Sunday, August 3, 2014

Design - Excavation

This post was written at an early planning stage whereby I intended to minimize cost by doing most of the work myself.  When it came time actually to do the trenches for the French drains and the AGS conduits, we were in the midst of the rainiest Spring in history. It became necessary to get as much work done as possible between rains so we enlisted professional help for the trenching as well as for grading for the slab floor.   It took several posts to cover the installation of the French drains and AGS conduits. Here are links to those posts:  First post on French drainsSecond post on French drainsLast post on French drains,  First post on AGS system

Excavating to Floor Level
Since the building site slopes about 15 degrees, the excavation for the house will be 
Building site -- 15 degree south-facing slope
about 6' below grade at the back wall and at grade at the front wall, which means it will involve cutting but no filling.  I estimate that the excavation for the house and garage will take four or five days with the track loader having a 6' long bucket and carrying the soil for storage 50' to the north.  The back wall will be two stories high which will eventually require an additional 6' of backfill on top of the original grade.

Excavating Below Floor Level
The excavation would be rather simple if it weren't for the need to bury the conduits for the Annualized GeoSolar (AGS) system (previous description of conduits for AGS). The conduits will be ten in number and range from 5' below the floor level at the front wall to 3' below floor level at the back wall.  To make things even more complicated, the piezometers that we placed and monitored for three years, told us that a French drain system* would be necessary to keep the AGS system isolated from the rainy-season water table.  It will comprise seven separate drains 15' - 20' apart east to west, about 10' below floor level, canted southward by 1/4" per foot and reaching daylight downhill where they will drain into a rain garden.

Excavation Equipment
Remember the adage, "When your only tool is a hammer, everything looks like a nail"? Well, our track loader is our hammer so I need to devise unorthodox excavation methods to stretch its functionality.   Even then I anticipate having to rent a mini-excavator (small backhoe) for a few days for final shaping of the French drains.

French Drain Trenches

After the basic  house excavation is complete, it will be necessary to trench down another 10' for the French drains.  It is too dangerous to work in a narrow trench even half that depth so, if it needs to be wider, why not use the hammer I have and make it 6' wide (which is probably not a whole lot wider than is necessary for safety?).  I will be moving a lot more dirt than a professional would but I have the loader for putting it back in the hole and all it will cost is a few extra tanks of diesel fuel and a few days time.

At the bottom of the 6' wide track loader "trenches", I plan to dig proper trenches for the French drains approximately a foot wide and a foot or so deep using a rented mini-excavator then finishing with selective hand-digging.

For the rest of the story, go to more details on our excavation.
*  Information on French drains.

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