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Manual for Abandoned Underground Mine Inventory and Risk Assessment
Section 10: Emergency Action / Road Closure

10.1 GENERAL DISCUSSION:

The purpose of this section is to provide general guidelines for consideration of emergency remedial construction and/or closure of the roadway to traffic. Such roadway conditions may be discovered during the Initial Site Investigations, Site Monitoring, or Priority Site Investigations. They may also be reported at any time to the coordinating District engineer by ODOT staff or by the general public.

Regardless of the amount of investigative information available, it is impossible to determine exactly when a collapse of a roadway may occur. Geologic and hydrologic conditions may vary considerably over a site. In addition, conditions of materials may change dramatically following a collapse of supporting roof rock or pillars. It is impossible to fully investigate 100 % of a site and fully know present conditions. Consequently an attempt to predict future stability and safety of the supporting overburden and roadway is, at best, an informed guess.

Specific criteria to determine the safety of a roadway and whether a roadway should be closed cannot be given. Questions and factors to consider are offered in this section. The possible danger of a site should not be disregarded. Alternatively, undue alarm and extreme reaction should not be expressed at every site with a possible hazard. A thoughtful balanced decision should be made using all available information. This decision should balance the safety of the mine site, and the safety and mobility consequences of the detour route. It is expected that, since the decision is ultimately an informed guess, errors of judgement may occur.

10.2 INVESTIGATIONS

The coordinating District engineer should use his or her best judgement in the field management of such a site. Extreme conditions may only require visual inspection to make an initial determination of risk. Less extreme conditions may be impossible to evaluate without initiation of site investigations. Investigation should continue as far as necessary until enough information is available to make a reasonably informed decision Until such time as the safety of the traveling public is assured, such a site should be considered as a priority site requiring immediate investigation per Section 7. Once the existence of such a site is verified, the coordinating District engineer should notify the appropriate ODOT staff and outside agencies as discussed in Subsection 7.2.

WARNING:

The District and the county need to be prepared to manage the worst case conditions that might be revealed during the investigations. Investigations may indicate the need for immediate road closure and/or emergency remediation. The availability and identification of reasonable detour routes, as documented in the Detailed Site Evaluation, should be reviewed with the District Roadway Services Manager and the County Manager.

10.3 FACTORS TO CONSIDER

Several aspects of the site conditions, and the public exposure to those conditions, should be considered:

  1. Can a sudden collapse occur in the roadway without warning? Some factors to consider include:

    1. Type and condition of pavement (CRCP should provide support with some deflection before failure)

    2. Number of subsidence features that have already occurred.

    3. Type and condition of overburden beneath the roadway. Fractured rock indicates that collapse and movement is already occurring.

    4. Granular soils can collapse abruptly.

    5. Deep soils overlying small amounts of mine roof rock can allow rapid upward movement of subsidence to the surface.

    6. Proximity (angle of draw) of adjacent collapses or shafts.

    7. Voids encountered under the roadway.

  2. What is the exposure of motorists to the possible danger in the event of a collapse? Some factors to consider include:

    1. Speed.

    2. Density of traffic.

    3. Type of Traffic (Number of heavy vehicles).

  3. Can motorists reasonably observe and avoid a potential collapse? Some factors to consider include:

    1. Speed of Traffic.

    2. Density of traffic.

    3. Type of traffic.

    4. Roadway geometrics.

    5. Roadway lighting.

  4. Would a detour provide a safer, or less safe, condition? Some factors to consider include:

    1. Underground mines under detour.

    2. Detour geometrics and capacity.

    3. Increased number of intersections and pedestrians on detour.

  5. Would you want your family to drive over this site?

10.4 ALTERNATIVE RESPONSES

The available options for the management of such a site can be defined by two levels of risk. These levels of risk and their associated alternatives are:

10.4.1 Site Conditions Represent No Perceivable Immediate Risk:

10.4.1.1 No Action:

The site may be determined to not pose a threat to the safety of the traveling public. No action would be required in such cases. Monitoring would continue to follow normal procedures.

10.4.1.2 Increased Monitoring and Possible Site Reevaluation:

The site may be determined not to pose an immediate threat to the safety of the traveling public, but to warrant increased monitoring. Forms of increased monitoring should be determined in the best judgement of the coordinating District engineer.

The coordinating engineer should also consider reevaluation of the site because of the changed conditions.

10.4.2 Site Conditions Warrant a Measured Response :

If action is to be taken, the first decision to be made is whether the roadway can safely remain open while on-going Priority Site Investigations or emergency construction is undertaken. Action will be undertaken either while maintaining traffic or under road closure. If emergency construction is chosen, the coordinating District engineer should keep in mind that remediation may unintentionally induce additional or new settlements in adjacent lanes carrying traffic.

10.4.2.1 Maintaining Traffic:

If the coordinating District engineer determines in his or her best judgement that the safety of the traveling public can be maintained while action is taken, then one of the following courses of action should be undertaken:

  1. Initiation of Priority Site Investigations

  2. Initiation of Emergency Construction

10.4.2.2 Road Closure:

If the coordinating District engineer determines, in his or her best judgement, that site conditions represent a possible risk to the traveling public, the coordinating District engineer shall notify: 1) the District Deputy Director; 2) the District Highway Management Administrator; 3) the District Public Information Officer; 4) the County Manager, and; 5) the Administrator of the Office of Highway Management in the Central Office. The coordinating District engineer shall await the decision of the District Deputy Director as to the desired management of the site. If road closure occurs, one of the following actions should be undertaken:

  1. Initiation of Priority Site Investigations

  2. Initiation of Emergency Construction

10.5 SITE RECORDS

A record of all communications, site information, and actions taken should be maintained as a permanent file.

10.6 SITE MONITORING

Monitoring requirements will be determined by the coordinating District engineer on a site-by-site basis.

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Updated: 04/07/2011

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United States Department of Transportation - Federal Highway Administration