Open slope fractured rock mass advanced grouting reinforcement method

Abstract

The invention discloses an advanced grouting reinforcement method for fractured rock mass of an open slope, and belongs to the technical field of open-pit mine mining. The method comprises the following steps: firstly, establishing a fracture density characterization model by quantifying fracture density, and determining a fractured rock mass area; secondly, converting the fracture density characterization model into a mechanical parameter characterization model, non-uniformly assigning mechanical parameters to each unit grid in the slope numerical model, and simulating and determining an area to be reinforced; and in the area needing to be reinforced, grouting holes with equal intervals are constructed in an array mode perpendicular to the final boundary platform, segmented pressurized grouting is conducted in the grouting holes from the bottom, and the advanced grouting reinforcing structure is formed. The fractured rock masses to be exposed are bonded into a whole by filling the cracks with the cement mortar, blasting excavation disturbance is jointly borne, the stability of the side slope is improved, and the method has the advantages of being simple in construction process, low in cost, high in construction efficiency and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of open-pit mining, and particularly relates to a method for advance grouting reinforcement of broken rock mass of open-pit slope. BACKGROUND

[0002] Traditional open-pit slope support methods include single support methods such as soil nails, anchor rods (cables), anti-slide piles, and combined support methods such as lattice beams and anchor rods (cables). However, these traditional support methods are implemented after the formation of the final boundary slope of the open-pit mine. The slope support operation at this time often affects the continuous production of mining, resulting in reduced production efficiency. At the same time, due to the irreversible structural damage of the final boundary slope under the action of multiple blasting disturbances, the strength of the rock mass itself is significantly reduced. During the construction of the support structure, the slope is in an unstable state, and there is a high risk of landslides. On the one hand, this directly threatens the safety of on-site workers, and on the other hand, if a landslide accident occurs during the support process, it will not only increase the cost of support and reinforcement, but also prolong the support period, further affecting the overall mining progress and economic benefits.

[0003] The existing advance reinforcement method usually uses single assignment for the mechanical parameters of the numerical model when identifying the potential sliding surface. Due to the non-uniformity of the mechanical parameters of the rock mass in real engineering, the identification accuracy of the potential sliding surface is often insufficient when the mechanical parameters in the numerical model are assigned singly, which makes the reinforcement method not fully applicable to engineering. In addition, the existing advance reinforcement technology uses steel and concrete as the advance reinforcement structure, which has a complex construction process and is not conducive to on-site construction operation. Moreover, the steel will be chemically corroded in the wet concrete, affecting the strength of the later support and shortening the service period. SUMMARY

[0004] The present application provides a method for advance grouting reinforcement of broken rock mass of open-pit slope, which identifies the broken rock mass before the final slope is exposed and performs advance grouting reinforcement on the corresponding position of the slope. The cement mortar bonds the broken rock mass to be exposed into a whole by filling the cracks, and bears the blasting excavation disturbance together, improving the stability of the slope.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] A method for advance grouting reinforcement of broken rock mass of open-pit slope, comprising the following steps:

[0007] Step 1: Advance identification of broken rock mass area: identify the pre-splitting hole exposed cracks, quantify the crack density change with depth in each pre-splitting hole; construct a slope crack density representation model for the final mining boundary with each pre-splitting hole as the control line; extract the area with crack density exceeding the preset critical value as the broken rock mass area.

[0008] Step 2, determining the pre-reinforcement area: after converting the fracture density into the geological strength index (GSI), the fracture density characterization model is converted into a mechanical parameter characterization model by introducing the Hoek-Brown strength criterion; a numerical simulation software is used to construct a numerical model of the slope in the broken rock mass region and divide the unit grid; based on the mechanical parameter characterization model, the mechanical parameters corresponding to each unit grid are determined, and the unit grid is valued; the position of the potential sliding surface and the safety factor of the slope are simulated and determined, and the area with a safety factor less than the preset threshold is determined as the area to be reinforced.

[0009] Step 3, implementing the pre-grouting reinforcement scheme: in the area to be reinforced, the grouting holes are constructed in an array perpendicular to the final boundary platform with an equal interval, and the segmented pressurized grouting is carried out from the bottom in the grouting hole, and the final grouting height is leveled with the final boundary platform, forming a pre-grouting reinforcement structure.

