A rapid design method for vertical isolation barriers based on land risk screening and judgment
Through the rapid design method of vertical isolation barrier based on plot risk screening and discrimination, the problems of insecure design and complex calculation in the prior art are solved, and a more convenient and efficient design method is realized, which is suitable for vertical isolation barrier design in conventional contaminated areas.
Patent Information
- Application Number
- CN202411886945.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-20
- Publication Date
- 2025-04-04
AI Technical Summary
The existing technology lacks mature vertical isolation barrier design methods, which leads to the design results that may be unsafe, and the parameters are numerous and the calculations are complex, making it difficult to apply in actual engineering.
A rapid design method for vertical isolation barrier based on land risk screening is proposed. By judging whether the conventional polluted area is a heavy metal pollutant or an organic pollutant, the permeability coefficient, blocking factor and breakdown standards are determined, and the design thickness of the barrier is calculated using the design service life and experience calculation formula.
It provides a more convenient and more in line with engineering practice design method, taking into account the risk level, pollution status and hydrogeological conditions of the site, and is simpler and more efficient than the original design method.
Smart Images
Figure CN119761032A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of environmental geotechnical engineering, and in particular relates to a rapid design method for a vertical isolation barrier based on land risk screening and identification. Background Art
[0002] Pollution isolation technology refers to the technology that blocks the migration and diffusion of pollutants in the soil medium by laying a barrier layer, isolates the polluted medium from the surrounding environment, and prevents pollutants from contacting the human body and migrating with precipitation or groundwater to cause harm to the human body and the surrounding environment. Since the 1990s, vertical isolation has received high attention at home and abroad. The vertical barrier is one of the most important components of isolation and sealing technology. Generally, a mixing device is used to spray the curing agent (cement, lime and other materials) into the deep soft soil layer. Under the action of water, a series of physical and chemical reactions occur between the curing agent and the soil to form a complete low-permeability anti-seepage wall.
[0003] However, since the relevant technical research lags behind the development of foreign countries for decades, there is no mature vertical barrier design method and technology in China. It mainly draws on the empirical formula of water conservancy projects, that is, taking the allowable hydraulic gradient as the control condition and taking the safety factor into account in the allowable hydraulic gradient. In actual engineering, this design method may make the result unsafe. In recent years, some isolation barrier design methods that consider the migration mechanism of pollutants have also been developed, but there are many parameters and complex calculation formulas, which makes it difficult to implement in actual engineering applications. Therefore, it is necessary to propose a rapid isolation barrier design method based on site risk level identification and existing isolation barrier construction technology. Summary of the invention
[0004] The purpose of the present invention is to provide a rapid design method for vertical isolation barriers based on land risk screening and identification in accordance with the above-mentioned deficiencies in the prior art. The design method is suitable for conventional pollution areas with low risks. The permeability coefficient, blocking factor and breakdown standard of the vertical isolation barrier are determined by judging whether the conventional pollution area is a heavy metal pollutant or an organic pollutant. The thickness is calculated by substituting the design service life of the vertical isolation barrier with the help of the corresponding design thickness empirical calculation formula.
[0005] The purpose of the present invention is achieved by the following technical solutions: A method for rapid design of vertical isolation barriers based on land risk screening and identification, characterized in that the design method comprises the following steps: S1: Determine whether the target site is a conventional pollution area or a high-risk pollution area according to the regional risk identification criteria; If the target site is a high-risk contamination area, it will be terminated; If the target site is a conventional contaminated area, proceed to the next step to design a vertical isolation barrier; S2: For conventional contaminated areas with heavy metal pollutants, the permeability coefficient of the vertical isolation barrier is selected as 10 - 7 cm / s, the blocking factor is selected as 3, and the breakdown standard is selected as 10% of the pollutant concentration; the empirical calculation method for the design thickness of the vertical isolation barrier is to substitute the design service life T into the two calculation formulas below for calculation, and the larger of the two minimum design thickness values obtained by calculation is selected as the design thickness of the vertical isolation barrier: H = 0.4386 oeLh -0.1083; H = 0.0217 oeLh -0.6066; For conventional contaminated areas with organic pollutants, the permeability coefficient of the vertical isolation barrier is selected as 10 -7 cm / s, the blocking factor is selected as 1, and the breakdown standard is selected as 10% of the pollutant concentration; the empirical calculation method for the design thickness of the vertical isolation barrier is to substitute the design service life T into the two calculation formulas below for calculation, and the larger of the two minimum design thickness values obtained by calculation is selected as the design thickness of the vertical isolation barrier: H = 0.7472 lnT- 0.2243; H = 0.0371 lnT- 0.9915; Where: H is the minimum design thickness of the vertical isolation barrier; T The designed service life of the vertical isolation barrier.
