A rapid comparison method for river terraces based on gravel hardness measurement

Abstract

The present invention discloses a rapid comparison method for river terraces based on gravel hardness measurement. The method includes the following steps: collecting gravel samples along the river terraces according to a preset sampling grid; measuring the hardness of the collected gravel samples using a rebound hammer; establishing a gravel weathering index model and calculating the comprehensive weathering index of each terrace based on the model; classifying the river terraces according to the weathering index. The method of the present invention also includes a correction mechanism based on geomorphic morphology and chronometric data, as well as a complete reliability assessment system. The method is simple to operate, low in cost, can rapidly realize the identification and comparison of river terraces, and has important theoretical value and practical significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of terrace measurement, and particularly relates to a rapid comparison method for river terraces based on gravel hardness measurement. Background Art

[0002] River terraces are important geomorphic units. Terrace sediments record the climate and environmental information of their formation period. Terraces formed in different periods can reflect the response of rivers to climate change. The material composition of terrace sediments can indicate the changes in climate conditions in the source area. The development sequence of terraces reflects the river incision process and the evolution history of the valley. At the same time, the formation, distribution, and preservation characteristics of river terraces can indicate the nature and intensity of regional tectonic activities. The deformation, faulting, and elevation changes of terraces can reflect the characteristics of neotectonic movements. By analyzing the terrace sequence, the regional tectonic uplift history can be reconstructed, and its research has important scientific significance and practical value. In addition, river terraces are important sites for industrial and agricultural production, living, and engineering construction. The classification, comparison, and stability assessment of terraces are of great significance for engineering safety.

[0003] However, there are some problems with existing river terrace research methods. Traditional morphological comparison methods mainly rely on geomorphic morphological features and relative height for comparison, which are greatly affected by terrain undulation and the integrity of terrace preservation, and lack objective quantitative indicators. The sediment analysis method requires a large amount of field sampling and indoor experiments, with a long analysis period, high cost, and the results are easily affected by local factors. The dating method has high requirements for test samples, difficult sampling, expensive testing costs, not all terraces have materials suitable for dating, and the dating method has a certain lag. In addition, existing rapid identification methods generally lack systematic quantitative standards, are highly subjective, have poor repeatability, and it is difficult to establish regional comparison standards.

[0004] Therefore, there is an urgent need to establish a rapid, objective, and quantifiable river terrace comparison method. Summary of the Invention

[0005] The purpose of the present invention is to provide a rapid comparison method for river terraces based on gravel hardness measurement, so as to achieve the purpose of rapid, objective, and quantifiable comparison of river terraces;

[0006] The specific technical solution is as follows:

[0007] The present invention provides a rapid comparison method for river terraces based on gravel hardness measurement, and the method includes the following steps:

[0008] Step 1, collect gravel samples at sampling points along the river terrace according to a preset sampling grid.

[0009] Further, the preset sampling grid is a 10m×10m grid divided along the river terrace, and at most 1 gravel sample is collected from each grid; the sampling interval of the preset sampling grid is: sampling once every 5-10 grids at intervals in the main flow direction, and sampling once every 2-5 grids at intervals perpendicular to the main flow direction; each sampling point collects gravel samples, , and the particle size range of the gravel samples is 2-10 cm.

[0010] Further, the gravel samples should be surface-treated before measurement, including: using a brush to remove the loose substances on the surface of the samples, rinsing the surface of the samples with distilled water and then air-drying them naturally for 24 hours.

[0011] Step two, use a rebound hammer to measure the hardness of each collected gravel sample to obtain the rebound value of each sample.

[0012] Further, the hardness measurement method includes the following steps:

[0013] Step S21, fix the gravel sample on a flat test bench.

[0014] Step S22, use a rebound hammer to perform times of rebound measurements on each gravel sample, , and record each rebound value .

[0015] Step S23, calculate the average rebound value after removing the maximum and minimum values .

[0016] Step three: Establish a gravel weathering index model, and calculate the comprehensive weathering index of each terrace based on the gravel weathering index model.

