A soil sample screening system and method

Abstract

The application discloses a soil sample screening system and method, belongs to the technical field of soil detection pretreatment, obtains a soil sample to be screened and a target particle size interval, collects a surface image, a water content and an electrical conductivity, and obtains an aggregate edge continuity degree according to the surface image; a cementation risk value is calculated according to the water content, the electrical conductivity and the aggregate edge continuity degree, when the cementation risk value is greater than or equal to a preset risk threshold value, a pre-loosening intensity, an intermittent air pressure value and a graded screen combination are determined; the soil sample is placed into a screening cavity, low-amplitude vibration pre-loosening is carried out according to the pre-loosening intensity, and reverse pulse air flow is synchronously applied to the graded screen combination according to the intermittent air pressure value; real-time permeation of each screen is obtained, vibration frequency is dynamically adjusted until the permeation per unit time is less than a preset permeation threshold value, and screening is completed; the application can reduce the risk of screen blocking and particle size transfer of wet, sticky and salt film cemented soil.

Description

Technical Field

[0001] This invention relates to the field of soil testing and pretreatment technology, specifically to a soil sample sieving system and method. Background Technology

[0002] In existing technologies, when analyzing soil samples from the edge area of ​​chromium slag dumps after rain for particle size analysis, agglomerates composed of clay particles, water-soluble salts, and tiny chromium salt crystals are often found in the soil. Traditional sieving methods typically involve drying followed by mechanical sieving, which can easily cause the outer salt film of the agglomerates to become brittle, leading to the transfer of pollutant particles originally attached to the fine-grained soil to the coarse-grained residue. Manual dispersing methods, on the other hand, can damage the true particle size structure of the agglomerates. Especially during the sieving process for particles between 100 μm and 500 μm, wet, sticky agglomerates easily clog the sieve openings, resulting in prolonged sieving time, insufficient recovery of fine particles, and consequently affecting the assessment of pollutant spatial distribution and the delineation of remediation boundaries. Summary of the Invention

[0003] The purpose of this invention is to provide a soil sample sieving system and method to address the shortcomings of the prior art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for sieving soil samples, comprising: Obtain the soil sample to be screened and the target particle size range, collect the surface image, moisture content and electrical conductivity of the soil sample to be screened, and obtain the continuity of the aggregate edge based on the surface image; The cementation risk value is calculated based on the moisture content, electrical conductivity, and agglomerate edge continuity. If the cementation risk value is greater than or equal to a preset risk threshold, the pre-loosening strength and intermittent wind pressure value are determined based on the cementation risk value, and the grading screen combination is determined according to the target particle size range. The soil sample to be screened is placed into the screening chamber, and the soil sample to be screened is pre-loosened by low-amplitude vibration according to the pre-loosening intensity. At the same time, a reverse pulse airflow is applied to the grading screen assembly according to the intermittent wind pressure value. The real-time throughput of the graded sieve assembly is obtained, and the vibration frequency is dynamically adjusted according to the real-time throughput until the throughput per unit time of each sieve is less than the preset throughput threshold, thus completing the soil sample sieving.

[0005] Preferably, obtaining the aggregate edge continuity based on the surface image includes: The pixel width is obtained by converting the surface image to pixel scale based on the lower limit of the target particle size range. Using the pixel width as the offset distance, the outline of the aggregates in the surface image is offset inward and outward at equal distances to form a cross-edge sampling ring; Gray-scale variation features are extracted within the cross-edge sampling loop along the tangential direction of the aggregate contour, and the edge continuity of the aggregate is obtained based on the gray-scale variation features.

[0006] Preferably, obtaining the edge continuity of the aggregate based on the grayscale change characteristics includes: Within the cross-edge sampling ring, the mean gray values ​​of the inner and outer sides are obtained along the normal of the aggregate contour, and the gray phase value is calculated. The gray-level phase reversal point is determined based on the sign change of the gray-level phase value of adjacent sampling points; Contour segments whose distance between adjacent grayscale phase reversal points is less than the pixel width are merged into effective continuous edges, and the continuity of the aggregate edge is obtained based on the ratio of the cumulative arc length of the effective continuous edges to the total arc length of the aggregate contour.

[0007] Preferably, the cementation risk value is calculated based on the moisture content, electrical conductivity, and agglomerate edge continuity, including: The moisture content and electrical conductivity were dimensionlessly converted for the same batch to obtain the water film strength value and the salt film strength value, respectively. The harmonic coupling value between the water film strength value and the salt film strength value is calculated, and the harmonic coupling value is amplified by using the edge continuity of the aggregate as a closure gate factor to obtain the edge cementation nucleus value; The bonding risk value is obtained based on the difference between the edge bonding core value and the water film strength value and the salt film strength value.

[0008] Preferably, when the cementation risk value is greater than or equal to a preset risk threshold, determining the pre-loosening strength and intermittent wind pressure value based on the cementation risk value includes: Calculate the difference between the cementation risk value and the preset risk threshold to obtain the risk excess amount, and generate a cementation release coefficient based on the risk excess amount; The cementation release coefficient is constrained by the lower limit of the target particle size range to obtain the constrained cementation release coefficient. The pre-loosening strength is determined based on the bond release coefficient after constraint, and the intermittent wind pressure value is determined based on the difference between the bond release coefficient and the bond release coefficient after constraint.

[0009] Preferably, the grading screen combination is determined according to the target particle size range, including: The upper screen is selected based on the upper limit of the target particle size range, and the lower screen is selected based on the lower limit of the target particle size range. The upper and lower screens are installed in the sieving chamber in descending order of screen mesh size; Based on the intermittent wind pressure value, the lower screen is set as a pulse wind-receiving screen, so that the reverse pulse airflow passes through the screen holes from the back of the lower screen towards the screen surface.

[0010] Preferably, the soil sample to be sieved is pre-loosened by low-amplitude vibration according to the pre-loosening strength, and a reverse pulse airflow is simultaneously applied to the grading screen assembly according to the intermittent wind pressure value, including: The soil sample to be screened is laid on the upper screen without pressing or kneading, and the laying thickness is matched with the upper limit of the target particle size range. A low-amplitude vibration is applied to the sieving chamber according to the pre-loosening strength, causing relative displacement of the cemented aggregates in the soil sample to be sieved; During low-amplitude vibration, a reverse pulse airflow is applied to the pulse-receiving screen according to the intermittent wind pressure value to release the adhesion and blockage at the small-aperture screen.