[0006] The regional risk identification criteria are: S1.1: Determine whether there are hydrogeological conditions outside the vertical isolation barrier that are likely to cause high head difference; if so, determine that the target site is a high-risk pollution area; if not, proceed to the next step to continue the determination; S1.2: Determine whether there is NAPL within 1 meter of the inner side of the vertical isolation barrier; if so, determine that the target site is a high-risk contaminated area; if not, proceed to the next step to continue determination; S1.3: Determine whether the pollutant concentration inside the vertical isolation barrier exceeds the standard by 20 times or more; if so, determine that the target site is a high-risk pollution area; if not, proceed to the next step to continue the determination; S1.4: Determine whether there is a silty soil layer inside the vertical isolation barrier; if so, determine that the target site is a high-risk contaminated area; if not, determine that the target site is a conventional contaminated area.
[0007] The advantages of the present invention are: it provides a more convenient design method for the design of vertical isolation barriers for conventional contaminated sites. The isolation barriers involved in this method fully consider the risk level, pollution status and hydrogeological conditions of the site, and are more in line with engineering practice and simpler and more efficient than the original design method. BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Figure 1 It is a flowchart of the regional risk identification criteria in the present invention; Figure 2 This is an empirical formula diagram for estimating the design thickness when the target pollutant is a heavy metal pollutant in the present invention; Figure 3 This is an empirical formula diagram for estimating the design thickness when the target pollutant is an organic pollutant in the present invention; Figure 4 The calculation result table of design thickness for different design years in the present invention; Figure 5 It is a schematic diagram of the model box in the present invention; Figure 6 It is a design table of the scale test in the present invention; Figure 7 This is a table of heavy metal concentrations in the sand samples outside the isolation wall of the present invention. DETAILED DESCRIPTION
[0009] The features of the present invention and other related features are further described in detail below through embodiments in conjunction with the accompanying drawings to facilitate understanding by those skilled in the art: Example: Figure 1-7 As shown, this embodiment specifically relates to a rapid design method for a vertical isolation barrier based on land risk screening and discrimination. The design method is suitable for use when the vertical isolation barrier is set in a low-risk conventional pollution area, and includes the following steps: (S1) Determine whether the target site is a conventional pollution area or a high-risk pollution area according to the regional risk identification criteria; If the target site is a high-risk contamination area, terminate the process and the design of vertical isolation barriers is not suitable for this method; If the target site is a conventional contaminated area, proceed to the next step to design a vertical isolation barrier.
[0010] The regional risk identification criteria are: S1.1: Determine whether there are hydrogeological conditions outside the vertical isolation barrier that are likely to cause high head difference; if so, determine that the target site is a high-risk pollution area; if not, proceed to the next step to continue the judgment; S1.2: Determine whether there is NAPL within 1 meter of the inner side of the vertical isolation barrier; if so, determine that the target site is a high-risk contaminated area; if not, proceed to the next step to continue the determination.
[0011] S1.3: Determine whether the pollutant concentration inside the vertical isolation barrier exceeds the standard by 20 times or more; if so, determine that the target site is a high-risk pollution area; if not, proceed to the next step to continue the judgment.
