Method for determining anti-permeation corrosion service life of cemented sand gravel dam

Abstract

The invention provides a method for determining the permeation-corrosion-resistant service life of a cemented sand gravel dam, and belongs to the technical field of detection, and the permeation-corrosion-resistant allowable service life of the cemented sand gravel of a dam body and an anti-seepage body is calculated by adopting a CaO limit value allowed to be taken away from the cemented sand gravel; an original grading large-size test piece is adopted, the real conditions, including coarse aggregate segregation, coarse hole containing, communicating hole containing and the like, in the test piece can be reflected better, on the basis of the test, the permeation corrosion resistance allowable service life of the structural body is quantitatively calculated according to a CaO accumulative dissolution amount fitting curve equation, and the permeability corrosion resistance allowable service life of the structural body is calculated according to the hydraulic gradient ratio of the test piece to the structural body. And calculating the allowable service life.

Description

Technical Field

[0001] This invention relates to a method for determining the service life of cemented gravel dams against seepage and erosion, belonging to the field of testing technology. Background Technology

[0002] Dissolution damage is a problem that has existed since concrete was first used in water conservancy and hydropower projects. Due to the presence of defects such as pores, voids, and lack of compaction in concrete, leakage channels can be formed under pressure water. The leaking water dissolves Ca(OH)2 from the hydration products through physicochemical processes. Concrete penetration and dissolution mainly involve soluble hydration products migrating through the capillaries inside the concrete and being dissolved by the surrounding water under the gradient of lime concentration, leading to a decrease in concrete strength and structural damage.

[0003] Cemented gravel dams are a new type of dam developed in recent years. They conform to the dam construction concept of "suitable materials and appropriate structures," emphasizing the use of local materials and reducing waste. Cemented gravel materials require less cement, with a cement content of only 40-50 kg / m3. The construction process of cemented gravel materials is simpler than that of conventional concrete. The aggregates are sourced locally and undergo only simple coarse screening. The maximum particle size of the aggregates is generally 150 mm, and the gradation is worse than that of conventional concrete with a large fluctuation range. This results in increased porosity in the concrete structure, an increase in the number of coarse pores and interconnected pores, and a decrease in the corrosion resistance of cemented gravel.

[0004] It is generally believed that the durability of cemented gravel mainly lies in its resistance to seepage and erosion. Currently, there is limited research in the industry on the seepage and erosion resistance of cemented gravel in dam bodies and slurry-rich cemented gravel in dam seepage barriers. Existing studies often only utilize wet-sieved specimens for relevant tests, and no quantitative calculations have been made to determine its service life against seepage and erosion. Therefore, comprehensively determining the service life of cemented gravel against seepage and erosion through testing and analytical calculations can provide strong technical support and assurance for its widespread application in permanent engineering projects. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for determining the service life of cemented gravel dams against seepage and erosion, comprising the following steps:

[0006] Step S1: Form large-size permeation and dissolution specimens of the original gradation;

[0007] Step S2: Curing until the designed age is reached, followed by a penetration and dissolution test;

[0008] Step S3: Test the permeability coefficient of the etched specimen and the concentration of CaO dissolved in the permeation water for different permeation and dissolution durations;

[0009] Step S4: Based on the amount of water that seeps in and the concentration of dissolved CaO during the corrosion test, calculate the amount of CaO dissolved and fit the cumulative CaO dissolution curve equation of the corrosion test.

[0010] Step S5: Based on a cumulative CaO leaching limit of 10%, calculate the allowable service life of cemented sand and gravel for indoor corrosion resistance according to the fitted curve equation.

[0011] Step S6: Based on the hydraulic gradient ratio between the indoor specimens and the on-site structure, calculate the allowable service life of the cemented sand and gravel structure against seepage and corrosion.

[0012] Preferably, the size of the etching specimen fabricated indoors in step S1 is Φ400mm*400mm.

[0013] Preferably, in step (2), the corrosion specimens are cured in a standard curing room to the designed age, such as the designed age (180 days); the test uses a penetration corrosion tester to increase the penetration water pressure and accelerate the penetration corrosion test process, and the test pressure is 1.5MPa to 2.0MPa.

[0014] Preferably, in step S3, the permeability coefficient k is calculated according to Darcy's law, k= k is the permeability coefficient (cm / s); Q is the seepage volume (ml); L is the seepage diameter (cm); h is the osmotic pressure head (cm); A is the specimen area (cm²). 2 t represents the penetration duration, in seconds;

[0015] The amount of CaO dissolved in cemented sand and gravel was determined by EDTA complexometric titration, referring to the "Calcium Oxide Determination" method in the "Test Procedure for Hydraulic Concrete" SL352-2006.

