A method for evaluating and controlling subgrade compaction quality based on PFWD detection depth

Abstract

The application discloses a subgrade compaction quality evaluation and control method based on a PFWD detection acting depth, and relates to the technical field of subgrade compaction quality detection. In view of the fact that the existing PFWD detection result is difficult to correspond to the actual stress layer range and is difficult to directly serve the layered compaction quality control, the scheme comprises the following steps: placing a PFWD at a to-be-detected point of a subgrade, obtaining the radius of a circular steel bearing plate, the uniform load applied by the circular steel bearing plate to the surface of the subgrade, the radial distance from the to-be-detected point to the center of the circular steel bearing plate, and the dynamic stress response at different depths in the subgrade, and determining the effective acting depth of the PFWD under different working conditions; calculating a matching coefficient based on the effective acting depth and the compaction thickness of a construction layer, judging the detection adaptability, identifying single-layer, double-layer or multi-layer responses, and then combining the dynamic modulus of resilience measured by the PFWD to evaluate the compaction quality.

Description

Technical Field

[0001] This invention relates to the field of roadbed compaction quality testing technology, specifically a method for evaluating and controlling roadbed compaction quality based on PFWD detection depth. Background Technology

[0002] The quality of subgrade compaction directly determines the overall stability, load-bearing capacity, and long-term service performance of the road structure. If there are compaction defects such as insufficient compaction, uneven compaction, or "compact on top and loose on the bottom" during the construction phase, it is very easy to induce uneven settlement, cracking, rutting, and other defects in the pavement. Therefore, it is urgent to develop a subgrade compaction quality control method that can achieve rapid detection, accurate evaluation, and direct guidance for adjusting on-site construction parameters.

[0003] Existing methods for testing the compaction quality of roadbeds include the sand cone method, ring cutter method, Benkelman beam method, bearing plate method, and various dynamic testing methods. Traditional static testing methods offer reliable accuracy but suffer from drawbacks such as low testing efficiency, cumbersome operation procedures, and occupation of construction work areas, making them unsuitable for real-time quality control requirements in large-scale, rapid construction scenarios. In contrast, the PFWD (Portable Falling Weight Deflectometer) offers advantages such as lightweight design, fast impact loading speed, high testing efficiency, and ease of on-site operation, and is now widely used for testing the bearing capacity, resilient modulus, and dynamic deflection index of roadbeds.

[0004] However, existing PFWD (Power Factor Measurement and Control) systems only output two types of test indicators: deflection value and dynamic modulus. These indicators characterize the comprehensive mechanical response of multi-layer subgrade soil within the instrument's detection depth range, and cannot separately reflect the compaction state of the surface fill layer. If the detection depth of the PFWD under the corresponding construction conditions is not determined, it is impossible to distinguish whether the test data is controlled by the current fill layer, the underlying layer, or the coupling effect of multiple soil layers, ultimately leading to distorted subgrade compaction quality evaluation results and misjudgments.

[0005] Existing research on the depth of PFWD detection is mostly limited to theoretical deduction or empirical estimation, and a complete technical system linking "detection depth identification, quantitative evaluation of layered compaction state, and on-site construction control schemes" has not yet been formed. Meanwhile, variables such as the diameter of the bearing plate, the magnitude of the impact load, and the thickness of the subgrade layers all affect the effective detection depth of PFWD during on-site construction. Without a unified and quantitative evaluation logic, it is impossible to directly conduct engineering compaction quality control based on actual PFWD measurement data. Summary of the Invention

[0006] This invention addresses the shortcomings of existing PFWD (Power Factor Difference) detection results, which are difficult to correspond to the actual stress layer range and cannot directly serve the quality control of layered compaction. It provides a method for evaluating and controlling the compaction quality of roadbed based on the PFWD detection depth.

[0007] The present invention provides a method for evaluating and controlling the compaction quality of roadbed based on PFWD detection depth, and the technical solution adopted to solve the above-mentioned technical problems is as follows: A method for evaluating and controlling the compaction quality of roadbed based on PFWD (Power Factor Width Depth) detection, comprising the following steps: PFWD is placed at the test points on the roadbed to obtain the radius of the circular steel bearing plate, the uniformly distributed load applied to the roadbed by the circular steel bearing plate in contact with the roadbed surface, the radial distance from the test point to the center of the circular steel bearing plate, and the dynamic stress response at different depths inside the roadbed, so as to determine the effective depth of PFWD under different working conditions. The matching coefficient is calculated based on the effective depth of action and the compaction thickness of the construction layer to determine the test suitability, identify single-layer, double-layer or multi-layer response, and then evaluate the compaction quality by combining the dynamic rebound modulus measured by PFWD.

