J. Cent. South Univ. (2018) 25: 1524-1534
DOI: https://doi.org/10.1007/s11771-018-3845-1
Backfill support’s backfill and operation properties and evaluation
ZHANG Qiang(张强)1, 2, DU Chang-long(杜长龙)1, ZHANG Ji-xiong(张吉雄)2,WANG Jia-qi(王佳奇)2, LI Meng(李猛)2, QI Wen-yue(齐文跃)2
1. School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, China;
2. State Key Laboratory of Coal Resources and Safe Mining, School of Mines,China University of Mining and Technology, Xuzhou 221116, China
Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract:
To ensure compacted backfilling, it is essential to ensure the reliability of the performance of a solid backfill support, key equipment for integrating backfilling and mining. To evaluate the backfilling performance of a backfill support, the concept of backfill and operation properties is proposed in this study. Moreover, it is elaborated in terms of five aspects, namely, structural property, supporting property, tamping property, mechanical response property, and geological adaptation property, which are specifically reflected by 14 indexes including the supporting intensity and vertical roof gap. Seven separate evaluation indexes are selected to build a backfill and operation properties based system for evaluating the design schemes of the backfill support via a multi-index comprehensive evaluation method; then, the evaluation method and process together with measures to control the backfill and operation properties are proposed. By using this system, 11 schemes for optimizing the ZC5200/14.5/3 backfill support at Zhaizhen Coal Mine are evaluated, and scheme #10 is found to show superior vertical roof gap and other backfill and operation properties, thus demonstrating the reasonability of the evaluation system. On this basis, the backfill support research framework of designing initial scheme, optimizing design scheme, selecting the best evaluation indexes, evaluating optimizing scheme, and evaluating operation properties is built; this should serve as an important reference for further studies on the roof controlling performance of a backfill support.
Key words:
Cite this article as:
ZHANG Qiang, DU Chang-long, ZHANG Ji-xiong, WANG Jia-qi, LI Meng, QI Wen-yue. Backfill support’s backfill and operation properties and evaluation [J]. Journal of Central South University, 2018, 25(6): 1524–1534.
DOI:https://dx.doi.org/https://doi.org/10.1007/s11771-018-3845-11 Introduction
Fully mechanized solid backfill coal mining is an environment-friendly approach in which solid waste (gangue, coal ash, loess, aeolian sand, and building waste) is backfilled into the goaf at the workface. The solid backfill support is the core equipment in this approach. It not only supports the roof and pushes the conveyer and coal mining machine but also plays a role in conveying and tamping the backfilling and auxiliary materials. Therefore, ensuring its reliable performance is essential for compacted backfilling [1–3].
Many existing studies have focused on solid backfilling support. ZHANG et al [1–3] and MIAO [4] derived an analytical solution for the trace of the roof deformation and displacement caused by the active force of a support by building a mechanical model for controlling the roof deformation and displacement due to initial loading of the support. WANG et al [5] analyzed the relationship between the mining support and the surrounding rock as well as the movement characteristics of overlaying strata to evaluate the roof load and conducted verifications by examining practical backfilling mining cases. CUI et al [6] introduced the main structure and working principle of a backfill hydraulic support with six columns, determined the working resistance and related equipment selection, designed the rear tamping units, and adopted a PSOD system to analyze the stress on the hydraulic support and optimized the related parameters. ZHANG et al [7–9] studied the influencing factors and design and judgment methods for a reasonable horizontal roof gap for a solid backfill support. JUNKER et al [10] explained the role of the pillar stress and tamping arm of the backfill support. XU et al [11] analyzed the maximum concentrated load of the support and stress of each pillar when reaching the expected backfilling effect. BI [12] designed a backfilling support based on practical geological conditions to analyze the supporting unit and its strength at the rear beam and investigated the design of the backfilling and tamping units and the material conveying system.
