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Bridges & Structures


ODOT Abandoned Underground Mine Inventory and Risk Assessment Workshop

Meeting Agenda

Photos from the Workshop

Columbus, Ohio
September 16-18, 1997

Tuesday, September 16, 1997

Opening Remarks

Rick Ruegsegger, Geotechnical Design, ODOT, opened the Workshop with an explanation of the Workshop schedule, the materials available, brochures, etc.

Chris Runyan, Assistant Director for Transportation Policy, ODOT, and Ernie Blais, Program Operations Engineer, FHWA, gave the welcoming address to the participants.

Introduction to the ODOT Abandoned Underground Mine Inventory and Risk Assessment Process - Rick Ruegsegger

This process is a systematic and organized method to identify sites, develop an inventory, and assess the risk for each site. The process can be used to assess mines under existing highways and also be used as a tool in the design of new projects. The goal is to avoid surprises and protect the safety of the traveling public.

Ohio Mining History and Abandoned Mine Records - Doug Crowell, ODNR, DGS

Underground mining in Ohio started in 1748. There are 4,600 documented mines in Ohio, and more than 2,000 undocumented. The cost of the I-70 collapse was determined to be $3.8 million. Maps are available at the National Repository of Mine Maps in Pittsburgh. There are ten active underground mines in Ohio. Maps are also available for these mines.

Cooperative Efforts Between Sister State Agencies for Mutual Public Gain - Harry Payne,ODNR, DMR

Funding is obtained from coal severance taxes of $.35/ton for surface mined coal and $.15/ton for underground mined coal. ODNR has digitized maps of underground mine limits available. They are also planning to scan available mine maps and all mine attributes to the map database. Harry also introduced John Husted, Division of Mines and Reclamation. ODNR took over the emergency program from OSM in 1992. The majority of the emergency work is subsidences. They also repair some landslides, vertical openings, burning gob, etc. They can remediate private land but cannot repair damaged structures over the land. When reviewing the eligibility of a site for funding the regulations require a review to determine whether another agency has the ability to act expeditiously in responding to the event. Structural damage is handled through the Ohio Mine Subsidence Insurance Program available to homeowners which is mandatory in some counties and optional in other counties. Most subsidence sites are remediated by injection. Voids 2' and greater are filled with concrete, voids less than 2' are filled with grout. State and Federal Abandoned Mine Land funds pay for injection holes on private land; the Ohio Mine Subsidence Insurance Program pays for structural damage. There are over 600,000 acres of underground mines in Ohio.

Initial Informational Review and Establishment of Site Inventory - Rick Ruegsegger

Three sources of information are used to identify sites: ODOT Field Reports and associated Office Investigations, several forms of ODNR, DGS abandoned underground mine documents, and reports of subsidence activity adjacent to the roadway documented by other state and federal agencies. It is cautioned that available information may not be entirely accurate. As an example the north arrow on the mine map may indicate magnetic north rather than true north. It was suggested that latitude and longitude be included on the Inventory Site Listing. ODNR locates sites by latitude and longitude. If ODOT located their sites by latitude and longitude there could be mutual access to information.

Initial Site Investigation and Evaluation - George Beiter, Planning, District 5, ODOT

The information obtained during the initial site investigation produces a permanent record of site characteristics and conditions to be used for initial and detailed site evaluation. Site investigations, who to contact, equipment needed, etc. were all discussed. The initial site evaluation subdivides the sites into five risk assessment site groups by applying weighted criteria to information gathered during office and site investigations.

Site Monitoring and Reevaluation - Gene Geiger, Geotechnical Design, ODOT

All sites will require periodic monitoring. Monitoring will be site-specific. Several guidelines are listed in the manual distributed at this Workshop.

Detailed Site Evaluation - Tom Lefchik, Assistant Bridge Engineer, FHWA, Ohio Division

The detailed site evaluation uses weighted criteria to prioritize sites within each site group. Each group is evaluated in priority order after all sites in the previous group are remediated.

Priority Site Investigation - Tom Lefchik

This is the investigation of the highest priority site. The purpose of the investigation is to provide information for the determination of the type and extent of remediation. The investigation progresses in three steps: gathering available information, performing non-intrusive investigation, and performing intrusive investigation.

