路面弯沉值测量（Pavement deflection measurement）

路面弯沉值测量（Pavement deflection measurement） 路面弯沉值测量(Pavement deflection measurement) Pavement deflection measurements (2010-10-10, 12:24:48) reproduced Tags: on Classification: Roadbed The road deflection value is the vertical deformation value of the road surface under the wheel load of the automobile. It is a comprehensive index reflecting the overall compressive strength of the road surface. At present, the methods for Measuring Pavement Deflection include Backman deflectometer, automatic deflection tester, pavement deflection test method and dynamic deflection measurement method. This book mainly introduces the measuring method of Backman deflectometer. I. test methods, objectives and scope of application 1 、 Backman deflection deflectometer method of measurement The Backman deflectometer was developed by the American Association of road engineers in the western states in 50s. Our country uses this kind of instrument at present, usually by the aluminum alloy material the pole type instrument. See figure 4-1. In order to meet the needs of measuring different road level, the main use of the deflectometer models of full-length 5.4m and 3.6m two, the leverage ratio is 2:1, the portable, rapid measurement, simple calculation, in the actual operation results, pavement deflection value two times for dial indicator readings. 2, the purpose and scope of application 1) the deflection and deflection of the wheel surface under the vertical static load of the rear wheel of the standard test vehicle were measured by deflection deflectometer, which was used as an index to evaluate the strength of the road surface. 2) the rebound deflection value of the subgrade or whole pavement material is measured, and then the modulus of elasticity of subgrade or pavement material is calculated according to the vertical displacement formula of the elastic half space theory. 3) the rebound deflection value of layered structure is measured, and the modulus of resilience of pavement structure is calculated according to the vertical displacement theory of elastic layered system. 4) the main instrument and equipment for measuring method of Backman deflectometer (a) deflectometer 1 - 2 (Fig. 4-1) Pavement deflectometer by Backman beam, and dial indicator table frame, Backman beam made of aluminum alloy, a vial, the forearm (contact Road) and arm (with dial indicator) length ratio is 2:1. There are two kinds of deflectometer: one is long 3.6m, the other is 2.4m and 1.2m respectively: another lengthened deflectometer is long 5.4m, and the front and rear arms are 3.6m and 1.8m respectively. When measuring on semi-rigid base asphalt pavement or cement concrete pavement, Backman beam deflection deflectometer with length 5.4m should be adopted, and BZZ-100 standard car is adopted. The amount of deflection indicator, automatic recording device can also be used to measure. B) standard car for testing Change and test of green pavement deflection Change and test of deflection of Asphalt Pavement Change and test of deflection of Asphalt Pavement [article] deflection change and test of Asphalt Pavement Abstract: This paper discusses the three stages of change of asphalt pavement deflection and the determination of the correct time of deflection, the key focuses on Backman beam deflectometer test deflection, and briefly introduces the other three test deflection. Key words: asphalt pavement deflection test The deflection of pavement not only reflects the whole strength and stiffness of each structural layer and soil foundation, but also has some internal connection with the pavement. Therefore, before the completion of the project, the deflection of the pavement as an important indicator reflects the overall strength and quality of the road surface. In the quality evaluation of the sub item of the road engineering, the deflection scores of the highway and the first grade highway are 15 and 20, respectively. If the deflection is not enough, the sub item can not reach the good grade. Therefore, it is very important for the correct evaluation of pavement quality to know the change law of pavement deflection and to test the deflection of pavement correctly. 1 the change law of pavement deflection The change of deflection of road surface is a complex process of many factors. The material properties of each layer, subgrade and pavement structure type, compaction condition, compaction degree, temperature and humidity, weather conditions, traffic detection, environmental conditions and use of equipment and testing personnel detection level has great effect on the deflection of the size. The surface deflection process of asphalt pavement is divided into three stages. The first 1~2 years after the completion of the road are in the first stage. At this stage, As the repeated rolling of the vehicle load gradually compacted, plus semi-rigid base material with age strength increases, resulting in road surface deflection will gradually decrease, about second years after completion of the road to reach the minimum. Second to fourth years after the completion of the road is the second stage. At this stage, the performance of road surface deflection increases continuously. This is because the strength increase of semi-rigid base has been very slow, and gradually tends to be relatively stable; on the other hand, due to changes in repeated vehicle load and water and temperature conditions, and the pavement mixture itself for uniform mixing, which affect the strength of heterogeneity and other factors, micro defects the internal structure of the local scope due to stress concentration and expansion, local damage and the gradual