Method for thickening design of steel reinforcement cover of marine pipe pile based on convection diffusion model

Abstract

This invention relates to the technical field of methods for protecting the reinforcing steel of old marine engineering pipe piles, specifically to a design method for increasing the thickness of the protective layer for the reinforcing steel of marine engineering pipe piles based on a convection-diffusion model; including the following steps: (1) collecting chloride ion concentration data on the surface of the pipe pile, and according to... c s (1-e) ‑αt (1) Fit the form; (2) Calculate the corrosion time of the steel reinforcement and determine whether the calculated corrosion time of the steel reinforcement is lower than the design life of the pipe pile; (3) If the calculated corrosion time of the steel reinforcement is lower than the design life of the pipe pile, the thickness of the steel reinforcement protective layer should be increased; (4) Calculate the increased thickness of the steel reinforcement protective layer; Taking into full account the structural characteristics and environmental conditions of the marine pipe pile, the chloride ion concentration on the surface of the marine pipe pile during service is collected regularly to obtain the development law of chloride ion concentration on the surface of the pipe pile during service. Then, the chloride ion concentration of the outer boundary in contact with seawater is set as a concentration function related to time. This algorithm is more in line with the actual situation and can more accurately estimate the required increase in the thickness of the steel reinforcement protective layer.

Description

Technical Field

[0001] This invention relates to the technical field of methods for protecting the reinforcing steel bars of old marine engineering pipe piles, specifically to a design method for increasing the thickness of the protective layer for marine engineering pipe piles based on a convection-diffusion model. Background Technology

[0002] With the rapid development of marine engineering construction in my country, marine pipe piles, as an important foundation structural material, are widely used in various marine engineering projects. However, during the use of marine pipe piles, due to the long-term impact of various factors such as seawater environment, wave impact, and freezing, the protective layer of their reinforcing steel is prone to damage and detachment, leading to steel corrosion and thus affecting the service life and safety of the pipe piles.

[0003] To address the aforementioned issues, the traditional method currently used in my country is mainly to conduct regular inspections and maintenance of offshore pipe piles. However, this cannot fundamentally solve the problem of steel reinforcement corrosion, and the maintenance costs are high and the cycle is long. Currently, there are no clear guidelines for increasing the thickness of the steel reinforcement protective layer. Therefore, developing a design method for thickening the steel reinforcement protective layer of aging offshore pipe piles to improve their service life and safety has significant theoretical and engineering application value.

[0004] This invention proposes a design method for thickening the protective layer of reinforcing steel bars in aging marine pipe piles based on a convection-diffusion model. By analyzing the mass transport process between the protective layer and seawater using the convection-diffusion model, the relationship between the protective layer thickness and chloride ions at the reinforcing steel bars is revealed, providing a theoretical basis for the design of thickening the protective layer of reinforcing steel bars in aging marine pipe piles. Furthermore, this method fully considers the structural characteristics and environmental conditions of marine pipe piles, demonstrating high practicality and broad application prospects. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a highly practical design method for increasing the thickness of the concrete cover of marine pipe piles based on a convection-diffusion model. This method fully considers the structural characteristics and environmental conditions of marine pipe piles, analyzes the material transport process between the concrete cover and seawater using a convection-diffusion model, reveals the relationship between the thickness of the concrete cover and chloride ions at the steel reinforcement, and provides a theoretical basis for the design of increasing the concrete cover thickness of old marine pipe piles.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a design method for increasing the thickness of the protective layer for reinforcing steel bars in marine pipe piles based on a convection-diffusion model, comprising the following steps:

[0007] S01: Collect chloride ion concentration data on the surface of the pipe pile, according to c s (1-e -αt Fitting is performed in the form of ), where c sThe concentration of chloride ions in seawater is α, which is determined based on the collected data on the chloride ion concentration on the surface of the pipe pile.

[0008] S02: c is the result of fitting the collected chloride ion concentration data on the surface of the pipe pile. s (1-e -αt The inner and outer radii, permeability coefficient, diffusion coefficient, and static seawater pressure borne by the pipe pile are incorporated into the pipe pile diffusion model without increasing the thickness of the steel reinforcement protective layer. The steel reinforcement corrosion initiation time is calculated, and it is determined whether the calculated steel reinforcement corrosion initiation time is lower than the design life of the pipe pile.

[0009] S03: If the calculated corrosion initiation time of the reinforcing steel is not less than the design life of the pipe pile, then there is no need to increase the thickness of the reinforcing steel protective layer; only the chloride ion concentration on the surface of the pipe pile needs to be collected. If the calculated corrosion initiation time of the reinforcing steel is less than the design life of the pipe pile, then the thickness of the reinforcing steel protective layer needs to be increased.

