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 No. 9083 
 
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JQJ 9083 
 
 Bureau of Mines Information Circular/1986 
 
 Subsidence Investigations 
 Over Salt-Solution Mines, 
 Hutchinson, KS 
 
 By Robert C. Dyni 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 V- 
 
u^ 
 
 Information Circular 9083 
 
 Subsidence Investigations 
 Over Salt-Solution Mines, 
 Hutchinson, KS 
 
 By Robert C. Dyni 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
 This report is based upon work done under an agreement between the Solution Mining 
 Research Institute and the Bureau of Mines. 
 
Library of Congress Cataloging in Publication Data: 
 
 
 pO J 
 
 Dyni, Robert C 
 
 Subsidence investigations over salt-solution mines, 
 
 Hutchinson, KS. 
 
 (Bureau of Mines Information circular; 9083) 
 
 
 
 Bibliography: p. 19-20. 
 
 
 
 Supt. of Docs, no.: I 28.27:9083. 
 
 
 
 1. Mine subsidences -Kansas -Hutchinson. 2 Solution 
 Salt mines and mining-Kansas-Hutchinson. I. Title. 
 (United States. Bureau of Mines); 9083. 
 
 mining-Kansas-Hutchinson. 3. 
 II. Series: Information circular 
 
 TN295.U4 [TN319] 622 s 
 
 [551.3] 
 
 86-600096 
 
CONTENTS 
 
 Page 
 
 Abstract 
 
 Introduction 
 
 Acknowledgments 
 
 Geologic setting 
 
 Sinkhole failure mechanisms 
 
 Subsurface investigations 
 
 Cargill 1974 sinkhole (first investigation) 
 
 Barton 1952 sinkhole (second investigation) 
 
 Carey 1978 sinkholes (third investigation) 
 
 Carey well 56 (fourth investigation) 
 
 Bureau of Mines surface subsidence investigations 
 
 First and second investigations 
 
 Carey 1978 sinkholes (third investigation) 
 
 Background 
 
 Subsidence-monitoring network design and construction 
 
 Monitoring procedures 
 
 Results — vertical movement 
 
 Results — horizontal movement 
 
 Carey well 56 (fourth investigation) 
 
 Background 
 
 Subsidence-monitoring network design and construction 
 
 Monitoring procedures 
 
 Results 
 
 Interpretation of results 
 
 First and second investigations 
 
 Third investigation 
 
 Fourth investigation 
 
 Conclusions 
 
 References 
 
 bibliography * 
 
 Appendix A. — Final vertical control survey of Carey brinefield 
 
 Appendix B. — Final horizontal control survey of Carey brinefield 
 
 ILLUSTRATIONS 
 
 1. Extent and thickness of Hutchinson Salt Member 3 
 
 2. Cavity collapse with surface deformations 4 
 
 3. Location of Cargill and Barton sinkholes 5 
 
 4. Location of boreholes at Cargill sinkhole 5 
 
 5. Cross sections of Cargill sinkhole 6 
 
 6. Location of boreholes at Barton sinkhole 7 
 
 7. Cross section of Barton sinkhole 8 
 
 8. Location of Carey sinkholes 8 
 
 9. Location of boreholes and subsidence monuments at Carey brinefield 10 
 
 10. Cross section of Carey sinkholes 11 
 
 11. Cross sections of Carey well 56 12 
 
 12. Detail of Bureau-designed subsidence monument 13 
 
 13. Subsidence from R-4 to R-15 14 
 
 14. Subsidence from R-16 to R-39 14 
 
 15. Subsidence from R-40 to R-58 14 
 
 1 
 
 2 
 
 2 
 
 3 
 
 3 
 
 5 
 
 5 
 
 7 
 
 8 
 
 9 
 
 12 
 
 12 
 
 12 
 
 12 
 
 12 
 
 13 
 
 14 
 
 15 
 
 16 
 
 16 
 
 16 
 
 16 
 
 16 
 
 17 
 
 17 
 
 17 
 
 18 
 
 19 
 
 19 
 
 20 
 
 21 
 
 22 
 
11 
 
 ILLUSTRATIONS— Continued 
 
 16. Subsidence from S-l to S-12 , 
 
 17. Subsidence from S-13 to S-21 , 
 
 18. Subsidence from T-l to T-12 , 
 
 19. Subsidence from T-13 to T-20 , 
 
 20. Horizontal movement of R-4 to R-15. 
 
 21. Horizontal movement of S-l to S-12. 
 
 Page 
 
 15 
 
 15 
 
 15 
 
 15 
 
 16 
 
 16 
 
 
 UNIT 
 
 OF MEASURE 
 
 ABBREVIATIONS 
 
 USED 
 
 IN 
 
 THIS REPORT 
 
 
 ft 
 
 
 foot 
 
 
 yd 3 
 
 
 cubic ya 
 
 ird 
 
 in 
 
 
 inch 
 
 
 yr 
 
 
 yr 
 
 
 pet 
 
 
 percent 
 
 
 
 
 
 
SUBSIDENCE INVESTIGATIONS OVER SALT-SOLUTION MINES, 
 
 HUTCHINSON, KS 
 
 By Robert C. Dyni 1 
 
 ABSTRACT 
 
 The Bureau of Mines in cooperation with the Solution Mining Research 
 Institute conducted surface and subsurface investigations over five 
 solution-mined salt cavities in the Hutchinson, KS , area. The purpose 
 of these investigations was to determine the mechanisms that lead to the 
 formation of sinkholes above collapsed solution cavities. Of the five 
 salt-solution cavities investigated, four had collapsed and produced 
 sinkholes prior to the time of the investigations; the fifth cavity was 
 considered stable. Exploratory drilling and coring operations were con- 
 ducted at all five sites; surface stability monitoring was conducted at 
 three of them. The results of these studies indicate that excessive 
 dissolution at the salt-shale contact of each collapsed cavity produced 
 large, unsupported roof spans that ultimately exceeded the structural 
 integrity of the overburden. The stable cavity was not exposed to ex- 
 cessive dissolution at the salt-shale contact; this limited the roof 
 span and ensured a stable cavity. The data also show that surface 
 settlement in the vicinity of the two surface-monitored sinkholes con- 
 tinued for approximately 7 years after the sinkholes formed, indicating 
 that the rubble piles of the collapsed cavities were undergoing gradual 
 consolidation. 
 
 'Physicist, Denver Research Center, Bureau of Mines, Denver, CO. 
 
INTRODUCTION 
 
 The Bureau of Mines is actively in- 
 volved in making mineral production com- 
 patible with the environment. The forma- 
 tion of sinkholes due to the structural 
 failure of solution-mined cavities in 
 salt is a potentially hazardous event 
 that can threaten lives and damage 
 or destroy structures and property. The 
 Bureau, in cooperation with the Solution 
 Mining Research Institute (SMRI), con- 
 ducted a series of four investigations 
 designed to provide an understanding of 
 the physical parameters and mechanisms 
 involved in sinkhole formation. The re- 
 sults of this research will assist in 
 establishing a basis for sound salt- 
 solution cavity design that will prevent 
 cavity collapse and sinkhole formation. 
 
 Extensive research has been performed 
 by SMRI and others in an attempt to un- 
 derstand the geologic parameters associ- 
 ated with sinkhole formation, but little 
 work has been done to correlate 
 solution-cavity deformations to ground 
 surface movements. 2 Therefore, the pri- 
 mary methodologies of the four investiga- 
 tions conducted by the Bureau and SMRI 
 were designed to correlate these two 
 parameters. 
 
 The study sites chosen for the four 
 investigations were located over salt- 
 solution mining operations in the Hut- 
 chinson, KS, area. In 1977 the Bureau 
 and SMRI conducted the first investiga- 
 tion at a sinkhole that had formed on the 
 property of Cargill Salt in October 1974. 
 This investigation consisted of a drill- 
 ing and coring program designed to deter- 
 mine the shape of the underlying solution 
 cavity, to evaluate the composition 
 and condition of the overburden, and to 
 determine the mechanisms that led to the 
 formation of the sinkhole. The Bureau 
 
 was responsible for contracting the 
 drilling and coring operations; SMRI 
 contracted for the analyses of the data 
 and preparation of the report of the 
 investigation. 
 
 In 1978 the second investigation was 
 carried out at a sinkhole that had formed 
 in June 1952 on the property of the 
 Barton Salt Co. , now owned by Cargill 
 Salt. As in the previous investigation, 
 a Bureau-contracted drilling and coring 
 program was conducted, and the data were 
 analyzed and a report of the investi- 
 gation was prepared under contract to 
 SMRI. 
 
 The third investigation was performed 
 in 1979 in the vicinity of two sinkholes 
 that had formed in 1978 at the Carey Salt 
 brinefield. The Bureau again funded a 
 drilling and coring program, and an SMRI 
 contractor analyzed the data and pre- 
 pared a report of the investigation. The 
 Bureau also installed and monitored a 
 surface survey network designed to detect 
 any ground surface movements associated 
 with the two cavity failures. 
 
