Geomechanical Musings

This is the right way to dig a hole

The best children’s story is Mike Mulligan and his Steam Shovel. About this there can be no debate. It was my favorite story growing up, and it remains pertinent to my work today. You dads and moms can get a copy here: Mike Mulligan and Mary Anne

You’re welcome.

This is Mary Anne’s grandchild

It’s about a hardworking owner-operator named Mike, his stalwart coal-fired excavator Mary Anne, and how together they navigate the difficult transition from steam to hydraulic power in the North American construction industry. There’s a heartwarming ending. I won’t spoil it for you.

Pertinent today is the way that Mike and Mary Anne dig a hole: neat and square. At each stage the hole is manifestly neat and square. When they finish, you guessed it, the hole is neat and square. The book doesn’t emphasize excavation techniques; it’s not a trenching manual. Neat and square is just how Mike, an operator so skilled they wrote a book about him, digs a hole. If you’re not digging like Mike and Mary Anne, you’re probably digging wrong. Read by my parents with great enthusiasm, this story taught 4-year old me the two most important characteristics of an excavation:

  1. Neat
  2. Square.

I have time to write these thoughts on a Friday afternoon as the crew works diligently to wrap up a shoring submittal for a hole that is not square. Not by a long shot. It’s not pear-shaped or anything; but it zig-zags all over Honolulu through some comically soft ground. There are odd-angled corners. Several of them.

The reason that we’re struggling to wrap up the design is because I failed to insist that we dig like Mike. The Contractor, a highly experienced excavator, prefers long stretches of braced sheetpiles with open corners that allow in-trench pipe fusing. The the shoring has angles that are measured in 32nds of a circle. It is not at all square, and our bracing design are far from neat. The level of effort has more than doubled.

To avoid suffering similar difficulties, I encourage you all to stay true to the example of Mike and Mary Anne, a lesson so important that every right-thinking parent reads it over and over again to their budding young engineer-children. Dig your excavations neat and square. Your shoring designs will go smoothly, and your Friday afternoons will be greatly improved.

The Atlas Geotechnical crew is privileged to work all over the world, collaborating with squared-away engineers of varied backgrounds and sharing stories that range from tall tales to practical advice.

I’ve learned that every community includes at least a little folklore in how they design and build. Always there is some inexplicable local practice, unique to the area and unknown elsewhere, that designers, regulators, and builders all assert is necessary to project success.

A fairy tale is created when the lesson learned from a real experience, over time, becomes disassociated with its context and starts being applied to all projects. What started as sound practice turns into a guiding fable that, more often than not, just adds cost and difficulty without any benefit.

As an example: “House your family in the sturdiest structure you can afford” becomes, over time, “don’t build a house out of straw because a wolf will come and huff and puff and blow it down.” Practical advice. Brick houses are better against wolf-blowing and also generally. But if all you have is straw, and you’re a professional engineer, maybe your best course of action is to engineer a wolf-proof straw bunker.

Vibratory Pile Hammers: On Oahu in the early 1980’s a contractor was extracting timber piles from the sand backfill of a closed wharf, some of which were near the sheetpile quaywall. A few interlocks had separated below the waterline. Of course vibrating the sand flows it out the defective interlocks. Subsidence broke the wharf; it was a legitimate problem. Instead of learning to inspect interlocks before extracting waterfront piles, the Owner invented a myth that vibratory hammers are dangerous and shall not be used. Henceforth all piles, including sheetpiles, are driven with impact hammers. Far far away from the water, on different islands, specifications prohibit vibratory hammers. This Owner is influential; engineers accept that vibratory hammers are dangerous and ban them from all of their projects, not just their wharf projects. It would be a charming superstition if it weren’t so costly. Vibratory hammers have been proscribed for nearly 30 years. The engineer who made the rule nears retirement. It may take another 30 years for the fable to fade into distant memory and for Engineering once again to prevail in Honolulu.

Scarify and Recompact: In San Diego and parts of southern California, all earthwork begins (after stripping) by removing 6″ of soil, moisture conditioning, and rolling it back down as fill. Maybe at a few sites this upper soil might have been compressible, in which case for heaven’s sake perform remedial grading and make it suitable. But blindly converting 6″ of competent semi-formational flat ground into fill just increases your fill thickness. It is equally effective as stepping over the sidewalk cracks while walking home from school. Upon arriving you find that your mother’s back is, in fact, not broken. Maybe your superstition works; maybe you just walked home funny.

