Category Archives: Slope Stability

DFI Publishes Landslide Stabilization and Excavation Support Report

The Deep Foundations Institute (DFI) has just published a new report entitled Guidance for Factoring Deep Foundation Structural Resistance for Landslide Stabilization and Excavation Support“, Final Report, CPF-2017-LAND-1 .  The authors are our very own Ben Turner, Dan Ding, Erik Loehr, and Paul Axtell.

To borrow from the authors’ introduction:

This report provides guidance for factoring deep foundation passive structural resistance for use in two-dimensional limit-equilibrium SSA, and is intended to serve as a consensus document on this subject. The report is divided into two main sections. The first section provides an overview of the basic framework for incorporating deep foundation elements into global stability analyses, followed by a discussion of the different possible methods for factoring (or not) structural resistance at different stages of the analysis. From this discussion, various plausible combinations of methods for including or not including load and resistance factors are identified, including a simple example.  In the second section of the report, the various factoring methods are applied to three case studies in order to analyze the influence of factoring method on reliability. The report concludes with a summary of the recommended approach for incorporating deep foundation resistance in SSA, informed by the conclusions presented in the earlier sections.

The report can be downloaded for free from DFI at the Committee Project Fund page (https://www.dfi.org/cpf) . Scroll down and look for the Landslides and Slope Stabilization Committee.    The DFI committees fund a lot of projects that result in reports such as this that benefit our industry and the state of practice.

 

While the report is free, you can access so much more, including the DFI Journal, by becoming a member.

Instrumentation at US 231 bridge and Slide

(Written by Andy Boeckmann – DBA)

After successful design and construction of the US 231 emergency slide repair in Lacey’s Spring, Alabama, DBA shifted gears to install a state-of-the-art monitoring system for the project. The monitoring system allows DBA and ALDOT to remotely detect any movement of the drilled shafts, changes in groundwater levels, and movement of the slope, itself.

The monitoring system includes ShapeAccelArray (SAAV) devices to measure displacement profiles with depth. SAAVs, which are manufactured by Measurand, consist of a chain of rigid segments, each 1.5-ft long and about 1-inch diameter. DBA installed 27 SAAV devices at US 231. Each of the 24 drilled shafts has one SAAV, which DBA installed in a 1-inch conduit welded to the drilled shaft reinforcement and emerging from the top of the grade beams connecting the shafts. The other three SAAVs are “free-field” SAAVs, installed in the soil between bridge bents. DBA worked with ALDOT’s drill crews to install the free-field SAAVs.

ALODT drill crew installing a free-field SAAV under the Northbound bridge.

 

Completed free-field and foundation instruments at Bent NB4.

 

DBA also worked with the ALDOT drill crews to install vibrating wire piezometer devices at six locations across the site. Each location includes two piezometers, one in the soil and one just below the top of rock. The piezometers were installed using the fully-grouted method. The piezometers measure pore pressure, which DBA uses to interpret groundwater conditions at the site.

 

Datalogger atop a vibrating wire piezometer.

 

All of the instruments are connected wirelessly to two central hubs that collect the data. The hubs are solar powered.  One of the hubs is equipped with a cellular modem that facilitates remote collection of the data.  RST Instruments manufactures the monitoring equipment as well as the vibrating wire piezometers.

Housing for SAAV devices installed in drilled shafts.

 

R-star hub and solar panel mounted to SB Bent 6.

 

Inside of data collection hub.

 

Results of the monitoring program indicate the foundation system is performing as designed. The US 231 structure has passed its first wet season with flying colors. Despite several periods of heavy rain that resulted in localized slope movement, the drilled shafts have shown only very small movement, typically less than 0.05 inch. The movement shown in the shafts indicates they are resisting loading from the slope movement, but with plenty of reserve capacity. The monitoring system has successfully captured realistic results from all instruments, including the drilled shaft and free-field SAAVs and piezometers.

Piezometer data shows strong correlation between rainfall and increases in groundwater levels.
Example of SAAV drilled shaft displacement. Shaft displacements are very small, typically less than the stated accuracy of the SAAV devices.