Priority site recommendations - Gene Geiger

This section involves the determination of the type and extent of remediation by using information previously gathered. Individual site conditions affect the decision.

Remediation and Emergency Action/Road Closure - Jim Graham, Highway Management, District 11, ODOT

The contract documents should allow flexibility during construction. For emergency situations site investigations should be performed. The decision process often evolves from trying to justify a road closure to trying to justify keeping the road open. At the beginning of the investigations, preparations should be made for an immediate road closure in case it becomes necessary. The safety of the traveling public is the primary consideration.

Preliminary and Final Development Applications, and Process Summary - Rick Ruegsegger

The process outlined in the manual should be integrated into roadway planning and design. A number of slides were used for this presentation.

GUE-70-14.10 Project Presentation - Rick Ruegsegger

Subsidences had occurred in the area of this project prior to a sudden collapse of the roadway. ODOT was in the process of developing remediation plans and was monitoring the roadway every four hours. The entire roadway was closed in response to the collapse and an emergency contract was sold. Remediation consisted of drilling approximately 1800 holes and placing approximately 50,000 CY of grout into the water filled mine voids and constructing two double reinforced concrete "land bridges". Cost of the project, including land bridge installations and pavement replacement, was approximately $3.6 million.

IR-70.IR-77 Interchange Project Presentation - Tom Lefchik and Harold Neuhart, Highway Management, District 5, ODOT

Reports of past subsidences in the infield areas of the interchange prompted investigation using borings. Mine voids varied in depth from 10' - 100' from the pavement surface. Numerous roof falls were discovered and it was found that the sandstone roof rock had weathered badly in some locations. Remediation consisted of drilling 2600 holes and placing 80,000 cy of grout in subsurface void areas. The cost of the project was approximately $4.7 million.

BEL-470 Project Presentation - Jim Graham

The investigation of this site progressed in an orderly manner after the discovery of subsidence features. Investigation included ground survey, profilometer, falling weight deflectometer, ground penetrating radar, borings, and down hole camera. The media was informed that ODOT was performing investigations and were invited to the site. Remediation consisted of approximately 400,000 total yards of roadway excavation, new pavement, signs, lights guardrail, striping and revegetation. The project was completed in 14 weeks at a cost of approximately $3 million.

TDR Applications for Monitoring Settlements Related to Abandoned Underground Mines - George Beiter

TDR - (Time Domain Reflectometry). This process was developed in the 60s for locating discontinuity in television cable lines. It was adapted for use in locating rock movement in 1978. It involves sending a pulse down the cable and measuring the reflections.Vertical and horizontal ground movements can be detected through the installed TDR cables. ODOT has installed several cables and recently installed remote monitoring equipment at one site. One cable has registered some movement.

Detection of Underground Voids in Ohio by Use of Geophysical methods - Rod Sheets, USGS, Columbus Office

Discussed the use of ground-penetrating radar for investigating mine sites in eastern Ohio and a karst site in western Ohio. Soils types do not allow good results in eastern Ohio. Better results were obtained at the karst site. A final report of this work for ODOT should be available from U.S.G.S. later this year.

Wednesday, September 17, 1997

Illinois Presentation - Alan Goodfield, Illinois Department of Transportation

For bridge rehabilitation/repair projects a bridge condition report is prepared. At the time of the preparation of the report the Illinois Geological survey is contacted to determine if a mine exists under the bridge. If a mine exists the Illinois Geological Survey sends a mine map and mine notes which describe the mine thickness, percent extraction and any mine history or reputation. All of this information is put in a permanent record for the structure. Integral abutments are not used when mine subsidence is possible. Collapse problems on highways as occur in Ohio are not known in Illinois.

Coal is approximately 200' deep at Springfield and up to 1000' deep in southern Illinois. Longwall mining is now primarily practiced.

There was one instance of active longwall mining under a roadway. The operator was required to provide a maintenance crew around the clock with a grader, supply roadway lighting. Breakup of the pavement was experienced. No bridges were involved.

When mining is permitted under a bridge the extraction is limited to 40%. Research has indicated that subsidence is not expected at an extraction up to 40%.

Three miles south of Springfield a 250' long, three span bridge over I-55 subsided 2' uniformly and did not experience any distress.


IDOT uses Tan 15 degrees times the depth of coal to define the limit to which present day mining operations may approach the edge of the roadway. Sometimes entries are allowed across the road for haulage and/or ventilation purposes.

