Simulation Analysis and Experimental Study on the Working State of Sinking Headframe in the Large Underground Shaft

Based on the newly developed sinking headframe for the deep and large shaft, the finite element model of the full-scale headframe was established by using SAP2000. /rough the calculation, the theoretical stress of the headframe at sinking depths of 40m, 143m, 223m, 518m, 762m, 1000m, 1250m, and 1503m was obtained and then compared with the field measured stress. /e results show that with the increase of shaft sinking depth, the theoretical stress of finite element simulation and the field measured stress of each member of the sheave wheel platform and the headframe increase linearly, and for the maximum member stress in the upper, middle, and lower layers of the headframe, the numerical simulation value is greater than the field measured value and less than the designed steel strength. In other words, under normal working conditions, headframe members are in the elastic stress stage and meet the design requirements, and instability failure of headframe members will not occur. /e end-restraint mode of the supporting bars has a great influence on the force of the topmember./e reasonable selection of the restraint mode in the simulation is the key to the accuracy of the calculation results. /e simulation results well reflect the actual stress of the headframe and provide a reliable guarantee for the follow-up work of the project.


Introduction
China has one of the richest coal reserves in the world. According to incomplete statistics, China's proven coal reserves are about 1 trillion tons, with complete coal types and wide distribution areas, which provides a reliable material guarantee for the development of the coal industry [1][2][3][4][5]. With the mining of mineral resources gradually shifting to the deep, the proportion of large diameter (more than 8 m) and deep shaft (more than 1000 m) exploitation will be further increased. In mine construction, the shaft construction is generally regarded as the key project, and the sinking headframe is the main stress component in the shaft construction process [6][7][8][9]. In the actual construction, the sinking headframe in the large shaft is subject to extremely complex stress, and its bearing capacity not only depends on its own structure but also closely related to the layout of the shaft sinking equipment and the ground winch lifting equipment [10][11][12]. e reason and limit value of derrick inclination are determined by experiment and finite element modeling analysis. e inclination of derrick, support settlement, and corrosion of support beam are measured by experiment, and the bearing capacity is analyzed by considering defects in the finite element model [13][14][15].
With the development of test and analysis technology, field tests of prototype structure can be used to verify and develop the calculation theory and then directly applied to production practice to solve problems. More importantly, tracking and monitoring, fault alarm, and automatic control of important buildings are realized to ensure safe operation [16][17][18]. Due to the limitation of funds and conditions, it is impossible to monitor a large number of structures. Within the operation of structure for a certain time, field tests can be used to detect or diagnose the fault to achieve the purpose of troubleshooting [19][20][21][22]. Only through the field test of the prototype structure, various kinds of structural parameters, boundary conditions, and load distribution rules in line with the actual situation and the satisfactory results of the theoretical analysis can be obtained. e field test is also the best way to develop the theory of prototype structure testing [23][24][25]. In a word, field tests and the monitoring of prototype structure play an irreplaceable role in both the theory development and the solution of practical production and scientific research problems [26,27].
Kong [28] simulated and analyzed the structural changes of the headframe after lifting in the main and auxiliary shafts through the finite element analysis software and improved the stress state of some components of the headframe close to the critical stress state. Xiao et al. [29] used the anchoring agent, screw-thread steel, and concrete foundation reinforcement methods to reinforce the headframe leg foundation. As a result, the further settlement deviation of the headframe foundation was prevented after the use of the freezing method in a mine, and the construction safety and smooth sinking construction were ensured. In previous studies [30][31][32][33], the headframe stress caused by headframe deflection was analyzed. Gusella et al. [34] studied the dynamic characteristics of headframe structure and determined its influencing factors based on the simulation analysis. Link [35] regarded the element stiffness parameter as a modified parameter in the process of relevant research and modified the design scheme appropriately based on the obtained results. In these studies [36,37], the fatigue stress and deformation of various components of headframe were intuitively and comprehensively analyzed based on the field measurement method [38,39].
With the continuous increase of energy demand, the required sinking speed and production efficiency have been improved, and the diameter and depth of the construction shaft have been increased; thus, the lifting capacity of the headframe should be increased greatly. However, the conventional sinking headframe cannot meet the needs of deep and large shaft construction, and the stress analysis of the super large shaft headframe is rarely reported. In this study, the stress of the large sinking headframe developed for the auxiliary shaft (net diameter 10 m, depth 1503.9 m) in the Sishanling iron mine was comprehensively analyzed.