[0008] Optionally, the PFWD involved includes an impact loading system, a sensing and acquisition system, and a data terminal system. The impact loading system includes a guide rod, a liftable drop hammer, a buffer damping device, and a circular steel bearing plate. The sensing and acquisition system includes a load sensor, an earth pressure sensor, and a displacement sensor. The data terminal system includes a data acquisition terminal, storage and computing software, and a display screen. Multiple earth pressure sensors are respectively deployed at different vertical depths directly below the center of the circular steel bearing plate, as well as at different radial positions at the same depth, to collect and record dynamic stress time history data inside the subgrade under the impact load of the PFWD. The physical loading process of the PFWD is as follows: The PFWD is placed stably at the test point on the roadbed, and the liftable drop hammer is lifted to a fixed height along the guide rod and then released freely; the liftable drop hammer falls along the guide rod and impacts the buffer damping device, applying an instantaneous pulse impact load to the circular steel bearing plate below; the impact load is evenly transferred to the roadbed soil through the circular steel bearing plate, causing the soil to undergo instantaneous vertical elastic deformation; after the impact load disappears, the soil rebounds and returns to its initial shape; throughout the entire loading and deformation process, the sensing acquisition system simultaneously completes the acquisition of multiple types of data: the load sensor acquires and records the impact load time history, multiple earth pressure sensors acquire and record the dynamic stress time history data inside the roadbed, and the displacement sensor acquires and records the vertical displacement time history curve of the soil; all acquired data is uniformly transmitted to the data terminal system to complete data storage and mechanical index calculation.

[0009] Alternatively, the uniformly distributed load applied to the roadbed by the circular steel bearing plate in contact with the roadbed surface can be calculated based on the following formula: , In the formula, P represents the uniformly distributed load; F represents the peak value of the impact load, which is obtained by recording the impact load time history and extracting the peak value from the load sensor; a represents the radius of the circular steel bearing plate, which is a known parameter.

[0010] Alternatively, a coordinate system can be established with the center of the circular steel bearing plate as the origin, defining the radial distance r along the horizontal direction of the roadbed surface and the vertical downward direction as the depth z direction. In this case: The radial distance r of the measuring point located directly below the center of the circular steel bearing plate is 0; the radial distance r from the measuring point to the center of the circular steel bearing plate is the horizontal distance from the point to the center of the bearing plate; the burial depth z of the earth pressure sensor is the vertical distance from the sensor placement location to the top surface of the roadbed; each earth pressure sensor collects dynamic stress time history data inside the roadbed under PFWD impact load; the current compaction thickness h of the construction layer is obtained through the on-site layer filling log, the actual measured thickness after compaction, or the construction quality archive record.

[0011] Alternatively, the following steps can be performed to determine the effective depth of PFWD under different operating conditions: (1) According to the theory of elastic half-space, the vertical stress inside the subgrade under a uniformly distributed circular load gradually decreases with increasing depth. To quantitatively characterize this stress attenuation law, a stress attenuation coefficient λ is defined, and the burial depth z of each earth pressure sensor is calculated based on the following formula. i Stress attenuation coefficient λ at the location i : , In the formula, Indicates burial depth z i The peak value of vertical dynamic stress collected by the soil pressure sensor; This represents the peak vertical dynamic stress on the roadbed surface at the center of the circular steel bearing plate. (2) A preset stress attenuation threshold λ0 is used to distinguish between the effective action zone and the ineffective action zone: when λ>λ0, it indicates that a high proportion of impact stress is still retained at this depth, which has a significant impact on the measured dynamic rebound modulus of PFWD and belongs to the effective action zone; when λ≤λ0, it indicates that the impact stress at this depth has attenuated to a low level and has a relatively weak impact on the PFWD test results and belongs to the ineffective action zone. (3) Search along the depth direction for the condition λ i >λ0 and λ i+1 For adjacent measuring points ≤λ0, the effective depth H of PFWD is located at the measuring point depth z. i With z i+1 In this case, H is solved using linear interpolation, and the calculation formula is as follows: , When a certain measuring point exactly satisfies λ iWhen =λ0, directly take H=z i When the soil pressure sensor at the deepest point satisfies λ zmax When the depth of the earth pressure sensor is greater than λ0, it indicates that the current depth of the earth pressure sensor deployment has not yet covered the complete effective range, and it is necessary to add earth pressure sensors at a deeper location and then retest; when the earth pressure sensor at the shallowest point satisfies λ... zmin When the depth of action is ≤λ0, it is necessary to add earth pressure sensors at shallower locations or reduce the spacing between earth pressure sensors to improve the accuracy of determining the effective depth of action.

