WO2023000837A1

WO2023000837A1 - Deep stope overburden rock type evaluation standard, and thickening reformation design method for thin bedrock

Info

Publication number: WO2023000837A1
Application number: PCT/CN2022/096738
Authority: WO
Inventors: 张广超; 陶广哲; 李友; 左昊
Original assignee: 山东科技大学
Priority date: 2021-07-22
Filing date: 2022-06-02
Publication date: 2023-01-26
Also published as: JP2023535664A; CN113569401A; CN113569401B

Abstract

A deep stope overburden rock type evaluation standard and a thickening reformation design method for a thin bedrock. First, on the basis of the principle of stress arch formation, a critical thickness at which a stable stress arch can be formed in a bedrock is determined, and then a deep stope overburden rock type evaluation standard is established, such that the gap in terms of evaluation standards for overburden rock structure types in deep, thick loose layer and significantly varied bedrock thickness stratum conditions is filled. On the basis of the standards, a bedrock thickening reformation design solution for ultra-thin bedrock and thin bedrock stratum conditions is provided, which comprises the length, thickness, etc. of an area subjected to thickening reformation design; and finally, a thin bedrock thickening reformation design method is provided, and a multi-plane inclined top forward grouting solution and a construction method are provided; and parameters such as a drilling layout and a grouting material are designed, such that the active control of a stope disaster accident can be achieved, and a disaster accident caused by a previous passive stope control measure is avoided.

Description

Overlying strata type evaluation standard for deep buried stope and design method for thin bedrock thickening reconstruction

technical field

The invention relates to the field of mine pressure and strata control, in particular to the evaluation standard for overlying rock types in deep buried stopes and the design method for thickening and transforming thin bedrock.

Background technique

With the large-scale mining in recent decades, the shallow buried coal resources in eastern my country (Shandong, Anhui, Henan, Hebei) are almost exhausted, and mines are mining deep buried coal resources under the conditions of Quaternary thick loose layers and thin bedrock. . On-site geological exploration in the eastern region shows that the thickness of the bedrock overlying the deeply buried coal seam varies greatly. The bedrock thickness in some areas is only a dozen meters thick, and the bedrock thickness in some areas reaches hundreds of meters. The law of mine pressure in the stope and the mine pressure caused by it are very different, and the influence of the stability control of the stope surrounding rock is significantly different. However, through literature search, it is found that there are two defects in the classification of stope overlying rock and its movement disaster control under such stratum conditions:

(1) At present, there is no research on the evaluation criteria of stope overlying rock types under the conditions of this type of stratum (deep burial, thick unconsolidated bed, significant change in bedrock thickness). The existing stope overburden classification and evaluation system mainly focuses on shallow buried strata conditions (buried depth ≤ 200m), and only uses the three zones of the stope as indicators for classification, and the evaluation method does not consider the formation of stress arches caused by overlying rock movement. and maintain stable mechanical conditions.

(2) As we all know, when the bedrock reaches a certain thickness, the rock formation will form an arch structure during the sinking process, which has a protective effect on the lower stope; when the bedrock thickness is small, such an arch protection structure cannot be formed, resulting in Accidents such as end face caving and chipping occurred. In order to reduce disasters and accidents under the condition that the bedrock is too thin to form an arch, the current measures are mainly coal-rock reinforcement and grouting at the end face, but these measures are all carried out in the working face stope covered by bedrock. It is a passive control measure. In fact, the structure and movement of the overlying strata in the stope is the fundamental driving force for stope accidents. At present, there are no active control measures from the perspective of overburden structural transformation.

Contents of the invention

In view of the stratum condition that the key layer cannot be formed in the upper rock stratum of the coal seam, this patent proposes an evaluation standard for the overlying strata type of the deep buried stope and a design method for thickening and reforming the thin bedrock. First, based on the principle of stress arch formation, determine the critical thickness that can form a stable stress arch in the bedrock, and then establish the evaluation criteria for overlying rock types in deep-buried stopes; then, based on the established evaluation criteria, for ultra-thin bedrock and thin According to the stratum conditions, the design plan for thickening and reconstruction of bedrock is proposed, including the length and thickness of the design area for thickening and reconstruction; finally, the design method for thickening and reconstruction of thin bedrock is proposed, including drilling layout and parameters, grouting materials, grouting Pressure, grouting time, process, labor organization, etc.