Selection of the Headframe for Large
Shaft Sinking e auxiliary shaft of the Sishanling iron mine was located in Benxi City, Liaoning Province. e net diameter of the shaft was 10.0 m, and the shaft neck section was 40 m in total. e temporary lock section was 3.7 m, which was supported by 1000 mm thick brick. e neck section of the shaft was supported by 1000 mm thick reinforced concrete. e shaft sinking equipment included the lifting system, transportation system, ventilation system, air pressure system, drainage system, and water supply system.
For the engineering conditions of the shaft with a diameter over 8 m and a depth over 1000 m, the existing V-type headframe with the largest specification cannot meet the construction conditions. According to the construction requirements of drilling equipment and the large shaft, the SA-III type headframe was selected.
is headframe was developed by China University of Mining and Technology and Handan Design Engineering China Coal Co., Ltd. meet the development trend of overdepth and large-diameter shaft in China. e Q345 steel was selected as the main and auxiliary materials of the large-scale sinking headframe. Figure 1 shows its structural form, and Figure 2 shows the sinking headframe in working condition.
According to the characteristics of large diameter and deep depth of the auxiliary shaft in Sishanling iron mine and the construction technology of the shaft, the shaft sinking equipment included a hoist and bucket, a Φ 9800 mm threelayer hanging plate, the YSJZ-6.12 hydraulic umbrella drill, and two HZ-6B central rotary rock grabs. According to the selected drilling equipment, eight kinds of drilling depth were obtained: 40 m, 143 m, 223 m, 518 m, 762 m, 1000 m, 1250 m, and 1503 m; then, the working loads of wire rope of sinking equipment under eight working conditions were obtained. e loads of wire rope were transmitted to the sheave wheel platform and then to the stress bars of the headframe. Figure 3 shows the number and corresponding position of the stress bars.
A FBD-2 × 55 kW counter rotating fan with a Φ 1000 mm FRP air duct is installed near the wellhead for forced ventilation. Two 35 W × 7 − Φ 42-1960 steel wire ropes and two JZ-40/1800 stable car suspensions are selected. A Φ 57 × 3.5 water supply pipe is arranged in the shaft, and the surface is connected with the underground reservoir. A pressure reducing valve is installed in the water supply pipe in the shaft to meet the water pressure requirements of the rock drill.

Simulation Analysis of Working State of the Large Sinking Headframe
In the SAP2000 finite element numerical simulation analysis, the number and position of the large sinking headframe were consistent with the measuring points of the headframe, and working conditions of the numerical simulation analysis were consistent with the working condition of the sinking depth measured in the field. e corner columns and supporting bars of large sinking headframe were mainly axial forcebearing bars, and the normal stress at each point on the crosssection was σ � N/A, and the cross-sections were all Φ 325 mm × 16 mm. According to the length, these members can be divided into eight types, I-II corner columns and III-VIII supporting bars. e end spring stiffness of the supporting bars was 1000 N/mm. rough the force analysis of members and side beam of the sheave wheel platform, the steel of the HN 1350 mm × 600 mm × 25 mm × 45 mm was adopted for the sheave wheel platform. e calculated length coefficient of the supporting bars was taken as 0.9, and the calculated length coefficient of the axial compression member hinged at both ends is 1.0. Table 1 provides the parameters of the members. rough the calculation of σ � N/A, the stress was obtained. e stress at the sinking depth of 40 m (the release of the hanging plate) was taken as the reference value in the field measurement. rough the above equations, the theoretical stress of corner column and supporting bars for the

