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Geotechnical Engineering

 

Manual for Abandoned Underground Mine Inventory and Risk Assessment
Section 1: Introduction

1.1 GENERAL DISCUSSION

The ODOT Abandoned Underground Mine Inventory and Risk Assessment process was conceived as a proactive response to the need to locate and assess the risk of all mapped or otherwise identified roadway sites beneath which abandoned underground mines exist. The scope of such an undertaking is extremely formidable. Hundreds of such roadway sites potentially exist in Ohio. The age of the majority of the abandoned underground mines associated with these sites ranges from 50 to 150 years. Available records for these mines can vary greatly between the different sites.

The process documented in this manual is the most logical and practical approach to establishing such an inventory. Due to the large number of sites, it is not logistically or financially responsible to commit limited forces and funding to investigation and remediation of random sites. A cornerstone of this inventory and risk assessment process is the concept of being as informed as possible before ever committing limited resources to individual sites for detailed investigations and, if necessary, remediation. The sites which pose the greatest threat to public safety should be assessed as having the highest priority

This document is not a design manual. The purpose of this manual is to provide a means of site inventory and risk assessment. English units of measurement are utilized in this manual since a large part of this process involves review of historic documents utilizing such units of measurement. All detailed design work and construction documents which might be undertaken as a result of the site inventory and risk assessment process documented in this manual should be either in metric units of measurement or dual units of measurement.

1.2 OVERVIEW

The process documented in this manual is comprised of four basic activities: 1) the establishment of an inventory of all roadway sites beneath which abandoned underground mines may exist ; 2) site monitoring ; 3) the assessment of the risk to the safety of the traveling public which each site represents and; 4) remediation, if necessary. A process flow chart is presented as Figure 1.1. The definitions of commonly used terms in this manual are provided in Appendix A: Glossary of Terms.

Abandoned Underground Mine Inventory and Risk Assessment
Figure 1 - Process Flow Chart. The figure shows a flow chart to the Abandoned Underground Mine Inventory and Risk Assessment Process.  It starts with an initial informational review then goes to site inventory.  The process continues to initial site investigation and initial site evaluation which results in classifying into one of five groups (Surface Deformation, Mine Opening, High Rating, Low Rating, or Eliminated Sites).  The process proceeds to periodic monitoring, detailed site evaluation, prioritized site listing and priority site investigation.  All of these steps feed back to site reevaluation and possible reclassification to a different group.  From priority site investigation the process proceeds to priority site recommendations, development of construction contract documents, remedial construction, then to an active file and back to monitoring.
Figure 1.1: Process Flow Chart

1.2.1 Establishing An Inventory of Sites: An initial comprehensive site listing should be established for the inventory area. This effort will include review of available records for abandoned underground mines within the inventory area. Field report forms should be discussed and provided to roadway authority personnel for the purpose of gathering field information which might reflect mine-related problems beneath the roadway. Such reports should then be investigated by staff who are involved with the inventory process and are familiar with signs of mine-related problems.

Next all sites should be visited and certain field information should be recorded. Every effort should be made to obtain enough information from one site visit to allow for the risk assessment of the site through Initial and Detailed Site Evaluations as described in this manual. Following this initial site visit, each site shall be subject to periodic monitoring.

1.2.2 Site Monitoring: Interim periodic monitoring will be initiated on all inventory sites. The frequency and extent of required monitoring activities will depend on site conditions as well as they can be identified at this point in the process. All sites will ultimately be periodically monitored on a permanent basis. Frequency of monitoring will be determined on a site-specific basis.

1.2.3 Risk Assessment: The risk assessment portion of this process takes into account two basic factors: 1) the existing site conditions and; 2) the level of the traveling public's exposure to those existing site conditions.

1.2.3.1 Initial Site Evaluation: An Initial Site Evaluation of all sites in the established inventory will be performed by applying applicable site evaluation criteria to available information and field observations. This Initial Site Evaluation process will determine into which of the five risk-assessment site groups each site will be placed. The Low Rating Site Group will be placed under a permanent monitoring program and remain as active files in the inventory program. The Eliminated Site Group will become inactive permanent record files in the inventory program.