The monitoring system is more than just bells and whistles: it is an integral part of DBA’s design philosophy for the US 231 project. DBA engineers were able to implement the innovative strategy of drilled shafts through an active landslide because we knew performance of the foundation system would be actively monitored. This strategy represents a modern take on the observational method, which has represented best geotechnical engineering practice since the profession originated. DBA will also use results of the monitoring program to inform future designs, consistent with our commitment to using state of the art to improve the state of practice.

To read more in detail about the design and construction of the bridge foundations, we published an article i nthe April 2021 issue of Foundation Drilling Magazine:

Thompson, W.R. and Dapp, S.D. (2021). “Innovative Landslide Solution”, Foundation Drilling, Vol XLII, No. 3April 2021, pp51-62.

US 231 Emergency Slide Repair – Laceys Spring, Alabama

DBA had the great fortune to be working with the Alabama Department of Transportation (ALDOT) on a very interesting bridge project in Lacey’s Spring, Alabama just south of Huntsville, Alabama.  On February 12 and 13, 2020 a large landslide occurred on SR-53 (US-231) at milepost 301.7 in Morgan County approximately 1.7 miles south of the Laceys Spring Community.  The slide completely severed the 4-lane divided highway which is a major commuting route between Huntsville and several communities south of the city.  Many of the workers at the U.S. Army Redstone Arsenal, NASA Marshall Space Flight Center, and the contractors and vendors that support these two major installations live in the communities impacted by the closure of the highway.  Detours were established on existing state and county roads, but these added 30 to 60 minutes to commute times, depending on time of day.  ALDOT was under significant pressure from the impacted communities to quickly solve the problem and reopen the road.

ALDOT drill rigs performing exploratory drilling (DBA)

 

ALDOT drilling crews were immediately mobilized to the site to begin drilling exploratory borings and install slope inclinometer casings for monitoring slide movements.  The Department of Civil Engineering at Auburn University was engaged to perform geophysical testing in conjunction with an existing research project for ALDOT.  Geotechnical engineering firm TTL also assisted with field investigation efforts. 

DBA and ALDOT immediately began evaluating several alternate concepts for stabilizing the slide and reopening the road during the soil and rock exploratory drilling.  The design team looked at several retaining wall options, a complete rebuild of the roadway, and bridges.  ALDOT selected a solution that removed most of the existing roadway embankments (built in 1947 and 1970) to reduce loading on the slope and then spanning the slide area with bridges built on the existing road alignments, with the bridges designed to withstand future movements of the slope.  Excavation was begun by Reed Contracting before bridge design was complete in order for the rough grading to be done before the bridge contractor mobilized.

The bridges are two-lane structures, one Northbound and one Southbound, each about 947 ft in length.  The superstructure is AASHTO BT-72 concrete girders and a concrete deck.  There are seven spans in each bridge each about 135ft long.  The grading work was begun while the bridge was still being designed to accelerate the schedule and shorten the time the road would be closed.

The foundations for each pier are a pair of 9.5ft diameter, permanently cased drilled shafts with 9ft diameter rock sockets.  The sockets are 14ft long into the limestone and shale bedrock.  The limestone uniaxial compressive strengths range from 10,820 psi to 28,100 psi. 

After much design and analysis in a highly compressed schedule, a bridge contract was let for bid in early May 2020, less than 3 months after the slide occurred.  Brasfield & Gorrie was the successful bidder and awarded a $15 million contract that has incentives for finishing early, and disincentives for finishing late. 

