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Geotechnical Engineering

 

Manual for Abandoned Underground Mine Inventory and Risk Assessment
Section 9: Remediation

9.1 GENERAL DISCUSSION:

The purpose of this section of the manual is to provide general guidelines and advice for the remediation of priority sites. This remediation effort should consist of the development of remedial construction documents and the performance of the remedial construction.

9.2 DEVELOPMENT OF CONSTRUCTION DOCUMENTS:

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 using English units. 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 prepared in metric units or dual units of measurement.

Information obtained during the Priority Site Investigation should be used to select the remediation technique and to develop construction documents. The design engineer should consult with the coordinating District engineer throughout the design process. Specific documents for the various remedial construction techniques are not provided in this inventory and risk assessment manual.

9.2.1 Flexibility of Contract Documents:

All information developed through Priority Site Investigations and Recommendations is limited and does not necessarily define every possible condition which may be encountered throughout remedial construction work. Non-intrusive investigations do not precisely define subsurface conditions. Intrusive investigations precisely define conditions at specific locations.

The design engineer is faced with the task of making decisions and developing contract documents for the repair or replacement of the existing overburden structure. However, the design engineer is only given general information or limited detailed information (borehole logs, etc.) of the location, dimensions, and condition of the existing overburden structure. The designer should be aware that the mine maps, if available, may not be accurate regarding the location and extent of the mine. The extent of secondary mining, mine deterioration, and possible mine collapses will not be known.

Because of the limited site information available, design decisions should remain conservative and construction contract documents should be flexibly structured. This flexibility should allow for as many adjustments as can be foreseen prior to performing the work. Contingency items should be included for work which may or may not be needed. This flexibility should reduce or eliminate the need for negotiation of new items during construction.

9.2.2 Determination of Work Limits:

Work limits should be extended beyond the expected area of roadway needing remediation. This guideline is recommended because the actual extent of the needed remediation will only be revealed through the execution of the work. An increased project work area cleared for construction activities should help in minimizing any complications related to the possible need during construction to expand project limits.

9.2.3 Progression of Project Work:

The sequencing of construction operations should be tailored for each site. The following guidelines should be considered in the development of construction documents.

9.2.3.1 Excavation Operations, and Drilling and Grouting Operations:

Work should generally be specified to progress from an unaffected area of roadway on one side of the remediation site, to a similar unaffected area of roadway on the other side. This guideline is intended to minimize the possibility of the project being completed without addressing all areas requiring remediation.

9.2.3.2 Shaft Stabilization:

All initial operations should be performed with equipment and on-site storage of materials being located beyond the pre-determined Shaft Danger Zone, as described in 7.4.2.2.2 and shown in Figure 7.2. Shafts which are to be backfilled should be cleared by cranes or other equipment, and then backfilled. Shafts which are to be stabilized by drilling and grouting should be angle drilled and grouted by equipment located beyond the Shaft Danger Zone.

9.2.3.3 Other Forms of Remediation:

Other sequencing of construction operations may be required due to unique site conditions or constraints.

9.2.4 Compliance With Applicable Regulations:

Any person performing work related to underground mines must note that significant legal consequences may stem from failure to comply with all relevant environmental laws. The coordinating District engineer should contact the appropriate Ohio EPA (OEPA) District Office contact person capable of advising ODOT on all areas of environmental compliance about which ODOT must be concerned. The coordinating District engineer should refer to Appendix D: Contacts for the appropriate OEPA District Office contact person for each project location. The coordinating District engineer should also process the projects through the District Environmental Coordinator for clearance through the Department's environmental process as documented in ODOT's Transportation Development Process (and implementing manuals).

If the remote placement of stable backfill materials in subsurface voids is the chosen form of remediation, boring locations and logs, and material placement records are critical to ODOT. They will also be required for compliance with reporting requirements of the OEPA injection well permit program described in the following paragraph.

Drilling and grouting programs must comply with the OEPA UIC Permit to Install / Permit To Operate A Class V -Injection Well Area Permit for Well Code 5X13. Compliance with this OEPA injection well permit program is a requirement for a drilling and grouting program, even if an actual permit is not required. Such a situation could occur for a given project if industrial waste materials, such as flyash, comprised less than 50% by weight of the components in the chosen grout mixes. If remote placement of stable backfill materials in subsurface voids is being considered for site remediation, the coordinating District engineer should contact the appropriate Ohio EPA UIC-specific contact person to assist with this permit program. This OEPA contact should be in addition to the OEPA District Office contact which should also be made. OEPA UIC-specific contact information is provided in Appendix D: Contacts.