[0016] C CaO =V1*56.08*1000 / V, C CaO V1 is the calcium oxide content in the water sample, mg / L; C is the concentration of the EDTA standard solution; V1 is the volume of EDTA standard solution consumed during titration, ml; V is the volume of the water sample, ml; 56.08 is the molar mass of calcium oxide, g.

[0017] Test frequency: For the first 3 months, collect the seepage volume once every 7 days to test its permeability coefficient and CaO concentration in the seepage water. After that, collect and test once every 15 days.

[0018] The penetration and dissolution test should last for no less than one year.

[0019] Preferably, in step S4, the amount of water permeated during the permeation and dissolution process, Q (L), is calculated based on the permeability coefficient k (cm / s).

[0020] Calculate the amount of CaO dissolved during the period (mg) based on the permeate flow rate Q (L) and the CaO concentration in the permeate (mg / L).

[0021] The permeability coefficient k and the CaO concentration in the permeate water decrease with age, showing a convergent state.

[0022] Calculate the cumulative CaO dissolution amount (mg);

[0023] Plot a curve with the duration of penetration and dissolution (d) on the x-axis and the cumulative amount of CaO dissolved (mg) on ​​the y-axis;

[0024] Fit the equation for the cumulative CaO dissolution curve.

[0025] Preferably, in step S5, the cumulative leaching amount of CaO is limited to 10%. Scholar BM Moskwin summarized existing research data and believes that when 10% of CaO is leached from concrete, the strength of concrete drops rapidly, and the state of cement stone in concrete becomes unstable.

[0026] The allowable service time (days) for corrosion resistance of cemented sand and gravel in indoor tests was calculated based on the fitted curve equation.

[0027] Convert to the allowable service life (years) for indoor test resistance to penetration and corrosion.

[0028] Preferably, in step S6, the hydraulic gradient represents the ratio of head loss to seepage path length, J=h / L;

[0029] Calculate the hydraulic gradient J0 in the indoor test;

[0030] Calculate the maximum hydraulic gradient J1 of the cemented sand and gravel in the structure;

[0031] From k= It can be seen that t= = That is, the allowable service life is inversely proportional to the hydraulic gradient; the allowable service life (in years) of the cemented sand and gravel structure against seepage and corrosion is estimated from the ratio of the hydraulic gradient of the test specimen and the structure.

[0032] This invention provides a method for determining the service life of cemented gravel dams against seepage and corrosion. It calculates the permissible service life of the dam body and seepage barrier by using a limit on the amount of CaO that can be removed from the cemented gravel. Using large-size specimens with the original gradation better reflects the true internal conditions of the specimens, including coarse aggregate segregation and the presence of coarse pores and interconnected pores. Based on the experiment, the permissible service life of the structure against seepage and corrosion is quantitatively calculated according to the fitted curve equation of the cumulative CaO leaching amount. The permissible service life is then extrapolated from the hydraulic gradient ratio between the test specimen and the structure. Attached Figure Description

[0033] Figure 1 This is a flowchart of the present invention;

[0034] Figure 2This is a graph showing the change in permeability coefficient with age according to an embodiment of the present invention;

[0035] Figure 3 This is a graph showing the change in CaO concentration in the permeate water over time according to an embodiment of the present invention.

[0036] Figure 4 The curve showing the relationship between the cumulative dissolution of CaO and the permeation time, and the equation for fitting the cumulative dissolution curve of CaO, are provided in this embodiment of the invention. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings.

[0038] Example

[0039] like Figures 1-4 As shown, the method for determining the service life of a cemented gravel dam against seepage and erosion according to the present invention includes the following steps:

[0040] Step S1: Form large-size permeation and dissolution specimens of the original gradation;

[0041] Step S2: Curing until the designed age is reached, followed by a penetration and dissolution test;

[0042] Step S3: Test the permeability coefficient of the etched specimen and the concentration of CaO dissolved in the permeation water for different permeation and dissolution durations;

[0043] Step S4: Based on the amount of water that seeps in and the concentration of dissolved CaO during the corrosion test, calculate the amount of CaO dissolved and fit the cumulative CaO dissolution curve equation of the corrosion test.