 The fourth investigation was also 
 carried out at the Carey brinefield 
 in 1981-82. This investigation differed 
 from the other three in that it was con- 
 ducted at a brine cavity that had not ex- 
 perienced any apparent ground movements 
 and yet had a mining history similar 
 to those of the neighboring cavities that 
 had failed. The subsidence-monitoring 
 network installed for the previous inves- 
 tigation was extended to accommodate mon- 
 itoring of the area over the stable 
 cavity. Another Bureau-contracted drill- 
 ing and coring program was conducted, and 
 the data analysis and report preparation 
 were again done under contract to SMRI. 
 
 ACKNOWLEDGMENTS 
 
 The personnel at the Cargill Salt 
 Co. and the Carey Salt Division of Pro- 
 cessed Minerals, Inc., Hutchinson, KS , 
 
 2 The bibliography preceding the appen- 
 dixes at the end of this report lists 
 relevant previous research on sinkhole 
 formation. 
 
 provided valuable assistance in conduct- 
 ing this research. In particular, Larry 
 Schulte, vice president and director of 
 manufacturing, Carey Salt, made signifi- 
 cant contributions to the project by pro- 
 viding access to company property and 
 company mining records. 
 
GEOLOGIC SETTING 
 
 The Hutchinson Salt Member of the Per- 
 mian Wellington Formation underlies a 
 large area of central and south-central 
 Kansas and north-central Oklahoma. Fig- 
 ure 1 depicts the extent and thickness 
 of the Hutchinson Salt Member. The zero 
 thickness line in figure 1 indicates a 
 depositional edge to the west, northwest, 
 north, and northeast. The southwest edge 
 of the salt undergoes a facies change 
 to anhydrite and dolomite, and the east 
 edge is erosional. The salt bed in the 
 Hutchinson area is approximately 400 ft 
 beneath the surface and has a thick- 
 ness of about 325 ft. It consists of 
 bedded halite with interbeds of shale. 
 Overlying the salt is an aquitard com- 
 prised of 350 ft of Permian shales and 
 siltstones. The surface deposits that 
 overlie the aquitard are aquifers 
 comprised of unconsolidated sand and 
 gravel beds with a combined thickness of 
 about 45 ft (6_, pp. 5-10; 7_, p. 12). 3 A 
 complete description of the regional 
 geology of the Hutchinson area is given 
 by Walters (6, pp. 5-26). 
 
 LEGEND 
 
 — 200'— Thickness of salt deposit in ft 
 — Facies change 
 
 FIGURE 1.— Extent and thickness of Hutchinson Salt 
 Member. 
 
 SINKHOLE FAILURE MECHANISMS 
 
 According to Hendron (4^ pp. 2-13), 
 rapid sinkhole development above solu- 
 tion-mined cavities in bedded salt for- 
 mations as found in the Kansas region 
 requires four conditions: 
 
 1 . The presence of a large unsupported 
 roof span at the salt-shale contact. 
 
 2. A large-volume cavity beneath the 
 unsupported shale roof. 
 
 3. Triggering mechanisms. 
 
 4. In situ conditions that preclude 
 arch formation in the shale roof. 
 
 Large, unsupported roof spans in so- 
 lution cavities can be created in 
 various ways. The solution mining of 
 salt through single boreholes with casing 
 
 ■^Underlined numbers in parentheses 
 refer to items in the list of refer- 
 ences preceding the bibliography and 
 appendixes . 
 
 set in the shales above the salt and 
 tubing extending into the deposit can 
 develop cavities that expose the roof 
 rock to the deteriorating action of fresh 
 water or undersaturated brine. The prac- 
 tice of reverse circulation also leads to 
 this condition. Once these layers are 
 exposed and come in contact with fresh 
 water or brine, they disintegrate and 
 lose most of their shear strength and 
 arching capacity. When roof rock falls 
 from the roof of a solution cavity, the 
 resulting rubble pile propagates toward 
 the top of the cavity, and at the same 
 time the roof becomes progressively 
 higher. The distance from the top of the 
 cavity to the top of the rubble pile de- 
 creases during this process because of 
 the bulking of the rubble. If the dis- 
 tance between the top of the cavity and 
 the top of the rubble pile becomes zero 
 before the top of the cavity reaches the 
 
upper shale surface, then the roof will 
 start receiving support by the rubble and 
 the bulking process will be stopped 
 (fig. 24) . A shallow sinkhole may devel- 
 op as a result of the downward deflection 
 of the shale roof and the consolidation 
 of the rubble pile even though the bulk- 
 ing process has been halted (fig. 2B). 
 If, however, the distance between the top 
 of the cavity and the top of the rubble 
 pile does not become zero before the 
 roof reaches the upper shale layers, then 
 a chimney forms and propagates through 
 the upper shale layers to the unconsoli- 
 dated soils near the surface. This mate- 
 rial then flows down into the remaining 
 void and can create a deep sinkhole 
 (fig. 2C). 
 
 A trigger mechanism that reduces criti- 
 cal support from a marginally stable roof 
 can consist of a reduction of brine 
 pressure inside the cavity, a reduction 
 of the buoyancy effect on shale fragments 
 suspended from the roof of the cavity, 
 or the removal of critical roof support 
 by continuing salt dissolution. Hendron 
 (4) indicates that these conditions most 
 
 likely are interrelated and act simulta- 
 neously to initiate the failure of a cav- 
 ity roof. 
 
 If all four conditions for rapid sink- 
 hole development are met, a deep sinkhole 
 as shown in figure l£ will most likely be 
 the result. If, however, only a large 
 unsupported roof span at the salt-shale 
 contact and triggering mechanisms are 
 present, shallow sinkholes as shown in 
 figure 2S can possibly form. Shallow 
 sinkholes do not develop as rapidly 
 as deep sinkholes, and their dimensions 
 may increase with time. As mentioned 
 earlier, the bulking process in shallow 
 sinkholes does not progress up to the 
 ground surface, and no chimney is formed 
 in the shale layers. If only the first 
 condition is met, the unsupported shale 
 layers above the cavity will tend to de- 
 flect down into the opening, producing 
 subsidence on the ground surface. This 
 subsidence develops gradually over a 
 long period and affects a large surface 
 area over the cavity (4, pp. 3-4). Fur- 
 ther analysis on sinkhole failure mecha- 
 nisms is provided by Hendron (4). 
 
 FIGURE 2.— Cavity collapse with surface deformations. 
 
SUBSURFACE INVESTIGATIONS 
 
 The purpose of the subsurface investi- 
 gations was to provide information on the 
 conditions of the four brine cavities. 
 By using drilling and coring procedures, 
 information on overburden composition and 
 conditions and on general solution cavity 
 dimensions was obtained for each brine 
 cavity. 
 
 CARGILL 1974 SINKHOLE 
 (FIRST INVESTIGATION) 
 
 The site of the first cooperative in- 
 vestigation performed by SMRI and the 
 Bureau was a sinkhole that had formed 
 
 Hutchinson 
 
 LEGEND 
 ' ■ * * < Railroad 
 
 Scale, ft 
 
 south of the Cargill salt plant in 
 October 1974 (fig. 3). At the time of 
 the investigation, the sinkhole had an 
 approximate surface diameter of 300 ft 
 and a maximum depth of about 60 ft. 
 
 The investigation consisted of drill- 
 ing four vertical (V-l to V-4) and two 
 30° inclined (1-1 and 1-2) exploratory 
 borings in the vicinity of the sinkhole 
 (fig. 4). The borings were drilled along 
 two perpendicular lines that inter- 
 sected at the approximate center of 
 the sinkhole. Three of the six borings, 
 V-l, V-2, and 1-1, were drilled on the 
 northeast-southwest line; this line coin- 
 cided with the alignment of a series 
 of brine wells in the area. The other 
 three borings, V-3, V-4, and 1-2, were 
 drilled on the northwest-southeast line. 
 The vertical boreholes ranged in depth 
 from 268 ft in boring V-2 to 525 ft in 
 
 V-4 
 
 LEGEND 
 # Exploratory borehole 
 — i — i Railroad 
 
 FIGURE 3. — Location of Cargill and Barton sinkholes. 
 
 FIGURE 4.— Location of boreholes at Cargill sinkhole. 
 
boring V-3. The inclined boreholes 1-1 
 and 1-2 were each about 260 ft in depth. 
 Complete details on the drilling and cor- 
 ing procedures are given by Hendron (1_, 
 pp. 1-2). 
 
 Borings V-3 and V-4 each encountered 
 the top of the salt deposit at a depth 
 of approximately 420 ft. These borings 
 found no evidence of any surface sands 
 from the sinkhole, or any voids or dis- 
 turbances in the strata overlying the 
 salt. Borings V-l and V-2, however, both 
 found evidence of voids and disturbances 
 in the shale at depths of approximately 
 240 to 245 ft, and boring V-l also found 
 a large void and surface sands from 
 the sinkhole at a depth of about 388 ft. 
 These findings indicate that an elongated 
 cavity had developed in the northeast- 
 southwest direction under the sinkhole, 
 caused by the solution activity of the 
 neighboring brine wells. The evidence 
 also suggests that the roof shale over 
 
 the salt had caved upward about 30 ft at 
 the location of boring V-l, and that some 
 large block movements of the shale had 
 extended as much as 180 ft into the shale 
 above the elongated cavity (1_, pp. 7-8). 
 Walters (6_, p. 45) suggests that the con- 
 figuration of the elongated cavity ex- 
 ceeded the span capabilities of the 
 overlying rock layers. This allowed the 
 failure of these layers to breach the 
 uppermost shale layer and permit approxi- 
 mately 90,000 yd 3 of sand and gravel 
 to move down into the opening (2, p. 2). 
 The sand that was encountered in the in- 
 clined borings 1-1 and 1-2 indicates that 
 an approximately 100-ft-diam chimney of 
 sand was located below the center of the 
 sinkhole. The sinkhole and the chimney 
 both were elongated in the northeast- 
 southwest direction, indicating that the 
 influence of the underlying cavity elon- 
 gated along the line of brine wells 
 in the area (1, p. 8). Figure 5 shows 
 
 V-l I-l 
 
 Surface soils 
 
 Sinkhole 
 
 • Chimney 
 
 ■ V 
 
 -2 
 
 Surface 
 
 
 
 ■j^^ 
 
 
 •jfy \ 
 
 
 j J\ Shale layers 
 
 
 ■^^ f 
 
 
 fcrjxi 
 
 
 
 — — 
 
 
 A, Northwest - southeast orientation 
 
 B, Southwest - northeast orientation 
 
 FIGURE 5.— Cross sections of Cargill sinkhole. 
 
cross-sectional representations of the 
 sinkhole. Details of the drilling re- 
 sults and the conclusions drawn from 
 these results are given in a report by 
 Hendron (1). An analysis on the causes, 
 mechanisms, and time framework, of the 
 sinkhole is given by Walters (6_, pp. 32- 
 39, 45-46). 
 
 BARTON 1952 SINKHOLE 
 (SECOND INVESTIGATION) 
 
 The second investigation took place in 
 1978 in the vicinity of a sinkhole that 
 formed in June 1952 on the property of 
 the Barton Salt Co. , now owned by Cargill 
 Salt (fig. 3). The sinkhole had formed 
 in the vicinity of an old brine well 
 which was believed to have been drilled 
 in the late 19th or early 20th century by 
 the G & H Salt Co. The sinkhole had a 
 surface diameter of about 250 ft and a 
 maximum depth of about 30 ft, and was 
 backfilled shortly after it formed. The 
 sinkhole now lies beneath a parking area 
 and a section of the Cargill plant and 
 continues to undergo differential settle- 
 ments (_3, p.l; 6_, p. 29). 
 
 The investigation consisted of drilling 
 six shallow (S-l to S-6) and five deep 
 (V-l to V-5) exploratory borings in the 
 vicinity of the sinkhole (fig. 6). The 
 six shallow borings extended through the 
 unconsolidated surface soils to the upper 
 shale surface, and the five deep borings 
 extended to various depths in the shale. 
 The purpose of the shallow borings was to 
 determine the limits of the subsidence 
 area by defining the depression in the 
 upper shale surface, and to determine the 
 locations for the deep borings. Details 
 on the drilling and coring procedures are 
 given by Hendron (3, pp. 3-5). 
 
 The salt deposit was encountered at a 
 depth of 497 ft in boring V-l, 435 ft in 
 boring V-3, and 423 ft in boring V-5 
 (fig. 7). Boring V-l encountered intact, 
 but disturbed, shale down to a depth 
 of 442 ft; the remaining 55 ft consisted 
 of shale and salt roof-fall rubble which 
 filled the solution cavity. Boring V-3 
 encountered intact, but disturbed, shale 
 down to a depth of 425 ft; the remain- 
 ing 10 ft consisted of shale and salt 
 
 -f 
 
 V-2 
 
 + 
 
 LEGEND 
 — Approximate subsidence limits 
 
 Exploratory borehole 
 50 
 
 Scale, ft 
 FIGURE 6.'— Location of boreholes at Barton sinkhole. 
 
 roof rubble. Boring V-5 did not encoun- 
 ter any disturbed shale or roof-fall ma- 
 terial, and thus was considered to be 
 located outside the affected area. Bor- 
 ing V-2 terminated at 260 ft and boring 
 V-4 terminated at 406 ft, both because of 
 difficulties encountered while drilling. 
 The results from the shallow borings in- 
 dicate that the upper shale surface ex- 
 perienced a downward deflection in an 
 area centered around boring V-l. The 
 maximum deflection of the upper shale 
 surface was measured to be approximately 
 25 ft at boring V-l, and the entire af- 
 fected area had a diameter of approxi- 
 mately 240 ft. Based on the results of 
 the deep and shallow borings and gamma- 
 neutron logs, Hendron suggests that the 
 subsidence over the solution cavity was 
 
V-5 V-2 
 
 Surface 
 
 FIGURE 7.— Cross section of Barton sinkhole. 
 
 due to deterioration, tensile cracking, 
 s toping, and downward movement of the 
 basically intact shale mass. From the 
 results of the deep borings, Hendron in- 
 fers that no salt remained in the cavity 
 roof at the location of boring V-l and 
 that approximately 20 ft of shale had 
 s toped from the top of the cavity. The 
 deterioration of the roof ultimately led 
 to the loss of the ability of the roof to 
 span the cavity by arching, causing the 
 roof to break and sag and come to rest on 
 the rubble pile that filled the cavity 
 C3, PP. 26-31). 
 
 CAREY 1978 SINKHOLES 
 (THIRD INVESTIGATION) 
 
 The third investigation, jointly per- 
 formed by SMRI and the Bureau, took place 
 in 1979 at two sinkholes that formed in 
 
 
 Carey Blvd. 
 
 
 
 
 ^sa — z i ■ — 
 
 William St. 
 
 
 well 50^-J Carey brinefield 
 
 sinkhole 1 
 
 £•;':•;■:} Well 57 
 ^->^ sinkhole 
 
 300 
 
 600 
 
 _l 
 
 Scale, ft 
 FIGURE 8.— Location of Carey sinkholes. 
 
 1978 around two wells at the Carey Salt 
 brinefield (fig. 8). The two wells, well 
 50 and well 57, were both part of an in- 
 terconnected nine-well gallery. The area 
 around well 57 began subsiding on May 31, 
 1978, and continued to settle through 
 June 2. The resulting depression was ap- 
 proximately 120 ft in diameter and had 
 a depth of about 10 ft. The area around 
 well 50 began to subside on June 7, a 
 week after the first movements around 
 well 57 were observed, and continued 
 to subside for several days, leaving a 
 
depression approximately 260 ft in di- 
 ameter and 13 ft in depth (7, p. 8). De- 
 tails on production practices for the 
 wells operating in the area at the time 
 of the sinkhole formations are given by 
 Walters (_7_, pp. 6, 13-15). 
 
 The investigation consisted of explor- 
 atory drilling and coring around the 
 subsidence areas, and installing and 
 monitoring a subsidence-monitoring net- 
 work on the ground surface. The Bureau 
 installed and monitored the network, 
 while SMRI was responsible for supervis- 
 ing the Bureau-contracted drilling and 
 coring operations. Details on the moni- 
 toring network are given in the "Bureau 
 of Mines Surface Subsidence Investiga- 
 tions" section. 
 
 Five vertical borings (V-l to V-5) and 
 one inclined boring (1-1) were drilled in 
 the vicinity of the two subsidence areas 
 (fig. 9). Borings V-l to V-4 were de- 
 signed to determine the subsurface condi- 
 tions beneath the depression around well 
 57; boring V-5 was designed to delineate 
 gallery development between the two sub- 
 sidence areas; and boring 1-1 was de- 
 signed to determine the subsurface condi- 
 tions beneath the depression around 
 well 50. Boring V-l was advanced to a 
 depth of 456 ft, boring V-2 to 495 ft, 
 boring V-3 to 455 ft, boring V-4 to 431 
 ft, and boring V-5 to 451 ft. The in- 
 clined boring 1-1 was advanced to 347 ft 
 (5, pp. 7-10). Details on the drilling 
 and coring procedures are given by Hen- 
 dron (_5_, pp. 7-10). 
 
 The drilling and coring results in- 
 dicated Chat a large, unsupported roof 
 span existed above the well 57 solution 
 cavity (fig. 10). Borings V-l, V-3, and 
 V-4 each found evidence of a thin, 
 rubble-filled cavity. Boring V-2, lo- 
 cated near the center of the depression 
 area around well 57, indicated that this 
 same cavity had a much larger verti- 
 cal extent in this area. The materials 
 recovered from borings V-l and V-3 in- 
 cluded intact undisturbed shale, sagged 
 
 and disturbed shale, roof-fall rubble, 
 and undisturbed salt beneath the rubble. 
 Borings V-2 and V-4 recovered sagged and 
 disturbed shale, roof-fall rubble, insol- 
 ubles and fallen stringers (V-2 only), 
 and undisturbed salt beneath the rubble. 
 None of the borings drilled near well 57 
 found any evidence of salt in contact 
 with the shale that had formed the cavity 
 roof; thus, it was inferred that no salt 
 remained in the roof of the cavity prior 
 to its collapse (5_, pp. 31-40). Hendron 
 suggests that the formation of the two 
 subsidence areas around wells 50 and 57 
 was due to the development of large roof 
 spans in the solution cavities where the 
 shale had been exposed, softened, and 
 cracked during well operation. The com- 
 bination of these factors induced roof 
 collapse as well as excessive sagging of 
 the shale above the roof. Complete fail- 
 ure of the overlying shale did not occur 
 because the rubble that had stoped from 
 the roofs of the cavities provided sup- 
 port on which the shale came to rest. It 
 is possible that a hydraulic connection 
 developed between wells 50 and 57, in- 
 ducing the collapse of the overlying 
 shale (5, pp. 40-42). Details on the an- 
 alysis of the drilling and coring re- 
 sults are given by Hendron (5, pp. 31- 
 42). 
 
 CAREY WELL 56 (FOURTH INVESTIGATION) 
 
 The fourth investigation took place in 
 1982 in the vicinity of well 56 located 
 at the Carey brinefield. Well 56 is lo- 
 cated in the same gallery that contains 
 the failed cavities of wells 50 and 57 
 (fig. 9). Although the area around well 
 56 had not experienced any measurable 
 ground surface movements, the stability 
 of the solution cavity was unknown. Sur- 
 face monitoring would either confirm its 
 continued stability or detect any pos- 
 sible movements. The exploratory drill- 
 ing program would determine whether or 
 not the solution cavity was stable, if 
 
10 
 
 R-4o 
 
 MV-5Q 
 
 S-|o o o o o d.boooooS-12 
 
 MV-4Q 
 
 MV-3Q 
 
 MV-2G 
 
 MV-IO 
 
 T-IO 
 
 100 200 
 
 I I I 
 
 Scale, ft 
 
 
 \ 
 
 \ 
 
 N- 
 
 i 
 
 \ 
 
 \ 
 
 S-13 \ 
 
 - O OO OOS-21 
 
 I-, / 
 
 R-16 
 
 OMV-6 
 
 OT-20 
 
 000|0®00 00 om-9 
 G G V-lof X We "' 56 
 
 OR-58 
 ON-I 
 
 LEGEND 
 
 o Subsidence monument 
 
 -f- Exploratory borehole 
 
 ^' Subsidence boundary 
 
 a Control point 
 
 FIGURE 9.— Location of boreholes and subsidence monuments at Carey brlnefield. 
 
11 
 
 Well 57 
 
 FIGURE 10.— Cross section of Carey sinkholes. 
 
 the cavity was in some stage of progres- 
 sive failure, or if the cavity was pres- 
 ently stable but likely to fail in the 
 future. 
 
 The investigation consisted of drill- 
 ing and coring five (V-6 to V-10) ex- 
 ploratory borings and extending the sub- 
 sidence-monitoring network to the area 
 around well 56 (fig. 9). The Bureau was 
 responsible for extending and monitoring 
 the network, and SMR1 was responsible for 
 supervising the drilling and coring oper- 
 ations funded by the Bureau. Boring V-6 
 was advanced to a depth of 565 ft, boring 
 V-7 to 436.5 ft, boring V-8 to 515 ft, 
 boring V-9 to 502.5 ft, and boring V-10 
 to 552.5 ft (J2, pp. 8-9). Details on the 
 drilling and coring procedures are given 
 by Hendron (2, pp. 8-9). 
 
 The drilling and coring results in- 
 dicated the shale overlying the solu- 
 tion cavity was intact and undisturbed 
 to within several feet of the salt- 
 shale contact (fig. 11). Near the roof, 
 the shale had softened and undergone 
 
 bed separations. The cavity appeared to 
 be elongated in the southeast-northwest 
 direction with a roof span of about 
 150 ft. In the southwest-northeast di- 
 rection,- the roof span was estimated to 
 be approximately 50 ft. The restricted 
 roof span dimensions near the shale were 
 most likely due to the fact that well 56 
 had been operated by pumping fresh water 
 down the tubing that extended close to 
 the bottom of the salt deposit. This re- 
 sulted in most of the solutioning occur- 
 ring deep in the salt and away from the 
 overlying shale. The borings also indi- 
 cated that there was only a limited 
 amount of shale exposed in the roof of 
 the cavity that was subjected to deterio- 
 ration by fresh water (2^ pp. 37-39). 
 Hendron (2^, p. 39) suggests that the lim- 
 ited exposure of the shale to the de- 
 teriorating action of fresh water beneath 
 the well in combination with the limited 
 roof spans over the cavity led to a 
 stronger roof support and a stable 
 cavity. 
 
12 
 
 Surface 
 
 V-IOV-8 WeM V-6 
 
 n 56 
 
 
 
 
 
 
 
 
 
 
 
 
 Shale 
 
 layers 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 V-7 Well v-9 
 
 [1 56 p Surface 
 
 Surface soils 
 
 Surface soils 
 
 ^«a^T 
 
 
 
 
 
 
 
 Shale layers 
 
 
 
 
 
 
 
 
 
 
 A, Northwest - southeast orientation 
 
 B, Southwest - northeast orientation 
 
 FIGURE 11.— Cross section of Carey well 56. 
 
 BUREAU OF MINES SURFACE SUBSIDENCE INVESTIGATIONS 
 
 FIRST AND SECOND INVESTIGATIONS 
 
 The investigations carried out at the 
 Barton and Cargill sinkholes did not in- 
 clude surface monitoring programs, 
 
 CAREY 1978 SINKHOLES 
 (THIRD INVESTIGATION) 
 
 Background 
 
 In 1979 the Bureau installed a subsi- 
 dence-monitoring network around wells 50 
 and 57 in the Carey brinefield. A total 
 of 154 survey points were used to monitor 
 the horizontal and vertical ground sur- 
 face movements in the vicinity of the 
 
 two sinkholes. The network consisted of 
 1 existing control point, 4 Bureau-in- 
 stalled control points, 103 Bureau-in- 
 stalled subsidence monuments, 10 Carey- 
 installed subsidence monuments, and 
 survey marks set on the 6 exploratory 
 borings and on 30 brine wells. 
 
 Subsidence-Monitoring Network Design 
 and Construction 
 
 The network (fig. 9) was designed to 
 monitor any positional changes of the 
 ground surface associated with the two 
 sinkholes around wells 50 and 57, as well 
 as in other areas of the brinefield. The 
 S-line (S-l to S-21) and a portion of the 
 
13 
 
 R-line (R-4 to R-15) subsidence monuments 
 were positioned in the area around the 
 well 50 sinkhole. These two monument 
 lines intersected at right angles near 
 the center of the well 50 sinkhole. The 
 T-line (T-l to T-20) and the remainder of 
 the R-line (R-16 to R-58) monuments were 
 positioned in the area around the well 57 
 sinkhole. These two monument lines in- 
 tersected at right angles near the center 
 of the well 57 sinkhole. The monuments 
 R-16 to R-58 were also designed to moni- 
 tor the area between the two sinkholes 
 and were therefore oriented along the 
 axis between the two sinkhole centers. 
 The MV-line monuments were distributed 
 throughout the area around the sinkholes 
 to monitor any ground surface movements 
 due to neighboring wells. The remain- 
 der of the survey points, including the 
 wells, boreholes, and previously in- 
 stalled survey movements, were used to 
 monitor movements of the ground surface 
 over a large area around the two sink- 
 holes. Control points P-l, P-2, and P-3 
 were placed in areas that were considered 
 to be stable and not affected by solution 
 mining activities; these control points 
 were located in areas outside the area 
 shown in figure 9. Control points SC-1 
 and SC-2 were located in the brinefield 
 for the trilateration surveys and were 
 checked for stability prior to each 
 survey. 
 
 The k control points and the 103 monu- 
 ments installed by the Bureau at the 
 Carey brinefield were all of the same de- 
 sign and construction (fig. 12). The 
 monument consists of a small inner pipe 
 fitted with a pointed anchor on the bot- 
 tom and a reference-marked cap on the 
 top, and a large outer pipe which is used 
 to drive the anchor below frost depth. 
 The inner pipe extends through a cap on 
 top of the outer pipe. The outer pipe is 
 free to undergo movements due to frost 
 heave or swelling and shrinking soils 
 without affecting the inner pipe on which 
 measurements are made. The monuments 
 proved to be very stable and effectively 
 guarded against soil distances throughout 
 the entire time of the investigation. 
 
 / Inner pipe cap with 
 
 (.„ w , survey reference point 
 
 '/2-in-OD inner pipe 
 
 I'/^-in-OD outer pipe 
 
 FIGURE 12.— Detail of Bureau-designed subsidence monu- 
 ment. 
 
 The wells, boreholes, and structures that 
 were used as subsidence monuments all had 
 survey marks that provided consistent 
 reference points. 
 
 Monitoring Procedures 
 
 The procedures used to monitor posi- 
 tional changes in the network involved 
 various survey techniques. Trialteration 
 and traverse surveying procedures were 
 used for horizontal control, and trigono- 
 metric and differential leveling proce- 
 dures for vertical control. The horizon- 
 tal control surveys, as well as the 
 trigonometric level surveys, established 
 initial and subsequent coordinates and 
 elevations by measuring angles and dis- 
 tances from control points SC-1 and SC-2 
 
14 
 
 to the monuments in the network. 
 Although SC-1 and SC-2 were located with- 
 in the brinefield boundaries, their sta- 
 bility was verified before each survey by 
 using trilateration and differential 
 leveling procedures from control points 
 P-l, P-2, and P-3, which were located on 
 stable ground away from the brinefield. 
 The Bureau began surveying the network in 
 June 1979 and continued through February 
 1983. A total of 17 vertical and 12 hor- 
 izontal control surveys were performed. 
 
 maximum vertical settlement measured was 
 1.58±0.04 ft at R-15. From R-16 to R-39 
 (fig. 14) the subsidence was concentrated 
 in the vicinity of the two sinkholes, 
 with less movement at the midpoint be- 
 tween sinkholes. Vertical settlement in 
 the area around R-16 was 0.18±0.04 ft; 
 settlement in the area around the 
 midpoint between sinkholes (R-26) was 
 0.09±0.04 ft; and settlement in the area 
 around R-39 was 0.24±0.04 ft. Data from 
 R-40 to R-58 (fig. 15) showed that the 
 
 Results — Vertical Movement 
 
 The results from the vertical control 
 surveys indicated that both sinkholes ex- 
 perienced vertical settlements between 
 June 1979 and February 1983. Appendix A 
 contains data from the final vertical 
 control survey of the Carey brinefield; 
 these data were used to calculate the 
 maximum vertical displacements of the 
 subsidence monuments. 
 
 Data from the R-line indicated that 
 vertical settlements occurred between 
 monuments R-7 and R-50. From R-4 to R-15 
 (fig. 13) the settlements increased line- 
 arly, starting at monument R-8 and con- 
 tinuing toward the well 50 sinkhole. The 
 
 0.0 r 
 
 1.0 - 
 
 1.5 - 
 
 2.0 
 
 _L 
 
 J= 
 
 _L 
 
 R-4 R-5 R-6 R-7 R-8 R-9 R-10 R-ll R-12 R-13 R-14 R-15 
 SUBSIDENCE MONUMENT 
 
 FIGURE 13.— Subsidence from R-4 to R-15. 
 
 O 
 
 UJ 
 Q 
 CO 
 00 
 
 CO 
 
 0.0 i 
 
 .5 
 
 R-I6 
 
 ± 
 
 i i 
 
 I 
 
 R-20 R-25 R-30 
 
 SUBSIDENCE MONUMENT 
 FIGURE 14.— Subsidence from R-16 to R-39. 
 
 ■ ■ 
 
 R-35 
 
 R-39 
 
 UJ 
 
 o 
 
 z. 
 
 Ul 
 
 9 
 
 CO 
 
 m 
 
 3 
 CO 
 
 0.0 ,- 
 
 I.O 
 R-40 
 
 J. 
 
 ± 
 
 R-42 
 
 R-44 
 
 R-46 R-48 R-50 R-b^ 
 
 SUBSIDENCE MONUMENT 
 FIGURE 15.— Subsidence from R-40 to R-58. 
 
 R-54 
 
 R-56 
 
 R-58 
 
15 
 
 settlement around the well 57 sinkhole 
 began at R-49 and linearly increased 
 toward the center of the sinkhole. 
 The maximum settlement measured was 
 0.49±0.04 ft at R-40. 
 
 The S-line showed vertical settlement 
 between S-5 and S-20. The line from S-l 
 to S-l 2 began movement at S-6 and con- 
 tinued to minearly increase to S-12 (fig. 
 16). Maximum subsidence of 1.81±0.04 ft 
 was measured at monument S-12. Data from 
 S-13 to S-21 (fig. 17) showed that move- 
 ment began at S-20 and continued to line- 
 arly increase to S-13. The maximum sub- 
 sidence at S-13 was 0.20±0.04 ft. 
 
 Data from the T-line indicated that 
 vertical settlements occurred between T-8 
 and T-19. The line T-l to T-12 
 (fig. 18) experienced movements that 
 started at approximately T-9 and linearly 
 increased to T-12; the maximum subsidence 
 at T-12 was 0.23±0.04 ft. The line from 
 T-13 to T-19 (fig. 19) showed movement 
 that began at approximately T-18 and con- 
 tinued to linearly increase to T-13, 
 where a movement of 0.34±0.04 ft was 
 measured. 
 
 S-l S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-IO S-ll S-12 
 •SUBSIDENCE MONUMENT 
 
 FIGURE 16.— Subsidence from S-1 to S-12. 
 
 0.0 r 
 
 UJ 
 
 o 
 
 UJ 
 Q 
 CO 
 00 
 
 CO 
 
 -L 
 
 -L 
 
 J_ 
 
 I 
 
 S-I3 S-I4 S-I5 S-I6 S-I7 S-I8 S-I9 S-20 S-2I 
 SUBSIDENCE MONUMENT 
 FIGURE 17.— Subsidence from S-13 to S-21. 
 
 Results — Horizontal Movement 
 
 The results from the horizontal surveys 
 indicated that minor horizontal move- 
 ments occurred in the vicinity of the 
 well 50 sinkhole. However, the data from 
 the surveys were inconclusive as to 
 whether any movement had occurred around 
 the well 57 sinkhole. Any possible move- 
 ments along the R-line from R-16 to 
 R-58, from S-13 to S-21, and the entire 
 T-line were of a magnitude less than 
 could be detected by the surveys; the 
 minimum observable movement was cal- 
 culated to be ±0.35 ft. Appendix B con- 
 tains data from the final horizontal con- 
 trol survey of the Carey brinefield; 
 these data were used to calculate the 
 maximum horizontal displacements of the 
 subsidence monuments. 
 
 The R-line monuments underwent horizon- 
 tal displacements oriented along the 
 line from approximately R-10 to R-14 
 (fig. 20). The movement increased line- 
 arly in the direction toward the well 50 
 sinkhole. The movement at R-14 was ap- 
 proximately l.O±0.35 ft. 
 
 o.o 
 
 .5 
 
 _L 
 
 J_ 
 
 J- 
 
 i/> T-l T-2 T-3 T-4 T-5 T-6 T-7 T-8 T-9 T-10 T-l I T-12 
 
 SUBSIDENCE MONUMENT 
 
 FIGURE 18.— Subsidence from T-1 to T-12. 
 
 UJ 
 
 o 
 
 UJ 
 
 q 
 
 to 
 
 0Q 
 
 z> 
 
 00 T-13 T-14 T-15 T-16 T-17 T-18 T-19 
 
 SUBSIDENCE MONUMENT 
 
 FIGURE 19.— Subsidence from T-13 to T-20. 
 
 The S-line monuments underwent hor- 
 izontal movements that started at 
 approximately S-5 and continued through 
 S-12 (fig. 21). The movement was ori- 
 ented along the line and increased 
 linearly toward the well 50 sinkhole. 
 
16 
 
 0.5 r- 
 
 R-4 R-5 R-6 R-7 R-8 R-9 R-10 R-ll R-12 R-13 R-14 
 
 SUBSIDENCE MONUMENT 
 FIGURE 20.— Horizontal movement of R-4 to R-15. 
 
 I.O r 
 
 0*- 
 0.5 r 
 
 E 0^ 
 o 
 
 J I I L 
 
 S-l S-2 S-3 S-4 S-5 S-6 S-7 S-8 S-9 S-IO S-ll S-I2 
 SUBSIDENCE MONUMENT 
 
 FIGURE 21.— Horizontal movement of S-1 to S-12. 
 
 The maximum horizontal movement at S-12 
 was measured to be approximately 1.0±0.35 
 ft in the direction toward the sinkhole. 
 
 The results of the surveys taken on the 
 T-line and the R-line from R-16 to R-58 
 were inconclusive as to whether any hori- 
 zontal movement had taken place. If any 
 movement did occur, it was of a magnitude 
 less than could be ascertained by the re- 
 sults of the horizontal surveys. 
 
 CAREY WELL 56 (FOURTH INVESTIGATION) 
 
 Background 
 
 As part of the fourth investigation, 
 the Bureau monitored a subsidence net- 
 work in the vicinity of well 56 located 
 at the Carey brinefield. This network 
 was designed to detect any positional 
 changes of the ground surface due to cav- 
 ity failure around well 56. The network 
 consisted of 19 Bureau-installed subsi- 
 dence monuments. 
 
 Subsidence-Monitoring Network Design 
 and Construction 
 
 The area around well 56 was monitored 
 by two perpendicular lines of sub- 
 sidence monuments (fig. 9). The M-line 
 (M-l to M-9) was oriented in the east- 
 west direction, and the N-line (N-l to 
 N-10) was oriented in the north-south 
 direction. The intersection of these two 
 lines occurred at well 56. 
 
 The design of the subsidence monuments 
 used in the M-line and N-line was identi- 
 cal to that used for the monuments in the 
 previous investigation (fig. 12). These 
 monuments were installed by Carey person- 
 nel using the same techniques as were 
 used by the Bureau in the third 
 investigation. 
 
 Monitoring Procedures 
 
 As in the third investigation, the 
 Bureau used trilateration and traverse 
 surveying procedures for horizontal con- 
 trol of the subsidence-monitoring net- 
 work, and trigonometric and differential 
 surveying procedures for vertical con- 
 trol. The monitoring program began in 
 May 1981 and continued through February 
 1983. Seven vertical and five horizontal 
 surveys were performed. 
 
 Results 
 
 The data obtained from both the verti- 
 cal and horizontal surveys indicated that 
 
no apparent movement had occurred in 
 the area around well 56 during the time 
 of the fourth investigation. If any 
 
 17 
 
 movement did occur, it was of a magnitude 
 less than could be detected by the 
 surveys. 
 
 INTERPRETATION OF RESULTS 
 
 FIRST AND SECOND INVESTIGATIONS 
 
 The analyses of results for the 
 first and second investigations were not 
 performed by the Bureau and are therefore 
 omitted from this report. The analyses 
 can be found in publications by Hendron 
 (J_, _3-jy and Walters (6^). 
 
 THIRD INVESTIGATION 
 
 The survey data indicate that the sub- 
 sidence in the vicinity of the two sink- 
 holes continued throughout the period of 
 the investigation. The results from the 
 exploratory drilling program indicate 
 that sagging shale beds were resting on 
 the roof-fall rubble pile in the well 57 
 solution cavity; owing to the similarity 
 and proximity of the two wells it was in- 
 ferred that the well 50 cavity roof was 
 resting on the roof-fall rubble pile in 
 the well 50 cavity. The behavior of the 
 subsidence around the two sinkholes was 
 therefore most likely a result of the 
 gradual settling of the sagging shale 
 beds that was caused by the continued 
 consolidation of the rubble piles on 
 which the shale beds rested. As the 
 rubble piles gradually compacted, the 
 overlying strata responded with a gradual 
 downward deflection into the rubble- 
 filled cavities. If the consolidation 
 processes ceased, the subsidence would 
 also gradually cease; however, the subsi- 
 dence was not halted, implying that con- 
 solidation was still occurring in the two 
 collapsed cavities at the end of the in- 
 vestigation. It is logical to assume 
 that the consolidation processes occur- 
 ring in the rubble piles will, at some 
 point in time, be completed, and subsi- 
 dence still occurring after the comple- 
 tion of the investigation will eventually 
 decrease and stop. 
 
 The characteristics of the subsidence 
 occurring over the two failed cavities 
 
 indicate that gradual yet significant 
 settlement of the ground surface can be 
 expected after the initial collapse of a 
 solution cavity and the formation of 
 a sinkhole. This conclusion is further 
 supported by the continued settling of 
 other major sinkholes in the region; the 
 area around the 1952 Barton sinkhole, for 
 example, is still experiencing some minor 
 deformations (6). It is also logical to 
 assume that a larger volume cavity with 
 accompanying sinkhole will experience 
 surface deformations of greater magnitude 
 than a smaller volume cavity; a larger 
 volume cavity will contain a larger 
 rubble pile, and thus experience more 
 initial collapse and eventual consolida- 
 tion. This is evidenced by comparing the 
 deformations occurring above the well 50 
 cavity and the smaller well 57 cavity. 
 
 The symmetry of the ground surface de- 
 formations around the two sinkholes was 
 due to the geometries of the underlying 
 cavities, since the subsidence areas were 
 similar in plan to the probable cavity 
 geometries. The subsidence around well 
 50 was found to extend approximately 
 190 ft on the north and west sides of the 
 sinkhole. The area east of the sinkhole 
 was affected by a drainage canal that 
 runs north-south in the vicinity of well 
 50 (fig. 9); the canal and its effects on 
 the subsidence around the well 50 sink- 
 hole are explained later in this section. 
 The well 57 sinkhole, however, did not 
 have a similar ground surface deforma- 
 tion pattern. The subsidence around the 
 well 57 sinkhole was elongated in the 
 northeast-southwest direction and had a 
 total span of approximately 570 ft. The 
 span of subsidence in the southeast 
 direction was about the same as the di- 
 mensions for the well 50 sinkhole subsi- 
 dence pattern. This could have been the 
 result of a cavity extending in the 
 northeast-southwest direction, elongated 
 by hydraulic connections to other brine 
 
18 
 
 wells in the area. However, the drilling 
 data cannot confirm or deny this possi- 
 bility owing to the limited number of 
 holes that were drilled. Since both well 
 cavities were located in virtually iden- 
 tical geologic settings and were mined by 
 similar methods, it is likely that the 
 ground surface deformation patterns were 
 the result of a consistent failure pro- 
 cess that was dependent on the dimensions 
 of the two cavities. 
 
 The results from the survey data also 
 indicate that well 50 experienced more 
 vertical movement than did well 57. Hen- 
 dron (5, p. 31) suggests that stoping of 
 the well 50 cavity apparently progressed 
 higher into the overlying shale beds than 
 did stoping of the well 57 cavity, owing 
 to a larger, unsupported roof span in the 
 well 50 cavity. This would have created 
 a larger volume of rubble in the well 50 
 cavity. This larger rubble pile would 
 consolidate to a greater degree and cause 
 more vertical movement of the overlying 
 shale beds that were resting on it. This 
 in turn would create a sinkhole of 
 greater vertical extent. The subsidence 
 around the well 57 sinkhole, however, was 
 found to have extended much farther hori- 
 zontally than the subsidence around the 
 well 50 sinkhole. As proposed earlier, 
 this was possibly the result of an elon- 
 gated solution cavity. 
 
 Much of the ground surface movement in 
 the vicinity of the well 50 sinkhole con- 
 sisted of both horizontal and vertical 
 components, but it is estimated that vir- 
 tually all of the ground surface move- 
 ments contained both components. The 
 horizontal movements around well 50 were 
 always vectored toward the center of the 
 sinkhole; it was toward the center where 
 maximum vertical displacements were ob- 
 served. The horizontal movement in the 
 area of the well 50 sinkhole produced 
 tensional strains which were vectored to- 
 ward the area of maximum vertical move- 
 ment. Since the well 57 sinkhole had 
 formed under nearly identical conditions 
 to those at the well 50 sinkhole, it was 
 inferred that there had been horizontal 
 components of movement accompanying the 
 vertical deformations around well 57, al- 
 though these movements would have been 
 
 much smaller in magnitude owing to 
 smaller vertical movements. 
 
 The surveys also indicate that the 
 ground surface between sinkholes had 
 experienced considerable amounts of ver- 
 tical deformation (with presumed accom- 
 panying horizontal deformation). The two 
 solution cavities were known to be 
 hydraulically connected (5, p. 4); this 
 connection may have elongated the two 
 cavities along the area of communication. 
 When the two cavities failed, the elonga- 
 tions could have deformed the ground sur- 
 face above them. This explanation would 
 be in agreement with the characteristics 
 of the elongated subsidence pattern 
 around well 57 (fig. 9). 
 
 The drainage canal that runs north- 
 south through the brinefield (fig. 9) 
 arrested approximately 90 pet of the 
 ground surface deformations caused by the 
 well 50 sinkhole. The S-line from S-13 
 to S-21 was located entirely on the east 
 side of the canal; the first portion of 
 the S-line was located on the west side 
 of the canal, along with the well 50 
 sinkhole. The canal is approximately 25 
 ft wide and 15 ft deep. This reduction 
 in ground surface movement could be ex- 
 plained by the fact that the canal 
 severed the communication of the top 
 15 ft of the surface soil. This would 
 totally halt all tensional strains in the 
 top 15 ft of the soil that were brought 
 about by the formation of the sinkhole. 
 The horizontal and vertical displacements 
 that were measured would have been the 
 result of the communication of the soil 
 underneath the canal. 
 
 FOURTH INVESTIGATION 
 
 The results obtained from the drilling 
 and coring programs indicated that there 
 was no evidence of bed separations, sag- 
 ging, or stoping of the roof shales above 
 the well 56 solution cavity. The survey 
 results verified these findings by indi- 
 cating that virtually no ground surface 
 movements had occurred in the monitored 
 area. It was, therefore, concluded that 
 the solution cavity was , stable and not 
 undergoing deformational stresses. Since 
 the drilling and coring program found the 
 
19 
 
 well 56 cavity to have a smaller roof 
 span than the well 50 or well 57 
 cavities, it is apparent 
 
 that smaller 
 
 CONCLUS 
 
 horizontal cavity dimensions were respon- 
 sible for creating stable cavity condi- 
 tions for well 56. 
 
 The four investigations performed by 
 the Bureau in cooperation with the SMRI 
 were designed to determine the character- 
 istics and parameters of sinkhole for- 
 mation over solution-mined salt cavi- 
 ties. The results from the exploratory 
 drilling and coring investigations indi- 
 cated that the Cargill sinkhole, the Bar- 
 ton sinkhole, and the two Carey sinkholes 
 all were the result of solution-cavity 
 roof failures caused by large, unsup- 
 ported roof spans and deteriorating shale 
 roof rock. In the case of the Cargill 
 sinkhole, the cavity roof rock was com- 
 pletely breached, forming a chimney that 
 piped approximately 90,000 yd 3 of surface 
 soil into its interior. The overlying 
 shales of the Barton and the two Carey 
 solution cavities did not completely 
 fail, resulting in these beds sagging and 
 resting on the rubble piles in the solu- 
 tion cavities. The solution cavity of 
 well 56 in the Carey brinefield appeared 
 to be stable in that no sagging or major 
 deterioration of the overlying shales had 
 occurred. 
 