However, few studies have focused on evaluating the performance of the backfilling support. In this study, based on considerable practical experience of engineering applications of a backfill support, the concept of backfill and operation properties is proposed. Accordingly, independent evaluation indexes are determined. Then, a design scheme evaluation system and study system are established based on the backfill and operation properties; furthermore, an evaluation method and process as well as engineering controlling measures are provided for such properties. By integrating practical engineering cases, the best scheme is selected by evaluating support optimizing schemes with a comprehensive multi-index evaluation method [13–15]. The results of this study will serve as a great reference for further studies on the roof controlling performance of a backfill support.
2 Backfill and operation properties of backfill support
2.1 Contrastive analysis on conventional support and backfill support
A hydraulic support is key equipment for controlling the mining area pressure at the mining workface. Its main functions are to push the scraper conveyor as well as roof support and management through self-advancing realized by the supporting force generated by fluid pressure [16]. Moreover, depending on its type, a hydraulic support also has other key functions. For example, the key function of a top coal caving hydraulic support is to realize reasonable caving of the top coal; that of a large-dip-angle hydraulic support is skid and tilting prevention; and that of a backfilling mining hydraulic support is solid material conveying and compacted backfilling. Table 1 shows the functions of different hydraulic supports.
Table 1 Statistical analysis on functions of different kinds of hydraulic supports
2.2 Backfill and operation properties
The backfill and operation properties [8] refer to the comprehensive performance of the backfill support in protecting the backfilling space, providing a means for conveying backfilling material, and providing a tamping force and guaranteeing the compression ratio. As the basis for evaluating and determining the control performance and adaptation of the backfill support, these properties include the structural property, supporting property, tamping property, mechanical response property, and geological adaptation property. These are specifically reflected by 14 evaluation indexes, including the dip angle of pillar, trace of canopy tip, length ratio of canopy, supporting intensity, rear canopy strength, tamping force, horizontal roof gap, vertical roof gap, taming angle, pillar load ratio, and dynamic factor. Among these, the dip angle of pillar and swing and length ratio of canopy are structural properties; supporting intensity, rear canopy strength, and movement property are supporting properties; tamping force, horizontal roof gap, vertical roof gap, and tamping angle are tamping properties; and pillar load ratio and dynamic factor are mechanical response properties. The overall performance is reflected by the adaptation to the geological condition.
3 Evaluation index of backfill and operation properties
The performance of the backfilling support is mainly reflected by the optimization of the support structure parameters, roof supporting effect, and mechanical properties corresponding to the tamping of backfill materials and loading of overlaying strata. Specifically, 14 indexes, including pillar dip angle and trace of canopy tip, are used to reflect the actual performance. Some indexes have been introduced previously in relevant studies [11, 12]. This study mainly focuses on the trace of canopy tip and vertical roof gap. Figure 1 shows the structure of the solid backfill support.
Here, h is the supporting height (mm); Hl is the vertical roof gap (mm); Hk is the horizontal roof gap (mm); Lmin is the length (mm) when the tamping arm is completely retracted; Lmax is the length (mm) when the tamping arm is completely extended; αh is the tamping angle (°); a is the center distance (mm) of the dropping material; b is the length (mm) of the tamping plate; k is the width (mm) of the perforated scraper conveyor; g is the suspending height (mm) of the perforated scraper conveyor; J is the tamping head gap (mm); c is the hinging height (mm) of the tamping arm; L1 and L2 are the lengths (mm) of the front and rear roof canopies, respectively. The indexes are defined below.
Figure 1 Structure of solid backfill support
3.1 Trace of canopy tip
The trace of the canopy tip [6] refers to the swing distance of the canopy in the horizontal direction when the backfill support is raised. It may represent the optimization degree of the four-bar-linkage mechanism, and it is mainly influenced by the mining height and support size. When this mechanism moves along a normal curve, the hydraulic support will be under the most reasonable stress and floor-specific pressure; at this point, the canopy also swings in an acceptable data range. Figure 2 shows the trace of the canopy swing of a six-leg four-bar-linkage backfill support changing with the mining height.
