Method for detecting strength of highway subgrade based on semi-empirical modified curve

Abstract

This invention relates to the field of roadbed strength, specifically to a method for detecting the strength of highway roadbeds based on a semi-empirical modified curve. This invention records the pressure and displacement during impact using sensors on a falling weight deflectometer, calculates the vertical displacement of the road surface, selects a Beckman beam deflectometer and a test vehicle, installs the Beckman beam deflectometer between the two rear wheels of the test vehicle, corrects the test vehicle parameters, calculates the deflection value, corrects the diameter of the left and right tires of the test vehicle to 22.35 cm, and corrects the ground pressure of the left and right tires of the test vehicle to 0.75 MPa. The vertical displacement and deflection values ​​measured in steps (2) and (3) are recorded and compared with the national highway roadbed strength standard, thereby achieving rapid detection of roadbed strength without damaging the road structure. Furthermore, the test vehicle can be used to detect and evaluate the road smoothness of the selected road.

Description

Technical Field

[0001] This invention relates to the field of roadbed strength technology, and more specifically to a method for detecting the strength of highway roadbeds based on semi-empirical modified curves. Background Technology

[0002] Depending on the cut and fill height and the terrain, there are various cross sections for roadbeds. Roadbed design mainly includes roadbed body engineering design, roadbed protection and reinforcement engineering design, and roadbed retaining engineering design.

[0003] For example, Chinese Patent Publication No. CN104499473A discloses a method for detecting the strength of highway subgrade based on a semi-empirical modified curve. The steps are as follows: 1. Measure the penetration resistance qd of subgrade soil at different depths using a PANDA2 variable energy penetrator; 2. Divide the subgrade depth into two intervals based on the measured depths and calculate the average value of the penetration resistance qd for each interval; 3. Obtain the subgrade soil strength corresponding to different subgrade depths based on the relationship between the penetration resistance qd and the CBR value. The penetration resistance qd and the CBR value satisfy the following condition: lgCBR=0.352+1.057*lgqd. This invention discloses a method for detecting the strength of highway subgrade based on a semi-empirical modified curve. This method can not only effectively detect the strength of highway subgrade, but also quickly and effectively detect the subgrade soil strength (CBR value). Furthermore, the detection process does not require large loads or numerous equipment, offering the advantages of speed and effectiveness. The detection results can provide a scientific basis and technical guidance for the formulation of subgrade maintenance and management plans.

[0004] However, when using the above methods to inspect highways, it is necessary to damage the road surface structure before inspection, making it difficult to inspect existing road surfaces.

[0005] In conclusion, developing a method for testing the strength of highway subgrade based on semi-empirical modified curves remains a critical issue that urgently needs to be addressed in the field of subgrade strength testing. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a method for testing the strength of highway subgrade based on a semi-empirical modified curve. The method involves selecting an asphalt layer thickness of 33-35 cm, a cement layer thickness of 24-26 cm, and a crushed stone layer thickness of 56-57 cm for the test pavement. The test points are circular pavement areas with a surface area of ​​1 square meter, divided into 5-10 test points. A falling weight deflectometer is used to install support plates at the test points, which are then constrained. A falling weight impacts the support plates, generating a certain impact force. Sensors on the falling weight deflectometer record the pressure and displacement during the impact, and the vertical displacement of the pavement is calculated. A Beckman beam deflectometer and a test vehicle were selected. The Beckman beam deflectometer was installed between the two rear wheels of the test vehicle, and the parameters of the test vehicle were corrected. The deflection value was calculated. The diameter of the left and right tires of the test vehicle was corrected to 22.35 cm, and the ground pressure of the left and right tires of the test vehicle was corrected to 0.75 MPa. The vertical displacement and deflection values ​​measured in steps (2) and (3) were recorded and compared with the national highway subgrade strength standard. This allows for rapid detection of subgrade strength without damaging the road structure. The test vehicle can also be used to detect and evaluate the road smoothness of the selected road.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] (1) Select a 1km stretch of road for testing and divide the road into 5-10 testing points;

[0009] (2) Use a falling weight deflectometer to detect the detection points distinguished in step (1), calculate the vertical displacement of the road surface, and then test the strength of the roadbed.

