CN108660880B - Method for determining optimal modulus combination of asphalt pavement structure layer - Google Patents
Method for determining optimal modulus combination of asphalt pavement structure layer Download PDFInfo
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Abstract
The invention provides a method for determining the optimal modulus combination of an asphalt pavement structure layer, which comprises the steps of firstly, taking an upper layer, a middle layer and a lower layer as a whole, selecting n groups of base layer surface layer modulus ratios by taking a modulus median value as a surface layer uniform modulus according to the requirement of a value range of an elastic modulus in a specification; inputting the modulus of the surface layer, the modulus ratios of the n groups of base surface layers and the thicknesses of the structural layers into finite element software to obtain the mechanical response influence of design indexes of the asphalt pavement under different modulus ratios of the base surface layers, and determining the optimal modulus ratio of the base surface layers; finally, according to the requirement of the specification on the value range of the elastic modulus of the inorganic binder stable material, changing the modulus gradient of the upper surface layer and the lower surface layer under the condition of ensuring that the average value of the upper surface layer, the middle surface layer and the lower surface layer is the middle value of the modulus of the whole surface layer, adjusting the modulus of the upper surface layer and the lower surface layer, and taking the combination of m groups of upper surface layer, middle surface layer and lower surface layer modulus groups; the method realizes the combination of the optimal modulus ratio of the base layer and the optimal modulus group of the surface layer.
Description
Technical Field
The invention belongs to the technical field of highway pavement design, and particularly relates to a method for determining an optimal modulus combination of a bituminous pavement structure layer.
Background
At present, the inorganic binder type stable base asphalt concrete pavement structure widely applied in China has certain plate property, rigidity and strong diffusion stress, and has certain tensile strength, fatigue resistance and good water stability. And thereby cause reflective cracking of the asphalt pavement.
In high-grade highways on which traffic is built in China, more than 90% of inorganic binder type stable base asphalt pavements with inorganic binder type stable materials as base courses and asphalt concrete as surface courses are used. The inorganic binder stable base layer has higher strength and bearing capacity, good overall stability and durability, and provides reliable guarantee for realizing the structure of a 'strong base thin surface'. In view of the inherent characteristics of the semi-rigid base material, the semi-rigid base asphalt pavement almost inevitably cracks the inorganic binder stable base layer due to overlarge tensile stress of the inorganic binder layer in the using process to generate reflection cracks, so that the quality of the asphalt pavement is influenced, and the service life of the asphalt pavement is reduced.
In order to effectively reduce the reflection cracks of the inorganic binder stabilized base asphalt pavement, systematic research is carried out from various aspects, and a plurality of treatment measures are provided, such as: increasing coarse aggregate content in the base material and strictly designing gradation, increasing the thickness of the asphalt pavement, etc., but these methods are not very effective.
Disclosure of Invention
The invention aims to provide a method for determining the optimal modulus combination of an asphalt pavement structure layer, so as to reduce cracking of inorganic binder stable base layers and reflective cracks of asphalt pavements caused by the cracking.
The technical solution for realizing the purpose of the invention is as follows:
a method for determining the optimal modulus combination of a bituminous pavement structure layer comprises the following steps:
compared with the prior art, the invention has the following remarkable advantages:
(1) the optimal modulus combination design method for the structural layers of the asphalt pavement, provided by the invention, realizes the combination of the optimal base layer modulus ratio and the optimal surface layer modulus group; the cracking of the inorganic binder stable base layer and the asphalt pavement reflective cracks caused by the cracking are reduced, so that the service life of the pavement structure is prolonged.
(2) And the selection of the structural design modulus of the key pavement is effectively guided when the structural combination design of the inorganic binder stable asphalt pavement is carried out by using sensitivity analysis.
The present invention is described in further detail below with reference to the attached drawing figures.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
Fig. 2 is a schematic view of a pavement structure.
FIG. 3 is a graph of finite element analysis of the trend of shear stress for an inorganic binder stabilized base asphalt pavement for different base overlay modulus ratios in example 1.
FIG. 4 is a graph of finite element analysis of the maximum asphalt layer tensile strain for the inorganic binder stabilized base asphalt pavement for different base overlay modulus ratios of example 1.
FIG. 5 is a finite element analysis graph of the maximum inorganic binder bed base tensile stress for the inorganic binder stabilized base asphalt pavement at different base bed face modulus ratios of example 1.