Detensioning Tiebacks: At this year’s Spring Seminar in Seattle an engineer asked a panel of experts “why does the City require detensioning tiebacks?” Two panelists offered straightforward answers: (1) “that started before I took over administering the rules,” and (2) “yeah, we’ve been trying to get that requirement dropped for years now, despite running full-scale demonstrations.” One senior community member shared a story from the ’80’s about a bar tieback that got broken and jumped part-way out of its hole. A close call, sure, but how does that experience relate to strand tiebacks with heads confined by a cast basement wall? Folklore. An irrelevant cautionary tale, pure and simple. That community has recognized it and, over time, will dispel the local myth that tieback strands are unreasonably dangerous.

So here’s the question: What folklore have you incorporated into your practice? I promise you there’s some nugget of superstition in your reports and designs that your peers in other regions would struggle to understand. Do you test micropiles using an ASTM setup instead of PTI? Do you insist that only your techs are capable of performing quality assurance testing? Require 6″ of compacted crushed rock beneath footings even in dry weather?

I don’t advocate that we expunge all local traditions from our work. Consider, though, examining your practices, understanding the origins of your folklore, and retaining just the beneficial parts. The practice of engineering evolves constantly through the work of our whole community. The generational shift currently in process is our opportunity to improve our practices and better serve our communities.

We’ve got a particularly interesting problem on our desks here at Atlas Geotechnical. There’s a lot at risk, various stakeholders are frustrated with and suspicious of each other, and there’s not enough time. While working this problem through to a pretty tidy conclusion this afternoon, it occurred to me to share the process that we use to achieve a safe, efficient design.

It goes without saying that rigorous project framing is critical to any problem. Define the boundary limits and success factors. Write, refine, and document the basis of design. There’s no point in working really hard late into the night when you haven’t defined the problem you’re trying to solve.

Even when the project is framed and bounded correctly, the juiciest problems always offer sticking points; places where the natural tension between resources, budget, and performance simply don’t allow a path forward. When I get stuck at one of those obstacles, these are the techniques (in order) that I use to crack it:

  • Collect More Data: Usually when moving quickly through a conceptual design you adopt conservative and simplifying assumptions about important parameters. The best way to solve a problem is to collect real data and refine the assumed parameters. This is the most self-contained and linear problem solving technique.
  • Challenge Your Assumptions: Sometimes you’re limiting yourself. A classic is that soils are normally consolidated, when really there’s a desiccated crust and settlement will be less. The always-dependable Mohr-Coulomb constitutive model is another bountiful source of limiting assumptions embedded in our most useful analytical tools. Engineers in my office call this “doing it the hard way” but if it solves the problem, and nothing else would, how hard was it, really?
  • Push Back on External Constraints: This one is particularly effective here at Atlas, but you need to understand the discipline that you’re challenging along with the hopes and dreams (and fears) of the team member who imposed the limit. Someone tells you that you can’t drill through a pilecap? Can’t tolerate more than an inch of differential settlement? Can’t pump more than 150 gpm? Discover the simplifying assumptions embedded in that limit; perform Steps 1 and 2 on someone else’s work, and find a way to preserve project performance without complying with a simplistic limit.
  • Call a Friend: I can’t tell you the number of times that this one has saved my bacon. If I weren’t so proud it would be higher on my list. Clever engineers have been solving problems for millennia; one of my friends has, almost certainly, previously solved the problem that has puzzled me for an afternoon. This one can be humbling; try to be gracious. The corollary to this technique is “try to have clever friends.” I’m good friends with several old guys who’ve been everywhere, done everything, and shoots do they ever help me crack troublesome problems
  • Hold a Meeting: Just kidding. Meetings never solve problems.
  • Get Away from the Problem: Irv Olsen used to go see a movie; one of my best friends, an astonishingly effective engineer, hikes like a maniac; I thought up this post while swimming laps. You serve your clients best when you’re thinking creatively and clearly. Don’t stay at your desk putting on a show of hard work when really you should stretch your legs, clear your mind, and actually perform engineering. Sure, you’ll need to start again with Step 1 once you’ve blown the cobwebs out, but you already got down to this last step once without solving the problem, so what other choice do you have?

I’m considering distributing laminated cards to the younger engineers here at Atlas outlining these four steps. That or hardhat stickers.

While not a panacea, I’ve found that there are very few intractable problems when clever engineers, given a clear mandate through good project framing, apply themselves vigorously and enthusiastically.

