May 052011
 

I moved into my house in Seattle way back in 1994. Back then my front lawn was a mess. It was full of overgrown grass, Himalayan blackberry, and all sorts of other weeds. It was so bad that I had a feral cat taking up De facto residence. Compounding the problem of getting rid of the grass and weeds was that my lawn was full of boulders! The root systems of some of the more tenacious plants would hide under the boulders, so even if I trimmed the plants, they would often grow back.

I decided to wage war on the boulders. I reasoned that I would need to address the most fundamental problem first before trying to get my lawn in order. My front lawn is bisected by a concrete stairway. The east section is smaller than the west section. All in all, I figured there must have been about twenty(!) boulders in my front lawn. I decided to break up the boulders in the east section first. Using just a sledge hammer, I would blast away at the big rocks, cracking off chunks until they were small enough to carry away. Here’s a photo of one of the boulders, with the sledge hammer included to provide a sense of scale:

This was much harder work than I expected, as I simply underestimated how hard the rock was. I don’t know a great deal about geology, but I was told that the big rocks commonly found in Seattle were basalt. One factor that began to concern me was that tiny chunks would blast off, and I was worried that a chip might scratch the paint from someone’s car. Eventually I managed to clear the boulders from the first section. It was terribly strenuous labor, and often made my back ache. I basically put this project on hold for about 8 years.

Eventually, I decided to attack the boulders on the other side of my yard, this time using a rented electric jackhammer. You would think this would work like a charm, but it did little or nothing. I began to take notice that I was certainly not the only homeowner that had big “ornamental” boulders in my front lawn. I began to wonder why. Eventually I found the answer in a somewhat surprising place, a book on Washington architecture.

Authored by Sally B. Woodbridge and Roger Montgomery and published by the University of Washington Press, it’s an excellent introduction to a large subject.

An amazing photo is found on page 100:

It’s a bit hard to see in this photo, but there is a pile of boulders at the base of this huge mound of soil. The explanatory text is brief, but answered the question I harbored all these years.

Regarding the Denny regrade, in which high pressure water jets were used to move huge masses of soil, the text on pages 100 and 101 reads:

“Denny Hill, one of the most important topographical features of early Seattle, comprised sixty-two city blocks. The top featured a famous hotel and the first city park. Under the direction of Seattle’s most renowned city engineer, R. H. Thomson, the hill was leveled in several places beginning in 1891. Sluiced down by the method of hydraulicking that Thomson observed in the California goldfields, the hill produced enough earth to fill the rest of the tidal flats and, at the same time, to furnish garden designers and nurseries with a long-lasting supply of boulders for retaining walls and rockeries.”

At some point I learned that the ancient Romans had excavated tunnels by heating rock faces with fires, then dousing the hot rock with cold water. This would cause the rock to shatter, and the rubble could be removed. I bought a propane tank and one of those “50,000 BTU” fire wands. Working with a partner, I would blast the rock with fire, then my partner would spray water from a hose onto the rock. Sometimes it would work, but mostly it didn’t. I would then resort to the sledge hammer, but even then I concluded that the “Roman method” didn’t work on these rocks.

I finally came upon a solution that worked. I had a DeWalt roto hammer, with a 5/8″ diameter bit that was quite long. I would drill three holes in a line as close together as I could. It just so happened that a wood-splitting wedge would just fit within that width. The wedge would have to knock out the walls between the bore holes, but that was no biggie when struck by the sledge hammer. Furthermore, this process didn’t create any tiny high velocity projectiles that might upset the neighbors. As hard as it was, the rock was no match for the simple power of the wedge. I remember one day in particular, I believe I broke either two or maybe even three boulders using this technique!

Of course, this generated a huge amount of waste rock. In fact it took two full sized pickup loads to transport it all away. I found a rock pile down in Skyway, south of Seattle, near some railroad tracks. I assume it was owned and used by the railroad for rail bed ballast. So I didn’t feel morally wrong about “dumping” my rocks there, and in fact I like to think I was actually helping add to the railroad’s supply!

With the boulders totally gone, it was an easy matter to get rid of the noxious weeds and vegetation, especially the Himalayan blackberry. My front lawn is still not finished, but at some point I think I’d like to terrace it, so I don’t have to mow a harshly curved surface.

Deep in my mind, I hold the thought that long after I’m gone, someone will decide to decorate the front lawn with beautiful basalt boulders…

 Posted by on 05/05/2011 Personal History

  2 Responses to “Lawn Boulders”

  1. I have the same problem. I enjoyed your article and comments. The picture of your boulder is the same size as mine with a slightly different shape. I was thinking of using some sort of leverage. 8′ landscape logs can actually start to lift it at the corner but what would I lift it onto and could I drag it anywhere? It probably weighs 300-500lbs. I don’t want anyone to hurt themselves so I’m trying to figure out how logs and poles might do the trick. Ever try this?
    Thanks, Joann

  2. I would NOT recommend attempting to move giant boulders unless you had dedicated heavy machinery.

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