Tag Archives: Slope Stability

US 231 Emergency Slide Repair – Laceys Spring, Alabama

DBA has 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.  

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

 

Excavating first shaft on the site (DBA)

 

A.H. Beck (Beck) is the drilled shaft contractor, drilling each shaft, placing reinforcement, and placing concrete.   The permanent casing is 5/8 inch wall thickness spiral weld 60ksi steel. The shafts are reinforced with a 1.5inch wall thickness, 8ft diameter, 60ksi steel pipe. These pipes are rolled and welded.

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 are scheduled to be completed by the end of July 2020.  The deadline to have the bridge open to traffic is early December, 2020, but Brasfield and Gorrie has an aggressive plan to complete the project early and earn the bonus for early completion.   Volkert is the CE&I Consultant on the project for ALDOT, providing construction management and inspection services for the project.

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.

 

 

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

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.