[0044] Step S5: Based on a cumulative CaO leaching limit of 10%, calculate the allowable service life of cemented sand and gravel for indoor corrosion resistance according to the fitted curve equation.

[0045] Step S6: Based on the hydraulic gradient ratio between the indoor specimens and the on-site structure, calculate the allowable service life of the cemented sand and gravel structure against seepage and corrosion.

[0046] The size of the etched specimen fabricated indoors in step S1 is Φ400mm*400mm.

[0047] In step (2), the corrosion specimens are cured in a standard curing room to the designed age, such as the designed age (180 days). The test uses a penetration corrosion tester to increase the penetration water pressure and accelerate the penetration corrosion test process. The test pressure is 1.5MPa to 2.0MPa.

[0048] In step S3, the permeability coefficient k is calculated according to Darcy's law, k= k is the permeability coefficient (cm / s); Q is the seepage volume (ml); L is the seepage diameter (cm); h is the osmotic pressure head (cm); A is the specimen area (cm²). 2 t represents the penetration duration, in seconds;

[0049] The amount of CaO dissolved in cemented sand and gravel was determined by EDTA complexometric titration, referring to the "Calcium Oxide Determination" method in the "Test Procedure for Hydraulic Concrete" SL352-2006.

[0050] C CaO =V1*56.08*1000 / V, C CaO V1 is the calcium oxide content in the water sample, mg / L; C is the concentration of the EDTA standard solution; V1 is the volume of EDTA standard solution consumed during titration, ml; V is the volume of the water sample, ml; 56.08 is the molar mass of calcium oxide, g.

[0051] Test frequency: For the first 3 months, collect the seepage volume once every 7 days to test its permeability coefficient and CaO concentration in the seepage water. After that, collect and test once every 15 days.

[0052] The penetration and dissolution test should last for no less than one year.

[0053] In step S4, the amount of water that seeps in during the seepage and dissolution process is calculated based on the permeability coefficient k (cm / s).

[0054] Calculate the amount of CaO dissolved during the period (mg) based on the permeate flow rate Q (L) and the CaO concentration in the permeate (mg / L).

[0055] The permeability coefficient k and the CaO concentration in the permeate water decrease with age, showing a convergent state.

[0056] Calculate the cumulative CaO dissolution amount (mg);

[0057] Plot a curve with the duration of penetration and dissolution (d) on the x-axis and the cumulative amount of CaO dissolved (mg) on ​​the y-axis;

[0058] Fit the equation for the cumulative CaO dissolution curve.

[0059] In step S5, the cumulative leaching of CaO is limited to 10%. Scholar BM Moskwin summarized existing research data and believes that when 10% of CaO is leached from concrete, the strength of concrete drops rapidly, and the state of cement stone in concrete becomes unstable.

[0060] The allowable service time (days) for corrosion resistance of cemented sand and gravel in indoor tests was calculated based on the fitted curve equation.

[0061] Convert to the allowable service life (years) for indoor test resistance to penetration and corrosion.

[0062] In step S6, the hydraulic gradient represents the ratio of head loss to seepage path length, J=h / L;

[0063] Calculate the hydraulic gradient J0 in the indoor test;

[0064] Calculate the maximum hydraulic gradient J1 of the cemented sand and gravel in the structure;

[0065] From k= It can be seen that t= = That is, the allowable service life is inversely proportional to the hydraulic gradient; the allowable service life (in years) of the cemented sand and gravel structure against seepage and corrosion is estimated from the ratio of the hydraulic gradient of the test specimen and the structure.

[0066] The Xiyin Reservoir dam in Putian is a cemented gravel dam with a maximum height of 52.8m. The low cement content, low strength of the cemented gravel, and large fluctuations in aggregate gradation result in relatively poor impermeability, leading to durability issues due to seepage and erosion. According to the Xiyin Reservoir dam design data, the maximum head pressure (h) borne by the cemented gravel at the check flood level is 50.48m, and the maximum bottom width (b) is 55.0m. The impermeable body is approximately 2.5m thick. The cemented gravel mix proportions selected for the experiment are shown in Table 1, including representative mix proportions of the finest and coarsest gradations of gravel from the quarry.

[0067] Table 1. Mix proportions of cemented gravel for penetration and dissolution tests

[0068]

[0069] Note: In CSG-1 (fine gradation), the proportions of gravel (5~20mm): (20~40mm): (40~80mm): (80~150mm) are 26.1%: 21.8%: 28.8%: 23.1%.