I mineral rights were purchased prior to regulations then the company has the right to subside. If mineral rights were purchased after regulations then the company does not have the right to subside.

Kentucky has dropped structures up to 4' with longwall mining but must make sure that the coal is mined out completely.

Kansas Presentation - Bob Henthorne, Kansas Department of Transportation

Salt in central Kansas, limestone in NE Kansas, coal, lead, and zinc in SE Kansas.

The Crawford sink under I-70 has subsided 7'. The distance across this sag is approximately 1300 to 1500 feet. It is the result of a salt mine and leakage of water around the casing of oil wells. The mine is 1300-1600' deep with voids occurring at depths of 550 feet and 950 feet. Void heights at these two depths can be approximately 65 feet. Two unsuccessful attempts were made to seal the wells. An attempt was made to reduce surface water infiltration through the divertion of drainage. This redirection of drainage has slowed the settlement but has not stopped it.

A series of settlements occurred on K-7. Drilling investigation revealed mine voids. Grouting was performed. Confirmation drilling revealed that the grout flow followed the dip of the mine and the voids were not completely filled.

When a camera is used for drilling, the hole is cased with 8" PVC. Kansas has used a 35mm camera in a clear 6" PVC case. A 8mm video camera with a halogen headlight and a spotlight has also been used. The video camera must be tilted to get down the hole. Kansas has also made a periscope from 8" PVC and a mirror set at 45 degrees and a spotlight mounted on the bottom.

Kansas has used the column method where the mine is at uniform depth and there is good roof. A 15' spacing was used on early projects which resulted in overlap of the columns. Now a 20' spacing is used which gives a little bit of a gap between the columns. a 5-2-1 sand-flyash-cement mix is used. The barrier mix has a 3 inch slump and the production mix has a 12 inch slump.

Concrete slab bridges constructed at grade have been used in two cases. In one case a 36' span bridge with piles set through predrilled holes was used to span a drainage opening through a water filled mine on a grouting project. In another case a slab bridge was used to span settling fill in a mine shaft.

Lead and zinc mines can collapse suddenly - up to 170' deep. Backfilling has been used for these repairs.

Most projects are shared funding with OSME through KDHE. OSME funding can be obtained if a threat is posed to the public. KDOT management provides any funding needed for projects.

A 9" borehole is used for camera viewing. The camera has been used down to a 68' depth.

Roadways are checked shooting levels. When sags are noted drilling is performed within a week and monitoring begun.

Kansas uses a periscope for viewing a mine. Columns and barrier walls are used for grouting. KDOT has built a number of at-grade 36-foot slab bridges over mine collapse to keep waterways within abandoned underground mines open. The slab thickness is 14 inches. This work is typically constructed one lane at a time, with the roadway open to traffic in 7 days.

There have been a number of subsidences in the Galena area of Kansas. The area is a USEPA super fund site. Overburden bedrock exhibits high angle or vertical jointing. The drilling was performed with a downhole hammer due to chert in overburden.

75% of mine grouting beneath KDOT roadways has been funded by OSM.

Kentucky Presentation - Earl Wright, Kentucky Department of Highways

The entire state has been stratigraphically mapped. There are 22,000 mine maps. Mines and Minerals Department in Lexington has all maps. The available information includes method of mining, elevation of coal, size of openings, pillar dimensions, percent extraction, age of mining and roof fall records.

Design of roadways considers: history of subsidence in the area, multiple seam mining, position of openings in the mountains, presence of water, orientation of openings relative to the roadway, and anticipated damage from blasting and mine fires. Kentucky has eastern and western coal fields. A majority of the problems related to mines beneath state roadways occur in the eastern Appalachian coal field.

At the crossing of US-62 and Pennyrile Parkway an old mine exists. Subsidence began occurring 17 years ago because of possible pulling of the pillars. The bridge was temporarily shored and nothing has been done since. Tilt plates and ground survey points are utilized to monitor structures.

A factor of 0.72 times the size of mine void is used to determine possible depth of subsidence.

