Super-compensation grouting modification method for low-permeability soft rock

Abstract

The invention discloses a low-permeability soft rock super-compensation grouting modification method, and relates to the technical field of surrounding rock control of underground engineering such as mining and rock soil. The method comprises the steps that permeability is evaluated through multi-source data, Lurong values, fracture density, opening and fractal dimensions are obtained through a drilling water pressing test, panoramic imaging and micron CT scanning, and a model is constructed to accurately recognize the low-permeability soft rock. Multi-stage fracture construction is conducted, CO2 phase change low-energy blasting is adopted to form pre-fractures, 15-30 MPa high-pressure splitting and 1-20 Hz dynamic pulse grouting are combined, a pre-primary-secondary three-dimensional fracture network is alternately constructed, and it is ensured that the slurry vein volume ratio is larger than or equal to 20%; according to the design of a super-compensation material, superfine Portland cement is taken as a main material, nano SiO2, a polycarboxylate superplasticizer and an active MgO composite expanding agent are compounded, dense combination of a crack interface is realized through high pressure and self-expansion, and the contribution of the interface strength is greater than or equal to 1MPa; the method is green and efficient, is suitable for underground engineering low-permeability soft rock reinforcement and disaster prevention and control, and breaks through the bottleneck of the traditional grouting technology.

Description

Technical Field

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

[0002] Chinese patents ZL201510380977.5, ZL201510368674.1, ZL201510368674.1, etc. propose a high-pressure gas pre-splitting grouting device and method, which provides a good technical idea for solving the problem of grouting modification of low-permeability soft rock. However, there are still no more scientific and effective methods in aspects such as the permeability test and evaluation of the soft rock medium to be grouted, the construction of artificial fracture networks, and the performance design of grouting materials. Specifically, in terms of the permeability test and evaluation of the soft rock medium to be grouted, traditional permeability test and evaluation usually rely on the Lu value of the single-hole water pressure test. However, the single-hole water pressure test only reflects the macroscopic average permeability, ignores the influence of the local water-conducting dominant channels of macroscopic fractures, and at the same time cannot accurately describe the fracture aperture characteristics and the complexity of micro-fracture distribution under microscopic conditions. In terms of the construction of artificial fracture networks, although a dense fracture network can be generated by means of high-pressure gas fracturing alone, the fracture area is small and regional soft rock modification cannot be achieved. And although the high-pressure splitting grouting technology alone can form fractures with a larger extended length, the fracture system is simple (the number of fractures is limited and controlled by in-situ stress), and a high-density fracture network cannot be formed. Therefore, the soft rock modification effect is generally average. In terms of the selection and performance design of grouting materials, in the past, the selection of grouting materials and grouting performance parameters mainly relied on engineering experience, and specific characteristic parameters such as soft rock strength and fracture distribution were not comprehensively considered, resulting in the fact that the strength of the soft rock after grouting modification cannot be significantly improved or even lower than the strength of the soft rock before modification. Therefore, there is an urgent need to invent a green and efficient grouting modification method applicable to low-permeability soft rock strata 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 method for modifying low-permeability soft rock by over-compensated grouting, including accurately evaluating the permeability of the soft rock medium to be grouted through multi-source data, constructing a multi-level bifurcated three-dimensional fracture network through various artificial induction methods, and scientifically designing the performance parameters of the over-compensated grouting material through the modified strength mixing law theory. Finally, the mechanical properties of the soft rock after grouting modification exceed those of the original soft rock mass, providing a new scientific method for solving the problems of efficient green grouting modification and disaster prevention and control of low-permeability soft rock strata.

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

[0005] The present invention is a method for modifying low-permeability soft rock by over-compensated grouting, including:

[0006] S1: Obtain the Lu value, fracture density (F d ), average fracture aperture (b avg ), and fractal dimension (D f ) through the water pressure test in boreholes, panoramic imaging test in boreholes, and micro-CT scanning test of borehole cores, and jointly judge whether it belongs to low-permeability soft rock media based on multi-source data;

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

[0008] S3: Use a variety of artificial induction methods to form a fracture system with the coordinated action of pre-fractures, main fractures, and secondary fractures in the soft rock, and inject the super-compensated grouting material into the multi-level bifurcated three-dimensional fracture network to achieve the super-compensated grouting modification of the soft rock.