Figure 2 Trace of canopy tip-mining height curve
3.2 Vertical roof gap
The vertical roof gap [9] refers to the vertical distance between the front end of the tamping arm and the roof when the backfill support is fully extended (indicated by Hl in Figure 1). In practical engineering applications, the support has a theoretical vertical roof gap as well as an actual vertical roof gap. The vertical roof gap is mainly determined by the tamping angle, center distance of falling material, and suspension height of perforated scraper conveyor, and their specific relationship is shown as follows:
(1)
The vertical roof gap of the backfill support significantly impacts the control of the compaction ratio. The larger the vertical roof gap, the larger the distance between the end of the tamping arm; as a result, more material will remain uncompacted, which will then impact the compaction ratio of the entire backfilling workface. The factors influencing the vertical roof gap mainly include the support structure, supporting height, dip angle of coal seam, roof subsidence in advance, and tamping times [7].
3.3 Horizontal roof gap
The horizontal roof gap [10] refers to the horizontal distance between the front end of the tamping arm and the rear canopy when the backfill support is fully extended (indicated by Hk in Figure 1). It is mainly determined by the supporting height, suspension height and angle of perforated scraper conveyor, and tamping angle. Their specific relationship is shown as follows:
(2)
In engineering practice, the horizontal roof gap is small under a large supporting height, small suspension height, and angle and large tamping height, which will better facilitate the backfilling process.
3.4 Tamping head gap
The tamping head gap refers to the horizontal distance between the front end of the tamping arm and the discharging center of the perforated scraper conveyor (indicated by J in Figure 1). Based on this definition, the tamping head gap has the following relationship with the structural size of the discharging center:
(3)
The tamping head gap impacts the stacking status of the backfill materials and effect of the tamping arm. When the tamping arm operates at the maximum tamping angle, the tamping head gap becomes the maximum; however, when it operates at the minimum tamping angle, the gap is the minimum. With the determined supporting height, the tamping head gap will change between the maximum and the minimum values.
3.5 Supporting intensity
The supporting intensity refers to the working resistance provided by a unit supporting area of the support to the roof, and it is determined by the cylinder diameter of the pillar, length of canopy, pressure of pump station, opening pressure of safety valve, number of pillars, and supporting height.
(4)
where F1 and F2 are the supporting resistances of the front and rear pillars, respectively; L1 and L2 are the lengths (mm) of the front and rear canopy, respectively; and k0 is the width (mm) of the support.
The supporting intensity is very important for evaluating the roof supporting capacity of the support. During backfilling mining, the roof is managed by the backfill body, and the roof support is designed differently from that in mining by the conventional caving method. In this case, the main function of the support is to control the roof subsidence before a compacted roof is formed with the backfill body. The supporting intensity should be designed by integrating the strata behavior rules and controlling in backfilling mining.
3.6 Supporting intensity of rear canopy
The supporting intensity of the rear canopy [8] refers to the working resistance provided by the unit supporting area of the support to the roof, and it is determined by the cylinder diameter of pillar, length of rear canopy, support width, pump station pressure, opening pressure of safety valve, and supporting height.
(5)
For the backfill support, the supporting intensity of the rear canopy is the main index used for evaluating the backfilling performance, and it plays a major role in controlling roof subsidence in advance and maintaining sufficient backfilling space. With greater supporting intensity, the rear canopy will better control the roof subsidence in advance, which will then facilitate guaranteeing the backfill ratio and controlling the final compaction ratio.
4 Design scheme evaluation based on backfill and operation properties
In the process of optimizing the design schemes of the solid backfill support, from the perspective of both the backfilling performance [16–20] and the adaptation to the geological condition, multiple schemes satisfy the basic requirements. Then, the question is how to select one among multiple schemes and evaluate such schemes.
