A method for designing a vertical isolation barrier comprising a degradation layer in a contaminated site

Abstract

This invention discloses a design method for a vertical isolation barrier containing a degradation layer within a contaminated site, comprising the following steps: delineating the boundary of the contaminated site and detecting the contaminated site to obtain pollution parameters; performing simplified calculations based on the pollution parameters and a one-dimensional convection dispersion model to obtain the total thickness of the vertical isolation barrier set at the boundary of the contaminated site; determining whether a multi-functional barrier wall design is necessary based on the total thickness of the vertical isolation barrier; the design of a multi-functional barrier wall refers to replacing the middle layer barrier material isolation barrier in a conventional vertical isolation barrier with a middle layer degradation material isolation barrier, and performing equivalent calculations of the thickness D2 of the middle layer barrier material isolation barrier and the thickness D4 of the middle layer degradation material isolation barrier. The advantages of this invention are: designing based on the migration mechanism of pollutants in soil using a barrier + degradation mechanism, thereby increasing the service life of the isolation barrier while reducing the barrier thickness and lowering engineering costs.

Description

Technical Field

[0001] This invention belongs to the field of environmental geotechnical technology, specifically relating to a design method for a vertical isolation barrier containing a degradation layer in a contaminated site. Background Technology

[0002] Pollution isolation technology refers to the technique of laying a barrier layer to block the migration and diffusion of pollutants in the soil medium, thus isolating the polluted medium from the surrounding environment and preventing the pollutants from coming into contact with human bodies or migrating with precipitation or groundwater, thereby avoiding harm to human health and the surrounding environment. Since the 1990s, vertical isolation methods have gained considerable attention both domestically and internationally, but the application of vertical barrier technology for contaminated sites in China is still in its initial stage, with relatively few relevant engineering examples.

[0003] After years of practice and exploration, various isolation methods, such as soil-bentonite cutoff walls, plastic concrete cutoff walls, cement-bentonite cutoff walls (self-setting mortar), geomembrane-bentonite slurry composite cutoff walls, ordinary concrete cutoff walls, cement-soil mixing pile walls, grouting curtains, and steel sheet pile cutoff walls, have been gradually applied to risk isolation in landfills and contaminated sites. Different types of isolation barriers each offer advantages in terms of economy, constructability, and long-term service performance.

[0004] Regarding design methodologies, although isolation barriers are increasingly used in pollution control and prevention projects, a unified design philosophy has yet to be reached. While domestic and international scholars have conducted in-depth and extensive research on vertical isolation barriers, yielding significant results, certain problems have also been exposed. On the one hand, current research focuses more on the isolation materials, design methods, construction techniques, and emergency repair measures for vertical barriers, with relatively insufficient research on the design and construction forms of isolation barriers themselves. On the other hand, the contradiction between the short-term effectiveness and long-term service performance of isolation barriers is difficult to reconcile; overly idealistic designs neglect changes in hydraulic boundary conditions caused by rainfall, evaporation, and other factors.

[0005] Based on the migration mechanism of pollutants, this invention introduces novel degradable materials and a vertical isolation barrier design method with degradation and blocking functions, so that pollutants are degraded while being blocked by the isolation wall, thereby increasing the service life of the isolation barrier. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing a design method for a vertical isolation barrier containing a degradation layer in a contaminated site. This design method is based on the migration mechanism of pollutants in the soil, introduces novel degradable materials, and has a vertical isolation barrier design method with degradation and barrier functions. This allows pollutants to be degraded while being blocked by the isolation wall, thereby increasing the service life of the isolation barrier.

[0007] The objective of this invention is achieved through the following technical solutions:

[0008] A method for designing a vertical isolation barrier containing a degradation layer in a contaminated site, characterized in that the design method includes the following steps:

[0009] S1: Delineate the boundary of the contaminated site, and conduct tests on the contaminated site to obtain pollution parameters, including pollution depth and pollution type;

[0010] S2: Based on the pollution parameters and the one-dimensional convection dispersion model, a simplified calculation is performed to obtain the total thickness x of the vertical isolation barrier set at the boundary of the contaminated site;

[0011] S3: Determine whether a multi-functional barrier wall design is required based on the calculated total thickness x of the vertical isolation barrier. The determination method is as follows:

[0012] If the total thickness of the vertical isolation barrier is greater than D1+D3, proceed to step S4;

[0013] If the total thickness of the vertical isolation barrier is less than or equal to D1+D3, then the vertical isolation barrier adopts a conventional barrier material wall.

[0014] Wherein, D1 and D3 are the thicknesses of the inner and outer barrier materials of a conventional vertical barrier; the conventional vertical barrier, from the inside out, includes the inner barrier material barrier, the middle barrier material barrier, and the outer barrier material barrier.

