Anchoring the World’s Longest Floating Bridge

SR520 Bridge

Photo: WSDOT

 

You’re at the bottom of Lake Washington, 200 feet underwater. It’s flat as a pancake here, but the first 50 feet of soil is diatomaceous silt and clay, which is unspeakably unstable. Think microscopic glass Christmas tree ornaments with the consistency of chocolate mousse. Below that is 50 feet of very-soft clay (zero blowcount, to those in-the-know).

Try, just try, to anchor the new SR 520 Bridge in this chocolate mousse (remember, it’s a floating bridge that can’t be left to drift off to Renton or points unknown). And just for good measure, make each of the 58 anchors able to resist a horizontal load of 600 tons—four times what was needed for the old bridge.

Figure out that you’ll need three types of anchors. In areas along the side slopes, where the water is shallower and has competent soil, use a gravity anchor, but call it a box of rocks amongst your workmates.  Build it like a heavily reinforced concrete egg carton with only four compartments. Joke about the kind of eggs that would fit into a 40 foot by 40 foot by 23 foot carton.  Build them on a barge at the concrete plant in Kenmore at the north end of the lake.  Make them so heavy that that the only derrick large enough to lift one is too big to fit through the Ballard Locks. Tow the gravity anchors through the Ballard locks, though they barely fit, while the public looks on in astonishment.

Gravity anchor

Gravity Anchor on its way to the SR 520 Bridge site. Photo: Kiewit

Flood the 440-ton floating boxes with water to make them sink. Lower them to the lake-bottom and place them on a leveled-out gravel pad. Fill each of them with 1,700 tons of rock to make them heavy enough for lateral frictional resistance, or so they won’t budge.

Don’t stop there. Use a second type of anchor, a drilled shaft, along the shoreline where the lake is shallow enough that the box of rocks would have caused havoc as a navigational hazard. Make them ten feet in diameter and 100 feet tall, not as tall as the original Godzilla, but close enough.

Drilled Shaft

Ten-story-deep drilled shaft anchor. Image: KPFF Consulting Engineers

Then, use fluke anchors, the most technically challenging anchor, for the majority of the project. Make these fluke anchors from reinforced concrete plates three feet by 35 feet wide by 26 feet tall. Cast a steel tetrapod into the side so that the anchor cables can be attached to the I-bar at the end of the tetrapod. Explain that a “tetrapod” is a four-sided shape with triangular faces (not to be confused with a four-limbed vertebrate).

Fluke Anchor

Fluke anchor being jetted into the bottom of Lake Washington. Image: KPFF Consulting Engineers

Place the fluke anchors in a steel frame equipped with water jet tubes to drive them into the mud. Because the mud is chocolate mousse, place mounds of rock above and beside the fluke anchors. And then more rock. And then more rock. Good, that’s enough.

Now, celebrate. The Washington State Department of Transportation’s grand opening of the longest floating bridge in the world will be April 2 and 3, 2016. You can run, bike, or possibly meander across the bridge. Hopefully there will be food. You’re hungry after all that work.

Hart Crowser was the geotechnical engineer-of-record for the anchors for the new SR 520 Bridge. The design-build contractor was a joint venture of Kiewit/General/Manson. The structural engineer was KPFF Consulting Engineers.

Need more detail? Read the technical paper Geotechnical Design: Deep Water Pontoon Mooring Anchors or contact Garry Horvitz, PE, LEG, at garry.horvitz@hartcrowser.com

Fluke anchors on barge

Fluke anchors on barge.

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Why an Earthquake Warning System Should Not Be a Priority In The Pacific Northwest

Earthquake_damage_Cadillac_Hotel,_2001_SmallerThe newest and hottest topics when it comes to disaster discussions in Oregon and Washington, as well as on the national level, are an earthquake warning system and earthquake prediction possibilities. They are the new obsession that has come on the heels of the New Yorker articles this summer. While we don’t object to advancing both of these methods to better warn of impending quakes and hopefully save lives, we do think that the discussion is premature, especially here in the northwest.

The first reason is that an earthquake warning system like that in Japan has to be implemented only with a comprehensive, aggressive, and continuous public education program. Without a full understanding of what you should do when your phone emits an ear piercing shriek warning of impending shaking, we risk even greater panic and possibly more casualties. Running out of buildings with unreinforced masonry or weak facades just before the shaking could put people at more risk of falling hazards outside of the buildings. It could also cause major traffic hazards as drivers try desperately to get across or get off bridges and overpasses. Unless we develop a much better awareness of what the public should do when they receive the warning, it may cause more problems than it solves.

