Preparation method of organic matter-containing sediment remolded sample

Abstract

The invention provides a preparation method of a remodeling sample of sediment containing organic matters, which comprises the following steps: simulating organic matters insoluble in water in the sediment by using humic acid, and simulating organic matters soluble in water in the sediment by using fulvic acid; simulating an organic matter-containing sediment remolding sample according to the content and non-uniform distribution condition of organic matters in the in-situ sediment layer; according to the set volume of the target remolded sample, and in combination with the designed mass fraction of the organic matters, calculating the amount of the required humic acid and fulvic acid; when a saturated sample is manufactured, sediment and humic acid are mixed and then filled into a soil engineering sample manufacturing mold in five layers, the mixture is compacted to reach the target height, and fulvic acid solution with the designed required content is used for carrying out saturated maintenance on the sediment; when the unsaturated sample is manufactured, the fulvic acid solution, the humic acid and the sediment are mixed, the mixture is divided into five layers to be filled into a soil engineering sample preparation mold and compacted to reach the target height, preparation of the remodeling sample containing the organic matter sediment is successfully achieved, and the blank in an existing sample preparation method is filled up.

Description

Technical Field

[0001] The invention relates to the field of marine geotechnical engineering, and in particular to a method for preparing a reshaped sample of organic-containing sediment. Background Art

[0002] According to the different gas sources, the formation of seafloor hydrates can be divided into biological gas source mode, thermal gas source mode and mixed gas source mode. The biological gas source mode mainly comes from the microbial degradation of shallow organic matter. The thermal gas source mode mainly comes from the pyrolysis of deep organic matter at high temperature, producing thermal catalytic methane or other hydrocarbon gases. The formation of marine hydrates is affected by both biogas and thermal gas. Due to the formation process of marine sediments and hydrates, seafloor hydrate sediments contain more organic matter. According to the test results of Zhang et al. on marine sediments, the organic matter content can reach 16.2%. The organic matter content of diatomaceous earth obtained from the 112th voyage of the Ocean Drilling Program (off the coast of Peru) is between 2% and 11%. The presence of organic matter can significantly affect the physical and mechanical properties of soil. However, the effect of organic matter on the mechanical properties of hydrate sediments has rarely become the focus of research, mainly focusing on sediments without organic matter, and the mechanical properties of sediments containing organic matter are not clearly understood, and there is a lack of relevant preparation technology for organic soil samples. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a reshaped sample of an organic-containing sediment, so as to fill the gap in the existing sample preparation methods.

[0004] The types and forms of organic matter are very complex. Organic matter includes humus and undecomposed and incompletely decomposed organic matter. Humus refers to the black colloidal substance formed by the decomposition and transformation of fresh organic matter by microorganisms, which generally accounts for more than 85-90% of the total soil organic matter. Humus can be divided into: humic acid, also known as humic acid (HA), fulvic acid (FA), and humus according to its solubility in acid and alkali, among which humic acid and fulvic acid are the main ones. Humic acid is a type of humic substance that can be dissolved in alkaline solution and precipitated by acid solution. Humic acid has a lower acidity than fulvic acid, is slightly acidic, and has a higher absorption capacity. Fulvic acid is a type of humic substance that is soluble in both alkaline and acid solutions, and is strongly acidic. Humus can exist in the soil in the form of free humic acid and humic acid salts, or it can be in the form of gel and tightly combined with mineral clay particles to become an important colloidal substance. In order to simplify sample preparation, the present invention uses humic acid to simulate the organic matter insoluble in water in the sediment, and uses fulvic acid to simulate the organic matter soluble in water in the sediment.

[0005] The type and gradation of the reconstructed sediments should be determined according to the type of soil samples in the in-situ sediment layer; secondly, the content and distribution of organic matter in the sediments should be determined. These in-situ information are the basis for subsequent sample preparation.

[0006] The technical solution of the present invention is achieved in this way:

[0007] A method for preparing a reshaped sample of organic matter-containing sediment comprises the following steps:

[0008] Step 1: Analyze the collected sediment samples to determine the composition and gradation of the reshaped sediments, and mix the raw materials evenly according to the proportions to obtain a mixture;

[0009] Step 2: Weigh humic acid according to the designed mass ratio of water-insoluble organic matter content to sediment particles;

[0010] Step 3: Determine the specific gravity of the mixture of remodeled sediment and humic acid, and calculate the mass of the mixture required for a fixed volume of remodeled sample containing organic matter according to the designed porosity of the soil sample;

[0011] Step 4:

[0012] When making a sample with organic matter evenly distributed in the sediment layer, a fixed mass of the mixture is divided into five equal layers and filled into the geotechnical sample preparation mold, compacted to a fixed height according to the design requirements, and the surface is scraped before preparing the next layer;

[0013] When preparing samples with non-uniform distribution of organic matter in the sediment layer, for reshaped samples with layered distribution containing organic matter, a fixed mass of the mixture is divided into five equal layers and filled into a geotechnical sample preparation mold. The number of organic matter layers is set according to the design requirements. Sediment granular soil is placed between the organic matter layers. It is compacted to a fixed height according to the design requirements, and the surface is scraped before preparing the next layer of samples; for reshaped samples with block distribution containing organic matter, a fixed mass of organic matter particles is compacted and cut into blocks. The block organic matter and sediment soil samples are mixed and filled into a geotechnical sample preparation mold in five layers and compacted to the target height;

[0014] Step 5: prepare fulvic acid solution;

[0015] When making unsaturated organic matter samples, weigh the fulvic acid solution and mix it evenly with the mixture, place it in a fresh-keeping bag and seal it for curing, then divide it into five layers and fill it into the sample preparation mold provided, tamp it to a fixed height according to the design requirements, scrape the surface before preparing the next layer of samples;

[0016] When preparing saturated organic matter samples, when the reshaped sediment has a permeability coefficient of less than 10 -4 For low permeability silt and clay with a permeability of 10 cm / s, the vacuum saturation method is used, and the clean water injected into the vacuum cylinder is replaced with fulvic acid solution; when the reshaped sediment has a permeability coefficient greater than 10 -4When the sample is finely divided into silt and fine soil, the capillary saturation method is used. The fulvic acid solution is placed in a vacuum cylinder, and the sample mold is placed in the fulvic acid solution. The upper part of the sample mold is in contact with the air, and the vacuum cylinder is evacuated to saturate the sample. After the saturated sample preparation is completed, the sample is cured to allow the organic matter and soil particles to fully react.

[0017] Step 6: Use the cauterization method to determine the actual organic matter content of the sample.

[0018] Furthermore, in step 2, the mass ratio of water-insoluble organic matter to sediment particles is 0.01 to 30:100.

[0019] Furthermore, in step 5, the mass fraction of the fulvic acid solution is 0% to 5%.

[0020] Furthermore, in step 5, the curing time is 6-8 days, the curing temperature is 15°C-25°C, and the curing environment is sealed.

[0021] Furthermore, in step 5, the saturated sample is continued to be placed in the vacuum cylinder with the liquid level covering the sample, and cured for 6-8 days at a curing temperature of 15°C-25°C, and the curing environment is sealed.

[0022] For samples with organic matter evenly distributed in the sediment layer, the specific sample preparation steps are as follows:

[0023] Step 1: Determine the composition and gradation of the reshaped sediments and mix them evenly according to the proportions.

[0024] Step 2: According to the designed mass ratio of water-insoluble organic matter content to sediment particles (0.01-30:100), a certain mass of humic acid is weighed and evenly mixed with a fixed mass of reshaped sediment particles.

[0025] Step 3: Determine the maximum dry density, minimum dry density and specific gravity of the mixture, and calculate the mass of the mixture required to reshape the sample with a fixed volume containing organic matter based on the designed porosity of the soil sample.

[0026] Step 4: Divide the mixture of a fixed mass into five equal layers and fill them into the geotechnical sample preparation mold. Compact them to a fixed height according to the design requirements, scrape the surface and then prepare the next layer.

[0027] Step 5: Prepare a fulvic acid solution with a fixed mass fraction (0% to 5%). When making an unsaturated sample containing organic matter, weigh the required mass of fulvic acid solution and mix it evenly with the mixture, place it in a fresh-keeping bag and seal it for 6-8 days, then divide it into five layers and fill it into the sample preparation mold provided, tamp it to a fixed height according to the design requirements, scrape the surface and then prepare the next layer; when making a saturated sample containing organic matter, when the reshaped sediment has a permeability coefficient of less than 10 -4For low permeability silt and clay with a permeability of 10 cm / s, the vacuum saturation method is used, and the clean water injected into the vacuum cylinder is replaced with fulvic acid solution; when the reshaped sediment has a permeability coefficient greater than 10 -4 cm / s of silt, the capillary saturation method is used. The fulvic acid solution is placed in a vacuum cylinder, and the sample mold is placed in the fulvic acid solution. The upper part of the sample mold is in contact with the air, and the vacuum cylinder is evacuated to saturate the sample. After the sample preparation is completed, the sample needs to be cured for 6-8 days to allow the organic matter and soil particles to fully react.

