J. Cent. South Univ. (2017) 24: 1637-1646

DOI: 10.1007/s11771-017-3569-7

Structure optimal design research on backfill hydraulic support

ZHANG Qiang(张强), ZHANG Ji-xiong(张吉雄), QI Wen-yue(齐文跃), ZHOU Nan(周楠), TAI Yang(邰阳)

State Key Laboratory of Coal Resource and Safe Mining, School of Mines, China University of Mining & Technology, Xuzhou 221116, China

Central South University Press and Springer-Verlag Berlin Heidelberg 2017

Abstract: Backfill hydraulic support is the key equipment in achieving coal mining and solid backfilling simultaneously in solid backfill mining technology. Based on the summary and analysis of main types, basic structural properties and filed application of backfill hydraulic support, this work has firstly proposed the basic principle of backfill hydraulic support optimization design and provided the method of optimal design of key structural components, like four-bar linkage, rear canopy and tamping structure; the method is further elaborated as changing hinging position of upper bar to optimize four-bar linkage, by lengthening or shortening the rear canopy to optimize length ratio of canopy; and by changing length and hinging position of tamping structure as well as suspension height of backfill scrape conveyor to realize optimization of tamping structure. On this basis, the process of optimal design of backfill hydraulic support is built. The optimal design case of ZC5200/14.5/30 six columns-four bar linkage used in 7203W workface of Zhaizhen Coal Mine shows that the backfill properties like horizontal roof gap, vertical horizontal gap, tamping angle and tamping head gap are improved obviously through optimizing four-bar linkage, canopy length and tamping structure according to the optimal design method proposed in this work.

Key words: backfill hydraulic support; structure optimal design; four-bar linkage; rear canopy; tamping structure

1 Introduction

Since the research and development of solid backfill mining technology [1-9], it has been widely applied in many mining areas of Pingmei Group, Yankuang Group and Xinwen Group and has liberated many types of trapped coal, involving coals under buildings, water bodies and railways. The backfill hydraulic support is the key equipment of fully-mechanized solid backfill mining technology. Its structures and functions have been updated continuously along with the development of technology and its adaptability to geological conditions has been improved remarkably as well; the backfill hydraulic support also plays a vital role in this technology because it assists the transportation of solid backfill materials as well as directly provides the backfill space and tamping force of backfill materials. Due to these functions, the performance parameters of backfill hydraulic support need to be fully studied. It directly affects the backfill efficiency and the compactness of backfill body, so as to affect final rock strata control effect. The optimal design research of backfill hydraulic support contributes to the improvement of its performance parameters.

With respect to backfill hydraulic support, MIAO [10] established the mechanical model of mine pressure of solid backfill mining by the comparison of the differences between backfill coal mining and traditional fully-mechanized coal mining in the aspects of mine pressure control and support design philosophy. The analytical solutions to calculating active force of the support and displacement curve of roof were obtained. ZHOU et al [11] analyzed stress condition of canopy and stress relationship of three rows of columns by establishing the mechanical model of canopy of backfill hydraulic support; The movement properties of its lifting and descending process were also studied in this work. ZHANG et al [12-14] defined vertical roof gap of backfill hydraulic support, and analyzed its influence factors, then the change rules of mining height and vertical roof gap were studied. In this study, a design rationality judgment method with the vertical roof gap as the test index was then formed. Meanwhile, they proposed the concept of backfill properties [15] of backfill hydraulic support and elaborated the connotation of backfill properties and control measures. XU et al [16] analyzed the relationship between the maximum load of support and the force of each column by establishing a mechanics model of support and surrounding rock. CUI et al [16] introduced the methods of working resistance calculation of six- column backfill hydraulic support and the optimization of structural parameters of four-bar linkage. Above studies concentrate on the aspects like structure of the support, interaction between the support and surrounding rock as well as basic technical parameters, while there is hardly any study referring to the structure optimal design.

In order to scientifically and reasonably promote the performance of backfill hydraulic support and improve its backfill properties, in this work, the basic principle of optimal design of backfill hydraulic support is proposed based on the analysis of main types, basic structural properties and filed application of the support. Then, the design method of backfill hydraulic support is elaborated from the aspect of optimal design of key structural components like four-bar linkage, rear canopy and tamping structure. On this basis, the process of optimal design of backfill hydraulic support is built.

2 General situation of backfill hydraulic support

2.1 Introduction of main types of support

Backfill hydraulic support, which is widely applied at present, is mainly composed of front and rear roof canopy, column, base, tamping structure and four-bar linkage. Specifically, there are six-column-four-bar linkage and four-column-four-bar linkage. Take the four- column-four-bar linkage as the example, its typical structure is shown in Fig. 1.