[0012] S1.4: Determine whether there is a silty soil layer or other easily migrated soil layer inside the vertical isolation barrier; if so, the target site is determined to be a high-risk contaminated area; if not, the target site is determined to be a conventional contaminated area, and the conventional contaminated area here is a low-risk contaminated area.
[0013] (S2) Select the functional requirements of the vertical isolation barrier: Permeability coefficient of vertical isolation barrier: For the shallow soil layer in Shanghai, under the premise that the construction technology can ensure the mixing uniformity and the integrity of the pile body, for the cement soil vertical isolation barrier with an admixture of more than 10%, the engineering generally requires a permeability coefficient of less than 10 -7 cm / s, although the area with good wall quality can reach 10 -8 cm / s, but it is difficult to ensure the quality of construction. Once quality defects occur, the vertical isolation barrier will have an advantageous channel, thereby accelerating migration. Therefore, the permeability coefficient of the vertical isolation barrier in conventional contaminated areas can be calculated as 10 -7 cm / s is considered.
[0014] Anti-pollution performance (retardation factor) of vertical isolation barrier: In soil contaminated by heavy metal ions, the retardation factor can be 3-40. When calculating, the retardation factor is taken as 3 for safety reasons. The adsorption of organic pollutants depends on the organic content. The organic content of the vertical isolation barrier will be greatly reduced after construction, so the retardation factor of organic pollutants can be taken as 1.
[0015] Vertical isolation barrier breakdown standard: In conventional polluted areas, the pollutant excess (in groundwater) is generally within 10 times, and the breakdown standard can be considered as a relative concentration of 10%.
[0016] After completing the selection of functional requirements for the vertical isolation barrier, the types of pollution in conventional pollution areas are further distinguished based on the conventional pollution areas, which can be specifically divided into heavy metal pollutants or organic pollutants.
[0017] like Figure 2As shown in the figure, for the conventional contaminated area with heavy metal pollutants, the permeability coefficient of the vertical isolation barrier is selected as 10 -7 cm / s, the blocking factor is selected as 3, and the breakdown standard is selected as 10% of the pollutant concentration; the empirical calculation method for the design thickness of the vertical isolation barrier is to substitute the design service life T into the two calculation formulas below for calculation, and the larger of the two minimum design thickness values obtained by calculation is selected as the design thickness of the vertical isolation barrier: H = 0.4386 oeLh -0.1083; H = 0.0217 oeLh -0.6066; like Figure 3 As shown in the figure, for conventional contaminated areas with organic pollutants, the permeability coefficient of the vertical isolation barrier is selected as 10 -7 cm / s, the blocking factor is selected as 1, and the breakdown standard is selected as 10% of the pollutant concentration; the empirical calculation method for the design thickness of the vertical isolation barrier is to substitute the design service life T into the two calculation formulas below for calculation, and the larger of the two minimum design thickness values obtained by calculation is selected as the design thickness of the vertical isolation barrier: H = 0.7472 lnT- 0.2243; H = 0.0371 lnT- 0.9915; Where: H is the minimum design thickness of the vertical isolation barrier; T Design service life for vertical isolation barriers; Instructions attached Figure 2 and 3 The R² mentioned in the figure represents the fitting effect of the empirical calculation formula.
[0018] In order to verify whether the above two empirical calculation formulas for design thickness are accurate, an actual engineering case is provided for verification.
[0019] (1) Project background An industrial relocation site is mainly composed of clay soil, the maximum concentration of hexavalent chromium ions in groundwater is 0.5 mg / L, and the maximum pollution depth is 12 m. It is planned to use cement-soil mixing pile walls to isolate the polluted area. There are no obvious rivers in the surrounding area, which are likely to cause high head differences. The vertical isolation barrier design is carried out using the method of this embodiment.