 

ALDOT UAV flight June 16, 2020

ALDOT UAV flight July 07, 2020

ALDOT UAV flight July 23, 2020

ALDOT UAV flight July 28, 2020

ALDOT UAV Flight Aug 08, 2020

ALDOT UAV Flight Sep 2, 2020

ALDOT UAV Flight Sep 15, 2020

 

Excavating first shaft on the site (DBA)

 

A.H. Beck (Beck) was the drilled shaft contractor, drilling each shaft, placing reinforcement, and placing concrete.   The 9.5ft diameter permanent casing is 5/8 inch wall thickness spiral weld 60ksi steel fabricated by Nucor in Birmingham, Alabama.  The shafts are reinforced with a 1.5inch wall thickness, 8ft diameter, 60ksi steel pipe. These pipes were rolled and welded by Favor Steel in Birmingham, Alabama before being trucked to the site.  The steel plate was manufactured by SSAB in Axis, Alabama near Mobile.  So, the structural steel pipes were completely Alabama-made and the steel travel almost the length of the state!

8ft diameter x 1.5in wall steel pipe for shaft reinforcement (DBA)

 

Inner structural pipe (1.5in) and outer casing (5/8in) (DBA)

 

The pair of shafts for each pier is connected by a reinforced concrete grade beam 10ft wide by 7ft high by 46ft long. To connect the shafts to the grade beam, a 14ft long reinforcement cage is placed in each shaft, embedded 8ft into the shaft with 6ft embedded in the grade beam. The cage consists of 28 No.18 Grade 75 bars.

Grade beam at NB Bent 7 with column steel (DBA)

 

Completed shaft with reinforcing cage to embed in grade beam (DBA)

 

The project includes a robust instrumentation plan with ShapeArray inclinometers installed in each shaft and in the slope, supplemented by traditional inclinometers in the slope and vibrating piezometers to monitor groundwater levels.  DBA and ALDOT will monitor the bridge and slope, intending to be able to measure displacement and calculate strain and loads in the shafts should the slope move again in the future.

Foundations were completed a few days ahead of schedule at the end of July 2020.  The deadline to have the bridge open to traffic was early December, 2020, but Brasfield and Gorrie had an aggressive plan to complete the project early and earn the bonus for early completion.   The bridge was open to traffic September 28, 2021 to much rejoicing among the commuters and others that use this route.   Volkert was the CE&I Consultant on the project for ALDOT, providing construction management and inspection services for the project, ensuring all requirements were met to build the bridges.

To read more in detail about the design and construction of the bridge foundations, we published an article i nthe April 2021 issue of Foundation Drilling Magazine:

Thompson, W.R. and Dapp, S.D. (2021). “Innovative Landslide Solution”, Foundation Drilling, Vol XLII, No. 3April 2021, pp51-62.

Click HERE for some of the photos DBA team members have taken during construction.

To see aerial views from ALDOT’s UAV flight taken on July 10, 2020, click HERE.

 

 

Two Major Bridges in Minnesota Open to Traffic

St. Crox Crossing Extradosed Bridge; photo courtesy of MnDOT

Two DBA bridge projects in Minnesota opened to traffic recently.  The St. Croix Crossing near Stillwater and the Highway 53 Relocation in Virginia.  Both projects are milestones for MnDOT.  The St. Croix Crossing is the first extradosed bridge in the Midwest and only the second extradosed bridge in the United States.  The new Highway 53 Bridge is the tallest bridge in Minnesota.

Following a ribbon cutting and dedication ceremony on the morning of Wednesday, August 2nd, the St. Croix Crossing saw its first traffic later that evening and has already alleviated traffic congestion  in downtown Stillwater,  as intended.  The interstate project was also heralded as a noteworthy example of government cooperation by The Wall Street Journal.

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.

Hwy 53 Bridge Across The Rouchleau Pit; photo courtesy of OxBlue construction cameras

Ground Breaking of New TH 53 Bridge in Minnesota

TH 53 Bridge

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 Engineers Perform “Extreme” Geologic Investigation

DBA engineers prepare to go over the edge of the 200-ft tall west wall of the Rouchleau mine pit with the load test site in the background. From left to right: David Graham, Nathan Glinski, Ryan Turner, and Paul Axtell
DBA engineers prepare to go over the edge of the 200-ft tall west wall of the Rouchleau mine pit with the load test site in the background. From left to right: David Graham, Nathan Glinski, and Paul Axtell (far right).