2.2 Basic structural properties

To shield coal mining operation space and backfill operation space simultaneously, the roof-control distance (i.e. roof canopy length) of backfill hydraulic support has increased and the overall structure of the support is obviously different from traditional fully-mechanized hydraulic support. The specific structural properties are: 1) Roof canopy structure change: shield beam is changed into rear roof canopy and roof canopy is made up of front roof canopy and rear roof canopy; 2) The added backfill scrape conveyor is suspended inside of the rear roof canopy, to provide transportation power of solid backfill materials; 3) Tamping structure is hinged on the base, to provide tamping power of solid backfill materials. Tamping structure is hinged in the end of base to realize upper and lower swing with different angles; 4) Tamping board is set up at the front end of tamping structure, and pressure transmitted by tamping board is to realize compact tamping of solid materials.

Differences of structures [15] of six-column-four- bar linkage and four-column-four-bar linkage backfill hydraulic support respectively are:

1) Different numbers of columns. The former has six columns and the later type has four columns.

2) Different hinging positions of four-bar linkage and roof canopy. The former is hinged with middle part of front roof canopy and the later type shares the coaxial hinging with front and rear roof canopy.

3) Different control modes of tamping structures. The former types conduct control from lower part of tamping structure and the later type conducts control from upper part of tamping structure.

2.3 Application summary

Fig. 1 Structure diagram of backfill support with type of four-column-four-bar linkage

The backfill hydraulic support, key equipment for integrating backfilling and mining, has not only basic functions of traditional supports needed in coal mining, but also special functions needed in backfilling. Its technical properties include structural properties, supporting properties, tamping properties and mechanical response properties etc. Structural properties include number of columns, horizontal roof gap [13], vertical roof gap [14], roof canopy ratio, etc.; supporting properties include supporting intensity, floor specific pressure, etc.; tamping properties include tamping force, tamping angle, etc.; mechanical response properties include features of load distribution of columns, etc. The main technical parameters of backfill support are shown in Table 1.

Popularization and application [17] of backfill hydraulic support in many mining areas are shown in Table 2 and Fig. 2.

By summarizing engineering applications of backfill hydraulic support, main problems are: 1) low adaptability to dip angle of coal seam and special geological conditions; 2) low adaptability of tamping structure to mining height varying in large range; 3) cooperation efficiency of tamping structure and backfill scrape conveyor needed to be improved. In allusion to abovementioned defects in engineering applications, reasonable optimal design of structure of backfill hydraulic support needs to be conducted.

3 Basic principle of optimal design and key components design

3.1 Basic principle of optimal design

Functions of backfill hydraulic support are controlled strictly by its structure. As the structure of backfill hydraulic support is different from that of traditional support obviously, these two types of supports have different principles and methods of optimal design. The design of rear roof canopy and tamping structure equips the backfill hydraulic support with special functions of backfill shielding and implementation. The size parameters of key components like length of roof controlling, length ratio of roof canopy, form of four-bar linkage and hinging position affect the backfill properties like supporting properties, tamping properties and mechanical properties.

Table 1 Basic technical parameters of backfill support

Table 2 Application statistics of backfill support (part)

Fig. 2 Application situations of backfill support

The basic principle of backfill hydraulic support design optimization is to make backfill properties of the support reach the optimal state via optimization of key structures sizes combined with practical engineering conditions, which means in accordance with basic principles, i.e., satisfaction of design requirements of basic technical parameters, optimal and reasonable size configuration and realization of optimal state of backfill properties. Optimal design of the support is conducted from two aspects of components selection and sizes optimization. Sizes optimization in this work refers to four-bar linkage, rear roof canopy and tamping structure, and effectiveness of sizes optimization is checked via the evaluation system of backfill properties; specifically, the method of dynamic optimal design is adopted in virtue of machine design software, such as Pro/E.

3.2 Optimal design of four-bar linkage

Movement track of roof canopy’s front end, stress of linkage and front and rear roof canopys, coal mining and backfill space, etc. are determined by effectiveness of four-bar linkage. Graphic method and analytical method are frequently adopted to conduct optimal design [18, 19].

In optimal design of four-bar linkage of backfill hydraulic support, variables mainly include the maximum supporting height, h_max, the minimum supporting height, h_min, lemniscate amplitude, D₀, horizontal distance, A₀, between hinge point of rear linkage and base and hinge point of rear linkage and upper linkage, height, B₀, of hinge point of rear linkage and base, included angle, α₀, of rear linkage and horizontal line (in general no more than 85°, 75°-85° when the support is in the highest position, 25°-30° when it is in the lowest position), dorsal angle, β₀, of upper linkage (52°-70° when the support is in the highest position, 10°-16° when it is in the lowest position), as shown in Fig. 3(a).