Pneumatic stowing of mine openings and horizontal separations in upper-lying overburden is used in cut slopes. Typically #57 stone is used and a drainage pipe placed at the face and 6% cement added to the stone to seal the entry. Pneumatic stowing has been successful. Stowing is performed to the width of the lift. Kentucky uses a 25' minimum bench and a 60' maximum lift, with a backslope of ½:1.

In Martin County, Kentucky on Ky. Rt. 3, the proposed grade was lowered so as to daylight the mined coal seams. No mine map existed for this location. Damage to the overburden structure occurred as the result of pre-split blasting. The contractor was allowed to take the coal encountered in the excavation. Coal pillars 35 feet x 35 feet in plan dimension, supporting ribs of coal 35 feet x 1 foot and shaved pillars were encountered in the excavation.

Kentucky is currently studying alternatives for the construction of a new roadway and structure in a cut section which will be underlain by an abandoned underground mine on an upper-lying coal seam and an active underground mine on a lower-lying coal seam.

Maryland Presentation - Dave Martin, Maryland State Highway Administration

Maryland is a small state and highly centralized. Districts do not have the authority to make design changes without the approval of the central office.

Mining is limited to one county with only one mine located outside of that county. Ninety percent of ground mining is done in this one area of the upper northwest corner of the State. These mines are dry because they are in a syncline area. The syncline dip is approximately 1 ½ to 2 degrees in a Northerly direction. The mined seam is the Pittsburgh Coal. Mining in this area dates back to 1804.

In Garrett County a longwall underground mining operation 300' below the surface will cross Route 50 at a skew. The mining panels are 750 feet wide and 3000 feet long. Settlements of 3 feet have been observed over a period of 51 days. Surface settlements above the margin of mined panels gradually increase from 0 feet to 3 feet over a distance of 300 horizontal feet. There are no major structures on the roadway. There will be around the clock inspection of the roadway and an Automatic Road Analyzer will be used. The analyzer videotapes the road and measures cracks and rideability.

Most of Maryland's mine-related problems are related to landslides. In one case mines caused a major slide. Remediation work involved excavation of the slope resulting in exposure of 3 mine openings, draining of 3 to 5 million gallons of mine water, and placement of a rock buttress in mid-slope. Abandoned Mine Land funds paid for the drainage items on this job.

Maryland has serious problems with karst sinkholes. Some have occurred in areas adjacent to I-70 ramps.

A Geological Hazards Database has been created. This database will include data for landslides, quarries, sinkholes, minesinks, rockfalls, and wells. Only the sinkhole data has been entered.

All geologic features are located by latitudes and longitudes and a statewide grid system. Two grids are available, English and metric. This system facilitates coordination of information with other agencies. The database will be tied into the state GIS system. It does not provide any site priority or risk assessment. The main use of the database is to recover peripheral files. Only the sinkhole data has been entered into the database at this time.

Missouri Presentation - George Davis and Tim Newton, Missouri Department of Transportation

The number one mined commodity in Missouri is Galena (lead ore) . Missouri also produces silver and coal. The mined coal seam is the Pennsylvanian formation of the Kansas City Group. Mining began in Missouri in 1837. Many underground mines apparently did not follow any logical mining plan, and few mine maps are available.

Lots of mining in the Huntsville area - lead, clays, silver, coal, etc. Few mine maps are available. Some maps have been found at the County Recorder of Deeds.

"Telltale" monitors, installed in PVC cased holes, have been utilized for monitoring.

GPR is not effective on some sites due to the clay-shale overburden.

Geotechnical characteristics of previously mined lands in Missouri were shown, including overhead shots of collapsed mines in Joplin (numerous).

Lead-zinc mines were typically abandoned with no closure or reclamation effort. Missouri also has surface settlements related to Karst conditions.

Twelve steps of geotechnical evaluation of previously-mined land were discussed.

Visual observations, historical records, and type of mining associated with stratigraphic units are reviewed as a part of site investigations.

High Resolution Seismic Reflection, with geophones located on 10 foot centers and a truck mounted hammer with 20 to 40 feet of offset to geophones, has been utilized. This work has found anomalous data areas which were later verified through drilling as often being subsurface features.

A 500 mz GPR was successfully used to a depth of 15'. Processing time required one lab day for each field day. Seismic was successfully used for depths 15-500'.

Site plan views are developed which identify apparent boundaries or interfaces, as well as mine voids or shafts. Symbols are used to indicate the risk associated with identified features including: shaft, danger (red), caution (yellow), and safe (green). Adjustments of the proposed project footprint are made based on this plan view information and foundation types are selected.

