Optimization and adjustment method for water content of polluted soil

Abstract

The invention discloses an optimal adjustment method for the water content of contaminated soil. The method comprises the steps that the water content needing to be reduced and the adding amount of a drying agent are determined; comprehensively evaluating and establishing an evaporation coefficient model according to a plurality of influence factors such as the water holding capacity of the soil, the chemical adding type and the corresponding reaction coefficient, the environment temperature and the like, so as to correct and accurately calculate the actual water evaporation efficiency; according to the initial and target soil weight, the actually reduced water content, the added drying agent amount and the soil weight change caused by treatment, a mathematical model is established to comprehensively calculate the specific change condition of the soil treatment project amount in the water content adjusting process; in the implementation process, according to the treatment target requirement, the water content reduction and the polluted soil weight change amount are balanced, the engineering amount is calculated, and the polluted soil water content adjusting process is optimized. According to the method, soil moisture evaporation and soil engineering quantity change before and after soil moisture content adjustment can be accurately predicted and calculated, so that the polluted soil moisture content adjustment process is optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental engineering, and in particular to a method for optimizing and regulating the moisture content of contaminated soil. Background Art

[0002] In soil remediation, civil engineering, and agricultural production, soil moisture content is a key factor influencing soil properties, project performance, and project volume. Excessively high soil moisture content can lead to reduced foundation bearing capacity, impeded crop growth, and environmental pollution. In recent years, the use of external industrial kilns for the co-disposal of contaminated soil has been a popular method, but this typically requires a certain initial soil moisture content, necessitating pretreatment to adjust the moisture content. Therefore, rationally controlling soil moisture content is crucial for improving project quality, promoting agricultural production, and protecting the environment.

[0003] Adjusting soil moisture content typically involves adding chemicals and mixing them to improve or pre-treat the soil. This process involves changes in the amount of soil treatment work required. Excessive chemical addition can increase costs and work volume, and sometimes also pose potential disposal risks. For example, using quicklime as a desiccant can increase soil pH excessively in alkaline soils, creating unnecessary disposal requirements.

[0004] In existing soil engineering projects, the adjustment methods commonly used are relatively rough and are post-process evaluations. They are unable to predict and optimize the moisture content of contaminated soil in the early stages of the project and during construction, resulting in low efficiency and difficulty in optimizing costs. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a method for optimizing the moisture content of contaminated soil. During the process of adding a desiccant to adjust the soil moisture content, through scientific calculation and experimental verification, it is possible to accurately predict and calculate soil moisture evaporation and changes in soil engineering volume before and after soil moisture content adjustment, thereby optimizing the contaminated soil moisture content adjustment process and achieving an efficient and accurate soil moisture content adjustment process.

[0006] The present invention discloses a method for optimizing and regulating the moisture content of contaminated soil, comprising: Step 1: Determine the amount of soil moisture that should be reduced based on the target expected soil moisture content; Step 2: Determine the amount of desiccant to be added for adjusting the soil moisture content based on the amount of soil moisture to be reduced and a preset desiccant addition ratio or formula; Step 3: Comprehensively evaluate and establish an evaporation coefficient model based on multiple influencing factors to correct and accurately calculate the actual water evaporation efficiency; the multiple influencing factors include the water holding capacity of the soil, the type of desiccant and its corresponding reaction coefficient, and the ambient temperature; Step 4: Based on the parameters determined in steps 1 to 3, including the initial and target soil weights, the actual amount of moisture reduced, the amount of desiccant added, and the change in soil weight caused by the treatment, an engineering calculation model is established to comprehensively calculate the specific changes in the soil treatment project volume; Step 5: Measure the soil moisture content again after the treatment. If the target is not reached, adjust the subsequent dosage or mixing strategy based on the difference between the measured and predicted values ​​and recalculate the project volume. If the target is reached, adjust the subsequent dosage or mixing strategy based on the measured and predicted values ​​to balance the reduction in moisture content and the change in weight of the contaminated soil and recalculate the project volume.

[0007] As a further improvement of the present invention, the step 1 specifically includes: Measure the initial soil moisture content and set the target expected soil moisture content; calculate the difference between the two to determine the amount of soil moisture reduction.

[0008] As a further improvement of the present invention, in step 1, the calculation formula for reducing the amount of soil moisture is: ; in, Q The amount of water that should be reduced in the soil (kg) W is the weight of soil (kg), a 0 is the initial soil moisture content (%), a 1 is the target expected moisture content of the soil (%).

