The monitoring work includes dynamic monitoring of underground water regime, monitoring of floor stress and mining damage, and monitoring and early warning of floor water inrush.
(1) Above-well and underground water regime monitoring system
The dynamic change of groundwater level can directly and systematically reflect the hydrogeological conditions of aquifers, so long-term monitoring of the dynamic water level of multi-layer aquifers and mastering the temporal and spatial variation law of groundwater in mine fields are the basis for finding out the hydrogeological conditions and correctly formulating water prevention measures.
At present, the hydrogeological observation network of Daping Mine is not perfect, and only one long observation well (1 observation well) is used to observe the water level of Ordovician limestone, but there is no special observation well for Taiyuan Formation limestone. In addition, the observation of water inflow in underground mine, mining area and water inrush point is mainly manual observation. The disadvantages of manual observation are simple measurement method, poor measurement accuracy, complex observation work and a lot of data sorting work, low degree of automation and easy to make mistakes. In order to dynamically monitor the water level (pressure), old kiln water, water inrush, mine water inflow and mining area water inflow in different aquifers in the mine field, and provide technical basis and basic data for mine water prevention and control, it is urgent to establish a dynamic automatic observation system of mine water level (pressure) and water inflow combined with upper and lower wells. Here is a brief introduction to the monitoring principle.
XY-Ⅱ automatic water regime detection system is an intelligent monitoring system for real-time telemetry of groundwater level, water pressure, water temperature and flow changes through GSM wireless communication (ground) and wired communication (underground). It has the characteristics of high measurement accuracy, wide measurement range, simple operation, low power consumption and unattended all-weather automatic work. The system consists of long-hole ground water level (pressure) telemetry system, underground water regime (water pressure, water quantity and water temperature) monitoring system and ground base station.
1. System composition
The system consists of a main station (located in the monitoring center), several underground substations (located at the orifice of observation well, the chief hydrologist) and several underground substations.
2. System functions
1) main station function: ① send commands or receive data to substations through communication equipment; ② Save the data to disk; ③ Complete data display, query and editing; ④ Processing data, generating various reports and printing them; ⑤ Draw various graphs such as water level (water pressure), temperature, flow trend curve and histogram.
2) Substation function: ① data acquisition; ② data temporary storage; ③ data display; ④ Inoue substation transmits data to monitoring center through GSM short message; ⑤ The underground substation transmits data to the underground through the safety monitoring system.
The system has the characteristics of wide application range, integrated data processing, flexible configuration, high reliability, stable data communication, strong anti-interference, convenient installation, compatibility and independence. It is a water level (water pressure) observation system, which can continuously measure for a long time, make use of computer analysis and assist decision-making, and is suitable for various environments. It is of great practical significance for timely forecasting water disasters and ensuring normal and safe production in coal mines.
In this scheme, four newly designed long observation well (Od 1, Od2, Cd 1, Cd2) and 1 existing observation wells (observation well 1) are equipped with automatic water level recorders or remote sensing monitoring substations for long-term observation. By installing an automatic water meter underground, the water inflow of each mining area and the mine water inflow are observed for a long time. See Table 4-7 for details.
Table 4-7 List of Online Monitoring Points of Upper and Lower Water Regime in Daping Mine
(II) In-situ stress monitoring of bottom plate
Coal seam mining will inevitably lead to the stress adjustment of rock mass within a certain depth of the floor of the coal mining face, which will lead to a new stress-strain process: pre-pressure will occur in the floor rock mass with a certain depth before mining; In the mined-out area, the advance pressurization is transformed into pressure relief relaxation; The recovery of complex pressure caused by roof caving from goaf is a generalized mining effect. The formation and characteristics of mining effect depend on the characteristics of floor stress adjustment, and are closely related to the structural characteristics, physical and mechanical properties, hydrochemical characteristics, in-situ stress, groundwater action and mining stress action characteristics related to mining methods.
Another driving force causing water inrush from coal seam floor is the water pressure of confined water. The mechanical effect of confined water is realized through cracks in aquifer rock mass. Confined water in water-filled cracks has distributed load on the surrounding rock of cracks. When the fractured surrounding rocks are in a certain state of in-situ stress, they are in equilibrium. When the geostress state of surrounding rock changes or the confined water pressure changes, on the one hand, the original cracks may be closed, on the other hand, small cracks may be opened, thus reaching a new equilibrium state.
Water inrush from floor is the result of the interaction between mining ground pressure and confined water in floor, and mining ground pressure causes the redistribution of stress field in rock mass and seepage field in floor. As a result of the interaction between them, when the minimum principal stress of floor rock mass is less than the confined water pressure, fracturing expansion will occur and water inrush will occur. For a working face, the water pressure of confined water in the floor is generally known. The key problem is to measure the distribution of floor geostress field before and after mining and during mining, and then analyze the mining damage of coal floor, and predict the docking relationship between the mining damage water-conducting fracture zone and the underlying strong aquifer uplift fracture zone.