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

[0010] S1.1: Obtain the Lu value through the water pressure test in boreholes;

[0011] S1.2: Obtain the fracture density (F d ) through the panoramic imaging test in boreholes;

[0012] S1.3: Determine the average fracture aperture (b avg ) and fractal dimension (D f ) through the micro-CT scanning of borehole cores;

[0013] S1.4: Judge whether it belongs to low-permeability soft rock media according to the data obtained above. When the Lu value, fracture density (F d ), average fracture aperture (b avg ), and fractal dimension (D f ) simultaneously satisfy the following formula conditions, it is determined that the soft rock media to be grouted belongs to low permeability.

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

[0015] Main material: ultra-fine Portland cement, with a material particle size (D95) not exceeding 20 μm and a mass ratio of 70-90%;

[0016] Strength enhancement auxiliary material: nano-SiO2, with a particle size of 10-50 nm and a mass ratio of 5%-10%;

[0017] Rheology and bleeding joint regulator: polycarboxylate water reducer and bentonite, with a mass ratio of 2%-5%;

[0018] Expansion compensator: a composite system of reactive MgO and sulphoaluminate clinker, with a mass proportion of 3% - 5% and an expansion rate of not less than 0.1%.

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

[0020] In the formula: V g is the proportion of the grout vein volume, V g ≥20%; is the strength of the soft rock, determined by the standard laboratory rock mechanics test method; is the contribution of the combination of the grout and the soft rock fracture interface to the strength of the modified soft rock; is the target strength growth coefficient of the soft rock after super-compensated grouting modification; is the strength of the grout stone body, 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-fracture" network through CO2 phase change low-energy blasting technology;

[0023] S3.2: On the basis of the pre-fracture network, use high-pressure splitting grouting technology to form a "main fracture" network;

[0024] S3.3: On the basis of the main fracture network, apply dynamic cyclic pulse grouting technology to generate a "secondary fracture" network;

[0025] S3.4: Periodically and alternately implement high-pressure splitting grouting and 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 fracture: The peak blasting pressure is controlled at 30 - 80 MPa, the blasting energy does not exceed 1000 kJ, the length of the formed pre-fracture is ≥30 cm, and the fractal dimension of the pre-fracture network > 2.5;

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

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

[0030] As a preferred technical solution of the present invention, the specific conditions for alternate grouting in S3.4 are as follows: when the pressure drop of high-pressure splitting grouting > 50%, switch to the dynamic cyclic pulse grouting mode, resume high-pressure splitting grouting after 5 - 20 min, and execute cyclically until the grouting ends, and the final grouting pressure does not exceed the designed maximum splitting pressure and is stabilized for 5 - 10 min.

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

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

[0033] 1. Precise evaluation and targeted design: By constructing a permeability evaluation model through multi-source data fusion, breaking through the limitations of traditional single-stage water pressure tests, accurately identifying low-permeability soft rocks, providing a scientific basis for the grouting plan, and avoiding 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-fractures - main fractures - secondary fractures", which not only expands the fracture propagation range but also improves the fracture density, solves the problems of small fracture zones or simple systems in traditional methods, and significantly improves the slurry penetration efficiency and modification range.

[0035] 3. Green high-strength material system: Using ultrafine Portland cement as the main material, compounding environmentally friendly components such as nano-SiO2 and active MgO to replace highly polluting chemical grouting materials; through the design of the modified strength mixing law theory, realizing a dense combination at the interface between the slurry and the soft rock, and the strength of the modified soft rock exceeds that of the original rock mass, solving the problem of insufficient strength improvement in traditional grouting.