An evaluation standard for the type of overlying rock in a deep buried stope and a design method for thickening and reforming thin bedrock, comprising the following steps:

The first step is the evaluation standard of overlying rock type in deep buried stope

Step 1.1) Determine the critical arch thickness at which the bedrock stress arch remains stable

When a stable stress arch can be formed in the bedrock, the critical arch thickness expression of the stress arch is:

In the formula, D _arch is the thickness of the stress arch; H _arch is the height of the stress arch; l _arch is the span of the stress arch; q(x) is the uniform load of the overlying rock layer on the bedrock; included angle; R is the vertical stress on the arch foot; T is the horizontal stress on the arch foot; the expressions of R and T are:

Among them, the stress arch height H _arch is taken as the height from the coal seam to the key layer; the stress arch span l _arch is taken as the periodic pressure step distance; ~0.7) times the cycle to press the step distance; θ is 5~10° according to the empirical value;

Step 1.2) Determine the critical bedrock thickness capable of forming a stress arch

The minimum thickness that can form a stable stress arch in the bedrock is called the critical bedrock thickness, and its expression is as follows:

∑H _min ＝D _arch +∑H _c +∑H _L (4)

In the formula, ∑H _min is the critical bedrock thickness that can form a stress arch; D _arch is the critical arch thickness; ∑H _c is the height of the _caving zone; _∑H _L is the height of the fracture zone; To investigate the lithological strength of the overlying rock, select the empirical formula in Table 1 to calculate the height of the stope caving zone and fracture zone.

Table 1. Formulas for determining the height of caving zone and fissure zone

Step 1.3) Overburden Type Evaluation Criteria for Deep Buried Stopes

The stopes are classified into ultra-thin bedrock, thin bedrock and normal bedrock based on the relative relationship between the overburden collapse zone height ∑Hc, fissure zone height ∑H _f , stress arch thickness D _arch and bedrock thickness ∑h rock; according to the degree of mine pressure in the stope under the occurrence conditions of ultra-thin bedrock, thin bedrock and normal bedrock, it is necessary to thicken the ultra-thin bedrock and thin bedrock strata;

The second step is the ultra-thin bedrock and thin bedrock area thickening reconstruction design scheme

Step 2.1) Determine the ultra-thin bedrock and thin bedrock thickening reconstruction area and design size;

Step 2.1.1) Using multiple boreholes to carry out geological exploration on the surface to obtain rock formation columnar diagrams in different regions;

Step 2.1.2) According to the change of bedrock thickness, the area where the bedrock thickness is less than ∑H _min is determined as the design area for thickening reconstruction.

Step 2.1.3) Determine the design strike length w and dip length l of the thickening and reconstruction area, w is the extension length of the thin bedrock area along the coal seam strike, and l is the dip length of the working face.

Step 2.1.4) Determine the thickness D of the design area for thickening and reconstruction as:

D＝∑H _min -∑H (6)

In the formula, D is the thickness of the thickening design reconstruction area; ∑H _min is the critical bedrock thickness that can form stress arch; ∑H is the actual bedrock thickness;

Step 2.2) Ultra-thin bedrock and thin bedrock area thickening reconstruction construction plan

Step 2.2.1) Excavate the grouting roadway along the coal seam direction

At the height of 1.5D from the bedrock, at the place where the inclination length of the thickening design and reconstruction area is 1/2, a grouting roadway is excavated along the coal seam direction, and the cross-sectional size of the roadway is 3m high × 4m wide;

Step 2.2.2) Layout the grouting pipeline

Adopt multi-horizontal inclined top synchronous grouting scheme. During the implementation process, hydraulic drilling rigs are used to drill inclined holes from the floor of the grouting roadway, and the angle between the inclined holes and the horizontal plane is adopted.

The vertical height is 1.5D, the distance between adjacent drilling holes along the working face is 50-80m, and the diameter of inclined drilling holes is 56-80mm; Right above the starting position, in the design area for thickening and reconstruction, the inclined boreholes are divided into multiple horizontal planes from bottom to top, and the adjacent horizontal and vertical distances are d, 4m≤d≤6m;

In a single horizontal plane, take the intersection of the inclined borehole and the horizontal plane as the center point, and arrange four divergent vertical horizontal boreholes around it, of which two boreholes are arranged along the inclination of the working face, and two boreholes are arranged along the direction of the working face; According to the size of the working face, the length of the horizontal drilling is determined to be 1/4, and the diameter of the drilling is 56-80mm.