[0010] S04: The thickness of the concrete cover for reinforcing steel needs to be determined based on the service life of the pipe pile, the existing chloride ion concentration distribution inside the pipe pile, and the known data of the pipe pile, using the convection-diffusion model of the pipe pile after increasing the thickness of the concrete cover for reinforcing steel. The service life of the pipe pile can be directly known from the actual situation, and the existing chloride ion concentration distribution inside the pipe pile can be determined by drilling and sampling during the construction process of increasing the thickness of the concrete cover for reinforcing steel.

[0011] Further, in step S01, c(t,r) e ) = c s (1-e -αt In the formula, c s Let be the chloride ion concentration in seawater, and α be a time-dependent parameter.

[0012] Furthermore, in step S02, the method for calculating the corrosion initiation time of the reinforcing steel is as follows:

[0013] The governing equation for chloride ion intrusion in pipe piles is based on convection-diffusion theory, and the formula is shown below:

[0014]

[0015] In the formula, c(t,r) is the chloride ion concentration at time t at a distance r from the pipe pile, in %; D is the chloride ion diffusion coefficient of the pipe pile, in m. 2 / s; v is the seawater infiltration velocity, m / s; r is the radial distance of the pipe pile, m; t is the chloride ion intrusion time, s.

[0016] The value of v is expressed by Darcy's law as follows:

[0017]

[0018] In the formula, k is the permeability coefficient of the pipe pile, p is the osmotic pressure of the pipe pile at point r, and γw The specific gravity of water;

[0019] Since the outer side of the pipe pile is subjected to seawater pressure while the inner side is not in contact with seawater, the following boundary conditions can be determined.

[0020] p(r e ) = p s (3)

[0021] p(r0)=0 (4)

[0022] above p s The hydrostatic pressure exerted by seawater on the outside of the pipe pile is expressed in Pa.

[0023] Combining equations (1) to (4), we can obtain:

[0024]

[0025] in

[0026] Since the pipe pile initially contains no chloride ions, and its outer side is in contact with seawater while its inner side is not, the following initial and boundary conditions can be determined.

[0027] c(0,r)=0 (6)

[0028] c(t,r0)=0 (7)

[0029] c(t,r e ) = c s (1-e -αt (8)

[0030] In the formula c s The concentration of chloride ions in seawater is given by α, which is a time-dependent parameter, s. -1 ;

[0031] We can simplify c(t,r) to c and create two new functions as follows:

[0032] c * =cr a / 2D (9)

[0033] c ** =c * -b(t)(r-r0) (10)

[0034] Substituting equations (9) to (10) into equations (5) to (8) above, we obtain the following equation:

[0035]

[0036] c ** (0,r)=0 (12)

[0037] c ** (t,r0)=0 (13)

[0038] c ** (t,r e )=0 (14)

[0039] In the above formula, υ=|a / 2D|,

[0040] By performing a Weber transformation on equations (11) to (14), and then substituting the transformed equations (13) to (14) into equation (11), we can obtain the following equations:

[0041]

[0042] in R υ (β m ,r)=Y υ (β m r e )J υ (β m r)-J υ (β m r e )Y υ (β m r); β m Through J υ (β m r0)Y υ (β m r e ) = J υ (β m r e )Y υ (β m r0);

[0043] Substituting equation (15) into equation (12) after the Weber transformation yields the following solution:

[0044]

[0045] in

[0046] Substituting equation (16) back into equations (9) to (10), we can obtain the following method for analyzing chloride ion intrusion in coastal pipe piles based on convection-diffusion theory:

[0047]

[0048] in

[0049] In equation (17), r is equal to the distance r between the reinforcing bars of the pipe pile. s When c(t,r) s The concentration of chloride ions in the reinforcing steel of the pipe pile is equal to the concentration of chloride ions that cause corrosion. c The corrosion initiation time T1 of the pipe pile reinforcement can be obtained.

[0050] Furthermore, in equation (2), γ w The specific weight of water is approximately 10 N / m³. 3 .

[0051] Furthermore, in step S02, equations (6) to (9) together constitute a mathematical model for the analysis method of chloride ion intrusion in coastal pipe piles based on convection-diffusion theory. By analyzing equations (5) to (8), the analysis method of chloride ion intrusion in coastal pipe piles based on convection-diffusion theory is obtained.

[0052] Furthermore, in step S02, equation (15) is a first-order partial derivative equation. Substituting equation (15) into equation (12) after the Weber transformation, equation (16) can be obtained.

[0053] Furthermore, in step S04, if the corrosion time T1 of the steel reinforcement in the pipe pile is less than the design life T of the pipe pile without increasing the thickness of the steel reinforcement protective layer, then the thickness of the steel reinforcement protective layer needs to be increased; assuming that the service time of the pipe pile before the steel reinforcement protective layer thickness is increased is t1, the service time of the pipe pile after the steel reinforcement protective layer thickness is increased is not less than T-t1.

