Geomechanical Musings

Earth processes are inexorable. Erosion, landslides, littoral movement, stream channel meandering, wetland formation, and habitat changes are all unavoidable. This is not new information, nor is just knowing it can’t be avoided particularly useful from an engineering perspective. These types of long-duration changes seem to conflict with a natural human trait of assigning permanence to conditions as they are first encountered. The way that a site looks on the day you take possession, either for development or habitat management, is somehow logged in our minds as the “correct” of “natural” site condition, rather than just the temporary status of an evolving landscape.

Midway Aerial

The most interesting example in my career is a habitat issue, not a terrain change, that involved pushing back against natural vegetation changes at Midway Atoll National Wildlife Refuge. My customer managed the remote island to maximize Laysan Albatross habitat.  You can guess from the name, the birds used to be most closely associated with Laysan Atoll, not Midway.  But as soon as the Navy built and maintained a big wide golf course at the Naval Air Station in support of the Korean War efforts, they created perfect nesting habitat for the graceful and endangered seabird.

Adult gooneybirds have a 7-foot wingspan and are basically unable to fly through or land between brush and trees. Nesting area, critical for the species, had to be almost dead flat and free of obstacles. Like a golf course or a parade ground or the lawn in front of the base commander’s office. You get the idea. So for 35 or 40 years the Navy put energy into maintaining the open areas on the atoll, pushing back the ironwood trees and invasive shrubs from the middle of the island, and the Laysan Albatross thrived as a corollary benefit.

When the Navy closed the base at Midway, they took with them their landscape maintenance crews along with their submarines and radar surveillance aircraft. Without the external energy infusion directed toward removing vegetation, the meadow-like lawns were able to resume a natural transformation from meadow to forest, to the detriment of Laysan albatross nesting habitat.

The Fish and Wildlife Service knew well enough that it would happen, but the level of effort was more than they were prepared to invest. When we managed the island we mowed, pulled brush, and cut trees constantly, devoting whatever resources we could make available in between solving serious infrastructure problems. FWS continues to do good work at Midway, though there is something ironic about how a Federal habitat agency invests such huge resources, essentially without end, preventing a natural landscape process in order to preserve habitat that was created, inadvertently, by a Korean War-era base commander enthusiastic about golf.

Laysan Albatross chicks at Midway NWR. The 7-foot wingspan of these majestic seabirds prevents them from nesting in the trees.

Laysan Albatross chicks at Midway NWR. The 7-foot wingspan of these majestic seabirds makes them graceless on land, earning them their “gooneybird” nickname and also preventing them from nesting in the trees that, without significant effort, will spread out into the lawns.

We are on the defense side of two dispute resolution efforts that have a similar component. In both cases the landowner cites some prior condition of their land as the way that it “should” be, and claims that actions taken or not taken by my client caused their land to deviate from the acceptable initial condition. Both landowners, coincidentally, have chosen the time with the most advantageous site condition as the “correct” time, and are not particularly interested in hearing about how their sites looked before all the work was done to bring them into that erroneously “natural” initial condition.

Surveying the revetment elevation at Majuro International Airport


I would imagine that you can see the extension of this “permanence thinking”  to the much more significant issue of sea level rise.  Sea levels have fluctuated by hundreds of feet in the geologic past, shaping coastal terrains with terraces and submerged valleys. The geologic record indicates that sea level rise is inevitable, but slower seems to be better for cities established near the water. Artificial influence on a dynamic system is much more difficult to evaluate than if the sea were completely static, a fact not at all lost on groups who benefit from denying the collected evidence and delaying the start of necessary mitigating actions. To consider the sea level at some time, say 1929, as the “correct” sea level is just as pointless as assuming that the vegetation or stream channel location on a site has somehow always been the same.

It’s much more complicated to consider transient conditions on sites in an engineering design. We drill borings to separate recent grading and fills from natural soil deposits and rock formation, and then handle the two types of materials separately. We simplify groundwater fluctuations by assigning a static, conservatively high, level. I’ve only worked on one project where we timed tasks to coincide with low tides. Sea level rise was also assigned a static level in our revetment projects in the Marshall Islands. Erosion, habitat growth and transformation, and similar longer-period fluctuations are not commonly considered. I am curious how long-lifespan infrastructure like roads and ports might benefit from explicitly considering terrain changes over the service life.

Have a great weekend, everyone.

sunset

Sunset at North Beach, Midway Atoll NWR

 

 

Good friend and Atlas mentor Gary Lee shared this traditional piledriving method with us:

I can’t tell which I like better:

1.  The tambourine used to set the cadence, or
2.  How the penetration rate increased when that last guy jumps up to increase the effective ram weight, or
3.  How the whole human hammer system knew when the pile had reached the design tip elevation.

Because I’m an irredeemable nerd, I estimated the hammer energy like this:

6 guys x 65 kg/guy x 9.81 N/kg x 0.1 m stroke = 382 N/blow

A western interpretation of a small piledriving arrangement.That’s tiny. Absolutely miniscule. It’s about 2% of the smallest diesel hammer that Delmag can supply.  And it got the job done.  Sure, the piles are 80 mm square and are probably reaching a hard bearing layer, and it looks like there several per column.  But that’s exactly the point: compatibility. The site and the foundation and the column loads and the available construction equipment are all compatible, part of a system that is getting the job done.

1.0 m stroke drop hammer with HP14 cap

It reminded me of MacDow’s (http://www.macdow.com.au/) choice to use a drop hammer instead of a modern hydraulic hammer to drive some bridge abutment piles in American Samoa. Simpler definitely is better when working far from a source of spare parts. The drop hammer was slow.  There were some frustrating days.  And it got the job done at a difficult remote site.

