CN111008758B - Design method of excavation time for gob-side coal roadway in extra-thick coal seam based on double index weighting method - Google Patents

Abstract

The invention relates to a design method of the driving time of an extra thick coal seam gob-side entry driving based on a double-index weight method, which comprises 1) determining the driving time T of the gob-side entry driving by taking the basic roof subsidence as an index ₁ 2) determining reasonable digging time T by taking the deformation rate of surrounding rock of a roadway as a time index ₂ And 3) determining reasonable driving time T of the gob-side entry. The basic top subsidence and the overlying strata movement stabilization time are obtained on the basis of fully considering the differences of coal and rock mass, so that the method is more in line with the field reality and the result is more accurate; introducing the deformation rate of the surrounding rock of the roadway as an additional index to form a double-index system of the digging time of the gob-side entry; the deformation rate of surrounding rock is 70% of the maximum basic roof subsidence value<4 mm/day is used as an evaluation index of the roadway driving time, the weight proportion of the two is determined according to specific geological conditions, the driving time of the roadway along the sky is comprehensively obtained, the surrounding rock of the roadway along the sky is ensured to be safe and stable, the driving time of the ultra-thick coal seam along the sky is reduced, and the normal succession of mining is ensured.

Description

Design method of excavation time for gob-side coal roadway in extra-thick coal seam based on double index weighting method

technical field

The invention relates to the field of coal mine roadway excavation and support, in particular to a method for designing the excavation time of a gob-side coal roadway in an extra-thick coal seam based on a double-index weighting method.

Background technique

Narrow coal pillar roading along the goaf refers to the preservation of coal pillars by leaving 3-5m narrow coal pillars at the edge of the goaf under the condition that the movement of the overlying strata in the adjacent goaf terminates and the stress redistribution caused by it tends to be stable. down the laneway. At present, gob-side entry with narrow coal pillars is mainly used in thin coal seams and medium-thick coal seams. Thin coal seams refer to coal seams with a single layer thickness less than 1.3m, and medium-thick coal seams refer to those with a single layer thickness greater than 1.3m and less than 3.5m. coal seam. However, in the process of mining thick and extra-thick coal seams, narrow coal pillars are rarely used along the gob roadway, and the roadway protection method with 20-30m wide coal pillars is mostly used. The thick coal seam refers to the thickness of a single layer greater than 3.5m and less than 8.0m m coal seam, extra-thick coal seam refers to a coal seam with a coal body thickness greater than 8.0m. In recent years, in order to improve the coal recovery rate, narrow coal pillar gob-side entry technology has been used in thick and extra-thick coal seams. However, a large number of theoretical studies and engineering practices have shown that when the thickness of the coal seam is less than 6.0m, The theory, technology, and process of the process can be used for reference or continue to use the existing theory and technology of gob-side entry in thin and medium-thick coal seams. However, as the thickness of the coal seam further increases, the law of movement of the overlying rock and the stress field caused by it begin to change significantly. Medium-thick coal seams are quite different, and the existing thin and medium-thick gob-side entry theories, technologies, and techniques cannot be used under this condition.

The following takes the excavation time of gob-side roadway as an example to illustrate. As we all know, the excavation time of gob-side roadway is the key factor to ensure the stability of the surrounding rock of the gob-side roadway and the normal replacement of excavation. The single evaluation index of the excavation time of the empty roadway, that is, the roadway is excavated when the roof subsidence reaches the maximum value. Under the given conditions, the basic roof subsidence is calculated based on the characteristics of caving rocks; however, for extra-thick coal seams above 15m, coal recovery is mostly carried out by fully mechanized caving mining. Due to the limitations of fully mechanized caving mining technology, nearly One of the coal seams (thickness greater than 4m) cannot be mined, and it will fall into the gob together with the rock. The basic roof settlement tendency will be significantly slowed down (approximately 35% to 45% reduction in the basic roof sinking amount). If the existing theoretical calculation method is adopted, ie ignoring the differences in crushing and strength of coal and rock, the calculated roof settlement characteristics and gob-side excavation time will be seriously inconsistent with production practice. Therefore, it is urgent to propose a theoretical research method for the excavation time of gob-side roadway in extra-thick coal seam.

