A method for quality evaluation and reserve determination of river terrace gravel material

Abstract

The application discloses a kind of river terrace sand gravel material quality evaluation and reserve determination method, it is related to natural building material exploration technical field, including: grid exploration and stratified sampling are implemented to target river terrace, and the corresponding terrace plane area, stratum thickness and loose coefficient of each stratum are measured and obtained, and geological reserves are calculated;Through test, the missing file situation, silt content, lithology composition, firmness index, crushing index, saturated compressive strength and freeze-thaw loss rate of each sample corresponding stratum are obtained;Lithology combination coefficient is calculated based on lithology composition, and the comprehensive quality evaluation of sand gravel material is carried out;Quality rejection rate, freeze-thaw rejection rate and gradation rejection rate are determined respectively, and total rejection rate is obtained;Based on geological reserves and total rejection rate, reliable reserves are calculated.The application realizes the accurate classification of river terrace sand gravel material quality in high altitude area and repeatable evaluation, solves the limitation of single index evaluation in existing specification.

Description

Technical Field

[0001] This invention relates to the field of natural building materials exploration technology, specifically to a method for quality evaluation and reserve determination of river terrace gravel. Background Technology

[0002] The scale of water conservancy, hydropower, and transportation projects in high-altitude areas is constantly expanding, leading to a continuous increase in demand for concrete aggregates. However, due to factors such as high altitude, fragile ecosystems, and limited transportation conditions, purchasing aggregates from distant locations is costly and uneconomical. Meanwhile, rivers in high-altitude areas widely develop terraced gravel deposits, which are formed by alluvial, diluvial, and glacial deposits and are abundant, representing a potential high-quality source of concrete aggregates.

[0003] However, existing natural building material exploration and evaluation technologies have significant shortcomings and technological gaps in the quality evaluation and reserve verification of river terrace gravel in high-altitude areas, making it difficult to adapt to the special geological characteristics of this type of gravel. Specific defects include: (1) Lack of a targeted comprehensive quality grading system: Existing standards mostly use a single indicator (such as mud content and crushing index) to independently evaluate aggregate quality. Due to the large fluctuation in the content of hard and soft rocks in this type of sand and gravel, and the uneven thickness of the mud coating on the particle surface, the existing single indicator evaluation cannot accurately reflect the true quality of the material source, and is prone to evaluation deviation.

[0004] (2) The depth of freeze-thaw impact lacks scientific basis: Freeze-thaw cycles are frequent in high-altitude areas, and the surface gravel has developed freeze-thaw cracks and high water absorption rate. Existing technologies rely on empirical estimation for peeling thickness and lack quantitative standards, which can easily lead to insufficient peeling and mixing of inferior materials, or excessive peeling and waste of resources, affecting the quality of material sources and utilization efficiency.

[0005] (3) The reserve evaluation does not take into account the process adaptability: The existing reserve demonstration is mostly based on pure geological volume calculation, and only divides the reserves into general survey, detailed survey and exploration reserves. It does not take into account the actual needs of the project, such as the compatibility of sand and gravel gradation and the stratification and elimination of quality. The problem of "sufficient geological reserves, but lack of gradation, high proportion of inferior materials, and insufficient actual usable reserves" often occurs, which leads to misjudgment of engineering decisions and affects the progress of the project and investment control. Summary of the Invention

[0006] In view of one or more shortcomings of the existing technology, the present invention provides a method for quality evaluation and reserve determination of river terrace gravel, which can realize accurate grading of the quality of river terrace gravel in high-altitude areas and provide a reliable basis for decision-making on engineering aggregate sources.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for evaluating aggregate quality and determining reserves of river terrace gravel includes the following steps: Grid exploration and stratified sampling were carried out on the target river terraces to obtain samples of each stratum. The muddy coating of the sand and gravel in each sample was tested to obtain the average thickness of the muddy coating. The terrace plane area, stratum thickness and loosening coefficient of each stratum were measured and obtained. The geological reserves were calculated based on the terrace plane area, stratum thickness and loosening coefficient. The samples were subjected to particle sieving tests, mud content tests, lithological composition and strength tests, and stratified freeze-thaw tests to obtain the missing strata, mud content, lithological composition, mass loss rate, crushing index and freeze-thaw loss rate of each sample. Based on the lithological composition and the average thickness of the muddy shell, the lithological combination coefficient is calculated. According to the lithological combination coefficient, the mud content, the mass loss rate, the crushing index and the freeze-thaw loss rate, the gravel is divided into three quality grades: A, B and C. The quality rejection rate is determined based on the quality grade; the distribution of the freeze-thaw deterioration layer is divided based on the freeze-thaw loss rate and the freeze-thaw rejection rate is determined; the gradation rejection rate is determined based on the missing grade situation; the quality rejection rate, the freeze-thaw rejection rate and the gradation rejection rate are summed to obtain the total rejection rate. The reliable reserves are calculated based on the geological reserves and the total rejection rate, and the reliable reserves are used as the basis for determining whether the target river terrace can be used as a source of concrete aggregate.