[0011] Preferably, obtaining the real-time throughput of the graded screen assembly and dynamically adjusting the vibration frequency based on the real-time throughput includes: The real-time throughput of each screen level is statistically analyzed according to the same time window, and the throughput decay curve of each screen level is obtained based on the real-time throughput within the continuous time window. The inter-screen hysteresis is obtained by performing discrete time shift comparison on the attenuation curves of the transmission of two adjacent screens; the screen blockage discrimination value is obtained by combining the inter-screen hysteresis value with the slope of the transmission decrease of the previous screen; and the vibration frequency is adjusted according to the screen blockage discrimination value.

[0012] Preferably, the vibration frequency is adjusted according to the sieve blockage discrimination value until the per-unit-time throughput of each sieve is less than the preset throughput threshold, thereby completing the soil sample sieving, including: When the screen blockage discrimination value increases relative to the previous time window and the increase exceeds the discrimination stability band, the vibration frequency is adjusted to an alternating offset sweep state with the current vibration frequency as the center on both sides. During the frequency sweep process, the real-time transmission rate, inter-screen hysteresis rate, and screen blockage detection rate are continuously updated, and the frequency offset is gradually reduced as the screen blockage detection rate decreases continuously. When the sieve blockage discrimination value decreases and the per-unit-time throughput of each sieve is less than the preset throughput threshold in multiple consecutive time windows, the vibration frequency adjustment is stopped and the soil sample sieving is completed.

[0013] The present invention also provides a soil sample sieving system, comprising: The sample feature acquisition module acquires the soil sample to be screened and the target particle size range, collects the surface image, moisture content and electrical conductivity of the soil sample to be screened, and obtains the continuity of the aggregate edge based on the surface image. The cementation risk control module calculates the cementation risk value based on the moisture content, electrical conductivity, and agglomerate edge continuity. If the cementation risk value is greater than or equal to a preset risk threshold, it determines the pre-loosening strength and intermittent wind pressure value based on the cementation risk value, and determines the grading screen combination according to the target particle size range. The pre-loosening and pulse execution module places the soil sample to be screened into the screening chamber, performs low-amplitude vibration pre-loosening on the soil sample according to the pre-loosening intensity, and simultaneously applies reverse pulse airflow to the grading screen assembly according to the intermittent wind pressure value. The dynamic sieving feedback module obtains the real-time throughput of the graded sieve combination and dynamically adjusts the vibration frequency according to the real-time throughput until the throughput per unit time of each sieve is less than the preset throughput threshold, thus completing the sieving of the soil sample.

[0014] The technical effects and advantages provided by the present invention in the above technical solution are as follows: This invention differs from existing technologies that involve drying followed by mechanical sieving or manual kneading before sieving. Its core lies in starting with the actual surface morphology of the soil sample to be sieved, converting the lower limit of the target particle size range into an image analysis scale. It identifies the continuity of aggregate edges through cross-edge sampling rings, gray-scale phase reversal points, and effective continuous edges. Then, it combines moisture content and conductivity to determine the cementation risk caused by water film, salt film, and edge closure. This method does not rely solely on empirical sieving based on sample humidity or salinity; instead, it uses whether aggregates form continuous cementation boundaries at the target particle size scale as a control criterion. It can identify latent cemented aggregates formed by wet, sticky fine particles and salt films in scenarios such as the edge areas of chromium slag dumps after rain and saline-alkali contaminated sites. Therefore, it can determine which samples are at risk of sieve blockage and particle size transfer before formal sieving, avoiding direct strong vibration that could cause aggregate breakage and cross-size migration of fine pollutants, thus improving the authenticity and stability of sample recovery within the target particle size range.

[0015] This invention further distinguishes itself from existing sieving methods using fixed frequency and fixed air pressure. Its core lies in determining the pre-loosening strength and intermittent air pressure value based on the cementation risk value, and setting the small-aperture screen as a pulsed airflow screen. This allows low-amplitude vibration and reverse pulsed airflow to act synchronously on the sample layer and easily clogged sieve holes. Low-amplitude vibration loosens the weak connections of the water film and salt film on the outside of the aggregates, while the reverse pulsed airflow removes the adhesion of wet, sticky particles and salt film cement from the back of the screen to the small-aperture sieve holes. These two aspects respectively address the two practical physical problems of "aggregate loosening" and "sieve hole unclogging," avoiding particle breakage caused by simply increasing vibration intensity. Subsequently, the real-time throughput of each sieve level is used to form the inter-sieve hysteresis and sieve clogging discrimination values. A frequency sweep method with alternating offsets on both sides of the current vibration frequency is used to break up bridging on the sieve surface. This allows the sieving process to adaptively intervene before clogging is fully formed, thereby reducing sieve hole clogging, shortening sieving time, and reducing the risk of cross-level migration of target particle size samples. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0017] Figure 1 This is a flowchart of the method of the present invention.

[0018] Figure 2 This is a flowchart of the system modules of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1, please refer to Figure 1 As shown in this embodiment, a soil sample sieving method includes: Obtain the soil sample to be screened and the target particle size range, collect the surface image, moisture content and electrical conductivity of the soil sample to be screened, and obtain the continuity of the aggregate edge based on the surface image.

[0021] In one possible embodiment of the present invention, when obtaining the soil sample to be screened and the target particle size range, the target particle size range is determined according to the requirements of subsequent soil pollutant detection or particle size analysis, denoted as [dmin, dmax], where dmin is the lower limit particle size of the target particle size range and dmax is the upper limit particle size of the target particle size range. The soil sample to be screened is a sample obtained by uniformly reducing it after the same sampling. During the reduction process, the soil is not rubbed, crushed, or ground to avoid artificially damaging the original aggregate structure.

