Super-compensation grouting modification method for low permeability soft rock

Abstract

The present invention discloses a method for super-compensation grouting modification of low-permeability soft rock, which relates to the technical field of surrounding rock control in underground engineering such as mining and geotechnical engineering. The method includes multi-source data assessment of permeability, obtaining Lu Rong value, crack density, aperture and fractal dimension through borehole water pressure test, panoramic imaging and micron CT scanning, and constructing a model to accurately identify low-permeability soft rock; multi-stage crack construction, using CO2 phase change low-energy blasting to form pre-cracks, combining 15-30MPa high-pressure splitting and 1-20Hz dynamic pulse grouting, alternately constructing a "pre-primary-secondary" three-dimensional crack network to ensure that the slurry vein volume accounts for ≥20%; super-compensation material design, using ultrafine silicate cement as the main material, compounded with nano-SiO2, polycarboxylic acid water reducer and active MgO composite expansion agent, achieving dense bonding of the crack interface through high pressure and self-expansion, and the interface strength contribution is ≥1MPa; the present invention is green and efficient, suitable for the reinforcement of low-permeability soft rock in underground engineering and disaster prevention, breaking through the bottleneck of traditional grouting technology.

Description

Technical Field

[0001] The invention belongs to the technical field of surrounding rock control in underground engineering such as mining and rock and soil, and particularly relates to a method for modifying low-permeability soft rock by super-compensation grouting. Background Art

[0002] Chinese patents ZL201510380977.5, ZL201510368674.1, and ZL201510368674.1 propose devices and methods for pre-cracking grouting using high-pressure gas, which provide a good technical approach to solving the problem of grouting modification of low-permeability soft rock. However, there is still a lack of more scientific and effective methods in terms of permeability testing and evaluation of the injected soft rock medium, construction of artificial fracture networks, and performance design of grouting materials. Specifically, traditional permeability testing and evaluation of injected soft rock media typically relies on the Lu Rong value (Lu) of a single borehole water pressure test. However, the borehole water pressure test only reflects the macroscopic average permeability, ignoring the influence of local water-conducting pathways within macroscopic fractures. It also fails to accurately describe the characteristics of fracture aperture and the complexity of microfracture distribution under microscopic conditions. Regarding artificial fracture network construction, although high-pressure gas fracturing alone can produce dense fracture networks, the fracture area is small and cannot achieve regional soft rock modification. While high-pressure splitting grouting alone can form fractures with large extension lengths, the fracture system is simple (the number of fractures is limited and controlled by ground stress), making it impossible to form a high-density fracture network, resulting in a mediocre soft rock modification effect. In terms of grouting material selection and performance design, the selection of grouting materials and grouting performance parameters has traditionally relied primarily on engineering experience, failing to comprehensively consider specific characteristic parameters such as soft rock strength and fracture distribution. As a result, the soft rock strength after grouting modification cannot be significantly improved, or may even be lower than the pre-modification soft rock strength. Therefore, there is an urgent need to invent a green and efficient grouting modification method that can be applied to low permeability soft rock formations to meet the needs of low permeability soft rock disaster prevention and control projects. Summary of the Invention

[0003] The purpose of the present invention is to provide a super-compensating grouting modification method for low-permeability soft rock, including accurately evaluating the permeability of the injected soft rock medium through multi-source data, constructing a multi-level bifurcated three-dimensional fracture network through a variety of artificial induction methods, and scientifically designing the performance parameters of super-compensating grouting materials through a modified strength mixing law theory, ultimately achieving the mechanical properties of the soft rock after grouting modification exceeding that of the original soft rock mass, providing a new scientific method for solving the difficult problems of efficient and green grouting modification and disaster prevention and control of low-permeability soft rock formations.

[0004] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0005] The present invention is a method for modifying low-permeability soft rock by super-compensation grouting, comprising:

[0006] S1: Through the borehole water pressure test, borehole panoramic imaging test and borehole core micron CT scanning test, the Lu Rong value (Lu), fracture density (F d ), average crack opening (b avg ) and fractal dimension (D f ), based on multi-source data, jointly determine whether it belongs to low permeability soft rock medium;

[0007] S2: Design and prepare super-compensating grouting materials based on the modified strength mixing law theory;

[0008] S3: A variety of artificial induction methods are used to form a crack system with synergistic effects of pre-cracks, main cracks and secondary cracks in the soft rock, and super-compensating grouting materials are injected into the multi-level bifurcated three-dimensional crack network to achieve super-compensating grouting modification of soft rock.