[0012] Alternatively, after determining the effective depth of PFWD, the matching coefficient η between the effective depth and the compacted thickness of the construction layer can be calculated. The calculation formula is as follows: , In the formula, H represents the effective depth of PFWD; h is the compacted thickness of the construction layer; η characterizes the coverage of the effective depth of PFWD on the current compacted thickness of the construction layer. It is an evaluation index for judging whether the measured dynamic rebound modulus of PFWD can represent the current construction layer and reflect the response of a single layer of soil or the coupled response of multiple layers of soil.

[0013] Alternatively, a minimum matching threshold η0 can be preset, and then the detection suitability can be determined based on the calculated matching coefficient η, according to the following rules: when When the effective depth of PFWD cannot cover the main body of the current construction layer, the measured dynamic rebound modulus cannot be used as the evaluation basis for the overall compaction quality of the current construction layer. when When the effective depth of PFWD is well matched with the current compaction thickness of the construction layer, the measured dynamic rebound modulus serves as the main evaluation basis for the current compaction quality of the construction layer. when When the effective depth of PFWD extends to the underlying layer, the measured dynamic rebound modulus reflects the comprehensive mechanical response of the current construction layer and the underlying layer. when This indicates that the PFWD test results are affected by the combined coupling effect of two or more layers of subgrade soil, and are not suitable for direct evaluation of the compaction quality of the current construction layer.

[0014] Alternatively, after determining the compatibility of the matching coefficient η, the compaction quality can be evaluated by combining the dynamic resilient modulus measured by PFWD, as follows: when If the measured dynamic rebound modulus of PFWD is not representative of the overall compaction state of the current construction layer, even if the measured dynamic rebound modulus meets the preset control index, it cannot be determined that the overall compaction of the current construction layer has met the standard. It is necessary to adjust the test parameters, change the diameter of the circular steel bearing plate, change the effective depth, or reduce the thickness of the single layer filling before retesting. when If the dynamic rebound modulus measured by PFWD meets the preset control index, the current construction layer is judged to be of qualified compaction quality; if the dynamic rebound modulus measured by PFWD is lower than the preset control index, the current construction layer is judged to be insufficiently compacted, and additional compaction or adjustment of the backfill moisture content is required before retesting. when This indicates that the dynamic rebound modulus measured by PFWD is affected by both the current construction layer and the underlying soil. If the dynamic rebound modulus measured by PFWD is lower than the preset control index, it is necessary to comprehensively identify the weak layer by combining the number of compaction passes of the current construction layer, the moisture content of the fill, the fill thickness, the historical dynamic rebound modulus of the underlying layer, and the deep stress response of the soil. If the construction parameters of the current construction layer meet the preset control index, but the deep response exceeds the preset threshold, it is determined that there is a risk of compaction weakness in the underlying layer. when When the dynamic rebound modulus measured by PFWD is affected by the coupling effect of two or more soil layers, it cannot independently characterize the compaction of the current construction layer and can only be used to evaluate the overall bearing capacity of the subgrade. In this case, it is necessary to reduce the diameter of the circular steel bearing plate, reduce the impact load to reduce the scope of the test, or carry out verification test by layer retesting.

[0015] The present invention provides a method for evaluating and controlling the compaction quality of roadbed based on PFWD (Power Factor Difference) detection depth, which has the following advantages compared with the prior art: This invention obtains the radius of the circular steel bearing plate, the uniformly distributed load applied to the roadbed surface by the on-site loading of the PFWD (Powered Forced Load), the radial distance from the test point to the center of the circular steel bearing plate, and the dynamic stress response at different depths within the roadbed, by loading the PFWD in situ. This determines the effective depth of PFWD under different working conditions. Subsequently, the effective depth of PFWD is combined with the construction layer thickness, PFWD test indicators, and deep response characteristics to evaluate the current layer compaction quality, the underlying layer support status, and the compatibility of layer compaction. Based on this, control measures such as additional compaction, layer thickness adjustment, re-inspection of the underlying layer, and optimization of test parameters are proposed. This invention overcomes the shortcomings of existing PFWD test results, which are difficult to correspond to the actual stress layer range and cannot directly serve the layer compaction quality control. Attached Figure Description

[0016] Appendix Figure 1 This is a schematic diagram illustrating the relationship between the stress attenuation coefficient and depth, and the effective depth of action of the present invention. Appendix Figure 2 This is a simplified structural diagram of the PFWD of the present invention; Appendix Figure 3 This is a flowchart of the subgrade compaction quality evaluation based on PFWD detection of effective action depth and matching coefficient.

[0017] The information indicated by the labels in the attached diagram is as follows: 1. Liftable drop hammer; 2. Guide rod; 3. Buffer damping device; 4. Load sensor. 5. Circular steel bearing plate; 6. Earth pressure sensor. Detailed Implementation

[0018] To make the technical solution, the technical problem solved, and the technical effect of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments.