[0022] The soil samples to be screened were laid flat on a support surface, maintaining a visible gap between adjacent aggregates and exposing their outer surfaces. Surface images of the soil samples were then acquired, and moisture content and electrical conductivity were simultaneously measured from the same batch of samples. Moisture content characterizes the effect of water film and capillary water on aggregate adhesion strength, while electrical conductivity characterizes soluble salt content and salt film cementation tendency. Moisture content can be obtained by weighing or moisture sensing, and electrical conductivity can be obtained by measuring the conductivity of the soil-water mixture formed from the same batch of samples to ensure consistency between the moisture content, electrical conductivity, and the sample state corresponding to the surface images.

[0023] Before acquiring the surface image, the imaging field of view is pixel-calibrated to obtain the number of pixels k corresponding to a unit actual length, and then the formula is used. The lower limit particle size dmin of the target particle size range is converted into a pixel width Wp. The pixel width Wp serves as the ring width of the cross-edge sampling ring, ensuring that the image analysis scale corresponds to the smallest target particle size to be identified in subsequent sieving. The rationale for using dmin as the ring width is that edge grayscale perturbations smaller than dmin typically do not form independent target particle sizes in subsequent sieving; treating them as true edge breaks would result in low continuity of agglomerate edges. In contrast, continuous boundary changes larger than dmin are more likely to correspond to true agglomerate structures that can affect sieve clogging and particle size transfer.

[0024] If the calculated pixel width Wp is less than the preset minimum resolvable pixel width Wmin, the surface image is re-acquired after adjusting the imaging magnification. Wmin can be determined through a standard particle calibration experiment. Specifically, select a standard particle with a particle size close to dmin, continuously acquire multiple images and extract its edge position. When the deviation of the repeatedly extracted edge position is no greater than 10% of dmin, the corresponding pixel width is taken as Wmin. The 10% selection is based on the fact that when the edge positioning error is controlled within one-tenth of the lower limit of the target particle size, this error will not change the judgment result of whether the aggregate can pass through the target sieve, thus ensuring the stability of subsequent grayscale phase inversion calculations.

[0025] After obtaining the surface image, it is converted to grayscale, and the aggregate contours are extracted based on the regions of abrupt grayscale gradient changes. For each extracted aggregate contour, using the pixel width Wp as the offset distance, it is offset equidistantly inward and outward along the normal of the aggregate contour to obtain the inner and outer contours. A cross-edge sampling loop is formed by the area between the inner and outer contours. This cross-edge sampling loop simultaneously covers the inner edge region of the aggregate and the outer background region of the aggregate, thus reflecting the grayscale transition characteristics at the aggregate edge caused by particle adhesion, water film connection, or salt film cementation.

[0026] Sampling points are selected sequentially along the tangential direction of the aggregate contour according to a preset sampling step size, wherein the preset sampling step size is less than or equal to The sampling step size is selected based on the principle that when the distance between adjacent sampling points does not exceed half the width of the ring, it ensures that at least two sampling points cover an edge variation region at the dmin scale, avoiding missed detection of discontinuous edge positions corresponding to the lower limit of the target particle size. For each sampling point, the inner gray-level mean Gin and the outer gray-level mean Gout are obtained along the normal direction within the cross-edge sampling ring, and the gray-level phase value is calculated. When the sign of the gray phase value P of two adjacent sampling points changes, it is determined that there is a gray phase reversal point between the two adjacent sampling points; where the sign changes, it means that P changes from a positive value to a negative value, or from a negative value to a positive value.

[0027] To avoid misjudgments caused by tiny salt film bright spots, local shadows, or small pores, after obtaining the grayscale phase reversal points, the distance between adjacent grayscale phase reversal points along the aggregate contour direction is calculated. If this distance is less than the pixel width Wp, the contour segment between the two grayscale phase reversal points is considered a local disturbance smaller than the lower limit of the target particle size, and this contour segment is merged with its adjacent edge segments in the same direction before and after it as part of the effective continuous edge. If the distance between adjacent grayscale phase reversal points is greater than or equal to the pixel width Wp, the contour segment is considered to correspond to a true edge discontinuity that can affect subsequent sieving, and it is not included in the effective continuous edge. Thus, small-scale noise will not cut off the aggregate edge, while true discontinuity reaching the target particle size scale can be preserved, making the obtained edge continuity match the risk of sieve clogging during the sieving process.

[0028] For a single aggregate, the cumulative arc length L1 of its effective continuous edges is calculated, and the total arc length L0 of the aggregate's outline is also calculated. The ratio of L1 to L0 is taken as the edge continuity of the aggregate. When multiple aggregates exist in the surface image, the edge continuity of each aggregate is calculated separately, and a weighted average is performed using the total arc length of each aggregate's outline as the weight to obtain the edge continuity of the aggregates in the soil sample to be screened. The reason for using the total arc length as the weight is that aggregates with longer outlines have a higher probability of contacting the screen, bridging, or clogging during the screening process, and their edge continuity has a greater impact on the overall screening result.

[0029] The resulting aggregate edge continuity is used in conjunction with moisture content and electrical conductivity to calculate the cementation risk value. Higher aggregate edge continuity indicates more complete boundaries of the aggregates in the soil sample to be sieved at the target particle size scale, making them more likely to remain as whole aggregates on the sieve surface or clog the sieve openings during subsequent vibration sieving. Lower aggregate edge continuity indicates more discontinuous regions at the aggregate edges reaching the target particle size scale, making them more prone to separation along weakly connected locations during subsequent low-amplitude vibration pre-loosening. Through this method, the image analysis results can directly serve the subsequent calculation of cementation risk value, determination of pre-loosening strength, and determination of intermittent wind pressure value, thereby improving the stability of the sieving process and the accuracy of the particle size results for the soil samples to be sieved.

[0030] The cementation risk value is calculated based on the moisture content, electrical conductivity, and agglomerate edge continuity. If the cementation risk value is greater than or equal to a preset risk threshold, the pre-loosening strength and intermittent wind pressure value are determined based on the cementation risk value, and the grading screen combination is determined according to the target particle size range.