4.1 Evaluation system
According to the definition, the backfill and operation properties of the backfill support are reflected by 14 indexes including the pillar dip angle, setting load, tamping force, and horizontal roof gap. Obviously, it is quite impractical to evaluate and determine the backfilling performance and adaptation of the hydraulic support by taking all 14 indexes into account. To simplify the evaluation process and ensure accuracy and adhere to the principles of science, comprehensiveness, dynamics, independence, and operability, seven independent evaluation indexes (including trace of canopy tip and tamping head gap) are selected for each specific design scheme. Then, the evaluation index system for the backfill and operation properties is built as shown in Figure 3.
4.2 Evaluation process and methods
First, the geological data are analyzed to select the backfilling support model according to the coal seam occurrence conditions, roof and floor conditions, as well as mining technology and to determine the main technical parameters, which specifically include the supporting intensity, working resistance, setting load, maximum/ minimum supporting height, center distance, and width of support. Second, the hydraulic support sizes are optimized from three aspects of the tamping arm, four-bar linkage, and canopy length so as to determine the optimizing schemes. Third, Pro/E 3D machine design software is used to design support parts and build a skeleton model of the support; then, by using the simulation modules in Pro/E software [21], data are deduced for the backfill and operation properties of each scheme. Fourth, based on the backfill and operation evaluation system and comprehensive multi-index evaluation methods, the backfill and operation properties of the benchmark schemes and optimized scheme are evaluated. Lastly, the best scheme is determined. Figure 4 shows the process of evaluating the backfill and operation properties based on the backfill support design scheme.
5 Analysis of engineering cases in design scheme evaluation
5.1 Engineering overview
At the 7203W workface of the Zhaizhen Coal Mine, the vertical depth is 517.1–565.8 m, corresponding ground elevation is 177.1–181.2 m, underground elevation is –340.0 to –384.6 m, average advancing length is 286 m, average tilting length is 92.8 m, coal seam thickness is 2.7 m, average dip angle of coal seam is 10.5°, and recoverable reserve is 94000 t. The ZC5200/14.5/30 six-column four-bar-linkage backfill support is adopted. Table 2 shows the basic parameters.
Figure 3 Evaluation index of backfill support’s backfill and operation properties
Figure 4 Design scheme evaluation process based on backfill and operation properties
Table 2 Parameters of ZC5200/14.5/30 backfill support
5.2 Design scheme evaluation
Figure 5(a) shows the sizes of the support. To optimize the backfill and operation properties of the support and integrate practical support models, 11 design schemes including the benchmark scheme are obtained by optimizing the four-bar linkage, length ratio of canopy, and tamping arm. Table 3 shows the specific optimizing data of each scheme. Then, by adopting the Pro/E software, a skeleton model according to sizes of the support parts is designed as shown in Figure 5(b). Furthermore, by using the mechanism simulation module of Pro/E, data of the backfill and operation properties are summarized in Table 4.
Figure 5 Size chart and skeleton model of backfill support:
Seven backfill and operation properties (including swing and length ratio of canopy) and eleven design schemes are selected to form the index value matrix A=[aij]11×7 as shown in Formula (6).
To avoid the influence of the dimension difference on the evaluation, standardization and normalization processing is performed on matrix A. Then, the normalized matrix is obtained as R=[rij]11×7.
