Differential pre-treatment method suitable for open-pit mine bedding easy weathering slope

Abstract

The application is suitable for the differential pre-treatment method of open-pit mine bedding weathered slope, relates to the technical field of open-pit mine slope treatment engineering, and aims to solve the problems of poor adaptability of homogenization treatment in the existing open-pit mine bedding weathered slope treatment technology, obtain the occurrence information of the layer of the rock layer in the existing production blast hole drilling, obtain the spatial depth distribution of the adverse geological body in the production blast hole covered area, and obtain the spatial extension range of the adverse geological body in the non-blast hole target area not covered by the production blast hole, including the depth distribution; determine the spatial extension range of the adverse geological body in different slope areas according to the spatial depth distribution and the spatial extension range of the adverse geological body to determine the type of the slope area, including the slope area without obvious adverse geological body and the slope area containing adverse geological body; and determine the pre-treatment method according to the type of the slope area, the relationship between the layer inclination angle θ of the slope area without obvious adverse geological body and the design slope angle β.

Description

Technical Field

[0001] This invention relates to the field of open-pit mine slope treatment engineering technology, specifically to a differentiated pre-treatment method applicable to easily weathered slopes along bedding planes in open-pit mines. Background Technology

[0002] Bedding slopes in open-pit mines are a common engineering geological feature in both metallic and non-metallic sedimentary layered mines in my country. Their stability directly determines the production safety and economic benefits throughout the entire mining cycle. Currently, in open-pit mine slope treatment, existing technologies mostly employ conventional measures such as anchor bolt support, shotcrete slope protection, wire mesh spraying, and grouting anchor cable reinforcement. These measures typically provide some support and reinforcement in slope treatment scenarios with relatively good rock conditions and insignificant structural plane control, thus having wide engineering applications. However, for easily weathered bedding slopes in open-pit mines, homogeneous and uniform support parameters and treatment methods are commonly used across the entire slope. This indiscriminate treatment model may lead to insufficient support strength or over-support in high-risk conditions, resulting in serious waste of engineering costs and extremely poor adaptability of the treatment plan to the site geological conditions, failing to balance treatment effectiveness and economy. Furthermore, what criteria can clearly distinguish the effects of support parameters and treatment methods to achieve targeted treatment and specific support, ensuring support strength while saving engineering costs, and achieving a balance between treatment effectiveness and economy, is an urgent problem to be solved for those skilled in the art. Summary of the Invention

[0003] This invention addresses the core shortcomings of existing open-pit mine bedding-line weathered slope treatment technologies, such as poor adaptability due to homogeneous treatment, delayed treatment timing, insufficient protection of easily weathered rock strata, and disconnect between geological exploration and treatment scheme design. It provides a differentiated pre-treatment method suitable for open-pit mine bedding-line weathered slopes, enabling proactive prevention and control of slope instability risks, precise and differentiated treatment, and balancing long-term slope stability with engineering economics. This method meets the slope treatment needs of safe, efficient, and low-cost open-pit mining.

[0004] According to some embodiments of this application, a differentiated pretreatment method for easily weathered slopes along bedding planes in open-pit mines includes...

[0005] Obtain the attitude information of the rock strata in the existing production boreholes to obtain the rock strata dip angle θ;

[0006] Obtain the spatial depth distribution of adverse geological bodies within the area covered by the production boreholes, and obtain the spatial extension range, including depth distribution, of adverse geological bodies within the non-bombhole target area not covered by the production boreholes;

[0007] The spatial depth distribution and spatial extension range of adverse geological bodies are used to determine the spatial extension range of adverse geological bodies in different slope areas to determine the type of slope area, including slope areas without obvious adverse geological bodies and slope areas containing adverse geological bodies.

[0008] The pre-treatment method is determined based on the type of slope area and the relationship between the rock strata dip angle θ and the designed slope angle β in slope areas without obvious adverse geological bodies.

[0009] According to some embodiments of this application, a differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines is provided. The pre-treatment method is determined based on the type of the slope area and the relationship between the rock strata dip angle θ and the designed slope angle β in slope areas without obvious adverse geological bodies. Specifically, for slope areas without obvious adverse geological bodies:

[0010] If θ > β:

[0011] For a stepped slope with a designed slope angle β, wherein the stepped slope includes a step, the step includes an upper platform and a slope surface, high ductility fiber concrete is sprayed onto the slope surface of the stepped slope for rock surface sealing and reinforcement.

[0012] If θ < β:

[0013] For the stepped slope with the designed slope angle β, make a first opening perpendicular to the slope surface to a certain depth of the rock strata of the stepped slope.

[0014] The anchoring section of the long anchor cable is inserted into the first opening perpendicular to the slope surface, and concrete is poured into the first opening perpendicular to the slope surface to fix the anchoring section in the rock layer of the step slope. The free section of the long anchor cable is pulled out to apply prestress to the shallow step slope rock mass for suspension reinforcement.

[0015] High-ductility fiber-reinforced concrete was sprayed onto the slope surface of the stepped slope for rock surface sealing and reinforcement.

[0016] If θ = β:

[0017] For the stepped slope with the designed slope angle β, high-ductility fiber concrete is sprayed onto the slope surface of the stepped slope.

[0018] A second opening perpendicular to the slope surface is made to the rock strata at a certain depth on the step slope. Anchor rods and stress gauges with stress gauges installed coaxially in series are inserted into the second opening perpendicular to the slope surface. Concrete is poured into the second opening perpendicular to the slope surface to fix the anchor rods and stress gauges in the rock strata of the step slope in order to monitor the stress of the rock mass of the step slope.

[0019] If the stress is not lower than the first threshold, a third hole perpendicular to the slope surface is made on the slope surface of the stepped slope to a certain depth of the rock layer of the stepped slope. The anchoring section of the long anchor cable is inserted into the third hole perpendicular to the slope surface and concrete is poured into the third hole perpendicular to the slope surface to fix the anchoring section in the rock layer of the stepped slope. The free section of the long anchor cable is pulled out to apply prestress to the shallow stepped slope rock mass for suspension reinforcement.

[0020] Specifically, for slope areas containing unfavorable geological features:

[0021] S1. If it is determined that the upper platform of the designed stepped slope and the corresponding rock mass area covered by the slope contain unfavorable geological bodies, the upper platform of one step of the designed stepped slope is excavated, and a first vertical hole is made in the upper platform to a certain depth of the rock strata of the stepped slope. Grout is injected into the first vertical hole to cement and reinforce the unfavorable geological bodies and the rock mass.

[0022] S2. Excavate a temporary slope corresponding to the design slope angle β of the upper platform, wherein the height of the temporary slope is less than the design slope height;

[0023] S3. Make a fourth opening perpendicular to the slope surface to a certain depth of the rock layer on the step slope. Insert the anchoring section of the long anchor cable into the fourth opening perpendicular to the slope surface and pour concrete into the fourth opening perpendicular to the slope surface to fix the anchoring section in the rock layer of the step slope. Pull the free section of the long anchor cable to apply prestress to the shallow step slope rock mass for suspension reinforcement.

[0024] S4. High-ductility fiber-reinforced concrete is sprayed onto temporary slopes for rock surface sealing and reinforcement;

[0025] S5. Repeat steps S2 to S4 until the temporary slope height reaches the design slope height;

[0026] Based on the above steps, all steps of the designed slope angle β are excavated to obtain the stepped slope with the designed slope angle β.

[0027] According to some embodiments of this application, a differentiated pretreatment method for easily weathered slopes along bedding planes in open-pit mines is used, wherein high-ductility fiber-reinforced concrete silicate cement-based substrate is used as the base material, and 11-13 mm long PVA fibers are incorporated into the base material, with a volume content of 1.5%-2.0% for the PVA fibers.

[0028] According to the differentiated pretreatment method for easily weathered slopes along bedding planes in some embodiments of this application, the insertion length of the anchoring section of the long anchor cable is not less than 6m, and the depth of penetration into the solid rock layer of the step slope is not less than 3m. The free section of the long anchor cable is pulled out to apply prestressed tension to the shallow step slope rock mass, which is 50% to 70% of the design anchoring force.

[0029] According to the differentiated pretreatment method for easily weathered slopes along bedding planes in some embodiments of this application, the thickness of the high-ductility fiber concrete sprayed on the slope surface of the stepped slope is 100 mm.

[0030] According to some embodiments of this application, a differentiated pretreatment method for easily weathered slopes along bedding planes in open-pit mines is used, wherein a stepped slope with a designed slope angle β is excavated, wherein the slope height of the stepped slope is 1 / 4 to 1 / 3 of the designed height, the width of the upper platform of the temporary step is 5m, and the slope flatness deviation is no more than 5cm.