[0019] Example 1: This example proposes a method for evaluating and controlling the compaction quality of roadbed based on the PFWD detection depth, which includes the following steps: (i) Place the PFWD at the test point on the subgrade, obtain the radius of the circular steel bearing plate 5, the uniformly distributed load applied to the subgrade surface by the circular steel bearing plate 5, the radial distance from the test point to the center of the circular steel bearing plate 5, and the dynamic stress response at different depths inside the subgrade, and determine the effective working depth of the PFWD under different working conditions.

[0020] The above description will now be explained in detail.

[0021] Reference Appendix Figure 2The PFWD mentioned in this embodiment includes an impact loading system, a sensing and acquisition system, and a data terminal system. The impact loading system includes a guide rod 2, a liftable drop hammer 1, a buffer damping device 3, and a circular steel bearing plate 5. The sensing and acquisition system includes a load sensor 4, an earth pressure sensor 6, and a displacement sensor. The data terminal system includes a data acquisition terminal, storage and calculation software, and a display screen. Multiple earth pressure sensors 6 are respectively deployed at different vertical depths directly below the center of the circular steel bearing plate 5, as well as at different radial positions at the same depth, to collect and record dynamic stress time history data inside the subgrade under the impact load of PFWD. The physical loading process of the PFWD is as follows: The PFWD is placed stably at the test point on the roadbed, and the liftable drop hammer 1 is lifted to a fixed height along the guide rod 2 and then released freely; the liftable drop hammer 1 falls along the guide rod 2 and impacts the buffer damping device 3, applying an instantaneous pulse impact load to the circular steel bearing plate 5 below; the impact load is evenly transmitted to the roadbed soil through the circular steel bearing plate 5, causing the soil to undergo instantaneous vertical elastic deformation; after the impact load disappears, the soil rebounds and returns to its initial shape; throughout the entire loading and deformation process, the sensing acquisition system simultaneously completes the acquisition of multiple types of data: the load sensor 4 collects and records the impact load time history, multiple earth pressure sensors 6 collect and record the dynamic stress time history data inside the roadbed, and the displacement sensor collects and records the vertical displacement time history curve of the soil; all collected data are uniformly transmitted to the data terminal system to complete data storage and mechanical index calculation.

[0022] 1. The radius of the circular steel bearing plate 5 is a known parameter and can be obtained directly.

[0023] 2. The uniformly distributed load applied to the roadbed by the circular steel bearing plate 5 in contact with the roadbed surface can be calculated using the following formula: , In the formula, P represents the uniformly distributed load; F represents the peak value of the impact load, which is obtained by recording the impact load time history and extracting the peak value by the load sensor 4; a represents the radius of the circular steel bearing plate 5, which is a known parameter.

[0024] 3. Establish a coordinate system with the center of the circular steel bearing plate 5 as the origin. Define the radial distance r along the horizontal direction of the roadbed surface and the vertical downward direction as the depth z direction. At this time: the radial distance r of the measuring point located directly below the center of the circular steel bearing plate 5 is 0; the radial distance r from the point to be measured to the center of the circular steel bearing plate 5 is the horizontal distance from the point to the center of the circular steel bearing plate 5, which can be measured; the burial depth z of the earth pressure sensor 6 is the vertical distance from the sensor placement position to the top surface of the roadbed. z is a known parameter that can be directly obtained after measurement.

[0025] 4. Each earth pressure sensor 6 collects dynamic stress time history data inside the subgrade under PFWD impact load; the current compaction thickness h of the construction layer is obtained through the on-site layer filling ledger, the actual measured thickness after compaction, or the construction quality archive record.

[0026] The following steps are performed to determine the effective depth of PFWD under different operating conditions: (1) According to the theory of elastic half-space, the vertical stress inside the subgrade under a uniformly distributed circular load gradually decreases with increasing depth. To quantitatively characterize this stress attenuation law, a stress attenuation coefficient λ is defined, and the burial depth z of each earth pressure sensor is calculated based on the following formula. i Stress attenuation coefficient λ at the location i : , In the formula, Indicates burial depth z i The peak value of vertical dynamic stress collected by earth pressure sensor 6; This represents the peak value of the vertical dynamic stress on the roadbed surface at the center of the circular steel bearing plate 5. (2) A preset stress attenuation threshold λ0 is used to distinguish between the effective action zone and the ineffective action zone.