Step 2.2.3) Determination of grouting material and grouting amount

Select different grouting materials and proportions according to the crack rate of the loose layer. The selection of grouting materials is shown in the following table:

Table 2 Selection list of grouting materials

According to the size of the design area for thickening reconstruction determined in step 2.1), taking into account the degree of cracks in the rock formation and the filling rate of grout, the formula for calculating the grouting quantity Q is:

In the formula, λ is the grouting loss coefficient; V is the grouting volume; η is the crack rate; ε is the grout filling rate; m is the grouting stone rate; the expression of the grouting volume V is:

V＝lwD (8)

In the formula, l is the inclined length of the design area for thickening and reconstruction; w is the strike length of the design area for thickening and reconstruction; D is the thickness of the design area for thickening and reconstruction of thin bedrock;

The formula for calculating the grouting time T is:

In the formula, T is the time of grouting; Q is the total amount of grouting; c is the amount of grouting per hour; n is the number of grouting levels;

The third step is ultra-thin bedrock and thin bedrock area thickening reconstruction grouting method

Use a high-pressure pump to grout the horizontal borehole in the first horizontal plane, and the grouting time T is determined by formula (9); after the horizontal grouting in the first horizontal plane is completed, let it stand for 5 to 7 hours; continue to extend the inclined grouting hole to The second horizontal plane, and complete the grouting operation according to the horizontal grouting procedure in the first horizontal plane, and complete all the drilling and grouting operations in the entire working face according to the above steps.

Beneficial effects: (1) Based on the principle of stress arch formation mechanics, the present invention proposes a critical arch thickness expression for stable stress arch in bedrock, determines the critical bedrock thickness expression for bed rock to form a stable stress arch, and forms a deep The overburden type evaluation standard for buried stopes makes up for the gap in the overlying rock structure type evaluation standard for deep burial, thick unconsolidated layers, and significant changes in bedrock thickness.

(2) Based on the established critical bedrock thickness expression and the overlying rock type evaluation standard for deep buried stopes, the present invention realizes the quantitative and accurate quantification and accuracy of the design area dimensions for thin bedrock reconstruction in engineering practice: strike length, dip length, and thickness The computerized calculation improves the feasibility of implementing the bedrock reconstruction plan.

(3) From the perspective of overlying rock structure transformation, a multi-horizontal inclined top grouting scheme and construction method are proposed, and parameters such as drilling layout and grouting materials are designed. The scheme is reasonable in design and strong in operability , can realize active control of stope disaster accidents, and avoid disaster accidents caused by passive control measures in the stope in the past.

(4) A structure type evaluation and transformation system for overburden strata in deep buried stopes is proposed, which integrates the calculation of critical thickness of bedrock stress arch, overburden strata identification standard, overburden strata reconstruction scheme, and on-site construction technology. From theoretical design to field application, In-depth, cohesive, reasonable structure, clear thinking, and practical research plan.

(5) The grouting transformation technology can effectively avoid accidents of coal and rock roof fall and slabs at the end of the stope under the conditions of ultra-thin bedrock and thin bedrock stratum, improve the stability of the surrounding rock of the stope, reduce the cost of accident treatment, and ensure the normal mining of coal .

Description of drawings

Figure 1 is a schematic diagram of the pressure arch structure.

Figure 2a is a front view of the location of the thin bedrock thickening area.

Fig. 2b is a sectional view along line A-A of Fig. 3a.

Fig. 2c is a B-B sectional view of Fig. 3a.

Fig. 3a is the inclined geological profile of the 3301 working face of a certain mine in Example 1.

Fig. 3b is a histogram of drill holes in the ABCD area of the 3301 working face of a certain mine in Example 1.

Fig. 4a is a perspective view of the multi-horizontal inclined top synchronous grouting scheme in Embodiment 1.

Fig. 4b is a perspective view of a single grouting pipeline in Embodiment 1.

Fig. 4c is a front plan view of a single grouting pipeline in Embodiment 1.

Fig. 4d is a top plan view of a single grouting pipeline in Embodiment 1.

In the figure, 1-coal seam; 2-thin bedrock thickening area; 3-thin bedrock; 4-thick loose layer; 5-cutting hole of working face; 6-grouting roadway; ; w - design width of thickened and reconstructed area; ∑H _min - critical thickness of bedrock forming stress arch; ∑H - thickness of thin bedrock; D - design thickness of thickened and reconstructed area;

- The angle between the inclined borehole and the horizontal plane.

detailed description

The present invention will be further described below in conjunction with embodiment.