[0010] Further, in step 1, the pre-splitting hole revealed fissures in the image are identified by collecting the image in the pre-splitting hole.

[0011] Further, in step 1, the preset critical fracture density is 5 / m.

[0012] Further, in step 2, the distance power inverse ratio method is used to determine the mechanical parameters corresponding to each unit grid.

[0013] Further, in step 2, the safety factor preset threshold is 1.3.

[0014] Further, in step 3, the determination process of the pre-grouting reinforcement scheme is: the parameters to be determined in the scheme include the interval distance of the grouting hole, the drilling diameter and the drilling depth, the value range of each parameter is set, the parameter points are taken in the value range, and a plurality of groups of alternative schemes are formed by arranging and combining; according to the arrangement of the grouting hole in the slope numerical model constructed in step 2, the safety factor of the slope at different time after the grouting of the grouting hole is simulated, and the safety factor after reinforcement reaches the safety factor preset threshold as the standard, the scheme parameters and the step exposure time node are determined, the number of grouting holes is determined according to the interval distance, the length and pressure of each section of grouting are determined according to the relevant operation procedures, and the final implementation scheme is obtained. The interval distance value range is 1200mm~2000mm, the drilling diameter value range is 400mm~700mm, and the drilling depth needs to extend at least 5m below the potential sliding surface.

[0015] The beneficial effects of the present application are:

[0016] This invention features simple construction process, low cost, and high construction efficiency. Using the method of this invention, the fractured rock mass is identified before the final slope exposure, and the slope at the corresponding location is pre-grouted and reinforced. Cement mortar fills the cracks, bonding the fractured rock mass to be exposed into a whole, jointly bearing the disturbance of blasting excavation and improving the stability of the slope. Attached Figure Description

[0017] Figure 1 A schematic diagram of a cross-section for pre-grouting reinforcement of fractured rock mass on an open slope.

[0018] Figure 2 Plan view of the advanced grouting drilling scheme;

[0019] In the figure: 1-rock mass to be excavated, 2-final boundary, 3-pre-splitting hole, 4-pre-splitting hole revealing fissures, 5-grouting hole, 6-final boundary platform, 7-potential sliding surface, 8-grouting hole revealing fissures, 9-advanced grouting reinforcement structure. Detailed Implementation

[0020] The present invention will be further described in conjunction with the following embodiments.

[0021] like Figures 1-2 As shown, this embodiment takes the Wushan East Step as an example, with a step height of 30m, to further illustrate the invention. A method for pre-grouting reinforcement of fractured rock mass on an open slope includes the following steps:

[0022] Step 1, proactively identify fractured rock mass areas:

[0023] Using the pre-splitting holes 3 constructed in advance, the exposed fractures 4 of the pre-splitting holes 3 are identified through images acquired by borehole television. The fracture density within each pre-splitting hole 3 is quantified as a function of depth, where fracture density refers to the number of fractures 4 exposed per unit length. Using each pre-splitting hole 3 as a control line, and combining geostatistical methods, the fracture density of the entire area within the final mining boundary is interpolated based on the fracture density of each pre-splitting hole 3 to construct a slope fracture density characterization model. Areas exceeding the preset critical fracture density are identified as fractured rock mass areas. Specifically, in this embodiment, the geostatistical method used is the Kriging method, and the critical fracture density is set to 5 fractures / m.

[0024] Step 2, determine the area to be reinforced in advance:

[0025] For the fractured rock mass region identified in step 1, based on the fracture density characterization model thereof, the fracture density is converted into GSI according to the conversion relationship between fracture density and GSI; the GSI is substituted into the Hoek-Brown strength criterion, and finally the fracture density characterization model is converted into a mechanical parameter characterization model of the fractured rock mass region, the involved mechanical parameters including compressive strength, tensile strength, internal friction angle, elastic modulus, Poisson's ratio, shear modulus and deformation modulus.

[0026] By using the numerical simulation software FLAC3D, a numerical model of the slope in the fractured rock mass region is constructed and the element grid is divided; based on the mechanical parameter characterization model, the distance inverse power method is used to determine the mechanical parameters corresponding to each element grid, and the element grid is valued, the position of the potential sliding surface 7 and the safety factor of the slope are simulated and determined, and the region with a safety factor less than a preset threshold is determined as the region to be reinforced; in the embodiment, the safety factor preset threshold is 1.3. The mechanical parameters valued in the numerical model of the slope obtained in this way have non-uniformity, which is more in line with the actual engineering and improves the prediction and identification accuracy of the potential sliding surface 7.