[0031] Specifically, the moisture content of the current soil sample to be screened is denoted as M, the electrical conductivity as C, and the continuity of aggregate edges as E, where E is a value between 0 and 1. First, the moisture content M and electrical conductivity C are processed to be dimensionless for the same batch. The same batch refers to several soil samples to be screened that originate from the same sampling area, have the same testing purpose, and are stored under the same conditions. The maximum and minimum moisture contents in the same batch are denoted as Mmax and Mmin, respectively, and the maximum and minimum electrical conductivity are denoted as Cmax and Cmin, respectively. The water film strength W and salt film strength S of the current soil sample to be screened are determined as follows: When the difference between Mmax and Mmin is less than the resolution of the moisture content measurement, a pre-calibrated effective range of moisture content for similar soil samples is used to replace Mmax and Mmin; similarly, when the difference between Cmax and Cmin is less than the resolution of the conductivity measurement, a pre-calibrated effective range of conductivity for similar soil samples is used to replace Cmax and Cmin. The effective range can be obtained by sampling and measuring similar soil samples multiple times, and then removing obvious outliers. This avoids distortion of dimensionless results when the differences between samples from the same batch are too small.

[0032] The water film strength value W represents the relative contribution of the water film or capillary water to particle adhesion in the current sample, while the salt film strength value S represents the relative contribution of soluble salt or salt film crystals to particle cementation. To avoid misjudging a composite cementation state by either value being excessively high, this embodiment further calculates the harmonic coupling value H between the water film strength value W and the salt film strength value S. Specifically, when W + S = 0, H = 0; when W + S > 0, H = 2WS / (W + S).

[0033] It should be noted that the harmonic coupling value is used because soil sample cementation typically requires a water film to provide an adhesion medium, while a salt film or soluble salt crystals are needed to form a connecting structure. When either the water film strength value W or the salt film strength value S is low, the harmonic coupling value H decreases significantly as the lower term decreases, thus highlighting the cementation contribution when both water and salt films are present.

[0034] Subsequently, using the aggregate edge continuity E as a closure gating factor, the harmonic coupling value H is amplified to obtain the edge cementation nucleus value K. Specifically, the following can be used: Where λ is the edge closure amplification factor. λ can be determined through pre-screening calibration: select multiple groups of soil samples with different moisture contents, electrical conductivity, and aggregate edge continuity, and screen them under the same vibrating sieve conditions. Record the proportion of the pore-closing area of ​​the lower sieve or the attenuation rate of per-unit-time transmission. Adjust λ so that when there is a monotonic correspondence between the edge cementation nucleus value K and the proportion of the pore-closing area or the attenuation rate of per-unit-time transmission, the corresponding λ is taken as the edge closure amplification factor. The reason for amplifying the high continuity state is that low edge continuity usually indicates that there are many weakly connected areas in the agglomerates, and the contribution of edge closure to the risk of cementation is small. When the edge continuity is close to a high level, the agglomerates are more likely to remain on the screen surface or bridge and block the holes as a whole, so it is necessary to amplify the high continuity state more significantly.

[0035] Then, based on the difference between the edge bonding core value K and the larger of the water film strength value W and the salt film strength value S, the bonding risk value R is obtained. Specifically: Where max(W, S) represents the maximum relative impact that a single factor can produce. This differential method is used to extract the additional cementing risk generated by the combined effects of water film, salt film, and edge closure. When the edge cementing nucleus value K does not exceed the maximum value of a single factor, it indicates that the sample mainly exhibits single characteristics of moisture or single high salinity, and is not considered to form a significant complex cementing structure. When the edge cementing nucleus value K exceeds the maximum value of a single factor, it indicates that there is a complex cementing risk in the sample caused by the combined effects of water film, salt film, and continuous agglomerated edges.

[0036] In this embodiment, the preset risk threshold R0 is determined through a pre-screening test of similar soil samples. Specifically, multiple groups of similar soil samples are screened using a conventional vibrating sieve method, and the cementation risk value R, the proportion of sieve clogging area, the permeability decay rate per unit time, and the recovery rate of the target particle size range are recorded simultaneously. When the proportion of sieve clogging area exceeds three standard deviations of the average clogging area proportion of normal samples, or when the permeability per unit time continuously decreases below the average permeability of normal samples during continuous detection, the screening state is defined as an abnormal cementation state; the critical cementation risk value that can distinguish between the normal screening state and the abnormal cementation state is taken as the preset risk threshold R0. Therefore, the preset risk threshold R0 is not arbitrarily set, but corresponds to the actual sieve clogging and permeability decay results.

[0037] When the bonding risk value R is greater than or equal to the preset risk threshold R0, the risk excess D is calculated: The cementation release coefficient Q is generated based on the risk exceeding the limit D. Specifically, the following can be used: Where D50 is the half-release risk level, representing the risk exceeding the limit when the proportion of screen hole blockage area or the unit time permeability decay rate is improved to half of the abnormal state during pre-screening calibration. Using the above method, the cementation release coefficient Q increases with the risk exceeding the limit D, and always remains between 0 and 1. When the risk just exceeds the threshold, Q is small to avoid overly strong control; when the risk significantly exceeds the threshold, Q gradually increases to improve the degree of pre-loosening and reverse pulse treatment.

[0038] Subsequently, the cementation release coefficient Q is constrained by the lower limit particle size dmin of the target particle size range, resulting in the constrained cementation release coefficient Qd. Specifically: Wherein, dref is the particle size constraint reference value, and dmin and dref use the same length unit. dref can be obtained by calibrating the vibration intensity of similar soil samples. Specifically, the low-amplitude vibration intensity is gradually increased, and the particle size scale corresponding to when the sample in the target particle size range begins to show signs of breakage or cross-size migration is recorded, and this particle size scale is used as dref. The design principle of the above constraint relationship is that when dmin is small, subsequent sieving needs to retain finer particle size boundaries, and excessive vibration can easily cause particle size transfer, so Qd is restricted to a lower value; when dmin is large, the pre-loosening effect that the sample can withstand is relatively increased, and Qd increases accordingly.

[0039] The pre-loosening strength Iv is determined based on the bond release coefficient Qd after constraint. The pre-loosening strength Iv can be expressed as low-amplitude vibration acceleration, vibration energy level, or vibration intensity level identifiable by the equipment, specifically: Wherein, Imin is the minimum pre-loosening strength that can cause slight relative displacement of the sample layer without causing aggregate breakage, and Imax is the maximum pre-loosening strength, confirmed by calibration, that will not cause cross-size migration of samples within the target particle size range. Imin and Imax are determined through pre-loosening calibration tests: when different low-amplitude vibration intensities are applied to similar soil samples, if the recovery rate within the target particle size range is within the allowable error range and the aggregates on the sample surface do not show significant fragmentation, then this strength can be used as the usable strength range. Therefore, the pre-loosening strength Iv can increase with increasing cementation risk, while being limited by the lower limit particle size of the target particle size range.