emergence of a small range, which leads to the pavement stiffness is decreased, the road surface deflection increases rapidly. If the design is not proper, the quality of the project is not strictly controlled, or the quality of the project is uneven, it is possible that the early damage of the local road will occur at this stage. After 3-4 years of completion, the pavement reaches the limit and the failure state is the third stage of deflection. At this stage, the local strength of pavement due to various complicated factors of problem has been fully exposed, high energy density near the internal defects of local area savings has also been through the fault spreading and transfer, and automatically realizes the energy balance of the whole system, so that the internal structure of the further development of the suppression of damage. The overall stiffness of the pavement structure has reached a new, lower level of relative stability. As a result, the road curve sinks into a relatively stable, slowly changing phase. It is called the stable development stage of structural fatigue damage, and continues to the fatigue damage of pavement structure. In the 1-2 years after the completion of the road, the deflection of the road surface is the smallest. Thus, the overall structure of the pavement is in the maximum stiffness state during this period. However, in the determination of material parameters, the longest curing time of the base material design age is only 6 months. This time, just close to the bad season of the first year after the completion of the road. And statistical results show that the road surface Huang Jian: the deflection change of asphalt pavement and the deflection value of the unfavorable season in the first year after completion are close to the deflection value of the maximum stiffness. Therefore, after the completion of the first year of the road, the adverse season is approximately assumed to be the maximum stiffness of the overall structure of the pavement, and the design status of the asphalt pavement is obtained. This state is also the state in which we measure the value of the deflection of the road surface. 2 deflection test of Backman beam deflectometer Due to the current project on the widespread use of Backman beam deflectometer, so this paper introduces the method of using Backman beam deflectometer, modified from the standard car, deflectometer selection, temperature and deflection calculation and other aspects of the relevant points and matters needing attention. 2.1 standard car Standard car is a double axle and rear axle, each side is a double tire truck, and its standard axle load, tire size, tire clearance and tire pressure and other technical parameters are shown in table 1. Standard vehicle parameters for determination of deflection; standard axle load rating; rear axle standard; axle load P (kN); double side tire load (kN); tire inflation pressure (MPa); single wheel transmission surface equivalent circle diameter (CM) BZZ-100 100 + 150 + 0.5, 0.70 + 0.05, 21.30 + 0.5 BZZ-60 60 + 130 + 0.5, 0.50 + 0.05, 19.50 + 0.5 The width of the wheel gap shall meet the test requirements for freely inserting the probe of the deflectometer The test car can be selected according to the highway grade according to the needs. The highway, grade one and grade two highway should adopt the standard BZZ-100 of the rear axle 10t; other grade highways can adopt the BZZ-60 standard car of the rear axle 6t. The standard car for measuring deflection is very important. Our country has always stipulated that "Jiefang brand" "CA-10B" and "the Yellow River brand" "JN-150" should be used as standard cars with two loading levels. But the two models gradually eliminated and no longer produced, and gradually become extinct. Therefore, the specification of standard cars only provides the main parameters such as axle load, wheel pressure and air pressure, etc. all models conforming to these parameters can be used. In Before test, The axle load, wheel pressure and floor area of the test car shall be measured. The difference between the test and the standard car shall not exceed the value specified in table 1. In case of discrepancies, appropriate adjustments shall be made. Selection of 2.2 deflectometer and error correction of deflectometer Deflectometer by Backman beam, and table frame indicator. There are two kinds of deflectometer: one is 3.6m, the front and rear arms are 2.4m and 1.2m; another lengthened deflectometer is 5.4m, and the front and rear arms are 3.6m and 1.8m respectively. When measuring on semi rigid base asphalt pavement, Backman beam deflection deflectometer with length 5.4m should be adopted, and BZZ-100 standard car is adopted. This is because with the increase of the rigidity of the highway pavement, the deflection radius of the deflectometer is also increasing. Statistics show that in 60s the intermediate deflection of the radius of influence is 0.5 ~ 1m; 70s three asphalt pavement is 1 ~ 1.5m, two level pavement is 1.5 ~ 2m; 90s highway after construction of pavement deflection influence radius generally has been developed to the 3M, some have reached more than 4m. In this case, the fulcrum of the long arm of the 3.6m deflectometer has fallen into the deflection affected zone, so it is difficult to avoid the influence of the deformation of the bracket caused by the load vehicle, so that the measured deflection value is too small, resulting in measurement errors. Therefore, if we use 3.6m deflectometer test, determination should be fulcrum or deformation, the application of another test deflectometer installation deflectometer bending in the determination of the rear of the frame was determined by measuring points to pivot DEFLECTOGRAPH side. When the car opened, the simultaneous determination of two Taiwan deflectometer deflection readings, such as inspection deflectometer is that should be recorded dial indicator readings, adding two sink determination of bending deflection instruments, measured points of deflection, and fulcrum distortion correction. When measured on the same structure layer, it can be measured 5 times in different positions, and the average value is determined, which is used as the correction value in each subsequent determination. 