[0036] 4. Process optimization and cost-effectiveness: The periodic alternate grouting process improves the fracture propagation efficiency and reduces energy consumption; the material formula has low cost and good durability, significantly reducing the project cost, and is applicable to large-scale soft rock reinforcement and disaster prevention in underground engineering such as mining and geotechnical engineering, ensuring safe and efficient construction.

[0037] Of course, it is not necessary for any product implementing the present invention to simultaneously achieve all the above-mentioned advantages. Description of the Drawings

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0039] Figure 1 It is a schematic flow chart of the method of the present invention;

[0040] Figure 2 It is a schematic diagram of the fracturing of soft rock from the initial state by CO2 phase change low-energy blasting in the present invention;

[0041] Figure 3 It is a schematic diagram of the first high-pressure splitting grouting and the first dynamic cyclic pulse grouting in the present invention;

[0042] Figure 4 It is a schematic diagram of the second high-pressure splitting grouting and the second dynamic cyclic pulse grouting in the present invention. Specific Embodiments

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

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

[0045] S1. Comprehensive test and evaluation of the permeability of the soft rock medium to be grouted.

[0046] Combining the borehole water pressure test, borehole panoramic imaging test, borehole core micrometer CT scan test, etc., and using multi-source data such as "Lu value - fracture density - fracture aperture - fractal dimension" to comprehensively evaluate the permeability characteristics of the soft rock medium to be grouted. When the thickness of the soft rock medium to be grouted exceeds 5m, carry out segmented test and evaluation, and the length of each segment is 5m.

[0047] S1.1 Obtaining the Lu value (Lu) through the borehole water pressure test: Perform the double-packer water pressure test in accordance with the "Code for Borehole Water Pressure Test of Water Resources and Hydropower Engineering" (SL31 - 2003) and the "Code for Borehole Water Pressure Test of Hydropower Engineering" (NB / T 35113 - 2018), record the stable flow rate Q, and calculate the Lu value:

[0048]

[0049] Where: L is the length of the test section, taken as 5 m; P is the water injection pressure, taken as 0.3 MPa, 0.6 MPa and 1 MPa 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 fractures, count the number of fractures per unit length of the measurement line (borehole axial direction), and calculate the fracture line density:

[0051]

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

[0053] S1.3 Determination of the average aperture (b avg ) and fractal dimension (D f ) of fractures by micro-CT scanning of borehole cores: Use on-site borehole core samples to conduct micro-CT scanning tests (resolution ≤ 1 μm) in the laboratory, reconstruct the three-dimensional fracture structure model of the sample, statistically analyze the average aperture (b avg ), and calculate the fractal dimension (D f ) of the fracture network by the box dimension method.

[0054] S1.4 Comprehensive evaluation criterion for the permeability of the soft rock medium to be grouted: According to the above test results, judge whether the soft rock medium to be grouted belongs to low permeability according to the following criteria:

[0055]

[0056] Where: When the Lugeon value (Lu), fracture density (F d ), average aperture of fractures (b avg ), and fractal dimension (D f ) simultaneously meet the above four groups of conditions, it is determined that the soft rock medium to be grouted belongs to low permeability, and the super-compensated grouting modification method needs to be adopted under this condition.

[0057] S3. Construction of a complex artificial three-dimensional fracture network as shown in Figure 2 , Figure 3 , Figure 4 .

[0058] Adopt a method combining CO2 phase change low-energy blasting fracture, high-pressure splitting grouting, and dynamic cyclic pulse grouting to construct a multi-level bifurcated artificial three-dimensional fracture network of "pre-fractures + main fractures + secondary fractures" (as shown in Figure 2 ).

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

[0060] S3.2, Formation of "main - fracture" network by high - pressure splitting grouting: Based on the "pre - fracture" network formed by low - energy blasting of CO2 phase change, conduct high - pressure splitting grouting. Use high - pressure slurry of 15 - 30 MPa to drive the "pre - fractures" to expand and form a "grouted - fracture" network. The length of the main fractures is ≥2 m.

