Expert Advice: Soils Investigation was Truly Boring

As promised, Dave Williams from Zipper Geo returned on Friday 4/10 with a tiny drilling rig and two operators. It was Dave's birthday, and he brought Staff Geologist Bryan Fowler. They arrived at about 12:50 and stayed until about 3:15. Dave left early, maybe 2:30.

Dave brought me a section of a Seattle "Technical Requirements Manual" that suggests that a 70' steep slope needs a 500' setback for any kind of infiltration, like a rain garden. I told him Keith Cross warned me about dueling agendas: Storm sewer doesn't want my runoff, but ECA doesn't want it infiltrating into the ground. Maybe a big umbrella?

Before he left, Dave walked me out to the top of slope and told me he had climbed all the way down and back while they were drilling in the front yard. He said there were piles of debris down there--even concrete that had been tossed over the edge and he gave me a lecture on why that's bad. I told him I was a friend of the park and wouldn't use it as a dump, and he said he had to give basically the same lecture to Seattle Parks and Rec on a West Seattle project, where they found park employees doing the same kind of dumping. The problems with it include scraping off topsoil as the heavy debris moves inexorably down to the creek. Any bad chemicals leach into the groundwater, and the disturbed soil accelerates the slope erosion. Some kinds of debris will travel down the creek and form blockages that thwart the salmon. Geez, Dave, I said I wouldn't do it.

Bryan Fowler, Zipper Geo, center

The drilling was actually pretty noisy for a couple of hours. I saw Zoe and her kids watching from across the street as the rig came off the truck, so I went over and apologized for the noise. I told her I would like to show her and her husband some plans when the design is further along.

The end result of the drilling, by the way, was a set of baggies of soil taken at various depths. They said they would go 15 to 20 feet down; the report will show the actual depth. Bryan said that some of the soil samples would be further tested. Dave promised to get back to me with an estimated report completion date on Monday (4/13) and I reminded him that we had kind of said no later than 4/28. He seemed confident.

John Zehren
At 3:00 pm, Arborist John Zehren (Renaissance Tree Care) came by and spent time walking the property with me. He identified the small tree on the west side as a Dogwood (he didn't say, but I'm guessing Cornus florida) and the ornamental outside BR 1 as an Asian Pear (Pyrus sinensis) that will bear fruit. I asked him about moving the palm and he said it's easy because the root ball can be very small. You only have to protect the top, he said, but the tree is very heavy.

He was impressed by the Douglas Fir with the swooping trunk at the driveway. He wants me to remove the asphaltic concrete touching the bark at the south side, but he didn't like the idea of removing and replacing the entire driveway because it will expose the roots to damage. He thinks I should carefully cut out bumps caused by roots and fill the holes with gravel. We agreed that it's a special tree that deserves special treatment, but I'm not keen on gravel patches. He showed me that the bark on the east (sloping) side is finer grained than around the other sides--that indicates recent growth; the tree is compensating for its skewed base.

He agreed that the cedar drooping on the garage roof is a priority, and he used a laser pointer to show me the 3 or 4 limbs that he would cut. There's a limb from this tree drooping onto Rob's property next door, but we agreed we'd wait until someone complains.

In the back yard, John zeroed in on the cedar at the middle of the property. I told him I've seen squirrels going into it and he was concerned that the hollowness might be extensive. He noticed that someone has trimmed and topped it--it's not as tall as it should be. Nothing to do now, but be watchful, he said. Again, the bark and a bulge at the base suggests that the tree is working to give itself a better foundation. "The tree is aware of the damage and is putting its energy into repair," John said, paraphrasing.

Another thing Dave Williams of Zipper Geo mentioned was that there are no evergreen trees on the steep slope. That's a sign that the slope is moving--eroding, I guess--in geologic, or centuries, time. True, John said, but the trees are phototropic--growing straight up to the sun--as opposed to geotropic--growing perpendicular to the slope. If they were geotropic, it would indicate that the soil was more migratory.

I asked John to come back and trim the cedar and we agreed on Tuesday, 5/26. He's booked, and I'm not in a hurry. He gave me a price for other work, but I think I should wait to see his work on the cedar and get past the worst of the construction. As he left, he had one more piece of advice: When it's snowing, or the wind is blowing real good, just don't go outside, period. And don't park a car under the fir or cedar. Just don't. He was serious.

Structural Engineers
I contacted Michael Chamberlain (Strong Work Structural Engineering), who is too busy to meet this week, but he was chatty by email. He wrote:

For a roof garden, spanning 14 ft, a good option, if you can spare the roof depth, would be pre-manufacturer 2x trusses. I would guess that they might be about 18" deep. Although, I guess the first question is how much load are we talking? 3" of soil (green roof)? 6"? Big trees? Planters? 

Also, with a heavy roof, seismic bracing will be required.... meaning a seismic retrofit of the walls of the room below....or alternatively, the exterior walls of the floor below.
If the walls of that room are really tall, 10 ft plus, then you may need to go to 2x8 studs.

I replied 4" of soil, and he said "For those loads, you could also use 11-7/8" i-joists or 2x14's."

I also contacted John Apolis (CSES), who was slower to respond, but who can see me sooner. Mr. Apolis said "You can certainly come into the office with a set of plans and we can go over them, I’ll make suggestions or provide options, etc. Any meeting longer than about 15 minutes is billable, with a one hour minimum ($160). We can go through a lot of material in an hour. If you want to send PDFs of your plans, I can provide a fee proposal for the structural design." (I suspect I like someone with a Greek name because of Joe Apollonio, the expert engineer in Mr. Blandings Builds His Dream House (1948)--"See what she leans?")

So, thanks to various experts and engineers, it's been a productive week.