CO2 foam cement mortar material and soft rock reinforcing method and system

Abstract

The invention discloses a CO2 foam cement mortar material and a soft rock reinforcing method and system.The CO2 foam cement mortar material is prepared from CO2 foam and cement mortar, and the cement mortar is prepared from, by mass, 8%-10% of magnesium oxychloride cement, 16%-18% of fly ash, 3.5%-4% of bentonite, 51%-53% of river sand and 17%-19% of water; the mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is (0.5-2): 1. Portland cement commonly used in the CO2 foam cement mortar is replaced with the magnesium oxychloride cement, so that the strength of the cured slurry is improved, and the soft rock reinforcing capacity is enhanced; meanwhile, the mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is improved, and the result shows that the reinforcing capacity of the CO2 foam cement mortar is higher under the optimal mass ratio.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering technology, and in particular to a CO2 foam cement mortar material, a soft rock reinforcement method and a system. Background Art

[0002] In the process of underground engineering, tunnel construction and mining, the stability of soft rock formations is a key factor affecting engineering safety and progress. Due to its softness, expansion, strong rheology and poor injectability, soft rock formations are prone to deformation and damage during construction, leading to engineering accidents.

[0003] Traditional soft rock reinforcement methods include mechanical reinforcement, physical reinforcement and chemical grouting. Mechanical reinforcement methods such as anchors and steel mesh provide support, but they are not ideal and prone to failure under soft rock conditions with high expansion rate and high deformation. Physical reinforcement methods such as heating and freezing have limited application scope and high cost. Chemical grouting injects chemical slurry, which forms a high-strength consolidated body after solidification. However, conventional slurry has high viscosity and poor fluidity, making it difficult to penetrate fine cracks, resulting in uneven reinforcement effect. In addition, the consolidated body is not elastic enough and is difficult to adapt to long-term deformation of soft rock.

[0004] In order to overcome the shortcomings of the existing technology, it is necessary to provide a soft rock reinforcement method that can improve the permeability and uniformity of the slurry, improve the long-term performance, and reduce the possibility of geological disasters in soft rock formations during excavation. In contrast, pulsating grouting is an advanced reinforcement method that can increase the bearing capacity and anti-subsidence capacity of soft rock, thereby ensuring the safety and stability of soft rock. However, the formula of the CO2 foam cement mortar material currently used in pulsating grouting is relatively simple, and a large amount of silicate cement is required. It is necessary to improve the existing CO2 foam cement mortar material to meet more scenarios. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a CO2 foam cement mortar material, wherein the cement mortar comprises, by mass percentage, 8%-10% magnesium oxychloride cement, 16%-18% fly ash, 3.5%-4% bentonite, 51%-53% river sand, 17%-19% water; The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 0.5-2:1.

[0006] Furthermore, the foaming ratio of the CO2 foam to cement mortar is 3-5:1.

[0007] Furthermore, the method for preparing the CO2 foam comprises: Mixing a foaming agent, a foam stabilizer and water to obtain a foaming liquid; CO2 is passed into the foaming liquid for foaming to obtain CO2 foam.

[0008] Furthermore, the foaming liquid comprises, by mass percentage, 1%-2% of a foaming agent, 1.5%-3% of a foam stabilizer, and water as the balance.

[0009] In the present invention, the types of the foaming agent and the foam stabilizer do not need to be strictly limited. For example, the foaming agent may be tea saponin (TS), and the stabilizer may be sodium dodecylbenzene sulfonate (SDBS).

[0010] Furthermore, the volume of the CO2 foam is more than 5.5 times the volume of the foaming liquid, and the stability time of the CO2 foam is greater than 30 minutes.

[0011] Furthermore, the 2h precipitation rate of the CO2 foam cement mortar material is less than 5%.

[0012] The present invention also provides a soft rock reinforcement method, comprising: Complete drilling operations in soft rock formations that need to be reinforced, and run casing and grouting pipes; The CO2 foam cement mortar material is injected into the soft rock formation through a grouting pipe by pulsating grouting, wherein the grouting pipe is first lowered to the bottom for grouting, and then the grouting pipe is lifted up to complete the reinforcement of the soft rock formation in sections from bottom to top.

[0013] Furthermore, the pressure of the pulsating grouting is 0.5-2.0 MPa, and the pulsating frequency is 20-30 times / min.