FIG. 6 is a finite element analysis graph of the maximum subgrade top vertical compressive strain of the inorganic binder stabilized base asphalt pavement at different base surface modulus ratios in example 1.
FIG. 7 is a graph of a finite element analysis of the shear stress of an inorganic binder stabilized base asphalt pavement under different surface modulus gradients in example 1.
FIG. 8 is a finite element analysis graph of the maximum asphalt layer tensile strain of the inorganic binder stabilized base asphalt pavement under different surface modulus gradients in example 1.
FIG. 9 is a finite element analysis graph of the maximum inorganic binder bed tensile stress of the inorganic binder stabilized base asphalt pavement under different surface modulus gradients in example 1.
FIG. 10 is a finite element analysis graph of the maximum subgrade top vertical compressive strain of the inorganic binder stabilized base asphalt pavement under different surface modulus gradients in example 1.
FIG. 11 is a finite element analysis graph of the amplitude of the design parameter fluctuation versus the base course modulus ratio fluctuation in example 1.
FIG. 12 is a graph of a finite element analysis of the trend of shear stress for an inorganic binder stabilized base asphalt pavement for different base overlay modulus ratios in example 2.
FIG. 13 is a graph of finite element analysis of the maximum asphalt layer tensile strain for the inorganic binder stabilized base asphalt pavement for different base overlay modulus ratios in example 2.
FIG. 14 is a finite element analysis graph of the maximum inorganic binder bed tensile stress for the inorganic binder stabilized base asphalt pavement at different base bed modulus ratios for example 2.
FIG. 15 is a finite element analysis graph of the maximum subgrade top vertical compressive strain of the inorganic binder stabilized base asphalt pavement at different base surface modulus ratios in example 2.
FIG. 16 is a graph of a finite element analysis of the shear stress of an inorganic binder stabilized base asphalt pavement under different surface modulus gradients in example 2.
FIG. 17 is a finite element analysis graph of the maximum asphalt layer tensile strain of the inorganic binder stabilized base asphalt pavement under different surface modulus gradients in example 2.
FIG. 18 is a finite element analysis graph of the maximum inorganic binder layer base tensile stress of the inorganic binder stabilized base asphalt pavement under different surface modulus gradients in example 2.
FIG. 19 is a finite element analysis graph of the maximum subgrade top surface vertical compressive strain of the inorganic binder stabilized base asphalt pavement under different surface layer modulus gradients in example 2.
FIG. 20 is a finite element analysis graph of the amplitude of the design parameter fluctuation versus the base course modulus ratio fluctuation in example 2.
Detailed Description
For the purpose of illustrating the technical solutions and technical objects of the present invention, the present invention will be further described with reference to the accompanying drawings and specific embodiments.
The invention discloses a method for determining the optimal modulus combination of a bituminous pavement structure layer, which comprises the following steps:
And 2, inputting the modulus of the surface layer, the modulus ratios of the n groups of base layer surface layers and the thicknesses of the structural layers into finite element software to obtain the mechanical response influence of the design indexes of the asphalt pavement under different base layer surface layer modulus ratios, and determining the optimal base layer surface layer modulus ratio according to the mechanical response result.
Step 2.1, analyzing the maximum shear stress variation trend of the base asphalt pavement under the modulus ratios of the n groups of base surface layers;
step 2.2, analyzing the variation trend of the bottom tensile strain of the maximum asphalt layer under the modulus ratio of n groups of base layer surface layers;
step 2.3, analyzing the variation trend of the maximum tensile stress of the inorganic bonding material layer under the modulus ratio of the n groups of base layer surface layers;
step 2.4, analyzing the vertical pressure strain variation trend of the maximum roadbed top surface under the modulus ratio of the n groups of base layer surface layers;
the influence of the base layer surface modulus on four design indexes of the surface shear stress, the asphalt mixture layer bottom tensile strain, the inorganic binder layer bottom tensile stress and the roadbed top surface vertical compressive strain of the asphalt pavement with the asphalt binder base layer is comprehensively considered, so that the optimal base layer modulus is obtained.
And 3, according to the requirement of a dynamic modulus value range of a common asphalt mixture at 20 ℃ in 'road asphalt pavement design Specification' in 2017 (JTG D50-2017), keeping the middle layer modulus value constant, changing the modulus gradient of the upper layer and the lower layer under the condition of ensuring that the mean value of the upper layer, the middle layer and the lower layer is the middle value of the modulus of the whole surface layer, adjusting the modulus of the upper layer and the lower layer, and taking the combination of m groups of upper layer, middle layer and lower layer modulus groups. Preferably m.gtoreq.3. The larger m, the better the resulting optimum modulus combination.
