Evaluation Method of Floor Heave Damage Degree and a Case Study in Zaoquan Coal Mine, China

With the continuous increase of mining depth and complex mining geological conditions, the mileage of roadways in underground engineering such as coal mine is increasing year by year. Complex conditions lead to different floor heave failure laws, and the control technology and strategy should be changed accordingly. How to evaluate the damage degree of floor heave under different conditions has become an urgent problem. Firstly, this paper makes a statistical analysis on the main evaluation indexes of the damage degree of roadway floor heave. Then, the fuzzy comprehensive clustering method is used to establish the classification method of floor heave damage degree, taking the floor heave amount, floor rock fragmentation degree, coal pillar size, buried depth, and floor lithology as evaluation indexes. The damage degree of floor heave can be divided into five types: light type, obvious type, severe type, destructive type, and extremely severe type. Finally, the rationality and accuracy of the method are verified by the measured value and evaluation value of No. 130203 roadway in the Zaoquan coal mine. The results can provide reference for the evaluation of the damage degree of the floor rock in similar condition mine and provide guidance for the design of the support and stability control of the failure of the roadway floor heave.


Introduction
It is generally believed that if the nineteenth century is the era of the development of long bridges and the twentieth century is the era of the development of high-rise buildings, then the twenty-first century will be the era of the development of long tunnels and the development and utilization of underground space [1][2][3]. As the "throat" and "basic passage" into the underground space, the damage degree of surrounding rock is very important for the safety construction of underground engineering [4]. At present, the determination method of roadway floor heave degree and surrounding rock structure mostly adopts the method of classification and evaluation of roadway floor heave stability. After judging the stability category of roadway floor heave, the support form, support parameters, and construction method of roadway are determined for selection [5][6][7]. e existing classification of roadway floor heave is very statistical and fuzzy, and there are many classification methods, but most of them are difficult to quantify, or the factors are too single, and the applicability is low.
On the one hand, the damage degree of roadway floor rock reflects the support effect of roadway; on the other hand, it also reflects the bearing capacity of roadway surrounding rock itself. Due to the complexity of geological characteristics, the engineering analogy method is often used in the design of rock mass stability control, which is mainly based on the support parameters under similar engineering geological conditions [8][9][10]. In the existing engineering analogy support design methods, the degree of rock fragmentation is mostly described by the method of stability classification of rock mass, and the support parameters are given by experience.
e stability evaluation of roadway surrounding rock is a powerful tool for the existing support quality, and the next step to strengthen the support. It is a very important part of the roadway surrounding rock control design. At home and abroad, the research on the classification method of roadway surrounding rock started earlier, and there are many classification methods. Foreign countries began in the 1940s, such as the U.S. Terzaghi classification method. e rock mass quality classification in 1960s is represented by the rock quality index (RQD) classification of the United States. Most of these classification methods focus on the qualitative or quantitative classification of the single index [11][12][13][14]. Since the 1970s, rock mass classification has gradually developed from the single factor to multifactor, qualitative to quantitative. e representative ones are Barton's Q system classification and Bieniawski's RMR classification [15,16]. With the development of underground engineering in China, many achievements have been made in the classification of surrounding rock stability of roadway in China. In addition, some scholars have studied the influence of groundwater, in situ stress, rock integrity, and rock strength on the damage degree of surrounding rock. For example, Zhang et al. [17] studied the potential failure mode of surrounding rock based on in situ stress level evaluation, which is more suitable for deep high-stress underground engineering and makes it more convenient for field engineers to understand and apply. Luo et al. [18] studied the influence of water on the mechanical behavior of surrounding rock of the hard rock tunnel through the laboratory test. It was found that water changed the mesoscopic mechanism of spalling, reduced residual elastic strain energy, avoided over concentration of strain energy, and improved the rock burst resistance. Li et al. [19] used the model test and numerical simulation method to study the damage and failure law of surrounding rock of the straight wall arch tunnel under the action of principal stress in different directions. Zhao et al. [20] studied the influence of the surrounding rock structure on roadway failure degree. rough the above analysis, it can be found that there are many reasons for the deformation and failure of roadway surrounding rock. Under different geological structure conditions and engineering geological conditions, the deformation and failure of surrounding rock are different. erefore, the main controlling factors of roadway surrounding rock deformation are changing with the geological conditions. e deformation and failure of roadway surrounding rock are affected by many factors, such as uniaxial compressive strength of rock, rock structure, groundwater, geological structure, and in situ stress [21][22][23][24][25]. erefore, it is very important to consider a variety of factors and quantitatively evaluate the degree of floor heave damage, analyze and evaluate the stability of roadway surrounding rock, establish reasonable support types and construction parameters, and provide reference for roadway construction.
erefore, this paper first investigates and analyzes the main evaluation indexes and influencing factors of floor heave damage degree of various kinds of roadways at home and abroad. On this basis, a method of evaluation and classification of floor heave damage degree based on the fuzzy comprehensive clustering method is proposed. Finally, No. 130203 roadway in the Zaoquan coal mine is taken as an example to verify the rationality and accuracy of the method. e results can provide guidance for surrounding rock support design and stability control.

Main Evaluation Indexes of Floor Heave Damage Degree of Roadway
In order to reasonably evaluate the damage degree of floor heave, we should first have a systematic understanding of the existing main evaluation indexes and their influencing factors. erefore, this paper randomly investigates the underground tunnels such as coal mines, subway tunnels, and other underground tunnels at home and abroad. A total of 40 main subway tunnels and 20 coal mines roadways are investigated, and the main indexes of the damage degree of the floor heave are calculated. It mainly includes two categories: (1) the amount of floor heave; (2) broken degree of floor rock. ese two types are the direct indexes to evaluate the damage degree of floor heave. After the roadway is excavated, the floor rock is damaged and the floor heave is the most intuitive expression of the deformation and failure degree of the floor. In [26], the damage degree of floor heave was classified according to the amount of floor heave. is index is defined as D in this paper. the amount of floor heave is very large, the roadway is damaged seriously, and the loss of roadway section is more than 1/5, so it can be used only after many renovations.
e broken degree of floor rock is generally measured by ultrasonic wave velocity. e change of wave velocity reflects the failure degree of floor rock. Generally speaking, the smaller the wave velocity is, the lower the integrity of surrounding rock is and the higher the damage degree of floor heave is. e higher the wave velocity is, the higher the integrity of surrounding rock is and the lower the damage degree of floor heave is. e damage degree of floor heave corresponding to different acoustic wave velocities is shown in Table 1 [7]. e field investigation results and the comparison of previous literature further verify that the damage degree of floor heave is divided only according to the amount of floor heave and the degree of floor rock fragmentation. It is difficult to effectively guide the design of floor heave support and control, and there is a lack of extensive field engineering guidance. When evaluating the damage degree of floor heave, we need to consider the main factors that affect the 2 Shock and Vibration damage degree of floor heave and establish a more comprehensive classification system. It can provide reference for the design of floor heave support and the stability control of surrounding rock. erefore, in the field investigation, the main influencing factors of floor heave damage degree are counted, including coal pillar size (P), buried depth (B), floor lithology (Y), and other factors, which are indirect indicators to evaluate floor heave damage degree.
(3) Coal pillar size (P): due to the strata and surface movement caused by mining, the roadways and ground buildings in the affected area are damaged to varying degrees. In order to protect some important buildings, it is necessary to reserve protective coal pillars. e roadway is the throat of the working face, and the roadway support directly affects the normal production and safety management of the working face. At present, it is still the main method for many coal mines to set up coal pillars to protect the roadway. Reasonable width of coal pillar is the primary premise to ensure the stability of surrounding rock of roadway, and it is also one of the important contents of the roadway support design. e deformation of surrounding rock, especially floor heave, is closely related to the size of the coal pillar. e paper [27,28] has an impact on the amount of floor heave in roadway and classified the damage degree of floor heave. e results are shown in Table 2.
(4) Buried depth (B): generally speaking, the greater the buried depth, the greater the Earth stress. In situ stress is the most important external factor to induce the deformation and failure of roadway and the stability of surrounding rock. Geostress is composed of gravity stress and tectonic stress. It is produced by the Earth movement and exists in the strata. It is also called initial stress. e high initial stress is affected by regional geological structure, tunnel buried depth, valley topography, and rock strength. When excavating underground cavern in the high geostress area, a series of disasters will occur in surrounding rock. In the code, the in situ stress is expressed by the ratio of rock compressive strength R C to the maximum initial stress σ max in the direction perpendicular to the tunnel axis. e evaluation criteria of the in situ stress level proposed by Zhang et al. [17] are shown in Table 3.
(5) Floor lithology (Y): when the bottom plate is of different lithology, the rock strength of the bottom plate is different, and the bottom drum quantity is different. erefore, the influence of floor lithology on floor heave can be determined by the strength of floor rock. For hard rock roadway, the strength of surrounding rock is high, and the damage degree and scope of floor rock are small after roadway excavation. In the case of no support, the selfsupporting capacity of floor rock is still at a high level, and the floor heave is relatively small. For the soft rock roadway, the stress of surrounding rock is much greater than the strength of floor rock after excavation. e floor rock is seriously damaged and has a large range, the strength is greatly reduced, and the floor heave is naturally increased. Saturated uniaxial compressive strength, as an important index to evaluate the strength of floor rock block, refers to the value of uniaxial compressive strength measured under the condition of saturated water absorption. e strength of floor rock mass is different from that of floor rock block, so it is difficult to accurately test. erefore, the strength of floor rock block and the integrity degree of floor rock mass are often used to comprehensively reflect the stability of floor rock at all levels and the strength of floor rock mass. See Table 4 for details [29]. e saturated uniaxial compressive strength R C in Table 4 is the measured value, but when the measured value is missing, the rock point load strength index is 50, which can be used for conversion: (1) e investigated coal mines and subway tunnels include both foreign mines, subway tunnels, state-owned large and medium-sized mines, and subway tunnels, as well as local small mines and subway tunnels. It includes not only the shallow mine and subway tunnel but also the deep mine and subway tunnel. e investigated roadways include not only long-term maintenance chambers such as subway tunnels, underground car yards of coal mines, and substations but also short-term service chambers or roadways such as mining roadways and connecting roadways. It is widely representative.
To sum up, this paper selects the amount of floor heave (D), broken degree of floor rock (V), coal pillar size (P), buried depth (B), and floor lithology (Y) as evaluation indexes. Taking into account the classification standards, specifications, and related literature of floor heave damage degree at home and abroad, the damage degree of floor heave is divided into five grades I-V by the single factor method.
e measured values of each evaluation index are shown in Table 5.

Classification Method of Floor Heave Damage
Degree Based on Fuzzy Comprehensive Clustering Method

Principle of Fuzzy Comprehensive Clustering Method.
Fuzzy comprehensive clustering method is a comprehensive evaluation method based on fuzzy mathematics. According to the membership degree theory of fuzzy mathematics, the qualitative evaluation is transformed into quantitative evaluation, that is, the fuzzy mathematics is used to make an overall evaluation of the things or objects restricted by many factors [30,31]. e degree of floor heave damage is directly reflected in the amount of floor heave and the degree of floor rock fragmentation, and its damage is affected by many factors such as coal pillar size, buried depth, and floor lithology. e fuzzy comprehensive clustering method considers many factors and can give quantitative evaluation. e basic idea of using the fuzzy comprehensive clustering method to evaluate the damage degree of roadway floor heave is to replace "belong to" or "not belong to" with "belong to." at is to say, the degree of floor heave damage to be determined belongs to a certain type of damage, and which type of damage is the largest is the damage degree of this type. First of all, it is necessary to determine the influence index U � u 1 , u 2 , u 3 , . . . , u n and classification . . , v n of roadway floor heave damage degree. And, let the weight of each influence index be assigned as fuzzy subset A on u, denoted as weighted fuzzy en, the fuzzy relation matrix R � (r ij ) n×m is obtained by solving the membership relation of each influence index to the damage degree of roadway floor heave. en, according to equation (1), the fuzzy relation matrix and index weight are fuzzy operation and normalized. Finally, the fuzzy comprehensive evaluation result B � u 1 , u 2 , u 3 , . . . , u m is the fuzzy clustering matrix on V. e matrix is used to determine the type of floor heave damage: Table 5 shows the classification judgment table of each index of the damage degree of the floor heave of the roadway. After determining the classification standard, according to the different characteristics and actual conditions of each index, the fuzzy set of index composition, namely, the membership function of the index, is determined. Because the dimensions of different indicators are different, in order to classify the actual data, it is necessary to deal with the indicators dimensionless. e membership function of trapezoid distribution or semitrapezoid distribution is selected to deal with different sections. e membership function can be divided into three types, namely, small, large, and intermediate, as shown in Figure 1. Each classification grade has its corresponding membership function, where x is the actual value, a 1 and a 2 are the critical values of the two adjacent index grades, and the ordinate is the membership degree μ (x). e membership functions of the three types are equations (3)∼(5), from which the fuzzy relation matrix R of floor heave failure can be obtained.where μ ij is the membership degree of the actual value of the i index to class j.

Determination of Index Weight.
e weight is determined according to the overstandard weighting method, that is, the more the overstandard is, the greater the impact on the damage degree of roadway floor heave is and the greater the weight is, that is, where C i is the actual value of i index and C 0i is the average allowable critical value of the classification index at all levels. e weight of each index calculated by the above weight formula is a relative weight. In order to facilitate comparison, it is necessary to normalize, that is, the sum of the weight of each index is equal to 1: e weight matrix can be obtained:

Fuzzy Clustering Decision
Classification. e fuzzy clustering matrix can be obtained by substituting equations (6) and (9) into (2): According to the principle of maximum membership, if the result vector of fuzzy comprehensive clustering matrix B is μ r , the object belongs to class R: Shock and Vibration 5 the main production mine of Ningmei Energy Group. Its geographical coordinates are 106°30′∼106°35′E and 37°52′∼38°02′N. e mine field is 13 km long from north to south and 4 km wide from east to west, with an area of 52 km 2 . At present, 13 and 14 mining areas are under exploitation. e buried depth of the roadway has exceeded 700 mm, and the deepest is more than 800 m. e layout of the mine location and No. 130203 roadway is shown in Figure 2.

Case Analysis of Evaluation of Roadway Floor
e No. 130203 roadway is a gob-side entry, and the roadway section is rectangular with a width of 5.1 m height of 3.5 m. Because of the soft floor condition and some complex environmental factors (e.g., three highs and one disturbance) in deep mines, the floor of the No. 130203 roadway was seriously deformed, and the surrounding rock was also extensively damaged, as shown in Figure 3.  degree, the mechanical properties of the surrounding rock at 130203 roadway in the Zaoquan coal mine were obtained by the uniaxial compression test on in site rock specimens. e rock specimen properties were obtained through laboratory uniaxial compression tests on rock specimens as suggested by the International Society for Rock Mechanics [32]. As shown in Figure 4(a), the rock uniaxial compression test is carried out on the RLJW-2000 testing machine, and some test curves are obtained, as shown in Figure 4(b). Acoustic logging tool is used to detect the development of floor fractures. During monitoring, water should be injected into the borehole to ensure the transmission of sound wave. During the test, the probe of the ultrasonic instrument is placed at the bottom of the borehole. When the borehole is full of water, pull the probe outward 0.5 m each time to measure a little data until the orifice. e test mode of one transmitter and two receivers can be used in the test. e structure of the acoustic logging tool is shown in Figure 5. e in situ stress measurement is carried out in the roadway roof drilling. Firstly, the middle part of the roadway roof is drilled vertically upward with a diameter of 56 mm and a depth of 20 m. In the drilled hole, a pair of rubber packers is sent to the designated position of the hole by the drill pipe. en, high-pressure water is injected to inflate the packer and seal the rock hole between the two packers. Highpressure water injection was applied to the rock holes between packers until the surrounding rock was fractured. e direction of fracturing is the direction of maximum horizontal stress. e in situ stress measuring instrument is SYY-56 small aperture hydrofracturing in situ stress measuring device. e main technical indexes are as follows: (1) the diameter of the borehole is 56 mm. (2) e maximum depth is 30 m. (3) e maximum water pressure is 40 MPa. (4) e positioning accuracy is 3°. e in situ stress measuring device and its schematic diagram are shown in Figure 6.

Analysis of Floor Heave Damage Degree in Zaoquan Coal
Mine. According to the above measurement results, the field measured values of each index are listed in Table 6.
Using the fuzzy comprehensive clustering method, the damage degree of floor heave in 130203 return air roadway of the Zaoquan coal mine is classified. e membership degree of each index is calculated according to equations (3)∼(5), and the fuzzy relation matrix is obtained by substituting equation (6): en, according to equations (7)∼(9), the weight of each index is calculated and normalized (Table 7), and the weighted fuzzy set is obtained: A � (0.43, 0.16, 0.20, 0.11, 0.11).
According to equation (2), the fuzzy clustering matrix can be obtained: According to the principle of maximum subordination, the floor heave damage degree of No. 130203 roadway in the Zaoquan coal mine belongs to class V. It is the floor heave with serious damage. e evaluation method of floor heave damage degree is not only based on the floor heave amount and floor rock fragmentation degree but also considering the coal pillar size, buried depth, and floor lithology. It greatly improves the rationality and universality of evaluation and division of floor heave damage degree. It can provide more reliable guidance and reference for roadway surrounding rock support design and stability control.

Conclusions
In this paper, the fuzzy comprehensive method is used to evaluate the damage degree of roadway floor heave, and the accuracy and rationality of the discrimination method are verified by taking No. 130203 roadway in the Zaoquan coal mine as an example. e main conclusions are as follows: (1) rough the literature investigation of domestic and foreign coal mine roadway, subway tunnel, and other underground roadway, a total of 20 coal mine roadway and 40 subway roadway were investigated, and the main index of evaluating the roadway floor   e main indicators include floor heave amount, floor rock fragmentation degree, coal pillar size, buried depth, and floor lithology.
(2) According to the evaluation index of floor heave damage degree, the floor heave damage degree can be divided into five types: light type, obvious type, serious type, damage type, and extremely serious damage type. And, the range of the main index of different floor heave damage degrees is given. (3) e fuzzy comprehensive method is used to evaluate the floor heave damage degree of No. 130203 roadway in the Zaoquan coal mine. According to the maximum subordinate principle, the floor heave damage degree of No. 130203 roadway in the Zaoquan coal mine belongs to class V. It is the floor heave with serious damage. e accuracy and rationality of the method are also verified by field detection. (4) e evaluation method of floor heave damage degree is not only based on the size of floor heave and the broken degree of floor rock but also comprehensively considers the coal pillar size, buried depth, and floor rock lithology, which greatly improves the rationality and universality of evaluation and classification of floor heave damage degree. It can provide more reliable guidance and reference for roadway surrounding rock support design and stability control. However, the number of underground roadways such as the mine or subway is relatively small, and the next step is to increase the number of samples. In addition, this paper does not discuss the damage degree of complex cavern structure, geological particularity, special construction method, or operation environment. erefore, it is suggested to refine or adjust on this basis in specific engineering application.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no conflicts of interest.