TN 295 .U4 No. 9099 ■ G* V ♦^T** A < G»M«£^>o ,^\^-\ 0°*,^>>o .*V <•* 'O °"'7Vs* A <\ '».»* ,G V *e> ♦TJTT** A °o G v 'o, ^/^.T 4 A < %^ ■Q.V ^ ^ v \ . \^\<^ %^-*\ jy 6? ?• / \ w 4 A -.f5# /\ •«•• ** v \ iW. ; A : .l@f / 4 A t«* •-. °*o '-> ..... V°'" o*° - V^V . %*-•■•' /" V™V -1 *°^ "IKS' ^°^ "^ IC 9099 Bureau of Mines Information Circular/1986 Surface Subsidence Over Longwall Panels in the Western United States Monitoring Program and Final Results at the Price River Coal Co. No. 3 Mine, Utah By Alan J. Fejes UNITED STATES DEPARTMENT OF THE INTERIOR Information Circular 9099 Surface Subsidence Over Longwall Panels in the Western United States Monitoring Program and Final Results at the Price River Coal Co. No. 3 Mine, Utah By Alan J. Fejes UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES Robert C. Horton, Director Library of Congress Cataloging in Publication Data: Fejes, A. J. (Alan J.) Surface subsidence over longwall panels in the Western United States: monitoring programs and final results at the Price River Coal Co. no. 3 mine, Utah. (Information circular; 9099) Supt. of Docs, no.: I 28.27:9099. 1. Mine subsidences -Utah -Price River Watershed. 2. Longwall mining- Utah -Price River Watershed. I. Title II. Series: Information circular (United States. Bureau of Mines); 9099. TN295.U4 [TN319] 622 s [622'.334] 86-600182 CONTENTS Page Abstract 1 Introduction 2 Acknowledgments 2 Price River Coal Co. No. 3 Mine study site 3 Site selection 3 Site description 3 Regional geology 3 Panel geology 3 Mine plans 8 No. 3 Mine 8 No. 2 Mine 9 Subsidence-monitoring program 9 Monument locations 11 Monument spacing 14 Monument construction 14 Monitoring procedures and equipment 15 Data processing 16 Subsidence results 16 Conclusions 18 References 18 Appendix. — Measured subsidence values plotted in figures 16, 17, 19, and 20.... 20 ILLUSTRATIONS 1 . Project location map 3 2. Surface contours over longwall panels 4 3. Typical surface features over longwall panels 5 4. Regional geologic structures 6 5. Regional stratigraphy 7 6. Regional faulting 8 7. Generalized overburden stratigraphy 9 8. Price River Coal Co. No. 3 Mine plan 10 9. Overburden isopachs 11 10. Royal Coal Co. No. 2 Mine plan 12 11. Subsidence-monitoring network 13 12. Access to site limited by heavy snows 14 13. Monument installation using a sledge hammer 14 14. Theodolite with electronic distance meter 15 15. Target-prism unit 15 16. Final longitudinal subsidence profile for panel 4E 16 17. Final longitudinal subsidence profile for panel 5E 16 18. Damage to surface structure located over panel 5E 17 19. Subsidence development profiles for panel 4E 17 20. Subsidence development profiles for panel 5E 17 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT ft foot pet percent in inch ppm part per million in/yr inch per year s second SURFACE SUBSIDENCE OVER LONGWALL PANELS IN THE WESTERN UNITED STATES Monitoring Program and Final Results at the Price River Coal Co. No. 3 Mine, Utah By Alan J. Fejes 1 ABSTRACT As part of its mine subsidence research program, the Bureau of Mines and the American Electric Power Co. cooperated on a study, conducted at the Price River Coal Co. No. 3 Mine, directed toward developing the capability to estimate the surface subsidence resulting from longwall mining in a geologic, topographic, and mining environment common to coalfields in the Western United States. Subsidence was monitored at the No. 3 Mine over two adjacent longwall panels. The subsidence study area was reduced when the two planned panels were reduced in length because of equipment failure and a mine fire. Subsidence was measured for 21 months. Subsidence continued for 6 months after mining had been completed. A maximum of 2.2 ft of sub- sidence occurred over the two longwall panels rained at an overburden depth ranging from 300 to 1,500 ft. 