[0010] (3) Select the Beckman beam deflection meter and the test vehicle, install the Beckman beam deflection meter between the two rear axle wheels of the test vehicle, and correct the test vehicle parameters to calculate the deflection value.

[0011] (4) Record the vertical displacement and deflection values ​​measured in steps (2) and (3) and compare them with the national highway subgrade strength standard.

[0012] The present invention is further configured such that: in step (1), the thickness of the asphalt layer of the selected test road surface is 33-35cm, the thickness of the cement layer is 24-26cm, the thickness of the crushed stone layer is 56-57cm, and the test point is a circle with an area of ​​1㎡.

[0013] The present invention is further configured such that, in step (2), the detection step is as follows:

[0014] (21) Install a support plate on the surface of the detection point and limit the position of the support plate;

[0015] (22) A certain impact force is generated by impacting the support plate with a drop hammer;

[0016] (23) The pressure and displacement during impact are recorded by the sensors on the falling weight deflectometer.

[0017] The present invention is further configured such that, in step (2), the strength test of the roadbed includes the following steps:

[0018] S1. Excavate holes for the detection points selected in step (1);

[0019] S2. Place the static load test instrument in the hole and increase the load in stages.

[0020] S3. Record the data from the load sensor and settlement sensor, and simultaneously record the data from the setting column and measuring ruler around the hole;

[0021] S4. After step S3 is completed, the load is reduced in stages and recorded. The compression modulus and ultimate bearing capacity are then calculated.

[0022] S5. To address the impact of multiple environments, a data model is established between the roadbed strength parameters and test data to correct the calculation errors in S4.

[0023] The present invention is further configured such that, in step S1, the depth of the hole is 1.2-1.4m and the diameter of the hole is 0.5-0.7m.

[0024] The present invention is further configured such that: in step S2, the time for the staged increase of load is 11-13 minutes, and the loading speed of the staged increase of load is 7-9 tons / time.

[0025] The present invention is further configured such that, in step S4, the formula for calculating the compressive modulus is: In the formula, C is the compression modulus, β is the load magnitude, δ is the ratio of subgrade settlement to subgrade width, and the formula for calculating the ultimate bearing capacity is: In the formula, α is the maximum load on the roadbed, and R is the stress-bearing area of ​​the roadbed.

[0026] The present invention is further configured such that, in step (2), the formula for calculating the vertical displacement of the road surface is:

[0027]

[0028] In the formula: A is the vertical displacement to be determined, z is the meridional coordinate, f is the vertical coordinate, α is the radius of the support plate, B is the average load pressure of the support plate (MPa), C is the elastic modulus (MPa), β is the Poisson coefficient, w0(.) is the zero-order Bessel function, and q is the integration variable.

[0029] The present invention is further configured such that, in step (3), the diameter of the left and right tires of the modified test vehicle is 22.35 cm, and the ground pressure of the left and right tires of the modified test vehicle is 0.75 MPa.

[0030] The present invention is further configured such that, in step (3), the formula for calculating the deflection value is: Q r =Q + Yβ × M, where: Q r Yβ is the representative value of the deflection value of this road section, Q is the average value of the rebound deflection value of this road section, Yβ is the guarantee coefficient, and M is the standard deviation of the rebound deflection value of this road section.

[0031] Beneficial effects

[0032] Compared with known public technologies, the technical solution provided by this invention has the following advantages:

[0033] Beneficial effects:

[0034] 1. This invention selects an asphalt layer thickness of 33-35cm, a cement layer thickness of 24-26cm, and a crushed stone layer thickness of 56-57cm for the test road surface. The test point is a circular road surface with an area of ​​1㎡, and the road surface is divided into 5-10 test points. A falling weight deflectometer is used to install support plates at the test points, and the support plates are limited. A falling weight impacts the support plates to generate a certain impact force. The pressure and displacement during the impact are recorded by the sensors on the falling weight deflectometer, and the vertical displacement of the road surface is calculated. A Beckman beam deflectometer and a test vehicle are selected. The deflection meter is installed between the two rear wheels of the test vehicle, and the parameters of the test vehicle are corrected to calculate the deflection value. The diameter of the left and right tires of the test vehicle is corrected to 22.35 cm, and the ground pressure of the left and right tires of the test vehicle is corrected to 0.75 MPa. The vertical displacement and deflection values ​​measured in steps (2) and (3) are recorded and compared with the national highway subgrade strength standard. This allows for rapid detection of subgrade strength without damaging the road structure. The test vehicle can also be used to detect and evaluate the road smoothness of the selected road. Attached Figure Description

[0035] Figure 1 This is a flowchart of the highway subgrade strength detection method based on a semi-empirical modified curve according to the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] The present invention will be further described below with reference to embodiments.