Through a large number of literature searches, it is found that there are no theoretical research and practical reports on the excavation time of gob-side roadways in extra-thick coal seams above 15m. In the current engineering practice of ultra-thick coal seams above 15m, there are two commonly used methods to determine the excavation time of gob-side roadway: one is to excavate the roadway after 12 to 16 months after the movement of the overlying rock is fully stabilized. The surrounding rock of the roadway is stable, and the maintenance of the roadway is in good condition, but it seriously affects the succession of the normal production of the mine, resulting in difficulties in the succession of the mine and a sharp drop in profitability. The second is to continue to use the traditional 4-6 month digging time, that is, start digging 4-6 months after the mining of the adjacent working face is completed. This method can ensure normal mining succession. The empty roadway is seriously deformed and unstable. Therefore, how to determine a gob-side roadway excavation time determination method that can not only ensure the stability of the surrounding rock of the gob-side roadway but also realize normal mining replacement is of great significance for the safe, high-yield and efficient mining of extra-thick coal seams above 15m.

On the basis of considering the lack of previous theoretical research and engineering practice in the test scores, this patent proposes a dual-index comprehensive determination method for the excavation time of gob-side roadways in extra-thick coal seams above 15m based on the basic roof settlement law and roadway deformation rate. The subsidence is used as an evaluation index, and a reasonable settlement value rather than the maximum settlement value is determined as the evaluation standard for the stability of the overlying rock, based on which the reasonable excavation time of the gob-side coal roadway is calculated; secondly, when the coal body of the gob-side coal roadway is relatively weak and the strength When it is lower, the displacement and deformation will occur immediately after the excavation of the goaf coal roadway, which will lead to the rapid development and rupture of coal fissures. It occurs much earlier than the evolution of cracks and stress, that is, the roadway deformation (displacement) rate is the most intuitive, sensitive, and fundamental evaluation index for the stability of surrounding rock. Accordingly, this patent takes the change of surrounding rock rate as the second evaluation index. The excavation time of the gob-side coal roadway; thirdly, the basic roof settlement is the fundamental mechanical reason for the stable state of the surrounding rock of the gob-side coal roadway, and the displacement rate of the roadway is the result of the stable state of the roadway, but under different geological production conditions, the two indicators The contribution rate to the most reasonable tunneling time is different. Based on this, the weight ratio of the dual indicators under different geological conditions is designed to comprehensively determine the reasonable tunneling time along the goaf. Therefore, using the basic roof settlement law and roadway deformation rate as evaluation indicators to determine the most reasonable time for gob-side roadway excavation can not only ensure the stability of the surrounding rock of the coal roadway but also shorten the roadway preparation time, filling the gap in the method of determining the time for gob-side roadway excavation. Whitespace.

Contents of the invention

In order to overcome the problem of excavation time of gob-side roadway in extra-thick coal seam above 15m, the present invention provides a design method of excavation time of gob-side roadway in extra-thick coal seam based on double index weight method, which is divided into the following steps:

The first step is to use the basic roof subsidence as an index to determine the excavation time T ₁ of gob-side entry

Step 1.1) Field investigation and indoor experiment

Investigate the basic roof, direct roof, coal thickness and coal seam recovery rate; the laboratory measures the immediate roof and coal disintegration coefficient, the elastic modulus and viscosity modulus of the basic roof rock layer;

Step 1.2) Calculation of the maximum subsidence of the basic roof

Considering the low recovery rate of the coal body during the mining process of the extra-thick coal seam and the differences in the disintegration and strength of the coal and rock mass, nearly 25% of the unmined coal body will caving along with the direct roof and inhibit the basic roof subsidence. Based on this, the maximum sinking amount W _max of the basic roof is determined, and its expression is as follows:

W _max ＝M+∑h-∑h·k ₁ -(1-α)M·k ₂ (1)

In the formula, M is the thickness of the mining coal seam, ∑h is the thickness of the immediate top rock layer, k ₁ is the disintegration coefficient of the caving rock mass, k ₂ is the disintegration coefficient of the cracked coal body, and α is the top-coal discharge rate, above 15m Extra thick coal seam α=75%;

During the mining process of extra-thick coal seam, the expression of the dynamic equation of basic roof settlement is as follows:

In the formula, q _Z is the rock formation load on the basic roof, l _m is the fracture step distance of the basic roof, E and η are the elastic modulus and viscous modulus of the basic roof, and F is the comprehensive compression resistance of caving coal rock mass Intensity; the relationship of F is as follows:

In the formula, _F1 is the compressive strength of the caving rock mass, and _F2 is the compressive strength of the caving top-coal;

The dynamic equation (2) belongs to an exponential function, and its derivative represents the subsidence rate of the basic roof; it can be known from the characteristics of the exponential function that the subsidence rate of the basic roof will gradually decrease as time increases, that is, when the subsidence of the basic roof reaches a certain When the critical index is reached, the subsidence rate of the basic roof will be greatly reduced and approach 0; combined with a large amount of engineering practice experience, 70% of the maximum subsidence of the basic roof is used as the critical index, and when the subsidence of the basic roof reaches 70% W _max critical When the index is reached, the subsidence movement of the basic roof will tend to be slow and stable, with a low movement rate, no violent structural movement, and little impact on the stability of the underlying rock mass, that is,

The second step is to determine the reasonable excavation time T ₂ by taking the deformation rate of the roadway surrounding rock as the time index

Step 1.1) Establish a monitoring station 100m in front of the working face of the extra-thick coal seam, which is located within the production system of the adjacent working face, rather than in the advanced roadway of the working face;

Step 1.2) Install roof, floor and two-side displacement monitoring equipment in the section of the monitoring station, which can be measuring rods, measuring lines or other monitoring equipment, to ensure that the equipment can monitor the amount of surrounding rock movement in real time;

Step 1.3) Take the propelling position of the measuring station and the working face as the abscissa, and the approaching speed of the roof, floor, and two sides as the ordinate, and draw a graph. The monitoring work starts from Ym in front of the measuring station, and Y≥100m, until the deformation rate of the roadway decreases. It ends at 4mm/d; the deformation rate of the surrounding rock is less than 4mm/d, which means that the surrounding rock of the roadway is in a basically stable state;

Step 1.4) According to the average advancing speed of the working face, the time T ₂ required for the deformation rate to decrease to 4mm/d is obtained,

In the formula, S is the abscissa value when the deformation rate is reduced to 4mm/d, and v is the advancing speed of the working face;

The third step is to determine the reasonable excavation time T of gob-side roadway

Step 1.1) Determine the basic top equivalent parameter P and coal body equivalent parameter σ

The basic top equivalent parameter P is a comprehensive evaluation of the mechanical properties of rock mass, and its expression is as follows:

P=241.3ln(c ₀ )-15.5N+52.6h _m (6)

In the formula, C ₀ is the initial pressure step distance of the basic roof, N is the filling coefficient of the direct roof, and h _m is the mining height of the coal seam;

The coal equivalent parameter σ is a comprehensive evaluation of the mechanical properties of rock mass, and its expression is as follows:

In the formula, _σc is the uniaxial compressive strength of the coal body, GSI is the coefficient of coal fracture development degree, D is the mining influence index, and _mi is the constant of the coal body.