This is a project where the design team wasn’t allowed the option of offering a locally compatible design. The funding agency for the bridge insisted that the design comply with North American design standards, which assume essentially unlimited access to the most modern construction equipment in the world. And it was MacDow’s clever and diligent engineers that translated the design, as best could be managed, back to something locally compatible. They used an ancient technology, basically one step up from the “six guys and a tambourine” method, to bridge the gap between our developed-world pile bearing requirements and the actual site location.

The lesson here, the one that amazes me with its rich complexity, is that local engineers and builders already have a compatible system that includes architecture, building materials, construction systems, and life cycle maintenance. Our projects are best when they leverage, rather than supplant, these existing systems. Just because you don’t see a pile hammer on the island, for example, don’t assume that the local builders can’t drive piles to put a building on a soft site. Consider, at least as an alternative, aligning your designs with the local system rather than assuming the project needs you to import a crane, a pile hammer, skilled technicians, and the full logistics train stretching back to New Zealand to build something that, while better or safer, has not been necessary in the community up to the moment you got your contract.

I had an excellent day yesterday, and not just because my lunchtime presentation was pretty well received.  For those of you with interest, here’s a SlideShare link to the slides.

Putting the Civil in Civilization

Fair warning:  I asked Keynote to print all of the builds, and apparently I use a lot of builds in my slides, so you’ll be better off buzzing through them like an animated flip-book.  Also it seems like the best point were made verbally, with just a photo in the background for context.  I’ll link to the NextSpace YouTube channel when the video is posted.

The highlight of the day was visiting afterward with friends Michael Meyer and the Cosmic Crew. (http://designbycosmic.com/culture/)  Spirited conversation with insightful people is sometimes too rare for those of us who work mainly alone. It was a delightful change to hang out in the Cosmic studio with the rollup door open, talk design philosophy and how good architecture fosters creativity, and then walk down the block for excellent beer and conversation.

I’m fortunate to have found such a vibrant community here in Santa Cruz, including the cooltech geniuses at NextSpace, old friends from school days, and new friends who intrinsically understand the Atlas approach to delivering engineering services.

 

images Our life is frittered away by detail. Simplify, simplify, simplify! I say, let your affairs be as two or three, and not a hundred or a thousand; instead of a million count half a dozen, and keep your accounts on your thumb-nail.

Recently I’ve had a couple of interesting experiences simplifying technical topics for lay audiences. One for trial testimony and the other for a TED-style talk that I’m giving in a couple of weeks. Both require me to explain myself to an audience that lacks even the most basic understanding of soil mechanics.

The whole purpose of making presentations is for people to understand your point. But when you lack a common frame of reference, it falls to the presenter to adjust and create one.

Testimony this afternoon went well enough; I could tell that the jury was understanding what I was trying to explain. Apparently I succeeded in not frittering their afternoon away on detail. That’s mainly because I made only 2 or 3 points, not a hundred or a thousand.  I think that Mr. Thoreau’s advice is exactly right.

I’m hopeful that by the time my next talk comes up, with another lay audience even less informed about my topic, that I’ll be able to simplify all of the thousands of affairs that affect municipal infrastructure down to 2 or 3, and fit the point of my presentation on my thumbnail.


Logo

There are no new refineries.  Not in the continental US, anyway. So when you get a project in a refinery, it means you’ll be standing in the shadow of the Masters, the guys who figured consolidation rates with log paper and a sliderule. An observant engineer can learn a lot.

I told the plant engineer where I needed data, knowing that they would have borings right where I needed them. It’s a refinery. All refineries have a plethora of borings.  Not knowing who would be combing through the dusty tomes I described all the best features of the classic old reports. Thick.  It’s gotta be thick. And comb-bound with craft paper covers, ideally with a cut-out window.Maybe onionskin paper but likely not, as you didn’t send opnionskins to the customer, but rather kept them for your own files. At the Port of Oakland one time I saw a multi-volume report bound with twine. Possibly that would be too much to hope for.

And of course they had exactly the report that we needed, and it looked exactly like I expected (though not bound with twine). I could smell the dusty pages even though I was scanning through a PDF.  The report was not particularly old, not truly “golden age” vintage, because we are working in Unit 2. The classic site characterization would have been done for Unit one probably right after WWII.  Even still, the late 1960’s were a great time to be a foundation engineer, lots of borings but modern samplers, still lots of budget for laboratory tests including time-rate consols.  And the report, as you would expect, is a treasure trove of solid information that was useful then and is just as useful now. It also has the quirky old stuff that you just don’t see anymore. Hand-drafted figures showing settlement rate predictions. Sketches showing the failure mode of triaxial tests. Consolidation tests plotted using void ratio instead of strain.  Good times.

I wasn’t familiar with the company that wrote the report, and I was curious to learn more.  They’re named after an individual, the same as all the great firms from that era, and they proclaim their founding date right in their logo.  Tragically, the briefest research revealed that they had been gobbled up like most of the grand old consultancies. They gave up their brand in 2011, having done business for 90 consecutive years under the founder’s name. The shop only existed for me, though, for less than an hour.  I didn’t know of them at all (though I knew their type), then I learned of them and admired their work, and then I learned that they had been agglomerated by one of the big generic testing companies that, honestly, makes a lot of good work for us here at Atlas.

It’s inspiring at the same time as it’s disappointing, appreciating their contribution to the practice of foundation engineering even after the company has run it’s course. As I do my little project in the refinery, enjoying the view from the shoulders of an extinct giant of a firm, it’s important to remember that some day my small contribution may be passed on to the next engineers working on the next refinery improvement project. In 50 years their report aged from cutting edge to quaint without losing any of its usefulness. Our reports may likely be the only tangible reminder that we were careful and innovative and did good work, and we should bear that in mind as we write and deliver our reports..

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