[0008] As a further implementation, the calculation of the lithological combination coefficient based on the lithological composition specifically includes: The gravel materials of each layer were classified into hard rock, medium hard rock and weak rock according to their saturated compressive strength, and the content of each rock type was counted to obtain the content of hard rock, medium hard rock and weak rock. The lithological combination coefficient K is calculated using the following formula: K = (P) H +P M ) / (P S +0.5×T) In the formula, K is the lithological combination coefficient, which is dimensionless; P H Content of hard rock, in %; P M Medium-hard rock content, in %; P S % represents the content of weak rock; T represents the average thickness of the argillaceous crust in mm.

[0009] As a further implementation, the step of dividing the freeze-thaw deterioration layer distribution based on the freeze-thaw loss rate and determining the freeze-thaw removal rate specifically includes: Freeze-thaw tests were conducted on the samples at different depth ranges to obtain the freeze-thaw loss rate for each depth range. The stratigraphic intervals corresponding to depth ranges where the freeze-thaw loss rate exceeds the first threshold are designated as freeze-thaw deteriorated layers. The total volume of the freeze-thaw deteriorated layer is statistically analyzed, and the proportion of the total volume of the freeze-thaw deteriorated layer to the geological reserves is calculated to obtain the freeze-thaw removal rate.

[0010] As a further implementation method, determining the quality rejection rate based on the quality level specifically includes: Based on the aforementioned quality grades, the strata corresponding to gravel with a quality grade of C are classified as inferior strata. The quality rejection rate is obtained by calculating the proportion of the sum of the volumes of all the inferior strata to the geological reserves.

[0011] As a further implementation, determining the gradation rejection rate based on the missing grades specifically includes: The gradation elimination rate is obtained by statistically analyzing all strata with gradation deficiencies in the aforementioned missing gradation conditions and calculating the proportion of the sum of the volumes of all strata with gradation deficiencies to the geological reserves.

[0012] As a further implementation, before classifying the quality grades, the method also includes conducting an alkali activity test, which comprises two stages, and the specific execution process includes: In the first stage, the lithofacies method is used to screen for active minerals to obtain the content of active ingredients, and the content of active ingredients is compared with a second threshold. If the content of active ingredients in the sample is not greater than the second threshold, the gravel in the sample is determined to be non-active aggregate and can be used directly. If the content of the active ingredient is greater than the second threshold, then proceed to the second stage of the experiment: The mortar bar rapid test was used to test the samples and obtain the 14-day expansion rate of the gravel. Based on the 14-day expansion rate, the alkali activity level of the gravel was classified and treatment recommendations matching the alkali activity level were determined.

[0013] As a further implementation, the step of classifying the alkali reactivity level of the sand and gravel based on the 14-day expansion rate and determining the treatment recommendations matching the alkali reactivity level specifically includes: If the 14-day expansion rate is less than 0.10%, the gravel is determined to be non-reactive aggregate and can be used safely. If the expansion rate of 0.10% ≤ 14d < 0.20%, the gravel is determined to be a potentially reactive aggregate, and further tests are needed to determine its activity. If the 14-day expansion rate is ≥0.20%, the gravel is considered to be reactive aggregate and should not be used directly. It needs to be used in conjunction with other inhibition measures.

[0014] As a further implementation, the geological reserves are calculated based on the terrace plane area, stratum thickness, and loosening coefficient. The specific calculation formula is as follows:

[0015] In the formula, A i h represents the area of ​​the i-th terrace plane, in m². i λ represents the average thickness of the i-th layer, in meters (m). i is the loosening coefficient of the i-th layer; n is the total number of strata.

[0016] As a further implementation, the process of determining the lithological composition includes: For each layer of gravel, a number of gravels of the same size were randomly selected according to different particle size groups to carry out uniaxial compressive strength tests to obtain the saturated compressive strength of each gravel. Based on the saturated compressive strength, the gravel is divided into hard rock, medium-hard rock and soft rock. The lithological proportion of each grain size group is counted and the total lithological proportion of each stratum is summarized to obtain the lithological composition of each stratum.

[0017] As a further implementation method, the grid exploration and stratified sampling of the target river terrace specifically includes: Several exploratory pits were laid out in a grid pattern along the terrace direction and perpendicular to it. Sampling was carried out in equal-thickness layers according to the layers of each natural layer, and sampling was intensified at fixed depth intervals in the freeze-thaw influence zone. Drill holes are laid next to each of the aforementioned pits to simultaneously measure and obtain the plane area of ​​the terrace and the thickness of the stratum.

[0018] By adopting the above technical solution, the beneficial effects of the present invention are as follows: 1. This invention, by constructing a lithological combination coefficient and combining it with a multi-index comprehensive quality evaluation, achieves accurate grading and repeatable evaluation of the quality of river terrace gravel in high-altitude areas, overcoming the limitations of single-index evaluation in existing standards. Simultaneously, it proposes for the first time the concept of "credible reserves," introducing quality rejection rate, freeze-thaw rejection rate, and gradation rejection rate, combined with geological reserves, to achieve accurate conversion from geological reserves to actual usable reserves. This transforms reserve evaluation from "how much material is available" to "how much material is usable," providing a reliable basis for engineering aggregate source decision-making and helping to reduce engineering investment risks.