And 4, inputting the thickness of each structural layer and m groups of dynamic moduli into finite element software to obtain the mechanical response of the inorganic binder stable base asphalt pavement under different surface layer modulus gradients of the upper surface layer, the middle surface layer and the lower surface layer, and determining the final optimal modulus combination of the upper surface layer, the middle surface layer and the lower surface layer and the base layer according to the influence degree of the modulus gradients on control indexes.
4.1, analyzing the change trend of the shear stress of the inorganic binder stable base asphalt pavement under m groups of different surface modulus gradients;
4.2, analyzing the variation trend of the bottom tensile strain of the asphalt layer under m groups of different surface layer modulus gradients;
4.3, analyzing the variation trend of the bottom tensile stress of the inorganic binder stable base layer under m groups of different surface layer modulus gradients;
4.4, analyzing the variation trend of the vertical compressive strain of the top surface of the roadbed under the m groups of different surface layer modulus gradients;
the influence of the surface modulus gradient on four design indexes of the surface shear stress of the inorganic binder stable base asphalt pavement, the asphalt mixture layer bottom tensile strain, the inorganic binder stable base layer bottom tensile stress and the roadbed top surface vertical compressive strain is comprehensively considered, and the final optimal modulus combination of the upper, middle and lower surface layers and the base is determined.
And 5, researching the influence degree of the modulus of the base layer surface layer to the typical inorganic binder stable asphalt pavement structure combination design index through sensitivity analysis, thereby guiding the selection of the key pavement structure design modulus during the inorganic binder stable asphalt pavement structure combination design.
Firstly, inputting the optimal modulus combination and the modulus ratios of different base layer surface layers into finite element software to obtain the numerical values of the design indexes under the modulus ratios of different base layer surface layers, obtaining the influence of the modulus ratio of the base layer surface layers on the design indexes by using a sensitivity index formula, and sequencing the influence degrees to obtain the final optimal modulus ratio of the base layer surface layers.
The method comprises the steps of analyzing the influence rule of single parameter change on each design index, selecting the numerical value in the specification for other parameters, and matching with the local sensitivity analysis method, so that the local sensitivity analysis method is adopted, the design indexes are transformed by using a factor change method, namely each design index is used as an evaluation index, the relational expression of each design index and a key design parameter Xi is obtained respectively, the variation delta Xi of the pre-analyzed design index Xi is set, and the variation delta η of each design index is calculatediFinally, Δ η corresponding to different Δ Xi is usediThe degree of influence of each parameter on the design index is evaluated by using a value or sensitivity index delta ηiThe formula of (2) is shown in formula 4-2, and the sensitivity index SηThe calculation formula is shown in formula 4-3.
Let ηi＝f(Xi)
Then:
in the formula:
(xi) -each design index function expression;
Sη-sensitivity index for each index;
Δ Xi-amount of parameter change;
Δηiand the variation of each design index corresponding to the delta Xi.
The influence degrees of the modulus of the base course surface layer to each design index of a typical asphalt pavement are sequenced through sensitivity analysis, and the design parameter which is most influenced by the modulus of the base course surface layer is obtained, so that when the inorganic binder stable asphalt pavement structure is combined and designed, the modulus of the base course surface layer is controlled to enable each design index to be relatively excellent.
The following embodiment of the method is specifically described by taking two common and relatively excellent two sets of pavement structure thicknesses as examples: wherein the base course is made of 36cm cement stabilized macadam, the base course is made of 200mm lime stabilized soil, and the upper surface layer, the middle surface layer and the lower surface layer are respectively made of SMA-13, SUP-20 and SUP-25 grades.
The thicknesses of the upper layer, the middle layer, the lower layer, the base layer and the underlayer in example 1 are respectively 40mm, 60mm, 80mm, 360mm and 200 mm.
And 2, inputting the surface layer modulus, the six groups of base layer moduli and the thicknesses of the structural layers into finite element software to obtain the mechanical response influence of the design indexes of the asphalt pavement under different base layer surface layer modulus ratios, and determining the optimal base layer surface layer modulus ratio according to the mechanical response result.