[0027] Step 3, implement the advanced grouting reinforcement scheme:

[0028] In the region to be reinforced, the grouting holes 5 are constructed in an array perpendicular to the final boundary platform 6 with equal spacing, and the segmented pressurized grouting is performed in the grouting holes 5 from the bottom, and the final grouting height is leveled with the final boundary platform 6, forming an advanced grouting reinforcement structure 9;

[0029] The determination process of the advanced grouting reinforcement scheme is as follows: the parameters to be determined in the scheme include the spacing of the grouting holes 5, the drilling diameter and the drilling depth, the value intervals of the parameters are set, the parameter points are taken in the value intervals at intervals, and multiple groups of alternative schemes are formed by permutation and combination; wherein the spacing value interval is 1200mm~2000mm, the drilling diameter value interval is 400mm~700mm, and both are taken at intervals of 100mm, and the drilling depth is determined according to the position of the potential sliding surface 7, and needs to extend at least 5m below the potential sliding surface 7; according to the arrangement of the grouting holes 5 in the numerical model of the slope constructed in step 2, based on the change rule of the slurry distribution range and the slurry strength with time, the safety factor of the slope at different time lengths after the slurry injection under each alternative scheme is simulated, and the reinforced safety factor reaches the safety factor preset threshold as the standard, the scheme parameters and the step exposure time node are determined, the number of grouting holes 5 is determined according to the spacing, and the length and pressure of each section of grouting are determined according to the relevant operation procedures, and the final implementation scheme is obtained, as shown in Figure 1 and Figure 2 .

[0030] Specifically, in this embodiment, the final determined advanced grouting reinforcement scheme is as follows: Before the exposure of the fractured rock mass at the final boundary 2, in the area requiring reinforcement, 36 grouting holes 5 are constructed perpendicular to the final boundary platform 6 in a 3×12 array with equal spacing. The hole diameter is 600mm, and the hole depth is 20m. Based on experience and relevant regulations, segmented pressurized grouting is adopted during grouting. Starting from the bottom of the grouting hole 5, the concrete is grouted in three segments from bottom to top. The grouting pressure of each segment is determined according to the corresponding hole depth. Specifically, the grouting length of the first segment is determined according to relevant operating procedures. The first grouting section is set to 1 / 5 of the drilling depth, i.e., 4m, with a grouting pressure of 0.3~0.35MPa, so that the crushed stone at the bottom of the grouting hole 5 can fully fuse with the cement mortar. According to the principle of "shorter at the bottom and appropriately increased at the top" in the relevant operating procedures and combined with construction experience, the second grouting section is set to 1 / 2 of the drilling depth, i.e., 10m, with a grouting pressure of 0.15~0.3MPa. The third grouting section is 3 / 10 of the drilling depth, i.e., 6m, with a grouting pressure of 0.1~0.15MPa. The final grouting height is level with the final boundary platform 6. During the grouting process, the cement mortar will extend outwards along the potential sliding surface 7 and the cracks exposed by the grouting holes 8. After the cement mortar has cured to a certain strength, it will form an advanced grouting reinforcement structure 9. The advanced grouting reinforcement structure 9 refers to the columnar concrete piles formed by the cement mortar in the grouting holes 5 and the concrete layers formed by the cement mortar penetrating into each crack and the potential sliding surface 7. Finally, it will bond with the surrounding broken rock mass to form a whole. After reinforcement, the excavation work will be carried out on the rock mass 1 to be excavated and the final boundary 2 of the open-pit mine slope will be exposed.

