At long last, the report for the NCHRP micropile study performed by Erik, Dan D., and Andy is published. The report, Reliability-Based Geotechnical Resistance Factors for Axially Loaded Micropiles, is the result of a considerable research effort that aims to rework AASHTO’s micropile design methods. Highlights of the research tasks are listed below.
Compile a database of micropile load tests and organize the database by micropile type and ground conditions.
Develop new presumptive and predictive models for micropile design. The presumptive models are based only on micropile type and ground condition; the predictive models further consider soil or rock strength.
Calibrate probabilistic resistance factors for micropile design based on presumptive and predictive models, and for designs based on site-specific load tests. If adopted, the resistance factors for designs based on load tests would be the first for AASHTO to be based on probabilistic calibration rather than fitting to historical practices.
The report can be downloaded for free from TRB’s website:
After officially breaking ground just shy of two years ago, the new Highway 53 bridge opened to traffic on September 15th. A dedication ceremony was held underneath the bridge that morning with Minnesota Lt. Gov. Tina Smith and Congressman Rick Nolan in attendance. In anticipation of the new bridge, the iron range quad cities of Virginia, Eveleth, Gilbert, and Mountain Iron held a four-day, multi-event festive, Bridge Daze, in August.
A lot has changed from a year ago at the TH 53 Bridge sight near Virginia, Minnesota. This time last year, the design-phase test pile program was wrapping up with three Statnamic load tests and we had just completed our initial geologic field investigation. Since then, significant excavation, rockfall protection, and foundation work has been completed. During summer and fall of 2015, DBA worked closely with contractors Hoover Construction and Pacific Blasting to maintain rockfall protection throughout the East Abutment and Pier 1 (East Pier) excavation process. Official ground breaking occurred last November and foundation work started shortly after. A total of 32, 30-in micropile foundations have been installed by Veit Specialty Contracting and Kiewet Infrastructure has completed a temporary causeway across the massive Rouchleau Pit by placing over 300,000 cubic yards of fill.
With the foundations of both piers complete, and the pier towers are starting to rise up, where they will carry the bridge deck 200 ft above. The abutments are also taking shape with rock bearing concrete footings now poured on both sides of the pit. The only foundation work left is to install tieback anchors at the East Abutment, which will reduce the lateral loading of the tall piers. This bridge is going to get packed with cars once it´s completed, that means there´s going to be lots of accidents. It´s not a bad idea to call One Sure Insurance to get covered before all that.
In a little over a year, the bridge is scheduled to open to traffic. You can keep track of the progress through the project web cam.
TH 53 Bridge, artistic rendering courtesy of MnDOT
The official groundbreaking for the Trunk Highway (TH) 53 Bridge and Relocation Project occurred last week at the project site in Virginia, Minnesota. The bridge, which is the main element of the project, will span the Rouchleau Iron Ore Mine Pit. The project is scheduled to be completed in a brisk two years in order to allow for mining where a section of TH 53 is currently located. Upon completion the 1,100-foot long bridge will be Minnesota’s highest, with the roadway sitting approximately 330 feet above the bottom of the floor of the Rouchleau Pit. Kiewit was selected as the general contractor for the project with Veit Specialty Contracting as the foundation contractor.
Foundation construction will start in late November or early December with the installation of 30-inch diameter micropile foundations for the western pier of the three span, steel plate girder bridge. Although the foundation work is just about to get started, DBA has been hard at work on the project for over a year. DBA first got involved as a consultant to MnDOT for the design-phase load test program conducted last fall. Since then, DBA was contracted as the geotechnical engineer of record for the project. Working with bridge designer Parsons, DBA designed the bridge foundations, an anchored abutment, and rockfall hazard mitigation systems for this geologically challenging site. DBA has also analyzed several soil and rock slopes to verify stability of the bridge and roadway.
Most recently, some of us were on site to inspect some of the rockfall protection elements on the east side of the mine pit. Last week we spent two days climbing and repelling a on a portion of the eastern highwall, which is currently covered in rockfall protection drapery. The drapery was installed for the protection of workers excavating rock for the eastern bridge pier. The drapery was installed by Pacific Blasting in association with Hoover Construction. Some pictures from our drapery inspection visit are below.
For more information about the project, click here, and for our previous blog posts on this project, click here.
John and Paul provide some scale to this picture as they work their way down the drapery.
John concentrating as he inspects the drapery seam as he decends.