[0061] S3.3, Formation of "secondary - fracture" network by dynamic cyclic pulse grouting: Based on the "main - fracture" network formed by high - pressure splitting grouting, conduct dynamic cyclic pulse grouting. Induce the "Y" - type bifurcation fatigue expansion of the main fractures through pulsating pressure waves to form a "secondary - fracture" network. The frequency of the cyclic pulse pressure is 1 - 20 Hz, and the length of the secondary fractures is >5 cm.

[0062] S3.4, Alternate high - pressure splitting grouting and dynamic cyclic pulse grouting periodically. Through the sequential coupling of "splitting expansion" and "fatigue damage", form a complex three - dimensional fracture network. The implementation sequence is as follows: First, conduct high - pressure grouting. When the pressure drop of the high - pressure splitting grouting pressure is >50%, switch the high - pressure splitting grouting mode to dynamic cyclic pulse grouting. After executing dynamic cyclic pulse grouting for 5 - 20 min, switch back to the high - pressure splitting grouting mode again. Repeat this cycle until the grouting is completed. The grouting completion standard is to control the grouting pressure not to exceed the designed maximum splitting grouting pressure (15 - 30 MPa) and keep it stable for 5 - 10 min.

[0063] Calculation of the volume ratio of grout veins (V g ): After the grouting is completed and the grout has finally set, use the core - drilling statistical method or the borehole panoramic imaging test method to arrange representative boreholes in the grouting area and calculate the volume ratio of the grout injected (V g ):

[0064]

[0065] In the formula: L g is the cumulative length of the grout vein section, L t is the total length of the test section, and V g is the volume ratio of the grout veins. For over - compensation grouting, V g ≥20%.

[0066] S2. Design of the performance of over - compensation grouting materials.

[0067] To ensure the modification effect of soft rock over-compensated grouting, the performance of the grouting material shall meet the following modified over-compensated grouting strength mixing law theory:

[0068]

[0069] In the formula: V g is the proportion of the slurry vein volume, V g ≥20%; is the strength of the soft rock, which is determined by the standard laboratory rock mechanics test method; is the contribution of the combination of the slurry and the soft rock fracture interface to the strength of the modified soft rock; is the target strength growth coefficient after the modification of soft rock by over-compensated grouting; is the strength of the slurry stone body, which is determined by the standard laboratory rock mechanics test method. When the target strength growth coefficient is taken, the strength of the slurry stone body shall meet .

[0070] To meet the above strength performance of the slurry stone body, it is designed with the following material components: ultrafine Portland cement as the main material, the particle size (D95) of which does not exceed 20μm, and the mass ratio is more than 70-90%; strength enhancing auxiliary materials, nano-SiO2 with a particle size of 10-50nm, and the mass ratio is 5%-10%; rheology and bleeding combined regulator, using polycarboxylate water reducer and bentonite, and the mass ratio is 2%-5%; expansion compensator, using a composite system of active MgO and sulphoaluminate clinker, and the mass ratio is 3%-5%, and the expansion rate is not less than 0.1%.

[0071] Using the above grouting material, under the action of high-pressure drive and self-expansion stress, the slurry can be densely combined with the soft rock fracture interface. At the same time, part of the slurry can infiltrate into the interface micro-fractures to form a root pile anchoring micro-structure, significantly enhancing the contribution of the combination strength of the slurry and the soft rock fracture interface , ≥1MPa.

[0072] The comprehensive mechanical properties after the modification of soft rock by over-compensated grouting.

[0073] After the grouting is completed, the growth of the mechanical properties of the soft rock strength shall meet the following conditions:

[0074]

[0075] In the formula: is the original strength of the soft rock, is the strength of the modified soft rock, is the strength growth coefficient.