But the real issue is that these technologies are acting as the bright shiny objects that are distracting all of us, from the public to the president, from the real issue: our infrastructure is in dire need of upgrades not only to prevent casualties, but also to encourage long term recovery.  We doubt 30 seconds of warning will seem as beneficial when the public doesn’t have wastewater for one to three years.  Further, a warning system that stops surgery or an elevator is not as important as making sure that the hospital or building itself is designed to withstand shaking. Especially in Oregon and Washington, all of our energy and funds need to be focused first on comprehensive and intelligent infrastructure improvements that increase our community resilience. And that needs to happen as quickly as possible. We implore you not to follow the flashing light! Urge our government to focus on the real issues, and encourage your colleagues and neighbors to personally prepare.

For more information contact Allison Pyrch at (360) 816-7398 or Allison.pyrch@hartcrowser.com

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Invasions are not just military (Part 2)

 

Butterfly Bush

Butterfly bushes displace native vegetation and in spite of the name, negatively affect native butterflies. We didn’t have to go far to take this photo.

In a previous post about invasive species, we learned what invasion meant and who the invaders look like. Now let’s discuss how invasive species get a foot hold in the first place and what can be done about it.

How Invasions Happen

Invasive species can be introduced intentionally or unintentionally. They may be introduced intentionally to benefit the ecosystem by restoring habitat, increasing fish stock, or controlling pests. Unintentionally, they:

  • Are released in ship ballast;
  • Escape from fish farms;
  • Are used in recreational activities;
  • Are used as live bait;
  • Arrive through canals;
  • Are released/escape from aquariums;
  • Are used in unauthorized fish stocking; and
  • Can be introduced by many other means.

In order to successfully invade a new environment, certain biological characteristics are necessary. Many invasive species have high reproduction rates, short generations, long life, high dispersal rates, broad native range, and broad diet. However, not all species immediately survive in new environments. They can fail multiple times before flourishing. Invasion success is context dependent.

Controlling the Invasion

Strategies to control invasive species include (1) keeping potential invaders out, (2) eradicating potential invaders soon after invasion, (3) biological control, (4) chemical control, and (5) mechanical control.

Keeping potential invaders out

Keeping potentially damaging invaders out in the first place is the most cost-effective method. The danger can be reduced by monitoring the common invasion pathways such as ship ballast water, wooden packing material, and horticultural plants.

 Eradicating after Invasion

It is easier to eradicate invasive species if they are discovered quickly and population levels remain low. Even if it proves impossible to totally eliminate an invader, early intervention can keep the population at acceptably low levels. For example, Giant African Snails were effectively eliminated from Florida. Currently researchers in California are attempting to eradicate the marine green alga Caulerpa, a recent invader.

Biological Control

Biological control involves introducing an enemy of an invasive plant (for example, a disease, parasite, predator, or competitor) in an attempt to lower invader population size.

Sometimes introducing a natural enemy from the native range of the introduced pest can be effective. For example, prickly pear cactus, which invaded Australia from the Americas, has been effectively controlled by introducing a moth from South America whose caterpillar feeds on the cactus. In other cases finding an enemy from a different area (a novel association) works because the invader may not have evolved defenses to a species with which it has never been in contact. For example, a virus from South America has been used to control European Rabbits in Australia.

A disadvantage of biological control is that some agents attack nontarget species, becoming noxious invaders themselves, and it is very difficult to remove a troublesome introduced natural enemy once it is established.

Chemical Control

Although chemical pesticides can effectively control some species (for example, water hyacinth in Florida), it can have problems. Pesticides may affect non target species, can be expensive, and may only be effective for a limited time if pests evolve resistance.

Mechanical Control

Mechanical control involves using machinery or human effort to remove invaders, often manually. Mechanical control has been an effective control strategy for invasive Tamarix (arid climate adapted shrub) in the Southwestern United States. Volunteer convict labor has been used in Florida to cut paperbark trees and in Kentucky to rip out Eurasian musk thistle.