[0070] In CSG-1 (coarse gradation), the proportions of gravel (5~20mm): (20~40mm): (40~80mm): (80~150mm) are 13.3%: 15.4%: 27.3%: 44.0%.

[0071] The molded specimens were Φ400*400 and cured for 180 days (design age).

[0072] The test was conducted using a self-developed multi-functional penetrating and dissolving instrument, with a test pressure of 1.5 MPa.

[0073] The permeability coefficient was tested for each infiltration and erosion duration. In the first 3 months, the infiltration volume was collected every 7 days, and thereafter it was collected and tested every 15 days.

[0074] The curve showing the relationship between permeability coefficient and permeation time is shown below. Figure 1 ;

[0075] The CaO concentration in the permeate dissolved water at each test age was determined by EDTA complexometric titration. The relationship between the CaO concentration in the permeate dissolved water and the permeation time is shown in the graph. Figure 2 ;

[0076] The amount of CaO leached out was calculated based on the amount of permeate water and the CaO concentration in the permeate water during the experiment.

[0077] The curve showing the relationship between the cumulative CaO dissolution and the permeation time is shown below. Figure 3 ;

[0078] The curve equation of cumulative CaO dissolution as a function of permeation time was fitted using a modified logarithmic model y=aln(b*x+c)+d, where x is the permeation time (days), y is the cumulative CaO dissolution, and a, b, c, and d are constants to be fitted.

[0079] The fitted logarithmic curve equation for CSG-1 (fine gradation) is y = 19.94ln(0.22t + 0.33) + 2.70;

[0080] CSG-2 (coarse gradation) has a fitted logarithmic curve equation of y = 23.80ln(0.85t + 0.55) + 1.50;

[0081] The volume of a single indoor corrosion specimen is 50L, the cement dosage is 48kg / m3, and the CaO content in the cement is 48%. Therefore, the total CaO in a single corrosion specimen is 1.392kg.

[0082] The limit is 10% CaO dissolution, which is 139.2g;

[0083] The logarithmic model curve equation was fitted based on the experimental results;

[0084] Calculate the permeability and corrosion resistance allowable time (d) of cemented sand and gravel in the laboratory test, and convert it into permeability and corrosion resistance allowable service life (years).

[0085] Calculate the hydraulic gradient J0 for the indoor permeation and dissolution test: J0 = 150 / 0.4 = 375;

[0086] The hydraulic gradient of the designed dam body is calculated as J1 = 50.48 / 55 = 0.918;

[0087] Based on the hydraulic gradient ratio between the test specimen and the structure, the allowable service life (in years) of the cemented sand and gravel structure against seepage and corrosion can be estimated.

[0088] The calculation results are shown in Table 2.

[0089] Table 2. Permissible service life of cemented gravel against permeability and erosion.

[0090] Mixing ratio number Fitted curve equation The time t (days) for indoor specimens to reach dissolution failure. The conversion of indoor specimens reaching dissolution failure to years (years) <![CDATA[Hydraulic gradient J0 in laboratory tests]]> Design hydraulic gradient J1 Converted to the allowable service life of the structure against corrosion (years) CSG-1 (Fine Gradation) <![CDATA[y=19.94ln(0.22t+0.33)+2.70R 2 =0.985]]> 4270 11.7 375 0.918 4479 CSG-2 (coarse gradation) <![CDATA[y=23.8ln(0.85t+0.55)+1.50R 2 =0.989]]> 382 1.04 375 0.918 425

[0091] This implementation case uses representative fine-graded and coarse-graded gravel from an exploration quarry. Based on indoor permeability and dissolution tests of the original gradation, this invention employs a limit on the allowable CaO removal from cemented gravel. By fitting a deformation logarithmic curve equation based on the cumulative CaO leaching amount from the tests, the service life of the cemented gravel against permeability and dissolution is quantitatively calculated. The allowable service life of the cemented gravel dam body is then estimated from the hydraulic gradient ratio between the test specimen and the structural body. The service life against permeability and dissolution determined in this implementation case is significantly greater than the design service life, and it also reflects the significant differences in the service life against permeability and dissolution among different gravel gradations. This quantitative calculation of the service life against permeability and dissolution of cemented gravel provides technical support for the design and construction of new cemented gravel dam types, provides guidance for the utilization and mining of gravel quarries, and ensures the durability of the project.