[0028] Step 6: Use the calcination method to determine the actual organic matter content of the sample.

[0029] Due to the uneven distribution of plant and animal remains in the actual soil sample sediment process, organic matter exists in the form of layers, sheets, blocks, etc. For samples with uneven distribution of organic matter in the sediment layer, the sample preparation steps are as follows:

[0030] Step 1: Determine the composition and gradation of the reshaped sediments and mix them evenly according to the proportions.

[0031] Step 2: According to the designed mass ratio of water-insoluble organic matter content to sediment particles (0.01-30:100), weigh a certain mass of humic acid.

[0032] Step 3: Determine the specific gravity of the reshaped sediment mixture and calculate the mass of the mixture required for a fixed volume of organic matter-containing reshaped sample based on the designed soil sample porosity.

[0033] Step 4: For reshaped samples containing layered organic matter, divide a fixed mass of the mixture into five equal layers and fill them into the geotechnical sample preparation mold. Set the number of organic matter layers according to the design requirements. Between the organic matter layers are sediment granular soil. According to the design requirements, compact it to a fixed height and scrape the surface before preparing the next layer. For reshaped samples containing blocky organic matter, compact a fixed mass of organic matter particles and cut them into blocks. Mix the blocky organic matter and sediment soil samples, fill them into the geotechnical sample preparation mold in five layers and compact them to the target height.

[0034] Step 5: Prepare a fulvic acid solution with a fixed mass fraction (0% to 5%). When making an unsaturated sample containing organic matter, weigh the required mass of fulvic acid solution and mix it evenly with the mixture, place it in a fresh-keeping bag for curing for 6-8 days, seal the curing environment, and then divide it into five layers and fill it into the sample preparation mold provided. According to the design requirements, tamp it to a fixed height, shave the surface and then prepare the next layer; when making a saturated sample containing organic matter, when the reshaped sediment has a permeability coefficient of less than 10 -4 For low permeability silt and clay with a permeability of 10 cm / s, the vacuum saturation method is used, and the clean water injected into the vacuum cylinder is replaced with fulvic acid solution; when the reshaped sediment has a permeability coefficient greater than 10 -4When the particle size of the soil is silty (cm / s), the capillary saturation method is used. The fulvic acid solution is placed in a vacuum cylinder, and the sample mold is placed in the fulvic acid solution. The upper part of the sample mold is in contact with the air, and the vacuum cylinder is evacuated to saturate the sample. The sample is cured for 6-8 days to allow the organic matter and soil particles to fully react.

[0035] Step 6: Use the calcination method to determine the actual organic matter content of the sample.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The organic matter content of the sediment sample containing organic matter prepared by the method of the present invention is basically consistent with that of the original sample, with no significant difference, and can meet the preparation requirements of the sediment sample containing organic matter. In addition, the sample is stable and can withstand long-term storage.

[0038] The present invention uses humic acid to simulate the organic matter insoluble in water in the sediment, and uses fulvic acid to simulate the organic matter soluble in water in the sediment; simulates the remodeling sample of the sediment containing organic matter according to the content and non-uniform distribution of the organic matter in the in-situ sediment layer; calculates the required amount of humic acid and fulvic acid according to the set target remodeling sample volume and the designed mass fraction of the organic matter; when making a saturated sample, the sediment and humic acid are mixed and filled into a geotechnical sample preparation mold in five layers and compacted to reach the target height, and the sediment is cured with a fulvic acid solution with the required content; when making an unsaturated sample, the fulvic acid solution, humic acid and sediment are mixed, filled into a geotechnical sample preparation mold in five layers and compacted to reach the target height, and then cured for seven days; considering that the soluble organic matter will combine with soil particles, the actual organic matter content of the saturated sample needs to be measured and determined again after the sample preparation is completed. After the reshaped sample of organic-containing sediment is produced, geotechnical tests can be carried out, and it can also be used to subsequently produce hydrate-containing sediment samples. The samples can be used to carry out relevant tests, providing technical support for the commercial exploitation of natural gas hydrates and seabed disaster research. DETAILED DESCRIPTION

[0039] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0040] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0041] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0042] For saturated samples with non-uniform distribution of organic matter in the sediment layer, the sample preparation steps are as follows:

[0043] Step 1: Analyze the collected sediment samples to determine the composition and gradation of the reshaped sediments, and mix them evenly according to the proportions.

[0044] Step 2: Weigh a certain mass of humic acid according to the designed mass fraction of water-insoluble organic matter (0.01% to 30%).