[0040] After determining the pre-loosening strength Iv, the intermittent air pressure value P is determined according to the reverse compensation relationship. The intermittent air pressure value P is the peak gauge pressure acting on the back of the screen during the onset phase of the reverse pulse airflow, specifically: Wherein, Pmin is the minimum air pressure that can form a reverse airflow on the back of the sieve without significantly disturbing the sample layer, and Pmax is the maximum air pressure that will not cause particles in the target particle size range to be blown off the sieve surface or to migrate across sizes. Pmin and Pmax can be determined through empty sieve pressure drop tests and sample sieving tests: first, determine the minimum reverse airflow pressure that can pass through the sieve holes in the empty sieve state, and then gradually increase the air pressure in the sample state until abnormal migration of fine particles occurs or the mass loss in the target particle size range exceeds the allowable error, and take the previous air pressure as Pmax. The reason for using Q-Qd as the air pressure compensation is that when dmin is small and the pre-loosening strength is limited, the remaining release demand is large, and it is necessary to use reverse pulse airflow to remove the adhesion and blockage at the small aperture sieve; when the pre-loosening strength is sufficient to release most of the cemented structure, the intermittent air pressure is reduced to avoid particle size disturbance caused by airflow.

[0041] Finally, the grading sieve combination is determined according to the target particle size range [dmin, dmax]. Specifically, an upper sieve with an aperture corresponding to dmax and a lower sieve with an aperture corresponding to dmin are selected and installed in descending order of aperture size. The soil sample to be sieved first passes through the upper sieve, where particles larger than dmax are retained; after passing through the upper sieve, they reach the lower sieve, where particles smaller than dmin pass through; the portion retained on the lower sieve is the soil sample corresponding to the target particle size range.

[0042] When no standard screen has an aperture size exactly matching dmin or dmax, the standard screen aperture size closest to dmin or dmax that does not alter the target particle size distribution is selected. "Does not alter the target particle size distribution" means the screen aperture error is less than a preset proportion of the target particle size range width; this proportion can be determined by the allowable error of the detection method. Since the lower-level screen with smaller apertures is more easily clogged by wet, sticky particles, salt film cement, or micro-agglomerates, based on the determined intermittent wind pressure value P, the lower-level screen with smaller apertures is set as a pulsed airflow screen, so that the reverse pulsed airflow acts on the back side of this lower-level screen.

[0043] In this embodiment, the cementation risk value R is jointly determined by the moisture content, electrical conductivity, and the continuity of agglomerate edges; the pre-loosening strength Iv is jointly constrained by the cementation risk value and the lower limit particle size of the target particle size range; the intermittent wind pressure value P compensates for the cementation risk that cannot be released through pre-loosening due to particle size limitations; and the graded sieve combination directly corresponds to the target particle size range. Thus, a continuous correlation is formed between the steps, which can reduce sieve clogging while minimizing sample breakage and cross-grade migration within the target particle size range.

[0044] The soil sample to be screened is placed into the screening chamber, and the soil sample is pre-loosened by low-amplitude vibration according to the pre-loosening intensity. At the same time, a reverse pulse airflow is applied to the grading screen assembly according to the intermittent wind pressure value.

[0045] In one embodiment of the present invention, after determining the pre-loosening strength and the intermittent wind pressure value, the grading screens are assembled and installed in the sieving chamber, with the screen with larger apertures positioned above the screen with smaller apertures, serving as the pulse-flow receiving screen. An airflow buffer space is provided below the pulse-flow receiving screen, allowing the reverse pulse airflow to pass through the screen openings from the back of the screen towards the screen surface. This arrangement aims to ensure that the reverse pulse airflow preferentially acts on the smaller aperture screen, which is most prone to wet adhesion and clogging, rather than directly blowing away the soil sample to be sieved from above.

[0046] When placing the soil sample to be screened into the screening chamber, first spread it evenly on the upper screen of the grading screen assembly. During the spreading process, do not press, knead, or crush the soil sample. The spreading thickness can be determined based on the upper limit of the target particle size range, for example, controlled to be 1 to 3 times the upper limit particle size. This range is selected because if the spreading is too thin, the sample will not have sufficient contact with the screen surface, resulting in unstable pre-loosening; if the spreading is too thick, the upper agglomerates will not be able to be subjected to the combined effects of low-amplitude vibration and reverse airflow in time, easily leading to localized accumulation. If the sample volume is large, it can be placed into the screening chamber in batches to ensure that each batch of samples meets the above spreading thickness requirements.

[0047] After the soil samples are placed in the sieving chamber, low-amplitude vibration is applied to pre-loosen the sieving chamber according to the pre-loosening intensity. The pre-loosening intensity can correspond to the vibration acceleration, amplitude, or vibration level of the vibration actuator. When the equipment uses amplitude and frequency control, a correspondence table between pre-loosening intensity and amplitude and frequency can be established in advance through equipment calibration, and the corresponding amplitude and frequency can be called according to the determined pre-loosening intensity. The amplitude of the low-amplitude vibration is preferably less than the lower limit of the target particle size range. The design principle is that the vibration can destroy the weak cementation of the water film and salt film on the outside of the aggregates, but is insufficient to break the actual particle structure within the target particle size scale, thereby reducing cross-level migration.

[0048] While initiating low-amplitude vibration pre-loosening, a reverse pulse airflow is applied to the grading screen assembly according to the intermittent wind pressure value. Specifically, the pulse airflow is controlled to pass from below the pulse-receiving screen through the screen openings, and the peak gauge pressure during the pulse initiation phase is the intermittent wind pressure value. The reverse pulse airflow is not continuous but applied intermittently; this is because continuous airflow can easily cause fine-grained soil to remain suspended or shift for a long time, while intermittent pulses can quickly remove the wet adhesions at the edges of the screen openings, and then the closing interval allows the disturbed fine particles to fall back to the vicinity of the screen surface. The pulse initiation and closing times can be determined through pre-screening tests, specifically based on the ability of the adhering material at the screen openings to be blown away and the sample mass loss within the target particle size range not exceeding the allowable detection error.