'Mining engineer, Denver Research Center, Bureau of Mines, Denver, CO. INTRODUCTION In 1977, Congress passed the Surface Mining Control and Reclamation Act. Sec- tion 516 (5) (1) of the act requires the mine operator to "...adopt measures... to prevent subsidence causing material damage...." A method of predicting the approximate location and magnitude of subsidence is necessary to prevent or limit subsidence-related material damage. These methods are currently unavailable or inadequate for U.S. mining conditions. To expand prediction capabilities, a more inclusive subsidence data base must be developed. A more expansive data base would provide researchers and mine opera- tors with the information required to delineate the individual and combined effects of the many mining and geolog- ic parameters that contribute to mine subsidence. In the United States, approximately 40 million acres are subject to subsidence from past, present, and future coal min- ing. Only 8 million acres of this total area had been undermined prior to 1977 ( 1) . 2 Monitoring subsidence over the re- maining 32 million acres would be im- practical and uneconomical; therefore, a system of selective monitoring is re- quired to effectively and efficiently characterize mine subsidence to help de- velop subsidence prediction methods that can be used to limit the amount of damage to these remaining unmined lands. The first step in this characterization pro- cess is to select and systematically monitor representative sites in actively mined coalfields. Comparison and analy- sis of collected data will determine the affects and significance of individual mining and geologic parameters for each coalfield. The number of sites required for each coalfield will depend upon the consistency of collected subsidence data and the accuracy required for the predic- tion methods. In the Western United States, very little subsidence information is availa- ble for mine operators. Therefore, there is little data to correlate with data from other sections of the United States or other countries to determine the ap- plicability of existing subsidence pre- diction methods. The Bureau is especial- ly interested in western coalfields where a significant number of underground coal mines operate under Federal coal leases and therefore undermine public lands. The Bureau's subsidence research pro- gram promotes maximum utilization of both underground and surface natural resources by supporting the development of subsid- ence prediction methods. The ability to predict subsidence enables mine opera- tors to use high-extraction mining meth- ods, to maximize recovery and control subsidence, thereby avoiding or limiting surface and subsurface subsidence damage. The Rocky Mountain Coal Region site was established in cooperation with the American Electric Power Co. at the Price River Coal Co. No. 3 Mine in Carbon County, UT. The major objectives of the Price River study were as follows: 1. Measure surface subsidence caused by longwall mining in the Spring Canyon Sub 3 Seam coalbed. 2. Establish the final longitudinal subsidence profiles. 3. Determine the effects of subsid- ence on current and potential land use. ACKNOWLEDGMENTS The Price River Coal Co. provided val- uable assistance in conducting this ^Underlined numbers in parentheses re- fer to items in the list of references preceding the appendix. research. In particular, Laine Adair, Ken Hutchinson, and Ace Muse have made significant contributions to the project. Without the access that was provided to company property, mine plans, survey data, drill logs, and other informa- tion relating to the Price River Coal Co. No. 3 Mine, this have been conducted. PRICE RIVER COAL CO. NO. 3 MINE STUDY SITE study could not SITE SELECTION The Price River Coal Co. No. 3 Mine is situated in the Book Cliffs Coalfield; historically, the most productive coal- field in Utah. Production in 1981, from six underground coal mines in the Book Cliffs Coalfield, was 3.36 million short tons. Remaining recoverable reserves for the field are estimated at 1.4 billion short tons. (2). The geological and geo- graphical features of this site are typ- ical for western underground coal mines. The terrain is rugged and the over- burden contains a high percentage of strong sandstone strata. The results of this study are expected to be applicable to other sites within the Book Cliffs Coalfield and possibly to other western region coal mines. SITE DESCRIPTION The study site over the No. 3 Mine is located in Bear Canyon in Carbon County, UT, approximately 5 miles north- west of the town of Helper. The site includes parts of Sec. 34 and 35, T 12 S, R 9 E on the Standardville 7.5-min- ute U.S. Geological Survey quadrangle map (3). The project site location is illustrated in figure 1. The study site is approximately 300 acres within the Q^® 1 Price River \ I Coal Co. V, N 1 Study sire ft / is \y '"- — ^Sgrjng ^ Condon c /Helper ■7. U <> ^ Price FIGURE 1.