[0019] 2. This invention achieves accurate judgment of the depth of freeze-thaw impact on terraced gravel in high-altitude areas by measuring the freeze-thaw loss rate in layers, dividing the freeze-thaw deterioration layer, and quantifying the freeze-thaw removal rate. Compared with the traditional method of determining the stripping thickness based on experience, this invention significantly improves the controllability of material source quality and reduces ineffective mining costs. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of the process for quality evaluation and reserve determination of river terrace gravel in an embodiment of the present invention; Figure 2 This is a graph showing the vertical stratification structure of the terraced gravel and the variation of the K value. Detailed Implementation

[0022] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] Example 1 In one typical embodiment of this application, a method for quality evaluation and reserve determination of river terrace gravel is provided. Through systematic exploration planning, stratified sampling, indoor and outdoor testing, quality grading, and reliable reserve calculation, it provides a scientific basis for engineering decision-making. Figures 1-2 The method specifically includes: S1. Conduct grid exploration and stratified sampling on the target river terraces to obtain samples from each stratum. Detect the muddy coating of the sand and gravel in each sample to obtain the average thickness of the muddy coating. Measure the corresponding terrace planar area, stratum thickness, and loosening coefficient for each stratum. Calculate the geological reserves based on the terrace planar area, stratum thickness, and loosening coefficient.

[0025] Specifically, grid pits are laid out along the terrace direction and perpendicular to it, and samples are taken at fixed intervals according to the thickness of the natural strata. For the freeze-thaw influence zone, sampling is intensified at set depth intervals. Boreholes are laid next to each pit to obtain undisturbed samples, which facilitates physical and mechanical tests, verification of the accuracy of pit stratification, and determination of groundwater level and bedrock surface morphology.

[0026] During the exploration process, the terrace plane area of ​​each natural stratum was measured; the total number of strata n and the total stratum thickness h were measured, and the average thickness of each stratum was calculated; the loosening coefficient of each natural stratum was determined by the on-site pit excavation and water injection method.

[0027] In this embodiment, in accordance with the "Code for Investigation of Natural Building Materials for Hydropower Projects" (SL / T 251-2015) and the special requirements of high-altitude areas, the exploration work is divided into three stages: the general survey stage, the detailed survey stage, and the exploration stage. The exploration work and objectives of each stage are as follows: During the general survey phase, the exploration aims to initially select material sites and estimate potential reserves. The exploration interval is 200-300m, the number of test pits is ≥3, and the number of samples collected is ≥30 sets. During the detailed investigation phase, the exploration aims to delineate the mining area and divide the quality zones. The exploration interval is 100-150m, the number of test pits is ≥6, and the number of samples collected is ≥100 sets. During the exploration phase, the purpose of exploration is to determine recoverable reserves and provide design basis. The exploration spacing is 50m×30m (grid-like), the number of exploration pits is ≥20, and the number of samples collected is ≥300 sets.

[0028] Based on the exploration results, test pits are deployed in a grid pattern: along the terrace strike (parallel to the river flow direction) and perpendicular to the terrace strike (perpendicular to the river flow direction). The grid density during the exploration phase is 50m (strike) × 30m (vertical), determined based on the variability analysis of the lithological assemblage of terraces in high-altitude areas. When the range is 80-120m, a 50m spacing ensures effective control. The test pits have a planar dimension of 2.0m (length) × 1.5m (width), and the depth is excavated to the overburden interface or 1.0m below the groundwater level, aiming to expose a complete depositional sequence. One borehole with a diameter ≥110mm is placed within 3m of each test pit, with full-hole coring, to obtain undisturbed samples for physical and mechanical testing, verifying the accuracy of the test pit's stratification, and determining the groundwater level and bedrock surface morphology.

[0029] After the test pits were laid out, each natural layer of the strata was sampled layer by layer, specifically as follows: The depth range of each natural layer is measured to obtain the thickness of each natural layer. When the thickness of a natural layer is >1.0m, sampling is performed at fixed vertical depth intervals; in this embodiment, samples are taken at equal thickness intervals of 0.5m. Combined with... Figure 2As shown, separate sampling is taken for interlayers including fine sand, silty clay, and clay cemented layers; for the surface freeze-thaw influence zone, since this layer has a great impact on the quality of the project, denser sampling is adopted and the sampling interval is reduced. In this embodiment, the sampling interval is reduced from 0.5m to 0.25m, that is, denser sampling is carried out at intervals of 0~0.25m, 0.25~0.5m, 0.5~0.75m, and 0.75~1.0m respectively.

[0030] Each layer of sampling should weigh no less than 200 kg to meet the needs of subsequent full-gradation sieving, lithology identification, and various mechanical tests. The top 10cm of loose soil should be removed, and each sample should be placed in a waterproof woven bag with labels inside and out, indicating: project name, pit number, sampling depth, lithology description, sampling date, and sampler. Severe vibration should be avoided during sample transportation to prevent particle breakage.

[0031] In this embodiment, the total terrace deposits of the target river terrace, i.e., the geological reserves, are calculated according to formula (1). .

[0032] (1) In the formula, A i h represents the area of ​​the terrace plane of the i-th layer, in m², measured from the contour map of the top / bottom interface of the layer; i λ represents the average thickness of the i-th layer, in meters (m). i The looseness coefficient is dimensionless and is determined by the field digging and water filling method. The typical value for terraces in high-altitude areas is 1.15~1.25; n is the total number of layers.

