surprise to find about 300 – 400mm of water in the bottom. The water was pumped out and the substrate for the concrete floor was laid. The next day the water appeared to have returned to the level of the top of the substrate, approx. 300mm above the clay bottom of the excavation. A hole was drilled in the centre of the pit in an attempt to break through the clay into a permeable layer to act as a drain for the excavation. The hole was abandoned after drilling through approx. 1,500mm of very heavy clay (total depth approx. 3,200mm) and the hole has now filled with water to a level about 10 – 20mm below the top of the substrate.
My belief is that when the pit was originally excavated (Nov’06) the water table was below the bottom of the pit but owing to the severe weather, during December and early January, has now risen to be approx. 300mm above the original excavated depth. Is this feasible / realistic?
Have you any suggestions as to how we might proceed with establishing a solid floor on which to lay the dense concrete blocks to form the pit. We are obviously unhappy with attempting to lay concrete on what is a flooded and potentially unstable sub base.
Any help or advice would be most welcome.
Thank you again for the invaluable help to date.
