Advise on a French Drain?

[YerKiddin]

I have started a project at my home. I'm digging the trench for a French drain, in hopes of diverting the water that currently leaks into my basement. It was moving along nicely until I got to the corner, where a rock jutted about six inches into the trench, near the bottom, where the pipe will be. I have tried to dig the rock out, but so far I just keep finding more rock, rather than the other side of it.

As I see it, I have two choices: chip away the part of the rock that is in the way, or keep digging the rest of the rock out, and move it. I can't consider any sort of blasting, as there is a natural gas line supposedly within a foot from the rock.

I should have included something to give scale to the rock. There's more than a foot of rock shown here, and the rock comes up most of a foot from the bottom of the trench as well.

[Fred588]

I have started a project at my home. I'm digging the trench for a French drain, in hopes of diverting the water that currently leaks into my basement. It was moving along nicely until I got to the corner, where a rock jutted about six inches into the trench, near the bottom, where the pipe will be. I have tried to dig the rock out, but so far I just keep finding more rock, rather than the other side of it.

As I see it, I have two choices: chip away the part of the rock that is in the way, or keep digging the rest of the rock out, and move it. I can't consider any sort of blasting, as there is a natural gas line supposedly within a foot from the rock.

I should have included something to give scale to the rock. There's more than a foot of rock shown here, and the rock comes up most of a foot from the bottom of the trench as well.

If the trench is wide enough to use a sledge, you might be able to break the rock fairly easily. Or, weaken it with a hammer drill and then use the sledge. That's what I did with the Studio pits.

[YerKiddin]

I actually have a hammer drill. I've only ever used it as a drill, and didn't even think about it until reading that reply.

THANKS!

[Fred588]

In that enclosed space, especially, be sure to use ear protection as well asa eye protection.

[YerKiddin]

Well, shoot. Turns out 20 minutes with the hammer drill got 1/2 inch into the rock. I then got angry, and went after the rock with my railway pick. About the third good hit broke off 3" of the rock. (YAY!) After that, my next few hits seemed to bounce. Perplexed, I took a look at my pick:

[Duncan Edwards]

Better lay off the steroids.

[YerKiddin]

Shoot. That was pure pissed-off old guy. (Though, to be honest, it may have also involved an oddly grained rock and an inferior pick)

Today went really well! I borrowed a busting maul yesterday from in-laws.

What followed was two maybe-five-minute beatings, and I'm now back to digging.

[Fred588]

Shoot. That was pure pissed-off old guy. (Though, to be honest, it may have also involved an oddly grained rock and an inferior pick)

Today went really well! I borrowed a busting maul yesterday from in-laws.

What followed was two maybe-five-minute beatings, and I'm now back to digging.

I have found that the key to removing a rock, other than the plenet itself, is to remove whatever is beneath it, if possible. Rocks are terrific at resisting compression but poor at resisting torque. Beating on a rock that has support underneath is attempting to compress it, while beating on an edge that is not supported is applying a torque (bending it). The more it is undermined, the larger the piece that breaks off.

The purpose of a hammer drill is to make a hole that can the be pried on. This creates what is essentially a shearing force, which rocks are not good at resisting. If the rock has a grain this is also very important as the grain represents a naturally weak point of attack.

[YerKiddin]

The grain of the rock was the key to the success with the maul. Before, I'd been beating the rock top-down after digging out from under the part I wanted to break off. It just wasn't happening. Today, I started beating down and it was just sending chips very painfully at my shins. Then, I got out of the trench and started beating the rock on the side, and it just crumbled away. (well, after a few good hits it started crumbling, and then broke more and faster from there)

[YerKiddin]

Now, I'm trying to tunnel under the sidewalk. Woefully, it's 3 1/2 feet wide, but I'm not but about 2' of the way under it. I've started trying to dig from the other side, but that ground has even more gravel and roots than the previous digging had.