9.2.5 Site Monitoring During Document Development:

Provision should be made for continued site monitoring during development of construction contract documents. Existing conditions may change, or new conditions may develop on the site during this period. The coordinating District engineer should refer to Section 5: Site Monitoring for recommended guidelines on the forms and frequencies of monitoring which are applicable. Contract documents should alert the contractor to the requirement that he is to provide monitoring or allow access to ODOT for monitoring.

9.3 REMEDIAL CONSTRUCTION:

Since the actual limits and nature of all required project work may only be revealed through the completion of the work, the project engineer and inspection staff must remain well informed of work progress and changing conditions encountered. When most remediation projects are completed, the only picture of the final product will be the three-dimensional one in the mind's eye of the project engineer and inspection staff. The project engineer should be familiar with all facts obtained during the Priority Site Investigation and should be fully aware of the intent of the design.

9.3.1 Project Construction Inspection:

Close inspection of work as it progresses should be maintained. Inspectors should report changed conditions revealed by the work immediately to the project engineer. The project engineer should advise the design engineer and coordinating District engineer of any unusual or unexpected conditions encountered during the work. If conditions are encountered which substantially change the overall scope of the project, the design engineer and coordinating District engineer should be consulted. If for any reason the project engineer proposes a significant deviation from contract requirements, the design engineer and coordinating District engineer should be consulted, so that the intent of the design is not compromised.

The project engineer and inspection staff should work closely with the contractor to anticipate points during the progress of the work where efficient and informed decision making will be required for the work to proceed efficiently and without delay. Any operational changes, phasing of work operations, or other adjustments required during a given day or shift should be documented. These adjustments should also be explained to all other staff which might be inspecting the work on the following days or shifts.

All construction staff should make an effort to stay informed of work progress and changing conditions. Shared information and good inspection records will be the only means the project engineer and inspection staff will have to review the completed work.

9.3.2 Construction Testing:

If the remote placement of stable backfill materials in subsurface voids is the chosen form of remediation, confirmation boreholes should be performed and accurately logged. Any voids encountered by such confirmation boreholes should be filled with grout, as well as the boreholes themselves. Accurate drilling and grouting records of confirmation boreholes should be made part of the permanent project records.

Ground penetrating radar (GPR) or other forms of geophysical testing may also be considered as a means to verify the completion of remote placement of stable backfill materials.

Impact echo testing, selected borehole redrilling, and other forms of testing may be required for remedial work involving grouted boreholes.

9.3.3 Project Construction Records:

Accurate and thorough record keeping during project construction is essential. Most remediation work will involve construction below grade. Subsurface conditions may be highly variable throughout the work area. Accurate records should be kept of all work performed below grade. An accurate record of the actual work limits should be a part of this record keeping.

Subsidence events that occur during construction, as well as mine openings and other mine-related features or conditions encountered during construction, should be photographed. These photographs should be included in the permanent construction record.

Actual time and materials usage as compared to that anticipated in the construction documents should be monitored. This work will provide an indication of potential overruns of contract items, and/or subsurface conditions other than anticipated by the construction documents.

"As-built" drawings should be produced for all mine remediation projects when possible. These drawings should contain all modified or new information developed as the result of the project. This information should include the location of all new production boreholes, confirmation boreholes, adjacent mine workings, work performed under contingency items, and actual work limits.

The above described construction records are necessary for the future monitoring of the site. Post-construction inspection of completed work items, in the traditional sense, will not be possible due to the work being below final grade. Accurate construction records will be invaluable as a reference for post-construction monitoring and review of conditions adjacent to the project area.

Pertinent project records such as drilling and grouting summaries, photographs, "as-built" plans, etc. should be transferred to the coordinating District engineer after physical completion of the work.

9.3.4 Site Monitoring During Remedial Construction:

The site should be monitored for possible changes during remedial construction. Existing conditions may change, or new conditions may develop on the site. Certain forms of remediation may unintentionally induce additional mine-related settlements. The potential impact of such settlements should be a consideration in the development of a construction monitoring program.The coordinating District engineer should refer to Section 5: Site Monitoring for recommended guidelines on the forms and frequencies which are applicable during project construction.

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Updated: 04/07/2011

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