[0020] (2) Risk assessment of conventional vertical isolation barrier areas 2.1 Are there any hydrogeological conditions outside the vertical isolation barrier that are likely to cause high head differences? Answer: No; 2.2 Is there NAPL within 1 m of the vertical isolation barrier? Answer: Heavy metal pollution (hexavalent chromium) does not exist in NAPL; 2.3 Does the measured concentration inside the vertical isolation barrier exceed 20 times? Answer: No. The groundwater quality standard (Class IV water) for hexavalent chromium is 0.1 mg / L, and the maximum excess of this standard at this site is 4 times.
[0021] 2.4 Are there any easily migrated soil layers such as silty soil inside the vertical isolation barrier? Answer: No, the interior of the site is mainly clay soil.
[0022] Based on the above judgment, this site belongs to a conventional pollution area and can be calculated using a simple formula.
[0023] (3) Determination of design thickness Since the target site is mainly composed of heavy metal pollutants, the design thickness empirical calculation formula "H = 0.4386lnT-0.1083 and "H = 0.0217T + 0.6066" is used for calculation, and the larger value is taken. Figure 4 shown.
[0024] Based on the above considerations, when the design service life T is 10 years, cement mixing piles with a thickness of 0.9m can be selected as a barrier measure.
[0025] (4) Reasonableness of design thickness and test verification The above engineering case has been applied in a barrier project of a polluted site in Jiading District, Shanghai, and has been continuously observed, and no breakdown has occurred.
[0026] Since it is difficult to carry out barrier tests for more than 10 years, a scaled test is generally used, as follows: 4.1 Experimental model Model box size: 800×190×700mm (length×width×height), top view of the model box is as follows Figure 5 As shown, it is divided into three areas. The middle compartment area is used to place the pollution source (potassium dichromate solution), and its length is 300mm, which is much larger than the total thickness of the vertical isolation barrier. The other two compartment areas are used to place clean soil samples (containing saturated solution), and the length is 220mm each. Hexavalent chromium ions will migrate into the wall under the action of concentration gradient.
[0027] like Figure 6The design of the test plan is shown in the figure. The head difference in this test is set to 0.5m. The polluted liquid uses potassium dichromate produced by Sinopharm, and the standard concentration is 0.5mg / L.
[0028] 4.1.1 Vertical Isolation Barrier Fabrication (1) Preparation method The single vertical isolation barrier in this test is a cement soil barrier wall. The preparation process refers to the relevant requirements of the "Cement Soil Mix Design Code" JGJ / T233-2011, "Technical Code for Cement Soil Mixing Walls of Equal Thickness" DGTJ 08-2248-2017 and other specifications. The cement content is 11%, the water-cement ratio is 1:1, and the thickness of the pure isolation vertical barrier is 9m.
[0029] (2) Preparation process ①Preparation: Make the model box in advance, and prepare the materials needed for the cement soil barrier wall, sealing materials, naturally dried soil samples, etc.
[0030] ② Prefabrication of cement soil barrier wall A. Collect soil samples The soil sample (clay) required for the production of cement soil comes from the third layer of clay at a construction site in Shanghai. It has the characteristics of low permeability and high water content and is a typical engineering soil in the area.
[0031] B. Air drying, crushing and sieving of soil samples According to the requirements of the specification "Cement-Soil Mix Design Code" JGJ / T233-2011, the soil samples were naturally air-dried and passed through a 0.5mm sieve.
[0032] C. Prefabrication of cement soil barrier wall According to the above mix ratio, cement slurry is added into a certain proportion of mud and mixed evenly. The cement soil sample is placed in a mold, compacted layer by layer, and made into cement soil specimens. The production process strictly complies with the relevant requirements of "Cement Soil Mix Ratio Design Code" JGJ / T233-2011.
[0033] D. Forming and curing The cement soil barrier wall produced in the experiment was maintained at room temperature (25 degrees Celsius) and relative humidity of 70% for 28 days after forming.
[0034] 4.1.2 Clean soil sample area (1) Main components The clean soil sample area consists of saturated sand and deionized water.