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.

Geofoam and Slope Stability

A recent TRB E-newsletter (4/2/2013) was spotlighted by Randy Post (aka RockMan) at Geoprac.net.  The newsletter was about the publication in January of Research Results Digest 380: Guidelines for Geofoam Applications in Slope Stability Projects.

TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 380: Guidelines for Geofoam Applications in Slope Stability Projects explores the use of expanded polystyrene-block geofoam for slope stabilization projects. For the purpose of the report, slope stabilization projects include new roadways as well as repair of existing roadways that have been damaged by slope instability or slope movement.

The research was performed by the Department of Civil Engineering at The University of Memphis (UoM). David Arellano, Associate Professor of Civil Engineering at UoM, was the Project Director. The other project investigators were Timothy D. Stark, Professor and Consulting Engineer, Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign; John S. Horvath, Consulting Engineer and Professor, Civil and Environmental Engineering Department at Manhattan College; and Dov Leshchinsky, President of ADAMA Engineering, Inc., and Professor, Department of Civil and Environmental Engineering at the University of Delaware.

The digest is a summary of the NCHRP Project 24-11(02), “Guidelines for Geofoam Applications in Slope Stability Projects.”

This report presents the results of a study performed to develop a comprehensive document that provides both state-of-the-art knowledge and state-of-practice design guidance to facilitate the use of EPS-block geofoam for slope stabilization and repair. This report includes the following five primary research products: (1) summary of relevant engineering properties, (2) a comprehensive design guideline, (3) a material and construction standard, (4) economic data, and (5) a detailed numerical design example.

The project was initiated to develop comprehensive design guidelines for use of geofoam in slope stability applications.  According to the Digest, geofoam use is becoming more widespread in the U.S., but the adoption of it as a routine roadway construction material has been slowed by lack of design guidelines.

Although EPS-block geofoam for road construction is an established technology and despite the more than 30 years of extensive and continuing worldwide use of EPS-block geofoam, it has been underutilized in U.S. practice because a comprehensive design guideline for its use as lightweight fill in roadway embankments has been unavailable. There was, therefore, a need in the United States to develop formal and detailed design documents for use of EPS-block geofoam in roadway applications.

To learn more about the project, go here.  Click this link to download the project report.

And speaking of slopes and slides, RockMan has some posts on a recent slope failure in a copper mine in Utah and one on the WSDOT doing some rock blasting on I-90 (with cool video!).  Check them out:

WSDOT rock blasting on I-90 for Snoqualmie Pass

Bingham Canyon Slide

GeoCongress 2012–Dan Gives A SOP Lecture; John Turner paper published

GeoCongress 2012, Oakland, California

GeoCongress 2012 Proceedings

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.

Pages from DB drilled foundations 2012 Oakland GI [Compatibility Mode]

 

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):

Turner, J.P., Duffy, J.D., Buell, R. and Zheng, X (2012). “Foundations for the Bridge at Pitkins Curve”, GeoCongress 2012 State of the Art and Practice in Geotechnical Engineering, Geotechnical Special Publication No. 225, ASCE, pp414-423.

Micropiles for Slope Stabilization

An article by Eric and Dan on the use of micropiles for slope stabilization has been added to our Publications Page.  Published in the August 2010 issue of Foundation Drilling Magazine, the article summarizes key findings and recommendations from a study that reviewed and evaluated existing micropile design methods.  A new design method is proposed to better predict the mobilized resistance of micropiles used for slope stabilization. The full report prepared by Eric and Dan for the joint ADSC/DFI Micropile Committee, “A Method for Predicting Mobilization Resistance for Micropiles Used in Slope Stabilization Applications”, presents the details of this study.  Robert previously posted about this report here.

Loehr, J.E. and Brown, D.A. (2010). “Design of Micropiles for Slope Stabilization”, Foundation Drilling, Vol. 31, No. 6 August 2010.