[0009] As a further improvement of the present invention, in step 2, the calculation formula for the dosage of the desiccant is: ; in, b The addition ratio of desiccant, W is the weight of soil, Q To reduce the amount of water in the soil, Oh is the reaction coefficient of the desiccant.

[0010] As a further improvement of the present invention, the step 3 specifically includes: Step 31: Construct a heat transfer model to describe the distribution and transfer of heat within the soil. Based on the heat transfer principle, a one-dimensional unsteady-state heat conduction differential equation is established to describe the temporal and spatial distribution of the temperature inside the soil pile by the heat generated by the chemical addition, the soil thermal diffusivity, the soil depth, and the time gradient. The calculation formula is as follows: ; ; in, T is the internal temperature of the soil pile (℃), t is time (s), x is the soil depth (m), α is the soil thermal diffusivity (m² / s), k is the thermal conductivity of soil, c is the specific heat capacity ,r is the density, S(x,t) is the heat generated by the heat source per unit volume per unit time (W / m³); Step 32: Construct a water evaporation model: Use the Penman equation to simulate the water evaporation amount. Its simplified form is: ; ; ; in, E is the evaporation rate (mm / h), R n is the heat input (MJ / m² / h), G is the soil heat flux (MJ / m² / h), Δ is the slope of the saturated water vapor pressure curve (kPa / ℃), c is the psychrometric constant (kPa / ℃), e s is the saturated water vapor pressure (kPa), e a is the actual water vapor pressure (kPa), r a is the air density (kg / m 3 ), C p is the specific heat capacity of air (kJ / (kg·K)), T is the air temperature (℃), R s is the evaporation resistance, i ssat is the saturated moisture content of the soil surface, i s is the actual moisture content of the soil surface; Step 33, coupled calculation: Couple the heat transfer model and the water evaporation model, considering the effect of the heat generated by the desiccant reaction on the soil temperature, and the effect of the soil temperature on the water evaporation rate. The specific steps are as follows: a Initialization: Set the initial temperature and moisture content distribution of the soil; b. Solve the heat transfer equation: Use numerical methods (finite difference method) to solve the heat transfer equation and obtain the spatiotemporal distribution of soil temperature; c. Calculate the heat generated by the desiccant reaction: Based on the amount of desiccant added and the moisture content in the soil, calculate the heat generated by the desiccant reaction and add it as an internal heat source term to the heat transfer equation; d. Update soil temperature: Update soil temperature distribution according to the solved heat transfer equation; eCalculate hourly water evaporation: Use the Penman equation to build a water evaporation model, and combine the updated soil temperature, moisture content, air humidity, soil moisture content and other factors to calculate soil water evaporation; f Iterative solution: Repeat steps b to e until the deadline.

[0011] As a further improvement of the present invention, in step 4, the calculation formula of the engineering quantity accounting model established is as follows: set up i The amount of water evaporation at this moment is E i (mm / day), soil area is A (m²), the water evaporation mass and the final soil mass are calculated using the following formula: ; ; in, m i express i Momentary water evaporation; r The density of water is expressed in 1000 kg / m 3 count, W* Indicates the final mass of soil.

[0012] Compared with the prior art, the present invention has the following beneficial effects: This invention can accurately predict and calculate the changes in contaminated soil disposal workload caused by adjusting the soil moisture content, thereby optimizing the contaminated soil moisture adjustment process. It has broad application prospects and practical value. For contaminated soil disposal pretreatment, calculating and balancing the changes in desiccant dosage and the resulting workload caused by adjusting the soil moisture content is an important basis for project planning, cost budgeting, and construction effect evaluation. This invention is applicable to various civil engineering projects, including but not limited to various civil engineering projects, agricultural land improvement, contaminated soil remediation and pretreatment, and building foundation treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The present invention is a flowchart of the method for optimizing and regulating the moisture content of contaminated soil. DETAILED DESCRIPTION

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0015] The present invention is described in further detail below with reference to the accompanying drawings: The present invention discloses a method for optimizing and regulating the moisture content of contaminated soil, comprising: Step 1: Determine how much water the soil needs to be reduced: Measure the initial soil moisture content and set the target expected soil moisture content; calculate the difference between the two to determine the amount of soil moisture reduction required; the formula for calculating the amount of soil moisture reduction required is: ; in, Q The amount of water that should be reduced in the soil (kg) W is the weight of soil (kg), a 0 is the initial soil moisture content (%), a 1 is the target expected moisture content of the soil (%).