Example 1

On-site investigation of the 3301 working face of the Eastern Coal Mine mainly mines the 3# coal seam. The overlying rock of the coal seam is a weak rock stratum with an average thickness of 6m and a periodic pressure step of 37m, that is, the span of the stress arch is l _arch = 37m; the height of the rock arch is H _arch = 8m; q (x) is taken as 1.5x, x is taken as 25m; θ is taken as 5-10° according to the empirical value; the angle between the vertical section and the normal section of the rock arch is θ=5°, the grouting loss coefficient λ is taken as 1.1; the grout filling rate ε, Take 0.75; the grout firming rate m, take 0.85; the grouting volume c per hour, take 1500m ³ /h. The stress arch structure is shown in Figure 1.

Substituting the above parameters into the formulas (1), (2) and (3) to determine the critical arch thickness of the stress arch:

The coal seam overlying rock of the 3301 working face belongs to the weak rock formation, and the height of the caving zone, the fracture zone and the critical thickness of the stress arch can be obtained by looking up the empirical formula in Table 1:

∑H _min ≥D _arch +∑H _c +∑H _L ＝47.2m

Step 1.3) Overburden Type Evaluation Criteria for Deep Buried Stopes

Using the relative relationship between the height of the two zones of the overlying rock, the critical arch thickness of the stress arch and the thickness of the bedrock, the overburden of the 3301 working face is classified as follows:

(1) When the bedrock thickness is less than 10.78m, it is defined as ultra-thin bedrock;

(2) When the bedrock thickness is greater than 10.78m and less than 47.2m, it is defined as thin bedrock;

(3) When the bedrock thickness is greater than 47.2m, it is defined as normal bedrock.

Step 2 Design method for thickening reconstruction of thin bedrock area

Step 2.1) Determine the thickened reconstruction area and design size

Step 2.1.1) The inclined geological profile of the 3301 working face obtained from the geological survey from the cutting hole to the production stop line, as shown in Figure 3a; and the drilling histogram in the ABCD area, as shown in Figure 3b.

Step 2.1.2) According to the bedrock thickness change shown in the strata column diagram, the average thickness of the bedrock in the ABCD area is 35m, which is less than ∑H _min = 47.2m and greater than ∑H _c = 10.78m. According to the type evaluation standard, it belongs to the thin bedrock area, which needs to be thickened and reconstructed. The structural diagram of the thin bedrock thickened area is shown in Figure 2a-2c.

Step 2.1.3) According to the size of the ABCD area, determine the strike length w=150m and the dip length l=100m in the thickening reconstruction area.

Step 2.1.4) Determine the thickness of the design area for thickening and reconstruction

Substitute the data into formula (6) to obtain the design thickness D of the thickened area:

D＝∑H _min -∑H＝47.2-35＝12.2m

Step 2.2) Design and construction plan for thickening reconstruction of thin bedrock area

Step 2.2.1) excavate the grouting roadway

At a height of 18.3m from the bedrock, and at a place with a dip length of 50m in the design and reconstruction area of thin bedrock thickening, a grouting roadway is excavated along the coal seam. The cross-sectional size of the roadway is 3m high×4m wide;

Step 2.2.2) Arrange the grouting pipeline (as shown in Figure 4a, 4, 4c, 4d)

The multi-horizontal inclined top grouting scheme is adopted, and inclined drilling holes are added in the grouting roadway to the bottom plate. The angle between the inclined drilling holes and the horizontal plane is 30°, and the vertical height is 18.3m. The direction of adjacent drilling holes along the direction of the working face The spacing is 60m, and the diameter of the inclined borehole is 65mm; in the thin bedrock thickening reconstruction design area, the inclined borehole is divided into two horizontal planes from bottom to top, and the vertical distance between adjacent horizontal planes is 5m.

In a single horizontal plane, arrange four divergent vertical horizontal boreholes (A ₁₁ , A ₁₂ , A ₁₃ , A ₁₄ ) around the inclined boreholes, two of which are According to the layout of the face direction, the horizontal drilling length is determined to be 25m and the diameter of the drilling hole is 65mm according to the size of the working face.

Step 2.2.3) Determination of grouting material and grouting amount

Root is the result of on-site investigation. The fracture rate of the loose layer in the 3301 working face is 60%, which belongs to the rock layer with medium fracture rate. According to the grouting material table, the grouting material is a mixture of group A and B materials, of which group A is composed of sulfate cement, and group B is composed of Divided into lime and gypsum, the ratio is 1.3:1.