[0009] As a preferred technical solution of the present invention, the specific S1 includes:

[0010] S1.1: Obtain the Lu Rong value (Lu) by drilling water pressure test;

[0011] S1.2: Borehole panoramic imaging test to obtain fracture density (F d );

[0012] S1.3: Determination of average fracture aperture by micron CT scanning of drill core (b avg ) and fractal dimension (D f );

[0013] S1.4: Determine whether it is a low permeability soft rock medium based on the data obtained above. When the Lurong value (Lu), crack density (F d ), average crack opening (b avg ), fractal dimension (D f ) and satisfy the following formulas When the conditions are met, the injected soft rock medium is judged to be of low permeability.

[0014] As a preferred technical solution of the present invention, the formula of the super-compensating grouting material in step S2 is as follows:

[0015] Main material: ultrafine Portland cement, with a particle size (D95) not exceeding 20 μm, accounting for 70-90% by mass;

[0016] Strength enhancing auxiliary material: nano-SiO2, particle size 10~50nm, mass proportion 5%~10%;

[0017] Rheology and water separation combined regulator: polycarboxylate water reducer and bentonite, accounting for 2% to 5% by mass;

[0018] Expansion compensator: A composite system of active MgO and sulphoaluminate clinker, accounting for 3% to 5% by mass, with an expansion rate of not less than 0.1%.

[0019] As a preferred technical solution of the present invention, the modified super-compensated grouting strength mixing law theoretical formula in step S2 is:

[0020] Where: V g is the pulp vein volume ratio, V g ≥20%; is the strength of soft rock, measured by standard laboratory rock mechanics test methods; is the contribution of the interface between slurry and soft rock cracks to the strength of the modified soft rock; is the target strength growth coefficient of soft rock after super-compensation grouting modification; is the strength of the slurry stone body, which is determined by the standard laboratory rock mechanics test method.

[0021] As a preferred technical solution of the present invention, step S3 specifically includes the following steps:

[0022] S3.1: Generate a short and dense “pre-crack” network through CO2 phase change low-energy blasting technology;

[0023] S3.2: Based on the pre-fracture network, a "main fracture" network is formed using high-pressure splitting grouting technology;

[0024] S3.3: Based on the primary fracture network, a “secondary fracture” network is generated using dynamic cyclic pulse grouting technology;

[0025] S3.4: Periodically alternate high-pressure splitting grouting with dynamic cyclic pulse grouting to form a complex three-dimensional fracture network structure.

[0026] As a preferred technical solution of the present invention, in step S3:

[0027] CO2 phase change low-energy blasting cracking: the blasting pressure peak is controlled at 30~80MPa, the blasting energy does not exceed 1000kJ, the length of the pre-crack formed is ≥30cm, and the fractal dimension of the pre-crack network is >2.5;

[0028] High-pressure splitting grouting: The high-pressure grouting pressure is 15~30MPa, and the length of the main crack formed is ≥2m;

[0029] Dynamic cyclic pulse grouting: The cyclic pulse pressure frequency is 1~20Hz, and the length of the secondary cracks formed is >5cm.

[0030] As a preferred technical solution of the present invention, the specific conditions for alternating grouting in S3.4 are: when the pressure drop of high-pressure splitting grouting is greater than 50%, switch to dynamic cyclic pulse grouting mode, and resume high-pressure splitting grouting after 5 to 20 minutes. The cycle is executed until the grouting is completed, and the final grouting pressure does not exceed the designed maximum splitting pressure and is stabilized for 5 to 10 minutes.

[0031] As a preferred technical solution of the present invention, the slurry vein volume ratio V after grouting in S3.4 is g ≥20%, and the strength of the modified soft rock meets the following conditions: , where: is the original strength of soft rock, is the strength of soft rock after modification, is the strength growth coefficient.

[0032] The low-permeability soft rock super-compensation grouting modification method provided by the present invention has significant technical advantages and beneficial effects:

[0033] 1. Accurate assessment and targeted design: By integrating multi-source data to build a permeability assessment model, we break through the limitations of traditional single water pressure testing, accurately identify low-permeability soft rock, provide a scientific basis for grouting solutions, and avoid blind construction.

[0034] 2. Efficient fracture network construction: The synergistic effect of CO2 phase change low-energy blasting, high-pressure splitting and dynamic cyclic pulse grouting is used to form a multi-level bifurcated three-dimensional network of "pre-fracture-main fracture-secondary fracture", which not only expands the fracture extension range but also increases the fracture density. It solves the problems of small fracture area or simple system in traditional methods and significantly improves the slurry penetration efficiency and modification range.