[0092] The embodiments described above are merely preferred embodiments of the present invention, and are described in a relatively specific and detailed manner. However, the present invention is not limited to these embodiments. It should be noted that for those skilled in the art, any modifications made without departing from the spirit of the present invention fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for determining the service life of a cemented gravel dam against seepage and erosion, characterized in that, Includes the following steps: Step S1: Form large-size permeation and dissolution specimens of the original gradation; Step S2: Curing until the designed age is reached, followed by a penetration and dissolution test; Step S3: Test the permeability coefficient of the etched specimen and the concentration of CaO dissolved in the permeation water for different permeation and dissolution durations; Step S4: Based on the amount of water that seeps in and the concentration of dissolved CaO during the corrosion test, calculate the amount of CaO dissolved and fit the cumulative CaO dissolution curve equation of the corrosion test. Step S5: Based on a cumulative CaO leaching limit of 10%, calculate the allowable service life of cemented sand and gravel for indoor corrosion resistance according to the fitted curve equation. Step S6: Based on the hydraulic gradient ratio between the indoor specimens and the on-site structure, calculate the allowable service life of the cemented sand and gravel structure against seepage and corrosion.

2. The method for determining the service life of a cemented gravel dam against seepage and erosion according to claim 1, characterized in that, The size of the etched specimen fabricated indoors in step S1 is Φ400mm*400mm.

3. The method for determining the service life of a cemented gravel dam against seepage and erosion according to claim 1, characterized in that, In step (2), the corrosion specimens are cured in a standard curing room to the designed age. The test is conducted using a penetration corrosion tester, and the test pressure is 1.5MPa to 2.0MPa.

4. The method for determining the service life of a cemented gravel dam against seepage and erosion according to claim 1, characterized in that, In step S3, the permeability coefficient k is calculated according to Darcy's law, k= k is the permeability coefficient (cm / s); Q is the seepage volume (ml); L is the seepage diameter (cm); h is the osmotic pressure head (cm); A is the specimen area (cm²). 2 t represents the penetration duration, in seconds; The amount of CaO dissolved in cemented sand and gravel was determined by EDTA complexometric titration, referring to the "Calcium Oxide Determination" method in the "Test Procedure for Hydraulic Concrete" SL352-2006. C CaO =V1*56.08*1000 / V, C CaO V1 is the calcium oxide content in the water sample, mg / L; C is the concentration of the EDTA standard solution; V1 is the volume of EDTA standard solution consumed during titration, ml; V is the volume of the water sample, ml; 56.08 is the molar mass of calcium oxide, g. Test frequency: For the first 3 months, collect the seepage volume once every 7 days to test its permeability coefficient and CaO concentration in the seepage water. After that, collect and test once every 15 days. The penetration and dissolution test shall last for no less than one year.

5. The method for determining the service life of a cemented gravel dam against seepage and erosion according to claim 1, characterized in that, In step S4, the amount of water that seeps in during the seepage and dissolution process is calculated based on the permeability coefficient k (cm / s). Calculate the amount of CaO dissolved during the period (mg) based on the permeate flow rate Q (L) and the CaO concentration in the permeate (mg / L). The permeability coefficient k and the CaO concentration in the permeate water decrease with age, showing a convergent state. Calculate the cumulative CaO dissolution amount (mg); Plot a curve with the duration of penetration and dissolution (d) on the x-axis and the cumulative amount of CaO dissolved (mg) on ​​the y-axis; Fit the equation for the cumulative CaO dissolution curve.

6. The method for determining the service life of a cemented gravel dam against seepage and erosion according to claim 1, characterized in that, In step S5, the cumulative leaching of CaO is limited to 10%. Scholar BM Moskwin summarized existing research data and believes that when 10% of CaO is leached from concrete, the strength of concrete drops rapidly, and the state of cement stone in concrete becomes unstable. The allowable service time (days) for corrosion resistance of cemented sand and gravel in indoor tests was calculated based on the fitted curve equation. Converted to the allowable service life of resistance to penetration and corrosion in indoor tests.

7. The method for determining the service life of a cemented gravel dam against seepage and erosion according to claim 1, characterized in that, In step S6, the hydraulic gradient represents the ratio of head loss to seepage path length, J=h / L; Calculate the hydraulic gradient J0 in the indoor test; Calculate the maximum hydraulic gradient J1 of the cemented sand and gravel in the structure; From k= It can be seen that t= = That is, the allowable service life is inversely proportional to the hydraulic gradient; the allowable service life of cemented sand and gravel structures against seepage and corrosion can be estimated from the hydraulic gradient ratio of the test specimens and the structure.

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