[0038] Example:

[0039] Reference Figure 1 As shown, this invention provides a method for detecting the strength of highway subgrade based on a semi-empirical modified curve, comprising the following steps:

[0040] (1) Select a 1km stretch of road for testing and divide the road into 5-10 testing points.

[0041] Furthermore, the asphalt layer thickness of the test road surface is selected to be 33-35cm, the cement layer thickness to be 24-26cm, and the crushed stone layer thickness to be 56-57cm. The test point is a circle with an area of ​​1㎡.

[0042] (2) Using a falling weight deflectometer, the detection points distinguished in step (1) are detected, the vertical displacement of the road surface is calculated, and then the strength of the roadbed is tested.

[0043] Further, the detection steps are as follows:

[0044] (21) Install a support plate on the surface of the detection point and limit the position of the support plate;

[0045] (22) A certain impact force is generated by impacting the support plate with a drop hammer;

[0046] (23) The pressure and displacement during impact are recorded by the sensors on the falling weight deflectometer.

[0047] Furthermore, the strength testing of the roadbed includes the following steps:

[0048] S1. Excavate holes for the detection points selected in step (1);

[0049] S2. Place the static load test instrument in the hole and increase the load in stages.

[0050] S3. Record the data from the load sensor and settlement sensor, and simultaneously record the data from the setting column and measuring ruler around the hole;

[0051] S4. After step S3 is completed, the load is reduced in stages and recorded. The compression modulus and ultimate bearing capacity are then calculated.

[0052] S5. To address the impact of multiple environments, a data model is established between the roadbed strength parameters and test data to correct the calculation errors in S4.

[0053] Furthermore, the hole depth is 1.2-1.4m and the hole diameter is 0.5-0.7m.

[0054] Furthermore, the time for increasing the load in stages is 11-13 minutes, and the loading speed for increasing the load in stages is 7-9 tons / time.

[0055] Furthermore, the formula for calculating the compression modulus is: In the formula, C is the compression modulus, β is the load magnitude, δ is the ratio of subgrade settlement to subgrade width, and the formula for calculating the ultimate bearing capacity is: In the formula, α is the maximum load on the roadbed, and R is the stress-bearing area of ​​the roadbed.

[0056] Furthermore, the formula for calculating the vertical displacement of the road surface is:

[0057]

[0058] In the formula: A is the vertical displacement to be determined, z is the meridional coordinate, f is the vertical coordinate, α is the radius of the support plate, B is the average load pressure of the support plate (MPa), C is the elastic modulus (MPa), β is the Poisson coefficient, w0(.) is the zero-order Bessel function, and q is the integration variable.

[0059] (3) Select the Beckman beam deflectometer and the test vehicle, install the Beckman beam deflectometer between the two rear wheels of the test vehicle, correct the test vehicle parameters, and calculate the deflection value.

[0060] Furthermore, the diameter of the left and right tires of the test vehicle was corrected to 22.35 cm, and the ground pressure of the left and right tires of the test vehicle was corrected to 0.75 MPa.

[0061] Furthermore, the formula for calculating the deflection value is: Q r =Q + Yβ × M, where: Q r Yβ is the representative value of the deflection value of this road section, Q is the average value of the rebound deflection value of this road section, Yβ is the guarantee coefficient, and M is the standard deviation of the rebound deflection value of this road section.

[0062] (4) Record the vertical displacement and deflection values ​​measured in steps (2) and (3) and compare them with the national highway subgrade strength standard.