[0049] During the synchronous processing, low-amplitude vibration pre-loosening causes slight relative displacement of cemented aggregates in the soil sample to be screened, exposing weakly connected areas at the edges of the aggregates. The reverse pulsed airflow creates a momentary back-pushing effect on the back of the sieve openings, causing the loosened wet, sticky particles or salt film cement to detach from the sieve opening edges. Since the pre-loosening strength is determined by the cementation risk value and the lower limit of the target particle size range, and the intermittent air pressure value is determined by compensating for the remaining cementation risk not released by the pre-loosening strength, the two actions work in synergy: vibration reduces the overall cementation strength of the aggregates, while airflow relieves localized blockages at the small-aperture sieve openings.

[0050] Low-amplitude vibration pre-loosening and reverse pulse airflow continue until the preset pretreatment time ends, or until the sample layer in the sieving chamber changes from a continuous blocky accumulation to a loose state that can slide relative to the sieve surface due to vibration. The preset pretreatment time can be obtained through calibration with similar soil samples, and is selected based on the critical time when the increase in the throughput of the target particle size range is not significant when the treatment time is further extended, but the risk of breakage or cross-size migration begins to increase. In this way, the soil sample to be sieved is pre-loosened in a controlled manner before formal sieving, and the small-aperture sieve simultaneously receives reverse pulse pore-cleaning effect during the pre-loosening stage, thereby reducing the risk of sieve clogging and particle size transfer during the subsequent sieving process.

[0051] The real-time throughput of the graded sieve assembly is obtained, and the vibration frequency is dynamically adjusted according to the real-time throughput until the throughput per unit time of each sieve is less than the preset throughput threshold, thus completing the soil sample sieving.

[0052] In one embodiment of the present invention, after completing the low-amplitude vibration pre-loosening and reverse pulse airflow treatment, the process enters the dynamic sieving stage. The dynamic sieving stage uses the real-time throughput of each level of screen in the graded screen assembly as feedback to dynamically adjust the vibration frequency. The graded screen assembly includes at least two levels of screens, and the screens are arranged from top to bottom in descending order of aperture size.

[0053] Transmission measurement units are installed below each level of screen or on the screen outlet side to collect the transmission volume of the corresponding screen per unit time. For the upper screen, the transmission volume is the amount of sample passing through the upper screen and entering the area of ​​the next screen; for the bottom screen, the transmission volume is the amount of sample passing through the bottom screen and entering the bottom receiving area. The transmission volume measurement unit can adopt weighing measurement, material flow rate measurement, or light curtain particle throughput measurement methods, as long as it can obtain the amount of sample passing through the corresponding screen within the same time window.

[0054] Specifically, the real-time throughput of each screen level is statistically analyzed according to the same time window Δt. For the i-th screen, the real-time throughput in the n-th time window is denoted as Qi(n). The Qi(n) values ​​from multiple consecutive time windows are arranged in chronological order to obtain the throughput decay curve corresponding to the i-th screen. The time window Δt is determined based on the vibration frequency and the reverse pulse airflow period. Ideally, a time window should contain multiple complete vibration cycles and cover at least one opening and closing process of the reverse pulse airflow. This setting reduces the interference of single material drop fluctuations on the throughput decay curve while ensuring that changes in screen blockage can be captured in a timely manner.

[0055] After obtaining the transmission decay curves corresponding to each level of screen, the inter-screen hysteresis is calculated for adjacent screen levels. Taking the i-th level screen and the (i+1)-th level screen as an example, within the current observation interval, the transmission decay curve Qi of the i-th level screen and the transmission decay curve Q(i+1) of the (i+1)-th level screen are compared by discrete-time shift. Each shift is performed by a time window Δt, and the consistency of the changing trends of the two curves after the shift is calculated. The consistency of the changing trends can be expressed as the proportion of the increase or decrease in transmission in adjacent time windows being consistent, or as the first-order difference correlation coefficient after normalization of the two curves. When the consistency of the changing trends reaches its maximum value, the corresponding shift time is the inter-screen hysteresis Ti between the i-th level screen and the (i+1)-th level screen.

[0056] The inter-screen hysteresis Ti is used to characterize the degree of delay in the response of material on the next screen after it passes through the previous screen. If the inter-screen hysteresis Ti is small, it means that the change in the passage of material through the previous screen can be transmitted to the next screen in a timely manner; if the inter-screen hysteresis Ti increases, it means that the material may be retained on the previous screen surface, between the two screens, or at the inlet of the next screen surface, thus posing a risk of bridging or local clogging of the screen.

[0057] Simultaneously, the transmittance decrease slope Ai is calculated based on the transmittance decay curve of the previous stage screen. Specifically, within the current time window, the transmittance difference between the two time windows before and after the i-th stage screen is divided by the time window Δt, and a positive value is taken when the transmittance decreases from high to low, i.e.: Subsequently, the inter-sieve hysteresis Ti and the throughput decrease slope Ai are combined to obtain the clogging discrimination quantity Bi. Specifically, the inter-sieve hysteresis Ti is first normalized by dividing it by the length of the observation interval to obtain the normalized hysteresis; then the throughput decrease slope Ai is normalized by dividing it by the average decrease slope corresponding to the initial stable throughput of the sieve to obtain the normalized decrease; finally, the two are weighted and summed to obtain the clogging discrimination quantity Bi. The weights can be determined through pre-experiments with normal sieving samples and known clogging samples, so that the clogging discrimination quantity Bi is significantly higher in clogging samples than in normal samples. This combination method can distinguish between a decrease in throughput caused by the end of normal sieving and an abnormal decrease in throughput caused by bridging on the sieve surface: the former is usually not accompanied by a significant increase in inter-sieve hysteresis, while the latter is simultaneously characterized by a rapid decrease in throughput of the previous stage and a delayed response of adjacent sieves.