[0033] S2. Conduct particle sieving tests, mud content tests, lithological composition and strength tests, and stratified freeze-thaw tests on the samples to obtain the missing strata, mud content, lithological composition, mass loss rate, crushing index and freeze-thaw loss rate of each sample.

[0034] Specifically, it includes: (a) Conduct particle sieving tests to obtain the gaps in each stratum.

[0035] Particle sieving tests were conducted on the samples of each layer using a sieve tray to screen sand and gravel, and the mass data of sand and gravel on each sieve tray were obtained. Based on the mass data of each sieve tray, gradation curves were plotted for each layer of samples. The number of missing sieve holes was counted based on the gradation curves. Specifically, the particle gradation curves of each layer of samples were compared with the target gradation of concrete aggregate (the target gradation of concrete aggregate is determined according to the relevant design requirements of the target concrete to be configured, such as a continuous gradation of 5~40mm or a continuous gradation of 5~31.5mm) to identify the number of gradation gaps in the stratum.

[0036] During the process of counting missing sieve openings, the deviation between the cumulative sieve residue of each sieve opening and the target sieve opening value (such as 20mm, 40mm, etc.) is calculated. When the deviation of a certain sieve opening exceeds 15%, it is judged as a missing sieve opening. The number of missing sieve openings in each stratum is used to evaluate the missing sieve openings of the strata corresponding to each sample, which facilitates the subsequent calculation of the gradation rejection rate. If the number of missing sieve holes is 0, then the layer can be used directly; If the number of missing sieve holes is 1 to 2, other material sources need to be added or the material needs to be crushed and adjusted. If the number of missing sieve holes is ≥3, then this layer is not suitable as a source of concrete aggregate, or it needs to be treated before it can be used as a source of concrete aggregate.

[0037] (ii) Conduct mud content tests to obtain mud content evaluations for each stratum.

[0038] In this embodiment, the mud content (content of particles <0.075mm) of the samples was determined according to the mud content test (water washing method) specified in Clause 7.4 of "Construction Sand" (GB / T 14684-2022). Then, the mud content of each sample was evaluated, specifically including: First, particles with a diameter less than 0.075 mm fall within the statistical range for mud content. Based on the mud content range of the samples, the evaluation of sand and gravel is divided into four levels: excellent, medium, poor, and very poor. If the mud content is ≤1.0%, the mud content is rated as excellent, indicating that the sand and gravel can be used directly. If the mud content ranges from 1.0% to 3.0%, the mud content is rated as medium, indicating that the sand and gravel material needs to be washed with water before it can be used. If the mud content is in the range of 3.0% to 5.0%, the evaluation is poor, indicating that the sand and gravel needs to be washed more thoroughly and the cost of use is high. If the mud content is >5.0%, the evaluation is extremely poor, indicating that the sand and gravel is not suitable as a source of concrete aggregate or has poor suitability.

[0039] In addition, the proportion of particles with a diameter greater than 1.18 mm that can be broken down to less than 0.6 mm after being soaked in water and kneaded by hand is defined as the mud content. In this embodiment, the mud content is set to not exceed 0.5%. If the mud content exceeds this set proportion, the washing process cost will need to be increased.

[0040] (III) Conduct lithological composition and strength tests, specifically including uniaxial saturated compressive strength tests, firmness tests, and crushing index tests, to obtain the lithological composition, mass loss rate, and crushing index of each stratum for formation quality evaluation. The tests are described in detail below.

[0041] 1) Conduct uniaxial saturated compressive strength tests.

[0042] From the terrace gravel of each sample layer, 100 gravels were randomly selected from each of the four particle size groups (5-10 mm, 10-20 mm, 20-40 mm, and >40 mm) for uniaxial compressive strength tests (all gravels were taken if fewer than 100 were selected). The saturated compressive strength of each gravel was then measured. Based on the saturated compressive strength values, the lithology was classified into three categories: hard rock, medium-hard rock, and weak rock. The specific classification criteria are shown in Table 1.

[0043] Table 1

[0044] Based on the above standards, the proportions of hard rock, medium-hard rock, and weak rock in the test gravel of each layer sample were statistically analyzed to obtain the lithological composition of the corresponding stratum. This composition was used for quality grading of the sand and gravel. The lithological composition included: hard rock content P H (%), medium-hard rock content P M (%), P content in weak rocks S (%), where P H +P M +P S =100%.

[0045] 2) Conduct robustness tests.

[0046] In accordance with the "Construction Gravel and Crushed Stone" standard (GB / T 14685-2022), a soundness test was conducted using the sodium sulfate solution method. The test particle size groups should include 5~10mm, 10~20mm, and 20~40mm. The mass loss rate for each particle size group was obtained, and based on the mass loss rate, each particle size group was classified into four grades: excellent, medium, poor, and very poor, corresponding to different applicable ranges for concrete. The specific details are as follows, and the maximum threshold of the mass loss rate for each grade was taken as the soundness index corresponding to that grade: When the mass loss rate is ≤5%, the gravel is rated as excellent and is suitable for concrete strength grades of C30 and above. When the mass loss rate is 5%~10%, the evaluation is medium, and the applicable concrete strength grade is C25~C30; When the mass loss rate is 10%~15%, the evaluation is poor, and the applicable concrete strength grade is C20 and below. When the mass loss rate is >15%, the evaluation is extremely poor, and the gravel should not be used as concrete aggregate.

