A ground test method for the two-zone heights in the whole process of fully-mechanized top coal caving mining under goaf

Abstract

The invention discloses a ground test method for the two-zone heights in the whole process of fully-mechanized top coal caving mining under a goaf, belonging to the field of safe mining in mines. This method accurately obtains the quantitative values of the two-zone heights through the whole-process testing of the development heights of the two zones in fully-mechanized top coal caving mining under a goaf before, during, and after mining, and through comparative analysis. The steps are as follows: 1. Before mining, boreholes are constructed on the working face, and the consumption of the borehole flushing fluid and borehole television imaging are observed, and then the boreholes are sealed to the floor of the overlying goaf; 2. During the mining of the working face within a range of 60 m - 70 m before and after the boreholes, the water level change in the boreholes and the change in the water inflow of the underground working face are observed; 3. One to two months after the working face has passed the boreholes, boreholes are constructed again, and the consumption of the borehole flushing fluid and borehole television imaging after mining are obtained again; 4. Then, the consumption of the borehole flushing fluid and borehole television imaging before and after mining are compared, and the borehole water level and the water inflow of the working face during mining are compared, and finally the quantitative values of the development heights of the two zones are accurately obtained.

Description

Technical Field

[0001] The present invention relates to the field of safe mining in mines, and particularly relates to a ground testing method for the heights of the two zones in the whole process of fully-mechanized top coal caving mining under a goaf. Background Art

[0002] After underground coal seam mining, it will inevitably cause the deformation and failure of overlying strata and the development of fissures, forming the so-called caving zone and water-conducting fissure zone, namely the two zones. The development height of the two zones in mining under water bodies is a very important parameter. At present, the following methods are mainly used to obtain the height of the two zones: One is to mainly refer to the empirical formula given in the "Code for Setting and Pressing Coal Mining with Pillars Reserved for Buildings, Water Bodies, Railways and Main Roadways" revised in China in 2017. However, this empirical formula is only applicable to a single mining thickness of 1-3m and a cumulative mining thickness not exceeding 15m, and it is not very suitable for the current many fully-mechanized top coal caving mining conditions. Otherwise, the calculation results will have a large difference. Another method is to measure the consumption of the drilling flushing fluid through construction of boreholes above the goaf according to the "Observation Method of the Leakage Volume of Drilling Flushing Fluid for the Height of Water-Conducting Fissure Zones" (MT / T 865-2000). However, this method is only feasible for the goaf after the working face is mined, and the obtained heights of the two zones lack comparability, and the accuracy of the heights of the two zones is not easy to guarantee. The invention patent of CN103742127B "A Determination Method for the Heights of the Overlying Rock Caving Zone and Water-Conducting Fissure Zone by Borehole Television Detection" is also only suitable for constructing boreholes above the goaf, and the statistical analysis of the fissures in the borehole wall rock is obtained through borehole imaging, but there is a lack of comparison on how to distinguish primary and secondary fissures. The invention patent of CN106772681A "A Testing Method for the Heights of the Caving Zone and Water-Conducting Fissure Zone" is a testing combination method integrating calculation, geophysical exploration, water injection, borehole television and simulation, but it is only suitable for constructing boreholes above the goaf and lacks comparative observation of the whole process of mining. The above specifications and methods all consider exploring in the goaf and do not consider the problem of the heights of the two zones of the roof in the whole process of fully-mechanized top coal caving mining before, during and after mining under the goaf.

[0003] According to the geological, hydrogeological and mining conditions of the pre-mining working face in the research area, combined with the distribution characteristics of the overlying goaf, the pre-mined coal seam belongs to the lower group of thick coal seams with an average thickness of 6.0m and is mined by fully-mechanized top coal caving; there are goafs of 3-5 thin coal seams in the upper group of coal seams overlying this coal seam. Whether the height of the water-conducting fissure zone generated by the mining of the lower group of coal seams can reach the goaf of the upper group of coal seams is the key to ensuring the safe mining of the working face.

[0004] Therefore, it is very necessary to research and develop a ground testing method for the heights of the two zones in the whole process of fully-mechanized top coal caving mining under a goaf.

