Research and Application of Supporting Scheme for Over-mining Area of ​​South Wind Well in Lushan Gold Mine

0 Preface

Fu Shan gold mine now part of Shandong Mining Group Co., Ltd. under the jurisdiction of one of the mine, located in the northeast of exquisite gold field, Shandong mine strata are mainly groups plagioclase amphibolite, granulite and plagioclase schist, mostly The line fluid is in the mixed granite and develops under the Quaternary. Surrounding exquisite type of mine like to gneissoid biotite granite-based, and another group of Shandong is scattered, and the residue of metamorphic type Guojialing porphyritic granodiorite, ore f = 4 ~ 6, ore loose coefficient 1.70, the ore weight is 2.78g/m3, and the surrounding rock weight is 2.65t/m3. GENESIS epithermal fluid type filling and replacement, the crushing industry type gold-bearing alteration type, very small gold-bearing quartz vein mineralization by the NE, and the NEE of NNE control system faults, yellow iron ore Juan Yingyan.

China National Mining Corporation is carrying out a series of technical transformation projects. The Nanfeng Well of Lushan Gold Mine is one of the company's technical reconstruction projects. After the completion of the Nanfeng Well, it will form a new first-level lifting system with the original main shaft of the mine. A certain increase in the amount of fine ore and the return air task in the main ventilation system of the mine. At present, the Nanfeng wellbore is under construction as planned. However, during the construction of the previous wellbore, the wellbore encountered abandoned civil mining areas of different specifications and shapes, which seriously affected the construction and progress of the well.
1 Nanfeng well situation and problems encountered during construction
The construction of the South Wind Well Technical Reconstruction Project of Lushan Gold Mine was officially started on February 21, 2014. The original diameter of the original wellbore of Nanfengjing is 3.5m and the depth of the well is 325m. It is necessary to undergo technical transformation, the net diameter of the wellbore is as large as 5.5m and the depth of the well is 763m. When the wellbore brush is as large as +141.0~+117.0m, the wellbore and the abandoned civil mining roadway with different specifications and shapes are thoroughly penetrated. The abandoned roadway seriously affects the construction quality and progress of the infrastructure construction. After on-site investigation, there is no threat of water accumulation in the empty area, and the original rock of the wellbore has good stability and the hardness coefficient is 8-12. The gobs have a width of about 3 to 5 m and a height of 2 to 10 m, and are intersected, tangent, and circumferentially distributed around the wellbore (as shown in Figure 1). Among them, the mined-out area of ​​the surrounding manhole is less than 2m from the minimum thickness of the original rock wall.

2 support program research
2.1 Supporting scheme during normal construction
According to the nature of the surrounding rock of the mine, the height of the well section and the amount of water inflow, during the normal construction of the Nanfeng well, in order to prevent the deformation, destruction and collapse of the surrounding rock of the shaft wall and prevent the weathering of the surrounding rock, it is generally necessary to support the well wall in time. Protection to ensure the normal production [1]. The following three methods are adopted for the support measures for the surrounding rock during the construction of the mine south wind shaft.
(1) Anchor metal mesh support. As a temporary support during the construction of the Nanfeng Well, the support method uses anchor bolts to reinforce the surrounding rock and hang a metal mesh to block the debris from falling. Using a metal mesh is fixed to the wall anchor, galvanized material with a No. 16 wire, bolt length 1.8m, a pitch of 0.9 ~ 1.1m, having a diameter of 15mm. With the advancement of the heading face of the South Wind Well, the erection of the anchor metal mesh was carried out while drilling. [2]
(2) Shotcrete support. When the shaft is constructed, depending on the surrounding rock conditions of the shaft wall, the shotcrete can be used both as a temporary support method and as a permanent support method. For temporary support, the thickness of the spray layer is generally 50~100mm; for permanent support, the thickness of the spray layer is generally 100~l50mm. In case of serious weathering, large geological conditions with poor fracture surface, anchor rod, metal mesh or Steel bars and other joint support with shotcrete. Shotcrete has the functions of preventing weathering, filling cracks, sealing surrounding rock and increasing the integrity of surrounding rock. However, it is mainly used in shaft wellbore support applications for hard, stable and complete surrounding rock without large displacement after excavation. There are many applications in metal mine wellbore construction [3]. Shotcrete is applied as a temporary support method during the construction of the south wind shaft of the Lushan Gold Mine.
(3) Cast-in-place concrete support. Concrete (or cast-in-place concrete) support has the advantages of high integrity, high strength, good sealing performance and easy mechanized construction. It is widely used as a permanent support method in shaft construction, especially in formations that are not suitable for shotcrete. Medium [4]. The permanent support method of the south wind shaft of Lushan Gold Mine is the use of cast-in-place concrete support. The main quality technical requirements of concrete are shown in Table 1.