New York Presentation - Alex Yatsevitch, New York State Department of Transportation

New York State DOT has organizational groups with overlapping interests and responsibilities for subsurface concerns. The New York geotechnical section has a staff of 119.

New York has had two cases of subsurface subsidence related to underground mines.

Talc and salt are some of the mines in the State of New York that are still active at this time. Salt mines and solution wells are extracting salt in deep basinal deposits at an approximate depth of 1000 feet or more. Surface cones of depression with a radius of 700 feet and a depth of 90 feet have resulted from these mineral extraction operations.

Collapse of abandoned underground mine workings occurred in an area adjacent to the currently active Gouveneur Talc Co., Belmap Mine on Route 812. The only instrumentation installed to monitor the roadway were extensiometers. Depth to the mined interval was 131 feet. Remediation for this roadway site was accomplished through the relocation of the roadway five years after site monitoring had been initiated.

The AKZO-Nobel Salt Mine was also a site where mine collapse has occurred. This mine is approximately the same size as Manhattan. The overburden interval is comprised of 500 feet of soil overlying 500 feet of bedrock. Method of mining is room and pillar. The mine void heights are approximately 11 feet. This mine was flooded out in March of 1994 by 21-35,000 gallons of water per minute. New York DER tried to determine extent of mine collapse through drilling, but was unsuccessful. Subsidence is expected to take approximately 1 ½ year. Nobel is in the process of being sold. Subsidence caused some movement of a bridge. Mud volcanos are creating landslides, etc.

There is no central repository in New York where information regarding mines below roadways can quickly be found.

North Dakota Presentation - Bruce Beechie, North Dakota Public Service Commission

North Dakota has only four personnel in the office and their budget is $1.5 million per year. The North Dakota Service Commission is responsible for remediating all abandoned mine problems in North Dakota, whether they are on, or off, the state roadways. Site priority rankings are utilized. Remediation work includes eliminating highwalls on surface mines, correction of subsidences, and
other work. All design and construction management is done in-house.

Underground mining in the State of North Dakota occurred from 1880 until 1965. This mining occurred in the western half of the state. There are approximately 1000 abandoned mines. Average size of underground mines is 20-40 acres with the largest being 2000 acres and many 0.5 acre. The mined coal was lignite which is very soft and has a BTU value of 7,000. The coal seam varies in thickness from 6' to 40', with a dip of 1 ½ to 2 degrees. The typical mined thickness is 10 feet. The overburden ranges 20-250', with and average of 70'. Approximately 95% of mining is room and pillar. The typical mine room has dimensions of 35 feet by 250 feet.

A subsidence of 120' can occur over a 40' coal seam. A factor of 2-3 times the thickness of seam is used to estimate subsidence where the mine is flooded.

"Sinkholes don't have a conscience." They can happen anywhere.

Remediation methods include fill, overexcavate and fill, and grout. Contract drilling of 6 or 7 sites is performed in the winter. Grouting is performed under a separate contract in the spring. Implosion was tried but encountered some problems. Suggested implosion site characteristics: overburden depth of 50 feet or less, and no water wells or utilities. Blast one year, and grade out the next year. Ballpark loading densities for blasting would be 30 to 100 pounds per hole. Blasting hole diameter is 5 1/4 inches and spacing is typically 100 feet center-to-center.

A camera with spotlight and compass is used to view mines. A 5" diameter hole is cased with 3" PVC. Holes may be left open for as long as 5 years and viewed periodically.

Air drilling of 8-10' holes for grouting is used. Gravity fill was tried but filling of collapsed areas was not complete. North Dakota is now pressure grouting some collapsed areas that were gravity filled in the past.

Pressure grouting is done at 3-5 psi per foot of overburden. As long as a given borehole is still taking grout, they do not back off grouting until something happens such as significant ground heave. An area in a ditch is tried first to see what the pressure will do. Ground cracking is considered okay until the crack is big enough to twist an ankle.

Minimum grout strength is 150 psi at 28 days or no payment to the contractor. No problems achieving this. A 10.5' slump is used. Three grout samples are taken for each 50 cy placed.