TABLE 1 modulus of different substrates at different substrate to substrate modulus ratios
Step 2.1, analyzing the maximum shear stress variation trend of the base asphalt pavement under six groups of base surface layer modulus ratios:
and inputting the modulus of the surface layer, the modulus ratios of the six groups of base layer surface layers and the thicknesses of the structural layers into finite element software to obtain the influence of the maximum shear stress of the inorganic binder stable base layer asphalt pavement along with the change of the depth of the pavement under different base layer surface modulus ratios.
As can be seen from fig. 3, the overall trend of the maximum shear stress of the asphalt pavement structure surface layer under different base layer surface layer modulus ratios along the depth direction is increased and then gradually reduced. The specific change trend is that the shear stress value is increased firstly, then reduced, then increased and finally gradually reduced along the depth direction, wherein the maximum shear stress values are all present at a position 10mm away from a road surface and are positioned on an upper surface layer of the asphalt pavement; the shear stress value is larger in the depth range of 10 mm-100 mm. The shear stress variation trends of the asphalt pavement structures of the six different base layer modulus ratios are basically consistent, but the maximum shear stress value at a position 10mm away from a road surface increases along with the increase of the modulus ratio. Therefore, the modulus of the base surface layer has a certain influence on the maximum shear stress value in the stable base asphalt pavement structure of the inorganic binder.
Step 2.2, analyzing the variation trend of the maximum asphalt layer bottom tensile strain under six groups of base layer surface layer modulus ratios:
and inputting the modulus of the surface layer, the modulus ratios of the six groups of base layer surface layers and the thicknesses of the structural layers into finite element software to obtain the variation trend of the maximum asphalt layer bottom tensile strain under different base layer surface layer modulus ratios.
From fig. 4, it can be seen that the maximum asphalt layer base tensile strain of the inorganic binder stabilized base asphalt pavement structure is reduced and then increased along with the increase of the modulus ratio of the base layer, but the numerical value is smaller. Therefore, the base layer surface layer modulus has little influence on the maximum asphalt layer base tensile strain value of the stable base layer asphalt pavement structure of the inorganic binder.
Step 2.3, analyzing the variation trend of the maximum inorganic bonding material layer bottom tensile stress under six groups of base layer surface layer modulus ratios;
and inputting the modulus of the surface layer, the modulus ratios of the six groups of base layer surface layers and the thicknesses of all the structural layers into finite element software to obtain the variation trend of the maximum inorganic bonding material layer bottom tensile stress under different base layer surface layer modulus ratios.
From fig. 5, it can be seen that the maximum inorganic binder base layer tensile stress of the inorganic binder stabilized base layer asphalt pavement structure increases with the increase of the base layer surface modulus ratio, and the growth trend is larger. Therefore, the base layer surface layer modulus has a larger influence than the base tensile stress value of the inorganic binder layer in the stable base layer asphalt pavement structure of the inorganic binder.
2.4, analyzing the vertical pressure strain change trend of the top surface of the maximum roadbed under the modulus ratios of the six groups of base layer surface layers;
and inputting the modulus of the surface layer, the modulus ratios of the six groups of base layer surface layers and the thickness of each structural layer into finite element software to obtain the maximum vertical compressive strain variation trend of the top surface of the roadbed under different modulus ratios of the base layer surface layers.
From fig. 7, it can be seen that the maximum roadbed top vertical compressive strain of the asphalt pavement structure with the inorganic binder stabilized base layer is reduced along with the increase of the modulus ratio of the base layer surface layer, and the reduction range is larger. Therefore, the modulus of the base layer surface layer has a larger influence on the vertical pressure strain value of the top surface of the base in the stable base layer asphalt pavement structure of the inorganic binder.
Comprehensively considering the influence of the modulus ratio of the base layer surface layer on four design indexes of the surface layer maximum shear stress, the asphalt mixture layer bottom tensile strain, the maximum inorganic binder layer bottom tensile stress and the roadbed top surface vertical compressive strain of the asphalt pavement with the asphalt binder base layer, finding that the asphalt layer bottom tensile strain of the asphalt pavement with the asphalt binder base layer is influenced most by the change of the modulus ratio of the base layer surface layer, and controlling the numerical value not to be too large, so as to obtain the optimal modulus ratio of the base layer to the surface layer of 1.2.