[0054] Furthermore, in step S04, the convection-diffusion model of the pipe pile covers the outer diameter r′ of the pipe pile. e =r e +d, inner diameter r0, pipe pile permeability coefficient k, diffusion coefficient D, seawater chloride ion concentration c s The time-dependent parameter α, and the static seawater pressure p s , where t is the chloride ion intrusion time and r is any radial distance r of the pipe pile, and c(t,r) is the chloride ion concentration at r at time t; d is the thickened part of the steel reinforcement protective layer;

[0055] The control equation for chloride ion convection and diffusion in pipe piles after increasing the thickness of the concrete cover is as follows:

[0056]

[0057] in c′(t,r) represents the chloride ion concentration at time t at a distance r from the pipe pile after increasing the thickness of the steel reinforcement protective layer;

[0058] The initial time for the reinforcing steel cover thickness to be increased before the pipe pile is put back into use is defined as the initial moment, at which time the internal diameter of the pipe pile is from r0 to r. e The chloride ion concentration exists within the range, re to r′ e There is no chloride ion concentration within the range; the initial boundary is defined as a function related to r, as follows:

[0059] C(0,r)=g(r) (19)

[0060] The inner boundary conditions of the pipe pile remain unchanged, while the outer boundary conditions extend to r′. e The location is as follows:

[0061] C(t,r0)=0 (20)

[0062] C(t,r′ e ) = c s (1-e -αt ) (twenty one)

[0063] Equations (18) to (21) above together constitute the chloride ion convection and diffusion model of the pipe pile after increasing the thickness of the steel reinforcement protective layer;

[0064] We simplify C(t,r) to C and create two new functions as follows:

[0065] C * =Cr a′ / 2D (twenty two)

[0066] C ** =C * -b′(t)(r-r0) (23)

[0067] Substituting equations (22) to (23) into equations (18) to (21) above, we get:

[0068]

[0069] C ** (0,r)=g(r)r a′ / 2D -b′(0)(r-r0) (25)

[0070] C ** (t,r0)=0 (26)

[0071] C ** (t,r e ′)=0 (27)

[0072] In the above formula, v = |a′ / 2D|,

[0073] By performing a Weber transformation on equations (24) to (27), and then substituting the transformed equations (26) to (27) into equation (24), we can obtain the following equations:

[0074]

[0075] in R v (χ m ,r)=Y v (χ m r′ e )J v (χ m r)-J v (χ m r′ e )Y v (χ m r); χ m Through J v (χ m r0)Y v (χ m r′ e ) = J v (χ m r′ e ′ )Y v (χ m r0) is determined;

[0076] Equation (28) is a first-order partial derivative equation. Substituting equation (28) into equation (25) after the Weber transformation yields the following solution:

[0077]

[0078] in

[0079] Substituting equation (29) back into equations (22) to (23), we can obtain the analytical solution of the chloride ion convection and diffusion model for the pipe pile after increasing the thickness of the steel reinforcement protective layer, as shown below:

[0080]

[0081] in

[0082] In formula (30), r is equal to the distance r′ between the pipe pile reinforcement bars. s =r s +d; Let t = the expected service life of the pipe pile after increasing the thickness of the steel reinforcement protective layer, T2; When C(T2,r′) s The concentration of chloride ions (cc) in the reinforcing steel of the pipe pile is equal to the increase in the thickness of the protective layer (d) of the reinforcing steel.

[0083] Further, in step S04, the sampling method for the existing chloride ion concentration distribution inside the pipe pile is as follows: (1) First, detect whether there are cracks in the pipe pile. For pipe piles without cracks, use the drilling sampling method to take samples; (2) For pipe piles with cracks, take samples at the cracks. The sampling method is as follows: insert a sampling piece made of FRP with a width of 0.3-0.5 cm and a thickness of 3-5 mm into the crack. After standing for 3-5 days, detect the chloride ion concentration distribution data on the FRP sampling piece as the existing chloride ion concentration distribution data inside the pipe pile.

[0084] This invention presents a design method for increasing the thickness of the concrete cover for marine engineering pipe piles based on a convection-diffusion model. It fully considers the structural characteristics and environmental conditions of the marine engineering pipe piles, such as the outer side of the pile bearing seawater pressure while the inner side does not contact seawater, and the initial internal structure of the pile containing no chloride ions. The method periodically collects the chloride ion concentration on the surface of the marine engineering pipe pile during its service life. Through exponential nonlinear fitting, it obtains the development law of chloride ion concentration on the surface of the in-service pipe pile. Furthermore, it sets the chloride ion concentration at the outer boundary in contact with seawater as a concentration function correlated with time. This algorithm is more consistent with reality and can more accurately estimate the required increase in the thickness of the concrete cover.