[0005] The information in the above background art is only intended to increase the understanding of the overall background of the present invention, and should not be regarded as the information constituting the well-known technology known to those of ordinary skill in the art. Summary of the Invention

[0006] To solve the problems not solved in the background art, the present invention provides a ground testing method for the two-zone heights during the whole process of fully-mechanized top coal caving mining under a goaf, that is, a ground testing method for the caving zone and water-conducting fissure zone heights during the whole process of fully-mechanized top coal caving mining under a goaf. This method can conduct full-process testing on the development heights of the two zones during pre-mining, mining, and post-mining. After comparative analysis, the quantitative values of the two-zone heights can be accurately obtained.

[0007] The present invention is realized by the following technical solutions: A ground testing method for the two-zone heights during the whole process of fully-mechanized top coal caving mining under a goaf. This method conducts full-process testing on the development heights of the two zones during pre-mining, mining, and post-mining of fully-mechanized top coal caving mining under a goaf. After comparative analysis, the quantitative values of the two-zone heights can be accurately obtained. The specific steps are as follows:

[0008] (1) After the formation of the longwall face, ground boreholes are designed and constructed in the face in advance at intervals of 4-5 times the periodic weighting step distance, ensuring that the construction of boreholes with a distance of 60m - 70m from the face is completed.

[0009] (2) Before mining, boreholes are constructed, and the consumption of borehole flushing fluid and borehole television imaging are observed. Then, the boreholes are sealed to the floor of the overlying goaf.

[0010] (3) During mining within the range of 60m - 70m before and after the boreholes in the face, the water level change in the boreholes and the water inflow change in the underground working face are observed.

[0011] (4) One to two months after the working face has passed the boreholes, boreholes are constructed again to obtain the consumption of borehole flushing fluid and borehole television imaging after mining.

[0012] (5) Then, the consumption of borehole flushing fluid and borehole television imaging before and after mining are compared, and the borehole water level and the water inflow of the working face during mining are compared. Finally, the quantitative values of the development heights of the two zones are accurately obtained.

[0013] Further, the pre-mining test in step (2) is based on the occurrence of coal and rock strata in the working face and the mining direction. Before mining, two ground boreholes are constructed at appropriate positions 40m inward from the two roadways of the working face. The borehole diameter is 133mm, the casing diameter is 127mm. After the casing is lowered to the roof of the upper coal seam goaf, it is constructed to the floor of the goaf for a simple pumping test in the goaf to explore the water-richness of the upper coal seam goaf. Then, boreholes are constructed with a diameter of 94mm until the floor of the lower coal seam is reached. During the borehole construction from the floor of the upper coal seam to the floor of the lower coal seam, the consumption of borehole flushing fluid is observed and the wall rock of the borehole imaging is observed to obtain the development characteristics of the primary fissures in the overlying strata under the influence of non-mining of the lower coal seam. Finally, the boreholes are sealed to the floor of the upper coal seam goaf.

[0014] Further, the observation of the water level change in the boreholes during mining and the water inflow change in the underground working face in step (3) means that during the mining process of the working face within 60m - 70m before and after the measuring borehole, the water level of the old goaf water in the boreholes of coal seams 3 - 5 is observed. If the borehole does not expose the goaf of coal seams 3 - 5 but exposes the complete coal seams 3 - 5, then after grouting and sealing the borehole at the floor of coal seam 5, borehole water injection is carried out until the water level reaches the hole mouth, and it is noted to be basically stable. At the same time, the water inflow of the underground 2101 working face is observed, and the two are synchronized as much as possible. The observation frequency is determined according to the advancing speed of the working face.

[0015] Further, the post - mining test in step (4) is carried out by using a drill bit with a diameter of 113mm to construct again 1 - 2 months after the working face has passed the measuring borehole. During the construction, the record of the borehole flushing fluid and the logging of typical horizons are carried out, and the relevant data are recorded in the relevant tables. After the construction is in place, full - hole borehole imaging is carried out, and after the recording is completed and qualified, full - hole cement grouting and sealing safety treatment are carried out.