[0047] 3) Conduct crushing index tests.

[0048] The crushing index test was conducted in accordance with the standard "Construction Gravel and Crushed Stone" (GB / T 14685-2022). Samples with a particle size group of 10.0 mm to 20.0 mm were used for the test. The crushing index was calculated, and the samples were graded and evaluated according to the range of the crushing index. Specifically: When the compression index is ≤10%, it is rated as excellent and is applicable to concrete strength grades of C30 and above. When the compression index is 10%~16%, it is rated as medium, and the applicable concrete strength grade is C25~C30; When the compression index is 16%~20%, it is rated as poor, and the applicable concrete strength grade is C20 and below; If the compression index is >20%, the evaluation is extremely poor, and the gravel should not be used as concrete aggregate.

[0049] (iii) Conduct layered freeze-thaw tests to obtain the freeze-thaw loss rate of gravel in each layer of samples.

[0050] This step evaluates the mass loss of gravel after freeze-thaw cycles and quantitatively determines the depth of freeze-thaw impact, providing a scientific basis for surface peeling thickness. Sampling was conducted at the following depth ranges for each test pit: 0–0.5 m, 0.5–1.0 m, 1.0–1.5 m, 1.5–2.0 m, 2.0–2.5 m, and 2.5–3.0 m. 5 kg of samples with a particle size of 20–40 mm were taken from each depth range, and stratified freeze-thaw tests were performed to obtain the freeze-thaw loss rate (%) of the gravel. Different reference ranges for freeze-thaw loss rate (%) were assigned to each depth range. Based on these depth ranges and their freeze-thaw loss rate ranges, a grading evaluation was conducted. In this embodiment, each stratum was divided into five levels: severely deteriorated layer, moderately deteriorated layer, weakly deteriorated layer, transitional layer, and normal layer. The specific grading evaluation criteria are shown in Table 2.

[0051] Table 2

[0052] The required thickness of the strata to be stripped from the terrace is determined based on the freeze-thaw loss rate: the depth range with a freeze-thaw loss rate >3% is the freeze-thaw deteriorated layer that needs to be stripped. Typical stripping thicknesses in some high-altitude areas are 1.5–2.5 m.

[0053] In addition, in order to determine whether there are potential hazards in each layer of gravel, special property tests are required. In this embodiment, alkali reactivity tests are preferred to determine whether there are potential alkali-silicic acid reaction (ASR) hazards in the gravel.

[0054] The alkali reactivity test is divided into two stages. The first stage uses the petrographic method to perform thin section identification on samples from each layer and screen for active minerals.

[0055] If the content of active ingredients does not exceed the 1% threshold, the gravel in the material yard is directly judged to be non-active aggregate and can be used directly. If the content of active ingredients exceeds the 1% threshold, the process proceeds to the second stage. In the second stage, following the standard "Construction Gravel and Crushed Stone" (GB / T 14685-2022), the mortar rod rapid method is used to test samples exceeding the 1% threshold, obtain the 14-day expansion rate of the gravel, determine the alkali activity level based on the 14-day expansion rate, and propose corresponding treatment recommendations.

[0056] The alkali reactivity classification in the "Test Procedure for Sand and Gravel Aggregates in Hydraulic Concrete" (DL / T 5151-2014) is as follows: If the 14-day expansion rate is less than 0.10%, the gravel is determined to be non-reactive aggregate and can be used safely. If the expansion rate of 0.10% ≤ 14d < 0.20%, the gravel is determined to be a potentially reactive aggregate, and further tests are needed to determine its activity. If the 14-day expansion rate is ≥0.20%, the gravel is considered to be reactive aggregate and should not be used directly. It needs to be used in conjunction with other inhibition measures.

[0057] S3. Calculate the lithological combination coefficient based on lithological composition and average thickness of mud shell. According to the lithological combination coefficient, mud content, soundness index, crushing index, saturated compressive strength and freeze-thaw loss rate, the sand and gravel are divided into three quality grades: A, B and C. Specifically, the lithological combination coefficient K is defined as a quantitative index that comprehensively reflects the influence of the content of hard rock, weak rock, and mudstone crust thickness on aggregate quality in gravel. The larger the K value, the better the aggregate quality. The K value is calculated according to formula (2): K = (P) H +P M ) / (P S +0.5×T)(2) In the formula, P H Content of hard rock, in %; P M Medium-hard rock content, in %; P S The content of weak rock is expressed as %; T represents the average thickness of the clay crust in mm. The method for determining the average thickness T of the clay crust is as follows: 50 gravels are randomly selected from the 5-20 mm grain size group, the clay crust boundary is displayed using the methylene blue staining method, the maximum clay crust thickness is measured with vernier calipers, and the arithmetic mean is taken.