[0016] Step 2: Determine the dosage of desiccant: Based on the amount of soil moisture to be reduced and a preset desiccant addition ratio or formula, the amount of desiccant added for adjusting the soil moisture content is determined; wherein the calculation formula for the desiccant addition is: ; in,b The addition ratio of desiccant, W is the weight of soil, Q To reduce the amount of water in the soil, Oh is the reaction coefficient of the desiccant.

[0017] Step 3: Determine the evaporation coefficient: An evaporation coefficient model is established based on a comprehensive assessment of multiple influencing factors, including soil water holding capacity, desiccant type and its corresponding reaction coefficient, and ambient temperature, to correct and accurately calculate actual water evaporation efficiency. Step 3 outlines the technical modeling approach for simulating expected soil water evaporation based on the initial and post-treatment states of the soil medium, through changes in environmental conditions and reaction processes. This section describes the actual soil volume changes, using a combination of model construction and experimental measurement to calculate the specific changes in soil volume before and after treatment.

[0018] Specifically include: Step 31: Construct a heat transfer model to describe the distribution and transfer of heat within the soil. Based on the heat transfer principle, a one-dimensional unsteady-state heat conduction differential equation is established to describe the temporal and spatial distribution of the temperature inside the soil pile by the heat generated by the chemical addition, the soil thermal diffusivity, the soil depth, and the time gradient. The calculation formula is as follows: ; ; in, T is the internal temperature of the soil pile (℃), t is time (s), x is the soil depth (m), α is the soil thermal diffusivity (m² / s), k is the thermal conductivity of soil, c is the specific heat capacity ,r is the density, S(x,t) is the heat generated by the heat source per unit volume per unit time (W / m³); Step 32: Construct a water evaporation model: Use the Penman equation to simulate the water evaporation amount. Its simplified form is: ; ; ; in, E is the evaporation rate (mm / h), R n is the heat input (MJ / m² / h), Gis the soil heat flux (MJ / m² / h), Δ is the slope of the saturated water vapor pressure curve (kPa / ℃), c is the psychrometric constant (kPa / ℃), e s is the saturated water vapor pressure (kPa), e a is the actual water vapor pressure (kPa), r a is the air density (kg / m 3 ), C p is the specific heat capacity of air (kJ / (kg·K)), T is the air temperature (℃), R s is the evaporation resistance, i ssat is the saturated moisture content of the soil surface, i s is the actual moisture content of the soil surface; Step 33, coupled calculation: Couple the heat transfer model and the water evaporation model, considering the effect of the heat generated by the desiccant reaction on the soil temperature, and the effect of the soil temperature on the water evaporation rate. The specific steps are as follows: a Initialization: Set the initial temperature and moisture content distribution of the soil; b. Solve the heat transfer equation: Use numerical methods (finite difference method) to solve the heat transfer equation and obtain the spatiotemporal distribution of soil temperature; c. Calculate the heat generated by the desiccant reaction: Based on the amount of desiccant added and the moisture content in the soil, calculate the heat generated by the desiccant reaction and add it as an internal heat source term to the heat transfer equation; d. Update soil temperature: Update soil temperature distribution according to the solved heat transfer equation; eCalculate hourly water evaporation: Use the Penman equation to build a water evaporation model, and combine the updated soil temperature, moisture content, air humidity, soil moisture content and other factors to calculate soil water evaporation; f Iterative solution: Repeat steps b to e until the deadline.

[0019] Step 4: Calculate the changes in the amount of contaminated soil disposal work: Based on the parameters determined in steps 1-3, including the initial and target soil weights, the actual amount of moisture lost, the amount of desiccant added, and the change in soil weight due to treatment, an engineering calculation model was established to comprehensively calculate the specific changes in soil disposal engineering quantities. The calculation formula for the established engineering quantity calculation model is as follows: set up i The amount of water evaporation at this moment is Ei (mm / day), soil area is A (m²), the water evaporation mass and the final soil mass are calculated using the following formula: ; ; in, m i express i Momentary water evaporation; r The density of water is expressed in 1000 kg / m 3 count, W* Indicates the final mass of soil.

[0020] Step 5: Optimize the contaminated soil moisture adjustment process: Measure the soil moisture content again after the treatment is implemented; if the predetermined target is not reached, adjust the subsequent dosage or mixing strategy based on the difference between the measured and predicted values ​​and recalculate the project volume; if the predetermined target is reached, adjust the subsequent dosage or mixing strategy based on the measured and predicted values, balance the reduction in moisture content and the change in weight of contaminated soil, and calculate the project volume. Example 1:

[0021] The contaminated soil treated in this example is the surface contaminated soil of an organic contaminated site in Zibo City. The geological survey results show that the contaminated soil is mainly plain fill with an average moisture content of 30%. The target moisture content is reduced to below 20%. The engineering design uses a room temperature desorption remediation method for this site, with quicklime as the remediation agent (the heat output of quicklime is 1160kJ / kg, and the heat generation reaction efficiency is calculated as 80% based on the previous test). The dosing treatment machine uses ALLU bucket mixing, with a processing capacity of 60m 3 / h.