[0058] During dynamic sieving, the clogging discrimination value Bi is continuously updated. When the clogging discrimination value Bi of the current time window increases compared to the previous time window, and the increase exceeds the discrimination stability band, it is determined that there is bridging on the screen surface or a local clogging trend. The discrimination stability band is determined by the fluctuation range of the clogging discrimination value under normal sieving conditions, for example, by using a multiple of the standard deviation of the clogging discrimination value fluctuation in repeated normal sieving tests as the discrimination stability band. This setting can avoid frequent adjustments to the vibration frequency due to occasional material drop, sensor noise, or the passage of a single large particle.

[0059] When the sieve clogging discrimination value Bi increases, the vibration frequency is adjusted from the current vibration frequency fc to a sweeping state that alternates between the two sides of the current vibration frequency. The sweeping state includes: first adjusting the vibration frequency to fc + Δf and maintaining it for one half-cycle, then adjusting the vibration frequency to fc - Δf and maintaining it for one half-cycle, and repeating this cycle. The frequency offset Δf is determined based on the increase in the sieve clogging discrimination value Bi; the more significant the increase in Bi, the larger Δf; however, Δf does not exceed a preset offset upper limit. The preset offset upper limit is determined through sieve calibration tests on similar soil samples, and is selected based on the ability to break up bridging on the sieve surface within this offset range, while ensuring that the breakage rate or cross-grade migration of samples within the target particle size range does not exceed the allowable detection error.

[0060] The half-cycle of the frequency sweep can be determined based on the response time of the sample layer on the sieve surface. Specifically, it can be observed through preliminary experiments to determine the time required for the transmission to begin to stabilize after a change in vibration frequency, and this time can be used as the lower limit of the half-cycle. If the half-cycle is too short, the sample layer has not yet formed an effective relative displacement, making it difficult to break the bridging; if the half-cycle is too long, it will approach a fixed frequency vibration and cannot form an effective disturbance. Therefore, the half-cycle of the frequency sweep is selected as a time range that can induce a transmission response without causing the sample layer to re-stabilize and re-bridge.

[0061] During the frequency sweep process, the real-time throughput of each screen level is continuously counted according to the same time window Δt, and the throughput attenuation curve, inter-screen hysteresis Ti, and screen blockage discrimination value Bi are updated in real time. If the screen blockage discrimination value Bi decreases for several consecutive time windows, it indicates that the bridging or local screen blockage on the screen surface is being resolved. At this time, the frequency offset Δf is gradually reduced to bring the vibration frequency back to near the stable frequency required for the current screening. If the screen blockage discrimination value Bi continues to increase, the frequency offset Δf is maintained or appropriately increased under the condition that it does not exceed the preset offset upper limit.

[0062] When the sieve clogging discrimination value Bi decreases and the per-unit-time throughput of each sieve level is less than the preset throughput threshold, the vibration frequency adjustment is stopped and the soil sample sieving is completed. The preset throughput threshold is determined based on repeated sieving tests of similar soils. Specifically, in the later stages of sieving, the sieving time is extended. If the mass of the newly added sample in the target particle size range is less than the allowable detection error, and the newly added throughput corresponding to each sieve level is close to the noise level of the metrology unit, then the per-unit-time throughput at this time is taken as the preset throughput threshold. To avoid misjudgment caused by instantaneous low throughput, it is preferable to require that the per-unit-time throughput of each sieve level is less than the preset throughput threshold for multiple consecutive time windows before determining that the sieving is complete.

[0063] In this embodiment, the real-time throughput first generates throughput decay curves corresponding to each level of screen. These curves further yield inter-screen hysteresis and throughput decline slope. The combination of inter-screen hysteresis and throughput decline slope provides a screen clogging detection factor, which is then used to control the vibration frequency to enter or exit the frequency sweep state. This allows for the identification of bridging trends on the screen surface before complete clogging, and the breaking of bridging structures through alternating frequency shifts, thereby reducing screen clogging, shortening sieving time, and mitigating the risk of target particle size range breakage and cross-level migration caused by continuous high-intensity vibration.

[0064] Example 2, please refer to Figure 2 As shown in this embodiment, a soil sample sieving system includes: The sample feature acquisition module acquires the soil sample to be screened and the target particle size range, collects the surface image, moisture content and electrical conductivity of the soil sample to be screened, and obtains the continuity of the aggregate edge based on the surface image. The cementation risk control module calculates the cementation risk value based on the moisture content, electrical conductivity, and agglomerate edge continuity. If the cementation risk value is greater than or equal to a preset risk threshold, it determines the pre-loosening strength and intermittent wind pressure value based on the cementation risk value, and determines the grading screen combination according to the target particle size range. The pre-loosening and pulse execution module places the soil sample to be screened into the screening chamber, performs low-amplitude vibration pre-loosening on the soil sample according to the pre-loosening intensity, and simultaneously applies reverse pulse airflow to the grading screen assembly according to the intermittent wind pressure value. The dynamic sieving feedback module obtains the real-time throughput of the graded sieve combination and dynamically adjusts the vibration frequency according to the real-time throughput until the throughput per unit time of each sieve is less than the preset throughput threshold, thus completing the sieving of the soil sample.

[0065] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for sieving soil samples, characterized in that, include: Obtain the soil sample to be screened and the target particle size range, collect the surface image, moisture content and electrical conductivity of the soil sample to be screened, and obtain the continuity of the aggregate edge based on the surface image; The cementation risk value is calculated based on the moisture content, electrical conductivity, and agglomerate edge continuity. If the cementation risk value is greater than or equal to a preset risk threshold, the pre-loosening strength and intermittent wind pressure value are determined based on the cementation risk value, and the grading screen combination is determined according to the target particle size range. The soil sample to be screened is placed into the screening chamber, and the soil sample to be screened is pre-loosened by low-amplitude vibration according to the pre-loosening intensity. At the same time, a reverse pulse airflow is applied to the grading screen assembly according to the intermittent wind pressure value. The real-time throughput of the graded sieve assembly is obtained, and the vibration frequency is dynamically adjusted according to the real-time throughput until the throughput per unit time of each sieve is less than the preset throughput threshold, thus completing the soil sample sieving.