[0016] The beneficial effect of the method of the present invention is that it can conduct the whole - process test of the development height of the two zones in fully - mechanized top - coal caving mining under the goaf before, during, and after mining. After comparative analysis, the quantitative values of the two - zone heights can be accurately obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the plan view of the boreholes and the test process of the present invention;

[0018] Figure 2 is the flow chart of the ground test method for the two - zone heights in the whole - process of fully - mechanized top - coal caving mining under the goaf of the present invention;

[0019] Figure 3 is the borehole structure and hole - depth budget diagram of the ground test method for the two - zone heights in the whole - process of fully - mechanized top - coal caving mining under the goaf of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] For the convenience of those skilled in the art to understand and implement the present invention more clearly, the technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments.

[0021] Figure 1 Shown is the plan view of the boreholes and the test process of the ground test method for the two - zone heights in the whole - process of fully - mechanized top - coal caving mining under the goaf. This plan view shows the plane position, longitude and latitude lines, and compass of the 2101 working face, the positions of the already - constructed boreholes 419 and the two - zone boreholes in the working face, and the plane distribution ranges before, during, and after mining. The range of 120m - 140m centered on the two - zone borehole belongs to the mining - in - process stage. The area south of the mining - in - process stage belongs to the pre - mining stage, and the area north of the mining - in - process stage belongs to the post - mining stage. The two - zone borehole test is divided into three stages: pre - mining, mining - in - process, and post - mining.

[0022] Figure 2The figure shows a flow chart of a ground test method for the two-zone heights during the whole process of fully-mechanized caving mining under a goaf. From this flow chart, it can be seen that this method includes the monitoring contents and monitoring data in three stages: before mining, during mining, and after mining. Before mining, the original leakage volume of the flushing fluid during the drilling construction process, the characteristics of the primary fissures in the borehole wall, and the distribution characteristics of the original stratigraphic horizons can be obtained; during mining, the change data of the water level of the old goaf water in the borehole and the water inflow data of the 2101 working face in the mine can be obtained; after mining, the re-leakage volume of the flushing fluid during the drilling construction process, the characteristics of the secondary fissures in the borehole wall, and the stratigraphic horizon distribution characteristics can be obtained. Through the comparison curves of the change in the leakage volume of the flushing fluid in the borehole along the depth direction before and after mining, the primary fissures, secondary fissures, and stratigraphic horizon distribution, etc., the development heights of the caving zone and the water-conducting fissure zone can be judged; through the comparative analysis of the change in the water level of the old goaf water in the borehole and the change in the water inflow of the working face obtained during mining, it can be accurately judged whether the water-conducting fissure zone reaches the floor of the old goaf.

[0023] Figure 3 The figure shows the borehole structure and borehole depth budget diagram of a ground test method for the two-zone heights during the whole process of fully-mechanized caving mining under a goaf. This borehole structure and borehole depth budget diagram shows the borehole structure and the depth distribution characteristics of typical horizons in three stages: before mining, during mining, and after mining. 1183 represents the ground elevation of the two-zone borehole, with the unit of m, and Q bottom represents the bottom of the Quaternary system; the coal seams are numbered from top to bottom. Here, the 3-5 coal and 15 coal are workable coal seams. 133 mm represents the opening diameter of the borehole, 127 mm represents the casing diameter, and then a drill bit with a diameter of 94 mm or 113 mm is used to construct to the roof of the 15 coal seam. Before mining, the 15 coal below the two-zone borehole in the borehole design has not been mined, so it is filled with black; during mining, the borehole design indicates that partial mining has been carried out, the working face is advancing towards the two-zone borehole, a goaf has been formed on the left side of the two-zone borehole, and the right side is the solid 15 coal; after mining, the borehole design indicates that the 15 coal near the two-zone borehole has been completely mined.