— Project location map. Price River Resource Area. This area is managed by the U.S. Bureau of Land Management. The topography over the study area is extremely rugged with steep slopes, sheer cliffs, and numerous sandstone outcrops (figs. 2-3). Elevation at the site ranges from approximately 6,500 to 7,200 ft, and vegetation consists of sagebrush, scrub oak, and evergreens (fig. 3). The study area has a semiarid climate, with an average rainfall of 15.25 in. Most precipitation falls in the winter months in the form of snow, an average of 107 in/yr (4_). REGIONAL GEOLOGY The No. 3 Mine is located in the Spring Canyon Sub 3 Seam coalbed in central Utah, which is part of the Book Cliffs Coalfield (fig. 4). This field marks the southern border of the Uinta Basin (_5 ) . The overburden is composed primarily of sedimentary rocks with a regional dip averaging 5° northward. The overburden is composed of sandstone, shale, carbona- ceous shale, and coal. The rocks within the coalfield are subdivided into five formations (fig. 5). Ages of these rocks vary from upper Cretaceous to Tertiary. Figure 6 illustrates faulting within the Book Cliffs Coalfield (5)» Faulting is a significant problem for some mines in this area; displacements along major faults can range from 10 to 200 ft. How- ever, the Price River Coal Co. No. 3 Mine is relatively unaffected by faulting. The faults that do intersect the mine are considered insignificant since they only create small displacements that do not inhibit mining operations. PANEL GEOLOGY The No. 3 Mine produces coal from the Spring Canyon Sub 3 Seam coalbed in the coal-bearing zone of the Blackhawk Formation. This formation consists of 6 Bureau control points ° Bureau subsidence monuments FIGURE 2. — Surface contours over longwall panels. The subsidence monitoring network, shown as lines of circles, is discussed in the section "Monument locations." slope-forming siltstones and shales and cliff-forming sandstones. The major coalbeds occur in the lower this formation. The Spring Canyon Sub 3 has an average thickness of the study panels. The coal as hard, bright, and dense, and is ranked as high-volatile, A bituminous. An analysis of drill-hole records, sup- plied by the Price River Coal Co. , was used to determine the stratigraphy of the overburden above the longwall mining one-third of Seam coalbed 6 ft within is described operation. A generalized overburden stratigraphic column is shown on figure 7. The major unit in this column is the Castlegate sandstone. The Castlegate sandstone is located in the lower Price River Formation and is described by Doelling (_5) as a gray, fine- to medium-grained, massive sand- stone with occasional shale and coal partings occurring in the lower portion of the unit. Over the panels the sand- stone is approximately 500 ft thick. FIGURE 3.— Typical surface features over longwall panels. M /Book Cliffs Coalfield INDEX MAP L -N- 25 50 Scale, miles FIGURE 4.— Regional geologic structures. T3 O o STRATI GRAPHIC THICKNESS, DESCRIPTION o> o o. UNIT ft Q_ UJ Ter tiary NORTH HORN Formation 350- 2,500 Gray, calcareous, and silty shale, tan, fine- grained sandstone; and minor conglomerate. Unit thickens to west. E Yellow-gray medium-grained sandstone and > or Upper 500- 1,500 shaly sandstone with gray shale. Unit thickens along east edge of field. Gray, fine- to medium-grained, argillaceous o Castlegate 100- massive, resistant sandstone thinning east- O o 0- S.S. 500 wardly with subordinate shale. Cyclical littoral and lagoonal deposits with 6 major cycles. Littoral deposits of 3 O ■o E mainly massive cliff-forming, gray fine- a> o o •»- a> to medium-grained sandstone; individual > o o Upper 600- 1,100 beds separated by gray shale. Lagoonal