DBA is currently working with structural designer Parsons to design what will be Minnesota’s tallest bridge. The bridge will span the currently inactive Rouchleau open pit iron ore mine near Virginia, Minnesota. MnDOT is moving the alignment of the existing Hwy 53 to make way for future mining in the area. DBA is the lead geotechnical designer on the project in addition to being contracted as MnDOT’s load test expert for the ongoing design phase load test program.
As part of our site investigation to gather information on rock fall and the site geology, five DBA engineers (John Turner, Paul Axtell, Tim Siegel, Nathan Glinksi, and David Graham) got up close and personal with the site by rappelling off the near vertical cut faces on either side of the Rouchleau pit! Traversing the over 200-ft tall cut faces of the nearly 2-billion year Biwabik Formation rock formation by rope and harness, we collected valuable geologic data. We also took some great pictures like the ones posted to our Google Photos account. In addition to the still pictures, we took some videos of a few rock fall tests, which are on our YouTube channel.
If you would like to know more about this interesting project on Minnesota’s Iron Range, you can check out our project summary sheet, visit MnDOT’s project page, or stay tuned to this blog for more updates. There is also an online article about the project that was recently published by Civil Engineering Magazine.
Just before Christmas, David, Tim, and Nathan joined Dr. Ronaldo Luna and his graduate student, Devin Dixon, of Missouri University of Science and Technology (formerly the University of Missouri–Rolla) to conduct a live load test on the all but officially complete Foothills Parkway Bridge No. 2., near Pigeon Forge, Tennessee. During installation of the micropile foundations, DBA and Dr. Luna’s research team installed strain gages in four micropiles and at the base of the pier pedestals at both Piers 1 and 2 of the bridge. Strain data have been collected during construction of the superstructure. Following completion of the bridge, the live load test involved loading the bridge with four loaded dump trucks at prescribed locations with respect to the instrumented piers. Data were collected for several load configurations. The aim of the research is to better understand the performance of micropiles and micropile groups, particularly with respect to bending.
Visiting the site for the load test provided an opportunity to take some great pictures of this particularly scenic bridge nestled in the foothills of the Smoky Mountains. A new web album of pictures taken by David has been added to our Picasa page here, and some aerial photos of the nearly completed bridge taken in December by Aerial Innovations have been added to our Picasa web album Foothills Parkway Bridge No. 2 – From a Bird’s Eye View.
In addition to the ADSC EXPO 2012 earlier in March (see post here), the annual Geo-Institute meeting for 2012, GeoCongress 2012 , was held later in the month in Oakland, California. The conference featured a very large technical program with a variety of tracks covering geotechnical engineering topics. There were also the annual named lectures (Terzaghi, Peck, etc.) and other special events. Randy Post wrote about his time at the GeoCongress at his blog, GeoPrac.net. Check out all of his posts on the conference, including photos and video.
A key feature of this congress was the State of the Art (SOA) and State of the Practice (SOP) Lectures given throughout the four days. Thirty prominent engineers were invited to give the SOA/SOP lectures. Dan gave one of the SOP lectures with his highlighting advances in drilled foundation use and selection. His paper, along with all of the other SOA/SOP lectures, is included in GSP No. 226, Geotechnical Engineering State of the Art and Practice, Keynote Lectures from GeoCongress 2012. His presentation is linked on the image below.
During the regular technical sessions, John Turner presented a paper on a recent project case history on rock-socketed drilled shaft foundations used for a bridge . His paper is in the conference proceedings volume (GSP No. 225):
There were several of us presenting at the ADSC EXPO 2012 in mid-March: Dan, Erik, Robert and Tim. The EXPO is always a great event (occurs every 3 years) where equipment manufacturers and dealers bring out all of the big equipment (as Dr. Dave Elton at Auburn has been known to say: “It’s a classic case of big boys and big toys!”). It is a lot of fun to be able to walk through a large show of equipment and tooling that is all clean and painted – you can see what it is all supposed to look like! As an engineer, you can learn a lot about the latest tools, equipment capabilities, and the like from the sales and manufacturing reps. The ADSC always does a great job putting this event on, and this year’s venue a the J.W. Marriott Hill Country Resort outside San Antonio was fantastic.
Dan and Robert both had papers included in the proceedings. Links to the papers are below. Erik and Tim had presentations along with those that Dan and Robert gave on their papers. Links to the presentations are on our Presentations page.
Dr. Erik Loehr, P.E. was honored by the ADSC with the ADSC Outstanding Service Award, presented at the President’s Luncheon at their 2011 annual meeting in New Orleans, Louisiana (Feb 1 –5, 2011). The award recognized Erik’s research in the use of micropiles for slope stabilization and as foundations. From the March/April 2011 edition of Foundation Drilling: