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Deformation mechanism of roadways in deep soft rock at Hegang Xing’an Coal Mine
International Journal of Mining Science and Technology 23 (2013) 307–312
Contents lists available at SciVerse ScienceDirect
International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Deformation mechanism of roadways in deep soft rock at Hegang Xing’an Coal Mine Yang Xiaojie ⇑, Pang Jiewen, Liu Dongming, Liu Yang, Tian Yihong, Ma Jiao, Li Shaohua State Key Laboratory of Geomechanics and Deep Underground Engineering, Beijing 100083, China School of Mechanics and Civil Engineering, China University of Mining & Technology, Beijing 100083, China
a r t i c l e
i n f o
Article history: Received 9 July 2012 Received in revised form 7 August 2012 Accepted 15 September 2012 Available online 11 May 2013 Keywords: Deep Clay mineral Engineering soft rock type Deformation mechanics mechanism
a b s t r a c t Engineering geomechanics characteristics of roadways in deep soft rock at Hegang Xing’an Coal Mine were studied and the nature of clay minerals of roadway surrounding rock was analyzed. This paper is to solve the technical problems of high stress and the difficulty in supporting the coal mine, and provide a rule for the support design. Results show that mechanical deformation mechanisms of deep soft rock roadway at Xing’an Coal Mine is of IABIIABCIIIABCD type, consisting of molecular water absorption (the IAB-type), the tectonic stress type + gravity deformation type + hydraulic type (the IIABC-type), and the IIIABCD-type with fault, weak intercalation and bedding formation. According to the compound mechanical deformation mechanisms, the corresponding mechanical control measures and conversion technologies were proposed, and these technologies have been successfully applied in roadway supporting practice in deep soft rock at Xing’an Coal Mine with good effect. Xing’an Coal Mine has the deepest burial depth in China, with its overburden ranging from Mesozoic Jurassic coal-forming to now. The results of the research can be used as guidance in the design of roadway support in soft rock. Ó 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction Hegang mining area is located in the northeast of Heilongjiang province, it is an old mine with more than 70 years of mining history. With the increase of the mining intensity and the extension of mining range, shallow depth resources are increasingly exhausted, each mine began its deep mining in succession, so deep non-linear physical mechanical phenomena appear frequently, such as gas outburst, large area of roof falling and collapsing in roadway and stope, roof weighting, pressure bump and so on [1]. Especially, the roof falling, the two sides contracting, floor heaving and other large deformation damage phenomena produced in supporting process at depth that has seriously affected the mining schedule and endangered the safe production of the coal mine [2–6]. The problem of soft rock roadway supporting in Xing’an coal mining is the most serious in the Hegang mining area. This mine with the depth of 640 m at the fourth level is the deepest among the mines in coal-forming period of Jurassic in Mesozoic. Since 2005, the large area and high caving, the floor heaving, the large contraction at the two sides and other large deformation damage phenomenon appeared in the roadway project of loaded-car line for the shaft station at the fourth level, which affected the normal use of the roadway and the safe mining of the whole mine at this depth [7]. Therefore, the supporting problem of soft rock roadway for the loaded line in the shaft station at the fourth level needed to ⇑ Corresponding author. Tel.: +86 10 62339107. E-mail address: [email protected] (X. Yang).
be solved urgently. In order to ensure the success in the supporting project, the engineering soft rock type and the deformation mechanism were studied and an important theoretical basis for the road supporting design was provided. 2. Engineering geomechanics properties of roadway 2.1. Engineering situation The development of Xing’an Coal Mine is multi-level exploitation, it is divided into four levels and the ground elevation of this coal mine is +247 m. The elevation of the first level is +50 m, and the elevation of the second level is 100 m. Besides, the elevation of the third level is 300 m and the elevation of the fourth level is 502 m. The soft rock roadway for the loaded car lines of the shaft station in the fourth level has been damaged seriously routinely since 2005. Because of the depth, the high geostress, the complicated geomechanics environment as well as the soft and broken surrounding rock, the deformation such as high caving in a large area, floor heave, and large shrinkage between two sides appeared in the roadway during the roadway construction. These seriously affected the normal usage of the roadway and the mine production (Fig. 1) [7]. 2.2. Formation lithology of the roadway According to the measured geological profile of the roadway, it has passed through the inferior coal three times during the
2095-2686/$ - see front matter Ó 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology. http://dx.doi.org/10.1016/j.ijmst.2013.04.002
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direction or a different period. According to the cutting relationship between arc structure and south-north structure, shown in Fig. 2, the formation time of arc structure is earlier than the south–north structure, as it was cut by the south–north structure, so the south–north structure is the main control structure and the east–west direction is the central direction in the present stress field. Based on the maximum horizontal stress theory, the stability of a roadway’s roof and floor is mainly affected by the horizontal stress. The direction of the soft rock roadway for the loaded car line is from south to north, and it is vertical to the direction of the maximum horizontal stress in Xing’an Coal Mine, which is the basic reason why the stability of roof and floor is bad and the phenomenon of the large deformation is outstanding. 2.5. Rock mass structure of the surrounding rock Fig. 1. Deformation characters of roadway in Xing’an Coal Mine.
excavation process, the main lithology exposed are tuffaceous mudstone and tuffaceous siltstone.
By the observation of rock exposed in the field, structural planes like joints and bedding, are developed and the strata is breaking; according to microstructure analysis, micropore is developed and connectivity is good, so the type of the surrounding rock mass structure is of cataclastic texture (Fig. 3).
2.3. Geological structure The general geological structure of Xing’an mine field is faultfold type, its shape is in an arc from the south part to the north. The broad and gentle fold developed in the mine field, especially intermountain fault basin formed after hercynian fold. Due to the local basin lifting, the fault and magmatic activity caused the coal measure strata’s complexity on lithology and structure, and controlled the changes of strata. The mine field strike is SN, the dip is E, the dip angle is rather steep in shallow part, as shown in Fig. 2. The general geological structure of the roadway is rather complex, this area is beyond the arc shaped fault, the coal–rock strata has a big fluctuation because normal fault is flat and has a small horizontal displacement cut off by arc fault. Faults in this area are mainly concordant faults, and there are many associated faults in the middle of this area which have some effect on production. In the roadway surrounding rock, cracks are well developed and the rock is broken.
2.6. Physical and mechanical properties of the roadway surrounding rock Table 1 lists the physical and mechanical mean index of three different rock groups from the loaded car line surrounding rock on the fourth level. Obviously, the strength of the roadway surrounding rock is generally lower, especially the strength of mudstone exposed in the roadway is much lower. Among them, the compressive strength of mudstone is only 15.56 MPa, and the tensile strength is only 3.31 MPa. The water absorption is strong, for one thing the strength decreased evidently, for another thing stress caused by the swelling rock is bad for the roadway supports after water absorption. 3. Clay minerals characteristics of deep soft rock tunnel in Xing’an Coal Mine 3.1. Clay mineral composition analysis
2.4. Mechanical analysis of tectonic stress field Geological structure of the Xing’an mine field is complex, and the distribution characteristics of faulted structure and folded structure show that it is formed by the stress from a different
In order to determine rock mineral composition, clay mineral content, as well as swelling of clay minerals in the surrounding rock of heavy vehicle tunnel at No. 4 level of Xing’an Coal Mine, X-ray diffraction analysis of whole rock and clay minerals testing
Fig. 2. Geology structure of coal mine and the distribution of stress field.
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Fig. 3. Structure of roadway surrounding rock.
in China petroleum and gas Exploration and Development Research Institute of Experimental Center. The experimental apparatus is D/MAX 2500-ray diffraction (tube voltage 40 kV, tube current 100 mA). Experimental conditions: Cu target, wavelength: 1.54184; voltage 40 kV, current 100 mA; slit system: 1°, 1°, 0.3 mm; scanning speed: 4°/min [8]. (1) Whole-rock mineral X-ray analysis Whole-rock mineral analysis test procedure is as follows: sample crushing, grinding of all the particle size of less than 40 lm, putting the powder into the aluminum sample frame 20 18 mm box, the vertical compaction molding. Then the machine measured the peak X-ray diffraction to analyze the mineral
composition and content. Fig. 4 shows the whole rock-forming minerals X-ray spectra of the heavy vehicle line roof or floor mudstone and sandstone. The rock sample and the relative content of mineral species, as noted in Table 2. (2) X-ray diffraction analysis of clay minerals Clay minerals usually refer to the diameter less than 2 lm, water-bearing layered silicate minerals [9,10]. The X-ray spectrum of mudstone and sandstone clay mineral in the heavy vehicle line top and bottom is shown in Fig. 5. The types and relative content of clay minerals in the rock sample is shown in Table 3. According to X-ray diffraction analysis results, the stability of soft rock roadway surrounding rock has negative factors which are primarily high content of clay minerals, and one of the high expansion mineral:illite/smectite mixed layer. The lowest content of clay minerals in samples is 18.9%, and the highest content is 55%. And the rest is mostly 45%; the composition of clay minerals in samples is mainly of high expansive nature illite/smectite mixed layer, and it accounts more than 80% of the total clay minerals, but the maximum value is up to 89%. Therefore, surrounding rock of roadway on the four high level of heavy truck line in Xing’an Coal Mine is expansive rock with poor quality. According to the classification standards of expansive soft rock, as the content of montmorillonite and the illite/mixed-layer are more than 30%, it is strong expansion soft rock.
Table 1 Physical and mechanical property of different rock groups. Porosity (%)
Absorption (%)
Compressive strength (MPa)
Softening coefficiency
Tensile strength (MPa)
Elastic modulus (GPa)
Poisson’s ratio
Coal Mudstone Sandstone
14.0 25.3 25.6
5.88 2.63
2.02 2.74 1.22
15.56 50.36
0.16 0.91
3.31 4.78
9.11 18.25
0.149 0.135
20
30
10
40
20
30
2θ (°)
(c) Roof sandstone
40
d=2.563 d=2.458 d=2.394 d=2.336 d=2.282 d=2.239 d=2.187 d=2.160 d=2.128
10
4 2
10
d=4.9984 d=4.4892 d=4.2650 d=4.0370 d=3.7841 d=3.5814 d=3.5214
6
d=7.2016 d=6.4349
8 d=12.5470 d=10.0062
Intensity (×103 CPS)
d=2.5694 d=2.4616 d=2.3866 d=2.3394 d=2.2862 d=2.2403 d=2.1549 d=2.1310
12
d=4.4981 d=4.2731 d=4.0550 d=3.8686 d=3.7763 d=3.5843 d=3.5324 d=3.2454 d=3.1975 d=3.0005 d=2.9370 d=2.8246
d=5.0263
20
d=3.3495
14
d=3.3533
10
d=7.1958
d=14.5214 d=13.0647 d=10.0629
Intensity (×103 CPS)
5
40
(b) Bottom mudstone
(a) Roof mudstone
10
30
2θ (°)
2θ (°)
15
d=2.973 d=2.934 d=2.860
d=4.993 d=4.731 d=4.485d=4.263 d=4.035 d=3.948 d=3.864 d=3.778 d=3.678 d=3.478d=3.541 d=3.244
5
d=7.109 d=6.398
10
20
2θ (°)
d=3.2547 d=3.1930 d=2.9937 d=3.0355 d=2.9445 d=2.8151 d=2.7137 d=2.5953 d=2.5687 d=2.4934 d=2.4597 d=2.4263 d=2.3588 d=2.2845 d=2.2398 d=2.2104 d=2.1301 d=2.0911
10
15
d=9.984
5
d=2.5651 d=2.4987 d=2.4616 d=2.3866 d=2.3428 d=2.2856 d=2.2409 d=2.1612 d=2.1310
10
d=7.1903 d=6.5050
15
d=5.0068 d=4.4824 d=4.3881 d=4.2711 d=3.9675 d=3.7858 d=3.5829 d=3.4807 d=3.2442 d=3.2019 d=3.0025 d=2.9704 d=2.9125
20
20
d=14.244
25
d=3.194
25
Intensity (×103 CPS)
30
d=10.0402
Intensity (×103 CPS)
35
d=3.347
Gravity (kN/ m3)
d=3.3533
Lithology
30
(d) Bottom sandstone
Fig. 4. Rock-forming minerals X-ray spectra of the heavy vehicle line roof or floor mudstone and sandstone.
40
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Table 2 Results of whole-rock mineral X-ray analysis (%). No.
Rock property
1 2 3 4
Heavy Heavy Heavy Heavy
Mineral type and content Quartz
vehicle vehicle vehicle vehicle
line line line line
roof mudstone bottom mudstone roof sandstone bottom sandstone
2.7 12.3 14.6 20.5
Total clay mineral
Feldspar
Plagioclase
Calcite 4.8
3.4 4.0 2.5
5.1 4.8 5.8 3.5
Dolomite
Pyrite 1.6 1.3 2.0
5.5
Siderite
Amorphous 32.4 33.5
5.3 12.2 13.5
55.0 60.9 56.6 58.0
Note: Standard SY/T 5163-1995.
Intensity (×10 CPS)
30 25
3
Intensity (×103 CPS)
35
20 15 10 5 5
10
15 2θ (°)
20
25
50 45 40 35 30 25 20 15 10 5
30
5
Intensity (×103 CPS)
Intensity (×103 CPS) 15
20
25
30
(b) Bottom mudstone clay mineral
50 45 40 35 30 25 20 15 10 5 10
15 2θ (°)
(a) Roof mudstone clay mineral
5
10
20
25
50 45 40 35 30 25 20 15 10 5 5
30
10
15
20
25
30
2θ (°)
2θ (°)
(c) Roof sandstone clay mineral
(d) Bottom sandstone clay mineral
Fig. 5. X-ray spectrum of mudstone and sandstone clay mineral in the heavy vehicle line top and bottom.
Table 3 Clay mineral X-ray analysis. No.
Rock name
Relative content of clay mineral (%) S
1 2 3 4
Heavy Heavy Heavy Heavy
vehicle vehicle vehicle vehicle
line line line line
roof mudstone bottom mudstone roof sandstone bottom sandstone
Mixed-layer
I/S
I
K
C
83 87 89 89
11
3 13 11 11
3
C/S
I/S 30 50/25 45/25 45/25
Note: S, smectite; I/S, illite/mixed-layer; I, illite; K, kaolinite; C, chlorite; C/S, chlorite/mixed-layer; Standard SY/T 5163-1995.
3.2. Micro-structure analysis Five rock samples in soft rock roadway in the four levels of heavy trucks line in Xing’an Coal Mine were taken for electronic microscopy test. Scanning electron microscopy analysis of results (check the sample Nos. 1, 5, 10, 15), as shown in Fig. 6. It can be seen from No. 1 sample from a scanning electron microscope on the map (Fig. 6a): in 1500-fold amplification, we can observe the micro-cracks and dissolution holes; in 5000-fold amplification, we can see the mixed-layer mineral and small sheet kaolinites containing in the micro-cracks and the good connectivity.
From the analysis of sample No. 5 under scanning electron microscope (Fig. 6b), it shows that: zoom 4000 times, you can see cracks in the sheet kaolinites; further amplification, the particles can be seen in Chip I/S mixed-layer and the micro dissolution holes. From the analysis of sample No. 10 under scanning electron microscope (Fig. 6c), it shows that: zoom 500 times, about 5– 10 lm micro-cracks can be seen in the sample; magnified 6000 times, the tablets can be seen in I/S mixed-layer and microporosity. From the analysis of sample No. 15 under scanning electron microscope (Fig. 6d), it shows that: in the amplification 2000
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Deformation energy release
×1500
×5000
Bolt-mesh-anchor support
(a) Sample No.1
II ABC IIIABCD
Rock grouting
I AB IIABC IIIABCD
Threedimensi on optimization of anchor
Mine roadway repair
II AB
II B Flexible layer truss support
Fig. 7. Transformation process of the compound mechanical deformation mechanisms.
×4000
×5000
(b) Sample No.5
×500
×6000
(c) Sample No.10
×2000
×5000
(d) Sample No.15 Fig. 6. Scanning electron microscopy analysis.
times, micro-cracks and dissolution holes can be seen; in amplification 5000 times, we can see the good connectivity and a small amount of flaky kaolinites in the micro-fissures of the rock crystal. Based on the above test electron microscopy analysis, the micro-structural characteristics of roadway surrounding rock are that the I/S minerals and kaolinites occur either on the surface of the particles or in the micro dissolution holes. Another obvious feature is that the micro-fractures in the rock generally are more developed with good connectivity. 4. Mechanical deformation mechanisms of deep soft rock roadway in Xing’an Coal Mine 4.1. Determination of the engineering soft rock types The depth of loaded-car line in Xing’an Coal Mine is 750 m, and it can be estimated that the tunnel excavation site is about 15 MPa, and vertical self-weight stress and the maximum concentrated stress level can reach 30 MPa. From investigation of on-site roadway damage state and theoretical analysis, it can be confirmed that the critical depth of softening in Xing’an Coal Mine is about 400 m. Therefore, the soft rock roadway of loaded-car line has come into the deep non-linear high stress state. According to the results of the analysis of clay mineral characteristics, the illite/montmorillonite mixed layer in the roadway
surrounding rock has a high content and it is up to 89%, so the roadway surrounding rock has a strong expansive trend. After the roadway excavation, due to the changes in the environment, mudstone would adsorb moisture in the air and water. Then, it will lead to expansion or large deformation and it is very unfavorable to roadway support. Therefore, it can be determined that the engineering soft rock type of the roadway is the high-stress-swelling type. 4.2. Mechanical deformation mechanisms of deep soft rock roadway in Xing’an Coal Mine According to results of the roadway surrounding rock of loadedcar line clay mineral characteristics analysis, the illite/montmorillonite mixed layer in roadway surrounding rock has a high content and it is up to 89%, so the roadway surrounding rock has strong expansibility. Therefore, the roadway mechanical deformation mechanisms contain the IAB-type, that is, molecular water absorption intumescent type deformation mechanisms. From the research of soft rock roadway engineering geomechanics, combined with the soft rock engineering mechanics theory analysis, the major force which act on four levels of soft rock roadway in Xing’an Coal Mine is nearly horizontal tectonic stress and the angle between roadway strike, and horizontal stress is approximately vertical. In summary, it is extremely unfavorable for the stability of roadway. Self-weight stress acting on overlying strata is large. Moreover, the soft rock roadway is water-absorption, and the rock strength significantly decreases. Softening coefficient is very small, only as 0.16. Therefore, the roadway mechanical deformation mechanisms contain the IIABC-type, that is, tectonic stress type, gravity type and hydraulic type deformation mechanisms. According to analysis of roadway engineering geological conditions, it shows that the soft rock roadway in Xing’an Coal Mine totally have seven faults. There is a layer of coal through the roadway with s joints, bedding and other structural planes, and the type of the rock mass structure is cataclastic texture. Thus, it has a great impact on the roadway excavation and supporting. Therefore, the roadway mechanical deformation mechanism still contains the IIIABCD-type that is fault type, weak intercalation type and Bedding-type deformation mechanisms. Therefore, the deep soft rock roadway in Xing’an Coal Mine has a compound IABIIABCIIIABCD type mechanical deformation mechanism. To achieve successful roadway support, it must be converted to a single type, for which we have proposed the transformation process of the compound mechanical deformation mechanisms (Fig. 7) that provides an important theoretical basis to successful roadway support. The roadway design has been successfully applied in engineering practice and achieved good effect.
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5. Conclusions (1) The deep soft rock roadway in Xing’an Coal Mine has a large deformation and failure. The reason is that the expansive clay minerals illite/montmorillonite mixed layer has a high content (80%); with the depth of 749 m, self-weight stress act on overlying strata is large; horizontal tectonic stress is large and the angle between the direction of horizontal tectonic stress and axial direction of roadway is approximately vertical (90°); surrounding rock body structure is cataclastic texture; soft rock absorbent and the rock strength would be further reduced (softening coefficient is 0.16). (2) Mechanical deformation mechanisms of the deep soft rock roadway in Xing’an Coal Mine is IABIIABIIIABC type, and the key to support successfully is to convert the compound mechanical deformation mechanisms into a single type. (3) According to the compound mechanical deformation mechanisms, it is put forward the corresponding mechanical control measures and conversion technologies, and these technologies have been successfully applied to roadway supporting practice of deep soft rock roadway in Xing’an Coal Mine and achieved good effect. (4) From Mesozoic Jurassic coal-forming to now, Xing’an Coal Mine is the maximum burial depth coal mine in China. The results of the research can guide the roadway supporting of deep soft rock for other mines. Acknowledgments The authors thank Prof. He Manchao for the selflessly guidance in this research work. Meanwhile, this research is partially sup-
ported by program for the New Century Excellent Talents in University (No. NCET-08-0833), the National Natural Science Foundation of China (No. 41040027), and the Special Fund of Basic Research and Operating Expenses of China University of Mining and Technology, Beijing. These are gratefully acknowledged. References [1] He MC, Xie HP, Peng SP, Jiang YD. Study on rock mechanics in deep mining engineering. Chin J Rock Mech Eng 2005;24(16):2803–13. [2] Ma JR, Cui GX, Qin Y. Experimental research on unloading properties of clay under high stress. J China Univ Mining Technol 2008;18(1):122–5. [3] He MC, Yang XJ, Sun XM. Clay mineral characteristics of softrock in Chinese Coal Mine. Beijing: Coal Industry Press; 2006. [4] He MC, Sun XM. Support design and construction guide for roadway within soft rock in China. Beijing: Science Press; 2004. [5] He MC, Jing HH, Sun XM. Soft rock engineering mechanics. Beijing: Science Press; 2004. [6] Yang XJ, Chu LK, Liu DM, Chen KH. Research on Kaolinite in coal measures of West Beijing by Mossbauer spectroscopy. J China Univ Mining Technol 2006;16(1):61–3. [7] Li GF, He MC, Zhang GF, Tao ZG. Deformation mechanism and excavation process of large span intersection within deep soft rock roadway. Mining Sci Technol 2010;20(1):28–34. [8] Sun XM, Cai F, Yang J, Cao WF. Numerical simulation of the effect of coupling support of bolt–mesh–anchor in deep tunnel. Mining Sci Technol 2009;19(3):352–7. [9] Sun XM, He MC, Yang XJ. Research on non-linear mechanics design method of bolt–net–anchor coupling support for deep soft rock tunnel. Rock Soil Mech 2006;27(7):1061–5. [10] He MC, Li GG, Wang J, Cai J. Study on supporting design for large area serious roof caving of deep soft rock roadway in Xing’an Coal Mine. Chin J Rock Mech Eng 2007;26(5):959–64.
Contents lists available at SciVerse ScienceDirect
International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Deformation mechanism of roadways in deep soft rock at Hegang Xing’an Coal Mine Yang Xiaojie ⇑, Pang Jiewen, Liu Dongming, Liu Yang, Tian Yihong, Ma Jiao, Li Shaohua State Key Laboratory of Geomechanics and Deep Underground Engineering, Beijing 100083, China School of Mechanics and Civil Engineering, China University of Mining & Technology, Beijing 100083, China
a r t i c l e
i n f o
Article history: Received 9 July 2012 Received in revised form 7 August 2012 Accepted 15 September 2012 Available online 11 May 2013 Keywords: Deep Clay mineral Engineering soft rock type Deformation mechanics mechanism
a b s t r a c t Engineering geomechanics characteristics of roadways in deep soft rock at Hegang Xing’an Coal Mine were studied and the nature of clay minerals of roadway surrounding rock was analyzed. This paper is to solve the technical problems of high stress and the difficulty in supporting the coal mine, and provide a rule for the support design. Results show that mechanical deformation mechanisms of deep soft rock roadway at Xing’an Coal Mine is of IABIIABCIIIABCD type, consisting of molecular water absorption (the IAB-type), the tectonic stress type + gravity deformation type + hydraulic type (the IIABC-type), and the IIIABCD-type with fault, weak intercalation and bedding formation. According to the compound mechanical deformation mechanisms, the corresponding mechanical control measures and conversion technologies were proposed, and these technologies have been successfully applied in roadway supporting practice in deep soft rock at Xing’an Coal Mine with good effect. Xing’an Coal Mine has the deepest burial depth in China, with its overburden ranging from Mesozoic Jurassic coal-forming to now. The results of the research can be used as guidance in the design of roadway support in soft rock. Ó 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction Hegang mining area is located in the northeast of Heilongjiang province, it is an old mine with more than 70 years of mining history. With the increase of the mining intensity and the extension of mining range, shallow depth resources are increasingly exhausted, each mine began its deep mining in succession, so deep non-linear physical mechanical phenomena appear frequently, such as gas outburst, large area of roof falling and collapsing in roadway and stope, roof weighting, pressure bump and so on [1]. Especially, the roof falling, the two sides contracting, floor heaving and other large deformation damage phenomena produced in supporting process at depth that has seriously affected the mining schedule and endangered the safe production of the coal mine [2–6]. The problem of soft rock roadway supporting in Xing’an coal mining is the most serious in the Hegang mining area. This mine with the depth of 640 m at the fourth level is the deepest among the mines in coal-forming period of Jurassic in Mesozoic. Since 2005, the large area and high caving, the floor heaving, the large contraction at the two sides and other large deformation damage phenomenon appeared in the roadway project of loaded-car line for the shaft station at the fourth level, which affected the normal use of the roadway and the safe mining of the whole mine at this depth [7]. Therefore, the supporting problem of soft rock roadway for the loaded line in the shaft station at the fourth level needed to ⇑ Corresponding author. Tel.: +86 10 62339107. E-mail address: [email protected] (X. Yang).
be solved urgently. In order to ensure the success in the supporting project, the engineering soft rock type and the deformation mechanism were studied and an important theoretical basis for the road supporting design was provided. 2. Engineering geomechanics properties of roadway 2.1. Engineering situation The development of Xing’an Coal Mine is multi-level exploitation, it is divided into four levels and the ground elevation of this coal mine is +247 m. The elevation of the first level is +50 m, and the elevation of the second level is 100 m. Besides, the elevation of the third level is 300 m and the elevation of the fourth level is 502 m. The soft rock roadway for the loaded car lines of the shaft station in the fourth level has been damaged seriously routinely since 2005. Because of the depth, the high geostress, the complicated geomechanics environment as well as the soft and broken surrounding rock, the deformation such as high caving in a large area, floor heave, and large shrinkage between two sides appeared in the roadway during the roadway construction. These seriously affected the normal usage of the roadway and the mine production (Fig. 1) [7]. 2.2. Formation lithology of the roadway According to the measured geological profile of the roadway, it has passed through the inferior coal three times during the
2095-2686/$ - see front matter Ó 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology. http://dx.doi.org/10.1016/j.ijmst.2013.04.002
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X. Yang et al. / International Journal of Mining Science and Technology 23 (2013) 307–312
direction or a different period. According to the cutting relationship between arc structure and south-north structure, shown in Fig. 2, the formation time of arc structure is earlier than the south–north structure, as it was cut by the south–north structure, so the south–north structure is the main control structure and the east–west direction is the central direction in the present stress field. Based on the maximum horizontal stress theory, the stability of a roadway’s roof and floor is mainly affected by the horizontal stress. The direction of the soft rock roadway for the loaded car line is from south to north, and it is vertical to the direction of the maximum horizontal stress in Xing’an Coal Mine, which is the basic reason why the stability of roof and floor is bad and the phenomenon of the large deformation is outstanding. 2.5. Rock mass structure of the surrounding rock Fig. 1. Deformation characters of roadway in Xing’an Coal Mine.
excavation process, the main lithology exposed are tuffaceous mudstone and tuffaceous siltstone.
By the observation of rock exposed in the field, structural planes like joints and bedding, are developed and the strata is breaking; according to microstructure analysis, micropore is developed and connectivity is good, so the type of the surrounding rock mass structure is of cataclastic texture (Fig. 3).
2.3. Geological structure The general geological structure of Xing’an mine field is faultfold type, its shape is in an arc from the south part to the north. The broad and gentle fold developed in the mine field, especially intermountain fault basin formed after hercynian fold. Due to the local basin lifting, the fault and magmatic activity caused the coal measure strata’s complexity on lithology and structure, and controlled the changes of strata. The mine field strike is SN, the dip is E, the dip angle is rather steep in shallow part, as shown in Fig. 2. The general geological structure of the roadway is rather complex, this area is beyond the arc shaped fault, the coal–rock strata has a big fluctuation because normal fault is flat and has a small horizontal displacement cut off by arc fault. Faults in this area are mainly concordant faults, and there are many associated faults in the middle of this area which have some effect on production. In the roadway surrounding rock, cracks are well developed and the rock is broken.
2.6. Physical and mechanical properties of the roadway surrounding rock Table 1 lists the physical and mechanical mean index of three different rock groups from the loaded car line surrounding rock on the fourth level. Obviously, the strength of the roadway surrounding rock is generally lower, especially the strength of mudstone exposed in the roadway is much lower. Among them, the compressive strength of mudstone is only 15.56 MPa, and the tensile strength is only 3.31 MPa. The water absorption is strong, for one thing the strength decreased evidently, for another thing stress caused by the swelling rock is bad for the roadway supports after water absorption. 3. Clay minerals characteristics of deep soft rock tunnel in Xing’an Coal Mine 3.1. Clay mineral composition analysis
2.4. Mechanical analysis of tectonic stress field Geological structure of the Xing’an mine field is complex, and the distribution characteristics of faulted structure and folded structure show that it is formed by the stress from a different
In order to determine rock mineral composition, clay mineral content, as well as swelling of clay minerals in the surrounding rock of heavy vehicle tunnel at No. 4 level of Xing’an Coal Mine, X-ray diffraction analysis of whole rock and clay minerals testing
Fig. 2. Geology structure of coal mine and the distribution of stress field.
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Fig. 3. Structure of roadway surrounding rock.
in China petroleum and gas Exploration and Development Research Institute of Experimental Center. The experimental apparatus is D/MAX 2500-ray diffraction (tube voltage 40 kV, tube current 100 mA). Experimental conditions: Cu target, wavelength: 1.54184; voltage 40 kV, current 100 mA; slit system: 1°, 1°, 0.3 mm; scanning speed: 4°/min [8]. (1) Whole-rock mineral X-ray analysis Whole-rock mineral analysis test procedure is as follows: sample crushing, grinding of all the particle size of less than 40 lm, putting the powder into the aluminum sample frame 20 18 mm box, the vertical compaction molding. Then the machine measured the peak X-ray diffraction to analyze the mineral
composition and content. Fig. 4 shows the whole rock-forming minerals X-ray spectra of the heavy vehicle line roof or floor mudstone and sandstone. The rock sample and the relative content of mineral species, as noted in Table 2. (2) X-ray diffraction analysis of clay minerals Clay minerals usually refer to the diameter less than 2 lm, water-bearing layered silicate minerals [9,10]. The X-ray spectrum of mudstone and sandstone clay mineral in the heavy vehicle line top and bottom is shown in Fig. 5. The types and relative content of clay minerals in the rock sample is shown in Table 3. According to X-ray diffraction analysis results, the stability of soft rock roadway surrounding rock has negative factors which are primarily high content of clay minerals, and one of the high expansion mineral:illite/smectite mixed layer. The lowest content of clay minerals in samples is 18.9%, and the highest content is 55%. And the rest is mostly 45%; the composition of clay minerals in samples is mainly of high expansive nature illite/smectite mixed layer, and it accounts more than 80% of the total clay minerals, but the maximum value is up to 89%. Therefore, surrounding rock of roadway on the four high level of heavy truck line in Xing’an Coal Mine is expansive rock with poor quality. According to the classification standards of expansive soft rock, as the content of montmorillonite and the illite/mixed-layer are more than 30%, it is strong expansion soft rock.
Table 1 Physical and mechanical property of different rock groups. Porosity (%)
Absorption (%)
Compressive strength (MPa)
Softening coefficiency
Tensile strength (MPa)
Elastic modulus (GPa)
Poisson’s ratio
Coal Mudstone Sandstone
14.0 25.3 25.6
5.88 2.63
2.02 2.74 1.22
15.56 50.36
0.16 0.91
3.31 4.78
9.11 18.25
0.149 0.135
20
30
10
40
20
30
2θ (°)
(c) Roof sandstone
40
d=2.563 d=2.458 d=2.394 d=2.336 d=2.282 d=2.239 d=2.187 d=2.160 d=2.128
10
4 2
10
d=4.9984 d=4.4892 d=4.2650 d=4.0370 d=3.7841 d=3.5814 d=3.5214
6
d=7.2016 d=6.4349
8 d=12.5470 d=10.0062
Intensity (×103 CPS)
d=2.5694 d=2.4616 d=2.3866 d=2.3394 d=2.2862 d=2.2403 d=2.1549 d=2.1310
12
d=4.4981 d=4.2731 d=4.0550 d=3.8686 d=3.7763 d=3.5843 d=3.5324 d=3.2454 d=3.1975 d=3.0005 d=2.9370 d=2.8246
d=5.0263
20
d=3.3495
14
d=3.3533
10
d=7.1958
d=14.5214 d=13.0647 d=10.0629
Intensity (×103 CPS)
5
40
(b) Bottom mudstone
(a) Roof mudstone
10
30
2θ (°)
2θ (°)
15
d=2.973 d=2.934 d=2.860
d=4.993 d=4.731 d=4.485d=4.263 d=4.035 d=3.948 d=3.864 d=3.778 d=3.678 d=3.478d=3.541 d=3.244
5
d=7.109 d=6.398
10
20
2θ (°)
d=3.2547 d=3.1930 d=2.9937 d=3.0355 d=2.9445 d=2.8151 d=2.7137 d=2.5953 d=2.5687 d=2.4934 d=2.4597 d=2.4263 d=2.3588 d=2.2845 d=2.2398 d=2.2104 d=2.1301 d=2.0911
10
15
d=9.984
5
d=2.5651 d=2.4987 d=2.4616 d=2.3866 d=2.3428 d=2.2856 d=2.2409 d=2.1612 d=2.1310
10
d=7.1903 d=6.5050
15
d=5.0068 d=4.4824 d=4.3881 d=4.2711 d=3.9675 d=3.7858 d=3.5829 d=3.4807 d=3.2442 d=3.2019 d=3.0025 d=2.9704 d=2.9125
20
20
d=14.244
25
d=3.194
25
Intensity (×103 CPS)
30
d=10.0402
Intensity (×103 CPS)
35
d=3.347
Gravity (kN/ m3)
d=3.3533
Lithology
30
(d) Bottom sandstone
Fig. 4. Rock-forming minerals X-ray spectra of the heavy vehicle line roof or floor mudstone and sandstone.
40
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Table 2 Results of whole-rock mineral X-ray analysis (%). No.
Rock property
1 2 3 4
Heavy Heavy Heavy Heavy
Mineral type and content Quartz
vehicle vehicle vehicle vehicle
line line line line
roof mudstone bottom mudstone roof sandstone bottom sandstone
2.7 12.3 14.6 20.5
Total clay mineral
Feldspar
Plagioclase
Calcite 4.8
3.4 4.0 2.5
5.1 4.8 5.8 3.5
Dolomite
Pyrite 1.6 1.3 2.0
5.5
Siderite
Amorphous 32.4 33.5
5.3 12.2 13.5
55.0 60.9 56.6 58.0
Note: Standard SY/T 5163-1995.
Intensity (×10 CPS)
30 25
3
Intensity (×103 CPS)
35
20 15 10 5 5
10
15 2θ (°)
20
25
50 45 40 35 30 25 20 15 10 5
30
5
Intensity (×103 CPS)
Intensity (×103 CPS) 15
20
25
30
(b) Bottom mudstone clay mineral
50 45 40 35 30 25 20 15 10 5 10
15 2θ (°)
(a) Roof mudstone clay mineral
5
10
20
25
50 45 40 35 30 25 20 15 10 5 5
30
10
15
20
25
30
2θ (°)
2θ (°)
(c) Roof sandstone clay mineral
(d) Bottom sandstone clay mineral
Fig. 5. X-ray spectrum of mudstone and sandstone clay mineral in the heavy vehicle line top and bottom.
Table 3 Clay mineral X-ray analysis. No.
Rock name
Relative content of clay mineral (%) S
1 2 3 4
Heavy Heavy Heavy Heavy
vehicle vehicle vehicle vehicle
line line line line
roof mudstone bottom mudstone roof sandstone bottom sandstone
Mixed-layer
I/S
I
K
C
83 87 89 89
11
3 13 11 11
3
C/S
I/S 30 50/25 45/25 45/25
Note: S, smectite; I/S, illite/mixed-layer; I, illite; K, kaolinite; C, chlorite; C/S, chlorite/mixed-layer; Standard SY/T 5163-1995.
3.2. Micro-structure analysis Five rock samples in soft rock roadway in the four levels of heavy trucks line in Xing’an Coal Mine were taken for electronic microscopy test. Scanning electron microscopy analysis of results (check the sample Nos. 1, 5, 10, 15), as shown in Fig. 6. It can be seen from No. 1 sample from a scanning electron microscope on the map (Fig. 6a): in 1500-fold amplification, we can observe the micro-cracks and dissolution holes; in 5000-fold amplification, we can see the mixed-layer mineral and small sheet kaolinites containing in the micro-cracks and the good connectivity.
From the analysis of sample No. 5 under scanning electron microscope (Fig. 6b), it shows that: zoom 4000 times, you can see cracks in the sheet kaolinites; further amplification, the particles can be seen in Chip I/S mixed-layer and the micro dissolution holes. From the analysis of sample No. 10 under scanning electron microscope (Fig. 6c), it shows that: zoom 500 times, about 5– 10 lm micro-cracks can be seen in the sample; magnified 6000 times, the tablets can be seen in I/S mixed-layer and microporosity. From the analysis of sample No. 15 under scanning electron microscope (Fig. 6d), it shows that: in the amplification 2000
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Deformation energy release
×1500
×5000
Bolt-mesh-anchor support
(a) Sample No.1
II ABC IIIABCD
Rock grouting
I AB IIABC IIIABCD
Threedimensi on optimization of anchor
Mine roadway repair
II AB
II B Flexible layer truss support
Fig. 7. Transformation process of the compound mechanical deformation mechanisms.
×4000
×5000
(b) Sample No.5
×500
×6000
(c) Sample No.10
×2000
×5000
(d) Sample No.15 Fig. 6. Scanning electron microscopy analysis.
times, micro-cracks and dissolution holes can be seen; in amplification 5000 times, we can see the good connectivity and a small amount of flaky kaolinites in the micro-fissures of the rock crystal. Based on the above test electron microscopy analysis, the micro-structural characteristics of roadway surrounding rock are that the I/S minerals and kaolinites occur either on the surface of the particles or in the micro dissolution holes. Another obvious feature is that the micro-fractures in the rock generally are more developed with good connectivity. 4. Mechanical deformation mechanisms of deep soft rock roadway in Xing’an Coal Mine 4.1. Determination of the engineering soft rock types The depth of loaded-car line in Xing’an Coal Mine is 750 m, and it can be estimated that the tunnel excavation site is about 15 MPa, and vertical self-weight stress and the maximum concentrated stress level can reach 30 MPa. From investigation of on-site roadway damage state and theoretical analysis, it can be confirmed that the critical depth of softening in Xing’an Coal Mine is about 400 m. Therefore, the soft rock roadway of loaded-car line has come into the deep non-linear high stress state. According to the results of the analysis of clay mineral characteristics, the illite/montmorillonite mixed layer in the roadway
surrounding rock has a high content and it is up to 89%, so the roadway surrounding rock has a strong expansive trend. After the roadway excavation, due to the changes in the environment, mudstone would adsorb moisture in the air and water. Then, it will lead to expansion or large deformation and it is very unfavorable to roadway support. Therefore, it can be determined that the engineering soft rock type of the roadway is the high-stress-swelling type. 4.2. Mechanical deformation mechanisms of deep soft rock roadway in Xing’an Coal Mine According to results of the roadway surrounding rock of loadedcar line clay mineral characteristics analysis, the illite/montmorillonite mixed layer in roadway surrounding rock has a high content and it is up to 89%, so the roadway surrounding rock has strong expansibility. Therefore, the roadway mechanical deformation mechanisms contain the IAB-type, that is, molecular water absorption intumescent type deformation mechanisms. From the research of soft rock roadway engineering geomechanics, combined with the soft rock engineering mechanics theory analysis, the major force which act on four levels of soft rock roadway in Xing’an Coal Mine is nearly horizontal tectonic stress and the angle between roadway strike, and horizontal stress is approximately vertical. In summary, it is extremely unfavorable for the stability of roadway. Self-weight stress acting on overlying strata is large. Moreover, the soft rock roadway is water-absorption, and the rock strength significantly decreases. Softening coefficient is very small, only as 0.16. Therefore, the roadway mechanical deformation mechanisms contain the IIABC-type, that is, tectonic stress type, gravity type and hydraulic type deformation mechanisms. According to analysis of roadway engineering geological conditions, it shows that the soft rock roadway in Xing’an Coal Mine totally have seven faults. There is a layer of coal through the roadway with s joints, bedding and other structural planes, and the type of the rock mass structure is cataclastic texture. Thus, it has a great impact on the roadway excavation and supporting. Therefore, the roadway mechanical deformation mechanism still contains the IIIABCD-type that is fault type, weak intercalation type and Bedding-type deformation mechanisms. Therefore, the deep soft rock roadway in Xing’an Coal Mine has a compound IABIIABCIIIABCD type mechanical deformation mechanism. To achieve successful roadway support, it must be converted to a single type, for which we have proposed the transformation process of the compound mechanical deformation mechanisms (Fig. 7) that provides an important theoretical basis to successful roadway support. The roadway design has been successfully applied in engineering practice and achieved good effect.
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5. Conclusions (1) The deep soft rock roadway in Xing’an Coal Mine has a large deformation and failure. The reason is that the expansive clay minerals illite/montmorillonite mixed layer has a high content (80%); with the depth of 749 m, self-weight stress act on overlying strata is large; horizontal tectonic stress is large and the angle between the direction of horizontal tectonic stress and axial direction of roadway is approximately vertical (90°); surrounding rock body structure is cataclastic texture; soft rock absorbent and the rock strength would be further reduced (softening coefficient is 0.16). (2) Mechanical deformation mechanisms of the deep soft rock roadway in Xing’an Coal Mine is IABIIABIIIABC type, and the key to support successfully is to convert the compound mechanical deformation mechanisms into a single type. (3) According to the compound mechanical deformation mechanisms, it is put forward the corresponding mechanical control measures and conversion technologies, and these technologies have been successfully applied to roadway supporting practice of deep soft rock roadway in Xing’an Coal Mine and achieved good effect. (4) From Mesozoic Jurassic coal-forming to now, Xing’an Coal Mine is the maximum burial depth coal mine in China. The results of the research can guide the roadway supporting of deep soft rock for other mines. Acknowledgments The authors thank Prof. He Manchao for the selflessly guidance in this research work. Meanwhile, this research is partially sup-
ported by program for the New Century Excellent Talents in University (No. NCET-08-0833), the National Natural Science Foundation of China (No. 41040027), and the Special Fund of Basic Research and Operating Expenses of China University of Mining and Technology, Beijing. These are gratefully acknowledged. References [1] He MC, Xie HP, Peng SP, Jiang YD. Study on rock mechanics in deep mining engineering. Chin J Rock Mech Eng 2005;24(16):2803–13. [2] Ma JR, Cui GX, Qin Y. Experimental research on unloading properties of clay under high stress. J China Univ Mining Technol 2008;18(1):122–5. [3] He MC, Yang XJ, Sun XM. Clay mineral characteristics of softrock in Chinese Coal Mine. Beijing: Coal Industry Press; 2006. [4] He MC, Sun XM. Support design and construction guide for roadway within soft rock in China. Beijing: Science Press; 2004. [5] He MC, Jing HH, Sun XM. Soft rock engineering mechanics. Beijing: Science Press; 2004. [6] Yang XJ, Chu LK, Liu DM, Chen KH. Research on Kaolinite in coal measures of West Beijing by Mossbauer spectroscopy. J China Univ Mining Technol 2006;16(1):61–3. [7] Li GF, He MC, Zhang GF, Tao ZG. Deformation mechanism and excavation process of large span intersection within deep soft rock roadway. Mining Sci Technol 2010;20(1):28–34. [8] Sun XM, Cai F, Yang J, Cao WF. Numerical simulation of the effect of coupling support of bolt–mesh–anchor in deep tunnel. Mining Sci Technol 2009;19(3):352–7. [9] Sun XM, He MC, Yang XJ. Research on non-linear mechanics design method of bolt–net–anchor coupling support for deep soft rock tunnel. Rock Soil Mech 2006;27(7):1061–5. [10] He MC, Li GG, Wang J, Cai J. Study on supporting design for large area serious roof caving of deep soft rock roadway in Xing’an Coal Mine. Chin J Rock Mech Eng 2007;26(5):959–64.