[0027] The stress attenuation threshold λ0 = 0.3 is preset first. That is, the position where the peak value of the vertical dynamic stress inside the subgrade decreases to 30% of the peak value of the vertical dynamic stress on the subgrade surface at the center of the bearing plate is taken as the boundary between the effective action zone and the ineffective action zone: a) When λ > 0.3, it indicates that a high proportion of impact stress is still retained at this depth, which has a significant impact on the measured dynamic resilient modulus of PFWD and belongs to the effective action zone; b) When λ ≤ 0.3, it indicates that the impact stress at this depth has decreased to a low level and has a relatively weak impact on the PFWD test results and belongs to the ineffective action zone. (3) Search along the depth direction for the condition λ i >λ0 and λ i+1 For adjacent measuring points ≤λ0, the effective depth H of PFWD is located at the measuring point depth z. i With z i+1 In this case, H is solved using linear interpolation, and the calculation formula is as follows: , When a certain measuring point exactly satisfies λ i When =λ0, directly take H=z i When the soil pressure sensor 6 at the deepest point satisfies λ zmax When the depth of the earth pressure sensor 6 is greater than λ0, it indicates that the current deployment depth of the earth pressure sensor 6 has not yet covered the complete effective range, and it is necessary to add earth pressure sensor 6 at a deeper location and then retest; when the earth pressure sensor at the shallowest point satisfies λ... zminWhen the depth of action is less than or equal to λ0, it is necessary to add earth pressure sensors 6 at a shallower location or reduce the spacing between earth pressure sensors 6 to improve the accuracy of determining the effective depth of action.

[0028] (ii) Calculate the matching coefficient based on the effective action depth and the compaction thickness of the construction layer, determine the test suitability, identify single-layer, double-layer or multi-layer response, and then evaluate the compaction quality by combining the dynamic rebound modulus measured by PFWD.

[0029] After determining the effective depth of PFWD, the matching coefficient η between the effective depth and the compacted thickness of the construction layer is further calculated. The calculation formula is as follows: , In the formula, H represents the effective depth of PFWD; h is the compacted thickness of the construction layer; η characterizes the coverage of the effective depth of PFWD on the current compacted thickness of the construction layer. It is an evaluation index for judging whether the measured dynamic rebound modulus of PFWD can represent the current construction layer and reflect the response of a single layer of soil or the coupled response of multiple layers of soil.

[0030] A minimum matching threshold η0 is preset, and then the detection suitability is determined based on the calculated matching coefficient η, according to the following rules: (a1) When When the effective depth of PFWD cannot cover the main body of the current construction layer, the measured dynamic rebound modulus cannot be used as the evaluation basis for the overall compaction quality of the current construction layer. (a2) When When the effective depth of PFWD is well matched with the current compaction thickness of the construction layer, the measured dynamic rebound modulus serves as the main evaluation basis for the current compaction quality of the construction layer. (a3) When When the effective depth of PFWD extends to the underlying layer, the measured dynamic rebound modulus reflects the comprehensive mechanical response of the current construction layer and the underlying layer. (a4) When This indicates that the PFWD test results are affected by the combined coupling effect of two or more layers of subgrade soil, and are not suitable for direct evaluation of the compaction quality of the current construction layer.

[0031] After determining the compatibility of the matching coefficient η, the compaction quality is evaluated based on the dynamic resilient modulus measured by PFWD, as follows: (b1) When If the measured dynamic rebound modulus of PFWD is not representative of the overall compaction state of the current construction layer, even if the measured dynamic rebound modulus meets the preset control index, it cannot be determined that the overall compaction of the current construction layer has met the standard. It is necessary to adjust the test parameters, change the diameter of the circular steel bearing plate, change the effective depth, or reduce the thickness of the single layer filling before retesting. (b2) When If the dynamic rebound modulus measured by PFWD meets the preset control index, the current construction layer is judged to be of qualified compaction quality; if the dynamic rebound modulus measured by PFWD is lower than the preset control index, the current construction layer is judged to be insufficiently compacted, and additional compaction or adjustment of the backfill moisture content is required before retesting. (b3) When This indicates that the dynamic rebound modulus measured by PFWD is affected by both the current construction layer and the underlying soil. If the dynamic rebound modulus measured by PFWD is lower than the preset control index, it is necessary to comprehensively identify the weak layer by combining the number of compaction passes of the current construction layer, the moisture content of the fill, the fill thickness, the historical dynamic rebound modulus of the underlying layer, and the deep stress response of the soil. If the construction parameters of the current construction layer meet the preset control index, but the deep response exceeds the preset threshold, it is determined that there is a risk of compaction weakness in the underlying layer. (b4) When When the dynamic rebound modulus measured by PFWD is affected by the coupling effect of two or more soil layers, it cannot independently characterize the compaction of the current construction layer and can only be used to evaluate the overall bearing capacity of the subgrade. In this case, it is necessary to reduce the diameter of the circular steel bearing plate 5, reduce the impact load to reduce the scope of the test, or carry out verification test by layer retesting.

[0032] Based on the descriptions in (I) and (II) above, a field loading test was conducted using PFWD on a certain roadbed test section. The test employed a circular steel bearing plate 5, load sensors 4, displacement sensors, earth pressure sensors 6, and a data acquisition system. The diameters of the circular steel bearing plate 5 were 10cm, 20cm, and 30cm, respectively, i.e., the radii a were 5cm, 10cm, and 15cm, respectively. Earth pressure sensors 6 were embedded at positions 10cm, 20cm, 30cm, 40cm, and 50cm directly below the center of the circular steel bearing plate 5.