Main constraint conditions include: track of canopy’s front end always tends to rib side in the supporting process from high to low supporting height; ratio of distance between hinge point of front linkage and upper hinge point to distance between hinge point of front linkage and hinge point of rear linkage shall be controlled within 4:1-6:1. The optimization schematic of four-bar linkage of backfill hydraulic support is shown in Fig. 3(b). Key indexes control of optimal design of backfill hydraulic support is shown in Table 3.

Optimal design of four-bar linkage in this work mainly via changing the ratio of hinge point of front linkage, which is changing the length of ME in Fig. 3(a) from S to S’ in Fig. 3(b). This change will lead to the difference of movement track of roof canopy’s front end, stress of linkage and front and rear roofcanopys, coal mining and backfill space, etc.

3.3 Optimal design of rear roof canopy

Fig. 3 Optimization schematic of four-bar linkage

Table 3 Key indexes control table for optimization design of backfill support

Changes of length ratio of roof canopy obviously influence stability of the support, load distribution of roof canopy, load bearing of support and tamping properties; length ratio of roof canopy is an important optimization objective in optimal design of the support. Different types of backfill hydraulic supports enjoy different length ratios of roof canopy; the length ratio of roof canopy of 6-column backfill support is between 1:0.80 and 1:0.56 while the length ratio of roof canopy of four-pillar backfill support is between 1:1.33 and 1:0.53. The optimization of length ratio of roof canopy is realized mainly by optimizing length of rear roof canopy (changed from L₂ to L₂’ in Fig. 4) in this study. Specifically, indexes of structural properties, supporting properties, tamping properties and mechanical response properties are derived by changing length of rear roof canopy, and then degree of optimization is judged via the comprehensive evaluation of indexes. The optimization schematic of length ratio of roof canopy is shown in Fig. 4.

3.4 Optimal design of tamping structure

Fig. 4 Optimization schematic of canopy length ratio

Tamping structure is the important structure influencing tamping properties, specifically reflecting in area of tamping board and size of tamping oil cylinder determine the size of tamping force; hinging position of tamping structure as well as the maximum and minimum length of tamp arm affect the sizes of horizontal roof gap, vertical roof gap and tamping head gap; tamp arm and suspension position of backfill scraper conveyor jointly affect the size of tamping angle. Tamping force, vertical roof gap, horizontal roof gap, tamping angle and tamping head gap are specific connotations of tamping properties. The optimization tamping structures in this research mainly refer to changing length and hinging position of tamping structure as well as suspension height of backfill scraper conveyor (changed from L_min to L_min’, a to a’ and g to g’ respectively in Fig.5). The optimization schematic of tamping structure is shown in Fig. 5.

Fig. 5 Optimization schematic of tamping structure

4 Process of optimal design

First, basic types of hydraulic supports are selected according to requirements and basis of design and optimization of hydraulic support, namely, satisfaction of requirements of relevant standards and codes, adaptation of occurrence condition of coal seam, satisfaction of requirements of coal mining technology, reasonable structure, good stress state, certain stability, good support moving ability and effective supporting intensity providing, which specifically include six-columns-four- bar linkage and four-column four-bar linkage; in the meantime, according to occurrence condition of coal seam, condition of roof and base board as well as coal mining technology, main technical parameters of hydraulic support are determined, which specifically include supporting intensity, working resistance, setting load, the maximum/minimum supporting height, center distance and width of support, etc.. And then the sizes of all components of hydraulic support are designed and optimized preliminary; Pro/Engineer or SolidWorks 3D machine design software is used to design components of the support so as to establish 3D solid model of the support; and then based on the evaluation system of backfill properties, the support components’ structures and sizes are optimized and indexes of backfill properties are distinguished, then the final design result of the support is obtained eventually. Design process of backfill hydraulic support is shown in Fig. 6.

Fig. 6 Designing process of backfill support

Thereof, the optimization of structures and sizes includes three aspects: optimization of four-bar linkage, optimization of length ratio of roof canopy and optimization of tamping structure. The evaluation system of backfill properties includes structural properties, supporting properties, tamping properties, mechanical response properties and geological adaption properties.

5 Engineering application

5.1 Basic engineering profile

At 7203W workface of 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--384.6 m; average advancing length is 286 m; average working face length is 92.8 m; coal seam thickness is 2.7 m; average dip angle of coal seam is 10.5° and the recoverable reserve is 94000 t. ZC5200/ 14.5/30 six-column-four-bar linkage backfill hydraulic support is adopted with the basic parameters shown in Table 4.

Table 4 Parameters of backfill support

5.2 Optimal design and application

In accordance with the design process of backfill hydraulic support, the optimization of its structures and sizes mainly includes three parts, i.e., optimization of four-bar linkage, optimization of length ratio of roof canopy and optimization of tamping structure. The optimization schematic (can be referred to Fig. 7).