1.2.3.2 Detailed Site Evaluation: Detailed Site Evaluation risk assessment will be performed on the Surface Deformation, Mine Opening, and High Rating Site Groups as determined by the Initial Site Evaluations. This work will be performed for each site group in order of their group's priority level of risk. All sites within a site group will be evaluated using site evaluation criteria considered pertinent to the nature of the sites within the group. Detailed Site Evaluation risk assessment will be completed utilizing existing information and information gathered during the initial inventory site visit. The result of the Detailed Site Evaluation process will be a prioritized listing of the sites for the Surface Deformation, Mine Opening, and High Rating Site Groups as defined by the Initial Site Evaluation process.

1.2.3.3 Priority Site Investigations: Priority Site Investigations will be performed on each site within each of the three Detailed Site Evaluation site groups. These site investigations shall be performed in the order of the prioritized listing of the sites for each of the Detailed Site Evaluation risk assessment site groups. All sites within the particular Detailed Site Evaluation risk assessment group will be individually evaluated before evaluation proceeds to sites in the next lower Detailed Site Evaluation group. These investigations will result in Priority Site Recommendations.

1.2.3.4 Priority Site Recommendations: The Priority Site Recommendation shall either specify remediation of defined site conditions, with periodic monitoring to follow construction, or periodic monitoring only. Some recommendations may involve emergency action or temporary road closure. Interim, site-specific monitoring requirements will be specified for the period prior to the implementation of remedial construction or permanent monitoring.

1.2.4 Remediation:

1.2.4.1 Development of Construction Documents: In the case of Priority Site Recommendations requiring the remediation of potentially hazardous conditions, construction drawings, specifications and special provisions will be developed for each individual site. Regardless of the extent of investigations performed, the actual site conditions cannot be fully determined prior to construction. Therefore, this manual places emphasis on flexibility of methods, quantities and project limits.

Existing conditions may change, or new conditions may develop on the site in the period required for contract document development. Guidance is included in this manual for continued site monitoring during Development of Construction Contract Documents.

1.2.4.2 Remedial Construction: Remedial construction shall be performed on those sites where such work is recommended by the Priority Site Recommendations. Close inspection of the work, monitoring of time and materials usage, and accurate record keeping is important during construction. Accurate records will be invaluable for post-construction monitoring and reference in the case of future subsidence conditions occurring adjacent to the project area.

Existing conditions may change, or new conditions may develop on the site during remedial construction. Certain forms of remediation may unintentionally induce additional mine-related settlement. Site monitoring to detect possible changes during remedial construction should be performed.

1.3 SUMMARY

1.3.1 Expected Benefits:

1.3.1.1 Public Safety: The process will minimize the possibility of sudden abandoned underground mine subsidence in roadways, which could result in fatalities or bodily injuries.

1.3.1.2 Reduced Liability: The process will identify and prioritize high risk sites permitting a systematic response.

1.3.1.3 Budgetary Mechanism: This process will identify levels of risk and associated costs. This information can be used to develop budgets to reduce risks to a predetermined level. This is a proactive process to identify high risk locations. Accordingly, these locations with the highest risk of failure will be identified and remediated first resulting in fewer instances of sudden collapses requiring emergency treatment.

1.3.1.4 Informational Resource: This process will create a new database of information available to all staff. This database will be a tool which can be utilized to avoid or anticipate potentially unstable underground conditions during project planning, design, construction and maintenance.

1.3.2 Governing Principles: Basic principles governing this process include:

  1. Working on the highest risk identified site at all times.

  2. Being as informed as possible before committing resources to a site.

  3. Being prepared to encounter "worst case" conditions for the nature of the site to be investigated or remediated.

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Updated: 04/07/2011

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United States Department of Transportation - Federal Highway Administration