[0031] According to some embodiments of this application, a differentiated pretreatment method for easily weathered slopes along bedding planes in open-pit mines is used for cementing and reinforcing adverse geological bodies and rock masses. The grouting is P.O42.5 grade ordinary Portland cement grout with a water-cement ratio of 0.8~1.0, a grouting pressure of 0.5~1.5MPa, and a final pressure of 2.0MPa, which is then stabilized for 15 minutes.

[0032] According to the differentiated pretreatment method for easily weathered slopes along bedding planes in some embodiments of this application, the vertical distance between the nozzle of the slope spraying and the rock surface is 0.8m to 1.2m, the spraying angle is no more than 15° with the normal of the rock surface, the spraying is carried out in layers from bottom to top, the thickness of a single spraying is controlled at 50mm to 60mm, and the forming thickness is 100mm.

[0033] According to the differentiated pretreatment method for easily weathered slopes along bedding planes in open-pit mines in some embodiments of this application, the attitude information of the bedding planes of the rock strata in the existing production boreholes is obtained by borehole television testing; the spatial depth distribution of adverse geological bodies in the area covered by the production boreholes is obtained by cross-hole wave velocity testing; and the spatial extension range of adverse geological bodies in the non-bombhole target area not covered by the production boreholes is obtained by high-density electrical resistivity tomography.

[0034] The beneficial effects are:

[0035] The dip angle of the strata in a bedding slope easily forms three combinations with the design slope angle: "strata dip angle θ > design slope angle β", "strata dip angle θ = design slope angle β", and "strata dip angle θ < design slope angle β". The inventors discovered that when θ < β, the strata dip angle is gentler than the design slope angle, and the strata are directly exposed on the excavated slope, possessing complete geometric and mechanical conditions for bedding slip. This is the state with the highest overall instability risk among the three conditions, and it is also the most typical and most dangerous instability mode for bedding slopes in open-pit mines, making it extremely prone to large-scale bedding slip disasters. When θ = β, the strata dip angle is completely consistent with the design slope angle. When the rock strata are parallel to the excavated slope, the slope rock mass is in a critical state of limit equilibrium for bedding-parallel sliding. The sliding resistance reaches the critical minimum value. Under the coupled effects of multiple factors such as excavation unloading disturbance, rainfall infiltration softening, and rock mass weathering and deterioration, even a slight decrease in the shear strength of the rock strata can break the critical equilibrium and trigger overall bedding-parallel sliding of the slope. When θ > β, the rock strata dip angle is steeper than the design slope angle, and the rock strata are not exposed on the slope surface. They do not have the geometric conditions for overall bedding-parallel sliding, and the overall stability is the best. There are only local risks such as rapid strength decay due to weathering after the rock mass is exposed by excavation, surface weathering and spalling, and rockfall. In summary, the stability of bedding slopes varies significantly with different dip angle combinations, and the instability modes and risk levels show obvious differentiation characteristics. They are a key source of geological hazards to be controlled during open-pit mining. It is evident that the geometric combination of the rock stratum dip angle θ and the design slope angle β can serve as a control factor for the stability of bedding rock slopes. Furthermore, this control factor is also affected by whether the slope area contains adverse geological bodies.

[0036] Based on the above findings, existing remediation schemes fail to adequately consider the stability differences corresponding to different combinations of rock stratum dip angles and design slope angles, and the need for differentiated remediation measures based on instability modes. They generally employ homogeneous and uniform support parameters and remediation methods across the entire slope. This indiscriminate remediation approach easily leads to insufficient support strength in high-risk slip conditions (θ < β), failing to prevent bedding-parallel slip disasters at the source. Simultaneously, it results in over-support in stable conditions (θ > β), severely wasting engineering costs. Furthermore, the remediation scheme exhibits extremely poor adaptability to site geological conditions, failing to balance remediation effectiveness and economy. The specific remediation scheme of this invention improves adaptability, balancing remediation effectiveness and economy.

[0037] Existing technologies generally adopt a passive "post-excavation reinforcement" approach, resulting in a significant delay in intervention and an inability to proactively prevent risks in bedding slopes. Furthermore, traditional treatment methods are often only implemented after abnormal slope deformation monitoring data or even localized instability and failure have occurred, failing to anticipate risks before excavation and implement pre-reinforcement concurrently with excavation. The core instability risk of bedding slopes often stems from the rapid attenuation of rock strata strength due to excavation unloading. If support and reinforcement are not completed simultaneously during the excavation phase, sudden bedding-line sliding disasters can easily occur, causing significant casualties and property damage. The solution described in this invention can anticipate risks before slope excavation, implement pre-reinforcement concurrently with excavation, and complete support and reinforcement simultaneously during the excavation phase, thereby reducing the risk of sudden bedding-line sliding disasters.

[0038] Existing protection technologies have poor adaptability to the engineering characteristics of bedding-parallel easily weathered rock strata, resulting in insufficient long-term protection. After excavation and exposure to the atmosphere, easily weathered rock strata are subject to rapid weathering due to wet-dry cycles, freeze-thaw cycles, and oxidation, leading to a significant decrease in the mechanical strength of the rock mass within a short period. Furthermore, conventional shotcrete, commonly used in existing technologies, is brittle, has poor crack resistance, and insufficient adhesion to the rock surface. Under the influence of minor rock deformation and changes in environmental temperature and humidity, it is prone to cracking and spalling, failing to provide long-term effective sealing of the rock surface and hindering the weathering and deterioration process. This results in a rapid decline in the overall stability of the slope over time, significantly increasing the difficulty and cost of subsequent maintenance and remediation. The aforementioned support scheme of this invention can improve the overall stability of the slope.

[0039] Existing geological exploration and remediation scheme design are severely disconnected, lacking precise geological basis for scheme formulation and failing to achieve precise risk control. Current exploration methods are limited, relying heavily on historical geological boreholes in mines and a few supplementary exploration boreholes. This makes it difficult to obtain core geological parameters such as the dip angle of strata, bedding weak interlayers, and spatial distribution characteristics of adverse geological bodies like fractured rock zones across the entire slope area in a cost-effective, efficient, and comprehensive manner. Furthermore, the lack of effective integration between exploration data and remediation scheme design prevents the matching of corresponding differentiated remediation measures based on precise geological conditions, resulting in insufficient targeting of remediation schemes and hindering precise control of slope instability risks. The above-mentioned scheme of this invention, by acquiring occurrence information and the spatial depth distribution of adverse geological bodies, realizes a three-dimensional geological information model of the target area of ​​the slope combining points, lines, and surfaces. This achieves effective integration of exploration data and remediation scheme design, providing accurate and comprehensive basic information for differentiated remediation measures, making the scheme more targeted, and achieving precise control of slope instability risks.

[0040] In summary, existing technologies have not yet formed a systematic pre-treatment system that can adapt to different dip angle combinations of easily weathered bedding slopes in open-pit mines, taking into account advanced prevention and control, precise treatment, and long-term protection. This is particularly true for complex scenarios where different dip angle combinations coexist and where bedding weak interlayers and fractured zones are distributed. It fails to solve the core technical challenges of differentiated treatment of bedding slopes, advanced prevention and control in high-risk conditions, and long-term stability assurance of easily weathered rock strata, making it difficult to meet the current slope treatment needs for safe, efficient, and low-cost open-pit mining. Therefore, this invention develops a comprehensive pre-treatment method based on bedding slope stability criteria, enabling advanced detection, differentiated design, simultaneous pre-treatment, and dynamic reinforcement, thereby controlling slope instability risks from the source. This invention establishes a differentiated pre-treatment method based on the stability criteria of bedding slopes, solving the problems of poor adaptability and insufficient economy of existing homogeneous treatment schemes, and improving the matching degree between support schemes and slope conditions. It constructs a full-process system of "advanced detection - simultaneous excavation and treatment - dynamic monitoring and reinforcement", transforming post-event passive reinforcement into proactive prevention and control, which can effectively prevent bedding slip risks. It adopts a suitable special high-ductility fiber concrete, which improves the problems of easy cracking and insufficient adhesion to the rock surface of conventional shotcrete, and enhances the long-term protection effect of easily weathered rock layers. It utilizes existing production blast holes to construct a "point-line-surface" detection system, eliminating the need for a large number of additional exploration boreholes, reducing detection costs, and providing accurate geological basis for treatment design. Attached Figure Description

[0041] Figure 1 This is a flowchart of the overall method of the present invention.

[0042] Figure 2 This is a schematic diagram of a slope, where a is the upper platform and b is the slope surface.

[0043] Figure 3 This refers to the process of excavating a stepped slope in a slope area containing unfavorable geological features.