[0017] Further, the mathematical expression of the gravel weathering index model is:

[0018] ; where is the comprehensive weathering index of the gravel; is the average rebound value of the th gravel sample, is the standard rebound value of fresh unweathered gravel, is the average thickness of the weathered layer on the surface of the gravel, in mm; is the reference thickness, with a value of 1 mm; is the percentage content of the weathering products on the surface of the gravel; the determination method of the weathering product content is: select 3 test areas of 1 cm×1 cm on the surface of the gravel; use a digital microscope to photograph the test areas; use image analysis software to calculate the percentage of the covered area of the weathering products; take the average value of the 3 test areas as ; is the reference content, with a value of 1%; , , are the weight coefficients, and the symbol means multiplying both sides;

[0019] ; ; .

[0020] is the coefficient of variation of the rebound value; is the coefficient of variation of the weathered layer thickness; is the coefficient of variation of the weathering product content, .

[0021] Step four, classify the river terraces according to the quantitative calculation results of the comprehensive weathering index of the gravels.

[0022] Furthermore, the river terraces are divided into five levels. Among them, the first-level terrace: ; the second-level terrace: ; the third-level terrace: ; the fourth-level terrace: ; the fifth-level terrace: .

[0023] Furthermore, the calculation method of the average thickness of the weathered layer on the gravel surface is: ; where is the number of measurement points, ; is the thickness of the weathered layer at the th measurement point, measured using a vernier caliper.

[0024] Furthermore, the gravel weathering index model in step three further includes a step of correcting the comprehensive weathering index of the gravels by using geomorphic morphology and / or dating data;

[0025] Furthermore, when the relative height data of a certain terrace is obtained, before classifying the river terraces, the comprehensive weathering index of the gravels is corrected using the following formula: ; where, is the corrected comprehensive weathering index of the gravels, is the relative height of the terrace, in units of m; is the reference height, with a value of 10 m; is the geomorphic correction coefficient, ; the calculation formula of the geomorphic correction coefficient is: ; is the slope of the terrace surface, is the reference slope, with a value of 5 degrees.

[0026] Further, when the dating data of a certain terrace is obtained, a corresponding relationship between the weathering index and the age is established to correct the comprehensive gravel weathering index: , where and are the regional first fitting coefficient and the second fitting coefficient respectively, and their calculation methods are:

[0027] , ;

[0028] is the sample age of the known age, is the corresponding comprehensive gravel weathering index, is the initial estimated age, is the average weathering index of the known sample, is the number of samples of the known age.

[0029] Further, the rapid comparison method further includes a reliability evaluation step: calculating the coefficient of variation of each terrace sample : ; is the sample standard deviation, is the sample mean. When , the measurement result is reliable; when , the number of samples needs to be increased; when , the sampling points need to be reselected.

[0030] Further, after removing the maximum and minimum values and calculating the average rebound value in step S23, it further includes a step of correcting the rebound value based on environmental impact: measuring the environmental temperature (°C) and relative humidity (%); calculating the environmental correction coefficient:

[0031] , and multiplying the measured rebound value by for correction.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] The present invention provides a rapid comparison method for river terraces based on gravel hardness measurement. Through systematic gravel sample collection and standardized measurement processes, the rapid, objective, and quantifiable research of river terraces is achieved. Compared with traditional methods, the present invention has the advantages of simple operation, low cost, and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] ​Figure 1 Flow chart of a rapid comparison method for river terraces based on gravel hardness measurement according to the present invention. Detailed implementation manners

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be described clearly and completely below. Apparently, the described implementation manners are some but not all of the implementation manners of the present invention. All other implementation manners obtained by those of ordinary skill in the art without making creative efforts based on the implementation manners in the present invention belong to the scope of protection of the present invention.

[0036] It should be noted that gravel, as a common component in river terraces, has a close relationship between its weathering degree and the formation age of the terraces; through systematic research on the weathering characteristics of gravel and establishing a standardized measurement and evaluation system, a new technical approach can be provided for the rapid comparison of river terraces; based on this idea, the present invention uses portable equipment to measure the hardness and weathering characteristics of gravel on-site, and combines mathematical models to establish a quantitative evaluation standard, which can quickly realize the identification and comparison of river terraces, and has important theoretical value and practical significance.

[0037] As Figure 1 shown, it is a flow chart of a rapid comparison method for river terraces based on gravel hardness measurement according to the present invention. The method includes the following steps:

[0038] Step 1: Collect gravel samples at sampling points along the river terrace according to a preset sampling grid.

