Video: Load Testing for the Winona bridge

New video, below, shows how explosions are used to test the bedrock for the new Highway 43 bridge in Winona.

Bridge engineers use “pile load testing”  to find out how much weight and resistance the ground will bear. It not only saves time and money, but helps design a bridge that will sit securely on the bedrock, below the river.

The statnamic test used in the video is one part of this process.

Winona Bridge Statnamic Test

 

How load testing works: 

It begins with digging and pounding.

Two different kinds of piles are put into the ground:

  • A hollowed shaft, which is filled with rebar and concrete. It goes 30 to 50 feet below the bedrock to create a solid pillar that can assess how much weight and sway the ground will bear.
  • A steel pipe that is hammered into the ground. Since the bedrock is about 100 to 150 feet below the river, these pipes are welded together end-to-end to reach that length.

Once the piles are in, they’re tested two different ways.

  • Pile Dynamic Analysis, with gauges affixed to the top of the pile to read the pressure put on it when hit with a pile driver.
  •  A Statnamic test (shown in videos), which involves accelerating a heavy weight by setting off a controlled combustion reaction. This shows how much resistance the pile can take.

Once the data is collected for the bridge design, the piles are cut off two feet below the river bed.

Mobile imagery, LiDAR help MnDOT maintain its assets

How do you quickly and cost-effectively get an accurate inventory of transportation assets spread out along more than 1,100 miles of roadway?

That was the problem facing the Minnesota Department of Transportation’s Metro District, which needed an inventory of its plate beam guardrail and concrete barriers.

To accomplish this, engineers in the district launched an innovative research implementation project using a pair of mobile mapping technologies — Light Detection and Ranging (LiDAR) and mobile imaging — that can collect vast amounts of geospatial data on highway infrastructure in a safe and efficient manner.

Mobile imaging uses a camera mounted on a vehicle driving at highway speeds to take high-resolution photos at regular intervals. It’s accurate to within 1 foot, which makes it suitable for use in preliminary (30 percent) design plans without additional field surveys. In this project, researchers collected mobile images of roadway barriers and extracted data from them along Metro District roadways, including all ramps, overpasses, interchanges, weigh stations, rest areas and historical sites.

A MnDOT worker replaces a section of broken guardrail.
A MnDOT worker replaces a section of broken guardrail on I-94 near the Lowry Tunnel in Minneapolis. (Photo by Dave Gonzalez, MnDOT)

Researchers also collected LiDAR data at three Metro District sites. LiDAR uses a laser range finder and reflected laser light to measure distances. It provides survey-grade data accurate to within 0.1 foot, but it is significantly more expensive to collect than mobile imaging.

“Mobile imagery and mobile LiDAR are relatively new technologies, but this research shows that they are options that we can use. Collecting this information manually would have taken a lot more time and money,” said MnDOT Asset Management Engineer Trisha Stefanski.

MnDOT’s barrier inventory will provide invaluable information for design, planning and maintenance. The data will be published on MnDOT’s Georilla map server, where it will be beneficial to a variety of projects and recurring tasks. For example, if a vehicle hits a barrier, maintenance staff will be able to check the database to see the type of barrier and end treatment to ensure they bring the right equipment to make repairs. Although the project focused on barriers, the imagery contains data on other assets as well. MnDOT has already used the imagery to extract noise wall and sign data.

This blog post was adapted from an article in our upcoming issue of Accelerator, MnDOT’s research and innovation newsletter.

3D-vertical
Thousands of data points can be extracted from this image of a Highway 61 roadway segment created with LiDAR Technology.

‘High Bridge’ study yields insights on bridge deck maintenance

One of St. Paul’s most iconic landmarks is helping the Minnesota Department of Transportation find the most cost-effective methods of maintaining concrete bridge decks.

For the last three years, the Smith Avenue High Bridge, which connects downtown St. Paul with the city’s west side, has served as a test bed for a variety of products used to seal cracks on bridge decks. Through MnDOT-funded research, various sealant products have been applied on different areas of the bridge deck, with their performance tracked over time.

“This project will help MnDOT make cost-effective maintenance decisions to preserve its current bridge infrastructure,” said Sarah Sondag, a senior engineer with MnDOT Bridge Operations Support.