Ecosystem Management

The newest technology for managing invaders is ecosystem management, in which the entire ecosystem is subject to a regular treatment (such as a simulated natural fire regime) that tends to favor adapted native species over most exotic invaders. Because it is so new, the specific ways in which ecosystem management can be employed must be determined in each type of habitat.

Want to learn more?

Invasive species are everyone’s problem. Learn more about what you can do to help prevent them:

Washington Invasive Species Council

Washington Department of Fish and Wildlife Aquatic Invasive Species

US Department of Agriculture, Invasive Species State by State

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How Many Soil Borings Do Development Sites Need?

One of the challenges that developers – both public and private – face from a geotechnical and environmental standpoint is the inherent uncertainty in what’s underground at the development site. Generally, we’d like to know the geologic layers, soil types, groundwater levels and potential environmental contaminants across a site. But trying to characterize a fairly large volume of soil with just a few pieces of information inevitably leaves knowledge gaps.

An illustration for this challenge comes from an unexpected source – a children’s book. “Sam & Dave Dig a Hole,” written by Mac Barnett and illustrated by Jon Klassen, is a funny, deadpan story about two boys (and a dog) who dig a hole, hoping to find “something spectacular” (website here). 

Sam and Dave Dig a Hole

Photos courtesy of Mac Barnett and Jon Klassen

As the boys dig through the ground, they come close to, but never discover, several spectacular gems.

Sam and Dave miss the gem

In fact, they seem to navigate around everything spectacular.

Sam and Dave digging around the gem

While the book is an admittedly whimsical analogy to geotechnical and environmental subsurface exploration, it actually serves to illustrate an important point – there may be more beneath the surface of a site than a couple of borings will indicate. Skimping on borings increases the chances that zones of contamination or soft soils, may be missed, only to be discovered during or after construction. More borings can help fill in gaps and increase confidence that the site has been well-characterized. In many cases, spending bit more money on site exploration may reduce overall project costs by reducing uncertainty about the site and what may be encountered during construction. And depending on project needs and site conditions, the use of less conventional site investigation methods (Cone Penetration Test, strataprobe) may be appropriate. These can often provide better spatial coverage at similar costs to traditional Standard Penetration Test borings, because they’re cheaper. 

Of course, there’s no one-size-fits-all approach to subsurface exploration. The best exploration program for a project will balance project needs, budget, and local experience with geologic conditions. But in order to minimize the chances of pulling a Sam and Dave, maximizing spatial coverage in the explorations program should be a consideration.

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Invasions Are Not Just Military

Atlantic Salmon

Atlantic Salmon. Photo: Maine Atlantic Salmon Commission

One of the most destructive forces on an ecosystem is a non-native species with no natural predators or other natural controls. These species can overtake their new home in an extraordinarily short period of time by multiplying, consuming prey, and colonizing, crowding out essential local species.

An invasive species is an organism (plant, animal, fungus, or microbe) that is not only foreign to a specific area or habitat but also has negative effects on its new environment and, eventually, on our economy, our environment, or our health. Not all introduced species are invasive; the distinction is how aggressively they interact with their new surroundings.

Why we Care

Invasive species are the second greatest threat to biodiversity (the first is habitat loss). Almost half of the species at risk of extinction in the United States are endangered directly due to the introduction of non-native species alone, or because of its impact combined with other processes. In fact, introduced species are considered a greater threat to native biodiversity than pollution, harvest, and disease combined. They threaten biodiversity by (1) causing disease, (2) acting as predators or parasites, (3) acting as competitors, (4) altering habitat, or (5) hybridizing with local species.

Invasive species are costly to both society and nature by:

  • Costing Americans more than $137 billion a year (Pimentel et al. 2000)
  • Impacting nearly half the species listed as threatened or endangered
  • Possibly devastating key industries including seafood, agriculture, timber, hydro-electricity, and recreation
  • Impeding recreation such as boating, fishing, hunting, gardening, and hiking
  • Spreading easily by wind, water, animals, people, equipment, and imported goods
  • Increasing the frequency of localized wildfires and adversely affect watering availability
  • Destabilizing soil and alter hydrology of streams, rivers, lakes, and wetlands

Washington State Invasive Species Examples

There are over 50 priority invasive species of concern in Washington State. Here are a few examples that threaten Western Washington.