[0014] The present invention also provides a soft rock reinforcement system, comprising a cement mortar unit and a grouting unit; The cement mortar unit is used to prepare and store the above-mentioned CO2 foam cement mortar material; The grouting unit is used to inject the CO2 foam cement mortar material in the cement mortar unit into the soft rock formation that needs to be reinforced by using pulse grouting.

[0015] Furthermore, the grouting unit includes a pulsating pump and a grouting pipe connected to each other, and a telescopic device, wherein the telescopic device is used to lift or lower the grouting pipe. Compared with the prior art, the present invention has the following beneficial effects: The present invention replaces the commonly used silicate cement in CO2 foam cement mortar with magnesium oxychloride cement, so that the strength of the slurry after curing is improved and the ability to reinforce soft rock is enhanced; at the same time, the mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is improved. The results show that under the optimal mass ratio, the reinforcement ability of the CO2 foam cement mortar is stronger. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 The preparation flow chart of CO2 foam cement mortar material is shown; Figure 2 The structural schematic diagram of the cement mortar unit is shown; Figure 3 A schematic diagram showing a grouting unit injecting grout into a formation is shown; Figure 4 A detailed view of grouting through a grouting pipe is shown; Figure 5 The schematic diagram of pulsed segmented splitting grouting in soft rock formation is shown; Description of reference numerals: 1. CO2 gas cylinder; 2. Air inlet valve; 3. First air pump; 4. Second air pump; 5. Control box; 6. High-pressure mixing container; 7. Foaming liquid tank; 8. Bubble valve; 9. Foam tank; 10. Pulsating pump; 11. Flow meter; 12. Pressure gauge; 13. Orifice sealer; 14. Grouting pipe; 15. CO2 foam cement mortar material; 16. Mud wall protection; 17. Dendritic slurry veins; 18. Soft rock layer; 19. Telescopic device; 20. Grouting hole; 21. Grouting plug; 22. Flower pipe section. DETAILED DESCRIPTION

[0018] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0019] The following will be combined with the specific embodiments of the present invention and the drawings of the specification to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0020] Example 1 A CO2 foam cement mortar material, with a 2h precipitation rate of less than 5%, is obtained by mixing CO2 foam and cement mortar at a foam-mortar ratio of 4.5:1. The CO2 foam comprises 0.5% TS, 1.5% SDS and 98% water by mass, and the cement mortar comprises 8% magnesium oxychloride cement, 18% fly ash, 4% bentonite, 52% river sand and 18% water by mass. The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 1:1.

[0021] Example 2 A CO2 foam cement mortar material, with a 2h precipitation rate of less than 5%, is obtained by mixing CO2 foam and cement mortar at a foam-mortar ratio of 4.5:1. The CO2 foam comprises 0.5% TS, 1.5% SDS and 98% water by mass, and the cement mortar comprises 9% magnesium oxychloride cement, 17% fly ash, 4% bentonite, 52% river sand and 18% water by mass. The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 1:1.

[0022] Example 3 A CO2 foam cement mortar material, with a 2h precipitation rate of less than 5%, is obtained by mixing CO2 foam and cement mortar at a foam-mortar ratio of 4.5:1. The CO2 foam comprises 0.5% TS, 1.5% SDS and 98% water by mass, and the cement mortar comprises 10% magnesium oxychloride cement, 16% fly ash, 4% bentonite, 52% river sand and 18% water by mass. The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 1:1.

[0023] Example 4 A CO2 foam cement mortar material, with a 2h precipitation rate of less than 5%, is obtained by mixing CO2 foam and cement mortar at a foam-mortar ratio of 4.5:1. The CO2 foam comprises 0.5% TS, 1.5% SDS and 98% water by mass, and the cement mortar comprises 9% magnesium oxychloride cement, 17% fly ash, 4% bentonite, 52% river sand and 18% water by mass. The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 0.5:1.

[0024] Example 5 A CO2 foam cement mortar material, with a 2h precipitation rate of less than 5%, is obtained by mixing CO2 foam and cement mortar at a foam-mortar ratio of 4.5:1. The CO2 foam comprises 0.5% TS, 1.5% SDS and 98% water by mass, and the cement mortar comprises 9% magnesium oxychloride cement, 17% fly ash, 4% bentonite, 52% river sand and 18% water by mass. The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 2:1.