[0044] Figure 4 For on-site application in pre-treatment projects. Detailed Implementation

[0045] This specific embodiment is a further detailed description of the technical solution of the present invention, and is only used to explain the present invention, not to limit the scope of protection of the present invention. Modifications, adjustments, and adaptations made by those skilled in the art based on the core technical concept of the present invention without inventive effort are all within the scope of protection of the present invention.

[0046] Example 1: A differentiated pretreatment method for easily weathered slopes along bedding planes in open-pit mines, comprising the following steps:

[0047] Step 1: Utilize existing production blast holes in the open-pit mine to conduct borehole television testing and cross-hole wave velocity testing. Borehole television testing obtains the attitude information of the rock strata within the borehole, including the dip angle θ. Cross-hole wave velocity testing determines the spatial location, including depth, of adverse geological bodies within the area covered by the production blast holes. These adverse geological bodies include weak interlayers and fractured rock zones. After completing the exploration of the production blast hole area, high-density electrical resistivity tomography (EDS) is used to conduct area exploration of the non-blast hole target area, determining the spatial extent of adverse geological bodies within this area, including depth. Finally, a three-dimensional geological information model combining point, line, and area mapping is formed for the slope target area.

[0048] Step Two: Based on the 3D geological information model obtained from advanced exploration, and using the classic stability criterion for bedding slopes corresponding to the combination of rock strata dip angle θ and design slope angle β as the core classification basis, and combined with the spatial distribution of adverse geological bodies, a differentiated pre-treatment method matching the slope instability risk is designed. Ideally, all pre-treatment measures should be implemented simultaneously within 24 hours after the excavation of the corresponding step slope.

[0049] The pretreatment method uses special high-ductility fiber concrete as the core material for slope rock surface reinforcement and sealing. The high-ductility fiber concrete uses C25 concrete as the base material, and 12mm long PVA fibers are added to the base material. It is constructed using a 18MPa high-pressure wet spraying process.

[0050] The stepped slope includes steps, and each step includes an upper platform and a slope surface.

[0051] The pre-treatment method is specifically as follows:

[0052] (1) For slope areas without obvious distribution of the aforementioned adverse geological bodies, differentiated pre-treatment shall be implemented according to the combination relationship between θ and β. The specific steps are as follows:

[0053] a. When θ>β, after the stepped slope excavation is completed according to the designed slope angle, 100mm of high-ductility fiber concrete is immediately sprayed onto the slope surface to achieve full sealing of the fresh rock surface of the slope.

[0054] b. When θ < β, after the step slope excavation is completed according to the design slope angle, long anchor cables are immediately constructed, and holes are made in the slope surface, i.e., transverse holes. The anchoring section of the long anchor cable is fixed in the deep stable rock layer of the slope with concrete, and prestress (pull-out) is applied to the free section to form a suspension reinforcement. Then, 100mm thick high ductility fiber concrete is sprayed onto the step slope surface to form a synergistic support system of deep anchoring and shallow closure.

[0055] c. When θ=β, after the step slope excavation is completed according to the designed slope angle, immediately spray 100mm thick high ductility fiber concrete onto the slope rock surface for initial sealing reinforcement. At the same time, open holes in the slope surface, install anchor stress gauges on the rock mass through the holes and carry out real-time stress monitoring. When the monitored stress change value exceeds the design warning threshold, refer to the long anchor cable construction method in step (1)b of this step to reinforce the slope rock mass.

[0056] (2) For slope areas with unfavorable geological features, implement special pre-treatment measures:

[0057] Based on the depth (lateral and longitudinal) of the adverse geological features extending into the slope, i.e., the upper platform of the terrace and the corresponding area of ​​the slope covered by rock contain adverse geological features, holes are drilled in the upper platform of the previously excavated terrace slope, and the adverse geological features are cemented and reinforced using a drilling and grouting process. The upper platform of each terrace is 5m wide, and the slope flatness is ≤5cm.

[0058] After the reinforcement is completed, a temporary slope surface is formed by excavating from top to bottom in stages according to 1 / 3 or 1 / 4 of the slope height of the designed steps of the open-pit mine slope; the long anchor cable is constructed in accordance with the long anchor cable construction method in step (1)b of this article, and high ductility fiber concrete is sprayed on the slope surface for sealing and reinforcement.

[0059] Based on the aforementioned temporary slope, continue excavating using the steps described above to form the next temporary slope (a continuous slope), and construct long anchor cables and perform sealing reinforcement according to the same steps. Repeat the above steps until the total height of the continuous temporary slopes equals the designed slope height, at which point one step has been excavated. Repeat the above steps to complete the designed number of steps, thus completing the designed stepped slope.

[0060] In step one, the test step distance for the borehole television test is set to 5mm, and the image resolution is not less than 1920×1080; the main frequency of the transmitting and receiving transducers for the cross-hole wave velocity test is not less than 10kHz, the distance between adjacent boreholes is controlled at 8m~15m, and the parallelism deviation between the two boreholes is not greater than 1‰; the high-density electrical resistivity tomography uses a Wenner four-stage device, the electrode distance is set to 2m~5m, the test line is arranged parallel to the slope direction, and the line spacing is controlled at 10m~15m.

[0061] In step two, the high-ductility fiber-reinforced concrete substrate has a fineness modulus > 2.5 for fine aggregates and a content of sand particles smaller than 0.075mm ≤ 20%, and coarse aggregates are of continuous gradation with a maximum particle size ≤ 10mm. The volumetric content of the PVA fiber is 1.5%~2.0%, added to the substrate in two batches on site. First, 60% is added and mixed evenly, then the remaining 40% is added and mixed until the fiber is evenly dispersed and free of lumps. C25 strength grade commercial concrete conforming to GB / T 14902-2012 "Ready-Mixed Concrete" standard is selected, with a fineness modulus > 2.5 for fine aggregates and a content of sand particles smaller than 0.075mm ≤ 20%, coarse aggregates of continuous gradation with a maximum particle size ≤ 10mm, and a slump controlled at 180mm~220mm to meet the requirements for on-site fiber dispersion and high-pressure wet spraying.

[0062] In step two (1)b, the anchorage section of the long anchor cable is not less than 6m, and the depth into the deep stable rock layer is not less than 3m. The prestress value of the anchor cable tension is 50% to 70% of the design anchorage force.

[0063] In step two (1)c, the anchor stress gauges are arranged in a rectangular array with a horizontal spacing of 4m and a vertical spacing of 6m on the slope. The slope is arranged with holes in the horizontal direction. Each anchor is equipped with two anchor stress gauges, which are installed in the middle of the anchor body and the front end of the anchoring section, respectively. The monitoring frequency is once every 15 minutes. The design warning threshold is 170% of the initial stress.

[0064] In step two, the grouting boreholes are arranged perpendicular to the upper platform, with a depth of not less than 1m penetrating the unfavorable geological body into the intact rock strata. Ordinary Portland cement grout of P.O42.5 grade is used for grouting, with a water-cement ratio of 0.8~1.0, a grouting pressure of 0.5~1.5MPa, and a final pressure of 2.0MPa that is stabilized for 15 minutes.

[0065] In step two, during the high-pressure wet spraying of high-ductility fiber concrete, the vertical distance between the nozzle and the rock surface is controlled at 0.8m to 1.2m, the spraying angle is no more than 15° with the normal to the rock surface, and the spraying is carried out in layers from bottom to top. The thickness of each spray is controlled at 50mm to 60mm, and the final forming thickness is 100mm. After spraying, the water curing time is no less than 7 days.

[0066] Example 2: A differentiated pretreatment method for easily weathered slopes along bedding planes in open-pit mines, comprising the following steps:

[0067] 1. By fully utilizing existing production blast holes in open-pit mines, the need for extensive additional exploration drilling is eliminated. This allows for precise identification of the geological conditions across the entire slope area in a low-cost and highly efficient manner, providing a complete geological basis for the subsequent design of differentiated treatment plans. Details are as follows:

[0068] Simultaneous borehole television testing and cross-hole wave velocity testing are conducted using existing production blast holes in open-pit mines: Borehole television testing provides a panoramic scan of the rock mass within the blast hole, accurately acquiring information on the dip and inclination of the rock strata; cross-hole wave velocity testing, based on the differences in the propagation speed of elastic waves in rock masses of different qualities, identifies the spatial location of local unfavorable geological bodies within the area covered by the production blast holes, including weak interlayers and fractured rock zones.

[0069] After completing the exploration of the production borehole area and clarifying the attitude of the rock mass strata and the location of adverse geological bodies, high-density electrical resistivity tomography was used to conduct planar exploration of the non-bombhole areas not covered by the production boreholes. Based on the resistivity differences of different rock masses, the spatial extension range of adverse geological bodies in the non-bombhole areas was determined. Finally, a complete geological information model combining "point-line-surface" was formed for the entire slope area, achieving full coverage and accurate detection of the dip angle of the bedding slope and adverse geological bodies.

[0070] 2. Based on the geological information model obtained from advanced detection, and taking the classic stability criterion corresponding to the combination relationship between the rock layer dip angle θ and the design slope angle β as the core classification basis, combined with the spatial distribution of adverse geological bodies, we design differentiated pre-treatment methods that are precisely matched with the slope instability risk, and complete the pre-reinforcement simultaneously with the excavation of the slope steps to achieve advanced risk prevention and control.

[0071] The pretreatment method uses special high-ductility fiber concrete as the core material for slope rock surface reinforcement and sealing. The high-ductility fiber concrete uses C25 ordinary silicate cement as the base material, and 12mm long PVA fibers are added to the base material. It is constructed using a 18MPa high-pressure wet spraying process.

[0072] The differentiated pre-treatment method of this invention, tailored to slope areas with different geological conditions, is as follows:

[0073] (1) Differentiated pre-treatment in areas without obvious adverse geological bodies

[0074] For slope areas without obvious weak interlayers or fractured rock zones, corresponding pre-treatment methods are matched based on the stability level and risk characteristics corresponding to three typical combinations of rock strata dip angle θ and design slope angle β:

[0075] a. When θ > β, the slope has no geometric conditions for overall bedding slip under this condition, and the overall stability is the best. The core engineering problem is the rapid weathering and deterioration of the easily weathered rock layer after excavation and exposure, resulting in surface spalling and rockfall, which in turn leads to a continuous decrease in rock mass strength. Therefore, after the stepped slope is excavated according to the designed slope angle, a 100mm thick layer of high-ductility fiber concrete should be sprayed onto the slope rock surface immediately to achieve immediate full sealing of the fresh rock surface. Through the excellent crack resistance and rock surface adhesion properties of the material, weathering, spalling and surface rockfall on the surface of the easily weathered bedding slope rock mass are prevented, thus inhibiting the deterioration of rock mass strength from the source and ensuring the long-term stability of the slope surface.

[0076] When θ < β, the rock strata are open and connected on the slope surface under this condition, possessing complete geometric and mechanical conditions for bedding-parallel slip. This is the state with the highest risk of instability among the three types of conditions. The core risk is bedding-parallel slip failure along the bedding plane. Therefore, after completing the excavation of the stepped slope according to the designed slope angle, long anchor cables are immediately constructed. The anchoring section of the long anchor cables is set in the deep stable rock strata of the slope. The free section of the long anchor cables is used to apply prestressed tension to the shallow slope rock mass after excavation, forming a suspended reinforcement structure. This directly offsets the sliding force of the rock mass along the weak bedding plane, fundamentally suppressing the risk of bedding-parallel slip. Subsequently, 100mm thick high-ductility fiber concrete is sprayed onto the slope rock surface to achieve secondary synergistic reinforcement of the slope rock mass after suspension reinforcement. The high-ductility fiber concrete forms a continuous integral concrete layer on the slope surface, enhancing the bonding force between the easily sliding elements of the slope and improving the overall shear strength of the slope, forming a synergistic support system of deep anchoring and shallow closure.

[0077] c. When θ = β, the rock strata are parallel to the excavated slope surface under this condition. The slope rock mass is in a critical state of limit equilibrium due to bedding slip. The risk of instability changes dynamically with factors such as mining unloading, rainfall infiltration, and rock weathering. After the stepped slope is excavated according to the designed slope angle and the designed slope surface is formed, the anchor bolt series stress gauge is immediately installed and fixed. Then, 100mm thick high-ductility fiber concrete is sprayed onto the slope rock surface for initial sealing and reinforcement to prevent the rock mass from weathering and deteriorating beyond the critical equilibrium state. Simultaneously, real-time stress monitoring of the anchor bolt stress gauge is carried out. After the sprayed concrete is cured, the initial value of the anchor bolt stress gauge is recorded, and the stress change of the slope rock mass is continuously tracked. Subsequently, when the monitored stress change value exceeds the warning threshold (170% of the initial value), the long anchor cable construction method of the above θ < β condition is immediately referred to to reinforce the slope rock mass, forming a treatment system of initial protection - real-time monitoring - precise reinforcement.

[0078] 2. Pre-treatment of areas containing unfavorable geological bodies

[0079] For slope areas with bedding weak interlayers and fractured rock zones, these adverse geological conditions can alter the local stress state of the slope. Even in stable conditions where θ > β, local slippage and rockfall risks may occur. Therefore, controlling excavation disturbance, enhancing the strength of the adverse geological body itself, and coordinating with a support system are necessary to achieve comprehensive risk control. Specifically:

[0080] Based on the depth (lateral and longitudinal) of the fractured zone and weak interlayer extending into the slope, i.e., the upper platform of the step and the area of ​​the rock covering the slope corresponding to the poor geological body, holes are first opened on the upper platform of the excavated step slope, and the poor geological body is cemented and reinforced by drilling and grouting technology, so that the fractured zone and weak interlayer are cemented together with the surrounding intact rock mass, thereby improving the strength and integrity of the poor geological body itself.

[0081] After reinforcement, a temporary slope is excavated in stages from top to bottom, forming a step, according to 1 / 3 or 1 / 4 of the designed slope height of the open-pit mine slope. This controls the disturbance range of adverse geological bodies caused by single-step excavation, i.e., reducing the impact on adverse geological bodies by excavating a small area. The upper platform of each temporary step is 5m wide to ensure the effectiveness of subsequent grouting construction, even if the grouting truck can reach the upper platform. The slope flatness is ≤5cm, making it easier to absorb and level. Long anchor cables are constructed according to the method described above for the θ<β condition, and high-ductility fiber concrete is sprayed for sealing reinforcement, forming an integral concrete layer on the slope to bind easily movable elements into a whole, improving the overall shear strength of the slope and achieving full coverage treatment of high-risk areas. Based on the above temporary slope, the next temporary slope (continuous slope) is excavated through the above steps, and long anchor cables and sealing reinforcement are constructed according to the above steps. The above steps are repeated until the total height of the continuous temporary slopes is equal to the designed slope height, at which point the excavation of one step is completed. Repeating the above steps to complete the designed number of steps completes the excavation of the designed stepped slope. When encountering adverse geological conditions, the significance of layered excavation reinforcement for open-pit mine slopes lies in transforming a large-scale, one-time disturbance into a small-scale, phased, and controllable construction process. Its beneficial effects are mainly reflected in: effectively reducing the damage to the overall slope structure caused by excavation unloading, avoiding landslides caused by stress concentration and sudden deformation increases; facilitating the phased implementation of anchor bolts, shotcrete, and other measures, allowing support to be carried out simultaneously with excavation, improving the targetedness and timeliness of reinforcement; and simultaneously improving construction safety conditions, reducing accident hazards, and providing reliable guarantees for the long-term stability of the slope and safe production in the mine.

[0082] As a preferred technical solution of the present invention, in step one, the test step distance of the borehole television test is set to 5mm, and the image resolution is not less than 1920×1080; the main frequency of the transmitting and receiving transducers of the cross-hole wave velocity test is not less than 10kHz, the distance between adjacent boreholes is controlled at 8m~15m, and the parallelism deviation between the two holes is not greater than 1‰; the high-density electrical resistivity tomography uses a Wenner four-stage device, the electrode distance is set to 2m~5m, the measuring line is arranged parallel to the slope direction, and the line spacing is controlled at 10m~15m.

[0083] As a preferred technical method of the present invention, in step two, in the high ductility fiber concrete substrate, the fine aggregate fineness modulus is >2.5 and the content of particles with a particle size of less than 0.075mm in the sand is ≤20%, and the coarse aggregate is continuous in size with a maximum particle size of ≤10mm; the volume content of the PVA fiber is 1.5%~2.0%, and it is added to the substrate in two batches on site. First, 60% is added and stirred evenly, and then the remaining 40% is added and stirred until the fiber is evenly dispersed and there are no lumps.

[0084] As a preferred technical method of the present invention, in step two (1)b, the length of the anchoring section of the long anchor cable is not less than 6m, and the depth of the cable entering the deep stable rock layer is not less than 3m. The prestress value of the anchor cable tension is 50% to 70% of the design anchoring force.

[0085] As a preferred technical method of the present invention, in step two (1)c, the anchor stress gauges are arranged in a rectangular array with a horizontal spacing of 4m and a vertical spacing of 6m. Each anchor rod is equipped with two anchor stress gauges, which are installed in the middle of the anchor rod body and the front end of the anchoring section, respectively. The monitoring frequency is once / 15min. The design warning threshold is 170% of the initial stress.

[0086] As a preferred technical method of the present invention, in step two (2), the grouting borehole is arranged perpendicular to the upper platform, and the depth of the borehole penetrates the unfavorable geological body into the intact rock layer by no less than 1m. Ordinary silicate cement grout of P.O42.5 grade is used for grouting, with a water-cement ratio of 0.8~1.0, a grouting pressure of 0.5~1.5MPa, and the final pressure is stabilized at 2.0MPa and stabilized for 15min.

[0087] As a preferred technical method of the present invention, in step two, during the high-pressure wet spraying construction of high-ductility fiber concrete, the vertical distance between the nozzle and the rock surface is controlled at 0.8m~1.2m, the spraying angle is not greater than 15° with the normal of the rock surface, the spraying is carried out in layers from bottom to top, the thickness of a single spraying is controlled at 50mm~60mm, the final forming thickness is 100mm, and the water curing time after spraying is not less than 7 days.

[0088] Example 3: This invention is applicable to the treatment of easily weathered slopes along bedding planes in various sedimentary layered metal and non-metal open-pit mines, especially to the advanced pre-treatment of open-pit mine slopes with strongly weathered rock strata and well-developed soft interlayers / fracture zones.

[0089] I. Specific Implementation of Advanced and Detailed Exploration of Slope Geological Conditions

[0090] The core of this phase is to utilize existing production blast holes in the open-pit mine to construct a precise detection system that covers all points, lines, and areas, without requiring the construction of a large number of additional exploration boreholes. The specific implementation steps are as follows:

[0091] 1. Implementation of borehole television testing based on existing production blast holes

[0092] A panoramic digital borehole television testing system was adopted. The probe diameter of the equipment was adapted to the existing production borehole diameter in open-pit mines (common diameters are 120mm~250mm), the test step distance was set to 5mm, and the image resolution was no less than 1920×1080. Before the test, the slag and water inside the borehole were cleaned to ensure that the borehole wall was clear. The probe was fixed in the center at the borehole opening and lowered at a constant speed via cable, continuously capturing panoramic images of the borehole wall and recording the borehole depth data simultaneously. The lowering speed was controlled to be less than 8m / min. After the test, the images were analyzed using the accompanying software to accurately extract the dip and inclination information of the rock strata in the borehole, clarify the correspondence between the rock strata dip angle θ and the designed slope angle β, and roughly identify the location, thickness, and development degree of weak interlayers and fracture zones in the borehole.

[0093] 2. Implementation of cross-hole wave velocity testing based on existing production boreholes

[0094] A cross-hole acoustic wave testing system was adopted, with the main frequency of the transmitting and receiving transducers not lower than 10kHz. Two adjacent, collinear existing production boreholes were selected as the excitation borehole and the detector borehole, respectively, with the borehole spacing controlled between 8m and 15m and the parallelism deviation between the two boreholes not exceeding 1%. Before testing, clean water was filled into the two boreholes as a coupling medium. The transmitting and receiving transducers were lowered to the bottom of the two boreholes, keeping the elevation of the two transducers consistent. The sampling interval was set not to exceed 2μs, and the sampling length was not less than 1024 points. The test was conducted point by point using a synchronous upward movement at equal elevations, with the measurement point spacing set at 0.5m. Each measurement point was tested three times and the average value was taken. After the test, the longitudinal wave velocity of the rock mass at different elevations was calculated. Based on the wave velocity difference, the rock mass integrity level was classified, and the spatial location and vertical distribution range of unfavorable geological bodies such as weak interlayers and fracture zones within the area covered by the production boreholes were located.

[0095] 3. Implementation of high-density electrical resistivity tomography in non-bomb hole areas

[0096] A distributed high-density resistivity resistivity resonator was used, employing a Wenner four-stage device. The electrode spacing was set to 2m-5m, with a minimum isolation coefficient of 1 and a maximum isolation coefficient of 16. The survey lines were arranged parallel to the slope direction, with a line spacing controlled at 10m-15m, covering the non-blowhole areas of the target area not explored by the production boreholes. The electrode burial depth was not less than 0.3m, and salt water was used to reduce grounding resistance, ensuring that the grounding resistance was less than 2kΩ. Before testing, system self-testing and leakage current detection were performed to ensure data acquisition stability. After testing, data preprocessing was performed using the accompanying software to remove distorted data and generate a two-dimensional resistivity profile. Combined with the borehole test calibration results, the spatial extension, attitude, and connectivity of adverse geological bodies in the non-blowhole area of ​​the target area were determined.

[0097] 4. Construction of 3D geological model of slope

[0098] By integrating data from borehole television testing, cross-hole wave velocity testing, and high-density electrical resistivity tomography, a local slope geological information model was constructed. This model clarifies the dip angle θ of rock strata and the spatial distribution characteristics of adverse geological bodies in different areas of the slope, providing a complete and accurate geological basis for subsequent differentiated pre-treatment design.

[0099] II. Preparation and Construction Technology of Special High-Ductility Fiber Reinforced Concrete

[0100] The special high-ductility fiber concrete used in this invention is the core material for slope rock surface reinforcement and sealing. The specific preparation and construction process are as follows:

[0101] Ready-mixed concrete of grade C25 conforming to GB / T14902-2012 "Ready-mixed Concrete" standard was selected. The fine aggregate fineness modulus was >2.5, and the content of sand particles smaller than 0.075mm was ≤20%. The coarse aggregate was of continuous size with a maximum particle size ≤10mm. The slump was controlled between 180mm and 220mm to meet the requirements for fiber dispersion and high-pressure wet spraying on site. A forced mixer was used on site, adding 12mm long PVA fibers in two batches: first, the ready-mixed concrete mixture was added to the mixer, followed by 60% of the PVA fibers, and stirred until the fibers were initially dispersed. Then, the remaining 40% of the PVA fibers were added, and stirring continued until the fibers were evenly dispersed in the mixture, without clumping or fiber bundles, thus preparing a special high-ductility fiber-reinforced concrete mixture.

[0102] A high-pressure wet concrete spraying machine with a rated working pressure of not less than 20MPa is used, and the working pressure of the wet spraying system is stabilized at 18MPa. The nozzle is fixed to the front end of the hydraulic cantilever machine's robotic arm using a special clamp. Through the multi-degree-of-freedom adjustment of the cantilever machine, the distance and angle between the nozzle and the slope rock surface are precisely controlled. The vertical distance between the nozzle and the rock surface is controlled between 0.8m and 1.2m, and the angle between the spraying angle and the normal to the rock surface is not greater than 15°. The spraying is carried out in layers from bottom to top, with the thickness of each spraying controlled between 50mm and 60mm. The interval between two sprayings is not less than 30 minutes, and the final thickness is 100mm. During the spraying process, the cantilever machine is moved at a uniform speed to avoid local over-spraying or under-spraying, ensuring that the thickness of the sprayed layer is uniform and the surface is flat across the entire slope. After spraying, water is sprayed to cover and cure the layer for no less than 7 days. During the curing period, the sprayed layer is protected from disturbance, sun exposure, and rain.

[0103] III. Specific Implementation of Differentiated Pre-treatment Methods

[0104] Based on the three-dimensional geological information model constructed by advanced detection, the classic stability criterion corresponding to the combination relationship between the rock layer dip angle θ and the design slope angle β is used as the core classification basis. Combined with the spatial distribution of adverse geological bodies, differentiated pre-treatment is implemented in different regions. All pre-treatment measures are implemented simultaneously after the excavation of the corresponding step slope is completed, so as to achieve advanced risk prevention and control.

[0105] 1. Differentiated pre-treatment implementation in areas without obvious adverse geological bodies

[0106] For slope areas with non-bedding weak interlayers, fractured rock zones, and relatively good rock mass integrity, corresponding pre-treatment measures are implemented according to three types of dip angle combinations:

[0107] (1) Implementation of pre-treatment for θ>β working conditions

[0108] Under this condition, the slope has no geometric conditions for overall bedding slippage, and its overall stability is good. The core control target is the surface weathering and deterioration of the easily weathered rock layer. After the stepped slope excavation is completed according to the designed slope angle, the loose rock debris and loose rock blocks on the rock surface are cleaned up. Immediately afterward, the above-mentioned high-pressure wet spraying process is used to spray a 100mm thick layer of high-ductility fiber concrete onto the slope rock surface to achieve complete sealing of the fresh rock surface after excavation, thereby inhibiting rock weathering, spalling, and surface rock shavings.

[0109] (2) Implementation of pre-treatment for θ<β working conditions

[0110] Under this condition, the rock strata are open and connected on the slope, possessing complete geometric and mechanical conditions for bedding-parallel slip, making it a high-risk instability condition. The core control objective is to suppress bedding-parallel slip. After completing the stepped slope excavation according to the designed slope angle, prestressed long anchor cables are immediately constructed: the anchor cable boreholes are arranged perpendicular to the rock strata, the anchoring section is set in the deep stable rock strata of the slope, the length of the anchoring section is not less than 6m, and the depth into the stable rock strata is not less than 3m, and the free section length covers the slip risk area; after the anchor cables are installed, grouting is carried out. After the grout strength reaches 100% of the design strength, prestress is applied, with the prestress value being 50%~70% of the design anchoring force, forming a suspended reinforcement structure to offset the rock mass sliding force; after the anchor cable construction is completed, the rock surface is cleaned, and 100mm thick high-ductility fiber concrete is sprayed to form a collaborative support system of "deep anchoring + shallow sealing".

[0111] (3) Implementation of pre-treatment and dynamic monitoring reinforcement for θ=β working conditions

[0112] Under this condition, the rock strata are parallel to the excavated slope, and the slope is in a critical state of limit equilibrium due to bedding slip. The core control objective is to control the risk of instability in this critical state and achieve dynamic early warning and reinforcement. A row of anchor bolts and stress gauges are installed and fixed at lateral intervals of 2-4m. The anchor bolts are arranged perpendicular to the slope. The stress gauges are installed coaxially and in series with the anchor bolts. Each anchor bolt is equipped with two stress gauges: one installed in the middle of the anchor bolt body (corresponding to the center of the easily weathered rock layer thickness), and the other installed at the front end of the anchoring section (corresponding to the interface between the stable rock layer and the easily weathered rock layer). The anchor bolt length is not less than 3m, preferably 3m, and it must penetrate the easily weathered rock layer to enter the lower stable rock layer by at least 0.5m, preferably 0.5m. After installation, the equipment sensitivity and data transmission stability are verified to ensure compliance with monitoring requirements. The requirements are as follows: After the stepped slope excavation is completed according to the designed slope angle, a 100mm thick layer of high-ductility fiber concrete should be sprayed immediately for initial sealing and reinforcement to prevent rock weathering and deterioration from causing critical equilibrium instability. After the sprayed concrete has cured, the initial values ​​of the anchor stress gauge should be recorded, and real-time stress monitoring should be carried out at a frequency of once every 15 minutes. The design warning threshold is 170% of the initial stress. When the monitored stress change value exceeds the design warning threshold, the slope rock mass should be reinforced with prestressed anchor cables immediately, referring to the long anchor cable construction method for the above-mentioned θ<β condition, to form a closed-loop treatment system of "initial protection-real-time monitoring-precise reinforcement".

[0113] 2. Implementation of special pre-treatment measures for areas containing unfavorable geological features

[0114] For slope areas with bedding weak interlayers and fractured rock zones, a special pre-treatment plan is implemented, with the following specific steps:

[0115] First, based on the depth (lateral and longitudinal) of the adverse geological body extending into the slope, i.e., the area of ​​the upper platform of the step and the corresponding rock-covered area of ​​the slope containing the adverse geological body, holes are drilled on the upper platform of the excavated step slope, and the adverse geological body is cemented and reinforced using a drilling grouting process. Specifically, the drilling grouting process is used, with the borehole perpendicular to the upper platform, and the hole depth penetrating the adverse geological body into the intact rock layer by no less than 1m, preferably 1m. Ordinary Portland cement grout of P.O42.5 grade is used for grouting, with a water-cement ratio of 0.8~1.0, a grouting pressure of 0.5~1.5MPa, and a final pressure stabilized at 2.0MPa for 15 minutes, so that the fractured zone, weak interlayer and the surrounding intact rock mass are cemented and reinforced into one.

[0116] After the grouting strength reaches 100% of the design strength, temporary slope surfaces are formed by excavating in layers from top to bottom, according to 1 / 3 or 1 / 4 of the slope height of the designed steps on the open-pit mine slope. The height of a single excavation step should not exceed 4m, preferably 4m, and the width of each temporary step should be controlled at 5m. After the temporary excavation is completed, the slope is manually trimmed to ensure that the slope flatness deviation is not greater than 5cm, so as to avoid secondary damage to the unfavorable geological body caused by excavation disturbance. Then, prestressed long anchor cables are constructed according to the above-mentioned θ<β working condition method. The anchor cable anchoring section penetrates the unfavorable geological body into the deep stable rock layer, and then 100mm thick high ductility fiber concrete is sprayed to seal and reinforce the slope surface, so as to achieve full coverage treatment of high-risk target areas.

[0117] Example 4: This example uses the treatment project of easily weathered slope along the bedding plane in a sedimentary magnetite open-pit mine in North my country as the background to illustrate the specific implementation process, effects and technical and economic comparison of the method of the present invention.

[0118] I. Project Overview

[0119] This open-pit mine is a typical sedimentary layered mine, with a designed final mining depth of 420m, a bench height of 30m, and a designed slope angle β=50°. The slope rock mass consists of strongly weathered biotite granulite, moderately weathered biotite granulite, and slightly weathered biotite granulite. Prolonged exposure after excavation has led to surface weathering and erosion. Several small landslides have occurred locally due to the influence of fracture zones and weak interlayers, classifying it as a high-risk, bedding-parallel, easily weathered slope. Based on preliminary geological data, the slope is divided into four typical areas:

[0120] Area A: The rock strata dip angle θ = 60° (θ > β), there are no obvious adverse geological bodies, and the overall stability is good;

[0121] Area B: The rock strata dip angle θ = 40° (θ < β) and the rock strata are connected in the open space, which is a high risk zone for slippage;

[0122] Area C: The rock strata dip angle θ = 50° (θ = β), and the slope is in the critical state of limit equilibrium of bedding slip.

[0123] Zone D: The slope contains weak interlayers and fractured zones, making it a special area with high local risk.

[0124] II. Implementation of Advanced and Detailed Detection

[0125] For the target slope treatment in this open-pit mine, existing production blast holes (150mm diameter, 10m spacing) were fully utilized, supplemented by a small number of supplementary exploration boreholes (150mm diameter, 50m~150m depth). A "point-line-surface" joint detection system was constructed strictly according to the method of this invention, and the specific implementation is as follows:

[0126] 1. Borehole television testing and cross-hole wave velocity testing: Testing was conducted simultaneously on 108 existing production boreholes and 2 existing supplementary exploration boreholes. For borehole television testing, a step distance of 5mm and an image resolution of 1920×1080 were used. Before testing, slag and water inside the boreholes were cleaned. The probe was centered and fixed, and lowered at a constant speed of 6m / min (less than 8m / min). Images of the borehole wall were continuously captured throughout the test. After the test, the dip and dip angle of the rock strata within the borehole were manually extracted from the borehole images to roughly identify the location, thickness, and development degree of weak interlayers and fracture zones. Cross-hole wave velocity testing used 12kHz transmitting and receiving transducers, selecting adjacent collinear... The blast holes were used as excitation holes and detector holes, respectively, with a hole spacing of 10m and a parallelism deviation of 0.8%. Before testing, the holes were filled with clean water as a coupling medium. The transducers were synchronously lowered to the bottom of the holes and kept at the same elevation. The sampling interval was set to 2μs, and the sampling length was 1024 points. The test was carried out point by point using the synchronous upward movement method with equal elevation. The distance between the measuring points was 0.5m. Each measuring point was tested three times and the average value was taken. After the test, the longitudinal wave velocity of the rock mass was calculated. Based on the wave velocity difference, the rock mass integrity level was classified, and the spatial location and vertical distribution range of the adverse geological bodies in the area covered by the blast holes were accurately located.

[0127] 2. High-density electrical resistivity tomography (EDT) in non-blowhole target areas: A distributed high-density EDT instrument was used, employing a Wenner level 4 device. Six parallel survey lines were laid out in the non-blowhole target areas not covered by the production boreholes. The survey lines were arranged parallel to the slope direction, with a line spacing of 12m and an electrode spacing of 3m (within the range of 2m to 5m). The electrode burial depth was 0.4m (not less than 0.3m). The grounding resistance was reduced to 1.8kΩ (less than 2kΩ) by pouring salt water. Before testing, the system self-test and leakage current detection were performed. After testing, the data were preprocessed to remove distorted data, and a two-dimensional resistivity profile was generated. The profile was then calibrated in conjunction with the borehole test results to determine the spatial extension, attitude, and connectivity of adverse geological bodies in the non-blowhole area.

[0128] 3. Construction of 3D geological information model: Integrate the full data of borehole television test, cross-hole wave velocity test, and high-density electrical resistivity tomography, and combine them with the existing geological exploration data of the mine to construct a local 3D geological information model of the target slope, clarify the rock strata dip angle θ and the spatial distribution characteristics of adverse geological bodies in the four types of areas, complete the precise zoning of the slope treatment area, and provide a complete and accurate geological basis for the subsequent design of differentiated pre-treatment schemes.

[0129] III. On-site preparation of special high-ductility fiber-reinforced concrete

[0130] The special high-ductility fiber-reinforced concrete used in this embodiment was prepared strictly in accordance with the aforementioned preparation process of this invention. The specific parameters and implementation procedures are as follows:

[0131] The base material is C25 commercial concrete conforming to GB / T14902-2012 "Ready-mixed Concrete". The fineness modulus of the fine aggregate is 2.8, the content of particles with a diameter <0.075mm in the sand is 15%, the coarse aggregate is 5~10mm continuous crushed stone, and the slump is 200mm, which meets the requirements of on-site fiber dispersion and high-pressure wet spraying.

[0132] On-site, a forced mixer was used to add 12mm long PVA fibers in two batches: first, commercial concrete mixture was added to the mixer, 60% of the PVA fibers were added and stirred for 5 minutes until the fibers were initially dispersed, then the remaining 40% of the PVA fibers were added and stirred for another 5 minutes until the fibers were evenly dispersed in the mixture, without clumping or fiber bundles, thus completing the preparation of the special high ductility fiber concrete mixture.

[0133] The spraying operation uses a high-pressure concrete wet spraying machine with a rated working pressure of 22MPa. The working pressure of the wet spraying system is stable at 18MPa. The nozzle is fixed to the front end of the mechanical arm of the hydraulic cantilever machine by a special clamp. Precise spraying operation is achieved by adjusting the cantilever machine.

[0134] IV. Implementation of Differentiated Pre-treatment

[0135] Based on the three-dimensional geological information model constructed by advanced detection, differentiated pre-treatment was implemented strictly according to the method of this invention for four types of zones. All pre-treatment measures were implemented simultaneously after the excavation of the corresponding bench slope was completed, as detailed below:

[0136] 1. Area A (θ > β condition): After completing the excavation of the stepped slope according to the designed slope angle, immediately clean the loose rock and debris from the rock surface. Then, use the aforementioned high-pressure wet spraying process to spray a 100mm thick layer of high-ductility fiber concrete onto the slope surface. Spraying should be carried out in layers from bottom to top, with a single spray thickness of 50mm and an interval of 30 minutes between sprays. This avoids excessive thickness in one spray, which could lead to detachment, and achieves complete sealing of the fresh rock surface after excavation, inhibiting weathering and erosion of the rock surface.

[0137] 2. Area B (θ < β condition): After completing the excavation of the stepped slope according to the design slope angle, immediately construct φ15.24mm prestressed long anchor cables. The anchor cable holes are arranged perpendicular to the rock strata, with a spacing of 3m × 3m and an anchorage length of 6m, penetrating 4m into the deep stable rock mass. The free section length completely covers the slip risk area. After the anchor cables are installed, P.O42.5 grade ordinary Portland cement grout is used for grouting. After the grout strength reaches 100% of the design strength, a prestress of 120kN is applied (60% of the design anchorage force, within the range of 50%~70%) to form a suspended reinforcement structure to offset the rock mass sliding force. After the anchor cable construction is completed, clean the rock surface and spray 100mm thick special high-ductility fiber concrete according to the same layered wet spraying process as Area A to construct a collaborative support system of "deep anchorage + shallow closure".

[0138] 3. Zone C (θ=β condition): Before the bench excavation, a row of anchor bolts and vibrating wire anchor bolt stress gauge assemblies are installed and fixed at a transverse spacing of 4m. The anchor bolts are φ25mm HRB400 threaded steel anchor bolts, 4m in length, penetrating the easily weathered rock layer and entering the lower stable rock layer for 1m (not less than 0.5m), and arranged perpendicular to the slope surface. Each anchor bolt is equipped with 2 anchor bolt stress gauges (range 0~120kN), which are installed in the middle of the anchor bolt body (corresponding to the center position of the easily weathered rock layer thickness) and the front end of the anchor bolt anchoring section (corresponding to the interface position between the stable rock layer and the easily weathered rock layer), respectively. The anchor bolt stress gauges are installed in series coaxially with the anchor bolts. After installation, the sensitivity of the equipment and the stability of data transmission are verified to ensure that they meet the monitoring requirements. After the stepped slope excavation was completed according to the designed slope angle, a 100mm thick layer of high-ductility fiber concrete was immediately sprayed using the same layered wet spraying process as in Area A for initial sealing and reinforcement to prevent rock weathering and deterioration from causing critical equilibrium instability. After the sprayed concrete has been cured for 7 days, the initial values ​​of the anchor stress gauges were recorded, and real-time stress monitoring was carried out at a frequency of once every 15 minutes. The designed warning threshold was 170% of the initial stress. During the monitoring period, the anchor stress count values ​​were all within the safe range and did not trigger the warning threshold, so no reinforcement was required.

[0139] 4. Zone D (including adverse geological conditions): Holes are drilled on the upper platform of the previously excavated stepped slope to reinforce the adverse geological conditions using grouting. The grouting holes are arranged perpendicular to the upper platform, penetrating the adverse geological conditions to a depth of 1m into the intact rock strata. P.O42.5 grade ordinary Portland cement grout is used, with a water-cement ratio of 0.9. The grouting pressure is controlled at 1.0~1.5MPa, with a final pressure stabilized at 2.0MPa for 15 minutes, thus cementing the weak interlayers and fractured zones to the surrounding intact rock mass. After the grout reaches 100% of its design strength, the designed stepped slope will be... The slope is excavated in stages from top to bottom to form temporary steps. The excavation height of each step is no more than 4m, and the width of each step, i.e., the width of the upper platform, is controlled at 5m. After excavation, the slope is manually trimmed to ensure that the slope flatness deviation is no more than 5cm, avoiding secondary damage to the adverse geological body caused by excavation disturbance. Then, prestressed long anchor cables are constructed according to the construction method of Area B. The anchor cable anchoring section penetrates the adverse geological body into the deep stable rock layer. Then, 100mm thick special high-ductility fiber concrete is sprayed using the same layered wet spraying process as Area A to seal and reinforce the entire slope, achieving full coverage treatment of the high-risk target area. Based on the above temporary slope, the above steps are continued to excavate to form the next temporary slope (continuous slope), and long anchor cables and sealing reinforcement are constructed according to the above steps. The above steps are repeated until the total height of the continuous temporary slope is equal to the design slope height, at which point one step is completed. The above steps are repeated to complete the designed number of steps, thus completing the designed stepped slope.

[0140] V. Implementation Results and Technological and Economic Comparison

[0141] After three months of continuous monitoring following the completion of the treatment, the anchor stress gauge data remained stable with no exceedances, indicating good overall slope stability. The high-ductility fiber-reinforced concrete layer showed no cracking, spalling, or hollowing; rock surface weathering was completely suppressed, with no surface spalling, demonstrating superior performance compared to traditional wire mesh and shotcrete reinforcement. Furthermore, the material and construction cost of high-ductility fiber-reinforced concrete is approximately 120 yuan / m². 2 The traditional cost of reinforced mesh and shotcrete reinforcement materials and construction is approximately 200 yuan / m². 2 From the perspective of field engineering applications, the special high-ductility fiber concrete in this invention has the advantages of rapid construction and good concrete adhesion, which fully demonstrates that the pre-treatment method of this invention has significant economic advantages and engineering application value.

[0142] Experimental example:

[0143] Experimental Methods: To verify the effectiveness of the high-ductility fiber-reinforced concrete material of this invention in rock interface protection, concrete-rock composite samples were prepared from the same original rock, with interface undulation angles set at 0°, 25°, 45°, and 60°. The experimental group used high-ductility fiber-reinforced concrete incorporating PVA fibers, while the control group used ordinary concrete without PVA fibers. The mass fraction of PVA fibers in the high-ductility fiber-reinforced concrete was 0.6%. After standard curing for 28 days, the samples underwent 0, 10, 25, and 45 cycles of immersion and freeze-thaw treatment, respectively, and further interfacial shear tests were conducted to comprehensively evaluate the interfacial mechanical properties of the material under the influence of immersion and freeze-thaw cycles.

[0144] Results Analysis: Experimental results show that with the increase of immersion freeze-thaw cycles, the porosity of both ordinary concrete-rock samples and high-ductility fiber-reinforced concrete-rock samples increased, but the increase in porosity of the high-ductility fiber-reinforced concrete samples was significantly smaller. Taking 45 immersion freeze-thaw cycles as an example, the porosity of ordinary concrete-rock samples increased from 9.25% to 26.89%, while that of the high-ductility fiber-reinforced concrete-rock samples only increased from 9.13% to 19.64%. This indicates that the high-ductility fiber-reinforced concrete used in this invention can effectively inhibit pore expansion and crack penetration under immersion freeze-thaw conditions, and slow down the accumulation of internal damage in the material.

[0145] Furthermore, the results of the interfacial shear tests at different interface angles are shown in Table 1. Figure 1 The results show that the interfacial strength loss of the high-ductility fiber-reinforced concrete specimens of this invention is significantly lower than that of ordinary concrete specimens in all stages of immersion and freeze-thaw cycles. After 45 immersion and freeze-thaw cycles, under interfacial conditions of 0°, 25°, 45°, and 60°, the cumulative strength damage rates of ordinary concrete specimens were 75.1%, 59.2%, 46.5%, and 69.6%, respectively, while those of the high-ductility fiber-reinforced concrete specimens were 42.1%, 34.2%, 22.9%, and 33.4%, respectively. In particular, under the 45° interfacial condition, the strength damage of the specimens of this invention was minimal, indicating that this interfacial morphology and the high-ductility fiber-reinforced concrete material form a superior synergistic effect, which can significantly improve the interfacial shear capacity.

[0146] Table 1. Comparison of cumulative interfacial strength damage rates after 45 immersion-freeze-thaw cycles at different interfacial angles.

[0147]

[0148] Therefore, based on the analysis of the failure morphology of the samples, ordinary concrete samples are more prone to interfacial debonding, pore connectivity, and local disintegration after freeze-thaw cycles. In contrast, high-ductility fiber-reinforced concrete samples maintain better interfacial integrity under the same conditions, and can continue to dissipate energy through fiber bridging during the post-peak failure stage, thus delaying crack propagation and macroscopic instability. Therefore, the high-ductility fiber-reinforced concrete of this invention not only improves the concrete-rock interface's resistance to freeze-thaw damage caused by water immersion, but also significantly enhances interfacial shear strength and structural durability, demonstrating good engineering application value.

[0149] The method of this invention, through differentiated pre-treatment based on classical stability criteria, significantly reduces direct engineering costs and long-term maintenance costs while fully meeting the requirements for slope safety and stability. It also shortens the construction period and avoids the over-support and resource waste of traditional solutions. This fully verifies the technical superiority and economic rationality of this invention compared to existing technologies, providing an efficient and economical solution for the treatment of easily weathered slopes along bedding planes in open-pit mines.

[0150] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines, characterized in that, Includes the following steps: Obtain the attitude information of the rock strata in the existing production boreholes to obtain the rock strata dip angle θ; Obtain the spatial depth distribution of adverse geological bodies within the area covered by the production boreholes, and obtain the spatial extension range, including depth distribution, of adverse geological bodies within the non-bombhole target area not covered by the production boreholes; The spatial depth distribution and spatial extension range of adverse geological bodies are used to determine the spatial extension range of adverse geological bodies in different slope areas to determine the type of slope area, including slope areas without obvious adverse geological bodies and slope areas containing adverse geological bodies. The pre-treatment method is determined based on the type of slope area and the relationship between the rock strata dip angle θ and the designed slope angle β in slope areas without obvious adverse geological bodies. Among them, the pre-treatment method is determined based on the type of slope area and the relationship between the rock strata dip angle θ and the designed slope angle β in slope areas without obvious adverse geological bodies. Specifically, for slope areas without obvious adverse geological bodies: If θ > β: For a stepped slope with a designed slope angle β, wherein the stepped slope includes a step, the step includes an upper platform and a slope surface, high ductility fiber concrete is sprayed onto the slope surface of the stepped slope for rock surface sealing and reinforcement. If θ < β: For the stepped slope with the designed slope angle β, make a first opening perpendicular to the slope surface to a certain depth of the rock strata of the stepped slope. The anchoring section of the long anchor cable is inserted into the first opening perpendicular to the slope surface, and concrete is poured into the first opening perpendicular to the slope surface to fix the anchoring section in the rock layer of the step slope. The free section of the long anchor cable is pulled out to apply prestress to the shallow step slope rock mass for suspension reinforcement. High-ductility fiber-reinforced concrete was sprayed onto the slope surface of the stepped slope for rock surface sealing and reinforcement. If θ = β: For the stepped slope with the designed slope angle β, high-ductility fiber concrete is sprayed onto the slope surface of the stepped slope. A second opening perpendicular to the slope surface is made to the rock strata at a certain depth on the step slope. Anchor rods and stress gauges with stress gauges installed coaxially in series are inserted into the second opening perpendicular to the slope surface. Concrete is poured into the second opening perpendicular to the slope surface to fix the anchor rods and stress gauges in the rock strata of the step slope in order to monitor the stress of the rock mass of the step slope. If the stress is not lower than the first threshold, a third hole perpendicular to the slope surface is made on the slope surface of the stepped slope to a certain depth of the rock layer of the stepped slope. The anchoring section of the long anchor cable is inserted into the third hole perpendicular to the slope surface and concrete is poured into the third hole perpendicular to the slope surface to fix the anchoring section in the rock layer of the stepped slope. The free section of the long anchor cable is pulled out to apply prestress to the shallow stepped slope rock mass for suspension reinforcement. Specifically, for slope areas containing unfavorable geological features: S1. If it is determined that the upper platform of the designed stepped slope and the corresponding rock mass area covered by the slope contain unfavorable geological bodies, the upper platform of one step of the designed stepped slope is excavated, and a first vertical hole is made in the upper platform to a certain depth of the rock strata of the stepped slope. Grout is injected into the first vertical hole to cement and reinforce the unfavorable geological bodies and the rock mass. S2. Excavate a temporary slope corresponding to the design slope angle β of the upper platform, wherein the height of the temporary slope is less than the design slope height; S3. Make a fourth opening perpendicular to the slope surface to a certain depth of the rock layer on the step slope. Insert the anchoring section of the long anchor cable into the fourth opening perpendicular to the slope surface and pour concrete into the fourth opening perpendicular to the slope surface to fix the anchoring section in the rock layer of the step slope. Pull the free section of the long anchor cable to apply prestress to the shallow step slope rock mass for suspension reinforcement. S4. High-ductility fiber-reinforced concrete is sprayed onto temporary slopes for rock surface sealing and reinforcement; S5. Repeat steps S2 to S4 until the temporary slope height reaches the design slope height; Based on the above steps, all steps of the designed slope angle β are excavated to obtain the stepped slope with the designed slope angle β.

2. The differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines according to claim 1, characterized in that, in, The high-ductility fiber-reinforced concrete uses silicate cement as the base material, and incorporates 11-13 mm long PVA fibers in the base material. The volumetric content of the PVA fibers is 1.5%-2.0%.

3. The differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines according to claim 1, characterized in that, The anchoring section of the long anchor cable extends for no less than 6m and penetrates into the solid rock layer of the stepped slope for no less than 3m. The free section of the long anchor cable applies prestressed tension to the shallow stepped slope rock mass at 50% to 70% of the design anchoring force.

4. The differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines according to claim 1, characterized in that, The thickness of the high-ductility fiber concrete sprayed on the slope surface of the stepped slope is 100mm.

5. The differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines according to claim 1, characterized in that, in, Excavate a stepped slope with a designed slope angle β. The slope height of the stepped slope is 1 / 4 to 1 / 3 of the designed height. The width of the upper platform of the temporary steps is 5m, and the slope flatness deviation is no more than 5cm.

6. The differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines according to claim 1, characterized in that, in, Grouting is used to reinforce the cementation of adverse geological bodies and rock masses by injecting grout into the first vertical opening. The grouting is P.O42.5 grade ordinary Portland cement grout with a water-cement ratio of 0.8~1.0, a grouting pressure of 0.5~1.5MPa, and a final pressure of 2.0MPa, which is then stabilized for 15 minutes.

7. The differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines according to claim 1, characterized in that, The vertical distance between the nozzle of the slope spraying and the rock surface is 0.8m to 1.2m. The angle between the spraying angle and the normal of the rock surface is no more than 15°. The spraying is carried out in layers from bottom to top. The thickness of a single spraying is controlled at 50mm to 60mm, and the forming thickness is 100mm.

8. The differentiated pre-treatment method for easily weathered slopes along bedding planes in open-pit mines according to claim 1, characterized in that, The attitude information of the strata in the existing production boreholes is obtained by borehole television testing; the spatial depth distribution of adverse geological bodies in the area covered by the production boreholes is obtained by cross-hole wave velocity testing; and the spatial extension range of adverse geological bodies in the non-bombhole target area not covered by the production boreholes is obtained by high-density electrical resistivity tomography.

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