[0024] Combined with Figure 1 、 Figure 2 and Figure 3 shown, this method mainly includes borehole observations before mining, during mining, and after mining. The on-site measurements before mining mainly include: firstly, obtaining the original leakage volume of the flushing fluid by observing the leakage volume of the flushing fluid through the borehole; secondly, obtaining the characteristics of the primary fissures through borehole television inspection; thirdly, obtaining the original horizon through the exploration of landmark horizons. The on-site measurements during mining mainly include: firstly, obtaining whether the water level of the old goaf water drops by monitoring the water level of the old goaf water in the coal seam; secondly, obtaining whether the water inflow of the working face increases by monitoring the water inflow of the working face. The on-site measurements after mining mainly include: firstly, obtaining the re-leakage volume of the flushing fluid by observing the leakage volume of the flushing fluid through the borehole again; secondly, obtaining the characteristics of the secondary fissures through borehole television inspection again; thirdly, obtaining the horizon comparison through the re-exploration of landmark horizons. The specific implementation steps are as follows:

[0025] ①Pre-mining observation: According to the occurrence of coal and rock strata in the working face and the coal mining direction, two ground boreholes with two zones are designed and constructed at appropriate positions 40 m inward from the two roadways of the working face before mining. The ground elevation of the two-zone boreholes is 1,183 m, the borehole diameter is 133 mm, the casing diameter is 127 mm. After the casing is lowered to the roof of Coal Seam 3 in the goaf of the upper coal seam, it is constructed to the floor of Coal Seam 5 in the goaf. A simple pumping test in the goaf is carried out to explore the water-richness of the goaf of the upper coal seam. Then, a borehole is constructed with a diameter of 94 mm until the floor of the lower coal seam is encountered. During the borehole construction from the floor of the upper coal seam to the floor of the lower coal seam, the observation of the consumption of borehole flushing fluid and the observation of the surrounding rock of the borehole wall by borehole imaging are carried out to obtain the development characteristics of the primary fissures in the overlying strata under the influence of non-mining in the lower coal seam. Finally, the borehole is sealed to the floor of the goaf of the upper coal seam.

[0026] ②During the mining process of the working face, the water level of the old goaf water in the boreholes of Coal Seams 3-5 is observed within 60-70 m before and after the measurement borehole. If the borehole does not expose the goaf of Coal Seams 3-5 but exposes the complete Coal Seams 3-5, then after grouting and sealing the borehole at the floor of Coal Seam 5, borehole water injection is carried out, and the water injection level reaches the orifice, and attention should be paid to observing until it is basically stable. At the same time, the water inflow of the underground 2101 working face is observed, and the two should be as synchronous as possible. The observation frequency is determined according to the advancing speed of the working face. During the normal advancement of the working face, the water level of the borehole and the water inflow of the underground working face are observed every other day outside 30 m before and after the two-zone monitoring boreholes, and the water level of the borehole and the water inflow of the underground working face are observed once a day within 30 m.

[0027] ③One to two months after the working face has passed the measurement borehole, construction is carried out again with a drill bit with a borehole diameter of 113 mm. During the construction, the recording of the borehole flushing fluid and the logging of typical horizons still need to be carried out. It is necessary to record the relevant data in the relevant forms in a detailed and reliable manner. After the construction is in place, full-hole borehole imaging is carried out. After the recording is completed and qualified, safety treatment of full-hole cement sealing is carried out.

[0028] ④By comparing and analyzing the consumption of borehole flushing fluid and borehole imaging before and after mining in the working face, the quantitative values of the heights of the caving zone and the water-conducting fissure zone can be accurately obtained.

[0029] ⑤Analyze the relationship between the water level change in the borehole and the water inflow of the working face within the range of 60-70 m before and after the mining borehole in the working face. If the water level remains basically unchanged during the fluctuation and the water inflow of the working face does not increase, it is considered that the height of the water-conducting fissure zone caused by the mining of the lower coal seam does not affect the goaf of the upper Coal Seams 3-5 in the overlying strata.

[0030] ⑥By comparing and analyzing the data from the three aspects of pre-mining, during mining, and after mining, the quantitative values of the heights of the caving zone and the water-conducting fissure zone, that is, the two-zone heights, in fully-mechanized caving mining under the goaf can be accurately obtained, which has very important reference value for the future mine safety production.

