At present, the early diseases of asphalt pavement are prominent, which are mostly related to pavement performance and drainage except heavy load and construction factors. The following is my paper on the resilience modulus of asphalt pavement subgrade, welcome to refer to it!
abstract:
Taking the semi-rigid base scheme as the research object, the changes of pavement deflection value and surface shear stress under the condition of subgrade rebound modulus of 20~ 100MPa are analyzed by BISAR3.0 software. Finally, according to the data results, the following conclusions are drawn: ① With the increase of rebound modulus, its influence on pavement deflection value gradually weakens, and the rebound modulus of new highway should be determined above 40MPa; ② The modulus of subgrade resilience has little effect on the surface shear stress.
Keywords: subgrade; Resilience modulus; Pavement deflection value; Surface shear stress
Introduction to 0
Resilience modulus is very important in the structural design of asphalt pavement, and its value will not only affect the project cost, but also affect the overall use quality of highway. In this paper, with the help of BISAR3.0 calculation software, the actual influence of different elastic modulus on highway deflection and shear stress is deeply analyzed.
1 Determination of pavement structure scheme
As far as semi-rigid base is concerned, it has good rigidity, stability and strength, and is suitable as the main bearing layer of pavement. At the same time, it has many advantages such as low cost, mature design and construction, and is a typical pavement structure commonly used in China. Based on the elastic layered continuous system and its basic theory under uniaxial and double circumferential uniform loads, the actual variation laws of deflection, shear stress, surface compressive stress and base tensile stress under different levels of resilience modulus are analyzed to clarify the actual influence of resilience modulus on highway pavement. The parameters involved in this analysis are standard bearing, vertical load, etc. If the radius of the equivalent circle is equal to 10.65cm, the tread can be determined to be three times the radius of the equivalent circle. BISAR3.0 software is used for calculation and analysis. For the convenience of calculation, the following conditions are assumed: the transverse direction of the road surface is represented by Y axis; The direction of the vehicle is represented by the X axis, that is, the longitudinal direction of the road surface; The depth direction of the road surface is represented by the z axis. In the calculation results, the tensile stress is positive and the compressive stress is negative. When analyzing the sensitivity of one parameter, other parameters remain unchanged.
2 Analysis of the actual impact of resilience modulus
2. 1 deflection influence analysis
Deflection value refers to the sum of all structural levels in the pavement and the overall deformation of subgrade. In order to analyze the influence of deflection value on the change of resilience modulus, the resilience modulus of subgrade in nine cases is selected, and the change range is 20~ 100MPa (increase 100MPa), and the parameters of each structural layer are unchanged except deflection value. By comparing and analyzing the stress of pavement structure, the actual changing trend of rebound modulus is obtained. When the modulus of subgrade resilience is 20MPa, the deflection values of pavement and subgrade top surface are 0.58mm and 0.53mm respectively, and the latter accounts for 92% of the former. When the modulus of subgrade resilience is 30MPa, the deflection values of pavement and subgrade top surface are 0.45mm and 0.40mm respectively, and the latter accounts for 90% of the former. When the modulus of subgrade resilience is 40MPa, the deflection values of pavement and subgrade top surface are 0.38mm and 0.33mm respectively, and the latter accounts for 87% of the former. When the modulus of subgrade resilience is 50MPa, the deflection values of pavement and subgrade top surface are 0.33mm and 0.28mm respectively, and the latter accounts for 85% of the former. When the modulus of subgrade resilience is 60MPa, the deflection values of pavement and subgrade top surface are 0.30mm and 0.25mm respectively, and the latter accounts for 83% of the former. When the modulus of subgrade resilience is 70MPa, the deflection values of pavement and subgrade top surface are 0.27mm and 0.22mm respectively, and the latter accounts for 82% of the former. When the modulus of subgrade resilience is 80MPa, the deflection values of pavement and subgrade top surface are 0.25mm and 0.20mm respectively, and the latter accounts for 80% of the former. When the modulus of subgrade resilience is 90MPa, the deflection values of pavement and subgrade top surface are 0.24mm and 0. 19mm respectively, and the latter accounts for 79% of the former. When the modulus of subgrade resilience is 100MPa, the deflection values of pavement and subgrade top surface are 0.22mm and 0. 17mm respectively, and the latter accounts for 77% of the former. (1) The deflection value of pavement surface layer decreased by about 62%, the deflection value of subgrade top surface decreased by about 67%, and the percentage of subgrade top surface deflection value in pavement surface layer deflection value ranged from 77% to 92%. With the increase of rebound modulus, its influence on pavement deflection value gradually weakens. (2) Compared with the small modulus of resilience, the deflection value actually has a greater influence. If the rebound modulus is less than 40MPa, the deflection curve has a greater steepness; When it exceeds 40MPa, the curve is relatively flat [2].