And 3, according to the requirement of a dynamic modulus value range of a common asphalt mixture at 20 ℃ in 'road asphalt pavement design Specification' in 2017 (JTG D50-2017), keeping the middle layer modulus value constant, changing the modulus gradient of the upper layer and the lower layer under the condition of ensuring that the mean value of the upper layer, the middle layer and the lower layer is the middle value of the modulus of the whole surface layer, adjusting the modulus of the upper layer and the lower layer, and taking the combination of m groups of upper layer, middle layer and lower layer modulus groups. Taking m as 4, namely taking four groups of moduli of the upper, middle and lower surface layers: (7000, 10000, 13000), (9000, 10000, 11000), (11000, 10000, 9000), (13000, 10000, 7000) as shown in table 2.
TABLE 2 modulus of the layers
And 4, inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the mechanical response of the inorganic binder stable base asphalt pavement under different surface layer modulus gradients of the upper surface layer, the middle surface layer and the lower surface layer, and determining the final optimal modulus combination of the upper surface layer, the middle surface layer and the lower surface layer and the base layer according to the influence degree of the modulus gradients on control indexes.
4.1, analyzing the change trend of the shear stress of the asphalt pavement with the inorganic binder stable base layer under four groups of different surface modulus gradients;
inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the influence of the maximum shear stress of the inorganic binder stable base asphalt pavement along with the change of the pavement depth under different surface modulus gradient groups.
As can be seen from FIG. 7, the overall trend of the shear stress of the pavement structure surface layer of the asphalt pavement under different surface layer modulus gradient conditions along the depth direction is gradually reduced after being increased. The specific change trend is that the shear stress value is increased firstly, then reduced, then increased and finally gradually reduced along the depth direction, wherein the maximum shear stress values are all present at a position 10mm away from a road surface and are positioned on an upper surface layer of the asphalt pavement; the shear stress value is larger in the depth range of 10 mm-100 mm. The shear stress variation trends of the asphalt pavement structures with the four different surface layer modulus gradients are basically consistent, but the maximum shear stress value at a position 10mm away from a road surface is greatly different, the modulus gradient group a is minimum, and the modulus gradient group d is maximum. Therefore, the modulus gradient of the surface layer has a large influence on the maximum shear stress value in the asphalt pavement structure with the inorganic binder stable base layer.
4.2, analyzing the variation trend of the bottom tensile strain of the asphalt layer under m groups of different surface layer modulus gradients;
inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the variation trend of the maximum asphalt layer base strain of the inorganic binder stable base asphalt pavement under different surface layer modulus gradient groups.
From fig. 8, it can be found that the maximum asphalt layer tensile strain of the inorganic binder stabilized base asphalt pavement structure is greatly different along with the change of the surface layer modulus gradient, the maximum asphalt layer tensile strain of both pavement structures is smaller under the condition of the surface layer modulus gradient group b, and the maximum asphalt layer tensile strain of the modulus gradient group d is 7 times that of the modulus gradient group b. Therefore, the surface modulus gradient has great influence on the maximum asphalt layer bottom tensile strain value of the asphalt pavement structure with the inorganic binder stable base layer.
4.3, analyzing the variation trend of the bottom tensile stress of the inorganic binder stable base layer under m groups of different surface layer modulus gradients;
inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the variation trend of the maximum inorganic bonding material layer bottom tensile stress under different surface layer modulus gradient groups.
It can be found from fig. 8 that the variation difference of the maximum inorganic binder layer base tensile stress of the inorganic binder stabilized base asphalt pavement structure along with the modulus gradient of the surface layer is very small, and the variation laws of the first structure and the second structure are completely opposite, the maximum inorganic binder layer base tensile stress of the first structure is the maximum under the condition of the modulus gradient group a of the surface layer, and the maximum inorganic binder layer base tensile stress of the second structure is the maximum under the condition of the modulus gradient group d of the surface layer, but the numerical difference is very small. Therefore, the modulus gradient of the surface layer has little influence on the maximum tensile stress value of the inorganic binder layer of the asphalt pavement structure with the stable inorganic binder base layer.
4.4, analyzing the variation trend of the vertical compressive strain of the top surface of the roadbed under the m groups of different surface layer modulus gradients;
inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the maximum roadbed top surface vertical compression strain variation trend under different surface layer modulus gradient groups.