[0039] The preset sampling grid is a 10m×10m grid divided along the river terrace, and at most 1 gravel sample is collected from each grid. The sampling interval of the preset sampling grid is: sampling once every 5 - 10 grids at intervals in the main flow direction, and sampling once every 2 - 5 grids at intervals perpendicular to the main flow direction; taking a certain research area as an example, a complete terrace sequence is developed in this area, with an area of about 2 km². After dividing according to a 10m×10m grid, a sampling point is set every 50 - 100m (5 - 10 grids) at intervals in the main flow direction, and a sampling point is set every 20 - 50m (2 - 5 grids) at intervals perpendicular to the main flow direction, and finally 32 effective sampling points are determined; this sampling strategy not only ensures the representativeness of the data, but also avoids the increase in workload caused by over-dense sampling; one gravel sample is collected from each sampling point,

[0040] Before measurement, the gravel samples should be surface-treated, including: using a brush to remove loose substances on the sample surface, rinsing the sample surface with distilled water and then air-drying it naturally for 24 hours; in field work, it is found that the surface treatment of gravel has a significant impact on the measurement results. Through comparative tests, it is shown that for the samples cleaned with a brush and rinsed with distilled water, the coefficient of variation of the rebound value is reduced by an average of 15%, and the repeatability of the measurement is significantly improved. It is recommended to choose fine weather for field work to avoid the influence of sample moisture on the measurement results.

[0041] In practical applications, the method of the present invention has been verified in multiple typical river regions; for example, in the study of a tributary in the middle reaches of a certain river, this method was used to quickly identify and compare the 5th-order terraces within a 20-km river section; the results show that this method can complete all field work within 2-3 days, saving about 70% of the time compared with the traditional method, and the results have a good correspondence with the existing age data.

[0042] Step two, use a rebound hammer to measure the hardness of each collected gravel sample to obtain the rebound value of each sample.

[0043] The hardness measurement method includes the following steps:

[0044] Step S21, fix the gravel sample on a flat test bench.

[0045] Step S22, use a rebound hammer to perform times of rebound measurements on each gravel sample, , and record the rebound value each time .

[0046] Step S23, calculate the average rebound value after removing the maximum and minimum values .

[0047] Tests show that when the number of rebound measurements m = 20, the measurement results are the most stable. To ensure the accuracy of the measurement, a relatively flat surface of the gravel should be selected for measurement, the measuring point spacing should not be less than 1 cm, and obvious cracks and unevenness should be avoided.

[0048] Step three: Establish a gravel weathering index model, and calculate the comprehensive weathering index of each terrace based on the gravel weathering index model.

[0049] The mathematical expression of the gravel weathering index model is: ; where is the comprehensive gravel weathering index; is the average rebound value of the th gravel sample, is the standard rebound value of fresh unweathered gravel, is the average thickness of the weathered layer on the gravel surface, with the unit of mm; is the reference thickness, with a value of 1 mm; is the percentage content of the weathered products on the gravel surface; the determination method of the content of the weathered products is as follows: Select 3 test areas of 1 cm × 1 cm on the gravel surface; Use a digital microscope to photograph the test areas; Use image analysis software to calculate the percentage of the covered area of the weathered products; Take the average value of the 3 test areas as ; is the reference content, with a value of 1%; , , are the weight coefficients, and the symbol means multiplying both sides;

[0050] ; ; .

[0051] is the coefficient of variation of the rebound value; is the coefficient of variation of the thickness of the weathered layer; is the coefficient of variation of the content of the weathered products, .

[0052] Through the analysis of a large amount of experimental data, it is found that the model shows good applicability in gravels of different lithologies; for example, the test results of granite gravels show that the weathering index is significantly negatively correlated with the compressive strength measured in the laboratory (correlation coefficient R² = 0.87), which verifies the scientificity of the model.

[0053] Step Four: Classify the river terraces according to the quantitative calculation results of the comprehensive weathering index of the gravel.

[0054] The river terraces are divided into five levels, among which, the first-level terrace: ; the second-level terrace: ; the third-level terrace: ; the fourth-level terrace: ; the fifth-level terrace: .