2.3 bending test in frequency When measuring the deflection value, each lane of each kilometer should be taken as a rating section. Check 80~100 points per section. For multi lane highway, the number of lanes must be increased according to the ratio of lanes to two lanes. In 2.4 temperature correction For the asphalt pavement, deflection strength test is carried out in the asphalt pavement, and the surface area affected by the weather changes, the summer of asphalt pavement is weak, winter and hard brittle. Therefore, as measured in the summer, due to excellent, but also distortion. Therefore, a standard temperature is required to determine the deflection. The pavement deflection value is the standard condition of measuring the deflection value of asphalt pavement with 20 degree C. When the asphalt surface layer thickness is less than or equal to 5cm, does not need the temperature correction; when the surface temperature at 20 DEG C + 2 ~ C, no temperature correction; in other cases the determination of deflection value should be temperature correction. The calculation of temperature correction and rebound deflection should be carried out in the following steps. The determination of the average temperature of the asphalt layer calculated by the formula: X T = (T25TMTE) / 3 Type in T - Determination of asphalt layer in average temperature; T25 - according to T0 the 25mm below the surface in the temperature, degree in C; TM - according to T0 come to the middle of the asphalt layer depth temperature in degrees C; TE, according to the asphalt layer at the bottom of the T0 that the temperature of C degrees; in T0 - for the determination of the mean of the temperature of the road surface and the average temperature of 5D before the determination, C0; The average value and the average daily temperature for the daily maximum temperature and minimum temperature in the. Then, the average temperature of the asphalt layer is taken as the correction factor of the deflection temperature of the asphalt pavement: L20 = LT = K Type in K - temperature correction coefficient; simulation L20 - converted to 20 degrees C asphalt pavement rebound deflection value, 0.01mm; LT determination of bending springback when the average temperature of bituminous pavement is T sedimentation value, 0.01mm. Calculation of deflection of pavement 2.5 Rebound deflection value of pavement measuring points: LT = 2 (L1-L2) In the formula LT - the rebound deflection value at the pavement temperature T, 0.01mm; The maximum reading L1 - wheel deflectometer test center near the head of the dial indicator, 0.01mm; The final reading of L2 -- the car out of the deflection effect radius indicator, 0.01mm. When the deflection deformation of the deflection point of the deflection instrument is corrected, the rebound deflection value of the pavement measuring point is corrected: LT = 2 (L1-L2) + (L3-L4) Type in L3 - wheel deflectometer test center near the head detection in posterior maximum reading with deflectometer, 0.01mm; L4 - the car pulled out deflection influence radius test after final readings in using deflectometer, 0.01mm. The deflection value is the upper fluctuation limit of deflection measurement, and is calculated by the lower form: LR = L + Z - S. On behalf of the bending type in LR - an evaluation section of the sink, in 0.01mm; L: an assessment by the sections of each measuring point of the average value of the deflection correction; simulation S: an assessment of sections by all the measuring points of deflection of the standard revised in difference; Z. - and the guarantee rate of the relevant coefficients using the following values. High speed highway Z alpha = 2 x Two Z = 1.645 in the highway. The following two alpha = 1.5 in highway Z When calculating the mean and standard deviations, the deflection deflection value beyond L + (2~3) S should be discarded. For the point where the deflection value is too large, the boundary around it should be found to be treated. 2.6, the current major problems in deflection testing (1) the definition of flexible pavement design specification original allowable deflection for pavement in the maximum bending design using the most unfavorable season at the end of the period in the standard axle load under the allowable deflection value, it cannot be directly used as acceptance index, otherwise the standard is low, prone to early damage. In (2) at present, the deflection test of the semi-rigid base asphalt pavement mostly adopts the 3.6m Backman beam deflectometer, but the deformation of the bracket caused by the load car is seldom considered. In (3) the wheel pressure of the deflection test car is not enough, which results in smaller rebound deflection value. In (4) the deflection test car does not weigh or load deviation, and the tonnage is insufficient, which results in the deviation between axle load and standard axle load, and the deflection value is too small. In (5) the position of the measuring head of the deflectometer is incorrect. Generally speaking, the beam arm of the deflection tester shall not touch the tire when measuring, and the measuring head shall be placed at the measuring point, that is, 3 to 5cm ahead of the wheel gap center. In (6) the temperature correction is not correct, and the correction is usually made only by using the temperature at that time. In (7) when the deflection time is not correct, the deflection should be in the unfavorable season of the first year after the completion of the pavement. 