One piece at a time

How do you remove a boulder, weighing at least 50kg, from a hole in the ground that’s intended to take a gate post?

You could get out your tractor with back hoe.

You could borrow a friend’s mini-excavator.

You could hire a pneumatic drill and bore a hole through it. Or a stone saw and cut it up.

Or you could be completely bonkers and, on a day when the sun is blazing and the temperature has passed 26C, spend quite a few hours happily breaking it into small pieces.

By hand.

We have two fence lines that terminate in a shallow V.

Gates will hang at the end of each fence and close on a post that sits right in the V and marks the end of a third, yet to be built, fence.

I started digging the post hole for the pivotal post today but after digging down 45cm (18in) I hit a very, very large ironstone boulder.

The boulder extended well beyond the sides of the hole, which is 45cm in diameter.

I couldn’t dig the boulder out as that would make the hole too wide and I couldn’t move the post to a different position as two of the three fence lines are already in place.

Instead, I went down to the workshop and brought out my stone-breaking tools: heavy sledgehammer, heavy club hammer, cold chisels, rock drill and heavy crow bar.

I lugged them up the hill on my shoulder and set to work.

First, I cleaned all the loose dirt away from the top of the boulder before inspecting it closely, by eye and by feel, looking for fractures and flaws.

When I found one, I took the rock drill (a piece of hardened steel rod), stood it in the fracture, and then pounded it home with the club hammer.

After every 10 strokes with the club hammer, I’d rock the drill.

So long as the drill remained loose, I continued pounding it with the club hammer. When it eventually stood firmly in place, I changed to the sledgehammer and really got stuck in.

Even ironstone can’t take that for long and the fracture began to widen.

I put the hammer down, then levered the drill back and forth until a lump of rock broke off with a crack.

I fished the piece out of the hole. It was the size of my fist and I reckoned there must be at least another 100 pieces that size still to come.

And so it continued.

When the boulder was left with outcrops, I’d cut them off with a cold chisel.

When I couldn’t find a suitable fracture, I’d cut a hole in the boulder by turning the drill a quarter turn after every hammer blow. When the hole was deep enough, I’d use the sledge hammer to knock it from side to side until the stone fractured.

The post hole gradually grew deeper but without any sign of the bottom of the boulder.

When I finally quit after several hours I’d cut a hole almost a foot deep into the boulder and it looks as if I’ll have to do the same again tomorrow—because the post has to be set at least 90cm (36in) into the ground.

So that’s how I remove a boulder from a hole.

One piece at a time.

By this point, I’d cut my way down through 25cm of rock, or about 10 inches. The club hammer is lying on rock, the handle is pointing at rock, to the left is more rock, and there’s another, obvious spur of rock running to the right.

It’s difficult to see, but the drill is sitting in a natural fracture in the rock. It’s hammered in with the club hammer until it’s tight and then driven in further with the sledge hammer.

After 20 to 30 strikes with the sledge hammer, the drill penetrates far enough that the rock begins to fracture. At this point, it’s still not possible to break the fragments free but new fractures are opening up.

The drill is worked free and then driven into a fracture at right angles to the original one. Again, it’s club hammer first and then sledgehammer. Sometimes the rock will fracture sufficiently at this point for me to lift pieces out. At other times, a third drilling is needed parallel to the first one and at right angles to the second.

Finally, after digging through 45cm (18in) of soil and cutting through another 45cm of rock, I hit the right depth. I then lie on the ground, with my arms down the hole, and use the club hammer and cold chisels to square up the sides and level the bottom. Getting the sides reasonably square makes it easier to wedge the post in place, while a flat bottom to the hold helps the post sit level.