[0085] The present invention provides a design method for increasing the thickness of the protective layer for reinforcing steel bars in marine pipe piles based on a convection-diffusion model. Compared with existing technologies, this method has the following advantages:

[0086] 1. Currently, the traditional method mainly involves regular inspection and maintenance of marine pipe piles, but this cannot fundamentally solve the problem of steel reinforcement corrosion, and the maintenance cost is high and the cycle is long. This application can accurately estimate the required increase in the thickness of the steel reinforcement protective layer, and timely increase in the thickness of the steel reinforcement protective layer can effectively solve the problem of steel reinforcement corrosion, thereby reducing maintenance costs.

[0087] 2. Currently, there is no clear guiding method for increasing the thickness of the concrete cover for reinforcing bars. The technology in this application can accurately estimate the required increase in the thickness of the concrete cover for reinforcing bars and has developed a design method for increasing the thickness of the concrete cover for reinforcing bars in old marine engineering pipe piles, so as to improve the service life and safety of old pipe piles. It has important theoretical significance and engineering application value.

[0088] This invention presents a design method for increasing the thickness of the protective layer of steel reinforcement in marine pipe piles based on a convection-diffusion model. It optimizes the sampling method at cracks and avoids the problem of accelerated steel corrosion caused by drilling at cracks. Compared with the traditional drilling sampling method, the sampling method at cracks in this application has higher accuracy of detection results and is simpler to operate. Attached Figure Description

[0089] Figure 1 This is the calculation result of the convection diffusion model of the pipe pile in Embodiment 1 of the present invention;

[0090] Figure 2 This is a diagram showing the chloride ion concentration distribution inside a pipe pile after 50 years of service without increasing the thickness of the reinforcing steel protective layer, according to Embodiment 2 of the present invention.

[0091] Figure 3 This is a graph showing the development of chloride ion concentration at the steel reinforcement of the pipe pile with an increased steel reinforcement protective layer thickness of 22.4 mm in Embodiment 2 of the present invention. Detailed Implementation

[0092] The following embodiments can help those skilled in the art to more fully understand the present invention, but should not be construed as limiting the present invention in any way.

[0093] Example 1: Case where the thickness of the concrete cover for the reinforcing steel is not increased.

[0094] The design method for increasing the thickness of the concrete cover for offshore pipe piles based on a convection-diffusion model includes the following steps:

[0095] S01: Collect chloride ion concentration data on the surface of the pipe pile, c(t,r) e ) = c s (1-e -αt According to c s (1-e -αt Fitting is performed in the form of ), where c s The concentration of chloride ions in seawater is denoted as α, which is a time-dependent parameter determined based on the collected chloride ion concentration data on the surface of the pipe pile.

[0096] S02: c is the result of fitting the collected chloride ion concentration data on the surface of the pipe pile. s (1-e -αt The inner and outer radii, permeability coefficient, diffusion coefficient, and static seawater pressure borne by the pipe pile are incorporated into the pipe pile diffusion model without increasing the thickness of the steel reinforcement protective layer. The steel reinforcement corrosion initiation time is calculated, and it is determined whether the calculated steel reinforcement corrosion initiation time is lower than the design life of the pipe pile.

[0097] The method for calculating the corrosion initiation time of reinforcing steel is as follows:

[0098] The governing equation for chloride ion intrusion in pipe piles is based on convection-diffusion theory, and the formula is shown below:

[0099]

[0100] In the formula, c(t,r) is the chloride ion concentration at time t at a distance r from the pipe pile, in %; D is the chloride ion diffusion coefficient of the pipe pile, in m. 2 / s; v is the seawater infiltration velocity, m / s; r is the radial distance of the pipe pile, m; t is the chloride ion intrusion time, s.

[0101] The value of v is expressed by Darcy's law as follows:

[0102]

[0103] In the formula, k is the permeability coefficient of the pipe pile, p is the osmotic pressure of the pipe pile at point r, and γ w The specific weight of water is approximately 10 N / m³. 3 Since the outer side of the pipe pile is subjected to seawater pressure while the inner side does not come into contact with seawater, the following boundary conditions can be determined.

[0104] p(r e ) = p s (3)

[0105] p(r0)=0 (4)

[0106] above p s The hydrostatic pressure exerted by seawater on the outside of the pipe pile is expressed in Pa.

[0107] Combining equations (1) to (4), we can obtain:

[0108]

[0109] in

[0110] Since the pipe pile initially contains no chloride ions, and its outer side is in contact with seawater while its inner side is not, the following initial and boundary conditions can be determined.