[0076] In the description of this specification, the descriptions referring to the terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0077] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. Ultra-compensation grouting modification method for low-permeability soft rock, characterized in that Including: S1: Obtain the Lugeon value, fracture density, average fracture aperture, and fractal dimension through the water pressure test in boreholes, panoramic imaging test in boreholes, and micron CT scan test of borehole cores, and jointly judge whether it belongs to low-permeability soft rock media based on multi-source data; S2: Design and prepare a super-compensation grouting material based on the modified strength mixing law theory; S3: Use a variety of artificial induction methods to form a fracture system with the synergistic action of pre-fractures, main fractures, and secondary fractures in soft rock, and inject the super-compensation grouting material into the multi-level bifurcated three-dimensional fracture network to achieve the super-compensation grouting modification of soft rock.

2. The over-compensation grouting modification method for low-permeability soft rock according to claim 1, wherein Specifically, the above-mentioned S1 includes: S1.1: Obtain the Lugeon value through the water pressure test in boreholes; S1.2: Obtain the fracture density through the panoramic imaging test in boreholes; S1.3: Determine the average fracture aperture and fractal dimension through the micron CT scan of borehole cores; S1.4: Judge whether it belongs to low-permeability soft rock media according to the data obtained above. When the Lugeon value, fracture density, average fracture aperture, and fractal dimension simultaneously meet the conditions: Lugeon value ≤ 10, fracture density ≤ 1 fracture / m, average fracture aperture ≤ 50 μm, fractal dimension ≤ 2.0, it is determined that the soft rock media to be grouted belongs to low permeability.

3. The low-permeability soft rock ultra-compensation grouting modification method according to claim 1, characterized in that The formula of the super-compensation grouting material in the above-mentioned step S2 includes: Main material: ultra-fine Portland cement, with a particle size not exceeding 20 μm, and a mass ratio of 70% - 90%; Strength-enhancing auxiliary material: nano-SiO2, with a particle size of 10 - 50 nm, and a mass ratio of 5% - 10%; Rheology and bleeding combined regulator: polycarboxylate water reducer and bentonite, with a mass ratio of 2% - 5%; Expansion compensator: a composite system of active MgO and sulphoaluminate clinker, with a mass ratio of 3% - 5% and an expansion rate not less than 0.1%.

4. The low-permeability soft rock ultra-compensation grouting modification method according to claim 3, characterized in that, The corrected hyper-compensation grouting strength mixing law theoretical formula in the step S2 is as follows: , Where: V g is the proportion of the slurry vein volume, V g ≥ 20%; is the soft rock strength, which is determined by the standard laboratory rock mechanics test method; is the contribution of the combination of the slurry and the soft rock fracture interface to the strength of the modified soft rock; is the target strength growth coefficient after the modified soft rock by over-compensated grouting; 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 ultra-compensation grouting modification method according to claim 1, characterized in that The above-mentioned step S3 includes: S3.1: Generate a short and dense "pre-fracture" network through the CO2 phase change low-energy blasting technology; S3.2: Form a "main fracture" network on the basis of the pre-fracture network by using the high-pressure splitting grouting technology; S3.3: Generate a "secondary fracture" network on the basis of the main fracture network by applying the dynamic cyclic pulse grouting technology; S3.4: Periodically and alternately implement high-pressure splitting grouting and dynamic cyclic pulse grouting to form a complex three-dimensional fracture network structure.

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

7. The method for modifying low-permeability soft rock by over-compensated grouting according to claim 6, characterized in that The specific conditions for alternate grouting in the above-mentioned S3.4 are: When the pressure drop of high-pressure splitting grouting > 50%, switch to the dynamic cyclic pulse grouting mode, continue for 5 - 20 min and then resume high-pressure splitting grouting, and cycle until the grouting is completed, and the final grouting pressure does not exceed the designed maximum splitting pressure and stabilizes for 5 - 10 min.

8. The low-permeability soft rock ultra-compensation grouting modification method according to claim 7, characterized in that The proportion V of the volume of the grout veins after grouting in S3.4 g ≥ 20%, and the strength of the modified soft rock meets the following conditions: , where: is the original strength of the soft rock, is the strength of the modified soft rock, is the strength growth coefficient.

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