Step 1.2) Determine the weight coefficient

The corresponding weights of the two indicators are determined according to the basic top equivalent parameter P and the coal equivalent parameter σ, as shown in Table 1, where a is the weight occupied by T ₁ , and b is the weight occupied by T ₂ ;

Table 1 Distribution table of weight influencing factors

Step 1.3) Calculation of reasonable excavation time

Combining weight factors a and b into matrix A

The time T ₁ and T ₂ of gob-side coal roadway digging obtained in the first and second steps form a matrix B

Calculate the reasonable mining time T

Beneficial effects: 1) During the mining process of extra-thick coal seams above 15m, nearly a quarter of the coal seam cannot be extracted, and it will cascade down to the gob along with the direct roof and prevent the basic roof from sinking, because Significant differences in crushing properties and strength properties between the fractured coal mass and caving rock will significantly slow down the settlement trend of the overlying rock (about 35% to 45% reduction in the basic roof subsidence). The previous literature ignored the effect of caving coal mass and regarded it as rock mass uniformly, so the basic roof subsidence and overlying rock movement termination time are quite different from the actual situation. The present invention obtains the basic roof subsidence amount and the overlying rock movement stability time on the basis of fully considering the difference of coal and rock mass, which is more in line with the field reality and the result is more accurate. 2) In the past, the excavation time of gob-side roadway was based on the termination of overlying rock movement as a single judgment index. This patent is based on the basic roof settlement characteristic index, fully considers the mechanical properties of weak and low-strength coal and its failure and instability process, and innovates The deformation rate of the surrounding rock of the roadway is introduced as an additional index to form a double-index system for the excavation time of the gob-side coal roadway. The dual index not only takes into account the movement of overlying rock, but also fully considers the maintenance of surrounding rock of the roadway, which is more in line with the actual needs of the site. 3) In the past, the excavation time of the gob-side roadway was usually after the overlying rock movement of the adjacent working face was completely stabilized, that is, the basic roof subsidence reached the maximum value w _max , but this patent innovatively proposes 70% of the maximum basic roof subsidence value and the surrounding rock deformation rate <4mm/day are used as the evaluation index of roadway excavation time, and the weight ratio of the two is determined according to the specific geological conditions, and the excavation time of the gob-side roadway is obtained comprehensively. It can ensure the safety and stability of the surrounding rock of the gob-side roadway, and can effectively reduce the time for gob-side roadway digging in extra-thick coal seams, ensuring the normal replacement of mining.

Description of drawings

Figure 1 Location map of roadway deformation rate measuring station

Figure 2 Monitoring Section Layout

Figure 3 Roadway deformation rate curve

In the figure, 1. working face; 2, roadway for monitoring; 3, measuring station; 4, roof; 5, 6, two sides; 7, floor; distance from the bottom plate; b, the distance between the observation point of the roof and the bottom plate and the two sides.

Detailed ways

Step 1: Determine the excavation time T ₁ for gob-side entry with the basic roof subsidence as an index

(1) On-site investigation and indoor experiment

The 201 working face of a mine in Shanxi mainly mines 2# coal seam, with an average thickness of 15.0m. The immediate roof is sandy mudstone with an average thickness of 6.0m, and the basic roof is siltstone with an average thickness of 9.2m. The mine adopts fully mechanized caving mining technology for coal mining, the coal mining height is 3m, the coal setting height is 12m, and the coal recovery rate is 75%.

Laboratory experiments show that the coefficient of disintegration of the coal body is 1.3, the coefficient of dilation of the direct roof is 1.2, the modulus of elasticity of the basic roof is 4.39GPa, the modulus of viscosity of the basic roof is 85.34GPa, and the compressive strength of the caving direct roof is 63MPa. The compressive strength of the top coal is 17MPa.

(2) Substitute into formula (1) to get the maximum subsidence of the basic roof w _max

W _max =M+∑h-∑h·k ₁ -(1-α)M·k ₂ =15+6-6·1.2-(1-75%)·15·1.3=8.925

If the disintegration of the coal body is not considered, the maximum subsidence of the basic roof is 13.8m, which is much larger than the actual 8.925m. It can be seen that considering the coal release rate and the disintegration characteristics are more in line with the basic roof movement law.