[0035] 3. Green high-strength material system: Ultrafine Portland cement is used as the main material, compounded with environmentally friendly components such as nano-SiO2 and activated MgO, replacing highly polluting chemical grouting materials. Through a modified strength mixing law theory design, a dense bond between the slurry and the soft rock interface is achieved. The strength of the modified soft rock exceeds that of the original rock mass, solving the problem of insufficient strength improvement caused by traditional grouting.

[0036] 4. Process Optimization and Cost-Effectiveness: The periodic alternating grouting process improves fracture expansion efficiency and reduces energy consumption. The low-cost and durable material formula significantly reduces project costs. It is suitable for large-scale soft rock reinforcement and disaster prevention in underground projects such as mining and geotechnical engineering, ensuring safe and efficient construction.

[0037] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 Schematic diagram of the process of the present invention;

[0040] Figure 2 Schematic diagram of the fracturing of soft rock from its initial state by CO2 phase transformation low-energy blasting in the present invention;

[0041] Figure 3 Schematic diagram of the first high-pressure splitting grouting and the first dynamic cycle pulse grouting in the present invention;

[0042] Figure 4 This is a schematic diagram of the second high-pressure splitting grouting and the second dynamic cycle pulse grouting in the present invention. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0044] In order to achieve the above object, the specific steps of the present invention are as follows ( Figure 1 shown):

[0045] S1. Comprehensive testing and evaluation of the permeability of injected soft rock media.

[0046] By combining borehole water pressure testing, panoramic borehole imaging, and micron CT scanning of drill cores, the multi-source data of "Lü Rong value, fracture density, fracture aperture, and fractal dimension" is used to comprehensively assess the permeability characteristics of the injected soft rock medium. When the injected soft rock medium thickness exceeds 5 meters, segmented testing and assessment are carried out, with each segment being 5 meters long.

[0047] S1.1 Obtaining the Lu Rong value (Lu) from a borehole water pressure test: Perform a double-plug water pressure test in accordance with the "Regulations for Water Conservancy and Hydropower Engineering Borehole Water Pressure Test" (SL31-2003) and the "Regulations for Water Conservancy and Hydropower Engineering Borehole Water Pressure Test" (NB / T 35113-2018), record the steady-state flow rate Q, and calculate the Lu Rong value:

[0048]

[0049] Where: L is the length of the test section, which is 5m; P is the water injection pressure, which is 0.3MPa, 0.6MPa and 1MPa respectively.

[0050] S1.2 Borehole panoramic imaging test to obtain fracture density (F d ): Use a borehole panoramic imager to obtain high-definition digital images of the borehole wall, combine digital image processing methods to intelligently identify and mark cracks, count the number of cracks per unit length of the survey line (in the axial direction of the borehole), and calculate the crack line density:

[0051]

[0052] Where: L is the length of the survey line, which is the same as the length of the water pressure test section mentioned above, which is 5m; N is the total number of cracks identified and counted within the survey line length.

[0053] S1.3 Micron CT scanning of drill core to determine the average fracture opening (b avg ) and fractal dimension (D f ):Using on-site drilled core samples, micron CT scanning test (resolution ≤ 1μm) was carried out in the laboratory to reconstruct the three-dimensional crack structure model of the sample and statistically analyze the average crack opening (b avg ), and the fractal dimension of the fracture network (D f ).

[0054] S1.4 Comprehensive evaluation criteria for the permeability of injected soft rock media: Based on the above test results, determine whether the injected soft rock media is low permeable according to the following criteria:

[0055]

[0056] Where: When Lu Rong value (Lu), crack density (F d ), average crack opening (b avg ), fractal dimension (D f ) When the above four conditions are met at the same time, the injected soft rock medium is judged to be of low permeability, under which condition the super-compensation grouting modification method needs to be adopted.

[0057] S3. Construction of complex artificial three-dimensional crack network Figure 2 、 Figure 3 、 Figure 4 shown.

[0058] A multi-level bifurcated artificial three-dimensional fracture network of "pre-fracture + main fracture + secondary fracture" was constructed by combining CO2 phase change low-energy blasting fracturing, high-pressure splitting grouting, and dynamic cycle pulse grouting (such as Figure 2 shown).

[0059] S3.1. CO2 phase change low-energy blasting to form a "pre-crack" network: CO2 phase change low-energy blasting to form a short and dense "pre-crack" network. The peak pressure of CO2 phase change blasting is controlled at 30~80MPa, and the blasting energy does not exceed 1000kJ. The length of the pre-cracks formed in the soft rock after blasting is ≥30cm, and the fractal dimension of the pre-crack network is >2.5.

[0060] S3.2 High-pressure splitting grouting to form a "main crack" network: High-pressure splitting grouting is carried out on the basis of the "pre-crack" network formed by CO2 phase change low-energy blasting. The "pre-cracks" are driven to expand by high-pressure slurry of 15~30MPa to form a "filled crack" network with a main crack length ≥2m.

[0061] S3.3 Dynamic cyclic pulse grouting to form a "secondary crack" network: Dynamic cyclic pulse grouting is performed on the basis of the "main crack" network formed by high-pressure splitting grouting. The pulsating pressure wave induces the main crack to produce "Y"-shaped bifurcation fatigue expansion to form a "secondary crack" network. The cyclic pulse pressure frequency is 1~20Hz, and the secondary crack length is >5cm.

[0062] S3.4 High-pressure splitting grouting and dynamic cyclic pulse grouting are implemented alternately and periodically to form a complex three-dimensional fracture network through the temporal coupling of "splitting extension" and "fatigue damage". The implementation sequence is as follows: first, high-pressure grouting is performed. When the pressure drop of high-pressure splitting grouting pressure is greater than 50%, the high-pressure splitting grouting mode is switched to dynamic cyclic pulse grouting. After performing dynamic cyclic pulse grouting for 5 to 20 minutes, it is switched to high-pressure splitting grouting mode again. This cycle is repeated until the grouting is completed. The grouting end standard is to control the grouting pressure to not exceed the designed maximum splitting grouting pressure (15 to 30 MPa) and maintain the pressure for 5 to 10 minutes.

[0063] The volume ratio of pulp veins (V g ) Statistical calculation: After the grouting is completed and the slurry is finally set, the drilling core sampling statistical method or the drilling panoramic imaging test method is used to arrange representative boreholes in the grouting area and statistically calculate the slurry injection volume ratio (V g ):

[0064]

[0065] Where: L g is the cumulative length of the pulp vein segment, L t is the total length of the test section, V g is the volume ratio of slurry vein. For super compensation grouting, V g ≥20%.

[0066] S2. Performance design of super-compensating grouting materials.

[0067] To ensure the modification effect of super-compensation grouting on soft rock, the properties of grouting materials must meet the following modified super-compensation grouting strength mixing law theory:

[0068]

[0069] Where: V g is the pulp vein volume ratio, V g ≥20%; is the strength of soft rock, measured by standard laboratory rock mechanics test methods; is the contribution of the interface between slurry and soft rock cracks to the strength of the modified soft rock; is the target strength growth coefficient of soft rock after super-compensation grouting modification; The strength of the slurry stone body is determined by the standard laboratory rock mechanics test method. The strength of the serous stone should meet .

[0070] To meet the above-mentioned slurry stone strength performance, the following material components are designed: ultrafine silicate cement as the main material, with a material particle size (D95) not exceeding 20μm, accounting for more than 70% to 90% by mass; strength-enhancing auxiliary material, nano-SiO2 with a particle size of 10 to 50nm, accounting for 5% to 10% by mass; rheology and water precipitation combined control agents, using polycarboxylic acid water reducer and bentonite, accounting for 2% to 5% by mass; expansion compensator, using a composite system of active MgO and sulfoaluminate clinker, accounting for 3% to 5% by mass, and an expansion rate of not less than 0.1%.

[0071] Using the above grouting materials, the slurry can be tightly combined with the soft rock crack interface under the action of high pressure drive and self-expansion stress. At the same time, part of the slurry can penetrate into the micro cracks of the interface to form a root pile anchoring microstructure, which significantly improves the contribution of the bonding strength between the slurry and the soft rock crack interface. , ≥1MPa.

[0072] Comprehensive mechanical properties of soft rock after super-compensation grouting modification.

[0073] After grouting, the growth of soft rock strength and mechanical properties meets the following conditions:

[0074]

[0075] Where: is the original strength of soft rock, is the strength of soft rock after modification, is the strength growth coefficient.

[0076] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0077] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A super-compensation grouting modification method for low permeability soft rock, characterized in that: include: S1: Through borehole water pressure test, borehole panoramic imaging test and drill core micron CT scanning test, the Lu Rong value, fracture density, average fracture aperture and fractal dimension are obtained, and based on multi-source data, whether it belongs to low permeability soft rock medium is determined; S2: Design and prepare super-compensating grouting materials based on the modified strength mixing law theory; S3: Using a variety of artificial induction methods, a fracture system with synergistic effects of pre-cracks, main cracks and secondary cracks is formed in the soft rock, and super-compensation grouting material is injected into the multi-level bifurcated three-dimensional fracture network to achieve super-compensation grouting modification of the soft rock; Wherein said step S3 comprises: S3.1: Generate a short and dense "pre-crack" network through CO2 phase change low-energy explosion technology; S3.2: Based on the pre-fracture network, a "main fracture" network is formed using high-pressure splitting grouting technology; S3.3: Based on the primary fracture network, a "secondary fracture" network is generated using dynamic cyclic pulse grouting technology; S3.4: Periodically alternate high-pressure splitting grouting with dynamic cyclic pulse grouting to form a complex three-dimensional fracture network structure.

2. The low permeability soft rock super-compensation grouting modification method according to claim 1, characterized in that: Specifically, the S1 includes: S1.1: Obtain the Lv Rong value by water pressure test on the borehole; S1.2: Borehole panoramic imaging test to obtain fracture density; S1.3: Determination of average fracture aperture and fractal dimension using micrometer CT scanning of drill cores; S1.4: Determine whether the injected soft rock medium is low permeability based on the data obtained above. When the Lü Rong value, fracture density, average fracture aperture, and fractal dimension all meet the following conditions: Lü Rong value ≤ 10, fracture density ≤ 1 fracture / m, average fracture aperture ≤ 50 μm, and fractal dimension ≤ 2.0, the injected soft rock medium is determined to be low permeable.

3. The low permeability soft rock super-compensation grouting modification method according to claim 1, characterized in that: The super-compensation grouting material formula in step S2 comprises: Main material: ultrafine Portland cement, with a particle size of no more than 20 μm, accounting for 70-90% by mass; Strength enhancing auxiliary material: nano-SiO2, particle size 10~50nm, mass proportion 5%~10%; Rheology and water separation combined regulator: polycarboxylate water reducer and bentonite, accounting for 2% to 5% by mass; Expansion compensator: A composite system of active MgO and sulphoaluminate clinker, accounting for 3% to 5% by mass, with an expansion rate of not less than 0.1%.

4. The low permeability soft rock super-compensation grouting modification method according to claim 3, characterized in that: The intensity mixing law theoretical formula modified in step S2 is: , Where: V g is the pulp vein volume ratio, V g ≥20%; is the strength of soft rock, measured by standard laboratory rock mechanics test methods; is the contribution of the interface between slurry and soft rock cracks to the strength of the modified soft rock; is the target strength growth coefficient of soft rock after super-compensation grouting modification; is the strength of the slurry stone body, which is determined by the standard laboratory rock mechanics test method.

5. The low permeability soft rock super-compensation grouting modification method according to claim 1, characterized in that: In the step S3: CO2 phase change low-energy blasting cracking: the blasting pressure peak is controlled at 30~80MPa, the blasting energy does not exceed 1000kJ, the length of the pre-crack formed is ≥30cm, and the fractal dimension of the pre-crack network is >2.5; High-pressure splitting grouting: The high-pressure grouting pressure is 15~30MPa, and the length of the main crack formed is ≥2m; Dynamic cyclic pulse grouting: The cyclic pulse pressure frequency is 1~20Hz, and the length of the secondary cracks formed is >5cm.

6. The low permeability soft rock super-compensation grouting modification method according to claim 5, characterized in that: The specific conditions for alternating grouting in S3.4 are as follows: when the pressure drop of high-pressure splitting grouting is greater than 50%, switch to dynamic cyclic pulse grouting mode, continue for 5 to 20 minutes, and then resume high-pressure splitting grouting. The cycle is performed until the grouting is completed, and the final grouting pressure does not exceed the designed maximum splitting pressure and is maintained at a constant pressure for 5 to 10 minutes.

7. The low permeability soft rock super-compensation grouting modification method according to claim 6, characterized in that: The volume of the slurry vein in S3.4 after grouting is completed accounts for V g ≥20%, and the strength of the modified soft rock meets the following conditions: , where: is the original strength of soft rock, is the strength of soft rock after modification, is the strength growth coefficient.

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