[0022] like Figure 1 As shown, the optimization method of this embodiment has the following specific implementation steps: Step 1: Determine the amount of moisture that should be reduced, as follows: The initial moisture content of the soil is measured and the total amount of water that needs to be reduced is determined by calculating the difference between the two.

[0023] Table 1 Initial information and target values ​​of test soil

[0024] Step 2: Determine the dosage. Based on the amount of moisture to be reduced and the preset desiccant addition ratio or formula, determine the amount of desiccant to be added for adjusting the soil moisture content. The details are as follows: (1) Based on the experience of relevant domestic engineering projects and the conclusions of small-scale tests, lime is selected as the desiccant in this embodiment. For soils with high water content, the agent is added at a ratio of 1% of the lime addition ratio preset in the remediation plan.

[0025] (2) In this embodiment, an ALLU bucket is used to stir and mix the soil to be repaired and the quicklime agent.

[0026] Step 3: Construct an evaporation model: Based on multiple influencing factors such as soil water holding capacity, dosage and its corresponding reaction coefficient, ambient temperature, etc., comprehensively evaluate and establish an evaporation coefficient model to correct and accurately calculate the actual water evaporation efficiency. Specifically: 1. Construct a heat transfer model: describe the distribution and transfer of heat inside the soil.

[0027] This embodiment is a soil remediation project, the processing time is short, and the volume of the remediation pile is small, so the distribution and transfer of heat inside the soil pile are measured using a soil temperature measuring instrument.

[0028] Temperature measurement points are arranged every five meters horizontally and every two meters vertically, and the average value of the points is calculated. The measurement depth is 10 cm increments, with a maximum depth of 0.5 m (usually evaporation affects the soil layer), and the average temperature of the pile is measured. The finite element method is used to arrange the points, with a point every five meters horizontally and every two meters in the slope direction. Each unit represents an area of ​​approximately 10 m 2 .

[0029] Table 2 Spatiotemporal changes in soil temperature

[0030] 2. Water evaporation model: Penman equation is used to simulate the water evaporation. The initial parameters of the pile and environment are: Table 3 Initial model parameters of the pile and environment

[0031] 3. Coupled calculation: Couple the temporal and spatial data of pile temperature transfer with the water evaporation model, taking into account the effect of heat generated by quicklime reaction on soil temperature, and the effect of soil temperature on water evaporation rate. The specific steps are as follows: (1) Record the soil parameters after adding quicklime in each period of time with hourly gradient. The parameter changes are as follows: Table 4 Record of changes in reactor and environmental parameters after reaction

[0032] (2) Calculate the required parameters and determine the soil heat flux based on the temporal and spatial changes in temperature in step 3.

[0033] Table 5 Soil heat flux record after reaction

[0034] (3) Calculation of hourly water evaporation: Use the Penman equation to construct a water evaporation model, and combine the updated soil temperature, heat flux, moisture content, air humidity, soil moisture content and other factors to calculate the soil water evaporation.

[0035] Table 6 Calculation of soil moisture evaporation

[0036] Table 7 Calculation of soil water evaporation mass

[0037] Step 4: Calculate the final changes in project volume, as follows.

[0038] The final soil engineering quantity is calculated by formulas 7 and 8.

[0039] Table 8 Soil engineering quantity calculation

[0040] Step 5: Balance the contaminated soil disposal project volume, as follows: Under the condition of 1% lime addition, the soil moisture content decreased by about 8.2%. The lime addition ratio was adjusted to 0.5%, and the above model calculation and accounting process were repeated to calculate the water evaporation amount and the amount of contaminated soil engineering.