[0063] Working Principle: During operation, the asphalt layer thickness is 33-35cm, the cement layer thickness is 24-26cm, and the crushed stone layer thickness is 56-57cm. The test point is a circular area of ​​1㎡, divided into 5-10 test points. A falling weight deflectometer is used to install support plates at the test points, with the support plates being limited. A falling weight impacts the support plates, generating a certain impact force. The sensors on the falling weight deflectometer record the pressure and displacement during the impact and calculate the vertical displacement of the road surface. A Beckman beam deflectometer and test vehicle are selected. The Kerman beam deflectometer is installed between the two rear axle wheels of the test vehicle, and the test vehicle parameters are corrected to calculate the deflection value. The diameter of the left and right tires of the test vehicle is corrected to 22.35 cm, and the ground pressure of the left and right tires of the test vehicle is corrected to 0.75 MPa. The vertical displacement and deflection values ​​measured in steps (2) and (3) are recorded and compared with the national highway subgrade strength standard, so as to achieve rapid detection of subgrade strength without damaging the pavement structure. The road smoothness of the selected road can also be detected and evaluated through the test vehicle.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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 of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting the strength of highway subgrade based on a semi-empirical modified curve, characterized in that, Includes the following steps: (1) Select a 1km stretch of road for testing and divide the road into 5-10 testing points; (2) Using a falling weight deflectometer, the detection points identified in step (1) are detected, and the vertical displacement of the road surface is calculated. Then, the strength of the roadbed is tested. The strength test of the roadbed includes the following steps: S1. Excavate holes for the detection points selected in step (1); S2. Place the static load test instrument in the hole and increase the load in stages. S3. Record the data from the load sensor and settlement sensor, and simultaneously record the data from the setting column and measuring ruler around the hole; S4. After step S3 is completed, the load is reduced in stages and recorded. The compression modulus and ultimate bearing capacity are then calculated. S5. Regarding the impact of multiple environments, the calculation errors in S4 are corrected by establishing a data model between the roadbed strength parameters and the test data. The formula for calculating the vertical displacement of the road surface is as follows: ； In the formula: For the desired vertical displacement, For the meridional coordinates, The vertical coordinate is... For the radius of the support plate, The average load pressure (MPa) of the support plate. It represents the elastic modulus (MPa). Poisson's coefficient, It is a zero-order Bessel function. For integration variables; (3) Select the Benkelman beam deflectometer and the test vehicle, install the Benkelman beam deflectometer between the two rear axle wheels of the test vehicle, and correct the test vehicle parameters to calculate the deflection value; the formula for calculating the deflection value is as follows: In the formula: This is the representative value of the deflection for this road section. This represents the average value of the rebound deflection for this road section. To ensure the coefficient, This represents the standard deviation of the rebound deflection value for this road section. (4) Record the vertical displacement and deflection values ​​measured in steps (2) and (3), and compare them with the national highway subgrade strength standard; the formula for calculating the compression modulus is: In the formula, For compressibility modulus, For the size of the load, The ratio of subgrade settlement to subgrade width is given by the formula for calculating the ultimate bearing capacity: In the formula, The maximum load on the roadbed. This represents the stress-bearing area of ​​the roadbed.

2. The method for detecting the strength of highway subgrade based on a semi-empirical modified curve according to claim 1, characterized in that, In step (1), the thickness of the asphalt layer of the selected test road surface is 33-35cm, the thickness of the cement layer is 24-26cm, the thickness of the crushed stone layer is 56-57cm, and the test point is a circle with an area of ​​1㎡.

3. The method for detecting the strength of highway subgrade based on a semi-empirical modified curve according to claim 1, characterized in that, In step (2), the detection step is as follows: (21) Install a support plate on the surface of the detection point and limit the position of the support plate; (22) A certain impact force is generated by impacting the support plate with a drop hammer; (23) The pressure and displacement during impact are recorded by the sensors on the falling weight deflectometer.

4. The method for detecting the strength of highway subgrade based on a semi-empirical modified curve according to claim 1, characterized in that: In step S1, the depth of the hole is 1.2-1.4m and the diameter of the hole is 0.5-0.7m.

5. The method for detecting the strength of highway subgrade based on a semi-empirical modified curve according to claim 1, characterized in that: In step S2, the time for the phased increase of load is 11-13 minutes, and the loading rate for the phased increase of load is 7-9 tons / time.

6. The method for detecting the strength of highway subgrade based on a semi-empirical modified curve according to claim 1, characterized in that, In step (3), the diameter of the left and right tires of the modified test vehicle is 22.35 cm, and the ground pressure of the left and right tires of the modified test vehicle is 0.75 MPa.

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