(6)
(7)
Table 3 Structure and size optimization scheme design table
Table 4 Monitoring index summary table for each scheme (mining height of 2500 mm)
Based on engineering experience, a reasonable optimizing constraint range is set for each weight value:
(8)
A single-object optimization model is built to optimize the weight vector of the index; the specific model is shown as follows:
(9)
To minimize the deviation of the comprehensive scheme evaluation value and uncertainty of index weight, according to the maximum entropy principle, the maximum information entropy is set as the weight index for the backfill and operation properties. Then, by transforming into single object optimization, the following is obtained:
(10)
By setting ε=0.5, a nonlinear equation set is obtained as follows:
(11)
where sj and tj can be obtained by combining Eqs.(4)–(5):
s1=2.064; s2=3.743; s3=3.773; s4=3.848;
s5=3.591; s6=3.219; s7=3.183; t1=0.608;
t2=1.099; t3=0.377; t4=1.426; t5=0.559;
t6=0.820; t7=0.354 (12)
The equation set is solved using the Matlab Newton iteration method. To obtain the optimum weight coefficient of the technical index evaluation of the design schemes,
ω=[0.004 0.333 0.016 0.364 0.057 0.194 0.028](13)
Then, the comprehensive evaluation value based on each scheme is obtained as follows:
(14)
By inserting Eq. (13) into Eq. (14), the comprehensive evaluation value of each scheme is obtained as follows:
v0=0.495, v1=0.503, v2=0.490, v3=0.544, v4=0.463, v5=0.392, v6=0.604, v7=0.518, v8=0.481, v9=0.264, v10=0.728 (15)
As v10>v6>v3>v7>v1>v0>v2>v8>v4>v5>v9, scheme #10 is determined as the best design scheme; then, the backfill and operation properties of the solid backfill support are compared in Table 5.
According to this table, by optimizing the four-bar linkage, canopy length, and tamping arm, the backfill and operation properties such as the horizontal roof gap, vertical horizontal gap, tamping angle, and tamping head gap show obvious improvements. This proves that the design scheme evaluation methods set based on the backfill and operation properties are scientific and reasonable.
6 Building research system for backfill support
From the perspective of controlling the backfill and operation properties, the reliability of such properties is the basis of the compaction ration control, and it will directly influence the rock strata movement control effect in the process of backfilling mining [22–24]. In engineering practice, measures should be taken to strictly control the backfill and operation properties of the backfill support to ensure good backfilling performance. The analysis in this part indicates that the support structure, backfilling process, and geological conditions are the main factors influencing the backfill and operation properties. The basic principle of controlling these properties is to take appropriate design and engineering measures to mitigate the impact of the influencing factors. Specifically, measures for optimizing the support structure design, backfilling process, and workface deployment and for performing online monitoring are taken to ensure good backfilling performance [25, 26]. Figure 6 shows the principle of controlling the backfill and operation properties of the backfill support.
The content and evaluation indexes for the backfill and operation properties are described above in detail. Moreover, an evaluation system as well as evaluation methods and process for backfill and operation properties are also discussed. This will enable building a backfill support research framework for “designing initial scheme, optimizing design scheme, selecting the best evaluation indexes, evaluating optimizing scheme, and evaluating operation properties”, as shown in Figure 7.
Table 5 Optimization comparison table of backfill and operation properties
Figure 6 Principle of controlling backfill and operation properties of backfill support
Figure 7 Research framework of backfill support
7 Conclusions
1) The backfill and operation properties refer to the comprehensive performance of the backfill support in protecting backfilling space, providing a means for conveying backfilling material, providing a tamping force, and guaranteeing compression ratio; these are the key parameters for evaluating and estimating the backfilling performance of the hydraulic support. These properties mainly include the structural property, supporting property, tamping property, mechanical response property, and geological adaptation property, which are reflected by 14 indexes including the pillar dip angle, setting load, tamping force, and horizontal roof gap.
2) Seven independent evaluation indexes are selected from the 14 comprehensive indexes to build an evaluation system for the backfill and operation properties. Moreover, methods based on evaluating the backfill and operation properties for optimizing the design scheme of the backfill support as well as methods to control such properties are proposed.
3) By integrating an engineering application case at Zhaizhen Coal Mine and adopting a multi- index evaluation method, support optimization schemes are evaluated to select the best schemes. It is found that by optimizing the four-bar linkage, the best scheme shows obvious improvements in terms of the horizontal roof gap and other backfill and operation properties.
4) Based on the concept of backfill and operation properties as well as the reasonability of the evaluation system for the same, the backfill support research framework of “designing initial scheme, optimizing design scheme, selecting the best evaluation indexes, evaluating optimizing scheme, and evaluating operation properties” is built to provide a theoretical basis for designing and optimizing the backfill support and improving its backfilling performance.