According to step 2.1), the size of the design area for thin bedrock reconstruction is calculated, and the data are substituted into formulas (7), (8), and (9) to obtain:

V=lwD=150×100×12.2=183000m ³

The third step is the grouting method for thickening and reforming the thin bedrock area

The design of thin bedrock thickening reconstruction is completed before coal seam mining in this area. The first grouting hole is located directly above the starting position of the thin bedrock thickening reconstruction design area. During the implementation, hydraulic drilling rigs and self-grouting roadways are used Drill the inclined grouting holes upward on the bottom plate, and after reaching point A1 _on the _first horizontal plane, take point A1 as the center point, and drill holes _A11 , _A12 , _A13 , _A14 in the horizontal circumferential direction around it; use high-pressure pump to Grouting in the horizontal borehole at the first level, the grouting time is 23.6 hours.

After finishing the horizontal grouting on the first level, let it stand still for 5-7 hours; continue to extend the inclined grouting hole to the second level, and then use point A in the _second level as the center point, and drill holes A horizontally and circumferentially evenly around it ₂₁ , A ₂₂ , A ₂₃ , A ₂₄ , and follow the horizontal grouting procedure on the first level, the grouting time is 23.6 hours, and stand still for 5-7 hours, and complete all the drilling and grouting operations in the entire working face according to the above steps.

Claims

An evaluation standard for the type of overlying rock in a deep buried stope and a design method for thickening and reforming thin bedrock, characterized in that it includes the following steps:

The first step is the evaluation standard of overlying rock type in deep buried stope

Step 1.1) Determine the critical arch thickness at which the bedrock stress arch remains stable

When a stable stress arch can be formed in the bedrock, the critical arch thickness expression of the stress arch is:

In the formula, D arch is the thickness of the stress arch; H arch is the height of the stress arch; l arch is the span of the stress arch; q(x) is the uniform load of the overlying rock layer on the bedrock; included angle; R is the vertical stress on the arch foot; T is the horizontal stress on the arch foot; the expressions of R and T are:

Among them, the stress arch height H arch is taken as the height from the coal seam to the key layer; the stress arch span l arch is taken as the periodic pressure step distance; ~0.7) times the cycle to press the step distance; θ is 5~10° according to the empirical value;

Step 1.2) Determine the critical bedrock thickness capable of forming a stress arch

The minimum thickness that can form a stable stress arch in the bedrock is called the critical bedrock thickness, and its expression is as follows:

∑H min ＝D arch +∑H c +∑H L (4)

In the formula, ∑H min is the critical bedrock thickness that can form a stress arch; D arch is the critical arch thickness; ∑H c is the height of the caving zone; ∑H L is the height of the fracture zone; The lithological strength of the overlying rock is investigated, and empirical formulas are selected to calculate the height of the stope caving zone and fracture zone;

Step 1.3) Overburden Type Evaluation Criteria for Deep Buried Stopes

The stopes are classified into ultra-thin bedrock, thin bedrock and normal bedrock based on the relative relationship between the overburden collapse zone height ∑Hc, fissure zone height ∑H f , stress arch thickness D arch and bedrock thickness ∑h rock; according to the degree of mine pressure in the stope under the occurrence conditions of ultra-thin bedrock, thin bedrock and normal bedrock, it is necessary to thicken the ultra-thin bedrock and thin bedrock strata;

Step 2 Design plan for thickening and reconstruction of ultra-thin bedrock and thin bedrock areas

Step 2.1) Determine the ultra-thin bedrock and thin bedrock thickening reconstruction area and design size;

Step 2.1.1) Using multiple boreholes to carry out geological exploration on the surface to obtain rock formation columnar diagrams in different regions;

Step 2.1.2) According to the change of bedrock thickness, it is determined that the area where the bedrock thickness is less than ∑H min is the design area for thickening reconstruction;

Step 2.1.3) Determine the design strike length w and the dip length l of the thickened and reconstructed area, where w is the extension length of the thin bedrock area along the coal seam strike, and l is the dip length of the working face;

Step 2.1.4) Determine the thickness D of the design area for thickening and reconstruction as:

D＝∑H min -∑H (6)

In the formula, D is the thickness of the thickening design reconstruction area; ∑H min is the critical bedrock thickness that can form stress arch; ∑H is the actual bedrock thickness;

Step 2.2) Ultra-thin bedrock and thin bedrock area thickening reconstruction construction plan