[0111] c(0,r)=0 (6)

[0112] c(t,r0)=0 (7)

[0113] c(t,r e ) = c s (1-e -αt (8)

[0114] In the formula c s The concentration of chloride ions in seawater is given by α, which is a time-dependent parameter, s. -1 ;

[0115] Equations (6) to (9) together constitute the mathematical model of the coastal pipe pile chloride ion intrusion analysis method based on convection-diffusion theory. By analyzing equations (5) to (8), the coastal pipe pile chloride ion intrusion analysis method based on convection-diffusion theory is obtained.

[0116] We can simplify c(t,r) to c and create two new functions as follows:

[0117] c * =cr a / 2D (9)

[0118] c ** =c *-b(t)(r-r0) (10)

[0119] Substituting equations (9) to (10) into equations (5) to (8) above, we obtain the following equation:

[0120]

[0121] c ** (0,r)=0 (12)

[0122] c ** (t,r0)=0 (13)

[0123] c ** (t,r e )=0 (14)

[0124] In the above formula, υ=|a / 2D|,

[0125] By performing a Weber transformation on equations (11) to (14), and then substituting the transformed equations (13) to (14) into equation (11), we can obtain the following equations:

[0126]

[0127] in R υ (β m ,r)=Y υ (β m r e )J υ (β m r)-J υ (β m r e )Y υ (β m r); β m Through J υ (β m r0)Y υ (β m r e ) = J υ (β m r e )Y υ (β m r0);

[0128] Equation (15) is a first-order partial derivative equation. Substituting equation (15) into equation (12) after the Weber transformation yields the following solution:

[0129]

[0130] in

[0131] Substituting equation (16) back into equations (9) to (10), we can obtain the following method for analyzing chloride ion intrusion in coastal pipe piles based on convection-diffusion theory:

[0132]

[0133] in

[0134] In equation (17), r is equal to the distance r between the reinforcing bars of the pipe pile. s When c(t,r) s The concentration of chloride ions in the reinforcing steel of the pipe pile is equal to the concentration of chloride ions that cause corrosion. c The corrosion initiation time T1 of the pipe pile reinforcement can be obtained;

[0135] S03: If the calculated corrosion initiation time of the reinforcing steel is not less than the design life of the pipe pile, then there is no need to increase the thickness of the reinforcing steel protective layer; only the chloride ion concentration on the surface of the pipe pile needs to be collected. If the calculated corrosion initiation time of the reinforcing steel is less than the design life of the pipe pile, then the thickness of the reinforcing steel protective layer needs to be increased.

[0136] S04: Increasing the thickness of the concrete cover for reinforcing steel needs to be determined based on the service life of the pipe pile, the existing chloride ion concentration distribution inside the pipe pile, and the known data of the pipe pile, using a convection-diffusion model of the pipe pile after increasing the thickness of the concrete cover for reinforcing steel. The service life of the pipe pile is directly known from the actual situation, while the existing chloride ion concentration distribution inside the pipe pile is determined by drilling and sampling during the construction process of increasing the thickness of the concrete cover for reinforcing steel. If the corrosion initiation time T1 of the pipe pile is less than the design service life T of the pipe pile without increasing the thickness of the concrete cover for reinforcing steel, then the thickness of the concrete cover for reinforcing steel needs to be increased. Assuming that the service life of the pipe pile before the thickness of the concrete cover for reinforcing steel is t1, the service life of the pipe pile after the thickness of the concrete cover for reinforcing steel is increased is not less than T-t1.

[0137] The convection-diffusion model for the pipe pile covers the outer diameter r′ of the pipe pile. e =r e +d, inner diameter r0, pipe pile permeability coefficient k, diffusion coefficient D, seawater chloride ion concentration c s The time-dependent parameter α, and the static seawater pressure p s , where t is the chloride ion intrusion time and r is any radial distance r of the pipe pile, and c(t,r) is the chloride ion concentration at r at time t; d is the thickened part of the steel reinforcement protective layer;

[0138] The control equation for chloride ion convection and diffusion in pipe piles after increasing the thickness of the concrete cover is as follows:

[0139]

[0140] in c′(t,r) represents the chloride ion concentration at time t at a distance r from the pipe pile after increasing the thickness of the steel reinforcement protective layer;

[0141] The initial time for the reinforcing steel cover thickness to be increased before the pipe pile is put back into use is defined as the initial moment, at which time the internal diameter of the pipe pile is from r0 to r. e The chloride ion concentration exists within the range, r e to r′ e There is no chloride ion concentration within the range; the initial boundary is defined as a function related to r, as follows:

[0142] C(0,r)=g(r) (19)

[0143] The inner boundary conditions of the pipe pile remain unchanged, while the outer boundary conditions extend to r′. e The location is as follows:

[0144] C(t,r0)=0 (20)

