Backfil Material 1

[bobrob1892]

I will be backfilling a trench around a 7' deep basement wall in Southern Ontario and need some advice. A french drain will be laid at the bottom of the trench.

The soil in this area is clay like and holds on to water, shoud I discard the earth removed and backfill with a different soil, or mix the current soil with gravel or sand and then backfill?

Would appreciate your thoughts on this.

Bob

 

[DRC1]

Get rid of the material and get new material. 5% fines can significantly reduce the permibility of a soil. line the trench with Filter fabric. This ill prevent fines from moving into the drain. place slotted corr. plastic underdrain pipe in the bottom of the trench. Back fill the trench to about 6" from the top with 3/4 inch stone. lap the ends of the filter fabric over the top of the trench and top it off. Be sure the trnch is pitched to drain and has a place to drain to.

 

[bobrob1892]

Thanks DRC1. The trench is about 40' long (8'+12'+10'+10') , 7' deep and 3' wide. Would I use 3/4" stone to backfill the whole trench minus 6" from the top? If so, would it channel so much water as to overflow the sump pump/pit capacity i.e work too well?

Bob

 

[DRC1]

7 feet of stone is a bit much. Did not register when I responded. I would go maybe half way up with the stone and backfill the rest with a sandy material tht will drain, should be a lot cheaper. The stone and pipe will have the capacity to carry a lot of water, but how much water it actually sees is a function of the native soil, which appers to be low permiability and the topography - does surface water run to the house or away? I assume you basement is above water table. One other thing you should do is to collect your roof drains into a pipe just underground, possibly even in this trench and drain away from the house. I would not tie those into a sump pump as those volumes may overwhelm the pump. Otherwise if you can grade away, picking up runoff and ground water from a storm, A sumppump may be manageable. Drainage by gravity away from the house is more dependable- gravity never goes out in a storm.Talk to your local building inspector or town engineer- he has seen alot of basements in your area and probably has a good idea of what will and will not work.