[0025] Comparative Example 1 A cement mortar material comprises 8% magnesium oxychloride cement, 18% fly ash, 4% bentonite, 52% river sand and 18% water in terms of mass percentage. The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 1:1.

[0026] Comparative Example 2 A cement mortar material comprises, by mass percentage, 9% magnesium oxychloride cement, 17% fly ash, 4% bentonite, 52% river sand and 18% water. The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 1:1.

[0027] Comparative Example 3 A cement mortar material comprises, by mass percentage, 10% magnesium oxychloride cement, 16% fly ash, 4% bentonite, 52% river sand and 18% water. The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 1:1.

[0028] Comparative Example 4 A cement mortar material comprises, by mass percentage, 9% of No. 42.5 ordinary Portland cement, 16% of fly ash, 4% of bentonite, 52% of river sand and 18% of water.

[0029] Comparative Example 5 A CO2 foam cement mortar material, with a 2h precipitation rate of less than 5%, is obtained by mixing CO2 foam and cement mortar at a foam ratio of 4.5:1. The CO2 foam comprises 0.5% TS, 1.5% SDS and 98% water by mass, and the cement mortar comprises 9% No. 42.5 ordinary Portland cement, 17% fly ash, 4% bentonite, 52% river sand and 18% water by mass.

[0030] The viscosity and 7d compressive strength of the mortar materials of the embodiment and the comparative example were tested, and the results are shown in Table 1.

[0031] Table 1 Viscosity of mortar materials and 7d compressive strength results

[0032] From the test results in Table 1, it can be seen that the addition of CO2 water-based foam improves the early strength of the grouting material. The main reason is that the introduction of carbon dioxide foam leads to the consumption of hydration products near the voids and accelerates the carbonization reaction of cement particles around the void-cement interface. This promotes the solidification of the foam inside the cement paste and ultimately improves the early strength of the paste. At the same time, the addition of CO2 water-based foam reduces the viscosity of the grouting material, indicating that CO2 water-based foam helps to improve the permeability of the grouting, making it easier for the grouting material to penetrate into the soft rock, which in turn helps to fill the pores and cracks and improve the uniformity and stability of the grouting.

[0033] The magnesium oxychloride cement used in the embodiment has a better compressive strength than the comparative example using ordinary Portland cement, because MgO and MgCl2 react with water to generate hydrated magnesium silicate and other cementitious products, which improves the slurry strength. At the same time, optimizing the ratio of MgO and MgCl2 can further improve the slurry strength.

[0034] Example 6 A soft rock reinforcement method, the specific steps are as follows: S1. Complete the drilling operation in the soft rock formation that needs to be reinforced. Specifically, use a drilling rig to drill a hole at the predetermined location, ensure that the hole depth and hole diameter meet the design requirements, clean the debris and mud in the hole, put a casing at the hole mouth, and pour mud to form a mud wall; install the hole mouth sealer.

[0035] S2. Lower the grouting pipe to the predetermined position of the soft rock formation and clean the grouting section.

[0036] S3, such as Figure 1As shown, CO2 foam cement mortar material is prepared. Specifically, the preparation steps of cement mortar include pouring fly ash, bentonite, magnesium oxychloride cement and water into a mixer, stirring at a low speed (60-80 rpm) for 1-2 minutes, and then stirring at a medium speed (100-120 rpm) for at least 3-5 minutes to make a clean slurry without particle blocks; then pouring fine river sand and the remaining water into the mixer, stirring at a medium speed for 2-3 minutes until uniform; finally, gradually adding the clean slurry to the mixture of fine river sand and water, stirring at a low speed for 1-2 minutes, and then stirring at a medium speed for at least 3-5 minutes until the cement mortar is uniform and there is no dry powder or sand clumps. It should be noted that the mixing process should be carried out under appropriate temperature and humidity conditions to avoid the influence of high or low temperature environment on the quality of cement mortar. At the same time, after each mixing, clean the mixer in time to prevent the residue from drying and affecting the quality of the next mixing. The preparation of CO2 foam includes: mixing TS, SDBS and water to obtain a foaming liquid; passing CO2 into the foaming liquid for foaming, so that the volume of CO2 foam is more than 5.5 times the volume of the foaming liquid and the stability time is more than 30 minutes, thereby obtaining CO2 foam. CO2 foam and cement mortar are mixed at a foam-to-mortar ratio of 4.5:1 to obtain a CO2 foam cement mortar material.