2.2 South wind well over the goaf support program
In view of the encountering of the goaf during the construction of the Nanfeng Well, in order to ensure the construction safety and normal excavation of the Nanfeng Well, different support schemes were studied for the goafs of different heights and sizes. Through continuous trials and on-the-spot practice, the construction principles and methods of strengthening the support and forcibly crossing the Nanfeng well over the goaf section.
In order to prevent the lateral pressure of the loose body outside the well wall from being uneven, and the well wall is displaced, the meteorite at the bottom plate of the empty area shall be cleaned before the support. In order to improve the support strength and maintain the stability of the surrounding rock of the wellbore, a reinforced concrete wall seat is added under the support body to support the support of the entire goaf. The height of the wall seat is not less than 1.25m and the width is not less than 0.75m. And to ensure that the total thickness of concrete filled in the goaf (including the filling thickness of the empty area and the thickness of the masonry) is more than 2.5m, and the thickness of the design of the wellbore is increased from 300mm to 500mm, and the concrete strength is C20, ensuring the wall branch protection in line with "vertical shaft coal mine shaft and chamber design specifications," "non-ferrous metal mine shaft construction standard" requirement [5]. According to the height of the civil mining area, the following different support schemes are adopted [6-7]:

(1) When the height of the empty area is less than 4m, it is mainly supported by the method of brick wall sealing, concrete filling empty area and wall grouting. Before the plugging, use the drill rod of not less than 3m to construct the sounding eye perpendicular to the direction of the well wall. For the civil mining area with the original rock thickness less than 2m, first penetrate the empty area and clean the floor meteorite, and then together with the empty area The brickwork is blocked, and the retaining wall is reinforced with wooden piles before and after the retaining wall. The position of the retaining wall is not less than 2.0m from the well wall, and the thickness of the retaining wall is not less than 0.5m. Finally, the 4m hydraulic template is equipped with the waste rail for concrete filling.

(2) When the height of the empty area is between 4 and 10 m, the artificial false bottom and the steel bars are used for concrete support on the basis of the blockage of the wall. Firstly, the anchor rods are laid every 0.5m in the horizontal direction of the original rock in the empty area, and every 4m in the longitudinal direction. The channel steel is laid above the anchor rod and welded firmly with the iron plate, and then the reinforced concrete is poured for a section of height every 4m. The technical parameters are as follows: round steel anchors of Φ36, steel bars of 22# channel steel, Φ16, and the spacing of reinforcements are 300mm (see Figure 2).

3 safety quality assurance measures
3.1 Security Assurance Measures
(1) In order to prevent damage to the personnel and equipment during the process of shaft excavation, the construction of the construction unit will increase the intensity of sounding and water exploration, and always insist on “suspicious exploration”. The principle of “exploring and excavating first”, timely use the drill pipe with a depth of not less than 3m to construct the water exploration eye to the lower side, and explore the eye for at least one construction per shift.
(2) The mine adheres to the principle of “safety first, prevention first”, and carries out technical, quality and safety education for all construction personnel in the shaft. During the construction, it is necessary to strictly abide by the operating procedures, do a good job in technical delivery, ensure the quality of the project, and insist on Civilization Construction.
(3) Temporary support for the weathering section of the wellbore must be done. According to the softness and hardness of the rock formation, support means such as fixed anchor, hanging net, steel support frame, anchor spray, etc. should be taken in time, and the amount of charge should be strictly controlled during excavation and blasting. Ensure that the blast does not cause major damage to the shaft wall.
(4) The mine insists on the construction safety management and construction quality at the same time, pays equal attention to quality and safety, and manages personnel, engineering and technical personnel, and construction personnel to jointly manage and clarify their respective “job responsibilities” to avoid busy chaos and reasonable arrangements. The shaft construction process, timely resolve the contradiction between production safety and production schedule, and strictly abide by the safety regulations and specifications related to shaft construction.
(5) For the construction of the Nanfeng Well, the mine has formulated safety technical measures such as drilling blasting, rock loading and drainage, electromechanical management, ventilation, fire prevention, dust prevention and support to ensure the smooth construction of the Nanfeng Well according to the plan and requirements.
3.2 Quality Assurance Measures
(1) Strengthen the quality education of construction workers, improve the quality awareness, firmly establish the ideological concept of “a hundred years of planning, quality-oriented” and “quality responsibility is more important than Taishan”, strengthen the management of engineering quality from the system, and persist in the construction process. The principle of “who is responsible for construction”.
(2) Execute the quality inspection system, strictly control the entry procedures of raw materials, and at the same time do a good job in material inspection, sampling inspection and testing, do a good job in the protection of stacked materials in the site, regularly test materials that are prone to deterioration, and are not allowed to use quality. Qualified materials.
(3) Strictly implement the “three-inspection system” construction system. The process must be handed over by the next team. After the inspection team passes the inspection, the quality inspector re-examines and fills in the quality inspection and assessment form. The next process is completed. Must be based on the quality of the previous process quality inspection.
(4) Concrete should be sampled and sent for inspection when pouring or supporting the wellbore. Problems can be adjusted in time to ensure the rationality of the concrete mix ratio and ensure the safety of the south wall well wall support.
(5) During the excavation and support construction of the Nanfeng Well, strengthen the measurement and implement the three-level review system, and the special person shall be responsible for the measurement work. Each section shall re-examine the excavation section to ensure that the section size meets the design requirements and structural position. accurate.
(6) In the construction of the Nanfeng Well, strengthen the coordination between all units, departments, and processes, make timely quality inspection records, and collect and sort out various quality assurance materials.
4 application effects
After on-site construction practice, the support of the south wind shaft of the Laoshan Gold Mine through the use of artificial false bottom, brick blockage, increase the thickness of the masonry, increase the wall seat and other supporting schemes, combined with the relevant construction safety The quality assurance measures effectively protected the damage of the Nanfeng wellbore by the civil mining area. Practice has proved that this support method has a short construction period, low cost, and the support strength meets the requirements of the standard, ensuring the construction quality and progress of the Nanfeng well in the mine infrastructure construction process.
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