 The results of the surveying programs 
 that monitored the ground surface around 
 wells 50, 57, and 56 in the Carey brine- 
 field indicated a relationship between 
 cavity size and subsidence geometry. It 
 was inferred from the drilling and coring 
 program that the postfailure subsidence 
 was due to the consolidation of the 
 rubble piles on which the sagging shale 
 beds rested. 
 
 It is evident after evaluating the sur- 
 face monitoring and the drilling and 
 coring data that the large, unsupported 
 roof spans that ultimately failed were 
 the result of the well completion and 
 mining operation procedures used for each 
 collapsed solution cavity. These methods 
 allowed salt dissolution near the roofs 
 of the cavities, creating the large, un- 
 supported spans that eventually failed. 
 The methods used for salt dissolution in 
 the area have now been changed to prevent 
 salt dissolution near the top of solution 
 cavities so as to limit the dimensions of 
 the cavity roofs. The resulting cavity 
 configurations should be more stable. 
 
 REFERENCES 
 
 1. Hendron, A. J., Jr., R. E. Heuer, 
 and G. Fernandez-Delgado. Final Report, 
 Field Investigations at Cargill Sinkhole, 
 Hutchinson, Kansas. Solution Min. Res. 
 Inst., Woodstock, 1L, Rep. 78-0005-SMRI, 
 Aug. 1978, 9 pp. 
 
 2. Hendron, A. J. , Jr. , and P. A. Len- 
 zini. Subsurface Investigation at Well 
 No. 56 Carey Salt Brinefield Hutchinson, 
 Kansas. Solution Min. Res. Inst., Wood- 
 stock, IL, Rep. 83-0001-SMRI, Oct. 1983, 
 40 pp. 
 
 3. Hendron, A. J. , Jr. , P. A. Lenzini, 
 and G. Fernandez-Delgado. Field Investi- 
 gations of North Subsidence Area at Car- 
 gill, Kansas (Preliminary Report). Solu- 
 tion Min. Res. Inst. , Woodstock, IL, Rep. 
 79-0001-SMRI, Jan. 1979, 32 pp. 
 
 4. hendron, A. J. , Jr. , G. Fernan- 
 dez, and P. Lenzini. Study of Sinkhole 
 
 Formation Mechanisms in the Area of 
 Hutchinson, Kansas. Solution Min. Res. 
 Inst., Woodstock, IL, Rep. 79-0002-SMRI , 
 Jan. 1979, 17 pp. 
 
 5. . Field Investigations of 
 
 Subsidence Areas at Carey Salt Brine- 
 field, Hutchinson, Kansas. Solution Min. 
 Res. Inst., Woodstock, IL, Rep. 81-0002- 
 SMRI, July 1980, 45 pp. 
 
 6. Walters, R. F. Land Subsidence in 
 Central Kansas Associated With Rock Salt 
 Dissolution. Solution Min. Res. Inst. , 
 Woodstock, IL, Rep. 76-0002-SMRI, June 
 1976, 144 pp. 
 
 7. . Surface Subsidence Related 
 
 to Saltwell Operation - Hutchinson, Kan- 
 sas, 1978. Solution Min. Res. Inst., 
 Woodstock, IL, Rep. 79-0010-SMRI , Oct. 
 1979, 32 pp. 
 
20 
 
 BIBLIOGRAPHY 
 
 Chang, C-Y. , and K. Nair. Analytical 
 Methods for Predicting Subsidence Above 
 Solution-Mined Cavities. Paper in Pro- 
 ceedings, Fourth International Symposium 
 on Salt (Houston, TX, Apr. 8-12, 1973). 
 Northern OH Geol. Soc. , Inc. Cleveland, 
 OH, v. 2, 1973, pp. 101-117. 
 
 Dunrud, C. R. , and B. B. Nevins. Solu- 
 tion Mining and Subsidence in Evaporite 
 Rocks in the United States. U.S. Geol. 
 Surv. Map 1-1298, 1981, 2 sheets. 
 
 Ege, J. R. Surface Subsidence and 
 Collapse in Relation to Extraction of 
 Salt and Other Soluble Evaporites. U.S. 
 Geol. Surv. Open File Rep. 79-1666, 1979, 
 37 pp. 
 
 Nair, K. , C. Y. Chang, and A. M. 
 Abdullah. Analytical Techniques for Pre- 
 dicting Subsidence — Time-Dependent An- 
 alysis. Solution Min. Res. Inst. , Wood- 
 stock, IL, Rep. 72-0007-SMRI, Oct. 1972, 
 33 pp. 
 
 Nair, K. , and C. Y. Chang. Investi- 
 gation of the Influence of Certain 
 
 Variables on the Subsidence Above Mined 
 Areas. Solution Min. Res. Inst. , Wood- 
 stock, IL, Rep. 69-0004-SMRI, Dec. 1969, 
 53 pp. 
 
 Nigbor, M. T. State of the Art of So- 
 lution Mining for Salt, Potash and Soda 
 Ash. BuMines OFR 142-82, 1981, 90 pp. 
 
 Piper, T. B. Surveys For Detection and 
 Measurement of Subsidence. Solution Min. 
 Res. Inst., Woodstock, IL, Rep. 81-0003- 
 SMRI, Jan. 1981, 53 pp. 
 
 Serata, S. Annual Report (Nov. 1973- 
 Oct. 1974). Development of Research Pro- 
 gram for Detection, Prediction, and Pre- 
 vention of Surface Failure Over Solution 
 Cavities by Using REM Computer Techni- 
 ques. Solution Min. Res. Inst., Wood- 
 stock, IL, Rep. 74-0005-SMRI, Nov. 1974, 
 47 pp. 
 
 Wong, K. W. A Manual on Ground Surveys 
 for the Detection and Measurement of Sub- 
 sidence Related to Solution Mining. So- 
 lution Min. Res. Inst., Woodstock, IL, 
 Rep. 81-0003A-SMRI, 1982, 147 pp. 
 
APPENDIX A. —FINAL VERTICAL CONTROL SURVEY OF CAREY BRINEFIELD 
 (Positive values correspond to downward movement) 
 
 21 
 
 Subsidence 
 monument 
 
 Movement , 
 ft! 
 
 Subsidence 
 
 monument 
 
 Movement , 
 ft' 
 
 Subsidence 
 monument 
 
 Movement , 
 ft 1 
 
 M- 1 
 
 0.02 
 
 .00 
 
 -.01 
 
 -.04 
 
 -.03 
 
 -.01 
 
 -.01 
 
 .00 
 
 .01 
 
 .04 
 
 .01 
 
 -.01 
 
 .02 
 
 -.01 
 
 NA 
 
 .04 
 
 -.01 
 
 -.02 
 
 -.02 
 
 -.04 
 
 -.02 
 
 -.04 
 
 -.01 
 
 -.01 
 
 -.02 
 
 -.02 
 
 NA 
 
 .03 
 
 NA 
 
 .03 
 
 .05 
 
 .13 
 
 .37 
 
 .52 
 
 .74 
 
 1.03 
 
 1.31 
 
 1.58 
 
 .18 
 
 NA 
 
 NA 
 
 R- 1 9 
 
 R-20 
 
 R-21 
 
 R-22 
 
 R-23 
 
 R-24 
 
 R-25 
 
 R-26 
 
 R-27 
 
 NA 
 0.22 
 .13 
 .11 
 NA 
 .11 
 .09 
 .09 
 .16 
 .10 
 .12 
 .15 
 .12 
 .14 
 .16 
 .18 
 .29 
 .23 
 .23 
 .26 
 .24 
 .49 
 .42 
 .32 
 .30 
 .30 
 .27 
 NA 
 NA 
 NA 
 .07 
 .04 
 NA 
 .02 
 .03 
 .03 
 .02 
 .01 
 .01 
 .01 
 -.02 
 