Step 2.2.1) Excavate the grouting roadway along the coal seam direction

Step 2.2.2) Layout the grouting pipeline

A multi-horizontal inclined top grouting scheme is adopted. During the implementation process, a hydraulic drilling rig is used to drill downwards from the floor of the grouting roadway to drill inclined holes. The first grouting hole is located directly above the starting position of the thickening reconstruction design area. In the design area of thickening reconstruction, the inclined borehole is divided into multiple horizontal planes from bottom to top;

In a single horizontal plane, take the intersection of the inclined borehole and the horizontal plane as the center point, and arrange four divergent vertical horizontal boreholes around it, of which two boreholes are arranged along the inclination of the working face, and two boreholes are arranged along the direction of the working face;

The third step is ultra-thin bedrock and thin bedrock area thickening reconstruction grouting method

Use a high-pressure pump to grout the horizontal borehole in the first horizontal plane; the grouting time T is determined by formula (9); after the horizontal grouting in the first horizontal plane is completed, let it stand for a while; continue to extend the inclined grouting hole to the second The horizontal plane, and complete the grouting operation according to the horizontal grouting procedure in the first horizontal plane, and complete all the drilling and grouting operations on the entire working face according to the above steps.
According to claim 1, a deep buried stope overburden type evaluation standard and thin bedrock thickening reconstruction design method is characterized in that, in step 1.2), the caving zone height ΣHc and the fissure zone height ΣHf are The calculation formula is:

When the lithology of the overlying rock is hard rock formation and the uniaxial compressive strength is 40-80MPa

When the lithology of the overlying rock is medium-hard rock formation and the uniaxial compressive strength is 20-40MPa,

When the lithology of the overlying rock is weak and the uniaxial compressive strength is 10-20MPa,

When the lithology of the overlying rock is extremely weak and the uniaxial compressive strength is less than 10MPa,
According to claim 1, the overburden type evaluation standard for deep buried stope and the design method for thickening and reconstruction of thin bedrock are characterized in that, in step 1.3), the overlying rock classification method for deep buried stope is:

(1) When the bedrock thickness Σh is less than the caving zone height ΣHc, it is defined as ultra-thin bedrock;

(2) When the bedrock thickness Σh is greater than the caving zone height ΣHc and less than the sum of the caving zone height ΣHc, the fissure zone height ΣHf and the stress arch thickness D arch , it is defined as thin bedrock;

(3) When the bedrock thickness Σh is greater than the sum of the collapse zone height ΣHc, the fissure zone height ΣHf and the stress arch thickness D arch , it is defined as normal bedrock.
According to claim 1, a deep buried stope overburden type evaluation standard and thin bedrock thickening reconstruction design method is characterized in that, in step 2.2.1), at a height of 1.5D from the bedrock, add Thick design and reconstruction area dips to 1/2 of the length, and the grouting roadway is excavated along the coal seam. The cross-sectional size of the roadway is 3m high x 4m wide.
According to claim 1, a deep buried stope overburden type evaluation standard and thin bedrock thickening reconstruction design method is characterized in that, step 2.2.2) the angle between the inclined borehole and the horizontal plane
20°～40°, the vertical height is 1.5D, the distance between adjacent inclined drilling holes along the working face is 50～80m, and the diameter of inclined drilling holes is 56～80mm; the vertical distance between adjacent horizontal planes is d, 4m≤d≤ 6m; according to the size of the working face, the length of the horizontal drilling is l/4, and the diameter of the drilling is 56-80mm.
According to claim 1, a deep buried stope overburden type evaluation standard and thin bedrock thickening reconstruction design method is characterized in that the selection and proportioning of grouting materials in step 2.2.3) is determined by the type of fracture ratio and porosity determined by:

In the case of high crack rate and porosity of 75%-100%, the grouting material is ordinary cement slurry;

In the case of medium porosity and porosity of 50%-75%, the grouting material is mixed with group A and group B materials, wherein group A consists of sulfate cement, group B consists of lime and gypsum, and the ratio is 1.3:1;

In the case of low crack rate and porosity of 30%-50%, the grouting material is cement-water glass double slurry;

In the case of extremely low porosity and porosity less than 30%, the grouting material is water glass-calcium chloride slurry.
According to claim 1, an evaluation standard for overlying rock type in a deep buried stope and a design method for thickening and reforming thin bedrock, it is characterized in that in the third step, after the horizontal grouting, the method is left to stand for 5 to 7 hours respectively.