[0015] S4: The design of the vertical isolation barrier using a multi-functional barrier wall means replacing the middle layer barrier material isolation barrier in the conventional vertical isolation barrier with a middle layer degradable material isolation barrier, and performing equivalent calculations on the thickness D2 of the middle layer barrier material isolation barrier and the thickness D4 of the middle layer degradable material isolation barrier to obtain the thickness D4 of the equivalent replacement middle layer degradable material isolation barrier.

[0016] The vertical isolation barrier is arranged at a depth not less than the contamination depth.

[0017] The pollution types are divided into volatile pollution and non-volatile pollution, and horizontal isolation barriers are also arranged on the polluted sites where the pollution type is volatile pollution.

[0018] The pollution parameters also include the effective diffusion coefficient D of pollutants within the contaminated site. e , blocking factor R d And the initial concentration C0 of the pollutants in the contaminated site.

[0019] The formula for calculating the total thickness x of the vertical isolation barrier in step S2 is as follows:

[0020]

[0021] In the formula:

[0022] x represents the total thickness of the vertical isolation barrier, in meters (m).

[0023] t represents the service life of the vertical isolation barrier when it is made of barrier material, in years;

[0024] D e The effective diffusion coefficient of pollutants within the contaminated site is given in meters. 2 / year;

[0025] R d The blocking factor is dimensionless.

[0026] C0 represents the initial concentration of pollutants in the contaminated site, expressed in mg / L.

[0027] v represents the groundwater flow velocity, measured in m / s.

[0028] C represents the real-time concentration of pollutants in the contaminated site, in mg / L;

[0029] In step 2, the service life t is set according to the isolation requirements and C / C0=0.1 is set.

[0030] In step S3, when biaxial mixing piles are used in cohesive soil areas, D1 and D3 are 0.7m; when triaxial mixing piles are used, D1 and D3 are 0.85m.

[0031] The method for calculating the thickness D4 of the intermediate degradable material isolation barrier mentioned in step S4 is as follows:

[0032] S4.1: Calculate the relative concentration C of pollutants in the contaminated site after passing through the inner barrier material. D1 The calculation formula is:

[0033] ;

[0034] In the formula:

[0035] D1 is the thickness of the inner barrier material isolation barrier, in meters (m).

[0036] R d The blocking factor is dimensionless.

[0037] D h The height of the inner barrier material isolation barrier is expressed in meters (m).

[0038] v represents the groundwater flow velocity, measured in m / s.

[0039] t represents the residence time of the pollutant within the inner barrier material isolation barrier.

[0040] S4.2: Using the calculation formula C D2 =0.1 / C D1 Calculate the relative concentration CD2 of pollutants behind the isolation barrier of the middle layer barrier material. The relative concentration CD2 is equivalent to the relative concentration CD4 of pollutants behind the isolation barrier of the middle layer degradation material.

[0041] S4.3: Using C D2 =CD4=C D1 exp (-k1t1) calculates the residence time t1 of the pollutant within the intermediate layer of the degradation material barrier, where k1 is the reaction rate of one section of the degradation material within the intermediate layer of the degradation material barrier;

[0042] S4.4: Calculate the thickness D4 of the middle layer degradable material isolation barrier. The calculation formula is: D4=t1v.

[0043] The advantages of this invention are: it is designed based on the migration mechanism of pollutants in soil and adopts the barrier + degradation mechanism, which improves the service life of the isolation barrier, while reducing the thickness of the isolation barrier and reducing the engineering cost. Attached Figure Description

[0044] Figure 1 This is a schematic diagram showing the total thickness of the vertical isolation barrier in this invention;

[0045] Figure 2 This is a schematic diagram of a conventional vertical isolation barrier structure;

[0046] Figure 3 This is a schematic diagram of the vertical isolation barrier structure using a multifunctional barrier wall in this invention. Detailed Implementation

[0047] The features and other related features of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, so as to facilitate understanding by those skilled in the art:

[0048] like Figure 1-3 The markings in the diagram are as follows: Vertical barrier 1, Inner barrier material barrier 2, Middle barrier material barrier 3, Outer barrier material barrier 4, Middle degradable material barrier 5, and Conventional vertical barrier 6.

[0049] Example: Figure 1 , 2As shown in Figure 3, this embodiment specifically relates to a design method for a vertical isolation barrier containing a degradation layer in a contaminated site. The vertical isolation barrier design method includes the following steps:

[0050] (S1) Delineate the boundary of the contaminated site, and conduct tests on the contaminated site to obtain pollution parameters, including pollution depth and pollution type; determine the setting depth of the vertical isolation barrier by detecting the pollution depth, that is, the setting depth of the vertical isolation barrier needs to be deeper than the pollution depth; the pollution type is divided into volatile pollution and non-volatile pollution, and horizontal isolation barriers are also arranged on the contaminated site that belongs to volatile pollution.