[0031] Compared with existing advanced reinforcement schemes, the method of this invention uses non-uniform assignment of mechanical parameters in the model during the identification of potential sliding surfaces. Compared with single assignment, it can more accurately obtain the location of potential sliding surfaces, which is beneficial to improve the identification accuracy and facilitates the subsequent adoption of differentiated reinforcement schemes for areas requiring advanced reinforcement. The method of this invention has been applied in industrial trials in a large open-pit iron mine in China. The test results show that before the exposure of fractured rock mass, the method of this invention constructs advanced reinforcement piles in the fractured rock mass using cement mortar. At the same time, under pressure, the cement mortar penetrates into the fissures of the fractured rock mass to be exposed, firmly bonding the fractured rock mass to be exposed into a complete integral structure. This allows the rock mass and the advanced reinforcement structure to jointly bear the blasting disturbance generated during excavation, reducing the damage to the rock mass caused by blasting vibration and excavation unloading, inhibiting fissure expansion and rock mass loosening, thereby improving the long-term stability of the slope. In addition, the method of this invention only requires cement and does not require steel. Without reducing the reinforcement effect, it greatly simplifies the construction process, eliminates the risk of chemical corrosion, and extends the service life.

[0032] The embodiments provided above are mainly used to clearly demonstrate and explain the technical solutions of the present invention, and do not constitute a limitation on the scope of protection of the present invention. For those skilled in the art, based on a full understanding of the core concept disclosed in the present invention, appropriate adjustments and optimizations can be made to the specific technical solutions described in the embodiments, or equivalent means can be used to replace certain technical features. All such modifications and substitutions made based on the essential spirit of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for reinforcing a broken rock mass in an open pit slope by advance grouting, characterized in that, The method comprises the following steps: Step 1, pre-identifying the broken rock mass region: identifying the fissures exposed by the pre-split holes, quantifying the change of fissure density with depth in each pre-split hole, taking each pre-split hole as a control line to construct a fissure density representation model of the final mining boundary, and extracting the region with fissure density exceeding a preset critical fissure density as the broken rock mass region; Step 2, determining the pre-reinforcement region: converting the fissure density into GSI and then substituting it into the Hoek-Brown strength criterion, converting the fissure density representation model into a mechanical parameter representation model, constructing a numerical model of the slope in the broken rock mass region and dividing the element grid by using a numerical simulation software; Based on the mechanical parameter representation model, the mechanical parameters corresponding to each element grid are determined, and the element grid is valued; the position of the potential sliding surface and the safety factor of the slope are simulated and determined, and the region with a safety factor less than a preset threshold is determined as the region needing reinforcement; Step 3, implementing the pre-grouting reinforcement scheme: in the region needing reinforcement, the grouting holes are arrayed perpendicularly to the final boundary platform at an interval distance, the grouting holes are subjected to sectional pressurized grouting from the bottom, the final grouting height is leveled with the final boundary platform, and a pre-grouting reinforcement structure is formed.

2. The method according to claim 1, wherein, In step 1, the fissures exposed by the pre-split holes in the image are identified by collecting the images in the pre-split holes.

3. The method according to claim 1, characterized in that, In step 1, the preset critical fissure density is 5 / m.

4. The method for open-pit slope broken rock mass pre-grouting reinforcement according to claim 1, characterized in that, In step 2, the distance power inverse ratio method is used to determine the mechanical parameters corresponding to each element grid.

5. The method for open-pit slope broken rock mass pre-grouting reinforcement according to claim 1, characterized in that, In step 2, the preset threshold of the safety factor is 1.

3.

6. The method for open-pit slope broken rock mass pre-grouting reinforcement according to claim 1, characterized in that, In step 3, the determination process of the pre-grouting reinforcement scheme is as follows: the parameters to be determined in the scheme include the interval distance of the grouting holes, the drilling diameter and the drilling depth, the value intervals of the parameters are set, the parameter points are taken at intervals in the value intervals, a plurality of groups of alternative schemes are formed by permutation and combination, the grouting holes are arranged in the numerical model of the slope constructed in step 2 according to each alternative scheme, the safety factors of the slopes at different time lengths after the grouting of the grouting holes are simulated, the scheme parameters and the step exposure time nodes are determined according to the standard that the safety factor after reinforcement reaches the preset threshold of the safety factor, the number of grouting holes is determined according to the interval distance, the lengths and pressures of each section of the grouting holes are determined according to the relevant operation procedures, and the final implementation scheme is obtained.

7. The method according to claim 6, characterized in that, The value interval of the interval distance is 1200mm-2000mm, the value interval of the drilling diameter is 400mm-700mm, and the drilling depth needs to extend at least 5m below the potential sliding surface.

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