From fig. 10, it can be found that the difference of the maximum vertical compressive strain of the roadbed top surface of the asphalt pavement structure with the stabilized base layer by the inorganic binder is smaller along with the change of the modulus gradient of the surface layer, the maximum vertical compressive strain of the roadbed top surface is the largest under the condition of the modulus gradient a of the surface layer, and the influence of the modulus gradient of the surface layer on the maximum vertical compressive strain value of the roadbed top surface of the asphalt pavement structure with the stabilized base layer by the inorganic binder is small.
Comprehensively considering the influence of the surface layer modulus gradient on four design indexes of the surface layer shear stress, the asphalt mixture layer bottom tensile strain, the inorganic binder stable base layer bottom tensile stress and the roadbed top surface vertical compressive strain of the inorganic binder stable base layer asphalt pavement, the surface layer shear stress and the asphalt layer bottom tensile strain are greatly influenced by the surface layer modulus gradient change, and under the condition that the two indexes are controlled not to be too large, the surface layer modulus gradient group b is recommended to be the optimal combination scheme
And 5, researching the influence degree of the modulus of the base layer surface layer to the typical inorganic binder stable asphalt pavement structure combination design index through sensitivity analysis, thereby guiding the selection of the key pavement structure design modulus during the inorganic binder stable asphalt pavement structure combination design.
5.1, firstly inputting the optimal modulus combination and the modulus ratios of different base layer surface layers into finite element software to obtain the numerical values of the design indexes under the modulus ratios of the different base layer surface layers;
inputting the modulus gradient group b and the six groups of base layer surface layer modulus ratios into finite element software to obtain the numerical values of the design indexes under different base layer surface layer modulus ratios, as shown in table 3:
TABLE 3 different design index values for different bedding layer modulus ratios under modulus gradient set b
| Ratio of modulus of base layer to surface |
1 | 1.3 | 1.5 | 1.8 | 2 | 2.5 |
| Maximum shear stress/MPa | 0.194 | 0.1986 | 0.204 | 0.21 | 0.2121 | 0.2286 |
| Asphalt layer bottom tensile strain/mu epsilon | 3.517 | 1.749 | 1.973 | 2.268 | 2.469 | 2.958 |
| Inorganic bond bed bottom tensile stress/MPa | 0.2279 | 0.2538 | 0.2688 | 0.2889 | 0.301 | 0.3276 |
| Vertical compressive strain/mu epsilon of roadbed top surface | 55.44 | 49.69 | 46.79 | 43.33 | 41.42 | 37.6 |
5.2, utilizing a sensitivity index formula to the numerical value of the design index to obtain the influence of the base layer surface layer modulus ratio on the design index, and sequencing the influence degree to obtain the final optimal base layer surface layer modulus ratio:
the numerical value of the design index obtained in table 3 is substituted into formula 4-3 to obtain the influence of the base layer surface modulus ratio on the design index, as shown in fig. 11.
Carry out sequencing analysis with the influence degree of base course surface course modulus ratio bituminous paving structure design index through sensitivity analysis, can see from figure 11 that base course surface course modulus ratio is the biggest to the vertical compressive strain influence degree of the top surface of the roadbed of these two kinds of typical bituminous paving structures, secondly is bituminous layer bottom tensile strain, consequently need pay attention to the thickness and the modulus of base material when bituminous paving structure combination design, chooses for use better base material. The modulus of the base material needs to be larger than that of the surface layer material, and the optimal ratio of the modulus of the surface layer of the base layer of the inorganic binder stabilized base asphalt pavement is 1.3-1.5.
The thicknesses of the upper layer, the middle layer, the lower layer, the base layer and the underlayer in example 2 are respectively 20mm, 80mm, 360mm and 200 mm.
And 2, inputting the surface layer modulus, the six groups of base layer moduli and the thicknesses of the structural layers into finite element software to obtain the mechanical response influence of the design indexes of the asphalt pavement under different base layer surface layer modulus ratios, and determining the optimal base layer surface layer modulus ratio according to the mechanical response result.
TABLE 4 modulus of different substrates at different substrate to facing modulus ratios
Step 2.1, analyzing the maximum shear stress variation trend of the base asphalt pavement under six groups of base surface layer modulus ratios:
and inputting the modulus of the surface layer, the modulus ratios of the six groups of base layer surface layers and the thicknesses of the structural layers into finite element software to obtain the influence of the maximum shear stress of the inorganic binder stable base layer asphalt pavement along with the change of the depth of the pavement under different base layer surface modulus ratios.