2. The method for sieving soil samples according to claim 1, characterized in that, The step of obtaining the continuity of aggregate edges based on the surface image includes: The pixel width is obtained by converting the surface image to pixel scale based on the lower limit of the target particle size range. Using the pixel width as the offset distance, the outline of the aggregates in the surface image is offset inward and outward at equal distances to form a cross-edge sampling ring; Gray-scale variation features are extracted within the cross-edge sampling loop along the tangential direction of the aggregate contour, and the edge continuity of the aggregate is obtained based on the gray-scale variation features.

3. The method for sieving soil samples according to claim 2, characterized in that, The continuity of the aggregate edge is obtained based on the grayscale change characteristics, including: Within the cross-edge sampling ring, the mean gray values ​​of the inner and outer sides are obtained along the normal of the aggregate contour, and the gray phase value is calculated. The gray-level phase reversal point is determined based on the sign change of the gray-level phase value of adjacent sampling points; Contour segments whose distance between adjacent grayscale phase reversal points is less than the pixel width are merged into effective continuous edges, and the continuity of the aggregate edge is obtained based on the ratio of the cumulative arc length of the effective continuous edges to the total arc length of the aggregate contour.

4. The method for sieving soil samples according to claim 3, characterized in that, The cementation risk value is calculated based on the moisture content, electrical conductivity, and agglomerate edge continuity, including: The moisture content and electrical conductivity were dimensionlessly converted for the same batch to obtain the water film strength value and the salt film strength value, respectively. The harmonic coupling value between the water film strength value and the salt film strength value is calculated, and the harmonic coupling value is amplified by using the edge continuity of the aggregate as a closure gate factor to obtain the edge cementation nucleus value; The bonding risk value is obtained based on the difference between the edge bonding core value and the water film strength value and the salt film strength value.

5. A method for sieving soil samples according to claim 4, characterized in that, When the cementation risk value is greater than or equal to a preset risk threshold, the pre-loosening strength and intermittent wind pressure value are determined based on the cementation risk value, including: Calculate the difference between the cementation risk value and the preset risk threshold to obtain the risk excess amount, and generate a cementation release coefficient based on the risk excess amount; The cementation release coefficient is constrained by the lower limit of the target particle size range to obtain the constrained cementation release coefficient. The pre-loosening strength is determined based on the bond release coefficient after constraint, and the intermittent wind pressure value is determined based on the difference between the bond release coefficient and the bond release coefficient after constraint.

6. The method for sieving soil samples according to claim 1, characterized in that, The grading screen combination is determined according to the target particle size range, including: The upper screen is selected based on the upper limit of the target particle size range, and the lower screen is selected based on the lower limit of the target particle size range. The upper and lower screens are installed in the sieving chamber in descending order of screen aperture size; Based on the intermittent wind pressure value, the lower screen is set as a pulse wind-receiving screen, so that the reverse pulse airflow passes through the screen holes from the back of the lower screen towards the screen surface.

7. A method for sieving soil samples according to claim 6, characterized in that, The soil sample to be sieved is pre-loosened by low-amplitude vibration according to the pre-loosening strength, and a reverse pulse airflow is simultaneously applied to the grading screen assembly according to the intermittent wind pressure value, including: The soil sample to be screened is laid on the upper screen without pressing or kneading, and the laying thickness is matched with the upper limit of the target particle size range. A low-amplitude vibration is applied to the sieving chamber according to the pre-loosening strength, causing relative displacement of the cemented aggregates in the soil sample to be sieved; During low-amplitude vibration, a reverse pulse airflow is applied to the pulse-receiving screen according to the intermittent wind pressure value to release the adhesion and blockage at the small-aperture screen.

8. A method for sieving soil samples according to claim 1, characterized in that, Obtaining the real-time throughput of the graded screen assembly and dynamically adjusting the vibration frequency based on the real-time throughput includes: The real-time throughput of each screen level is statistically analyzed according to the same time window, and the throughput decay curve of each screen level is obtained based on the real-time throughput within the continuous time window. The inter-screen hysteresis is obtained by performing discrete time shift comparison on the attenuation curves of the transmission of two adjacent screens; the screen blockage discrimination value is obtained by combining the inter-screen hysteresis value with the slope of the transmission decrease of the previous screen; and the vibration frequency is adjusted according to the screen blockage discrimination value.

9. A method for sieving soil samples according to claim 8, characterized in that, The vibration frequency is adjusted according to the sieve blockage discrimination value until the per-unit-time throughput of each sieve is less than the preset throughput threshold, thus completing the soil sample sieving, including: When the screen blockage discrimination value increases relative to the previous time window and the increase exceeds the discrimination stability band, the vibration frequency is adjusted to an alternating offset sweep state with the current vibration frequency as the center on both sides. During the frequency sweep process, the real-time transmission rate, inter-screen hysteresis rate, and screen blockage detection rate are continuously updated, and the frequency offset is gradually reduced as the screen blockage detection rate decreases continuously. When the sieve blockage discrimination value decreases and the per-unit-time throughput of each sieve is less than the preset throughput threshold in multiple consecutive time windows, the vibration frequency adjustment is stopped and the soil sample sieving is completed.

10. A soil sample sieving system for implementing the soil sample sieving method according to any one of claims 1-9, characterized in that, include: The sample feature acquisition module acquires the soil sample to be screened and the target particle size range, collects the surface image, moisture content and electrical conductivity of the soil sample to be screened, and obtains the continuity of the aggregate edge based on the surface image. The cementation risk control module calculates the cementation risk value based on the moisture content, electrical conductivity, and agglomerate edge continuity. If the cementation risk value is greater than or equal to a preset risk threshold, it determines the pre-loosening strength and intermittent wind pressure value based on the cementation risk value, and determines the grading screen combination according to the target particle size range. The pre-loosening and pulse execution module places the soil sample to be screened into the screening chamber, performs low-amplitude vibration pre-loosening on the soil sample according to the pre-loosening intensity, and simultaneously applies reverse pulse airflow to the grading screen assembly according to the intermittent wind pressure value. The dynamic sieving feedback module obtains the real-time throughput of the graded sieve combination and dynamically adjusts the vibration frequency according to the real-time throughput until the throughput per unit time of each sieve is less than the preset throughput threshold, thus completing the sieving of the soil sample.

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