IFCEE 09 Wrap-up and Papers Posted

IFCEE09 page

Last week’s International Foundation Congress and Equipment Exposition was a huge success!  Dan gave a keynote address on Tuesday on managing risk in deep foundations within the design-build delivery model.  Paul, Erik, and I also had papers to present.  The technical sessions were excellent, the indoor exhibits were excellent, and the outdoor exhibits of foundation equipment were outstanding!  The ADSC, Geo-Institute, and PDCA were the co-organizers of the event.  A big hats off to all of the staff of all three organizations that made the event a huge success!  Thanks and “atta boy” go to Mohamad Hussein, P.E. (Conference Chair) and to Dan (Technical Program Chair) for all of their work, as well as the rest of the organizing committee.

I have also blogged about the conference here at GeoPrac.net.

Here are some pictures of the outdoor exhibits:

IFCEE09 Exhibit 1 IFCEE09 Exhibit 2 IFCEE09 Exhibit 3

There were over 300 papers included in the conference.  The proceedings were published as three Geotechnical Special Publications:

GSP 185: Contemporary Topics in Deep Foundations

GSP 186: Contemporary Topics in In-Situ Testing, Analysis, and Reliability of Foundations

GSP 187: Contemporary Topics in Ground Modification, Problem Soils, and Geo-Support

The editors, Magued Iskander, Ph.D., P.E. (Polytechnic Institute of New York University), Debra Laefer, Ph.D. (University College Dublin, Ireland), and Mohamad Hussein, P.E. (GRL) all had their work cut out for them.

I have added all seven papers authored by DBA team members to our site.  The links are below, or you can go to our Publications page.

Axtell, P.J., Stark, T.D., and Dillon, J.C., 2009. “Strength Difference Between Clam-Shell and Long-Reach Excavator Constructed Cement-Bentonite Self-Hardening Slurry Walls”, 2009 International Foundation Congress and Equipment Expo, Contemporary Topics in Ground Modification, Problem Soils, and Geo-Support, Geotechnical Special Publication No. 187, ASCE, pp. 297-304.

Brown, D.A., 2009. “Management of Risk in Deep Foundations with Design-Build”, 2009 International Foundation Congress and Equipment Expo, Contemporary Topics in Deep Foundations, Geotechnical Special Publication No. 185, ASCE, pp. 1-11.

Brown, D.A. and Thompson, W.R., 2009. “Drilled Shaft Performance in Cemented Calcareous Formations in the Southeast United States”, 2009 International Foundation Congress and Equipment Expo, Contemporary Topics in Deep Foundations, Geotechnical Special Publication No. 185, ASCE, pp. 119-126.

Loehr, J.E and Huaco, D.R., 2009. “Probabilistic Calibration of Resistance Factors for Slope Stability”, 2009 International Foundation Congress and Equipment Expo, Contemporary Topics in In-Situ Testing, Analysis, and Reliability of Foundations, Geotechnical Special Publication No. 186, ASCE, pp. 297-304.

Parsons, R.L., Pierson, M., Han, J., Brennan, J.J., and Brown, D.A., 2009. “Lateral Load Capacity of Cast-in-Place Shafts Behind an MSE Wall”, 2009 International Foundation Congress and Equipment Expo, Contemporary Topics in In-Situ Testing, Analysis, and Reliability of Foundations, Geotechnical Special Publication No. 186, ASCE, pp. 560-567.

Rollins, K.M., Adsero, M.E., and Brown, D.A., 2009. “Jet Grouting to Increase Lateral Resistance of Pile Group in Soft Clay”, 2009 International Foundation Congress and Equipment Expo, Contemporary Topics in Ground Modification, Problem Soils, and Geo-Support, Geotechnical Special Publication No. 187, ASCE, pp. 265-272.

Thompson, W.R., Hill, J.R., and Loehr, J. E., 2009. “Case History: Value Engineering of Driven H-Piles for Slope Stability on the Missouri River”, 2009 International Foundation Congress and Equipment Expo, Contemporary Topics in Deep Foundations, Geotechnical Special Publication No. 185, ASCE, pp207-214.