The bridge was chosen in part because of its large deck area, which allowed for the application of 12 sealant products and three control sections.

Sealing deck cracks is a routine preventive maintenance task for bridge crews. Left untreated, cracks can allow moisture and chlorides to penetrate the bridge deck, which can lead to the corrosion of reinforcing steel, deck deterioration and the need for early deck replacement.

researcher testing permeability of a deck crack on the Smith Avenue Bridge
A researcher tests the permeability of a crack on the deck of the Smith Avenue High Bridge in St. Paul.

MnDOT maintains a list of approved bridge deck crack sealing products, but until now had little data on how well each one performs in the field. The recently published report also examined several products that are not currently on the Approved Products List.

Among the study’s findings: some of the products on MnDOT’s Approved Products List did not perform as well as other products that are not currently on the list. MnDOT is using the results of the study to update its qualification process for products to get on the approved list. Insights gained from studying application techniques will also be used to update MnDOT’s bridge maintenance manual.

*Note: This blog post was adapted from an article and technical summary that will be featured in the upcoming issue of the Accelerator newsletter.

More:

How roadside drainage ditches reduce pollution

Stormwater can pick up chemicals and sediments that pollute rivers and streams. Roadside drainage ditches, also known as swales, lessen this effect by absorbing water. But until recently, MnDOT didn’t know how to quantify this effect and incorporate it into pollution control mitigation measures.

In a recently completed study, researchers evaluated five Minnesota swales, measuring how well water flows through soil at up to 20 locations within each swale.

“There’s a big push in Minnesota, and probably everywhere, to do more infiltration,” Barbara Loida, MS4 Coordinator Engineer, MnDOT Metro District, said. “We know that our ditches are doing some of that, but we wanted to look at how much infiltration these ditches are providing.”

A key finding: grassed swales are significantly better at absorbing water than expected, which may reduce the need for other, more expensive stormwater management practices, such as ponds or infiltration basins.

This could save MnDOT and counties significant right-of-way and construction costs currently expended on more expensive stormwater management techniques. While swales were recognized in the Minnesota Pollution Control Agency’s new Minimal Impact Design Standards, there was a need to quantify the amount of water a swale can absorb so it could receive the appropriate MIDS credits.

Researchers also tested the ability of carbon, iron chips, steel wool and other materials to remove pollutants as ditch check filters—material put into swales to enhance removal of pollutants.

Gradations on a Modified Philip Dunne infiltrometer allow the measurement of stormwater infiltration.
Gradations on a Modified Philip Dunne infiltrometer allow the measurement of stormwater infiltration.
What’s Next?

A follow-up project, which the MPCA is participating in, will seek to clarify the impact of swale roughness on infiltration rates. The goal is a calculator for real-world infiltration rates that MnDOT and local agencies would be able to implement.

MPCA, MnDOT and the city of Roseville are also partnering on a project to install and test the effectiveness of ditch check filters in real-world locations.

Maintenance recommendations should help MnDOT and local agencies ensure that swales operate at maximum efficiency. These recommendations should continue to be revised as knowledge evolves.

Related Resources

*Editor’s note: This article was adapted from our upcoming edition of the Accelerator. Read the newsletter online, or sign up to receive by mail. 

Access Across America: University of Minnesota ranks accessibility to jobs by transit

New research from the Accessibility Observatory at the University of Minnesota ranks 46 of the 50 largest (by population) metropolitan areas in the United States for accessibility to jobs by transit.

The new rankings, part of the Access Across America study begun last year, focus on accessibility, a measure that examines both land use and transportation systems. Accessibility measures how many destinations, such as jobs, can be reached in a given time.

“This project provides the most detailed evaluation to date of access to jobs by transit,” says Andrew Owen, director of the Observatory. “We directly compare the transit accessibility performance of America’s largest metropolitan areas.”

The findings have a range of uses and implications. State departments of transportation, metropolitan planning organizations, and transit agencies can apply the evaluations to performance goals related to congestion, reliability, and sustainability. In addition, detailed accessibility evaluation can help in selecting between project alternatives and prioritizing investments.