[0037] S4. Use pulsating grouting, at a pressure of 1.5 MPa and a pulsating frequency of 25 times / min, to inject CO2 foam cement mortar material through the grouting pipe into the first predetermined position of the grouting section (biased towards the bottom of the grouting section), and then lift the grouting pipe to the next designated position for grouting, and complete the grouting of the soft rock formation in sections from bottom to top; S5. Continuously monitor the grouting pressure and grouting volume. After the grouting is completed, wait for the slurry to solidify. The solidification time of the slurry is 7-14 days, and check the grouting effect.

[0038] In order to adapt to the soft rock reinforcement method, a corresponding soft rock reinforcement system is also provided, including a cement mortar unit and a grouting unit. Figure 2 As shown, the cement mortar unit includes a CO2 gas cylinder 1, a first air pump 3, a high-pressure mixing container 6, a second air pump 4, a control box 5, a foaming liquid tank 7, a foam tank 9, and a cement mortar tank and a mixing tank ( Figure 2Not shown). Among them, the control box 5 is used to adjust the pressure inside the high-pressure mixing container 6; the CO2 gas cylinder 1, the first air pump 3, the high-pressure mixing container 6, the second air pump 4 and the foaming liquid tank 7 are connected in sequence, and the CO2 gas cylinder 1 is also provided with an air inlet valve 2 on the pipe at the connection point of the first gas cylinder; one end of the high-pressure mixing container 6 is connected to the foam tank 9, and a foaming valve 8 is provided on the pipe at the connection point; the foam tank 9 and the cement mortar tank are respectively connected to the mixing tank, and a feeding pump is provided on the pipe at the connection point. The homogeneous foaming liquid in the foaming liquid tank 7 is fed into the high-pressure mixing container 6 through the second air pump 4; the air inlet valve 2 and the first air pump 3 are opened so that the CO2 gas is stably transported to the high-pressure mixing container 6 and mixed with the foaming liquid; the pressure in the high-pressure mixing container 6 is adjusted to 200kPa using the control box 5, and the air inlet valve 2 is closed after the pressure is kept stable; since CO2 has a certain solubility in the solution, if the air pressure in the high-pressure mixing container 6 is found to drop significantly during the 20-minute standing period, CO2 needs to be re-introduced to ensure that the pressure is always maintained at 200kPa. During the static period, pay attention to the solubility of CO2 in the foaming liquid and ensure uniform mixing; after 20 minutes, open the foaming valve 8 of the high-pressure mixing container 6 to slowly release the CO2 foam, and ensure the stability and continuity of the CO2 foam release by controlling the foaming valve 8. The mixing tank is used to mix the CO2 foam and cement mortar at a foam ratio of 4.5:1 to obtain and store the CO2 foam cement mortar material 15.

[0039] like Figure 3 and Figure 4 As shown, the grouting unit includes a pulsating pump 10 connected to the mixing tank, and a grouting pipe 14 connected to the pulsating pump 10. A flow meter 11 and a pressure gauge 12 are also provided on the pipeline connecting the pulsating pump 10 and the grouting pipe 14. The grouting pipe 14 is a flower pipe, and a flower pipe section 22 of the grouting pipe 14 is provided with a grouting hole 20, and a grouting stopper 21 is provided at the upper and lower ends of the flower pipe section 22; the grouting pipe 14 is also provided with a telescopic device 19 for controlling the lifting or lowering of the grouting pipe 14.

