But the objective now is to put in the 4 inch PVC to act as a conduit for the new gas line. In a day here, a day there, when it was warm enough and not raining, I have created a deeper trench to get the PVC in the right place. It is now "level" enough that water runs the entire length of the ditch, not just at the end near the house. This helps some, since the water seems to soak into the ground better near the street, where the utility work seems to have made the soil more porous.
In addition, we have been digging near the house, from the current gas meter, over to near the property line and then towards the street to the wall formed by the edge of the front bed.
We have been careful to avoid damaging the existing gas pipeline, and the French drain. We have not been as successful with the main irrigation water supply line, having broken it in at least one place. We will need to repair that eventually, but for now it is turned off at the meter; it makes no sense to repair it while we are still digging.
We are down far enough -- as far as the current gas line -- near the house, and probably need to go a bit further down on the piece closer to the property line, but it is all underwater at the moment.
We did manage to break thru under the bed wall, connecting the main trench with the section near the house.
However, the water flow when we did that suggests that we are deeper closer to the house than in the trench, so the trench may need to go deeper, at least close to the bed wall. Plus, we will need to go low enough, on both sides of the French drain, to get the 4 inch PVC pipe under the French drain, and under the existing gas pipeline, which seems to go under the French drain, and then make a sharp right turn while it is there, coming out (on the house side) a couple of feet closer to the street.
So we need to tunnel under the French drain, and under the current gas pipeline, thru the rock that is under the French drain (and the gas pipeline). So a tunnel, about 44 inches long, at least 6 inches under the French drain. Since it is a horizontal tunnel, the jack hammer will be of little use. But the rock is fairly soft, so we will attempt to do this by hand, with a rock chisel.
We addressed the water problem by buying a pump, and a length of discharge hose. A 1/4 horse-power submersible utility pump and 24 feet of discharge hose ($66.37 from Home Depot), allows me to drain the water out and put it further into the back yard (and down hill). That allowed me to jack hammer down in the area by the house to get as low as I can go.
The rock changes character significantly as we go down. The top level of rock was crumbly and soft, very porous. Then was a layer of clay or gypsum like "rock" which could almost be pulled off with a hoe or rake. But then we hit real rock. Limestone. But very hard, and not brittle. We had hit some of this before. The jackhammer can be used to reduce it to dust or gravel, but only with lots of work. It sometimes shatters into small pieces with very sharp edges.
But luckily we don't have a lot of area that needs to be dug out. The main problem is the section under the French drain.
We want to tunnel under the French drain. We are constrained by the actual PVC pipe in the French drain, which is wrapped in landscape cloth and surrounded by river rock. Then there are a couple of inches of the soft crumbly rock. Then we hit the hard rock. We would like to get just 4 inches of clearance tunneled under the French drain, for our PVC pipe. But the rock is very hard. And the jack hammer cannot get to most of it. The jack hammer really only works vertically, and is ineffective tunneling horizontally.
So we rented a Bosch Hammer Drill and a 16-inch long rock bit. ($76.86 from Rent Equip). That allowed us to drill a hole thru the rock and then use a breaker bar, a chisel, and the jack hammer to mostly break up the rock around the hole that was drilled to get thru under the French drain. We were not able to get enough to get the 4 inch PVC thru, but we can get a 3 inch PVC thru.
Even at this point, there was a "hump" of rock left in the middle of the tunnel that made things difficult. All of the chisels, bits, and such would slide up the smooth, sloped sides of the hump. But I put a masonry cutting wheel on a right angle grinder that I have and was able to take the top off the hump, so that I can get the 3 inch PVC pipe thru. With a couple of connectors, I can go from the 4 inch PVC of most of the conduit, down to 3 inches under the French drain, and then back to 4 inches for the final stretch to the house.
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