facies consist of thin- to thick-bedded v> 3 o 5 gray sandstones, shaly sandstones, shale, o o and coal. Coalbeds form basis of Book O 0) m Cliffs Coalfield. Unit thins eastward o o ■*- OJ w- O Q. a. 3 Aberdeen Member}- grading into the Mancos Shale. CO to S? rina Member? Canyon j — -♦- ^^. Yellow-gray, massive, medium- to fine- c o 0_ o Storrs ~"^n 0- grained littoral sandstone tongues pro- To ng u e ^ -J 580 jecting easterly, separated by gray marine shale tongues projecting westerly. CO Panther"? Tongue i^ ■Gray marine shale, nonresistant , form- Ma us k ing flat desert surfaces and rounded w o c CO Shale 4,300- 5,050 hills and badlands. Separated mainly to the west into tongues by westward projecting littoral sandstone that Emery S.S^""^"" Member^" o eventually grades into shale. Sand- stones are fine- to medium-grained, u c yellow-gray to tan, and medium-bedded o 2 Bluegate Shale to massive and cliff forming. FIGURE 5.— Regional stratigraphy (modified from Doelling, pp. 251, 267). FIGURE 6.— Regional faulting (modified from Doelling, pp. 252-253). MINE PLANS The subsidence study site is located over multiple-seam mining. In addition to the Spring Canyon Sub 3 Seam coalbed being mined by the Price River Coal Co. in the No. 3 Mine, an upper bed was mined by the Royal Coal Co. in its No. 2 Mine. The abandoned No. 2 Mine, operated in the 1940's, lies approximately 430 ft above the No. 3 Mine. A description of each mine plan is included in this section. No. 3 Mine The mine plan for the No. 3 Mine is shown in figure 8. The study area con- sists of two adjacent longwall panels oriented on a bearing of N 75° 26 f 12" E to be retreat mined from east to west. Two longwall panels (2E and 3E) south of the two study panels (4E and 5E) were mined prior to the study. The development entries for panels 2E and 3E had three three-entry systems with cross-cuts on 105-ft centers; entry 2-1/2 East on a 70-ft center, 3rd East was on a 60-ft center, and 4th East was on a 50-ft center. The face lengths of panels 2E and 3E are 500 ft each, with lengths of 2,000 and 2,420 ft, respectively. The 5th and 6th East development en- tries for panels 4E and 5E were driven on 50-ft centers; crosscuts were driven on 105-ft centers. Panel 4E was 1,550 ft long with a face length of 450 ft; panel 5E was 1,950 ft long with a face length of 500 ft. 0- ,V ° ° \o V 300- 350- 400- 450- 500- 550- 600- 50- *> ~ ■ M^M 100- - — ' ;■'.;■. v'r .•■'.-' — — 150— SHVM - ~ T" 200- ■•: ■'•'::'' J*. . *> 3^E 250- • • — — — =— 300- '.•'.'. :.■■-■'.' 1 600 650- 700- 750- 800- 81 .WAfri j tm* Castlegate Sandstone Spring Canyon Sub 3 Seam LEGEND I*. ■■"'■I Alluvium ] Sandstone IsKBI Shale Interbeds ot sandstone and shale | — _-| Carbonaceous Coal FIGURE 7.— Generalized overburden stratigraphy. The depth of cover over panel 4E ranges from 800 to 1,500 ft; over panel 5E the cover ranges from 800 to 1,200 ft. The minimum overburden for panels 4E and 5E occurs near the center of the panels and increases toward both ends (fig. 9). The seam dips 9° on a strike of N 10° E, which was considered when calculating overburden depths. Panels 4E and 5E were only partially mined because of mining problems. Mining in panel 4E was discontinued when the longwall equipment failed. The longwall equipment was removed and a new longwall system was installed in panel 5E . While installing the new longwall, the coal remaining in panel 4E was partially room- and-pillar mined directly behind the abandoned longwall face. Panel 5E was abandoned when a fire was detected. The fire was believed to be in the room-and-pillar section located be- hind the 4E longwall face. Panels 2E , 3E , 4E , 5E , and 6E were sealed to contain the fire. No. 2 Mine The mining plan for the Royal Coal Co. No. 2 Mine (also known as the Cameron Mine) is shown in figure 10. The plan is included in this report to show that the study area was not located in a virgin area and may have affected subsidence values (6_). The mine is in the Castle- gate "D" (Kenilworth) bed, approximately 430 ft above the Sub 3 Seam coalbed. The No. 2 Mine was opened in 1912 and was actively mined until the workings were abandoned in 1962. The mining height