Nomenclature
h
Supporting height
H1
Vertical roof gap
Hk
Horizontal roof gap
Lmin
Length when the tamping arm is completely retracted
Lmax
Length when the tamping arm is completely extended
αh
Tamping angle
a
Center distance of the dropping material
b
Length of the tamping plate
k
Width of the perforated scraper conveyor
g
Suspending height of the perforated scraper conveyor
J
Tamping head gap
c
Hinging height of the tamping arm
L1
Length of the front roof canopy
L2
The length of the rear roof canopy
p
Supporting intensity
F1
Supporting resistance of the front pillar
F2
Supporting resistance of the rear pillar
k0
Width of the support
p′
Supporting intensity of rear canopy
A
Matrix of monitoring index
aij
Value of monitoring index
R
Normalized matrix of matrix A
rij
Normalized value of aij
ωj
Weight value
ε
Equilibrium coefficient
vi
Comprehensive evaluation value based on each scheme
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(Edited by YANG Hua)
中文导读
充填采煤液压支架充填与运转特性及评价
摘要：充填采煤液压支架是充填采煤技术实现充采一体化的核心设备，其性能的可靠性是实现致密充填的关键。为评价充填采煤液压支架的充填性能，本文提出充填运转特性的概念，并从结构特性、支护特性、夯实特性、力学响应特性及地质适应特性5个方面阐述其内涵，具体通过支护强度、夯实空顶距等14个指标综合体现。选择其中7个独立的评价指标，采用多指标综合评价方法，构建了基于充填运转特性的充填采煤液压支架设计方案评价体系，给出了评价的方法与流程，以及充填运转特性工程控制措施。运用该体系评价了翟镇矿ZC5200/14.5/30型充填采煤液压支架的11个优化方案，评选出的10#最佳方案在夯实离顶距等充填运转特性指标上具有明显优势，验证了评价体系的合理性。基于此构建了“初始方案设计、设计方案优化、评价指标优选、优化方案评价、运转特性控制”的充填采煤液压支架研究框架，为深入研究充填采煤液压支架控顶性能提供借鉴。
关键词：充填采煤；充填与运转特性；夯实力；夯实空顶距；夯实离顶距；评价方法
Foundation item: Project(2017QNA21) supported by Fundamental Research Funds for the Central Universities, China; Project supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD), China
Received date: 2017-04-20; Accepted date: 2017-10-30
Corresponding author: ZHANG Ji-xiong, PhD, Professor; Tel: +86–13912005505;E-mail: zjxiong@163.com; ORCID: 0000-0003- 0770-7407
Abstract: To ensure compacted backfilling, it is essential to ensure the reliability of the performance of a solid backfill support, key equipment for integrating backfilling and mining. To evaluate the backfilling performance of a backfill support, the concept of backfill and operation properties is proposed in this study. Moreover, it is elaborated in terms of five aspects, namely, structural property, supporting property, tamping property, mechanical response property, and geological adaptation property, which are specifically reflected by 14 indexes including the supporting intensity and vertical roof gap. Seven separate evaluation indexes are selected to build a backfill and operation properties based system for evaluating the design schemes of the backfill support via a multi-index comprehensive evaluation method; then, the evaluation method and process together with measures to control the backfill and operation properties are proposed. By using this system, 11 schemes for optimizing the ZC5200/14.5/3 backfill support at Zhaizhen Coal Mine are evaluated, and scheme #10 is found to show superior vertical roof gap and other backfill and operation properties, thus demonstrating the reasonability of the evaluation system. On this basis, the backfill support research framework of designing initial scheme, optimizing design scheme, selecting the best evaluation indexes, evaluating optimizing scheme, and evaluating operation properties is built; this should serve as an important reference for further studies on the roof controlling performance of a backfill support.