Atlantic Salmon

Atlantic salmon (many genetically modified) are raised along the Washington and British Columbia coasts; escapes from these aquaculture operations concern fishery biologists and others working to restore native Pacific Northwest salmon runs. As of 2006, the Aquatic Nuisance Species Project states that there have been sightings of juvenile Atlantic salmon on the West Coast. The last reported sightings were on Vancouver Island in 2000.

In recent years there has been specific concern about the potential impact on wild salmon stocks from sea lice (Lepeophtheirus sp.), originating from net pens of Atlantic salmon in British Columbia. Sea lice can kill juvenile fish, even at low infestation levels.

Spartina

Spartina

Spartina flowering in estuary
Photo: Washington State Magazine

Spartina species are aquatic grasses that grow on the mud flats and marshes of Puget Sound and our coastal estuaries. The plants tend to grow in circular clumps called ‘clones’ and are bright green. One particular species, Spartina anglica, was introduced either in shipments of oysters from the East Coast or as packing material in ships’ cargo. It creates large monocultures that outcompete native plant species for space, including rare and endangered plant species, reducing marsh biodiversity and ecological functions.

European Green Crab

European green crab

Juvenile green crab began showing up in Washington waters in 1998. Photo: Washington State Department of Fish and Wildlife

The European green crab is a small shore crab that is not necessarily green like its name implies. It typically is found in high intertidal areas and marshes in coastal estuaries and wave-protected embayments, and can live on a variety of surfaces including sand, mudflats, shells, cobble, algae, and rock. It is an opportunistic feeder and aggressive invader. It is native to the eastern Atlantic from Norway to North Africa.

The European green crab is a ravenous predator that eats small crustaceans and many other plants and animals, and can have dramatic negative impacts to native shore crab, clam, and oyster populations. First introduced to the East Coast of the US, green crabs are believed to have caused the collapse of the soft-shell clam industry in New England; their digging habits also have slowed eelgrass restoration efforts. One green crab can consume 40 half-inch clams a day, as well as other crabs its own size. On the West Coast, green crabs were introduced to San Francisco Bay either via ballast water or through the lobster trade. Further invasion north is facilitated by strong advective currents that are associated with El Nino events. The 1998 event brought crabs as far north as Vancouver Island; luckily populations have not established yet. This year’s El Nino may prove strong enough to bring crab larvae into Puget Sound and British Columbia again. How severe the invasion will be, only time will tell.

Scotch Broom

Scotch Broom

A member of the pea family, Scotch Broom has pretty flowers but an aggressive demeanor. Photo: King County

Scotch broom (Cytisus scoparius) is an upright shrub with yellow flowers in the pea family. It grows primarily in open, dry meadows and along roads. It is an aggressive early colonizer and typically shows up in recently disturbed areas. A European native, scotch broom crowds out native species and negatively impacts wildlife habitat by creating vast monocultures. It can form dense, impenetrable stands that displace farmland and/or prevent native species from colonizing. Scotch broom also produces toxic compounds, which in large amounts can cause mild poisoning in animals such as horses.

Coming up: in Part II, we will discuss how invasions happen and what can be done to stop them.

For more information, contact Jason Stutes at jason.stutes@hartcrowser.com.

References: Pimentel, D., Lach, L., Zuniga, R., Morrison, D., 2000. Environmental and economic costs associated with non-indigenous species in the United States. BioScience 50 (1), 53–65.

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Shaken and Stirred: Northwest Earthquake and Tsunami

Washington 9.0 earthquake--Are you ready? Oregon 9.0 Earthquake--Are you ready?Suddenly the Pacific Northwest is on the national stage for its earthquake and tsunami vulnerability, thanks to a New Yorker article. “The Really Big One,” by Kathryn Schulz, has triggered attention from dozens of local papers and news sites. Yet even before the New Yorker shook the Northwest (pun intended), Oregon Public Broadcasting had been featuring Hart Crowser engineer Allison Pyrch in its “Unprepared” series, to alert the region to the impending disaster in hopes that we will get prepared.

Also, Allison recently gave a presentation for the Lake Oswego Sustainability Network: “Surviving a 9.0, Lessons Learned from Japan and Beyond.” If you are involved in emergency management or just plain interested in massive disasters and their aftermaths, settle in for some powerful visuals and easy-to-follow explanations about earthquakes in Japan and Chile, how the 9.0 earthquake and tsunami will happen in the Pacific Northwest, and what you can to do to be resilient.