within the study area ranged from 6 to 8 ft. The coal within the study area was mined between 1946 and 1949. The Castlegate "D" coalbed was worked using standard room-and-pillar mining methods with pillars pulled in isolated, seemingly random sections. The extrac- tion ratio in the section above panel 4E is 0.28; above panel 5E the ratio is 0.43. The positions of panels 4E and 5E relative to the old workings are shown on figure 10. SUBSIDENCE-MONITORING PROGRAM Figure 11 shows the subsidence-monitor- ing network located over two adjacent longwall panels at the No. 3 Mine. The network was designed to measure the max- imum subsidence, the longitudinal subsid- ence profiles, and the rate at which subsidence progresses over the longwall panels. Major items that affected collected subsidence data included survey accuracy and frequency, monument spacing, monument construction, and surveying instrumenta- tion. The number and accuracy of sur- veys performed was affected by climatic and geographic conditions at the site. Heavy winter snows usually made the site 10 7tt> Eo«t N 75 26' 12 E V t- . : •""^gaDDDDDDDDDDDDDDDDQDDDDDaQaaaCDril Cl * * i . "H-" : r :. jgD DDDDaDDD D QQDg ggggs5g"oggpogpL '-*30Q< f '' - ' ** jr Panel 6E DDL oop cor ' ' •' j I - ^V 1 •* EG,f <> D ! A %**■% ]|_ JFS? ^_ . .._ _ ___.__., ■*•!■* 5 DC i l T ioor FIGURE 8.— Price River Coal Co. No. 3 Mine plan. 11 FIGURE 9.— Overburden isopachs. inaccessible from November into May (fig. 12), which prevented the Bureau from performing surveys at regular intervals throughout the year. Installation and monitoring of the network in the rugged terrain was physically intensive and time consuming. MONUMENT LOCATIONS The locations of the subsidence monu- ments were established from coordinates supplied by the Price River Coal Co. for surface control points in or near the study site and underground points on the longwall panel boundaries. All surface and underground surveys were tied to the Utah State Plane Coordinate System, which allowed direct correlation between sur- face and underground positions. The network layout consisted of two lines of monuments centered on the longi- tudinal axis of each panel. A transverse line of monuments was installed across panels 4E and 5E. However, mining in the two panels did not progress close enough to this monument line to cause it to subside. Had the entire lengths of the panels been mined as planned, the trans- verse monitoring line would have been located in the area of maximum subsid- ence. Because the line was outside the area of subsidence influence, no data were obtained. The location of stable control points was governed by the topography and vege- tation of the site and the location of underground workings. Five control points were established to monitor the entire network. One control point was located within the influence of subsid- ence to provide a line of sight to several particularly isolated subsidence monuments. This control point was tied to two stable control points prior to each survey of the network to ensure accuracy. 12 Scale, ft FIGURE 10.— Royal Coal Co. No. 2 Mine plan. 13 jf }* X, ,• ■■' ! r ,'i •: -Vi., ](__ 71* Eoi» N 73* 26' 12" E '■ * / ' r " ' : - ;!<; ';6QDDDDDDDaDaDDDDDDaDDDaaabaacDLDC]f -JwoDoa * '* At • - L • / * Panel 6E |00| ::lMt. Barrier 005/ oof or + + + +++'+++ + + + +++++ + + + +++ -KM+ + + + +++ + + . r r'jU ."; !i.0Ul I " ■;; ' iilQi Till ll'UJII i 1,1 iii ini ,f ■ I II II K :.rl Hlptt hiiaiM j,i,I! ii:i:"iii i KjOiiOun. ii if ' iifflnn :ruiVui.i! [inciiiicii •if - j ' * ~~i "7". iraESCT^Jen=>'.jr-3i.-.T.-:js'; I ni 1 ■. be-- jKaEJ®r.^na®£3aac ■,~, £3 K 1/ in [J ■ ! \ t ^ r '^n:Jii" v :' • : -: ^. ... 400 L :.c? ? Scale, ft 800 J 1,200 I FIGURE 11.— Subsidence-monitoring network. 