(3) Substitute into formula (3) to get the comprehensive compressive strength of coal and rock after crushing is 13.38MPa

Substitute into formula (2) to get the dynamic equation of the basic top motion

w(t)＝6.27·(1-e ^-0.026t )

(4) Taking the basic roof sinking to 70% of the maximum value as the index, _T1 is obtained as 221 days.

Step 2: Determine the reasonable excavation time T ₂ based on the deformation of surrounding rock in the roadway

(1) Excavate the roadway 2 for monitoring on the adjacent side of the 201 working face 1; due to the intense movement of the overlying rock in the extra-thick coal seam and the long impact period, the distance L between the measuring station 3 and the stop line is greater than 1000m.

(2) The roadway monitoring section in the measuring station, as shown in Figure 2, set monitoring points on the monitoring section roof 4, two sides 5, 6, and bottom plate 7, respectively, to monitor the deformation of the middle of the roof and bottom, and the middle of the two sides, a , b is half of the height and width of the roadway. Arrange specialized technical personnel to record the deformation of the roadway roof and floor and the deformation of the two sides every day.

(3) Take the advancing position of the measuring station and the working face as the abscissa, and the approach speed of the roof, floor and two sides as the ordinate, draw a curve, as shown in Figure 3. The monitoring work starts 100m in front of the measuring station and ends when the working face pushes past the measuring station 1050m.

(4) Taking the roadway deformation rate reduced to 4mm/d as an index, it can be seen from Figure 3 that when the working face pushes through the working face for 875m, the roadway deformation rate is as low as 4mm/d.

(5) According to the advance speed of 3m/day in the working face of extra-thick coal seam, it is obtained that the time T ₂ required for the deformation rate to decrease to 4mm/d = 258 days.

Step 3: Determine the reasonable excavation time T of gob-side roadway

(1) Determine the basic top equivalent parameter P and coal body equivalent parameter σ

The initial pressing step distance _{C of} the basic roof is 30m, the filling coefficient N of the direct roof is 1.3, and the coal seam mining height h _m is 3m, which is substituted into (6):

P=241.3ln(c ₀ )-15.5N+52.6h _m =958

In laboratory experiments, the uniaxial compressive strength σ _c of the coal body is taken as 24 MPa, the coal fracture development degree coefficient GSI is taken as 90, the mining influence index D is taken as 0.6, and the coal body constant mi _is taken as 5, which are substituted into the formula (7):

(2) Determine the weight coefficient

P=958, σ=1.994, according to Table 1, it can be seen that a=0.4, b=0.6.

(3) Calculation of reasonable excavation time

Substituting relevant parameters into formula (8)

That is to say, the optimal and reasonable time for gob-side roadway digging is 263.6 days.

Claims (3)

1. A kind of extra-thick coal seam gobside coal roadway excavation time design method based on double index weighting method, it is characterized in that, comprises the following steps: The first step is to use the basic roof subsidence as an index to determine the excavation time T ₁ of gob-side entry Step 1.1) Field investigation and indoor experiment Investigate the basic roof, direct roof, coal thickness and coal seam recovery rate; the laboratory measures the immediate roof and coal disintegration coefficient, the elastic modulus and viscosity modulus of the basic roof rock layer; Step 1.2) Calculation of the maximum subsidence of the basic roof Considering the low recovery rate of the coal body during the mining process of the extra-thick coal seam and the differences in the disintegration and strength of the coal and rock mass, nearly 25% of the unmined coal body will caving along with the direct roof and inhibit the basic roof subsidence. Based on this, the maximum sinking amount W _max of the basic roof is determined, and its expression is as follows: W _max ＝M+∑h-∑h·k ₁ -(1-α)M·k ₂ (1) In the formula, M is the thickness of the mining coal seam, ∑h is the thickness of the immediate top rock layer, k ₁ is the disintegration coefficient of the caving rock mass, k ₂ is the disintegration coefficient of the cracked coal body, and α is the top-coal discharge rate, above 15m Extra thick coal seam α=75%; During the mining process of extra-thick coal seam, the expression of the dynamic equation of basic roof settlement is as follows:

In the formula, q _Z is the rock formation load on the basic roof, l _m is the fracture step distance of the basic roof, E and η are the elastic modulus and viscous modulus of the basic roof, and F is the comprehensive compression resistance of caving coal rock mass Intensity; the relationship of F is as follows:

In the formula, _F1 is the compressive strength of the caving rock mass, and _F2 is the compressive strength of the caving top-coal; The dynamic equation (2) belongs to an exponential function, and its derivative represents the subsidence rate of the basic roof; it can be known from the characteristics of the exponential function that the subsidence rate of the basic roof will gradually decrease as time increases, that is, when the subsidence of the basic roof reaches a certain When the critical index is reached, the subsidence rate of the basic roof will be greatly reduced and approach 0; combined with a large amount of engineering practice experience, 70% of the maximum subsidence of the basic roof is used as the critical index, and when the subsidence of the basic roof reaches 70% W _max critical When the index is reached, the subsidence movement of the basic roof will tend to be slow and stable, with a low movement rate, no violent structural movement, and little impact on the stability of the underlying rock mass, that is,

The second step is to use the deformation rate of the surrounding rock of the roadway as the time index to determine the excavation time T ₂ of the gob-side roadway Step 2.1) A monitoring station is established in front of the working face of the extra-thick coal seam, and the monitoring station is located within the production system range of the adjacent working face, rather than in the advanced roadway of the working face; Step 2.2) Install roof, floor and two side displacement monitoring equipment in the section of the monitoring station to ensure that the equipment can monitor the amount of surrounding rock movement in real time; Step 2.3) Take the advancing position of the monitoring station and the working face as the abscissa, and the moving speed of the roof, floor, and two sides as the ordinate, and draw a graph. The monitoring work starts at Ym in front of the monitoring station, and Y≥100m, until the deformation rate of the roadway decreases. End as small as 4mm/d; the deformation rate of the surrounding rock is less than 4mm/d, which means that the surrounding rock of the roadway is in a basically stable state; Step 2.4) According to the average advancing speed of the working face, obtain the time T ₂ required for the deformation rate to decrease to 4mm/d,

In the formula, S is the abscissa value when the deformation rate is reduced to 4mm/d, and v is the advancing speed of the working face; The third step is to determine the excavation time T along the gob-side roadway Step 3.1) Determine the basic top equivalent parameter P and coal body equivalent parameter σ The basic top equivalent parameter P is a comprehensive evaluation of the mechanical properties of rock mass, and its expression is as follows: P=241.3ln(c ₀ )-15.5N+52.6h _m (6) In the formula, c ₀ is the initial pressure step distance of the basic roof, N is the filling coefficient of the direct roof, and h _m is the mining height of the coal seam; The coal equivalent parameter σ is a comprehensive evaluation of the mechanical properties of rock mass, and its expression is as follows:

In the formula, _σc is the uniaxial compressive strength of the coal body, GSI is the coefficient of coal fracture development degree, D is the mining influence index, and _mi is the constant of the coal body; Step 3.2) Determine the weight coefficient Determine the corresponding weight factors a and b of the two indicators according to the basic top equivalent parameter P and the coal mass equivalent parameter σ, where a is the weight factor of T ₁ , and b is the weight factor of T ₂ ; Step 3.3) Calculation of reasonable excavation time Combining weight factors a and b into matrix A

The gob-side roadway excavation time T ₁ and T ₂ obtained in the first and second steps form a matrix B

Calculate the excavation time T of gob-side roadway

2. A method for designing the excavation time of gob-side coal roadways in extra-thick coal seams based on the double-index weighting method according to claim 1, characterized in that a monitoring station is established at Ym in front of the working face of extra-thick coal seams, and Y≥100m. 3. A method for designing excavation time of gob-side coal roadway in extra-thick coal seam based on double index weighting method according to claim 1, characterized in that, in step 2.2), the monitoring equipment is a measuring rod or a measuring line.

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