[0058] Based on the K-value calculation results, a preliminary quality evaluation of the gravel was conducted, classifying it into three quality grades: A, B, and C. The specific grading standards are as follows: If the K value is ≥3.0, the gravel material is rated as Grade A; If the K value is between 1.5 and 3.0, that is, 1.5 ≤ K value < 3.0, then it is rated as Grade B; If the K value is less than 1.5, it will be rated as C.

[0059] Finally, based on the aforementioned quality indicators and the resulting quality grading of the gravel, a comprehensive quality evaluation was conducted on the gravel samples from each layer, resulting in three grades: A, B, and C, as shown in Table 3. When a single indicator exceeds the range of its grade, the worst-performing indicator is used for grading. For example, referring to Table 3, if the mud content of a sample is >3.0%, even if all other indicators are within the B grade range, the gravel quality of that sample will still be graded C. Similarly, if the crushing index of a sample is >20%, it will be directly graded C.

[0060] Table 3

[0061] S4. Determine the quality rejection rate based on the quality classification, divide the distribution of the freeze-thaw deterioration layer based on the freeze-thaw loss rate and determine the freeze-thaw loss rate, and determine the gradation rejection rate based on the missing grade situation; sum the quality rejection rate, freeze-thaw rejection rate and gradation rejection rate to obtain the total rejection rate.

[0062] Specifically, based on the quality grading results in step S3, gravel materials with a quality grade of C are selected, and the ratio of the volume of gravel materials with a quality grade of C to the geological reserves is calculated to obtain the removal rate R of grade C materials. C .

[0063] Based on the freeze-thaw loss rate results obtained in step S2, the ratio of the sum of the volumes of strata with freeze-thaw loss rates greater than 3% to the geological reserves is calculated, which is the ratio of the stripping thickness to the total depth of the terraces in step S3, thus obtaining the freeze-thaw removal rate R. frost .

[0064] Based on the results of the gradation gap situation in each stratum in step 2, all strata with a sieve hole count ≥3 are identified as strata with gradation gaps. The ratio of the sum of the volumes of strata with a sieve hole count ≥3 to the geological reserves is calculated to obtain the gradation gap removal rate R. grad .

[0065] Finally, the total rejection rate R was calculated. reject :R reject =R C +R frost +R grad .

[0066] S5. Based on geological reserves and total rejection rate, the credible reserves are calculated and used as the basis for judging whether the target river terrace can be used as a source of concrete aggregate.

[0067] Specifically, based on the geological reserves calculated in step S1 Compared with the total rejection rate R calculated in step S4 reject The credible reserves V are calculated based on formula (3). PT The amount of sand and gravel reserves at the target terrace that can be used as concrete aggregate sources is obtained, which serves as the basis for engineering mining.

[0068] V PT =V geo ×(1~R reject (3) After calculating the above-mentioned credible reserves, the feasibility study of the material source can be completed by combining the engineering aggregate demand, mining costs and environmental constraints, so as to provide a reliable basis for delineating the mining area and formulating a layered mining and stripping plan.

[0069] Example 2 This embodiment takes a hydropower station project located on a tributary in the middle reaches of the Yarlung Tsangpo River as an example to illustrate the application process of the quality evaluation and reserve determination method in Embodiment 1 in a specific project.

[0070] The total concrete aggregate requirement for this hydropower project is approximately 1.8 million m³, including about 1.2 million m³ of coarse aggregate and about 600,000 m³ of fine aggregate. Geological background of the project area: The dam site area features a Class IV erosional-depositional terrace, parallel to the river flow direction, approximately 1.8 km long, 0.4–0.7 km wide, and covering an area of ​​about 0.9 km². The terrace deposits are Late Pleistocene alluvial sand and gravel layers, with a total thickness of 12–18 m.

[0071] S1. Implementation of grid exploration and stratified sampling stage.

[0072] An exploration grid was set up within the terrace area. Six exploration lines were set up along the terrace direction with a line spacing of 50m. Test pits were set up at 30m intervals on each exploration line, for a total of 28 test pits. One borehole was set up 3m away from each test pit, for a total of 28 boreholes with a depth of 15~20m (3m into the bedrock).

[0073] Pit excavation and stratification: The exploratory pit is 2.0m × 1.5m in size and is excavated to a depth of 12~18m below the basement interface. Sampling is performed in natural layers combined with 0.5m equal-thickness stratification, resulting in a total of 6 natural layers, as shown in Table 4.

[0074] Table 4

[0075] Stratified sampling: Each layer of sampling weighs ≥200kg. Sampling was intensified at intervals of 0~0.5m, 0.5~1.0m, 1.0~1.5m, 1.5~2.0m, and 2.0~2.5m in the surface freeze-thaw influence zone (for stratified freeze-thaw testing). A total of 168 sets of samples were collected.

[0076] S2, the stage of conducting particle sieving tests, mud content tests, lithological composition and strength tests and stratified freeze-thaw tests.

[0077] S21: Taking a continuous gradation of 5~40mm as the target gradation, a gap analysis was performed, and the results are shown in Table 5.

[0078] Table 5

[0079] S22: The results of the mud content test are shown in Table 6.

[0080] Table 6

[0081] In addition, this embodiment also detected that: except for the mud content of layer ③ sample which was 0.3%, the mud content of the other five layers of samples all exceeded 0.5%, and the water washing process needs to be strengthened when applied to concrete aggregate.