[0040] Specifically, the operation method can be that there is a soft rock layer 18 at a certain depth below the ground level, a mechanical crushing method is adopted, and a drilling device is used to drill to a predetermined position of the soft rock layer 18. In this process, casing and grouting pipe 14 are lowered at the hole mouth, and mud is injected from the casing pump into the space between the casing and the well wall to form a mud wall 16 to prevent the well wall from collapsing, and the cleaning of the grouting section borehole is completed. After the drilling is completed, the hole sealer 13 is installed to prevent the hole from collapsing. The grouting pipe 14 is lowered to the predetermined position of the soft rock layer 18. After the grouting pipe 14 reaches the first predetermined position, the pulsating pump 10 is turned on and the grouting pressure of the pulsating pump 10 is set to 0.5-2.0MPa, and the pulsating frequency is 20-30 times / min. The pulsating pump 10 is used to send the CO2 foam cement mortar material 15 in the mixing tank into the grouting pipe 14. The CO2 foam cement mortar material 15 passes through the grouting hole 20 on the outer wall of the flower pipe and passes through the mud wall 16 into the soft rock layer 18. After the dendritic slurry veins 17 are formed, the pulsating pump 10 is temporarily turned off. Then the grouting pipe 14 is lifted up by the telescopic device 19 to the next designated position for grouting. Figure 5 As shown, the grouting of the soft rock formation is completed in sections from bottom to top until the grouting reinforcement is completed for all predetermined parts of the soft rock. During the pulsating grouting process, the grouting pressure and grouting volume are continuously monitored by the pressure gauge 12 and the flow meter 11 to ensure that the grouting pressure of each stage is kept within the set range and the grouting volume reaches the expected target. In the pulsating grouting process, a positive and negative pressure difference is generated between the grouting pressure and the ground stress by applying pulsating pressure. This pressure difference causes the weak parts of the soft rock layer 18 to form dendritic splitting and diffusion slurry veins. Subsequently, the CO2 foam cement mortar material 15 penetrates into the weakest pores in the soft rock layer 18, gradually filling the secondary weak pores, thereby forming dendritic slurry veins 17 within a certain range of the soft rock layer 18, thereby achieving the effect of enhancing the overall strength and stability of the rock and soil body, and ensuring the safety and smooth progress of the project.

[0041] After the grouting is completed, wait for the slurry to solidify, which usually takes 7-14 days. After solidification, the grouting effect is tested by drilling sampling, ultrasonic testing or other non-destructive testing methods to evaluate the reinforcement effect of the grouting area and the mechanical properties of the rock and soil.

[0042] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A CO2 foam cement mortar material, comprising CO2 foam and cement mortar, characterized in that: The cement mortar comprises, by mass percentage, 8%-10% magnesium oxychloride cement, 16%-18% fly ash, 3.5%-4% bentonite, 51%-53% river sand, 17%-19% water; The mass ratio of MgO to MgCl2 in the magnesium oxychloride cement is 0.5-2:

1.

2. The CO2 foam cement mortar material according to claim 1, characterized in that: The foaming ratio of the CO2 foam to cement mortar is 3-5:

1.

3. The CO2 foam cement mortar material according to claim 1, characterized in that: The preparation method of the CO2 foam comprises: Mixing a foaming agent, a foam stabilizer and water to obtain a foaming liquid; CO2 is passed into the foaming liquid for foaming to obtain CO2 foam.

4. The CO2 foam cement mortar material according to claim 3, characterized in that: The foaming liquid comprises, by mass percentage, 1%-2% of a foaming agent, 1.5%-3% of a foam stabilizer, and water as the balance.

5. The CO2 foam cement mortar material according to claim 3, characterized in that: The volume of the CO2 foam is more than 5.5 times the volume of the foaming liquid, and the stability time of the CO2 foam is more than 30 minutes.

6. The CO2 foam cement mortar material according to any one of claims 1 to 5, characterized in that: The 2h precipitation rate of the CO2 foam cement mortar material is less than 5%.

7. A soft rock reinforcement method, characterized in that: include, Complete drilling operations in soft rock formations that need to be reinforced, and run casing and grouting pipes; The CO2 foam cement mortar material according to any one of claims 1 to 6 is injected into the soft rock formation through a grouting pipe by pulsating grouting, wherein the grouting pipe is first lowered to the bottom for grouting, and then the grouting pipe is lifted up to complete the reinforcement of the soft rock formation in sections from bottom to top.

8. The soft rock reinforcement method according to claim 7, characterized in that: The pressure of the pulsating grouting is 0.5-2.0 MPa, and the pulsating frequency is 20-30 times / min.

9. A soft rock reinforcement system, characterized in that: Including cement mortar unit and grouting unit; The cement mortar unit is used to prepare and store the CO2 foam cement mortar material according to any one of claims 1 to 6; The grouting unit is used to inject the CO2 foam cement mortar material in the cement mortar unit into the soft rock formation that needs to be reinforced by using pulse grouting.

10. The soft rock reinforcement system according to claim 9, characterized in that: The grouting unit comprises a pulsating pump and a grouting pipe connected to each other, and a telescopic device, wherein the telescopic device is used to lift or lower the grouting pipe.

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