“It can help reveal how the costs and benefits of transportation investments are distributed,” Owen says.

Top 10 metro areas: job accessibility by transit (January 2014)

  1. New York
  2. San Francisco
  3. Los Angeles
  4. Washington
  5. Chicago
  6. Boston
  7. Philadelphia
  8. Seattle
  9. Denver
  10. San Jose

The report—Access Across America: Transit 2014—presents detailed accessibility values for each of the 46 metropolitan areas, as well as detailed block-level color maps that illustrate the spatial patterns of accessibility within each area. In addition, time-lapse map videos for each area are forthcoming and new analysis of the data from the accessibility to jobs by transit rankings will be published periodically. Upcoming reports in the Access Across America series will explore more detailed aspects of transit accessibility to jobs, including accessibility to jobs of different wage levels and a comparison with accessibility by car.

In the study, rankings were determined by a weighted average of accessibility, giving a higher weight to closer jobs. Jobs reachable within 10 minutes were weighted most heavily; jobs were given decreasing weight as travel time increases up to 60 minutes. Travel times were calculated using full transit schedules for the 7:00 to 9:00 a.m. period. The calculations include all components of a transit journey, including “last mile” access and egress walking segments and transfers.

“Accessibility is the single most important measure in explaining the effectiveness of the urban transportation system,” says David Levinson, University of Minnesota civil engineering professor and principal investigator on the project.

According to Owen, accessibility can be measured for various transportation modes, to different types of destinations, and at different times of day. “There are a variety of ways to define accessibility,” Owen explains, “but the number of destinations reachable within a given travel time is the most directly comparable across cities.”

The research is sponsored by the Center for Transportation Studies at the University of Minnesota. Accessibility Observatory reports, including the analysis of job accessibility by auto published last year and interactive maps, are available on the Access Across America: Transit 2014 web page.

RailVolution showcases Minnesota transit successes

Before a national audience of 1,400 urban planners and transit enthusiasts, Hennepin County Commissioner Peter McLaughlin and others told the story of how the Twin Cities metropolitan area was transformed into a community that embraces “livability” and mass transit, including light rail.

“The growth was horizontal and there were lots of people who were saying it wouldn’t work in Minnesota,” said McLaughlin, during the opening plenary of the RailVolution conference in Minneapolis.

But the metro region bucked years of infighting and helped pass a transportation bill in 2008 that allows counties to tax for the expansion of transit in the metro area. Anoka, Ramsey, Hennepin, Dakota and Washington Counties decided to pool their resources from the quarter-cent transit sales tax, which is why the Southwest Light Rail Line is able to move forward.

“They had to believe their day would come,” McLaughlin said of the counties.

MnDOT Commissioner Charles Zelle, who ran a regional bus company before being appointed to MnDOT, said it was faster for him to bike to the conference than to take his car.
MnDOT Commissioner Charles Zelle, who ran a regional bus company before being appointed to MnDOT, said it was faster for him to bike to the conference than to take his car.

This was the first time the annual conference has been held in the Twin Cities, allowing Minnesota leaders to share their success stories.

Minnesota Department of Transportation Commissioner Charlie Zelle, who biked the Greenway trail to get to the conference, spoke of MnDOT’s commitment to multi-modal transportation and maximizing the health of Minnesota’s people and economy.

“MnDOT is more than a highway department,” he said. “We have a statewide bike plan and we will probably be the second state in the union to have a statewide pedestrian plan.”

Michael Langley of Greater MSP said a mix of transportation types is critical to attracting  talented workers to the Twin Cities, especially millennials.

“Nearly every area of the world is facing a future workplace shortage,” he said. “It’s fueling a competition for talent like we’ve never seen.”

Federal Highway Administration Secretary Anthony Foxx on Tuesday addressed conference attendees about the need for a bipartisan compromise on funding. He proposed moving away from the Highway Trust Fund to a more inclusive transportation account (named the Surface Transportation Trust Fund) that also addresses rail needs, with $19 billion in proposed dedicated funding. He also discussed the recent announcement of $3.6 billion in resiliency funds for transit systems.

During his comments, he wore a red bicycle pin that the MnDOT commissioner frequently wears at multi-modal events.