[0041] Table 9 Work Quantity Accounting Record after Adjusting the Amount of Lime Added

[0042] Table 10 Soil engineering quantity calculation after adjustment

[0043] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for optimizing and regulating the moisture content of contaminated soil, characterized in that: include: Step 1: Determine the amount of soil moisture that should be reduced based on the target expected soil moisture content; Step 2: Determine the amount of desiccant to be added for adjusting the soil moisture content based on the amount of soil moisture to be reduced and a preset desiccant addition ratio or formula; Step 3: Comprehensively evaluate and establish an evaporation coefficient model based on multiple influencing factors to correct and accurately calculate the actual water evaporation efficiency; the multiple influencing factors include the water holding capacity of the soil, the type of desiccant and its corresponding reaction coefficient, and the ambient temperature; Step 4: Based on the parameters determined in steps 1 to 3, including the initial and target soil weights, the actual amount of moisture reduced, the amount of desiccant added, and the change in soil weight caused by the treatment, an engineering calculation model is established to comprehensively calculate the specific changes in the soil treatment project volume; Step 5: Measure the soil moisture content again after the treatment. If the target is not reached, adjust the subsequent dosage or mixing strategy based on the difference between the measured and predicted values ​​and recalculate the project volume. If the target is reached, adjust the subsequent dosage or mixing strategy based on the measured and predicted values ​​to balance the reduction in moisture content and the change in weight of the contaminated soil and recalculate the project volume.

2. The method for optimizing and adjusting the moisture content of contaminated soil according to claim 1, wherein: The step 1 specifically includes: Measure the initial soil moisture content and set the target expected soil moisture content; calculate the difference between the two to determine the amount of soil moisture reduction.

3. The method for optimizing and adjusting the moisture content of contaminated soil according to claim 1 or 2, characterized in that: In step 1, the calculation formula for the amount of water that should be reduced in the soil is: ； in, Q To reduce the amount of water in the soil, W is the weight of soil, a 0 is the initial moisture content of the soil, a 1 is the target expected moisture content of the soil.

4. The method for optimizing and adjusting the moisture content of contaminated soil according to claim 1, wherein: In step 2, the calculation formula for the dosage of the desiccant is: ； in, b The addition ratio of desiccant, W is the weight of soil, Q To reduce the amount of water in the soil, Ω is the reaction coefficient of the desiccant.

5. The method for optimizing and adjusting the moisture content of contaminated soil according to claim 1, wherein: The step 3 specifically includes: Step 31: Build a heat transfer model: Based on the heat transfer principle, a one-dimensional unsteady-state heat conduction differential equation is established to describe the temporal and spatial distribution of the temperature inside the soil pile by the heat generated by the chemical addition, the soil thermal diffusivity, the soil depth, and the time gradient. The calculation formula is as follows: ； ； in, T is the internal temperature of the soil pile, t For time, x is the soil depth, α is the soil thermal diffusivity, k is the thermal conductivity of soil, c is the specific heat capacity , ρ is the density, S(x,t) It is the heat generated by the heat source per unit volume per unit time; Step 32: Construct a water evaporation model: Use the Penman equation to simulate the water evaporation amount. Its simplified form is: ； ； ； in, E is the evaporation amount, R n is the heat input, G is the soil heat flux, Δ is the slope of the saturated water vapor pressure curve, γ is the psychrometer constant, e s is the saturated water vapor pressure, e a is the actual water vapor pressure, ρ a is the air density, C p is the specific heat capacity of air, T is the temperature, R s is the evaporation resistance, θ ssat is the saturated moisture content of the soil surface, θ s is the actual moisture content of the soil surface; Step 33, coupled calculation: Couple the heat transfer model and the water evaporation model, considering the effect of the heat generated by the desiccant reaction on the soil temperature, and the effect of the soil temperature on the water evaporation rate. The specific steps are as follows: a Initialization: Set the initial temperature and moisture content distribution of the soil; b. Solve the heat transfer equation: Use numerical methods to solve the heat transfer equation and obtain the spatiotemporal distribution of soil temperature; c. Calculate the heat generated by the desiccant reaction: Based on the amount of desiccant added and the moisture content in the soil, calculate the heat generated by the desiccant reaction and add it as an internal heat source term to the heat transfer equation; d. Update soil temperature: Update soil temperature distribution according to the solved heat transfer equation; eCalculate hourly water evaporation: Use the Penman equation to build a water evaporation model, and combine the updated soil temperature, moisture content, air humidity, and soil moisture content factors to calculate soil water evaporation; f Iterative solution: Repeat steps b to e until the deadline.

6. The method for optimizing and adjusting the moisture content of contaminated soil according to claim 1, wherein: In step 4, the calculation formula of the engineering quantity accounting model established is as follows: set up i The amount of water evaporation at this moment is E i , the soil area is A , the water evaporation mass and the final soil mass are calculated using the following formula: ； ； in, m i express i Momentary water evaporation; ρ represents the density of water, W* Indicates the final mass of soil.

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