14 Standard traverse surveying procedures and equipment, described in a later sec- tion, were used to locate the monument positions. MONUMMENT SPACING The network layout was designed with monuments spaced at 100-ft intervals. Topography, vegetation, and localized soil conditions dictated the actual loca- tion of each monument, thus final spacing ranged from 90 to 100 ft. The spacing, which varies between 0.07 to 0.13 times the overburden depth, is larger than the 0.05 recommended by the National Coal Board (NCB) Subsidence Engineers' Hand- book (6). However, closer spacing was considered excessive in the rugged ter- rain. The larger spacing was sufficient to provide the required data, while also reducing monument installation and sur- veying costs. MONUMENT CONSTRUCTION Two different types of subsidence mon- uments were installed at the Price River study site. Initially, 1-1/2-in steel pipes, beveled on one end to ease instal- lation, were installed over panel 4E. The remainder of the monitoring net- work was completed using 1-in steel rods with machined points. Monuments were installed using a sledge hammer to drive the monuments to a depth of 5 ft or until refusal (fig. 13). The 1-in steel rods are recommended because they are easier to store, transport, and install, and they are less expensive. Monuments of both types, which were located over stable ground, were monitored for the duration of the study. Statistical >- • r*- t^ Mikm FIGURE 12.— Access to site limited by heavy snows. FIGURE 13.— Monument installation using sledge hammer 15 analysis of the stable monuments showed a standard deviation on monument move- ment equal to the standard deviation of the surveying method. Therefore, these types of monuments provide equal sta- bility for subsidence monitoring in these conditions. MONITORING PROCEDURES AND EQUIPMENT Traverse surveys were used to measure both vertical and horizontal displace- ments. The surveys were performed by Bureau personnel and a contract surveyor using a second-order, optical-reading theodolite with micrometer readings of 1 s and an electronic distance-measuring (EDM) instrument with an accuracy of ±0.02 ft +6 ppm (fig. 14). Vertical and horizontal positions of each subsidence monument were calculated from horizontal and vertical angles and slope distances measured from instrument stations with known coordinates. The target-prism unit used for the traverse surveys is shown on figure 15. The unit consists of a prism for dis- tance measurement, a target for angle measurements, and a level bubble for vertical alignment. The interchangeable bottom clamp can be attached to circu- lar monuments ranging in diameter from 9/16 to 1-1/2 in. The compact, light- weight unit was ideal for carrying in the rugged terrain. If additional height was required for improved visibility, 1-ft aluminum extensions were attached between the clamp and the target. Survey accuracy was determined from coordinate data collected from subsidence monuments located on stable ground at the study site. The average standard FIGURE 14.— Theodolite with electronic distance meter. FIGURE 15.— Target-prism unit. 16 deviations for the eastings, northings, and elevations, were 0.16, 0.12, and 0.07 ft, respectively. DATA PROCESSING Following each traverse survey, field data were typed into computer files and stored. The raw survey data entered into these files consisted of station names, horizontal and vertical angles, slope distances, and target and instrument heights. The easting, northing, and ele- vation of each subsidence monument was then computed and stored in a mass stor- age file; this file was segregated according to individual surveys. In this form, the information was readily ac- cessed and used as input for programs that performed calculations such as coor- dinate and elevation differences between any two surveys. The data were also used for mapping monument locations and plot- ting subsidence profiles. Computation and storage requirements for a project of similar size and nature could be satisfied by a desk-top 16- bit microcomputer with printer and disk drive. Approximately 250,000 bytes of disk storage would be required, depending upon the exact amount of data being manipulated. Graphics capabilities would require the addition of a plotter and graphics software. SUBSIDENCE RESULTS The final longitudinal subsidence pro- files for panels 4E and 5E are shown on figures 16 and 17. (See appendix for data. ) A transverse monitoring line was installed across panels 4E and 5E; however, owing to the limited face ad- vance in both panels, the transverse