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Geotechnical Engineering

 

Interstate Technical Group on Abandoned Underground Mines
Fourth Biennial Abandoned Underground Mine Workshop

Abstract: Kansas Department of Transportation Abandoned Underground Mine Update

The past two years in Kansas have been fairly inactive as far as Abandoned Underground Mine problems. However, the two mine projects we do have are probably the most hazardous, extensive and costly to date.

Project: US-69, Cherokee County

The Kansas Department of Transportation has proposed reconstruction of a 12 mile stretch of US-69 Highway in Cherokee County. During the Discovery Phase of the project, approximately 18 months ago, it was brought to the designer's attention that the southern portion of the proposed roadway will pass over a ¾ mile section that is severely undermined.

This area is a portion of the Tri-State Mining District. Mining for lead and zinc began in this area in 1870 and continued until 1970. These mines vary in depth from 200 to 400 feet with openings of 10 to 90 feet. One section of US-69 has an unsupported area of over 630 feet with no roof support!

Investigation of the mined area will initially require a 2-D Seismic Tomography Survey along the existing roadway. This survey should delineate any unknown mined areas and caved zones. An expanded 3-D survey will be conducted based on the information obtained. NSA will be conducting the tomography studies. This work is scheduled to start in May of 2002.

This information will than be utilized in selecting the type of remediation.

Types of Remediation:

  1. Grouting: If grouting is selected, we will install 20-foot diameter grout bags on 50-foot centers.
  2. Real-Time Monitoring System: This system would be installed in the boreholes used in obtaining the seismic survey information. A complete warning system will be required with dial up and emergency capabilities.
  3. Construct the roadway without any remediation!

The cost of remediating deep underground mines is very expensive, however the cost is slight when compared to a catastrophic collapse of a newly reconstructed highway. With any luck we should begin the 2-D tomography survey of this project by the meeting date!

Project 2, US-69, Crawford County

This project is one of the most aggressive mine remediation projects in the history of Kansas. The town of Pittsburg has been growing and the existing by-pass to the west is inadequate to handle the projected traffic loads. The proposed by-pass will cross approximately 7 miles of abandoned coal mines. Abandoned strip pits will be crossed in the first two miles. We have identified two major hazards in this area: 1. Acidic Soils, derived from the breakdown of Pyritic shales and coal. 2. Surface drainage, the surface run-off is governed by the configuration of the strip-pits. The interruption and redirection of the drainage is a major concern.

The remaining 5 miles are undermined. These mines vary from 10 to 175 feet below the surface with openings of up to 10 feet. Numerous collapses have occurred in this area. We have proposed remediation of all underground mines that are less than 60 feet deep.

The cost of remediation of this project is estimated to be near 7 million dollars for the underground portion and 3 million dollars for the strip pit portion. However, due to recent budget problems this project has been placed on hold, with the cost of the proposed remediation a major part of this decision.

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Updated: 04/07/2011

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