As can be seen from fig. 12, the overall trend of the maximum shear stress of the asphalt pavement structure surface layer under different base layer surface layer modulus ratios along the depth direction is increased and then gradually decreased. The specific change trend is that the shear stress value is increased firstly, then reduced, then increased and finally gradually reduced along the depth direction, wherein the maximum shear stress values are all present at a position 10mm away from a road surface and are positioned on an upper surface layer of the asphalt pavement; the shear stress value is larger in the depth range of 10 mm-100 mm. The shear stress variation trends of the asphalt pavement structures of the six different base layer modulus ratios are basically consistent, but the maximum shear stress value at a position 10mm away from a road surface increases along with the increase of the modulus ratio. Therefore, the modulus of the base surface layer has a certain influence on the maximum shear stress value in the stable base asphalt pavement structure of the inorganic binder.
Step 2.2, analyzing the variation trend of the maximum asphalt layer bottom tensile strain under six groups of base layer surface layer modulus ratios:
and inputting the modulus of the surface layer, the modulus ratio of the base layer and the thickness of each structural layer into finite element software to obtain the variation trend of the maximum asphalt layer bottom tensile strain under different modulus ratios of the base layer and the surface layer.
From fig. 13, it can be seen that the maximum asphalt layer base tensile strain of the inorganic binder stabilized base asphalt pavement structure is reduced and then increased along with the increase of the modulus ratio of the base layer, but the numerical value is smaller. Therefore, the base layer surface layer modulus has little influence on the maximum asphalt layer base tensile strain value of the stable base layer asphalt pavement structure of the inorganic binder.
Step 2.3, analyzing the variation trend of the maximum inorganic bonding material layer bottom tensile stress under six groups of base layer surface layer modulus ratios;
and inputting the modulus of the surface layer, the modulus ratios of the six groups of base layer surface layers and the thicknesses of all the structural layers into finite element software to obtain the variation trend of the maximum inorganic bonding material layer bottom tensile stress under different base layer surface layer modulus ratios.
From fig. 14, it can be seen that the maximum inorganic binder base layer tensile stress of the inorganic binder stabilized base layer asphalt pavement structure increases with the increase of the base layer surface modulus ratio, and the growth trend is larger. Therefore, the base layer surface layer modulus has a larger influence than the base tensile stress value of the inorganic binder layer in the stable base layer asphalt pavement structure of the inorganic binder.
2.4, analyzing the vertical pressure strain change trend of the top surface of the maximum roadbed under the modulus ratios of the six groups of base layer surface layers;
and inputting the modulus of the surface layer, the modulus ratios of the six groups of base layer surface layers and the thickness of each structural layer into finite element software to obtain the maximum vertical compressive strain variation trend of the top surface of the roadbed under different modulus ratios of the base layer surface layers.
From fig. 15, it can be seen that the maximum topsides vertical compressive strain of the asphalt pavement structure with the inorganic binder stabilized base layer decreases with the increase of the modulus ratio of the base layer surface layer, and the decrease is larger. Therefore, the modulus of the base layer surface layer has a larger influence on the vertical pressure strain value of the top surface of the base in the stable base layer asphalt pavement structure of the inorganic binder.
Comprehensively considering the influence of the modulus ratio of the base layer surface layer on four design indexes of the surface layer maximum shear stress, the asphalt mixture layer bottom tensile strain, the maximum inorganic binder layer bottom tensile stress and the roadbed top surface vertical compressive strain of the asphalt pavement with the asphalt binder base layer, finding that the asphalt layer bottom tensile strain of the asphalt pavement with the asphalt binder base layer is influenced most by the change of the modulus ratio of the base layer surface layer, and controlling the numerical value not to be too large, so as to obtain the optimal modulus ratio of the base layer to the surface layer of 1.2.
And 3, according to the requirement of a dynamic modulus value range of a common asphalt mixture at 20 ℃ in 'road asphalt pavement design Specification' in 2017 (JTG D50-2017), keeping the middle layer modulus value constant, changing the modulus gradient of the upper layer and the lower layer under the condition of ensuring that the mean value of the upper layer, the middle layer and the lower layer is the middle value of the modulus of the whole surface layer, adjusting the modulus of the upper layer and the lower layer, and taking the combination of m groups of upper layer, middle layer and lower layer modulus groups. Taking m as 4, namely taking four groups of moduli of the upper, middle and lower surface layers: (7000, 10000, 13000), (9000, 10000, 11000), (11000, 10000, 9000), (13000, 10000, 7000) as shown in table 5.