[0145] C(t,r′ e ) = c s (1-e -αt ) (twenty one)

[0146] Equations (18) to (21) above together constitute the chloride ion convection and diffusion model of the pipe pile after increasing the thickness of the steel reinforcement protective layer;

[0147] We simplify C(t,r) to C and create two new functions as follows:

[0148] C * =Cr a′ / 2D (twenty two)

[0149] C ** =C * -b′(t)(r-r0) (23)

[0150] Substituting equations (22) to (23) into equations (18) to (21) above, we get:

[0151]

[0152] C ** (0,r)=g(r)r a′ / 2D -b′(0)(r-r0) (25)

[0153] C ** (t,r0)=0 (26)

[0154] C ** (t,r′ e )=0 (27)

[0155] In the above formula, v = |a′ / 2D|,

[0156] By performing a Weber transformation on equations (24) to (27), and then substituting the transformed equations (26) to (27) into equation (24), we can obtain the following equations:

[0157]

[0158] in R v (χ m ,r)=Y v (χ m r′ e )J v (χ m r)-J v (χ m r′ e )Y v (χ m r); χ m Through J v (χ m r0)Y v (χ m r′ e ) = J v (χ m r′ e )Y v (χ m r0) is determined;

[0159] Equation (28) is a first-order partial derivative equation. Substituting equation (28) into equation (25) after the Weber transformation yields the following solution:

[0160]

[0161] in

[0162] Substituting equation (29) back into equations (22) to (23), we can obtain the analytical solution of the chloride ion convection and diffusion model for the pipe pile after increasing the thickness of the steel reinforcement protective layer, as shown below:

[0163]

[0164] in

[0165] In formula (30), r is equal to the distance r′ between the pipe pile reinforcement bars. s =r s +d; Let t = the expected service life of the pipe pile after increasing the thickness of the steel reinforcement protective layer, T2; When C(T2,r′) sThe concentration of chloride ions in the reinforcing steel of the pipe pile is equal to the concentration of chloride ions that cause corrosion. c The increased concrete cover thickness d of the pipe pile can then be obtained.

[0166] The experiment was conducted using the method described in this embodiment: chloride ion concentration data on the surface of the pipe pile were collected periodically, and the seawater chloride ion concentration c was obtained by fitting the data. s =0.55%, α=10 -9 s -1 Pipe pile parameters: outer diameter r e =1000mm, inner diameter r0=500mm, permeability coefficient k=10 -12 m / s, diffusion coefficient D = 10 -12 m 2 / s, the pipe pile withstands the static seawater pressure p s =50kPa, reinforcement position r s =950mm, chloride ion concentration of reinforcing steel corrosion c c =0.2%. Importing the above data into a convection-diffusion model for pipe piles without increasing the thickness of the concrete cover, the calculated corrosion initiation time for the reinforcing steel is 66.4 years. Figure 1 As shown. If the design life of the pipe pile is 50 years, then it is considered that there is no need to increase the thickness of the steel reinforcement protective layer.

[0167] Example 2: Cases requiring increased reinforcement cover thickness

[0168] Supplementary Example 1: If the design life of the pipe pile is 120 years, or if a decision is made after a period of service that the total service life of the pipe pile needs to be 120 years, then the thickness of the reinforcing steel protective layer needs to be added based on Example 1. Assuming that the thickness of the reinforcing steel protective layer is increased after 50 years of service, the distribution of chloride ion concentration inside the pipe pile without the increased thickness of the reinforcing steel protective layer at this point can be analyzed through sampling. Figure 2 As shown.

[0169] Will Figure 3 By combining the aforementioned known data with the diffusion model of pipe piles requiring increased concrete cover thickness, the required increase in concrete cover thickness for a pipe pile that has already served for 50 years to serve another 70 years can be determined. Calculations show that the required increase in concrete cover thickness is 22.4 mm. Figure 3 The study showed that when the thickness of the concrete cover for the reinforcing steel increased by 22.4 mm, the corrosion initiation time of the reinforcing steel was 70 years. Adding this to the previous 50 years of service, the design life of the pipe pile is 120 years.