[0031] This method has high requirements for drilling construction, requiring two drillings and two hole sealings. During the drillings, it is necessary to observe the consumption of the drilling flushing fluid. For the first hole sealing, it only needs to be sealed to the floor of the goaf of the upper coal seam group. For the second time, all holes need to be sealed to ensure the hole sealing quality.

Claims

1. A ground test method for the two-zone heights in the whole process of fully-mechanized caving mining under a goaf, characterized in that, this method accurately obtains the quantitative values of the two-zone heights through the whole-process testing of the two-zone development heights in fully-mechanized caving mining under a goaf before, during and after mining, and through comparative analysis; specifically, it includes the following steps: (1) After the working face is formed, boreholes are designed and constructed in the working face in advance at a distance of 4-5 times the periodic weighting step distance, ensuring that the boreholes are constructed to a distance of 60m-70m from the working face; (2) Before mining in the working face, boreholes are constructed and the consumption of borehole flushing fluid and borehole television imaging are observed, and then the holes are sealed to the floor of the overlying goaf; Before mining, according to the occurrence of coal and rock strata in the working face and the mining direction, two ground boreholes are constructed at appropriate positions 40m inward from the two roadways in the working face before mining. The borehole diameter is 133mm, the casing diameter is 127mm. After the casing is lowered to the roof of the goaf of the upper coal seam, it is constructed to the floor of the overlying goaf, and a simple pumping test in the goaf is carried out to explore the water-richness of the goaf of the upper coal seam; Then boreholes are constructed with a diameter of 94mm until the floor of the lower coal seam is seen; During the borehole construction from the floor of the upper coal seam to the floor of the lower coal seam, the consumption of borehole flushing fluid is observed and the surrounding rock of the borehole wall is observed by borehole imaging to obtain the development characteristics of the primary fissures in the overlying strata under the influence of non-mining of the lower coal seam. Finally, the holes are sealed to the floor of the goaf of the upper coal seam; (3) During mining within a range of 60m-70m before and after the boreholes in the working face, observe the water level change in the boreholes and the water inflow change in the underground working face; Observing the water level change in the boreholes and the water inflow change in the underground working face during mining means observing the water level of the old goaf water in the boreholes of the 3-5 coal seams during the mining process within 60m-70m before and after the boreholes in the working face. If the boreholes do not expose the goaf of the 3-5 coal seams but expose the complete 3-5 coal seams, then after grouting and sealing the holes at the floor of the 5 coal seam, borehole water injection is carried out, and the water injection level reaches the hole mouth, and pay attention to observing until it is basically stable. At the same time, observe the water inflow of the 2101 underground working face. The two are synchronous, and the observation frequency is determined according to the advancing speed of the working face; (4) One to two months after the working face has passed the boreholes, boreholes are constructed again, and the consumption of borehole flushing fluid and borehole television imaging after mining are obtained again; After mining, testing is carried out by using a drill bit with a diameter of 113mm to construct again one to two months after the working face has passed the measuring boreholes. During the construction, the records of borehole flushing fluid and the compilation of typical horizons are carried out, and the relevant data are recorded in the relevant tables; After the construction is in place, full-hole borehole imaging is carried out. After the recording is completed and qualified, full-hole cement sealing and safety treatment are carried out, and comparative analysis is carried out with the relevant data before mining; (5) Then, compare the consumption of borehole flushing fluid before and after mining, borehole television imaging, and compare the borehole water level and the water inflow of the working face during mining, and finally accurately obtain the quantitative values of the two-zone development heights.

2. A ground test method for the two-zone heights in the whole process of fully-mechanized caving mining under a goaf according to claim 1, characterized in that, The determination of the aforesaid observation frequency according to the advancing speed of the working face means that: during the normal advancement of the working face, the water level of the monitoring boreholes in the two zones and the water inflow of the underground working face are observed every other day at a distance of more than 30 m before and after the monitoring boreholes, and the water level of the boreholes and the water inflow of the underground working face are observed once a day within 30 m.

Images