 S-2 
 
 0.02 
 
 M-2 
 
 S-3 
 
 S-4 
 
 .03 
 
 M-3 
 
 .03 
 
 M-4 
 
 S-5 
 
 .04 
 
 M-5 
 
 S-6 
 
 .07 
 
 M-6 
 
 S-7 
 
 NA 
 
 M-7 
 
 S-8 
 
 NA 
 
 M-9 
 
 S-9 
 
 S-10 
 
 .75 
 
 NA 
 
 MV-1 
 
 R-28 
 
 R-29 
 
 R-30 
 
 R-31 
 
 R-32 
 
 R-33 
 
 R-34 
 
 R-35 
 
 R-36 
 
 R-37 
 
 R-38 
 
 R-39 
 
 R-40 
 
 R-41 
 
 R-42 
 
 R-43 
 
 R-44 
 
 R-46 
 
 R-48 
 
 R-50 
 
 R-51 
 
 R-52 
 
 R-53 
 
 R-54 
 
 R-55 
 
 R-56 
 
 R-57 
 
 S- 1 1 
 
 1.44 
 
 MV-3 
 
 S-12 
 
 S-13 
 
 1.81 
 .20 
 
 MV-4 
 
 S-14 
 
 NA 
 
 MV-5 
 
 S-15 
 
 .15 
 
 MV-6 
 
 S-17 
 
 S-18 
 
 NA 
 
 MV-7 
 
 N- 1 
 
 .09 
 .08 
 
 - 
 
 N-3 
 
 N- 4 
 
 S-20 
 
 S-21 
 
 .04 
 .04 
 .03 
 
 N- 5 
 
 T- 1 
 
 .04 
 
 N-7 
 
 T-2 
 
 T-3 
 
 .04 
 .05 
 
 N-8 
 
 T-4 
 
 T-5 
 
 T-6 
 
 .05 
 
 N-9 
 
 N- 1 
 
 .04 
 .05 
 
 R-4 
 
 T-7 
 
 .01 
 
 R-5 
 
 T-8 
 
 .02 
 
 R-b 
 
 R-7 
 
 K-8 
 
 T-10 
 
 T- 1 1 
 
 NA 
 .08 
 
 .14 
 
 r-9 
 
 T-12 
 
 T-14 
 
 T-15 
 
 T-16 
 
 .23 
 
 R-10 
 
 R-11 
 
 K-12 
 
 R-13 
 
 .34 
 .21 
 .15 
 .10 
 
 R-14 
 
 T- 1 7 
 
 .05 
 
 8.-15 
 
 T-18 
 
 NA 
 
 R-16 
 
 T- 1 9 
 
 .02 
 
 R-17 
 
 R-58 
 
 S- 1 
 
 T-20 
 
 NA 
 
 R-18 
 
 
 
 Not availah 
 'Movement is el 
 
 le. 
 evation ch< 
 
 inge between initia 
 
 1 and final 
 
 . surveys. 
 
 
 It. — Survey accuracy is ±0.04 ft. The error limits were determined by statisti- 
 cally averaging the standard deviations of stable subsidence monuments for all 
 surveys. 
 
22 
 
 APPENDIX B. — FINAL HORIZONTAL CONTROL SURVEY OF CAREY BRINEFIELD 
 (Positive values correspond to increasing easting or northing) 
 
 Subsidence 
 
 AEasting, 
 
 ANorthing, 
 
 Subsidence 
 
 AEasting, 
 
 ANorthing, 
 
 monument 
 
 ft 1 
 
 ft 
 
 monument 
 
 ft' 
 
 ft 
 
 M-l 
 
 -0.17 
 -.19 
 -.06 
 -.14 
 -.20 
 -.16 
 -.06 
 -.06 
 -.04 
 
 0.04 
 .02 
 .05 
 .04 
 .01 
 .02 
 .10 
 .11 
 .14 
 
 R-20 
 
 NA 
 
 0.22 
 
 .11 
 
 .23 
 
 NA 
 
 .20 
 
 .14 
 
 .19 
 
 -.11 
 
 NA 
 
 M-2 
 
 -0.20 
 
 M-3 
 
 R-21 
 
 -.09 
 
 M-4 
 
 R-22 
 
 1.61 
 
 M-5 
 
 R-25 
 
 R-27 
 
 NA 
 
 M-6 
 
 .17 
 
 M-7 
 
 .18 
 
 M-8 
 
 .03 
 
 
 .49 
 
 MV-1 
 
 .09 
 
 .03 
 
 R-28 
 
 .17 
 
 -.02 
 
 MV-2 
 
 .07 
 .06 
 
 .03 
 .03 
 
 R-29 
 
 NA 
 .31 
 
 NA 
 
 
 .09 
 
 MV-4 
 
 .11 
 
 NA 
 NA 
 
 .23 
 
 NA 
 NA 
 
 R-33 
 
 .13 
 
 .20 
 
 NA 
 
 -.03 
 
 MV-5 
 
 -.08 
 
 
 NA 
 
 
 .01 
 
 .04 
 
 R-34 
 
 .27 
 
 -.08 
 
 N- 1 
 
 -.07 
 -.29 
 -.16 
 
 .05 
 .00 
 .03 
 
 R-36 
 
 R-37 
 
 -.02 
 .25 
 .22 
 
 .87 
 
 N-2 
 
 -.05 
 
 N-3 
 
 -.08 
 
 
 -.18 
 
 .02 
 
 
 .29 
 
 -.13 
 
 N-5 
 
 .01 
 
 .08 
 
 R-39 
 
 .05 
 
 -.04 
 
 
 -.22 
 
 -.01 
 
 
 -.22 
 
 .09 
 
 N-7 
 
 -.11 
 
 .05 
 
 
 .06 
 
 .07 
 
 N-8 
 
 -.16 
 -.03 
 
 .02 
 .12 
 
 
 .04 
 .08 
 
 .14 
 
 
 .13 
 
 N-10 
 
 -.12 
 .26 
 
 NA 
 
 .05 
 .02 
 
 NA 
 
 R-45 
 
 R-46 
 
 .14 
 
 NA 
 
 .15 
 
 .16 
 
 R-4 
 
 NA 
 
 R-5 
 
 .11 
 
 R-6 
 
 .26 
 
 .01 
 
 
 NA 
 
 NA 
 
 R-7 
 
 .22 
 
 -.04 
 
 
 NA 
 
 NA 
 
 R-8 
 
 .17 
 
 -.18 
 
 
 .26 
 
 .05 
 
 R-9 
 
 .22 
 
 -.40 
 
 R-50 
 
 .28 
 
 .01 
 
 R-10 
 
 .13 
 .17 
 
 -.57 
 -.62 
 
 R-51 
 
 NA 
 .28 
 
 NA 
 
 R-11 
 
 
 .06 
 
 
 .26 
 
 -.82 
 
 R-53 
 
 .28 
 
 .04 
 
 
 .01 
 
 -1.00 
 
 R-54 
 
 .61 
 
 .26 
 
 R- 1 4 
 
 .13 
 
 NA 
 
 -.97 
 
 NA 
 
 R-55 
 
 .33 
 .31 
 
 .08 
 
 R-15 
 
 R-56 
 
 -.02 
 
 R-16 
 
 NA 
 NA 
 
 NA 
 NA 
 
 R-57 
 
 .20 
 .25 
 
 .00 
 
 R-17 
 
 
 .00 
 
 
 NA 
 
 NA 
 
 
 .26 
 
 .04 
 
 See footnotes at 
 
 end of appen 
 
 dix. 
 
 
 
23 
 
 (Positive values correspond to increasing easting or northing) 
 
 Subsidence 
 
 monument 
 
 Atasting, 
 ft' 
 
 ANorthing, 
 ft 
 
 Subsidence 
 monument 
 
 AEasting, 
 ft' 
 
 ANorthing, 
 ft 
 
 S-2 
 
 0.31 
 .26 
 
 NA 
 .27 
 .36 
 .45 
 
 NA 
 .85 
 .97 
 
 NA 
 
 1.12 
 
 -.04 
 
 -.06 
 
 .01 
 
 NA 
 .14 
 .17 
 .17 
 .13 
 .13 
 
 0.13 
 
 .09 
 
 NA 
 
 -.02 
 
 .08 
 
 .06 
 
 NA 
 
 .09 
 
 .30 
 
 NA 
 
 -.09 
 
 -.11 
 
 -.46 
 
 -.17 
 
 NA 
 
 -.15 
 
 -.13 
 
 -.07 
 
 -.14 
 
 -.12 
 
 T- 1 
 
 0.34 
 .34 
 .33 
 .21 
 .28 
 .30 
 .23 
 .26 
 
 NA 
 .31 
 .32 
 .30 
 .04 
 .08 
 .06 
 .04 
 -.70 
 
 NA 
 .05 
 
 NA 
 
 -0. 15 
 
 S-3 
 
 T-2 
 
 -. 15 
 
 S-4 
 
 T-4 
 
 -.15 
 
 S-5 
 
 -.27 
 
 S-6 
 
 T-5 
 
 T-6 
 
 T-7 
 
 -.09 
 
 S-7 
 
 -.12 
 
 S-8 
 
 -.05 
 
 S-9 
 
 T-ll 
 
 -.07 
 
 S-10 
 
 NA 
 
 S-11 
 
 S-12 
 
 .04 
 .00 
 
 S-13 
 
 T-12 
 
 .02 
 
 S-14 
 
 S-15 
 
 T-15 
 
 -.19 
 
 -.06 
 
 S-lb 
 
 .04 
 
 S-17 
 
 S-18 
 
 S-19 
 
 T-18 
 
 .06 
 
 -.14 
 
 NA 
 
 S-20 
 
 S-21 
 
 
 .04 
 
 NA 
 
 NA Not 
 1 Moveme 
 
 available, 
 nt is change in horizontal coordinates between initial and final surveys. 
 
 NOTE. — Survey accuracy is ±0.35 ft. The error limits were determined by statisti- 
 cally averaging the standard deviations of stable subsidence monuments for all 
 surveys. 
 
 438ft 420 
 
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