Research Activities: 2010

 Imaging of Voids Beneath Bridge Bent Using Electrical Resistivity Tomography

 

Status

 Complete                         View Final Report: PDF
 

Sequential Number
R283
 

Identification Number
00035795
 

Matching Research Agency

 

Missouri Department of Transportation
 

Principal Investigator
Neil Anderson
Missouri University of Science and Technology
1401 North Pine Street
Rolla MO 65409
p 573-341-4852
f 573-341-6935
nanders@mst.edu
 

Student Involvement

Two graduate students

 
 

Project Objective

Construction work to expand the existing I-44 bridge across the Gasconade River bridge structure water-filled encountered voids in the bedrock on site. These voids reportedly range from approximately 3 to 6.5 feet in vertical dimension and are located beneath roughly 18 feet of alluvium soil and 2 feet of bedrock below ground surface (bgs). Groundwater is reportedly present at a depth of approximately 6 feet bgs. MoDOT desires to better understand and define the lateral and vertical extent of these voids, especially as they relate to the existing bridge footings which are understood to be spread footings bearing on bedrock.


In an effort to better understand and define the lateral and vertical extent of the voids, MS&T will acquire electrical resistivity tomography data along six traverses immediately adjacent to the bent in question at the Gasconade River site (beneath MoDOT bridge across I-44). Four of the traverses will be laid out parallel to the river, two on either side of the bridge bent in question. Depending on site access constraints, the other two traverses will be laid out roughly perpendicular or at a skewed angle to the river on either side of the existing bridge bent. Our layout may need to change due to site access and potential issues working around the construction at the site.

We will acquire geophysical data using a Supersting R8 resistivity unit. Resistivity probes will be placed on 2.5-foot centers. Our work will provide imaging to a depth of approximately 30-35 feet bgs. Deeper imaging could be provided, however vertical and horizontal image resolution would be less.

Project Abstract

In an effort to better understand and define the lateral and vertical extent of shallow water-filled voids beneath a bridge bent (I-44, across Gasconade River), MS&T will acquire electrical resistivity tomography (ERT) data along six traverses immediately adjacent to the bent in question. Four of the ERT traverses will be laid out parallel to the river, two on either side of the bridge bent in question. Depending on site access constraints, the other two ERT traverses will be laid out roughly perpendicular or at a skewed angle to the river on either side of the existing bridge bent. Our layout may need to change due to site access and potential issues working around the construction at the site. The intent is to use this non-invasive technology to map the lateral and vertical extent of the water-filled voids so that appropriate mitigation plans can be developed.
 

Anticipated Benefits

If MS&T is successful, we will demonstrate that the electrical resistivity tomography tool can be used to reliably image small water-filled voids at depths on the order of 25 ft.
 

Milestones
Project Start Date: 02/28/2011
Project End Date:

09/30/2013
 

Project Deliverables

Map and geologic cross-sections depicting the lateral and vertical extent of soil, rock and water-filled voids in proximity to the bent.
 

Technology Transfer Activities

Results will be presented at national conference (probably FHWA Geophysics Conference in 2012) and published. The deliverables will include an evaluation of the utility of the electrical resistivity tomography method for mapping shallow water-filled voids and a discussion of the degree of resolution provided by the tool. A discussion of optimum acquisition and processing parameters will also be included.
 

Transportation Research Board Keywords

Resistivity, tomography, voids, geophysics