During the five-day conference, attendees toured the recently completed Green Line and attended dozens of workshops on topics ranging from street walkability to bus-rapid transit to the use of mobile phones to enhance bus service. On Sunday, the Northstar commuter train traveled for the first time to St. Paul’s Union Depot and conference attendees took it back to Minneapolis.

Partnership planned for nation’s top pavement testing facilities

The nation’s two largest pavement testing centers are planning to partner in order to better leverage research performed at their cold and hot-weather facilities.

MnROAD, located in Albertville, Minnesota, and its southern U.S. equivalent, the National Center for Asphalt Technology in Auburn, Alabama, are full-scale test tracks that evaluate different types of pavement material under real-life conditions using semi-trailer truck and live interstate traffic.

Each facility has a history of evaluating the performance of pavement preservation treatments, including chip sealing, micro-surfacing, crack sealing and thin overlays. To address needs in both northern and southern climates, similar test sections would be developed at each facility to address national issues.

“By working together we can maximize the potential for each track,” said MnROAD Operations Engineer Ben Worel. “A closer relationship between NCAT and MnROAD is a logical progression in developing and evaluating new sustainable technologies, pavement systems and construction methods that lead to safer, quieter, lower-cost and longer-lasting roads.”

A test track at the National Center for Asphalt Technology in Alabama, MnROAD's hot-weather equivalent.
A test track at the National Center for Asphalt Technology in Alabama, MnROAD’s hot-weather equivalent.

The partnership idea was introduced to federal officials earlier this month at a national pavement performance conference in Minneapolis. Final details must still be worked out.

One of the workshops at the event discussed the proposed partnership between MnROAD and NCAT. Further talks are expected at the end of October.

“NCAT is thrilled about the opportunity for a partnership with MnROAD to address pavement research needs at a national level,” said NCAT Director Randy West. “Bringing NCAT and MnROAD results together will expand the climate base, loading distribution and other important pavement factors.”

Pavement conference

Pavement engineers from around the nation gathered Sept. 2 to 5 for the Midwestern Pavement Preservation Partnership forum and the SHRP2 R26 Workshop for the Preservation of High-Traffic-Volume Roadways, which featured tours of MnROAD, Minnesota’s cold weather pavement testing facility.

Conference participants also reviewed the latest preservation techniques being developed for high volume roads. MnROAD’s chip sealing study, which demonstrated that highways with an average daily traffic (ADT) of 58,000 can be successfully chip sealed, was especially attention-grabbing for agencies who don’t chip seal on roads with more than 2,000 ADT.

A national panel of speakers included Michael Trentacoste, director of the federal Turner-Fairbank Highway Research Center (pictured in top photo), who discussed Federal Highway Administration’s support of pavement preservation research and implementation.

With about 160 people in attendance over four days, MnDOT Materials Engineer Jerry Geib said the conference was successful in sharing the benefits of pavement preservation techniques with other state DOTs and federal highway officials who want adopt new practices to help alleviate budget constraints.

Drinking water solutions may help construction site runoff

The same chemicals used to treat drinking water might now be able to treat stormwater runoff to reduce the amount of pollutants entering Minnesota lakes and rivers from road construction sites.

A research project headed by Mankato State University and funded by the Minnesota Department of Transportation has identified three chemical flocculants that are effective at removing a broad range of Minnesota soils from water.

“Water is leaving construction sites carrying too much sediment,” said Minnesota State University-Mankato Environmental Engineering Professor Steve Druschel. “Chemical treatment has been used to treat drinking water for 70 to 80 years, and our thought was to try it in construction as well.”

Adding flocculant to a sample of water from the Minnesota River causes sediment to clump and sink.
Adding flocculant to a sample of water from the Minnesota River causes sediment to clump and sink.

Recent MnDOT research has investigated monitoring the amount of sediment in stormwater runoff and using temporary ponds to let sediment settle out of stormwater before it runs off the construction site. MnDOT also wanted to examine the possibility of treating  construction runoff with flocculants, which are chemicals that cause suspended sediment to form clumps that quickly settle out of the solution.

Researchers tested 21 chemicals to see how well they could remove 57 types of soil from water. While no chemical was effective for the entire range of Minnesota’s soils, three chemicals were broadly effective on a range of samples.