[0055] The calculation method of the average thickness of the weathered layer on the gravel surface is: ; where is the number of measuring points, ; is the thickness of the weathered layer at the th measuring point, measured with a vernier caliper.

[0056] The gravel weathering index model in Step Three further includes the step of correcting the comprehensive weathering index of the gravel by using geomorphic morphology and / or dating data;

[0057] When obtaining the relative height data of a certain terrace, before classifying the river terrace, the following formula is used to correct the comprehensive weathering index of the gravel: ; where is the corrected comprehensive weathering index of the gravel, is the relative height of the terrace, in m; is the reference height, with a value of 10 m; is the geomorphic correction coefficient, ; the calculation formula of the geomorphic correction coefficient is: ; is the slope of the terrace surface, is the reference slope, with a value of 5 degrees.

[0058] Taking a certain river terrace as an example, the relative height of this terrace is 25 m and the slope is 8°. Applying the geomorphic correction formula, it is calculated that λ = 0.16, and the corrected weathering index is increased from the original 0.75 to 0.82, which is more in line with the actual age characteristics of this terrace; this shows that the geomorphic correction mechanism can effectively improve the accuracy of the evaluation results.

[0059] When obtaining the age determination data of a certain terrace, establish the corresponding relationship between the weathering index and the age to correct the comprehensive weathering index of the gravel: , where , are the regional first fitting coefficient and the second fitting coefficient respectively, and their calculation methods are:

[0060] , ;

[0061] is the sample age of the known age, is the corresponding comprehensive weathering index of the gravel, is the initial estimated age, is the average weathering index of the known samples, is the number of samples of the known age.

[0062] In a certain research area, 12 terrace samples with known ages (age range 5 - 200 ka) were collected. Through fitting, the regional coefficients A = 12.5 ka and B = 2.3 were obtained; using these parameters to estimate the terraces with unknown ages, the deviation from the optically stimulated luminescence dating data is within 15%, proving that this method has good practical value.

[0063] The rapid comparison method also includes a reliability evaluation step: calculate the coefficient of variation of each terrace sample: ; is the sample standard deviation, is the sample mean. When , the measurement result is reliable; when , the number of samples needs to be increased; when , the sampling points need to be reselected.

[0064] In the step S23, after removing the maximum and minimum values and calculating the average rebound value , it further includes the step of correcting the rebound value based on the environmental impact; environmental factors have an obvious impact on the measurement result. For example, when the temperature rises from 20°C to 30°C, the uncorrected rebound value increases by about 1% on average; when the relative humidity drops from 60% to 40%, the uncorrected rebound value increases by about 0.4% on average; therefore, environmental correction is an important step to ensure measurement accuracy; measure the environmental temperature (°C) and relative humidity (%); calculate the environmental correction coefficient:

[0065] , multiply the measured rebound value by for correction.

[0066] Calculation of the coefficient of variation of the rebound value : For the gravel samples at each sampling point, calculate the average rebound value and the standard deviation :

[0067] ; ; .

[0068] Calculation of the coefficient of variation CVD of the weathered layer thickness: Select 5 gravel samples at each sampling point, and measure the weathered layer thickness at k points (k≥5) for each sample; calculate the average thickness and the standard deviation :

[0069] ; ;

[0070] ; where is the weathered layer thickness of the rd sample at the th measurement point.

[0071] Calculation of the coefficient of variation CVP of the weathering product content: Select 5 gravel samples at each sampling point, and measure the weathering product content in 3 regions for each sample; calculate the average content and the standard deviation :

[0072] ; ;

[0073] ; where is the weathered product content of the th sample in the th test area.

[0074] The preprocessing requirements for sample data include: performing outlier tests on each group of data and removing data that deviates significantly; when the deviation of a certain measurement value from the average exceeds 3 times the standard deviation, the data should be re-measured or removed; at least 5 valid sample data are required for the calculation of each coefficient of variation.

[0075] If any coefficient of variation CV > 50%, the number of measurements of this parameter needs to be increased. If the coefficient of variation is still > 50% after increasing the number of measurements, the sampling point should be reselected. All numerical calculations retain 3 significant figures.