[0033] Impact loads were applied using PFWD, and the peak load F and vertical stress response σ at different depths were recorded. z Based on the formula P=F / (πa²), calculate the uniformly distributed load. , The effective depth H is determined by the depth value corresponding to λ0=0.3, as shown in Table 1. In Table 1, the soil pressure sensors 6 labeled ①-⑤ correspond to burial depths of 10cm, 20cm, 30cm, 40cm and 50cm, respectively. H is the effective depth obtained by linear interpolation based on the stress attenuation coefficient of adjacent measuring points.

[0034] Table 1

[0035] As shown in Table 1, under the same vertical stress P = 0.10 MPa, as the diameter of the circular steel bearing plate 5 increases from 10 cm to 30 cm, the measured stress of the earth pressure sensor 6 at each depth increases overall, and the response of the deep earth pressure sensor 6 is more obvious, with the effective working depth H increasing from 16 cm to 38 cm. When the diameter of the circular steel bearing plate 5 remains unchanged at 10 cm, as the vertical stress increases from 0.10 MPa to 0.15 MPa, the effective working depth H increases from 16 cm to 22 cm, indicating that the diameter of the circular steel bearing plate 5 and the loading level both affect the effective working depth of the PFWD.

[0036] Based on the H values ​​in Table 1, the test adaptability under different construction layer thicknesses can be further evaluated.

[0037] A. Assuming that the current compaction thickness h of a certain roadbed construction layer is 20cm, test number 4 is selected as the current layer quality evaluation condition.

[0038] Table 1 shows that under this working condition, the vertical stress P is 0.13 MPa, the diameter d of the circular steel bearing plate 5 is 10 cm, and the corresponding effective action depth H is 19 cm. Therefore, the matching coefficient η = H / h = 19 / 20 = 0.95. Taking the lowest matching threshold η0 = 0.8, η satisfies η0 ≤ η ≤ 1.0, indicating that the effective action depth of PFWD can well cover the current construction layer and does not significantly penetrate the underlying layer. The dynamic rebound modulus test results can be used as the main evaluation basis for the compaction quality of the current construction layer (single layer).

[0039] B. Assuming that the current compaction thickness h of a certain roadbed construction layer is 30cm, test number 1 is selected as the thick layer filling test condition.

[0040] Table 1 shows that under this working condition, the vertical stress P is 0.10 MPa, the diameter d of the circular steel bearing plate 5 is 10 cm, and the corresponding effective action depth H is 16 cm. Therefore, the matching coefficient η = H / h = 16 / 30 ≈ 0.53. When η0 is 0.8, η < η0, indicating that the effective action depth of PFWD is insufficient to cover the main body of the current construction layer. The measured dynamic rebound modulus can only reflect the shallow local compaction state and cannot be directly used as the basis for evaluating the overall compaction quality of the current construction layer. In this case, the PFWD loading parameters should be adjusted, a larger diameter circular steel bearing plate 5 should be selected, or the construction layer thickness should be reduced and retested to avoid misjudging the overall quality due to insufficient testing depth causing the surface layer to be qualified.

[0041] C. Assuming that the current compaction thickness h of a certain roadbed construction layer is 20cm, test number 2 is selected as the double-layer coupling identification condition.

[0042] Table 1 shows that under this working condition, the vertical stress P is 0.10 MPa, the diameter d of the circular steel bearing plate 5 is 20 cm, and the corresponding effective action depth H is 32 cm. Therefore, the matching coefficient η = H / h = 32 / 20 = 1.6, satisfying 1.0 < η ≤ 2.0. This indicates that the measured dynamic rebound modulus reflects not only the current construction layer but also the underlying layer, representing a dual-layer coupled response. If the measured dynamic rebound modulus is lower than the preset control index, while the number of compaction passes and the moisture content of the fill soil in the current construction layer meet the preset control index, and the earth pressure sensor 6 (i.e., earth pressure sensor ③) near 30 cm shows a large response, then it can be determined that the low measured dynamic rebound modulus is mainly related to the weak compaction of the underlying layer. In this case, it is not appropriate to directly attribute the result to the current construction layer being unqualified alone; instead, supplementary testing, compaction, or local rework of the underlying layer should be carried out.

[0043] D. Assuming that the current compaction thickness h of a certain roadbed construction layer is 35cm, test number 5 is selected as the test condition for thick filling.