[0045] Step 3: Determine the specific gravity of the mixture and calculate the mass of the mixture required to reshape the sample with a fixed volume containing organic matter based on the designed porosity of the soil sample.

[0046] Step 4: For reshaped samples containing layered organic matter, divide the fixed mass of the mixture into five equal layers, and fill them into the geotechnical sample preparation mold in the order of one layer of mixture and one layer of organic matter. According to the design requirements, compact them to a fixed height, scrape the surface, and then proceed to sample the next layer.

[0047] Step 5: Prepare a fixed mass fraction of fulvic acid solution (0% to 5%). Reshape the sediment to a permeability greater than 10 -4 When the soil is finer than cm / s, the capillary saturation method is used. The fulvic acid solution is placed in a vacuum cylinder, and the sample mold is placed in the fulvic acid solution. The upper part of the sample mold is in contact with the air, and the vacuum cylinder is evacuated to saturate the sample. The sample is cured for 6-8 days (temperature 20℃±5℃, and the curing environment is sealed) to allow the organic matter and soil particles to fully react.

[0048] Step 6: Use the calcination method to determine the actual organic matter content of the sample.

[0049] Example 1

[0050] For unsaturated samples with organic matter evenly distributed in the sediment layer, the sample preparation steps are as follows:

[0051] Step 1: Analyze the collected sediment samples to determine the composition and gradation of the reshaped sediments, and mix them evenly according to the proportion. The mineral components of the marine hydrate cover sediment particles are mainly quartz (32.7%-57.0%), plagioclase (10.7%-17.0%) and calcite (4.4%-26.2%), as well as clay minerals (16.8%-27.1%). In this implementation case, quartz sand, plagioclase, calcite, illite, kaolin and chlorite with a weight of 0.50:0.10:0.10:0.15:0.075:0.075 are fully mixed to simulate clay-silty sediments, with a clay mass percentage of 30%. The specific gravity of the sediment (G s ) is 2.67, while the specific gravity of the natural sample (G s ) is 2.72. 50 The value is 7.48 μm, while the d 50 The particle size distribution ranges of natural samples and the present reconstructed sediments are generally similar.

[0052] Step 2: According to the designed mass ratio of water-insoluble organic matter content to sediment particles (1:10), a certain mass of humic acid is weighed and evenly mixed with a fixed mass of reshaped sediment particles.

[0053] Step 3: The specific gravity of the mixture is determined to be 2.63. Based on the designed soil sample porosity of 0.45, calculate the mass of the mixture required to reshape the sample with a fixed volume of organic matter.

[0054] Step 4: Divide the mixture of a fixed mass into five equal layers and fill them into the geotechnical sample preparation mold. Compact them to a fixed height according to the design requirements, scrape the surface and then prepare the next layer.

[0055] Step 5: Prepare a fixed mass fraction of fulvic acid solution (0%), i.e. purified water. When making unsaturated organic matter samples, weigh the required mass of purified water and mix it evenly with the mixture, place it in a fresh-keeping bag for curing for 6-8 days (temperature 20℃±5℃, curing environment sealed), and then divide it into five layers and fill it into the sample preparation mold provided, tamp it to a fixed height according to the design requirements, shave the surface before preparing the next layer.

[0056] Step 6: Use the calcination method to determine the actual organic matter content of the sample.

[0057] Example 2

[0058] For saturated samples with organic matter evenly distributed in the sediment layer, the sample preparation steps are as follows:

[0059] Step 1: Analyze the collected sediment samples to determine the composition and gradation of the reshaped sediments, and mix them evenly according to the proportions. In this embodiment, quartz sand, plagioclase, calcite, illite, kaolin and chlorite with a weight ratio of 0.50:0.10:0.10:0.15:0.075:0.075 are fully mixed to simulate clay-silty sediments, and the clay mass percentage is 30%.

[0060] Step 2: According to the designed mass ratio of water-insoluble organic matter content to sediment particles (1:10), a certain mass of humic acid is weighed and evenly mixed with a fixed mass of reshaped sediment particles.

[0061] Step 3: Determine the specific gravity of the mixture and calculate the mass of the mixture required to reshape the sample with a fixed volume containing organic matter based on the designed porosity of the soil sample (0.45).

[0062] Step 4: Divide the mixture of a fixed mass into five equal layers and fill them into the geotechnical sample preparation mold. Compact them to a fixed height according to the design requirements, scrape the surface and then prepare the next layer.

