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Studies

Rockbridge County – Route 11 Natural Bridge State Park

Project at a Glance

Locality
Rockbridge

District
Staunton

Contact
Susan Hammond, Lexington Residency
540-463-3108
Sandy Myers, Communications
540-332-9201

Overview

The Virginia Department of Conservation and Recreation and the Virginia Department of Transportation are partnering as DCR’s master plan efforts for Natural Bridge State Park move forward. Natural Bridge came under DCR management in 2016. 

Route 11 travels over the Natural Bridge geological formation. VDOT is responsible for the maintenance of the Route 11 road surface and roadbed. Route 11 at this location is not considered by modern standards to be on a bridge. Instead Route 11 sits on a geological formation made of limestone. This type of rock material is common throughout the Shenandoah Valley and results in karst features, like sinkholes and caves.

DCR manages the park and its assets including the Natural Bridge geological formation. Both DCR and VDOT are committed to preserving the formation for current and future generations and are working together toward this goal. 

As a partner in the master planning process VDOT will provide resources and expertise for a geological analysis of Natural Bridge. VDOT will also conduct a transportation and mobility study on Route 11.

VDOT and DCR will use the data and reports as a basis for working together establishing a long-range plan for the preservation of Natural Bridge. Route 11 will continue to be located on the Natural Bridge structure during the master planning process. To date, no data have emerged indicating the road is unsafe or the geological formation is affected by the road and its traffic

Geological Studies

Prior to summer 2017 the Natural Bridge geological formation was not inspected by VDOT. In the late 1990s VDOT performed a limited inspection along with another private study done for the owner of Natural Bridge at that time.

To assist DCR with its master planning work, VDOT engineers and geologists began planning a series of non-destructive geological tests to be completed in 2017. A written analysis is part of this work. VDOT has contracted testing services through an agreement between the Virginia Transportation Research Council in Charlottesville and Radford University. The testing will be led by Dr. Chester (Skip) Watts of the Environmental and Engineering Geosciences Program at the Department of Geology at Radford University. Dr. Watts specializes in engineering geology and is a Certified Professional Geologist in the Commonwealth of Virginia. Dr. Watts is the past Dalton Distinguished Professor of Geology at Radford University and now heads the Geohazards Research Center.

Below is a listing of each test, type of data collected and data purpose. This material will be reviewed by an advisory board whose members are independent of DCR and VDOT. At the conclusion of all testing an interim report will be produced by early 2018 with the final report in spring 2018.

Ground Penetrating Radar (GPR)
LiDAR surveys
Unmanned Aerial System Surveys
Resistivity
Seismic Reflection or Refraction
Vibration monitoring, geophones, or other monitoring tools
Other methods as deemed necessary

Ground Penetrating Radar (GPR)
When: July 2017
Data Type: Electromagnetic radiation in the microwave spectrum. Air-Coupled Radar and Ground-Coupled Radar
Data Purpose: This non-destructive test provides 2D imaging of existing roadway layers.

Terrestrial Light Detection and Ranging (LiDAR)
When: August and October 2017
Data Type: 3D laser surveying (high resolution 3D digital models from the ground below the rock arch) 
Data Purpose: The LIDAR surveys provide a three dimensional representation of the geological formation’s surface features.

Unmanned Aerial System Surveys
When: November 2017
Data Type: Digital Photogrammetry (high resolution photographs).  Photography from unmanned aerial vehicles (UAV).
Data Purpose: Provides visual surface photographs and enhances surface mapping, and can be used to build 3-dimensional computer models of the rock structure. Complements the LiDAR survey data.

Electrical Resistivity
When: October 2017
Data Type: 2D imaging of rock formation subsurface
Data Purpose: This test will lay wires across the road surface. Small electrical pulses travel through the rock formation and are measured at various locations. The measured resistivity of the material at various depths provides an indication of the material type (rock, sand, air) and water content. These data provides a 2-D image of the formation subsurface for use in later analyses.

Seismic Reflection or Refraction
When: October 2017
Data Type: Refraction seismology (or seismic reflection) is a method of non-destructive exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from refracted seismic waves. A hammer device will be used to strike the ground and measure seismic response.
Data Purpose: These tests help measure the density of rock and how sensitive the rock is to vibration.  This test will help add engineering properties to the structural map of the rock.

Vibration monitoring, geophones, or other monitoring tools
When: November 2017
Data Type: Geophones are small seismic sensors that will be placed in a pattern across the ground at various locations or on the geological formation itself. Geophones convert ground motion into analog electrical signals displayed as wavy lines (ground vibrations)..
Data Purpose The geophones measure ground movement, such as vibration from an external source.

Transportation Studies

Route 11 Alignment Study at Natural Bridge
VDOT has initiated a study of the 5.5-mile segment of Route 11 between Interstate 81 exit 175 (Natural Bridge) and exit 180 (Fancy Hill).  The study will inventory existing road-related features in the corridor, document existing conditions and deficiencies, and take a preliminary look at potential alignment alternatives that may address these concerns and the future transportation needs of the area.  Factors such as existing accident data, operational analysis/congestion areas, environmental constraints and cost will be investigated.  Once the information is collected, workshops and informational meetings will be held in the community to discuss the options and determine the need and scope of potential improvements.

The alignment study will begin in October 2017 and we anticipate presenting the preliminary findings in the Spring/Summer of 2018.

Technical Advisory Panel for the Natural Bridge Geological Investigation Project

An advisory committee of prominent geologists in the United States and Canada will review all geological testing results from 2017, testing summaries and conclusions and issue an independent report. 

Dr. Tony Szwilski, Ph.D., P.E. Huntington, WV
Director of the Center for Environmental, Geotechnical and Applied Sciences (CEGAS)

Dr. Thomas M. Murray, Ph.D. Blacksburg, VA
Professor Emeritus, Virginia Polytechnic University

Dr. Joe Carvalho, Ph.D., P.E. (CA). Mississauga, ON, CA
Principal, Golder Associates

Dr. Abdul Shakoor, Ph.D. Kent, OH
Professor Emeritus, Kent State University

Dr. Edward J. Hoppe, Charlottesville, VA
Associate Principal Research Scientist, Virginia Transportation Research Council

Mr. David Spears, Charlottesville, VA
State Geologist for the Commonwealth of Virginia

News Media Events

Natural Bridge Lidar Testing - Media Availability
Wednesday, August 16, 2017, 9:30 a.m.
Natural Bridge State Park Visitors Center, 6477 South Lee Highway, Natural Bridge, VA 24578 

Natural Bridge Geological Testing - Media Availability
Tuesday, October 3, 2017, 10:00 a.m.
Natural Bridge State Park Visitors Center, 6477 South Lee Highway, Natural Bridge, VA 24578

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Page last modified: Sept. 28, 2017