[0051] In addition, pollution parameters also include the effective diffusion coefficient D of pollutants within the contaminated site. e , blocking factor R d And the initial concentration C0 of pollutants in the contaminated site.

[0052] (S2) Based on the above pollution parameters and the one-dimensional convection dispersion model, a simplified calculation is performed to obtain the total thickness x of the vertical isolation barrier 1 set at the boundary of the contaminated site. Here, the vertical isolation barrier 1 is only calculated based on the thickness required when the barrier material is used. The specific calculation formula is as follows:

[0053]

[0054] In the formula:

[0055] x represents the total thickness of the vertical isolation barrier 1, in meters (m).

[0056] t represents the service life of the vertical isolation barrier 1 when it is entirely made of barrier materials, in years. The service life is set according to the isolation requirements.

[0057] D e The effective diffusion coefficient of pollutants within the contaminated site, expressed in meters (m). 2 / year;

[0058] R d The blocking factor is dimensionless.

[0059] C0 represents the initial concentration of pollutants in the contaminated site, expressed in mg / L.

[0060] v represents the groundwater flow velocity, measured in m / s.

[0061] C represents the real-time concentration of pollutants in the contaminated site, expressed in mg / L.

[0062] Based on the isolation requirements, C / C0 = 0.1.

[0063] (S3) Determine whether a multi-functional barrier wall design is necessary based on the calculated total thickness x of the vertical isolation barrier 1 when all barrier materials are used. The determination method is as follows:

[0064] If the total thickness x of the vertical isolation barrier 1 is greater than D1+D3, then a multifunctional barrier cavity design is adopted and the process proceeds to step S4, such as... Figure 3 As shown;

[0065] If the total thickness x of the vertical isolation barrier 1 is less than or equal to D1+D3, then the vertical isolation barrier shall be constructed using conventional barrier materials, such as... Figure 2 As shown, the conventional vertical isolation barrier 6 comprises, from the inside out, an inner layer barrier material isolation barrier 2, a middle layer barrier material isolation barrier 3, and an outer layer barrier material isolation barrier 4. It should be noted that the barrier materials mentioned in this embodiment can generally be cement, bentonite, or concrete, etc.

[0066] Wherein, D1 and D3 are the thicknesses of the inner layer barrier material 2 and the outer layer barrier material 4 of the conventional vertical isolation barrier 6; when biaxial mixing piles are used in cohesive soil areas, D1 and D3 are 0.7m; when triaxial mixing piles are used, D1 and D3 are 0.85m.

[0067] (S4) The design of the vertical isolation barrier using a multi-functional barrier wall refers to replacing the middle layer barrier material barrier 3 in the conventional vertical isolation barrier 6 with the middle layer degradable material barrier 5. The degradable material here can be an oxidizing material, a microbial material, a reducing material, etc. Generally, high-chain pollutants or pollutants with benzene rings are preferentially treated with microbial and reducing materials, while other low-chain organic pollutants can be treated with oxidizing materials. The thickness D2 of the middle layer barrier material barrier 3 is equivalently calculated to the thickness D4 of the middle layer degradable material barrier 5 to obtain the equivalent thickness D4 of the middle layer degradable material barrier 5 after replacement; the specific calculation method is as follows:

[0068] (S4.1) Calculate the relative concentration C of pollutants in the contaminated site after passing through the inner barrier material 2. D1 The calculation formula is:

[0069] ;

[0070] In the formula:

[0071] D1 is the thickness of the inner barrier material, isolation barrier 2, in meters (m).

[0072] R d The blocking factor is dimensionless.

[0073] D h The height of the inner barrier material isolation barrier 2 is in meters;

[0074] v represents the groundwater flow velocity, measured in m / s.

[0075] t represents the residence time of pollutants within the inner barrier material isolation barrier 2;

[0076] (S4.2) Using the calculation formula C D2 =0.1 / C D1 Calculate the relative concentration CD2 of pollutants after the middle layer barrier material isolation barrier 3. The relative concentration CD2 is equivalent to the relative concentration CD4 of pollutants after the middle layer degradation material isolation barrier 5.

[0077] S4.3: Using C D2 =CD4=C D1 exp (-k1t1) calculates the residence time t1 of the pollutant within the middle layer of the degradation material isolation barrier 5, where k1 is the reaction rate of one section of the degradation material within the middle layer of the degradation material isolation barrier 5;

[0078] S4.4: Calculate the thickness D4 of the middle layer degradable material isolation barrier 5. The calculation formula is: D4=t1v;

[0079] In the formula:

[0080] t1 is the residence time of pollutants within the middle layer of degradation material isolation barrier 5;

[0081] v represents the groundwater flow velocity, measured in m / s.