The research will contribute to improved treatment of stormwater runoff from construction sites and reduce the amount of sediment pollution entering the state’s rivers and lakes.

Although flocculants have been used to treat drinking water for seven decades, there has been only limited testing of their use in treating construction runoff. Research was needed to evaluate the effectiveness of this approach.

Adding flocculant to stormwater runoff can be as simple as drilling a hole in a bucket of the chemical and mounting it above the water (as shown here), although thorough mixing must be ensured. MnDOT hopes to develop a system that will automatically dispense a precise dose based on the amount of sediment in the water.
Adding flocculant to stormwater runoff can be as simple as drilling a hole in a bucket of the
chemical and mounting it above the water (as shown here), although thorough mixing must be ensured. MnDOT hopes to develop a system that will automatically dispense a precise dose based on the amount of sediment in the water.

Since it is not feasible for workers to constantly monitor sediment concentration in stormwater runoff, MnDOT hopes to leverage the knowledge gained from this project to develop an automated system that measures the amount of sediment in runoff and automatically adds the appropriate dose of flocculant to treat the water.

“We’re trying to develop a portable water treatment plant that can be applied to construction projects to deliver clean runoff water after a storm,” said MnDOT Environmental Specialist Dwayne Stenlund.

Any chemicals recommended for field usage will need to be approved by the Minnesota Pollution Control Agency, and methods for disposing of used chemicals will need to be identified as the environmental impacts of residual chemicals are unknown.

*Editor’s note: This article was adapted from the September-October 2014 issue of our Accelerator newsletter. Read it online or sign up for your free subscription.

Related Resources

MnDOT saves time, money with new contracting method

Thanks to a flexible new contracting method, the cost and time of delivering small highway projects in Minnesota should go down.

The Minnesota Department of Transportation is now able to put road construction contractors on standby for certain types of projects, rather than bid each project individually, due to the adoption of Indefinite Delivery/Indefinite Quantity (IDIQ) contracts.

“IDIQ contracts give MnDOT more flexibility and the ability to get to the field quicker for work that we need repeated routinely, such as culvert repairs, overlays and seal coats,” said Kevin Kosobud, project development engineer with MnDOT’s Office of Construction and Innovative Contracting.

IDIQs also provide flexibility when needs are uncertain.  Contracts are often used for multiple small projects that are similar in scope, but difficult to quantify in cost and timing.

For instance, the state of Florida awards IDIQs for hurricane debris removal, activating and paying contractors only when a hurricane necessitates the service.

Although IDIQs showed great promise, MnDOT had to develop a framework to implement them.

The federal government has used IDIQ contracts since the 1980s, but only a small number of state DOTS have used them to procure construction services. No standard procedures existed for their use by state DOTs, and federal procedures are not always applicable at the state level.

MnDOT hired Iowa State University researchers to examine IDIQ usage across the country and develop implementation procedures for Minnesota. (Read a summary of their research here.)

Researchers examined contracting practices at 14 different transportation agencies to  recommend guidelines for Minnesota to follow, which allowed MnDOT to begin awarding IDIQ contracts in April 2013.

Case study analyses show clear benefits where IDIQ has been used: acceleration of the project delivery period, reduced construction costs and flexible delivery scheduling.

“IDIQs can help DOTs get better prices for routine services via an economy of scale, for instance, by awarding a contract for a larger number of culvert repairs rather than awarding a single contract for each repair,” explained Doug Gransberg, professor of construction engineering at the Iowa State University Institute of Transportation.

Agencies can award IDIQ contracts individually or collectively.

With a single-award contract, a single contractor is awarded task orders based on the pricing furnished in the initial bid package; multiple-award contracts determine a pool of qualified contractors who may subsequently bid on task orders.

*Editor’s note: This article was adapted from the September-October 2014 issue of our Accelerator newsletter. Read it online or sign up for your free subscription.

Related Resources
  • Leveraging the Advantages of Indefinite Delivery/Indefinite Quantity Contracts – Technical Summary (1 MB, 2 pages); Final Report (expected Fall 2014)

Minnesota transportation research blog

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