[0170] This invention presents a design method for increasing the thickness of the concrete cover for marine pipe piles based on a convection-diffusion model. It fully considers the structural characteristics and environmental conditions of the marine pipe piles, such as the outer side bearing seawater pressure while the inner side does not contact seawater, and the initial absence of chloride ions inside the pile. The method periodically collects the chloride ion concentration on the surface of the marine pipe pile during its service life. Through exponential nonlinear fitting, it obtains the development law of chloride ion concentration on the surface of the in-service pipe pile. Furthermore, it sets the chloride ion concentration at the outer boundary in contact with seawater as a concentration function correlated with time. This algorithm is more consistent with reality and can more accurately estimate the required increase in the thickness of the concrete cover. Currently... Traditional methods mainly involve periodic inspections and maintenance of offshore pipe piles, but this cannot fundamentally solve the problem of steel reinforcement corrosion, and the maintenance costs are high and the cycle is long. This application can accurately estimate the required increase in the thickness of the steel reinforcement protective layer. Increasing the thickness of the steel reinforcement protective layer in a timely manner can effectively solve the problem of steel reinforcement corrosion, thereby reducing maintenance costs. At present, there is no clear guiding method for increasing the thickness of the steel reinforcement protective layer. The technology of this application can accurately estimate the required increase in the thickness of the steel reinforcement protective layer and develop a design method for thickening the steel reinforcement protective layer of old offshore pipe piles to improve the service life and safety of old pipe piles. It has important theoretical significance and engineering application value.

[0171] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A design method for increasing the thickness of the protective layer for reinforcing steel bars in marine pipe piles based on a convection-diffusion model, characterized in that, Includes the following steps: S01: Collect chloride ion concentration data on the surface of the pipe pile. ,according to c s (1-e -αt Fitting is performed in the form of ), where c s This refers to the chloride ion concentration in seawater. α The time-related parameter was determined based on the collected chloride ion concentration data on the surface of the pipe pile. S02: Fitted based on the collected chloride ion concentration data on the surface of the pipe pile c s (1-e -αt The inner and outer radii, permeability coefficient, diffusion coefficient, and static seawater pressure borne by the pipe pile are incorporated into a pipe pile diffusion model without increasing the thickness of the steel reinforcement protective layer. The corrosion initiation time of the steel reinforcement is calculated, and it is determined whether the calculated corrosion initiation time is lower than the design life of the pipe pile. The method for calculating the corrosion initiation time of the steel reinforcement is as follows: The governing equation for chloride ion intrusion in pipe piles is based on convection-diffusion theory, and the formula is shown below: (1) In the formula c ( t , r ( ) represents the distance between pipe piles r In t Chloride ion concentration at time %, % D Let m be the chloride ion diffusion coefficient of the pipe pile. 2 / s; v The seawater permeation velocity is expressed in m / s. r The radial distance between the pipe piles is in meters (m). t The time for chloride ion intrusion is s; The v Darcy's Law expresses this as follows: (2) In the formula k The permeability coefficient of the pipe pile, p For pipe piles in r Osmotic pressure at the location, γ w The specific gravity of water; Since the outer side of the pipe pile is subjected to seawater pressure while the inner side is not in contact with seawater, the following boundary conditions can be determined. (3) (4) The above formula p s The hydrostatic pressure exerted by seawater on the outside of the pipe pile is expressed in Pa. Combining equations (1) to (4), we can obtain: (5) in ; Since the pipe pile initially contains no chloride ions, and its outer side is in contact with seawater while its inner side is not, the following initial and boundary conditions can be determined. (6) (7) (8) In the formula c s This refers to the concentration of chloride ions in seawater. α For time-related parameters, s -1 ; Will c ( t , r (abbreviated as) c Two new functions are created as follows: (9) (10) Substituting equations (9) to (10) into equations (5) to (8) above, we obtain the following equation: (11) (12) (13) (14) In the above formula , ; By performing a Weber transformation on equations (11) to (14), and then substituting the transformed equations (13) to (14) into equation (11), we can obtain the following equations: (15) in ; ; ; ; pass ; Substituting equation (15) into equation (12) after the Weber transformation yields the following solution: (16) in ; Substituting equation (16) back into equations (9) and (10), we can obtain the following method for analyzing chloride ion intrusion in coastal pipe piles based on convection-diffusion theory: (17) in ; In formula (17) r Equal to the distance of the pipe pile reinforcement r s ,when c ( t , r s () equals the chloride ion concentration at which the reinforcing steel of the pipe pile corrodes. c c This allows us to obtain the corrosion initiation time of the reinforcing steel in the pipe pile. T 1; S03: If the calculated corrosion initiation time of the reinforcing steel is not less than the design life of the pipe pile, then there is no need to increase the thickness of the reinforcing steel protective layer; only the chloride ion concentration on the surface of the pipe pile needs to be collected. If the calculated corrosion initiation time of the reinforcing steel is less than the design life of the pipe pile, then the thickness of the reinforcing steel protective layer needs to be increased. S04: The thickness of the concrete cover for reinforcing steel needs to be determined based on the service life of the pipe pile, the existing chloride ion concentration distribution inside the pipe pile, and the known data of the pipe pile, using the convection-diffusion model of the pipe pile after increasing the thickness of the concrete cover for reinforcing steel. The service life of the pipe pile can be directly known from the actual situation, and the existing chloride ion concentration distribution inside the pipe pile can be determined by drilling and sampling during the construction process of increasing the thickness of the concrete cover for reinforcing steel. The convection-diffusion model for pipe piles covers the outer diameter of the pipe piles. , inner diameter r 0, permeability coefficient of pipe piles k diffusion coefficient D seawater chloride ion concentration c s Time-related parameters α seawater pressure p s Chloride ion invasion time t And any radial distance of the pipe pile r ,and t time r Chloride ion concentration at c ( t , r ); d This is the thickened portion of the concrete cover for the reinforcing steel. The control equation for chloride ion convection and diffusion in pipe piles after increasing the thickness of the concrete cover is as follows: (18) in , To increase the thickness of the concrete cover for the reinforcing steel, the spacing between the pipe piles r In t The chloride ion concentration at that time; The initial time is defined as the moment when the pipe pile is put back into use after the thickness of the reinforcement protective layer is increased. r 0 to r e Chloride ion concentration exists within the range. r e arrive There is no chloride ion concentration within the range; the initial boundary is defined as a region with... r The relevant functions are as follows: (19) The inner boundary conditions of the pipe pile remain unchanged, while the outer boundary conditions extend to... The location is as follows: (20) (21) Equations (18) to (21) above together constitute the chloride ion convection and diffusion model of the pipe pile after increasing the thickness of the steel reinforcement protective layer; Will C ( t , r (abbreviated as) C Two new functions are created as follows: (22) (23) Substituting equations (22) to (23) into equations (18) to (21) above, we get: (24) (25) (26) (27) In the above formula , ; By performing a Weber transformation on equations (24) to (27), and then substituting the transformed equations (26) to (27) into equation (24), we can obtain the following equations: (28) in ; ; ; ; pass Sure; Equation (28) is a first-order partial derivative equation. Substituting equation (28) into equation (25) after the Weber transformation yields the following solution: (29) in Substituting equation (29) back into equations (22)~(23), we can obtain the analytical solution of the chloride ion convection and diffusion model of the pipe pile after increasing the thickness of the steel reinforcement protective layer, as shown below: (30) in ; In formula (30) r Equal to the distance of the pipe pile reinforcement ;make t = Expected service life of pipe piles after increasing the thickness of the steel reinforcement protective layer T 2; when Equal to the chloride ion concentration of the reinforcing steel in the pipe pile c c This allows us to obtain the increased thickness of the steel reinforcement protective layer for the pipe pile. d .