Watch the whole “Surviving a 9.0” video to get unusual insight into what’s ahead, or if you’re pressed for time, skip to one of these minute points:

  • 9:00 Jan Castle introduces Allison Pyrch 10:56 Allison Pyrch’s presentation begins with how the Pacific Northwest 9.0 earthquake will happen
  • 14:25 Comparing the Japan and Chile quakes “It didn’t stop shaking for a day”
  • 21:45 Fire damage/natural gas 22:30 Water, wastewater, and electrical systems; liquid fuel; natural gas
  • 24:25 Lifelines/infrastructure/airports “PDX will not be up and running”
  • 28:35 Port damage/economics
  • 31:45 How prepared is the Pacific Northwest? When will it happen? “We are 9 ½ months pregnant”
  • 35:00 What will it look like?
  • 37:32 What you can do
  • 40:30 What businesses can do
  • 42:11 Can you be sustainable without being resilient?
  • 43:33 What about a resiliency rating system similar to LEED?
  • 53:30 Will utilities, transportation, hospitals be useable after the 9.0? “We’re toast”
  • 1:01:30 End of Allison’s presentation; additional information from Jan Castle on how to prepare
  • 1:19:19 How sustainability measures in your home lead to resiliency
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Applying Net Environmental Benefit Analysis to Contaminated Sites

Exxon Valdez oil spill site

Exxon Valdez oil spill site.

First, do no harm….

Or at least don’t do more harm than good.

That’s the idea behind NEBA—Net Environmental Benefit Analysis—as applied to the cleanup of contaminated sites. As defined by a vintage 1990s Department of Energy paper on the subject, net environmental benefits are:

“…the gains in environmental services or other ecological properties attained by remediation or ecological restoration, minus the environmental injuries caused by those actions.”

Spills like Exxon Valdez Spurred the NEBA
The NEBA concept originated with the cleanup of large marine oil spills. One of the first formal considerations of Net Environmental Benefits was the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989. After the spill, the U.S. National Oceanic and Atmospheric Administration (NOAA) looked at whether high-pressure, hot water washing of unconsolidated beaches might actually do more harm to the intertidal habitat—and the plants and animals that depend on it—than just simply letting the oil degrade naturally.

Since then, NEBAs have been used for a few other types of cleanups, including metals contamination in wetlands and organic contamination in sub-tidal sediment, but only infrequently and on an ad hoc basis.

No current NEBA Guidelines, However…
Formal consideration of net environmental benefits has not been more widespread in cleanup decisions, probably because federal and state cleanup frameworks, such as Washington’s Model Toxic Control Act (MTCA), do not explicitly allow consideration of the harm of the cleanup itself and don’t provide guidelines for when the process would apply and how the benefits and impacts should be evaluated.

But that might be changing. At least it is in Washington State, where the Department of Ecology thinks that the NEBA’s time has come. Ecology is working on new draft Terrestrial Ecological Evaluation (TEE) guidance that, for the first time, lays out the implementation of NEBA at cleanup sites under MTCA.

NEBA and Abandoned Underground Mines
In conjunction with Ecology, Hart Crowser has already “test driven” the NEBA concept as it applies to the cleanup of abandoned underground mines. Many of these sites pose risks to terrestrial plants and animals because of the toxic metals such as copper and zinc left behind in tailings and waste rock.

Although the risks to individual organisms living on the waste material might be high, the overall risk to plant or wildlife populations are often fairly low because the extent of the waste material is so small. Nonetheless, the remedy selection process under MTCA would typically lead to a decision to cap the contaminated material with clean soil or to dig it up and haul it away to be disposed of elsewhere.

Bringing Common Sense into Cleanup Decisions
But what if the cleanup involved building an access road? Through mature forest? Or up a steep, exposed mountain side? Or across a stream or wetland? How are those habitat or ecosystem injuries balanced against the benefits of the cleanup itself? Ecology’s upcoming NEBA guidance should go a long way to addressing these dilemmas and bringing some common sense into certain cleanup decisions.

“Especially Valuable Habitat”
The new guidance is expected to introduce the concept of “Especially Valuable Habitat” and how to use it as a threshold for judging whether or not a NEBA may be appropriate for a particular site. It’s also expected to allow some flexibility regarding how injuries and benefits are quantified and balanced.

In the meantime, check for updates on when the new guidance is expected at Ecology’s website.

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