[0076] The specific implementation manners described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only the specific implementation manners of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A rapid comparison method for river terraces based on gravel hardness measurement, characterized in that: The method comprises the following steps: Step 1: Collect gravel samples at sampling points along the river terrace according to a preset sampling grid; The preset sampling grid is a 10m×10m grid divided along the river terrace, and at most one gravel sample is collected in each grid; Each sampling point collects Gravel samples, , the particle size range of the gravel sample is 2-10 cm; Step 2: Use a rebound hammer to measure the hardness of each gravel sample collected to obtain the rebound value of each sample; The hardness measuring method comprises the following steps: Step S21, fixing the gravel sample on a flat test table; Step S22, using a rebound hammer to Rebound measurement, , record each rebound value ; Step S23, calculating the average rebound value after removing the maximum and minimum values ; Step 3: Establish a gravel weathering index model, and calculate the comprehensive weathering index of each terrace based on the gravel weathering index model; The mathematical expression of the gravel weathering index model is: ;in, is the comprehensive weathering index of gravel; For the The average rebound value of the gravel samples, is the standard rebound value of fresh unweathered gravel, is the average thickness of the weathered layer on the gravel surface, in mm; is the reference thickness, which is 1mm; is the percentage of weathering products on the gravel surface; is the reference content, with a value of 1%; , , is the weight coefficient, symbol It means multiplying both sides; ； ； ； is the coefficient of variation of the rebound value; is the coefficient of variation of the weathering layer thickness; is the coefficient of variation of weathering product content, ; Step 4, classifying the river terraces according to the quantitative calculation results of the gravel comprehensive weathering index; The river terraces are divided into five levels, among which the first level terrace is: ; Secondary terrace: ; Third terrace: ; Fourth terrace: ; Fifth terrace: .

2. A rapid river terrace comparison method based on gravel hardness measurement according to claim 1, characterized in that: The sampling interval of the preset sampling grid is: sampling once every 5-10 grids in the main flow direction, and sampling once every 2-5 grids perpendicular to the main flow direction.

3. A rapid river terrace comparison method based on gravel hardness measurement according to claim 2, characterized in that: The average thickness of the weathered layer on the gravel surface The calculation method is: ;in, is the number of measurement points, ; For the The thickness of the weathered layer at each measuring point is measured using a vernier caliper.

4. A rapid river terrace comparison method based on gravel hardness measurement according to claim 3, characterized in that: The gravel weathering index model in step 3 further includes the step of correcting the gravel comprehensive weathering index using geomorphology and / or dating data; When the relative height data of a terrace is obtained, the following formula is used to correct the gravel comprehensive weathering index before classifying the river terrace: ;in, is the modified gravel comprehensive weathering index, is the relative height of the terrace, in m; is the reference height, which is 10m; is the topography correction factor, ; When the dating data of a terrace is obtained, the corresponding relationship between weathering index and age is established to correct the gravel comprehensive weathering index: ,in , They are the regional first fitting coefficient and the second fitting coefficient, respectively, and their calculation method is: ， ； is the age of the sample of known age, is the corresponding gravel comprehensive weathering index, is the initial estimated age, is the average weathering index of known samples, is the number of samples with known age.

5. A rapid river terrace comparison method based on gravel hardness measurement according to claim 4, characterized in that: The rapid comparison method also includes a reliability assessment step; Calculate the coefficient of variation for each terrace sample : ; is the sample standard deviation, is the sample mean, when When When , the number of samples needs to be increased; when The sampling point needs to be reselected.

6. A rapid river terrace comparison method based on gravel hardness measurement according to claim 5, characterized in that: The gravel sample should be surface treated before measurement, including: using a brush to remove loose materials on the sample surface, rinsing the sample surface with distilled water and then air-drying it for 24 hours.

7. A rapid river terrace comparison method based on gravel hardness measurement according to claim 5, characterized in that: The percentage of weathering products on the gravel surface The determination method is as follows: select three 1 cm × 1 cm test areas on the gravel surface; use a digital microscope to photograph the test areas; use image analysis software to calculate the percentage of weathering product coverage area; take the average value of the three test areas as .

8. A rapid river terrace comparison method based on gravel hardness measurement according to claim 5, characterized in that: Landform Correction Factor The calculation formula is: ; is the terrace slope, The reference slope is 5 degrees.

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