Stress Analysis of Upper Members.
With the increase of sinking depth, the theoretical stress curves of the upper corner column and supporting bars are obtained, as shown in Figure 4 and Figure 5, respectively. As shown in Figures 4 and 5, the stress value of the upper member increases gradually with the increase of sinking depth. e stress growth rate of corner column G07 and supporting bar F17 is the fastest, while that of corner column G04 and supporting bar F01 is the slowest. e reason is that the load growth rate on the beam of the sheave wheel platform corresponding to G07 and F17 is greater than that of G04 and F01. When the sinking depth is 1503 m, the maximum compressive stress of G07 and F17 is 105.4 MPa and 69.7 MPa, which is far less than the designed tensile strength of Q345 steel (f � 310 MPa). It shows that the upper members are in the elastic stress stage, meeting the design requirements, and the instability failure of headframe members will not occur under the normal working condition within the sinking depth of 1503 m.

Stress Analysis of Middle Members.
With the increase of sinking depth, the theoretical stress curves of the middle corner columns and supporting bars are shown in Figure 6 and Figure 7.
As shown in Figures 6 and 7, the stress value of the middle members gradually increases with the increase of the sinking depth. e growth rate of compressive stress and tensile stress of corner column G08 and supporting bar F22 is the fastest, while that of corner column G05 and supporting bar F06 and supporting bar F04 is the slowest. e reason is that the load growth rate of G08, F22, and F20 corresponding to the sheave platform beam is higher than that of G05, F06, and F04. When the shaft sinking depth is

Stress Analysis of Lower Members.
With the increase of sinking depth, the theoretical stress curve of lower corner columns and supporting bars is obtained, as shown in Figure 8 and Figure 9. As shown in Figures 8 and 9, the stress value of lower members gradually increases with the increase of the sinking depth. e stress growth rate of corner column G09 and supporting bar F25 is the fastest, while that of corner column G06 and support bar F08 is the slowest. When the shaft sinking depth is 1503 m, the maximum compressive stress of G09 and F25 is 82.6 MPa and 78.6 MPa, which is far less than the designed tensile strength of Q345 steel (f � 310 MPa). It shows that the top members meet the design requirements and are in the elastic stress stage; the instability failure of headframe members will not occur under the normal working condition within the sinking depth of 1503 m.

Stress Analysis of Members in the Sheave Wheel Platform.
In the establishment process of the finite element model of the sheave wheel platform in the headframe, the bending moment and torque at the end of the supporting member should be   Figure 10. As shown in Figure 10, with the increase of the sinking depth, the theoretical stress of four measuring points L03, L04, l05, and L06 of the two middle beams of the sheave wheel platform and the four measuring points L01, L02, L07, and L08 of the two side beams of the sheave wheel platform in the finite element numerical simulation increases linearly under normal working conditions. When the shaft sinking depth is 1503 m, the maximum stress of the middle beam L05 (L06) of the sheave wheel platform is 34.1 MPa, which is far less than the designed tensile strength (f � 310 MPa). It shows that the headframe members are in the elastic stress stage, meeting the design requirements, and the instability failure of headframe members will not occur under the normal working condition within the sinking depth of 1503 m.
As shown in Figure 10, the stress growth rate of measuring point L05 (L06) in the middle beam of the sheave wheel platform is the fastest and the largest and that of measuring point L07 in the side beam of the sheave wheel platform is the slowest.
rough the analysis of the equipment layout on the beam of the sheave wheel platform in the headframe and the rigid connection at the end of the supporting bar, it can be concluded that there is no support constraint in the middle beam of the sheave wheel platform, and the middle beam is a single span simply supported beam. e load growth rate of measuring points L05 (L06) on the side beam of platform is faster than that of L03 (L04) on the middle beam of platform, and the stress in the midspan increases the fastest and the most. Because of the rigid connection at the end of the supporting bar, the center of the side beam of the platform is supported, so the side beam of the platform can be considered as the two-span continuous beam with a certain supporting function. Since the span is reduced by one time, the stress growth rate at the measuring point of the side beam of the platform is the slowest and the smallest.

