Open slope broken rock mass advance grouting reinforcement method

Abstract

The application discloses an open pit slope broken rock mass advanced grouting reinforcement method and belongs to the technical field of open pit mining. First, the broken rock mass region is determined by quantifying the fissure density and constructing a fissure density representation model; second, the fissure density representation model is converted into a mechanical parameter representation model, the mechanical parameters of each unit grid in the slope numerical model are non-uniformly valued, and the region needing reinforcement is simulated and determined; in the region needing reinforcement, the grouting holes are constructed in an array manner perpendicular to the final boundary platform with equal interval spacing, and segmented pressurized grouting is carried out from the bottom of the grouting holes to form an advanced grouting reinforcement structure. The application binds the broken rock mass to be exposed into an integral whole by filling the fissures with cement mortar, jointly bears the blasting excavation disturbance, improves the stability of the slope, and has the characteristics of simple construction process, low cost, high construction efficiency and the like.

Description

Technical Field

[0001] This invention belongs to the field of open-pit mining technology, specifically relating to a method for pre-grouting reinforcement of fractured rock mass on open-pit slopes. Background Technology

[0002] Traditional open-pit slope support methods include single support methods such as soil nailing, anchor bolts (cables), and anti-slide piles, as well as combined support methods using grid beams and anchor bolts (cables). However, these traditional support methods are all implemented after the final boundary slope of the open-pit mine has been formed. Slope support work carried out at this time often affects the continuous operation of mining production, leading to reduced production efficiency. At the same time, because the final boundary slope has already suffered irreversible structural damage from multiple blasting disturbances, its rock mass strength has been significantly reduced. During the construction of the support structure, the slope is in an unstable state, posing a high risk of landslides. This directly threatens the lives of on-site workers. Furthermore, if a landslide 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] Current advanced reinforcement methods typically employ a single value for the mechanical parameters of numerical models when identifying potential sliding surfaces. However, due to the non-uniformity of rock mass mechanical parameters in real-world engineering, a single value in the numerical model often fails to accurately reflect the actual situation, leading to insufficient accuracy in identifying potential sliding surfaces and rendering the reinforcement method unsuitable for engineering applications. Furthermore, existing advanced reinforcement technologies often use steel reinforced with concrete as the reinforcement structure. This construction process is complex, hindering on-site operations, and the steel is susceptible to chemical corrosion in moist concrete, affecting the strength of subsequent support and shortening the service life. Summary of the Invention

[0004] This invention provides a method for pre-grouting reinforcement of fractured rock mass on open slopes. Before the final slope is exposed, the fractured rock mass is identified and the slope at the corresponding location is pre-grouted and reinforced. Cement mortar fills the cracks and bonds the fractured rock mass to be exposed into a whole, which together bears the disturbance of blasting excavation and improves the stability of the slope.

[0005] To achieve the above objectives, this application provides the following solution:

[0006] A method for pre-grouting reinforcement of fractured rock mass on open slopes includes the following steps:

[0007] Step 1, advance identification of fractured rock mass areas: identify the fractures revealed by pre-splitting holes, quantify the change of fracture density in each pre-splitting hole with depth; use each pre-splitting hole as a control line to construct a slope fracture density characterization model for the final mining boundary; extract areas exceeding the preset critical fracture density as fractured rock mass areas.

[0008] Step 2, Determine the area requiring pre-reinforcement: Convert the fracture density into a geological strength index (GSI) and then input it into the Hoek-Brown strength criterion to convert the fracture density characterization model into a mechanical parameter characterization model; use numerical simulation software to construct a slope numerical model of the fractured rock mass area and divide it into unit grids; based on the mechanical parameter characterization model, determine the mechanical parameters corresponding to each unit grid and assign values ​​to the unit grids; simulate and determine the location of potential sliding surfaces and the safety factor of the slope, and determine the areas with a safety factor less than a preset threshold as areas requiring reinforcement.

[0009] Step 3, implement the advanced grouting reinforcement scheme: In the area to be reinforced, construct grouting holes with equal spacing in an array perpendicular to the final boundary platform. Perform segmented pressurized grouting in the grouting holes from the bottom, and finally grouting height is level with the final boundary platform to form an advanced grouting reinforcement structure.

[0010] Furthermore, in step 1, images of the pre-cracked holes are acquired to identify the pre-cracked holes in the images and reveal the cracks.

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

[0012] Furthermore, in step 2, the mechanical parameters corresponding to each unit grid are determined using the inverse power law of distance.

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

[0014] Furthermore, in step 3, the process of determining the advanced grouting reinforcement scheme is as follows: The scheme requires determining parameters including the spacing between grouting holes, borehole diameter, and borehole depth. Value ranges for each parameter are set, and parameter points are taken at intervals within these ranges. Multiple alternative schemes are formed through permutation and combination. Grouting holes are arranged within the slope numerical model constructed in step 2 according to each alternative scheme. The safety factor of the slope after grout injection at different times is simulated for each alternative scheme. The scheme parameters and the step exposure time are determined based on the safety factor reaching a preset threshold after reinforcement. The number of grouting holes is determined according to the spacing between grouting holes, and the grouting length and pressure for each section are determined according to relevant operating procedures, resulting in the final implementation scheme. Specifically, the spacing between grouting holes ranges from 1200mm to 2000mm, the borehole diameter ranges from 400mm to 700mm, and the borehole depth must extend at least 5m below the potential sliding surface.