[0082] The beneficial effects of this embodiment are as follows: based on the migration mechanism of pollutants in soil, a novel degradable material is introduced, and a vertical isolation barrier design method with degradation and blocking functions is adopted, so that pollutants are degraded while being blocked by the isolation wall, thereby increasing the service life of the isolation barrier.

Claims

1. A method for designing a vertical isolation barrier comprising a degrading layer in a contaminated site, characterized in that: The design method comprises the following steps: S1: demarcate the boundary of the contaminated site, detect the contaminated site to obtain a pollution parameter, the pollution parameter comprising a pollution depth and a pollution type; S2: perform a simplified calculation according to the pollution parameter and a one-dimensional convection-dispersion model to obtain a total thickness x of a vertical isolation barrier arranged at the boundary of the contaminated site; S3: judge whether the design of a multifunctional barrier wall is needed for the total thickness x of the vertical isolation barrier obtained by calculation, the judgment method being: if the total thickness of the vertical isolation barrier is greater than D1+D3, then step S4 is entered; if the total thickness of the vertical isolation barrier is less than or equal to D1+D3, then the vertical isolation barrier adopts a conventional barrier material wall; wherein D1 and D3 are the thickness of an inner layer barrier material isolation barrier and the thickness of an outer layer barrier material isolation barrier of a conventional vertical isolation barrier; the conventional vertical isolation barrier comprises, in sequence from inside to outside, the inner layer barrier material isolation barrier, a middle layer barrier material isolation barrier and the outer layer barrier material isolation barrier; the barrier materials used in the inner layer barrier material isolation barrier, the middle layer barrier material isolation barrier and the outer layer barrier material isolation barrier are cement, bentonite or concrete; S4: the design of the vertical isolation barrier adopting a multifunctional barrier wall means that the middle layer barrier material isolation barrier in the conventional vertical isolation barrier is replaced by a middle layer degradation material isolation barrier, and the thickness D2 of the middle layer barrier material isolation barrier is equivalent to the thickness D4 of the middle layer degradation material isolation barrier to obtain the thickness D4 of the middle layer degradation material isolation barrier after equivalent replacement; the arrangement depth of the vertical isolation barrier is not less than the pollution depth; said pollution parameters further comprising an effective diffusion coefficient D of the pollutant within said polluted site e , a retardation factor R d and an initial concentration Co of the pollutant in said polluted site; the calculation formula of the total thickness x of the vertical isolation barrier in step S2 is: ； wherein: x is the total thickness of the vertical isolation barrier, in units of m; t is the service life of the vertical isolation barrier when barrier material is adopted, in units of year; D e D is the effective diffusion coefficient of the contaminant in the contaminated site, in m2 / year. 2 D is the effective diffusion coefficient of the contaminant in the contaminated site, in m2 / year. R d R is a retardation factor, dimensionless; C0 is the initial concentration of the contaminant in the contaminated site, in units of mg / L; v is the groundwater flow rate, in units of m / s; C is the real-time concentration of the contaminant in the contaminated site, in units of mg / L; in step S2, the service life t is set according to the isolation requirement, and C / C0=0.1 is set; in step S3, when double-axis mixing piles are adopted in clayey soil areas, D1 and D3 are 0.7 m; when triple-axis mixing piles are adopted, D1 and D3 are 0.85 m; the calculation method of the thickness D4 of the middle layer degradation material isolation barrier in step S4 is: S4.1: Calculate the relative concentration C of the contaminant in the contaminated site after being isolated by the inner barrier material isolation barrier D1 The calculation formula is: ； wherein: D1 is the thickness of the inner layer barrier material isolation barrier, in units of m; R d R is a retardation factor, dimensionless; D h h is the height of the inner layer barrier material isolation screen, in m; v is the groundwater flow rate, in units of m / s; t is the residence time of the contaminant in the inner layer barrier material isolation barrier; S4.2: using the calculation formula C D2 = 0.1 / C D1 , the relative concentration CD2 of the pollution after the middle layer barrier isolation screen is calculated, and the relative concentration CD2 is equivalent to the relative concentration CD4 of the pollution after the middle layer degradation material isolation screen. S4.3: utilizing C D2 = CD4 = C D1 exp (-k1t1), where k1 is the rate of reaction of the degradation material within the middle degradation material isolation barrier, to calculate the residence time t1 of the contaminant within the middle degradation material isolation barrier. S4.4: calculate the thickness D4 of the middle layer degradation material isolation barrier, the calculation formula being: D4=t1v.

2. A method of designing a vertical isolation barrier comprising a degrading layer in a contaminated site according to claim 1, characterized in that The pollution type is divided into volatile pollution and non-volatile pollution, and a horizontal isolation barrier is further arranged on the contaminated site with the pollution type being volatile pollution.

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