I am owner-building a 30x20 story and a half home in NE Vermont on a frost protected monolithic (thickened edge slab. The site has approx. 5-6% slope, silty soils and is at the bottom of a watershed of approx. 250 acres that goes a mile back.
Excavation was done to get the topsoil off at the lower elevation, and cut back level upgrade. The excavation is about 4 feet wide - extending two feet from the outside of the 12" wide slab footing and approx. 8" to 12" from the inside of the footing. The plan was to place 8 inches of 3/4" crushed stone, then 8" 3/8" stone, then 8" of 3/4"crusher run to come up two and a half feet, then set the forms and pour the slab which will have sides 2 feet high and the footing 12" wide. When I first excavated, the groundwater was about 5-6 inches below the bottom of the trench and unfortunately did not get to compact the bottom before 3 inches of rain fell in 24 hours last weekend. Now the groundwater has come up about 4 to 6 inches so that there is about an inch of water in one corner of the excavation. We have been dry for 3-4 days and the water is receding slowly. The soils are silty - a ribbon can not be rolled smaller than 3/8 to 1/2 inch, and a meatball shines up (dilatancy). I can push a rebar in 9-10 inches with steady pressure.
What is the procedure when groundwater is hit in an excavation? I'm sure there is 4-6 inches of disturbed soil that has not been compacted. Can rock or gravel be pushed/compacted into the wet soil to give it stability or does it need to be drained before anything can be done? I am considering curtain draining the area, something I considered in early planning. Should I excavate wider to get a wider stone footing than the 4 feet I have now? I have been in touch with a local geo-eng, and my tentative is to get him out to look, maybe after I curtain drain it. I am eager to hear any other ideas. My problem is similar to that of ttowne in thread261-56444
Thanks for any help.
Tom
Excavation was done to get the topsoil off at the lower elevation, and cut back level upgrade. The excavation is about 4 feet wide - extending two feet from the outside of the 12" wide slab footing and approx. 8" to 12" from the inside of the footing. The plan was to place 8 inches of 3/4" crushed stone, then 8" 3/8" stone, then 8" of 3/4"crusher run to come up two and a half feet, then set the forms and pour the slab which will have sides 2 feet high and the footing 12" wide. When I first excavated, the groundwater was about 5-6 inches below the bottom of the trench and unfortunately did not get to compact the bottom before 3 inches of rain fell in 24 hours last weekend. Now the groundwater has come up about 4 to 6 inches so that there is about an inch of water in one corner of the excavation. We have been dry for 3-4 days and the water is receding slowly. The soils are silty - a ribbon can not be rolled smaller than 3/8 to 1/2 inch, and a meatball shines up (dilatancy). I can push a rebar in 9-10 inches with steady pressure.
What is the procedure when groundwater is hit in an excavation? I'm sure there is 4-6 inches of disturbed soil that has not been compacted. Can rock or gravel be pushed/compacted into the wet soil to give it stability or does it need to be drained before anything can be done? I am considering curtain draining the area, something I considered in early planning. Should I excavate wider to get a wider stone footing than the 4 feet I have now? I have been in touch with a local geo-eng, and my tentative is to get him out to look, maybe after I curtain drain it. I am eager to hear any other ideas. My problem is similar to that of ttowne in thread261-56444
Thanks for any help.
Tom