Waterproofing

[bank]

The contractor is trying to proofroll the soil on a road construction project. They have discovered that water is migrating into the area from an adjacent undeveloped area. This is preventing the soil from drying sufficiently for them to proofroll.

Geotechnical borings prior to completion of design showed no water in any of the borings. There will be a drainage ditch along the edge of the roadway, but it won't be installed until an outfall structure is constructed. At this time there is nowhere to pump the water to, since adjacent areas are either undeveloped or privately owned by others.

The question arose as to whether or not the ditch can be over-excavated, and some material placed in it to form a temporary barrier until the road and/or outfall system are completed. Does anyone have experience with this or other methods of preventing migrating water from entering a construction area? The affected area is probably no more than 500 feet long.

 

[Ron]

Use perimeter ditching and pump water from the ditch. You are apparently getting cross flow from adjacent properties. You have to intercept that flow with a ditch or swale that will allow access to the water to remove it.

You could use a grout curtain to intercept the flow, assuming you know the flow characteristics (limits of area, direction of flow). That's expensive, but might be expedient for the construction.

Are you sure the problem is from lateral flow and not vertical? I know your borings didn't show groundwater, but various soil conditions can be difficult to determine with respect to location, depth, and flow.

 

[oldestguy]

If you wish to make a dam, of sorts, assuming the ground is sufficiently porous to be carrying water laterally, you can cut it off, but the barrier needs to go down to an impervious layer.

Other than what Ron has suggested, a simple barrier, not necessarily good for 100% stoppage, is a trench filled with compacted clay. I've done that where a foundation was to be constructed in very porous stuff (fill)next to a river and it worked sufficiently well to get the job done without dewatering. Not fancy, but sufficiently tight to hold back the water.

 

[Dozerman56]

If it was my project I'd put the outfall structure in and get the permanent ditch in. I'd hate to go to the time and expense of putting in an impervious curtain only to find the water was coming from somewhere else. But if there's a real reason that can't be done, I'll go with Ron and say cut in some perimeter ditches, if you can't gravity drain them, bring in some pumps.

 

[bank]

Thanks guys. The answers confirmed what I hae been telling the engineer. It was decided to over-excavate the roadway an additional three feet and fill it with stiff clay to block the water. The stabilized subgrade and pavement will be put on top of that.