[0035] (2) Water The aqueous solution used was deionized water, and the mass ratio of water to sand was about 1:4. It was replenished regularly in subsequent tests to reduce the impact of evaporation.
[0036] (3) Sand sample The clean soil sample uses sandy soil, and the sand-rain method is used to prepare the sand model in layers. To ensure the uniformity of the overall dry soil sample, the sensor is placed at the preset position during the preparation process. After the dry sand model is prepared, degassed deionized water is slowly injected from bottom to top to saturate the model until the soil sample is completely saturated.
[0037] 4.2 Sampling monitoring results Similar monitoring results and rules were also obtained. Figure 7 The table shown gives the monitoring data of the original clean sand samples at time 0, 45, 90, 135, and 180. Only 2 samples had hexavalent chromium concentrations detected, and the values were 0.191 mg / L and 0.253 mg / L respectively.
[0038] The test results show that a 9mm wall is unsafe after 3 months of transport under a 0.5m head difference. It can be inferred that a 900mm wall will be unsafe after 150 months of transport under a 1m head difference (i.e. 12.5 years). In summary, the calculation using this simplified formula is slightly safer than the test results, taking into account both reliability and economy.
[0039] The advantage of this embodiment is that it provides a more convenient design method for the design of vertical isolation barriers for conventional contaminated sites. The isolation barriers involved in this method fully consider the risk level, pollution status and hydrogeological conditions of the site, and are more in line with engineering practice and simpler and more efficient than the original design method.
Claims
1. A rapid design method for vertical isolation barriers based on land risk screening and identification, characterized in that The design method comprises the following steps: S1: Determine whether the target site is a conventional pollution area or a high-risk pollution area according to the regional risk identification criteria; If the target site is a high-risk contamination area, it will be terminated; If the target site is a conventional contaminated area, proceed to the next step to design a vertical isolation barrier; S2: For conventional contaminated areas with heavy metal pollutants, the permeability coefficient of the vertical isolation barrier is selected as 10 -7 cm / s, the blocking factor is selected as 3, and the breakdown standard is selected as 10% of the pollutant concentration; the empirical calculation method for the design thickness of the vertical isolation barrier is to substitute the design service life T into the two calculation formulas below for calculation, and the larger of the two minimum design thickness values obtained by calculation is selected as the design thickness of the vertical isolation barrier: H = 0.4386 oeLh -0.1083； H = 0.0217 oeLh -0.6066； For conventional contaminated areas with organic pollutants, the permeability coefficient of the vertical isolation barrier is selected as 10 -7 cm / s, the blocking factor is selected as 1, and the breakdown standard is selected as 10% of the pollutant concentration; the empirical calculation method for the design thickness of the vertical isolation barrier is to substitute the design service life T into the two calculation formulas below for calculation, and the larger of the two minimum design thickness values obtained by calculation is selected as the design thickness of the vertical isolation barrier: H = 0.7472 lnT- 0.2243； H = 0.0371 lnT- 0.9915； Where: H is the minimum design thickness of the vertical isolation barrier; T The designed service life of the vertical isolation barrier.
2. A rapid design method for vertical isolation barriers based on land risk screening and discrimination according to claim 1, characterized in that The regional risk identification criteria are: S1.1: Determine whether there are hydrogeological conditions outside the vertical isolation barrier that are likely to cause high head difference; if so, determine that the target site is a high-risk pollution area; if not, proceed to the next step to continue determination; S1.2: Determine whether there is NAPL within 1 meter of the inner side of the vertical isolation barrier; if so, determine that the target site is a high-risk contaminated area; if not, proceed to the next step to continue determination; S1.3: Determine whether the pollutant concentration inside the vertical isolation barrier exceeds the standard by 20 times or more; if so, determine that the target site is a high-risk pollution area; if not, proceed to the next step to continue the determination; S1.4: Determine whether there is a silty soil layer inside the vertical isolation barrier; if so, determine that the target site is a high-risk contaminated area; if not, determine that the target site is a conventional contaminated area.