[0082] S23: Conduct uniaxial saturated compressive strength tests to obtain the lithological composition of each layer.

[0083] In this embodiment, the test data of 100 test gravels with a particle size ≥ 40 mm in layer ① are shown in Table 7.

[0084] Table 7

[0085] Based on the classification criteria in Table 1, in the ≥40mm grain size group of layer ① samples, hard rocks (including granite, quartzite and dense limestone) accounted for 34%, medium hard rocks (including sandstone and gneiss) accounted for 31%, and soft rocks (including mudstone, phyllite and strongly weathered sandstone) accounted for 35%.

[0086] Finally, the saturated compressive strength of all grain size groups of gravel in each layer was statistically analyzed, and the contents of hard rock, medium-hard rock, and soft rock in each layer (①, ②, ③, ④, ⑤, and ⑥) were determined to obtain the lithological composition of the strata corresponding to each sample, thus completing the lithological identification. The specific lithological identification results are shown in Table 8.

[0087] Table 8

[0088] S24: The mass loss rate results of each layer of the sample obtained from the robustness test in this embodiment are shown in Table 9.

[0089] Table 9

[0090] S25: For gravel with a particle size of 10~20mm, the crushing test results of this embodiment are shown in Table 10.

[0091] Table 10

[0092] S26: Results of the stratified freeze-thaw test Sampling was performed in stratified layers according to depth range, and 25 freeze-thaw cycles were conducted. The experimental data and classification results are shown in Table 11.

[0093] Table 11

[0094] Determination of freeze-thaw impact depth: The depth range of freeze-thaw loss rate >3% is 0~1.5m, so it is recommended that the peeling thickness be 1.5m (in this case, the top surface of layer ③ is at a depth of 2.5m, so all layers above layer ③ need to be peeled).

[0095] S27: Results of Alkali Activity Test Phase 1 (lithological method): Thin section analysis of samples from layers ③ and ④ revealed no active components such as chalcedony or opal, and the content of microcrystalline quartz was approximately 0.5%, below the 1% threshold; Phase 2: Not entered.

[0096] Conclusion: The gravel in this quarry is non-reactive aggregate and can be used directly.

[0097] S3, Calculation of lithological combination coefficient K value and comprehensive quality evaluation stage.

[0098] Taking layer ③ as an example: P H = 58%, P M = 25%, P S = 17%; Clay crust thickness T: 50 gravels were randomly selected from the 5-20 mm particle size group, stained, and the clay crust thickness was measured. Measured values: 0.5-1.5 mm, average T = 0.9 mm. Therefore, the calculated K value is: K = (58 + 25) / (17 + 0.5×0.9) = 83 / (17 + 0.45) = 83 / 17.45 =4.76; The calculation results of K values ​​for each layer are shown in Table 12.

[0099] Table 12

[0100] A comprehensive quality evaluation was conducted by combining K-value, mud content, crushing index, soundness, and freeze-thaw loss rate, and the grading results for each layer are shown in Table 13.

[0101] Table 13

[0102] S4. Calculation of rejection rate.

[0103] (1) Calculate the quality rejection rate R C .

[0104] Layer ⑥ is classified as Grade C, with a volume of 2.169 million m³, representing 2.169 million / 8.985 million = 24.1% of the geological reserves. Therefore, the quality rejection rate R is... C = 24.1%.

[0105] (2) Calculate the freeze-thaw rejection rate R frost .

[0106] Based on Tables 11 and 13, the depth with a freeze-thaw loss rate >3% is 0~1.5m (layer ① + layer ②). The thickness of layer ① + layer ② is 2.5m, accounting for 17.2% of the total thickness of 14.5m. Therefore, the freeze-thaw rejection rate R frost = 17.2%.

[0107] (3) Calculate the grade rejection rate R grad .

[0108] Layer ⑥ has ≥3 missing sieve holes, which has been included in Grade C material. Other layers do not have ≥3 missing sieve holes. Therefore, the gradation rejection rate R... grad = 0.

[0109] (4) Calculate the total rejection rate R grad .

[0110] R reject = 24.1% + 17.2% + 0 = 41.3%; S5, Calculation of credible reserves.

[0111] V PT =898.5 × (1 - 41.3%) = 5,274,000 m³ 3 .

[0112] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Those skilled in the art should understand that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for quality evaluation and reserve determination of river terrace gravel, characterized in that, Includes the following steps: Grid exploration and stratified sampling were carried out on the target river terraces to obtain samples of each stratum. The muddy coating of the sand and gravel in each sample was tested to obtain the average thickness of the muddy coating. The terrace plane area, stratum thickness and loosening coefficient of each stratum were measured and obtained. The geological reserves were calculated based on the terrace plane area, stratum thickness and loosening coefficient. The samples were subjected to particle sieving tests, mud content tests, lithological composition and strength tests, and stratified freeze-thaw tests to obtain the missing strata, mud content, lithological composition, mass loss rate, crushing index and freeze-thaw loss rate of each sample. Based on the lithological composition and the average thickness of the muddy shell, the lithological combination coefficient is calculated. According to the lithological combination coefficient, the mud content, the mass loss rate, the crushing index and the freeze-thaw loss rate, the gravel is divided into three quality grades: A, B and C. The quality rejection rate is determined based on the quality grade; the distribution of the freeze-thaw deterioration layer is divided based on the freeze-thaw loss rate and the freeze-thaw rejection rate is determined; the gradation rejection rate is determined based on the missing grade situation; the quality rejection rate, the freeze-thaw rejection rate and the gradation rejection rate are summed to obtain the total rejection rate. The reliable reserves are calculated based on the geological reserves and the total rejection rate, and the reliable reserves are used as the basis for determining whether the target river terrace can be used as a source of concrete aggregate.

2. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 1, characterized in that, The calculation of the lithological combination coefficient based on the lithological composition specifically includes: The gravel materials of each layer were classified into hard rock, medium hard rock and weak rock according to their saturated compressive strength, and the content of each rock type was counted to obtain the content of hard rock, medium hard rock and weak rock. The lithological combination coefficient K is calculated using the following formula: K = (P H + P M ) / (P S + 0.5 x T) where K is the lithology combination coefficient, dimensionless; P H is the hard rock content, unit is %; P M is the medium hard rock content, unit is %; P S is the soft rock content, unit is %; T is the average thickness of argillaceous envelope, unit is mm.

3. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 1, characterized in that, The step of dividing the distribution of freeze-thaw deteriorated layers and determining the freeze-thaw rejection rate based on the freeze-thaw loss rate specifically includes: Freeze-thaw tests were conducted on the samples at different depth ranges to obtain the freeze-thaw loss rate for each depth range. The stratigraphic intervals corresponding to depths where the freeze-thaw loss rate exceeds the first threshold are designated as freeze-thaw deteriorated layers. The total volume of the freeze-thaw deteriorated layer is statistically analyzed, and the proportion of the total volume of the freeze-thaw deteriorated layer to the geological reserves is calculated to obtain the freeze-thaw removal rate.

4. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 1, characterized in that, Determining the quality rejection rate based on the aforementioned quality level specifically includes: Based on the aforementioned quality grades, the strata corresponding to gravel with a quality grade of C are classified as inferior strata. The quality rejection rate is obtained by calculating the proportion of the sum of the volumes of all the inferior strata to the geological reserves.

5. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 1, characterized in that, The determination of the gradation rejection rate based on the missing grades specifically includes: The gradation elimination rate is obtained by statistically analyzing all strata with gradation deficiencies in the aforementioned missing gradation conditions and calculating the proportion of the sum of the volumes of all strata with gradation deficiencies to the geological reserves.

6. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 1, characterized in that, Before classifying quality grades, the method also includes conducting an alkali activity test, which consists of two stages. The specific execution process includes: In the first stage, the lithofacies method is used to screen for active minerals to obtain the content of active ingredients, and the content of active ingredients is compared with a second threshold. If the content of active ingredients in the sample is not greater than the second threshold, the gravel in the sample is determined to be non-active aggregate and can be used directly. If the content of the active ingredient is greater than the second threshold, then proceed to the second stage of the experiment: The mortar bar rapid test was used to test the samples and obtain the 14-day expansion rate of the gravel. Based on the 14-day expansion rate, the alkali activity level of the gravel was classified and treatment recommendations matching the alkali activity level were determined.

7. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 6, characterized in that, The method of classifying the alkali reactivity level of sand and gravel based on the 14-day expansion rate and determining treatment recommendations that match the alkali reactivity level specifically includes: If the 14-day expansion rate is less than 0.10%, the gravel is determined to be non-reactive aggregate and can be used safely. If the expansion rate of 0.10% ≤ 14d < 0.20%, the gravel is determined to be a potentially reactive aggregate, and further tests are needed to determine its activity. If the 14-day expansion rate is ≥0.20%, the gravel is considered to be reactive aggregate and should not be used directly. It needs to be used in conjunction with other inhibition measures.

8. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 1, characterized in that, Geological reserves were calculated based on the terrace surface area, stratum thickness, and loosening coefficient. The specific calculation formula is as follows: In the formula, A i h represents the area of ​​the i-th terrace plane, in m². i The average thickness of the i-th layer is expressed in meters. λ i is the loosening coefficient of the i-th layer; n is the total number of strata.

9. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 1, characterized in that, The process for determining the lithological composition includes: For each layer of gravel, a number of gravels of the same size were randomly selected according to different particle size groups to carry out uniaxial compressive strength tests to obtain the saturated compressive strength of each gravel. Based on the saturated compressive strength, the gravel is divided into hard rock, medium-hard rock and soft rock. The lithological proportion of each grain size group is counted and the total lithological proportion of each stratum is summarized to obtain the lithological composition of each stratum.

10. The method for quality evaluation and reserve determination of river terrace gravel as described in claim 1, characterized in that, The specific steps of conducting grid exploration and stratified sampling of the target river terraces include: Several test pits were laid out in a grid pattern along the terrace direction and perpendicular to it. Sampling was carried out in equal-thickness layers according to the layers of each natural layer, and sampling was intensified at fixed depth intervals in the freeze-thaw influence zone. Drill holes are laid next to each of the aforementioned pits to simultaneously measure and obtain the plane area of ​​the terrace, the thickness of the stratum, and the loosening coefficient.

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