2.2 Shear Stress Influence Analysis
Under the lateral force exerted by the wheel, the surface layer will produce certain shear stress. At the same time, with the help of BISAR3.0 software, the influence of different modulus of resilience on shear stress is analyzed. When the rebound modulus is less than 30MPa, the influence of depth and rebound modulus on shear stress is mainly discussed with the central position of a single circular load as the control datum.
2.3 Surface compressive stress impact analysis
Using BISAR3.0 software, the vertical stress at the bottom of pavement at each position of double-circle load center is calculated, and the subgrade resilience modulus is determined to be 30MPa. According to the calculation, the vertical stress at the bottom of the surface layer reaches the maximum at 15.98cm outside the double-circle load center. Different horizons are selected to analyze the actual influence of vertical stress caused by depth, and 6cm, 9cm and 15cm horizons are selected to study the actual influence of vertical stress on basement modulus. It can be seen from the analysis results that the vertical stress of the surface layer is inversely proportional to the depth, that is, with the increase of the depth, the vertical stress of the surface layer decreases. The resilience modulus of subgrade has little effect on compressive stress.
2.4 Analysis of the Influence of Tensile Stress on Basement
In semi-rigid base, no matter whether each layer is continuous or sliding, the surface layer is usually in the compression zone and can't play a controlling role, so the tensile stress of base is the main controlling factor of pavement structure. The practice shows that the tensile stress of the basement is the main reason for the cracking of the structural layer. Pavement will bear load for a long time in the process of use, and it will be under the superposition of stress and strain for a long time, which will lead to the continuous reduction of structural strength. After the load reaches a certain number of times, the tensile stress of the base will cause pavement cracking. By analyzing the influence of subgrade modulus on the tensile stress of basement, it is known that the modulus of resilience increases from 20MPa to 100 MPa, and the tensile stress of basement decreases by 3 1%.
3 Conclusion
In this paper, with the help of BISAR3.0 calculation software, taking semi-rigid base scheme as the main research object, the actual influence of different elastic modulus on deflection and shear stress is discussed. Finally, the following conclusions can be drawn: (1) The top surface deflection of subgrade accounts for about 80%~90% of the pavement deflection, and its influence on the pavement deflection gradually weakens with the increase of rebound modulus. When the resilience modulus is less than 40MPa, based on this, the resilience modulus of the new highway should be above 40MPa to improve the overall bearing capacity of the pavement. (2) When the depth is above 10cm, the surface shear stress decreases obviously with the increase of depth, which shows that the subgrade resilience modulus will not have much influence on the surface shear stress, and improving the resilience modulus is not an effective measure to solve the diseases such as waves and piling. (3) With the increase of depth, the vertical stress of the surface layer decreases. The resilience modulus of subgrade has little effect on compressive stress. (4) The tensile stress of the basement is the main reason for the cracking of the structural layer, and increasing the resilience modulus of the subgrade will reduce the actual impact on the tensile stress of the basement.
References:
[1] Kang Jianxun. Variation of subgrade resilience modulus and its influence on asphalt pavement structure [J]. Traffic World, 2015 (7):108-109.
Sue. Influence of subgrade resilience modulus on asphalt pavement design parameters [J]. Communication Science and Technology Heilongjiang, 20 13 (8): 9- 10.
Li huixun Analysis of the influence of subgrade resilience modulus on asphalt pavement structure design [J]. Traffic World, 20 16 (32): 34-35.
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