West Virginia geology demands complex bridge foundations

By Jack Scott, P.G.; Bob Barclay, P.G; and James Wang, P.E.

West Virginia is mistakenly perceived to be a relatively insignificant state with respect to the U.S. economy. Its diminutive size of approximately 24,000 square miles is coupled with the sparse population of 1.8 million residents, yet West Virginia fuels the U.S. economy with its rich, natural resources. Its coal production is second only to the state of Wyoming. It provides one of the best networks of state and national parks in the Eastern United States. Attractions such as first class skiing, rafting, climbing, fishing, and hunting buoy the state and local economy and make the state a draw for travelers and outdoor enthusiasts.

Blennerhassett Island Bridge
James Rumsey Potomac River Bridge

West Virginia Department of Highways
Michael Baker, Jr., Inc.
E.L. Robinson
Walsh Construction Company
Brayman Construction
HCN, a Terracon Company

Design focus
Award-winning structures require unique foundation design.

However, none of these resources would be realized without the transportation infrastructure that has been carefully orchestrated by the West Virginia Department of Highways (WVDOH). The highway system comprises approximately 38,000 miles through some of the most rugged terrain in the country. It is this ruggedness that creates much of the beauty for which West Virginia is known. With an average elevation of approximately 1,500 feet above sea level, West Virginia is the highest of any state east of the Mississippi. As a result, construction costs for roadways in West Virginia are among the highest nationally on a per-mile basis.

The WVDOH understands these challenges. It has long recognized and utilized consultants sensitive to site conditions who balance practicality with new technology. Every project is unique with no cookie-cutter solution. The department maintains a professional staff of mostly native West Virginians who embrace the stewardship role with which they have been charged.

Bridges in the mountain state are abundant. They come in all shapes and sizes to blend into the terrain. They must be functional yet aesthetically pleasing. Currently, almost 7,000 bridges are being maintained by the department. To give a feel for the complexity of the bridges in the state, this article shares some insight not typically comprehended when traveling in the Mountain State.

Blennerhassett Island Bridge
Spanning the main and back channels of the Ohio River, as well as historic Blennerhassett Island, the Blennerhassett Island Bridge unites Belpre, Ohio, with Parkersburg, W.Va. The bridge is the final piece to Corridor D (U.S. Highway 50) and a joint venture between Ohio and West Virginia. It was designed by the team of Michael Baker, Jr., Inc.; HNTB; and E.L. Robinson, and was subsequently constructed by Walsh Construction Company. HCN, a Terracon Company, was selected to provide geotechnical input to the design team, plus quality control services to the contractor during construction.

The Blennerhassett Island Bridge spanning the main and back channels of the Ohio River, as well as historic Blennerhassett Island, represents the largest highway contract in West Virginia history.

The bridge and its approaches represent the largest highway contract in West Virginia history. The Network Arch Bridge ranks as one of the longest span structures of its type in the world. With a total length, including approaches, of more than 4,000 feet, it has a tied arch section of 878 feet, an approximate 175-foot rise, and a 76-foot clearance for river traffic. The bridge type was selected as best suited for the crossing based on the site’s environmental, historical, and architectural sensitivity.

The Network Arch Bridge ranks as one of the longest span structures of its type in the world with a tied arch section of 878 feet.

As geotechnical engineer of record, it was important to understand the site geology, with particular emphasis on the deep alluvial deposits and the sensitivity of the underlying shales. A series of test borings were performed to fully evaluate subsurface conditions for the structure and its ancillary features. All analysis and design was based on the use of American Association of State Highway and Transportation Officials (AASHTO) Load Resistance Factor Design (LRFD) specifications. The result was that bridge pier number two and abutment two were supported on Gr. 50 HP 14×89 piles driven to refusal into the soft sandstone and shale bedrock. All other substructures were supported on caissons with a maximum diameter of 8 feet and socketed into rock. Significant pile shaft downdrag loads were estimated at the abutments because of the large amount of the mechanically stabilized earth (MSE) fill resulting from MSE walls as tall as 51 feet.

This structure is a fitting gateway when entering West Virginia from Ohio, or vice versa. It has received numerous awards and was ranked as one of the top 10 bridges in 2007 by Roads & Bridges magazine.

James Rumsey Potomac River Bridge
The James Rumsey Potomac River Bridge was another challenging project on which HCN provided geotechnical recommendations. The bridge unites Shepherdstown, W.Va., and Sharpsburg, Md., carrying MB 34 over the historic Potomac River. Michael Baker, Jr, Inc., was the design engineer for the WVDOH; Brayman Construction was the general contractor.

The bridge has a total length of approximately 1,100 feet. It is a three-span, curved steel haunch girder structure replacing the existing Wichert Truss Bridge, which is one of the last remaining in the United States.

The James Rumsey Potomac River Bridge is a three-span, curved steel haunch girder structure with a total length of approximately 1,100 feet.

A test boring program was conducted to evaluate the subsurface conditions. As expected, the limestone bedrock encountered at the site was karst. Test borings and subsequent excavations revealed widespread pinnacle and trough features, deep crevices, and large voids. As a result of encountered conditions, the foundation system consisted of a combination of driven H-piles for the abutments, a spread footing for the support of pier one, and micro piles for pier two.

The project also included a new footbridge crossing the Potomac River and 12 retaining walls as tall as 50 feet. The retaining walls were used to support embankments, abutments, scenic overlooks, the banks of a canal, and a nearby historic hotel. Retaining wall types included the use of tieback anchor walls, MSE walls, soldier pile-lagging walls, and MSE/soldier pile wall combinations.

This project was part of a U.S. Federal Highway Administration (FHWA) pilot study for LRFD bridge design. All bridge substructures were designed accordingly. The bridge won the 2006 Excellence in Highway Design Award in Category 3 (Major Highway Structures) presented by the FHWA.

As interesting as the landscape is when traveling West Virginia, know that its geologic history is just as rich and varied. From the quartzitic sandstones of the east central portion of the state to the soft shales of the Ohio River Valley, from the karst limestone of eastern West Virginia to the remnants of past and present coal mines common throughout most of the state, and from rock outcroppings to buried ancestral valleys of 200 feet, designers must recognize and understand the past to design for the future.

Division Manager Jack Scott, P.G., and Project Geologist Bob Barclay, P.G., are with H.C. Nutting (HCN), a Terracon Company. James Wang, P.E., formerly with HCN, also contributed to this article. HCN has provided services to the West Virginia Department of Highways and its precursor, the West Virginia State Road Commission, since 1941.

Posted in Uncategorized | January 29th, 2014 by

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