[0015] The beneficial effects of this invention 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 Figure 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 its fracture density characterization model, the fracture density is converted into GSI according to the conversion relationship between fracture density and GSI. The GSI is then substituted into the Hoek-Brown strength criterion, and finally the fracture density characterization model is converted into a mechanical parameter characterization model for the fractured rock mass region. The mechanical parameters involved include compressive strength, tensile strength, internal friction angle, elastic modulus, Poisson's ratio, shear modulus, and deformation modulus.

[0026] Using the numerical simulation software FLAC3D, a numerical model of the slope in the fractured rock mass area was constructed and divided into unit meshes. Based on the mechanical parameter characterization model, the mechanical parameters corresponding to each unit mesh were determined using the inverse power law of distance method, and values ​​were assigned to the unit meshes. The location of the potential sliding surface 7 and the safety factor of the slope were simulated and determined. Areas with a safety factor less than a preset threshold were identified as areas requiring reinforcement. Specifically, in this embodiment, the preset threshold for the safety factor is 1.3. The mechanical parameters assigned in the slope numerical model obtained in this way are non-uniform, which is more in line with 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 area requiring reinforcement, grouting holes 5 are constructed in an array with equal spacing, perpendicular to the final boundary platform 6. Segmented pressurized grouting is carried out in the grouting holes 5 starting from the bottom, and the final grouting height is level with the final boundary platform 6, forming an advanced grouting reinforcement structure 9.

[0029] The process for determining the advanced grouting reinforcement scheme is as follows: The scheme requires determining parameters including the spacing between grouting holes 5, the borehole diameter, and the borehole depth. Value ranges for each parameter are set, and parameter points are taken at intervals within these ranges. Multiple alternative schemes are formed through permutation and combination. Specifically, the spacing between grouting holes ranges from 1200mm to 2000mm, and the borehole diameter ranges from 400mm to 700mm. Both parameters are taken at 100mm intervals. The borehole depth is determined based on the location of the potential sliding surface 7 and must extend at least to... The potential sliding surface is 5m below 7 meters. Grouting holes 5 are arranged within the slope numerical model constructed in step 2 according to each alternative scheme. Based on the variation of grout distribution range and grout strength over time, the safety factor of the slope after grout injection at different times is simulated for each alternative scheme. The scheme parameters and step exposure time are determined based on the standard that the safety factor after reinforcement reaches the preset threshold. The number of grouting holes 5 is determined according to the spacing between rows. The grouting length and pressure of each section are determined according to relevant operating procedures to obtain the final implementation scheme. Figure 1 and Figure 2 As shown.

[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 pre-grouting reinforcement of fractured rock mass on open-pit slopes, characterized in that, include: Step 1, advance identification of fractured rock mass areas: identify the fractures revealed by pre-splitting holes, quantify the change of fracture density in each pre-splitting hole with depth; use each pre-splitting hole as a control line to construct a slope fracture density characterization model for the final mining boundary; extract areas exceeding the preset critical fracture density as fractured rock mass areas; Step 2, determine the pre-reinforcement area: convert the fracture density to GSI and input it into the Hoek-Brown strength criterion, convert the fracture density characterization model into a mechanical parameter characterization model; use numerical simulation software to construct a slope numerical model of the fractured rock mass area and divide it into unit meshes. Based on the mechanical parameter characterization model, the mechanical parameters corresponding to each unit grid are determined by the inverse power law of distance, and the unit grid is assigned a value; the potential sliding surface location and the safety factor of the slope are simulated and determined, and the area with the safety factor less than the preset threshold is identified as the area that needs to be reinforced; Step 3, implement the advanced grouting reinforcement scheme: In the area to be reinforced, construct grouting holes with equal spacing in an array perpendicular to the final boundary platform. Perform segmented pressurized grouting in the grouting holes from the bottom, and finally grouting height is level with the final boundary platform to form an advanced grouting reinforcement structure. The process of determining the advanced grouting reinforcement scheme is as follows: The scheme needs to determine parameters including the spacing between grouting holes, the borehole diameter, and the borehole depth. Set the value range for each parameter, and take parameter points at intervals within the value range. Multiple alternative schemes are formed by permutation and combination. Grouting holes are arranged in the slope numerical model constructed in step 2 according to each alternative scheme. The safety factor of the slope after grout injection under each alternative scheme at different times is simulated. The scheme parameters and the step exposure time node are determined based on the safety factor reaching the preset threshold after reinforcement. The number of grouting holes is determined according to the spacing between grouting holes. The grouting length and pressure of each section are determined according to the relevant operating procedures to obtain the final implementation scheme.

2. The method for pre-grouting reinforcement of fractured rock mass on an open slope according to claim 1, characterized in that, In step 1, images of the pre-cracked holes are acquired, and the pre-cracked holes in the images are identified to reveal the cracks.

3. The method for pre-grouting reinforcement of fractured rock mass on an open slope according to claim 1, characterized in that, In step 1, the preset critical fracture density is 5 fractures / m.

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

3.

5. The method for pre-grouting reinforcement of fractured rock mass on an open slope according to claim 1, characterized in that, The spacing between rows is between 1200mm and 2000mm, the borehole diameter is between 400mm and 700mm, and the borehole depth must extend at least 5m below the potential sliding surface.

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