Wednesday, September 1, 2010

First Line of Defense—Drain the Water

In the last post I showed the gash in the hillside where the house will sit.

View of the Excavation Site From the Southwest Corner Looking Northeast

Here is a second photo of the excavation site showing the pure clay and vertical banks formed by the excavator. On this dry, sunny September morning, the area looks so inviting, but that can change so quickly when the rains come. Uncontrolled water infiltration into and through the surrounding area may be the number one enemy of earth sheltered houses and Passive Annual Heat Storage (PAHS) systems. My biggest concern before the excavation began was that we would encounter a rock ledge or discover an underground spring. Fortunately the largest rock I saw was about 6" in diameter, and I didn't see any gravel or wet spots. Just a lot of clay as this image shows.

The problem with pure clay is that it's about the worst type of material to build in or on or sometimes even near, because its extremely small particle size and smooth surfaces yield low shear friction angles when wet. This means that wet clay will typically support less ground pressure than other types of soil, so foundations may more easily slide or sink when the soil is saturated with water. And the steep, exposed banks along the backside of the house may break free and slide down when they get wet. Some of the exposed banks are over 20' high, so the excavator stepped them back to reduce the severity of mud slides. Concern for worker safety was paramount.

Orange Stakes and Lines Locate the Walls and Outside Perimeter of Footings

Before the house footings could be poured, water and electrical had to be run underground from a Morton building about 150' away. In addition, a 4' deep French drain had to be installed around the perimeter walls that would face into the hillside. Another French drain would be installed down the center of the structure. And before all that could be done, the house profile had to be staked out and the outside perimeter of the footings marked with orange paint. An orange stake and part of the perimeter is shown in the above image. The water and electrical lines had already been installed when this photo was taken. Part of the trench for the French drain had already been dug as can be seen at the left edge of the photo.

The 2" PVC Electrical Conduit and Insulated Waterline
This image shows part of the 2" PVC electrical conduit and insulated waterline run from the Morton building in the distance up to the construction site. Part of the waterline was insulated to minimize heat transfer between it and the tempered soil beneath the floor and on the east side of the building that will be part of the PAHS system.

Laying a 4" Drain Tile 4' Deep Around the Perimeter of the Structure

The first task was to run water and electrical lines underground to the house as shown in the previous photo. This image shows the end of the waterline coming up vertically near the inside corner of the house where the utility room will be located. The waterline was enclosed in a box formed of 2.5" thick styrofoam insulation. To the right of the mini-excavator's blade can be seen a 2" PVC tube that will eventually hold three heavy copper wires for a 200 amp service. An electrical cable with four outlet plugs was initially threaded through the tube to supply power for construction. Part of the orange electrical cable is coiled around the end of the PCV tube.

The mini-excavator dug 4' deep trenches as close to the banks as possible so that they wouldn't interfere with the house footings that would go in later. After the drain tubes were laid, the trenches were backfilled with one-inch gravel to insure adequate drainage and support for the foundation. These outer drain tubes are the first line of defense for the footings and poured concrete floor. Any water that finds its way through the soil to the footings area will descend to four feet below floor level, keeping the immediate volume of soil under the footings and near floor level much drier.

Backfilling the 4' Drain Trench that Runs Down the Center of the House

As shown in this image, a second 4' deep trench was dug down the centerline of the house, running from one end to the other. A four inch drain tile was laid in this trench, and a second trench and tile were teed off it and run to daylight. This extra drain under the house will ensure that over time the soil beneath the concrete floors stays very dry.

During the incessant rains over the following months, thousands of gallons of water have flowed out of these drain tiles. They have done their job admirably.

September 30, 2009—The Rains Came and the Clay Banks Gave Way

This photo shows what a lot of rain in a short period of time can do to steep clay banks. I had draped 6 mil plastic over the banks and installed silt fence in a vain attempt to protect them from the water. But it got in anyway, and down they came. This collapse occurred right next to the waterline and electrical conduit shown in earlier photos

September 30, 2009—First Footings for the Back Wall Were Poured in the Mud

This view shows the first back wall footings. The edge of the waterline's insulation box can be seen in the lower, right corner, and the collapsed bank area in the previous photo is off to the right.

October 13, 2009—A Few More Footings Poured and a Lot of Mud

Almost two weeks have gone by and it has been too wet to get much done. That lovely first picture has been transformed to muck, and this is what we can expect right on up to mid summer 2010.

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