2. The design method for increasing the thickness of the protective layer of marine pipe pile reinforcement based on the convection-diffusion model according to claim 1, characterized in that, In the above formula (2) γ w The specific weight of water is approximately 10 N / m³. 3 .

3. The design method for increasing the thickness of the protective layer of marine pipe pile reinforcement based on the convection-diffusion model according to claim 1, characterized in that, In step S02, equations (6) to (9) together constitute a mathematical model for the analysis method of chloride ion intrusion in coastal pipe piles based on convection-diffusion theory. By analyzing equations (5) to (8), the analysis method of chloride ion intrusion in coastal pipe piles based on convection-diffusion theory is obtained.

4. The design method for increasing the thickness of the protective layer of marine pipe pile reinforcement based on the convection-diffusion model according to claim 1, characterized in that, In step S02, equation (15) is a first-order partial derivative equation. Substituting equation (15) into equation (12) after Weber transformation, equation (16) can be obtained.

5. The design method for increasing the thickness of the protective layer of marine pipe pile reinforcement based on the convection-diffusion model according to claim 1, characterized in that, In step S04, the corrosion initiation time of the pipe pile reinforcement is determined without increasing the thickness of the reinforcement protective layer. T 1 less than the design life of the pipe pile T If the concrete cover thickness is insufficient, then it is necessary to increase the thickness of the reinforcing steel cover; assuming the pipe piles for which the concrete cover thickness has not yet been increased have been in service for [duration missing]. t 1. The service life of the pipe pile after increasing the thickness of the steel reinforcement protective layer shall not be less than T - t 1.

6. The design method for increasing the thickness of the protective layer of marine pipe pile reinforcement based on the convection-diffusion model according to claim 1, characterized in that, In step S04, the sampling method for the existing chloride ion concentration distribution inside the pipe pile is as follows: (1) First, detect whether there are cracks in the pipe pile. For pipe piles without cracks, use the drilling sampling method to take samples; (2) For pipe piles with cracks, take samples at the cracks. The sampling method is as follows: insert a sampling piece made of FRP with a width of 0.3-0.5 cm and a thickness of 3-5 mm into the crack. After standing for 3-5 days, detect the chloride ion concentration distribution data on the sampling piece made of FRP as the existing chloride ion concentration distribution data inside the pipe pile.

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