monitoring line was not undermined, and therefore no transverse subsidence pro- file was obtained. Without the informa- tion from a transverse monitoring line, the surface effects of the chain pillars between panels 4E and 5E could not be determined. The maximum subsidence measured over the two panels was 2.2 ft, located near the midpoint of panel 4E at station C21; 2.2 ft is approximately 37 pet of the average extraction height of 5.9 ft. The maximum subsidence measured over panel 5E was 1.7 ft at station D20. Using an average overburden depth for each panel, the width-to-depth ratios for panels 4E and 5E were calculated to be 0.4 and 0.5, respectively. A higher width-to-depth ratio usually results in a higher value of subsidence when the ratio is subcritical. However, at this site, a larger maximum subsidence was measured over the panel with the lower width- to-depth ratio. The subsidence value over panel 4E probably was greater than that over panel 5E because of the con- tributory effects of the adjacent mining o -.5 -1.0 -1.5 -2.0 -2.5 1 1 1 r i C6 ,' — ^v C JJ C i 6 i C21 1 1 1 C26 C3I C36 C40 V \ V / \ \ \ \ V I / 6 \ \ \ 1 1 1 1 1 1 s / / KEY " - a Before subsidence o Final measured subsi V/A Unmined coal Pnnpl Jence 4E 1 6/17/81 '//////////////A , V////////////////////A 4E. 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 DISTANCE, ft FIGURE 16.— Final longitudinal subsidence profile for panel 0.5 -.5 8" -i.o z LU Q w -I.5 oo =) IT) -2.0 -2.5 - I Dl D6 r i DM DI6 — r~ D2I I - I I D26 030 D35, ,D40 } ^D» v ----c^ v - \ \ \ r- '"''' \ 1 6 *J i - KEY .P"' i a Before subsidence - o Final measured subsidence 6/17/81 sa Unmined coal _ Pani il 5E I W///AW//A \ V//////////////A 5E. 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 DISTANCE, ft FIGURE 17.— Final longitudinal subsidence profile for panel 17 in panels 2E and 3E (fig. 8). There was no mining adjacent to panel 5E other than panel 4E. The surface ground strain associated with mine subsidence was not monitored at this site. However, figure 18 provides visual evidence that significant surface strain was present. The effects of this strain are illustrated by the tension cracks in this surface structure located near subsidence monument D26 over panel 5E. The progression of subsidence over pan- els 4E and 5E is shown in figures 19 and 20. (See appendix for data. ) Sub- sidence was first detected over panel 4E in October 1979 (fig. 19) after the longwall face had retreated 1,450 ft, approximately 100 ft short of the final panel length of 1,550 ft. At this time, a maximum subsidence of 0.6 ft was mea- sured at stations C20 and C2 1 . The July 1979 survey showed no subsidence; there- fore, subsidence initially began over panel 4E between July and October of 1979, during which time the length of the mined panel was between 1,180 and 1,450 ft. Panel 4E was next surveyed in August 1980 after panel 5E had retreated 1,250 ft. The maximum subsidence over panel 4E increased to 1.3 ft at stations CI 9, C20, and C21. Subsidence contin- ued to increase over panel 4E until June 1981, at which time panels 4E and 5E had been completed for 19 months and FIGURE 18.— Damage to surface structure located over panel 5E. 0.5 -.5 -I.0 -I.5 -2.0 -2.5 e^em% —r- C6 Cll C2I C26 C3I C36 C40 \ Ik .-j/r- X W/7 KEY \ V^ J I a Before subsidence ^~\ / o 10/ 16/79 \ / A 8/18/80 V^ / + 6/17/81 final V Y/A Unmined coal Panel 4E \y///////////////A V/////////////////A 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 DISTANCE, ft FIGURE 19.— Subsidence development profiles for panel 4E. 0.5 -.5 UJ u -I.0 z UJ Q c/> -1. 5 m 3 en -2.0 -2.5 ^• **t;»* a ***** <, ^ :m&< ^S i^m^c. *fcv* •■* » ' 1 A" ;- 'W • v . t - • G^ % *^7f» A <> -».»• *o,»* ,G^ ^o. *^7i s A <>'».»* ^G v 'o Jp^ '^^ »v^» <%? :/gi^\ '++# °^m". «bv^ :2I^*- ^o^ ^°- ^°- ' .#fe- ++* G ^< \/ sgjk:. \o* c W° * / # % \ « c .*; v^^V*" "v^^V* %/^V*' X^ < ^V°'°% - ^^'^ % ' r . *j^w'. o .^ * V I- V V^f>\^ 7" 0^^ o%^f^'" c^n I **0« tV'""/^''" /•r-V""/'^" V.-. ; . ^* •*» W ••$&'• V -A- %/ ••$&• V* V^.«aS- '%,♦* .^- \/ :£&• ^ y-'Mk^ / • *. o. ^ -:•• , 5 /^ r« \ j> •»&*• % ^ ^ « " ^, /d ■ — ■ ». 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