3 other methods of Measuring Pavement Deflection 3.1 automatic deflection instrument to determine the deflection of pavement The automatic deflection deflectometer is a device which uses Backman beam determination principle to measure continuously and continuously, and tests the total deflection of the pavement continuously and the average value of the total deflection of the road section at regular intervals. The Locke Lou Wa Ge automatic deflection measuring car consists of three parts: testing automobile, measuring mechanism and data collecting system. The measuring mechanism is installed under the test vehicle chassis, and the measuring arm is clamped in the middle of the rear axle wheel gap. The speed of automatic deflectometer test must be stable and should be controlled in the range of 3 ~ 3.5km/h. In addition, when the road surface is seriously damaged, uneven and has a pit, the measuring equipment may be damaged, or when the flat curve radius is too small to be detected. 3.2 determination of pavement deflection by falling weight deflectometer Vehicle falling weight type pavement deflection rapid measuring instrument is one of the most advanced nondestructive testing equipment for pavement deflection strength in the world. To pull (or drop hammer loading type) and contains two kinds of drop hammer. FWD is a high impact load occurred in the standard quality of the hammer to fall under the action of the subgrade or pavement surface generated by the determination of instantaneous deformation, the determination of dynamic bending in dynamic loads deflection and deflection basin. The falling weight deflectometer consists of load generating device, deflection detecting device, operation control system and vehicle traction system. When measuring, start the falling weight device, the drop hammer is free to fall, the impact force on the loading plate, and immediately automatically upgrade to the original position. At the same time, each sensor detects the surface deformation of the structural layer. The recording system inputs the displacement signal to the computer and gets the peak value, namely, the deflection of the road surface and the deflection basin at the same time. Repeated measurements on each side should be no less than 3 times, because the result of the first hammer test is often unstable, so two hammers and three hammers must be struck, The results give the first hammer. 3.3 laser deflection tester The laser deflection meter is specially designed for the determination of minor deflection of the pavement. This kind of deflection is usually in the order of microns. For example, the asphalt concrete pavement under winter climatic conditions, using a general Backman beam deflectometer, has been unable to measure. Due to the mechanical friction between the errors have been slightly bent to cover, so only by laser diffraction method to measure its small deflection value. The laser deflection tester has the characteristics of simple operation, high accuracy, stable reading, small volume and light quality. 3.4 mutual conversion When using automatic deflection or falling weight deflectometer to determine, first of all should establish automatic bending or falling weight deflectometer and Backman beam detection Standard test with the standard car according to the need according to the highway, highway, grade one and grade two highways should adopt the rear axle 10T BZZ 100 standard vehicles, roads can adopt the rear axle 6t BZZ 60 standard car. C) contact type thermometer: the end is flat head, the graduation is not more than l degrees centigrade Other: D) tape, whistle, white paint or chalk, command flag. Two 、 determination method 1. Preparation 1) check the well to keep the standard car in good condition and good brake performance. The inner tire tube meets the required inflation pressure. 2) to the vehicle loading tank (iron or aggregate), and land scale weighing the total quality to meet the requirements of the rear axle, axle load, vehicle driving and measurement process, axle load shall not change. 3) measured tire contact area: About smooth rigid pavement with Jack for automobile rear jacking, laying a new carbon paper in the lower part of the tire, gently falling jack, that on a graph paper printed on the tire, by means of planimeter or number of squares of the measured tire contact area, accurate to 0.1cm2. 4) check deflectometer dialgauge measuring case sensitive. 5) when measured in the asphalt pavement, road surface thermometer test temperature and surface temperature (the temperature changing, the day should be determined, and the Meteorological Observatory) average temperature before 5D (mean daily maximum temperature and minimum temperature value). 6) record material, structure, thickness, construction and maintenance of asphalt pavement during construction or reconstruction. 2, subgrade and pavement rebound deflection test steps 1) the test points are arranged in the test section, and the distance is determined by the need of the test. The measuring points shall be on the wheel track of the road lane and marked with white paint or chalk. 2) the rear wheel gap of the test car is aligned at the position about 3~5cm after the measuring point. 