Since haul tunnels are typically 10' wide a 10' spacing of bore holes is used to assure that tunnels are not missed. Typically drilling is performed under one contract and grouting is performed under a different contract in a later year.

Barrier holes are not always used. The cost of the holes and stiffer grout is sometimes considered more costly than pumping the extra grout. Confirmation holes are drilled when grouting is done.

GPR was tried but did not work because of conductive clays and glacial deposits.

The grout mix used is 100 lb cement, 600 lb flyash, 70 oz superplasticizer and high range water reducer, water, sand. Some fly ash from Canada leached some heavy metals when tested.

Friday, September 18, 1997

Conference Questions and Answers Session - Tom Lefchik

Kansas Question - What type of deep(100ft.+) remediation has been tried? This is with 25' high or larger water filled rooms in lead and zinc mines.

Suggestions included gluing roof rock and reverse rock bolting of the remaining material from the road grade down to 100 feet, using pea gravel, adding sodium silicate to fly ash, and using sodium silicate to shield grout.

Illinois Question - Has your department experienced any problems with regard to active subsidence under existing structures/ If so, what type of remedial treatments were used, if any?

No state has dealt with this. Pennsylvania Turnpike grouts under new structures but does nothing on rehabilitations.

New York Question - Who has jurisdiction on underground mines in your state?

Illinois: For highways on the state system it is the DOT. Under houses the DNR administers AML funds.
Kansas: For highways the DOT geotech section is responsible for design and remediation. Do not work beyond shoulders.
Pennsylvania: DOT is responsible for highways. Try to stay in right-of -way as much as possible but go beyond if necessary. Districts do the analysis.
Kentucky: The Department of Mines and Minerals is responsible. An attempt is made to acquire mineral rights under the highway. Outside limits depend on draw angle. Crossings may be agreed to.

Maryland: The Highway Department handles it. May ask for outside money. If necessary to go beyond right-of-way, acquire it or get right of entry.

Missouri: DOT is responsible for highways. Cooperate with DGCS on information.

North Dakota: The North Dakota Public Service Commission handles projects on highways. For highways remediate entire area within the right-of -way because of possibility of roadway being widened. The DOT does not own the right-of-way. Highways occupy the property by easement. When grouting, do not worry about grout going beyond the right-of-way.

Ohio: The DOT remediates problems on highways. Concerned only with a safe driving surface (lanes and shoulders). Will go beyond the right-of-way if necessary to do work.

Illinois Question - Do geotechnical staff members in your department have direct input regarding structure type and/or foundation treatment as far as mined-out areas are concerned?

Kansas: The geotechnical section handles all aspects of foundations. Input is forwarded to bridge design.
Kentucky: For anything below the subgrade the geotechnical section is responsible.
Maryland: Geotech provides direct input.
Missouri: Similar to Kansas
New York: Structures Division does all structure design. Geotechnical Bureau does investigations. Foundations Unit gives recommendations. The geotechnical bureau would do remediation and get sign off.
North Dakota: No input to structural design.
Ohio: The geotechnical unit is under materials, and the foundations unit is under structures.
There is no process for communication, but there are informal lines of communication. 90-95% of design is by consultant.
Pennsylvania: The Bureau of Design, bridge section handles all bridge design.
Pennsylvania Turnpike: Most design is outsourced. A single report is provided by the designer which covers bridges and geotechnical.

Question -Has sodium silicate been used on a large scale?

On one project 12-15' high voids under a house were filled. It is difficult to get up to 12' and hold. It is typically okay up to 10'. Grout bags were used in slope entries with fiber reinforced concrete. Bags can be custom ordered. Filling of bags can be monitored with a camera. Should not fill the bags very fast. Rick Baylogh, Office of Surface Mining, Pittsburgh may be able to provide further information on use of grout bags.

Future Directions - Rick Ruegsegger and Tom Lefchik

Rick and Tom thanked everyone for their input and expertise. There was discussion on whether a working group should be formed and what form of organization it could be. There was general agreement that a working group should be formed.

Goals listed:

1. Risk Assessment
2. Identify Needs (lengthy discussion about the need for a formal group needs to be investigated) Nothing certain decided at this time
3. Mitigation Techniques
4. Investigation Techniques
5. Information Sharing (Activity Log)

Adjournment of Meeting

Updated: 06/27/2017
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