[0044] Table 1 shows that under this condition, the vertical stress P is 0.15 MPa, the diameter d of the circular steel bearing plate 5 is 10 cm, and the effective depth H of the PFWD is 22 cm. Therefore, η = H / h = 22 / 35 ≈ 0.63. If η0 is taken as 0.8, then η < η0, indicating that the effective depth of the PFWD is insufficient to cover the main body of the current construction layer. The measured dynamic rebound modulus cannot be used as the basis for evaluating the overall compaction quality of the current construction layer. In this case, the PFWD loading parameters should be adjusted, a larger diameter circular steel bearing plate 5 should be selected, or the thickness of the construction layer should be reduced before retesting.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating and controlling the compaction quality of roadbed based on PFWD (Power Factor Difference) detection depth, characterized in that, Includes the following steps: PFWD is placed at the test points on the roadbed to obtain the radius of the circular steel bearing plate, the uniformly distributed load applied to the roadbed by the circular steel bearing plate in contact with the roadbed surface, the radial distance from the test point to the center of the circular steel bearing plate, and the dynamic stress response at different depths inside the roadbed, so as to determine the effective depth of PFWD under different working conditions. The matching coefficient is calculated based on the effective depth of action and the compaction thickness of the construction layer to determine the test suitability, identify single-layer, double-layer or multi-layer response, and then evaluate the compaction quality by combining the dynamic rebound modulus measured by PFWD.

2. The method for evaluating and controlling the compaction quality of roadbed based on PFWD detection depth as described in claim 1, characterized in that, The PFWD includes an impact loading system, a sensing and acquisition system, and a data terminal system. The impact loading system includes a guide rod, a liftable drop hammer, a damping device, and a circular steel bearing plate. The sensing and acquisition system includes a load sensor, an earth pressure sensor, and a displacement sensor. The data terminal system includes a data acquisition terminal, storage and calculation software, and a display screen. Multiple earth pressure sensors are respectively deployed at different vertical depths directly below the center of the circular steel bearing plate, and at different radial positions at the same depth, to collect and record dynamic stress time history data inside the roadbed under the impact load of the PFWD. The physical loading process of the PFWD is as follows: The PFWD is placed stably at the test point on the roadbed, and the liftable drop hammer is lifted to a fixed height along the guide rod and then released freely; the liftable drop hammer falls along the guide rod and impacts the buffer damping device, applying an instantaneous pulse impact load to the circular steel bearing plate below; the impact load is evenly transferred to the roadbed soil through the circular steel bearing plate, causing the soil to undergo instantaneous vertical elastic deformation; after the impact load disappears, the soil rebounds and returns to its initial shape; throughout the entire loading and deformation process, the sensing acquisition system simultaneously completes the acquisition of multiple types of data: the load sensor acquires and records the impact load time history, multiple earth pressure sensors acquire and record the dynamic stress time history data inside the roadbed, and the displacement sensor acquires and records the vertical displacement time history curve of the soil; all acquired data is uniformly transmitted to the data terminal system to complete data storage and mechanical index calculation.

3. The method for evaluating and controlling the compaction quality of roadbed based on PFWD detection depth according to claim 2, characterized in that, The uniformly distributed load applied to the roadbed by the circular steel bearing plate in contact with the roadbed surface is calculated based on the following formula: ， In the formula, P represents the uniformly distributed load; F represents the peak value of the impact load, which is obtained by recording the impact load time history and extracting the peak value from the load sensor; a represents the radius of the circular steel bearing plate, which is a known parameter.

4. The method for evaluating and controlling the compaction quality of roadbed based on PFWD detection depth as described in claim 2, characterized in that, Establish a coordinate system with the center of the circular steel bearing plate as the origin. Define the radial distance *r* along the horizontal direction of the roadbed surface and the vertical downward direction as the depth *z*. Then: The radial distance r of the measuring point located directly below the center of the circular steel bearing plate is 0; the radial distance r from the measuring point to the center of the circular steel bearing plate is the horizontal distance from the point to the center of the bearing plate; the burial depth z of the earth pressure sensor is the vertical distance from the sensor placement location to the top surface of the roadbed; each earth pressure sensor collects dynamic stress time history data inside the roadbed under PFWD impact load; the current compaction thickness h of the construction layer is obtained through the on-site layer filling log, the actual measured thickness after compaction, or the construction quality archive record.