3) the deflectometer car into the gap between the rear wheels, consistent with the direction of vehicle, the beam arm must not touch the tire, deflection probe placed in the measuring point (the center of the gap in front of 3 round 5cm), determination of rod and installed on the dial indicator deflectometer, dial zero, gently with your fingers on bending deflectometer, check whether the stability of zero indicator. The deflection meter can be one sided measurement or bilateral simultaneous determination. 4) was the starting whistle command car slowly forward, with the increasing indicator pavement deformation and sustained forward rotation. When the hand rotates to the maximum, quickly read the initial readings L1. The car continues to move forward, the reverse rotation, the car pulled out of the deflection effect of half (above 3M), whistling and waved his flag, the car stopped. The hand rotary stability after reading the final reading L2 again. The speed of the car should be about 5km / h. 3 deflection correction of deflection deflectometer 1) when the length deflectometer of semi-rigid asphalt pavement, cement concrete pavement and 3.6m bending deflection measurement, may cause deflectometer bearing deformation, so the determination of when there is no deformation test point. At this point, another test deflectometer is installed at the rear of the measuring deflectometer. The measuring point is located beside the fulcrum of the deflection meter. When the car opened, the simultaneous determination of two Taiwan deflectometer deflection readings, such as inspection deflectometer indicator with a reader. That should be recorded and fulcrum distortion correction. When measured on the same structure layer, 5 times can be measured at different positions, and the average value is obtained, Each subsequent determination is used as a correction. The principle of the deformation correction of the fulcrum is shown in figure 4-2. 2) when the deflection gauge with length of 5.4m is used, the deformation of the fulcrum can not be corrected. Three, result calculation and temperature correction 1. The rebound deflection value of pavement measurement points is calculated according to the 4-1 formula: LT = (L1-L2) X 2 (4-1) Formula: LT - rebound deflection value (0.01mm) at pavement temperature T; L1 - wheel deflectometer test center near the head of the dial indicator (0.01mm); The final reading of L2 -- the car out of the deflection effect radius indicator (0.01mm). 2, when the deflection correction of the deflection instrument is needed, the rebound deflection value of the pavement measurement point is calculated according to the 4-2 formula. LT= (L1-L2), X, 2+ (L3-L4), X 6 (4-2) Type LT: the maximum reading (0.01mm) of deflection deflectometer is used when the wheel center is near the probe: L2 - the final reading of the deflection meter (0.01mm) is determined after the car has been bent out of its radius; L3 the maximum reading (0.01mm) of the deflectometer is checked when the wheel center is near the measuring head of the deflectometer; L4 - the final reading (0.01mm) of a deflectometer using a deflection tester after the car has broken out. Note: this type is suitable for Landing with deflection only bearing deformation, but the road has no indicator bracket deformation. 3, asphalt pavement thickness is greater than 5cm asphalt pavement, rebound deflection value should be temperature correction, temperature correction and rebound deflection calculation should be carried out according to the following steps. 1) the average temperature of asphalt layer is calculated according to the formula of 4-3: T = (T25+Tm+Te) / 3 (4-3) Type: T - Determination of dry average temperature (temperature) of asphalt layer; T25 - the temperature (DEG) at 25mm below the routing table determined by T0 in figure 4-2; Tm - the temperature (DEG) of the intermediate depth of the asphalt layer determined by T0, as shown in figure 4-2; Te - the temperature (DEG) at the bottom of the asphalt layer determined by T0, as shown in figure 4-2. In Figure 4-3, T0 is the sum of the mean temperature of the measured table temperature and the average temperature of 5D days before the determination, and the daily average temperature is the average of the maximum daily temperature and the minimum temperature. 2) the temperature correction factor K of the deflection value of asphalt pavement with different base is adopted. According to the average temperature of asphalt layer, T and the thickness of asphalt layer, they are obtained by Figure 4-4 and figure 4-5 respectively. 3) bituminous pavement rebound deflection calculated =LT K (4-4) K - temperature correction factor; L20 - 20 of the conversion for asphalt rebound deflection (0.01mm) LT determination of bending springback when the average temperature of bituminous pavement is T the sink value (0.01mm) 4) according to the 4-5 calculation, each assessment section represents deflection: Lr=+ZaS (4-5) Lr a method for assessing the rebound deflection (0.01mm) in a section The average value of deflection at each measuring point (0.01mm) in each section is evaluated S a standard deviation (0.01mm) for the deflection of all measured points in a road section Za - the coefficient associated with the guarantee rate, using the following values: Senior highway, highway Z =2.0. Two road Z =1.645. The following two highway Z =1.5. Four. Test report The lab report should include the following: 1, deflection value meter, deformation correction value of the fulcrum, the temperature and temperature correction of the road surface when testing. 2. The average value of deflection, standard deviation and deflection of each measuring point in each evaluation section.