The optimal indexes in the optimization process include vertical roof gap, horizontal roof gap, tamping head gap, etc and the control equation of optimal indexes is:

                  (1)

where H_l is the vertical roof gap (mm); h_j is the hinging height of tamping structure (mm); L_min is the length (mm) when tamping structure is retracted; μ is the tamping length coefficient; α_h is the tamping angle (°); a is the center distance (mm) of dropping materials; J is the tamping head gap (mm); r₁ and r₂ are the cylinder diameters of front column and rear column, respectively; P₁ and P₂ are the pressures (MPa) of front column and rear column, respectively; α and β (°) are the dip angles of front column and rear column respectively; L₁ and L₂ are the lengths (mm) of front roof canopy and rear roof canopy respectively; k, 1500 mm, is the width (mm) of the support; κ is the length ratio of roof canopy.

Wherein, the optimization of four-bar linkage is realized by changing hinging position of upper linkage; the optimization of length ratio of roof canopy is realized by changing length of rear roof canopy; the optimization of tamping structure is realized by changing length and hinging position of tamping structure as well as suspension height of backfill scraper conveyor. The optimization scheme design of structures and sizes is shown in Table 5. The support skeleton model of corresponding size is established through Pro/E software, as shown in Fig. 8, and the index data of corresponding backfill properties are obtained via the simulation modules in Pro/E software, as shown in Table 6.

Fig. 7 Backfill support’s structure and size optimization sketch

Table 5 Structure and size optimization scheme design table (taking 6-column-four-bar linkage as an example)

Fig. 8 Size chart and skeleton model of backfill support (Unit: mm)

Further optimization of above 11 schemes is conducted via the evaluation system of backfill properties and No. 10 scheme is identified as the optimal design scheme. Above table shows that backfill properties like vertical roof gap, horizontal roof gap, tamping angle and tamping head gap are improved obviously via the optimization of four-bar linkage, length ratio of roof canopy and tamping structure. The practical application of the support under final optimal design at 7203W underground backfill workface of Zhaizhen Coal Mine is shown in Fig. 9.

Table 6 Monitoring index summary table for each scheme (taking 6-column four-bar linkage as an example, 2500 mm)

Fig.9 Site operating conditions of ZC5200/14.5/30 backfill support

With the cooperation of backfill mining hydraulic support, shearer, scraper conveyor, backfill scraper conveyor and other backfill mining equipment, the cycling backfill mining technique [2, 12-14] is put into practice. The sequence of cycling operations continues front conveyor forward. Coal cutting is bidirectional by a double-drum shearer. The advancement of the hydraulic support follows closely behind shearer, and the backfill hydraulic support behind the back roller of the shearer advances first to support the immediate newly exposed roof after coal removal. The scrapers which load the broken coal onto a conveyor begin and then transport to the coal roadway. The backfill scraper conveyor begins to unload solid backfill materials into the gob and consolidate them with a tamping device on the back of the support. After that the backfill scraper conveyor is also shifted the double-drum shearer will cut coal in an opposite direction and all the operations will begin to cycle. This method can fill solid material into the gob densely while exploit the coal resource.

After the optimal design, backfill efficiency of backfill hydraulic support is improved obviously and compaction ratio is controlled above 90.0% [20], so that rock strata control effect of backfill workface is guaranteed greatly.

6 Conclusions

1) Main support types, basic structural features and field application are summarized and analyzed.

2) Basic principle of optimal design of backfill hydraulic support is proposed; methods of optimal design of key components like four-bar linkage, rear roof canopy and tamping structure are provided. The four-bar linkage optimization is elaborated with changing hinging position of upper linkage to optimize four-bar linkage, while the length ratio of canopy is optimized by changing length of rear roof canopy, then by altering the length and hinging position of tamping structure and suspension height of backfill scraper conveyor to optimize tamping structure.

3) The process of optimal design of backfill hydraulic support is established.

4) The case of optimal design engineering of 7203W workface ZC5200/14.5/30 six-column-four-bar linkage of Zhaizhen Coal Mine shows that backfill properties like vertical roof gap, horizontal roof gap, tamping angle and tamping head gap are improved obviously by optimizing four-bar linkage, length of roof canopy and tamping structure according to the optimal design method proposed. In practical application, backfill efficiency is improved obviously with the compaction ratio controlled beyond 90.0%.

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(Edited by YANG Hua)

Cite this article as: ZHANG Qiang, ZHANG Ji-xiong, QI Wen-yue, ZHOU Nan, TAI Yang. Structure optimal design research of backfill hydraulic support [J]. Journal of Central South University, 2017, 24(7): 1637-1646. DOI: 10.1007/s11771-017-3569-7.

Foundation item: Project(2017QNA21) supported by the Fundamental Research Funds for the Central Universities of China; Project supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD), China

Received date: 2015-07-06; Accepted date: 2015-12-30

Corresponding author: ZHANG Ji-xiong, Professor, PhD; Tel: +86-13912005505; E-mail: zjxiong@163.com