Field Measurement and Analysis of the Working State of Sinking Headframe in the Large Shaft
According to the stress characteristics of the headframe in this project, the constraints of site construction conditions and economic cost and other factors are considered, and the strain gauge electrical measuring system was used as the static test scheme of the headframe working state in this project. According to the basic situation of the auxiliary shaft engineering in Sishanling iron mine, combined with the main test contents of headframe in the SA-III vertical shaft sinking, the main measured headframe strain on-site was considered, and the actual bearing condition of the headframe was judged, and the datataker test system was adopted.
Eight times of static data acquisition were carried out onsite, including eight working conditions of 40 m, 143 m, 223 m, 518 m, 762 m, 1000 m, 1250 m, and 1503 m. e field data acquisition is shown in Figure 11.
According to the field measurement results and the conclusion of numerical simulation analysis, the most representative members of the upper, middle, and lower layers are selected for analysis. In other words, the members with the maximum stress of corner columns, vertical supporting bars, and diagonal supporting bars in the upper, middle, and lower parts are selected for comparison, as shown in Figure 12 As shown in Figure 12, the stress variation law of bars in the field measurement is consistent with that of simulation results. e stress of bars increases with the increase of shaft sinking depth, and the measured value is less than the theoretical value in the simulation calculation. erefore, the bar stress of the headframe is far less than the maximum bearing capacity of the bar within 1503 m of shaft sinking depth. In other words, these bars meet the design requirements and are in the elastic stress stage, and the instability failure of headframe members will not occur. Besides, with the increase of the shaft sinking depth, the measured stress value of the bars is gradually close to the simulated value. At the shaft sinking depth of 1503 m, the measured stress value of the bars is basically consistent with the simulated value. It can be concluded that the simulation results can better reflect the actual situation.

Analysis of the Influence of Different Constraint Modes on the Support End
e upper members mainly include corner column and supporting bar. According to the above simulation analysis and field measurement results, the top corner column G07, vertical supporting bars F17, and inclined supporting bars F18 are the most stressed. e stress variation curve of the upper member and the sheave wheel platform under different restraint modes with the shaft sinking depth is shown in Figure 13.
It can be seen that when the constraint of member changes from flexible to rigid, the slope of curves increases gradually. Within a certain range of sinking depth, the compressive stress of the flexible constraint has a greater change. Since the different constraint methods lead to different stress characteristics of the bar, the flexible constraint has a greater impact on the compressive stress of the bar.
As shown in Figure 13, the measured analysis results of the working state of the upper member are between the calculation results of the finite element numerical simulation of the rigid connection and the flexible connection. e corner column stress of the rigid connection at the end of the supporting bar is 55.7% lower than that of the flexible connection at the end of the supporting bar, and the supporting bar stress of the rigid connection at the end of the supporting bar is 36.17% and 58.3% higher than that of the flexible connection at the end of the supporting bar, respectively. It shows that the end-restraint mode of the supporting member has a great influence on the force of the uppermost member. erefore, in the finite element numerical simulation, the determination of the end-restraint mode of supporting bars is particularly important for the calculation analysis and optimization design of the headframe in the large shaft sinking.

Conclusions
Aiming at the field application of the newly developed steel headframe for the superlarge and ultradeep shaft in the auxiliary shaft of the Sishanling iron mine, the working state and mechanical performance analysis of the headframe are carried out in combination with the actual project. e results of field measurement and finite element numerical (2) e measured stress of headframe in the on-site working condition is less than the theoretical stress of headframe in the finite element numerical simulation. When the sinking depth is less than 1503 m, the reliability of this project is verified by the results of numerical simulation results and field measurement, that is, the headframe members are in the elastic stress stage, meeting the design requirements, and the instability failure of headframe members will not occur under the normal working condition within the sinking depth of 1503 m. (3) e end restraint mode of the supporting member has a great influence on the force of the top member. e reasonable selection of the end-restraint mode in the simulation is the key to the accuracy of the calculation results. e numerical simulation in this study can better reflect the stress state of the shaft headframe in the actual project and provide a reliable guarantee for the follow-up mining work. e simulation results and measured results show that the internal force of the member bar has a large surplus, and the bar can be optimized to achieve the purpose of saving steel, which will be further studied.

Data Availability
e data used to support the findings of this study are included within the article.

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