[0063] Step 5: Prepare a fulvic acid solution (1%) with a fixed mass fraction. Using the capillary saturation method, place the fulvic acid solution in a vacuum cylinder, place the sample mold in the fulvic acid solution, and place the upper part of the sample mold in contact with the air. Evacuate the vacuum cylinder to saturate the sample. After the sample preparation is completed, cure the sample for 6-8 days (temperature 20℃±5℃, curing environment sealed) to allow the organic matter and soil particles to fully react.

[0064] Step 6: Use the calcination method to determine the actual organic matter content of the sample.

[0065] The designed organic matter content of the sample was compared with the organic matter content of the prepared sample, and the results are shown in Table 1 below.

[0066] Table 1 Comparison of organic matter content of prepared samples and designed organic matter content

[0067]

[0068] The results show that the organic matter content of the sediment sample prepared by the method of the present invention is basically consistent with the designed organic matter content, with no significant difference. This also proves that the sample preparation in which organic matter is unevenly distributed in the sediment can also meet the preparation requirements of the sediment sample containing organic matter, and the sample is stable and can withstand long-term storage.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a reshaped sample of organic matter-containing sediment, characterized in that: The following steps are involved: Step 1: Analyze the collected sediment samples to determine the composition and gradation of the reshaped sediments, and mix the raw materials evenly according to the proportions to obtain a mixture; Step 2: According to the designed mass ratio of water-insoluble organic matter to sediment particles, humic acid is weighed and the humic acid is mixed evenly with the reshaped sediment mixture; Step 3: Determine the specific gravity of the mixture of humic acid and remodeled sediment, and calculate the mass of the mixture required for a fixed volume of organic matter remodeled sample based on the designed porosity of the soil sample; Step 4: When making a sample with organic matter evenly distributed in the sediment layer, a fixed mass of the mixture is divided into five equal layers and filled into the geotechnical sample preparation mold, compacted to a fixed height according to the design requirements, and the surface is scraped before preparing the next layer; When preparing samples with non-uniform distribution of organic matter in the sediment layer, for reshaped samples with layered distribution containing organic matter, a fixed mass of the mixture is divided into five equal layers and filled into a geotechnical sample preparation mold. The number of organic matter layers is set according to the design requirements. Sediment granular soil is placed between the organic matter layers. It is compacted to a fixed height according to the design requirements, and the surface is scraped before preparing the next layer of samples; for reshaped samples with block distribution containing organic matter, a fixed mass of organic matter particles is compacted and cut into blocks. The block organic matter and sediment soil samples are mixed and filled into a geotechnical sample preparation mold in five layers and compacted to the target height; After sample preparation, the sample is cured.

2. The method for preparing a reshaped sample of an organic matter-containing sediment according to claim 1, characterized in that: The sample preparation also includes step 5 of preparing a fulvic acid solution: When making unsaturated organic matter samples, weigh the fulvic acid solution and mix it evenly with the mixture, place it in a fresh-keeping bag and seal it for curing, then divide it into five layers and fill it into the sample preparation mold provided, tamp it to a fixed height according to the design requirements, scrape the surface before preparing the next layer of samples; When preparing saturated organic matter samples, when the reshaped sediment has a permeability coefficient of less than 10 -4 For low permeability silt and clay with a permeability of 10 cm / s, the vacuum saturation method is used, and the clean water injected into the vacuum cylinder is replaced with fulvic acid solution; when the reshaped sediment has a permeability coefficient greater than 10 -4 When the particle size is 1000 cm / s, the capillary saturation method is used. The fulvic acid solution is placed in a vacuum cylinder, and the sample mold is placed in the fulvic acid solution. The upper part of the sample mold is in contact with the air, and the vacuum cylinder is evacuated to saturate the sample.

3. The method for preparing a reshaped sample of an organic matter-containing sediment according to claim 1, characterized in that: Step 2: The mass ratio of water-insoluble organic matter to sediment particles is 0.01 to 30:

100.

4. The method for preparing a reshaped sample of an organic matter-containing sediment according to claim 2, characterized in that: The mass fraction of the fulvic acid solution is 0% to 5%.

5. The method for preparing a reshaped sample of an organic matter-containing sediment according to claim 1 or 2, characterized in that: For the preparation of unsaturated samples, the curing time is 6-8 days, the curing temperature is 15℃-25℃, and the curing environment is sealed.

6. The method for preparing a reshaped sample of an organic matter-containing sediment according to claim 1 or 2, characterized in that: The saturated sample continues to be placed in the vacuum cylinder with the liquid level covering the sample. Curing is carried out for 6-8 days at a curing temperature of 15℃-25℃ and the curing environment is sealed.

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