It’s really not important what this is or what it does. The point is that every step of planning, design, and implementation happened in the correct order.

One of our projects achieved a significant milestone on Friday, exactly according to plan. Like most of our projects, it’s interesting construction at a unique site, and there’s no similar recent project to guide design and construction.

We learned recently that the shoring design failed to address a subtle but important detail. Once it was identified, though, it didn’t take long for the team to embrace the need for a rapidly field-engineered solution. Thankfully, strong relationships allowed us to add a ringer of a Structural Engineer to round out our already very strong team. They responded to our design requirements with an absolutely gorgeous 2-sheet drawing package in less than 3 days. We could not have met our deadline without their contribution.

Just because the work was installed before the deadline doesn’t mean that everything went smoothly. Atlas still have equipment stuck in Customs Purgatory at the Canadian border. I dearly hope to receive my 25 ton hydraulic ram back. Collaboration within the team, though, went flawlessly. The crew were able to source replacement equipment and keep us on schedule.

The point of this post is not that we made a pair of little gizmos and installed them in the nick of time, or that our clever little solution avoided a 6-month project delay. The takeaway from this project is that we achieved success using the exact same process that we use to succeed on huge projects. This one was just distilled down to a very compressed timeframe and had no schedule allowance for mis-steps. Every element of a big complicated design was executed on this small complicated one, just really fast and with intense coordination.

  • The project manager established clear lines of responsibility.
  • We wrote up a basis of design and stuck to it.
  • We established concise performance expectations.
  • We sourced locally available materials.
  • We identified a need for and hired specialty expertise.
  • The structural engineer adapted the design on the fly, and
  • The team assured quality.

The design and execution procedure was exactly identical to one used on a much larger project; we just moved through it in 5 days instead of five months or five years.

I feel grateful to be working with such a competent and diverse team on this large, visible, terrifically interesting project. Our project manager gave us about a week to recover, perform maintenance, etc, and then we tackle the next of the three remaining big problems. With the team we’ve assembled I have no doubt we’ll resolve them all with style and grace.

Classic art for a classic management problem

2019 started strongly here at Atlas Geotechnical, but almost immediately we found ourselves overwhelmed re-working problems that we thought we had solved. And that re-work distracted us from other commitments, to the point where we nearly landed on one of our project’s critical paths. And of course when we’re working faster than we should small details don’t get checked, like the PE expiration date on a permit drawing, causing more re-work. As soon as we frantically cut off one head, another grows in its place and the project continues to disrupt our workflow. Rinse and repeat. The past 4 weeks have been tough.

It’s increasingly obvious that the problem is not a phase. We’ll never just “get through this;” our workflow is not going to smooth itself out. Something that we are doing, or not doing, in how we approach these fast-paced, complicated problems is preventing solved issues from staying solved. We need to conduct ourselves differently if we want to achieve better outcomes.

Atlas takes on complicated projects. It’s unavoidable that we start our work while data are being collected, and sometimes it’s unavoidable that our partially-complete engineering needs to be set aside in favor of new strategies. Sometimes. Sometimes it’s unavoidable, not always. I’ve noticed that almost all of our frustrating projects never had a credible plan to begin with. We’re re-designing because the initial concept was not fully planned out. “Ready, fire, aim” is not the way to solve complicated problems.

Better, more thorough up-front planning is how we’re going to improve subsequent engineering so that solved issues stay solved, so that the cut-off heads stop growing back and fighting us while we’re trying to do other work.

The oil-and-gas industry, who build some of the most complicated infrastructure in the world, uses an explicit engineering process called Front End Engineering Design (FEED). We’ve participated in a few FEED studies and have seen how investing in up-front planning yields overall cost and schedule savings. Researchers at Delft Technical University wrote up a really excellent overview:

So, we’re going to make an effort to adapt FEED practices to our more interesting projects.

  • We’ll assign ourselves more responsibility in the up-front work.
  • We’re going to exert more leadership over conceptual designs and means-and-methods choices.
  • We’ll host charettes, brainstorming sessions that include the full spectrum of stakeholders and subject matter experts.
  • We’re going to identify the likely problems before our customers order materials and mobilize equipment.

And if we’re successful, our first-try engineering solutions are going to stick and our fallback positions are going to deploy smoothly. We’re going to make a proper plan for killing the hydra all at once so we can stop frantically hacking at solutions during construction.

Look for an update in July for how things are turning out.