5. The method for evaluating and controlling the compaction quality of roadbed based on PFWD detection depth according to claim 4, characterized in that, Perform the following operations to determine the effective depth of PFWD under different operating conditions: (1) According to the theory of elastic half-space, the vertical stress inside the subgrade under a uniformly distributed circular load gradually decreases with increasing depth. To quantitatively characterize this stress attenuation law, a stress attenuation coefficient λ is defined, and the burial depth z of each earth pressure sensor is calculated based on the following formula. i Stress attenuation coefficient λ at the location i : ， In the formula, Indicates burial depth z i The peak value of vertical dynamic stress collected by the soil pressure sensor; This represents the peak vertical dynamic stress on the roadbed surface at the center of the circular steel bearing plate. (2) A preset stress attenuation threshold λ0 is used to distinguish between the effective action zone and the ineffective action zone: when λ>λ0, it indicates that a high proportion of impact stress is still retained at this depth, which has a significant impact on the measured dynamic rebound modulus of PFWD and belongs to the effective action zone; when λ≤λ0, it indicates that the impact stress at this depth has attenuated to a low level and has a relatively weak impact on the PFWD test results and belongs to the ineffective action zone. (3) Search along the depth direction for the condition λ i >λ0 and λ i+1 For adjacent measuring points ≤λ0, the effective depth H of PFWD is located at the measuring point depth z. i With z i+1 In this case, H is solved using linear interpolation, and the calculation formula is as follows: ， When a certain measuring point exactly satisfies λ i When =λ0, directly take H=z i When the soil pressure sensor at the deepest point satisfies λ zmax If the depth of the earth pressure sensor is greater than λ0, it means that the current depth of the earth pressure sensor deployment has not covered the complete effective range. It is necessary to add earth pressure sensors at a deeper location and then retest. When the shallowest earth pressure sensor satisfies λ zmin When the depth of action is ≤λ0, it is necessary to add earth pressure sensors at shallower locations or reduce the spacing between earth pressure sensors to improve the accuracy of determining the effective depth of action.

6. The method for evaluating and controlling the compaction quality of roadbed based on PFWD detection depth according to claim 5, characterized in that, After determining the effective depth of PFWD, the matching coefficient η between the effective depth and the compacted thickness of the construction layer is further calculated. The calculation formula is as follows: ， In the formula, H represents the effective depth of PFWD; h is the compacted thickness of the construction layer; η characterizes the coverage of the effective depth of PFWD on the current compacted thickness of the construction layer. It is an evaluation index for judging whether the measured dynamic rebound modulus of PFWD can represent the current construction layer and reflect the response of a single layer of soil or the coupled response of multiple layers of soil.

7. The method for evaluating and controlling the compaction quality of roadbed based on PFWD detection depth according to claim 6, characterized in that, A minimum matching threshold η0 is preset, and then the detection suitability is determined based on the calculated matching coefficient η, according to the following rules: when When the effective depth of PFWD cannot cover the main body of the current construction layer, the measured dynamic rebound modulus cannot be used as the evaluation basis for the overall compaction quality of the current construction layer. when When the effective depth of PFWD is well matched with the current compaction thickness of the construction layer, the measured dynamic rebound modulus serves as the main evaluation basis for the current compaction quality of the construction layer. when When the effective depth of PFWD extends to the underlying layer, the measured dynamic rebound modulus reflects the comprehensive mechanical response of the current construction layer and the underlying layer. when This indicates that the PFWD test results are affected by the combined coupling effect of two or more layers of subgrade soil, and are not suitable for direct evaluation of the compaction quality of the current construction layer.

8. The method for evaluating and controlling the compaction quality of roadbed based on PFWD detection depth according to claim 7, characterized in that, After determining the compatibility of the matching coefficient η, the compaction quality is evaluated based on the dynamic resilient modulus measured by PFWD, as follows: when If the measured dynamic rebound modulus of PFWD is not representative of the overall compaction state of the current construction layer, even if the measured dynamic rebound modulus meets the preset control index, it cannot be determined that the overall compaction of the current construction layer has met the standard. It is necessary to adjust the test parameters, change the diameter of the circular steel bearing plate, change the effective depth, or reduce the thickness of the single layer filling before retesting. when If the dynamic rebound modulus measured by PFWD meets the preset control index, the current construction layer is judged to be of qualified compaction quality; if the dynamic rebound modulus measured by PFWD is lower than the preset control index, the current construction layer is judged to be insufficiently compacted, and additional compaction or adjustment of the backfill moisture content is required before retesting. when When the dynamic rebound modulus measured by PFWD is lower than the preset control index, it is necessary to comprehensively identify the weak layer by combining the number of compaction passes of the current construction layer, the moisture content of the fill, the fill thickness, the historical dynamic rebound modulus of the underlying layer, and the deep stress response of the soil. If the current construction parameters of the construction layer meet the preset control indicators, but the deep response exceeds the preset threshold, it is determined that the underlying layer has a risk of weak compaction. when When the dynamic rebound modulus measured by PFWD is affected by the coupling effect of two or more soil layers, it cannot independently characterize the compaction of the current construction layer and can only be used to evaluate the overall bearing capacity of the subgrade. In this case, it is necessary to reduce the diameter of the circular steel bearing plate, reduce the impact load to reduce the scope of the test, or carry out verification test by layer retesting.

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