2 1 mining area is located in the axis of Daye syncline, and the floor is buried deeply, which is a relatively concentrated area of tectonic stress. In this scheme, in-situ stress monitoring is carried out in the first mining face of 2 1 mining area.
1. Purpose and tasks
Through the in-situ stress test of the first mining face in 2 1 mining area before and after mining, the original in-situ stress distribution characteristics of the face plane and profile are generally mastered. The maximum damage depth of floor and the rupture strength of water-resisting layer caused by mining under different stress States are detected, and the possibility of water inrush in this working face is predicted.
2. Monitoring work content, technical methods and construction sequence
According to the geological and hydrogeological conditions of the first mining face in 2 1 mining area and the analysis of comprehensive geophysical prospecting results, the concentrated and divergent sections of structural stress in the working face, the first weighting mining step and the maximum failure depth are preliminarily judged.
In the first mining face of 2 1 mining area, 5 ~ 6 floor stress measuring holes are respectively arranged in the sections where the stress in the upper and lower roadways is relatively concentrated and divergent, and 3 ~ 4 mining stress measuring holes are arranged in the section where the initial weighting is expected near the cut of the lower roadway. In-situ in-situ stress test was carried out on the layered section of the floor stress measuring hole, and the original in-situ stress field distribution of the floor of the working face was measured, and the distribution of the stress field was analyzed. After the test, plug the stress measuring hole; Test the change of mining stress field in the mining stress test hole.
After the test work, the mining effect of the floor of the working face was simulated by computer, and the depth and strength of mining damage were analyzed. The mining damage of the whole working face floor is predicted, and the water inrush risk of the working face is evaluated.
3. Monitor the project layout
This monitoring project is arranged in the material lane and transportation lane of the first mining face in 2 1 mining area. According to the test results and parameters, it is reasonably applied to other working faces and 1 coal mining technology.
The monitoring work should be carried out on the basis of the special design submitted by the undertaking unit.
(3) monitoring and early warning of floor water inrush
The monitoring of water inrush from the floor of working face is based on the results of underground geophysical exploration (audio-frequency electric perspective, direct current method) and the hydrogeological conditions exposed by working face after the formation of roadway in working face. In the process of mining the second floor 1 coal seam, the weak section with water inrush risk is selected as the monitoring position to monitor the changes of floor stress, strain, water pressure and water temperature parameters, so as to achieve the purpose of predicting water inrush in advance.
At present, only embedded monitoring method, namely multi-parameter monitoring system, is used to monitor the precursors of indirect water inrush from coal seam floor. The working procedure of this method is: pre-analysis of hydrogeological conditions of working face → determination of monitoring position → determination of monitoring content → monitoring of drilling construction → installation and monitoring of monitoring equipment → water regime forecast.
The 2 1 mining area in Daping Coal Mine is located in the axis of Daye syncline, and the floor is deeply buried, which bears high Ordovician limestone water pressure and is seriously threatened by Ordovician limestone water. In 2 1 mining area threatened by water disaster, it is necessary to monitor and warn the water inrush in the working face.
1. Determine the monitoring position.
According to the geophysical prospecting results and the hydrogeological conditions exposed by the working face, the weak section of coal seam floor with water inrush danger is selected as the monitoring position. If there are multiple weak links, they should be monitored at the same time. If it cannot be monitored at the same time, the position closest to the working face should be monitored first. The distance between the monitoring point and the mining face shall not be less than 60m.
2. Monitoring work content, technical methods and construction sequence
A drilling nest is built in the roadway beside the water inrush danger section of the working face, three drilling holes are built in the water-resisting layer of the coal seam floor, and stress, strain, water pressure and water temperature sensors are installed in the drilling holes; Establish underground substations and ground central stations, and install and debug equipment and instruments.
The stress, strain, water pressure, water temperature and other parameters of the water-resisting layer of the floor of the working face are monitored in real time during the mining process, and the computer of the ground central station will analyze the above dynamic data. Once the above parameters are abnormal, the reasons will be analyzed immediately, and different degrees of water inrush warning will be issued according to the abnormal degree of the parameters and the analysis results, and the plan for preventing water inrush from the floor will be started;
After working face mining, combined with the comprehensive analysis and monitoring results of working face mining, the failure depth and failure law of coal seam floor are studied.
3. Monitor the project layout
In this scheme, two working faces threatened by Ordovician limestone water are selected in 2 1 mining area to monitor floor water inrush. According to the test results and parameters, it is considered to be extended to working faces with similar conditions and a 1 coal seam mining.
The monitoring work should be carried out on the basis of the special design submitted by the undertaking unit.