TABLE 5 modulus of the layers
And 4, inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the mechanical response of the inorganic binder stable base asphalt pavement under different surface layer modulus gradients of the upper surface layer, the middle surface layer and the lower surface layer, and determining the final optimal modulus combination of the upper surface layer, the middle surface layer and the lower surface layer and the base layer according to the influence degree of the modulus gradients on control indexes.
4.1, analyzing the change trend of the shear stress of the asphalt pavement with the inorganic binder stable base layer under four groups of different surface modulus gradients;
inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the influence of the maximum shear stress of the inorganic binder stable base asphalt pavement along with the change of the pavement depth under different surface modulus gradient groups.
As can be seen from fig. 16, the overall trend of the shear stress of the pavement structure surface layer along the depth direction under different surface layer modulus gradient conditions is gradually reduced after being increased. The specific change trend is that the shear stress value is increased firstly, then reduced, then increased and finally gradually reduced along the depth direction, wherein the maximum shear stress values are all present at a position 10mm away from a road surface and are positioned on an upper surface layer of the asphalt pavement; the shear stress value is larger in the depth range of 10 mm-100 mm. The shear stress variation trends of the asphalt pavement structures with the four different surface layer modulus gradients are basically consistent, but the maximum shear stress value at a position 10mm away from a road surface is greatly different, the modulus gradient group a is minimum, and the modulus gradient group d is maximum. Therefore, the modulus gradient of the surface layer has a large influence on the maximum shear stress value in the asphalt pavement structure with the inorganic binder stable base layer.
4.2, analyzing the variation trend of the bottom tensile strain of the asphalt layer under m groups of different surface layer modulus gradients;
inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the variation trend of the maximum asphalt layer base strain of the inorganic binder stable base asphalt pavement under different surface layer modulus gradient groups.
From fig. 17, it can be found that the maximum asphalt layer tensile strain of the inorganic binder stabilized base asphalt pavement structure is greatly different along with the change of the surface layer modulus gradient, the maximum asphalt layer tensile strain of both pavement structures is smaller under the condition of the surface layer modulus gradient group b, and the maximum asphalt layer tensile strain of the modulus gradient group d is 7 times that of the modulus gradient group b. Therefore, the surface modulus gradient has great influence on the maximum asphalt layer bottom tensile strain value of the asphalt pavement structure with the inorganic binder stable base layer.
4.3, analyzing the variation trend of the bottom tensile stress of the inorganic binder stable base layer under m groups of different surface layer modulus gradients;
inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the variation trend of the maximum inorganic bonding material layer bottom tensile stress under different surface layer modulus gradient groups.
As can be seen from fig. 18, the variation difference of the maximum inorganic binder layer tensile stress of the inorganic binder stabilized similar-base asphalt pavement structure along with the modulus gradient of the surface layer is very small, and the variation laws of the first structure and the second structure are completely opposite, the maximum inorganic binder layer tensile stress of the first structure is the maximum under the condition of the modulus gradient group a of the surface layer, and the maximum inorganic binder layer tensile stress of the second structure is the maximum under the condition of the modulus gradient group d of the surface layer, but the numerical difference is very small. Therefore, the modulus gradient of the surface layer has little influence on the maximum tensile stress value of the inorganic binder layer of the asphalt pavement structure with the stable inorganic binder base layer.
4.4, analyzing the variation trend of the vertical compressive strain of the top surface of the roadbed under the m groups of different surface layer modulus gradients;
inputting the thickness of each structural layer and four groups of dynamic moduli into finite element software to obtain the maximum roadbed top surface vertical compression strain variation trend under different surface layer modulus gradient groups.
From fig. 19, it can be found that the difference of the maximum roadbed top surface vertical compressive strain of the inorganic binder stabilized base asphalt pavement structure along with the change of the surface layer modulus gradient is small, the maximum roadbed top surface vertical compressive strain is maximum under the condition of the surface layer modulus gradient a, and the influence of the surface layer modulus gradient on the maximum roadbed top surface vertical compressive strain value of the inorganic binder stabilized base asphalt pavement structure is small.
Comprehensively considering the influence of the surface layer modulus gradient on four design indexes of the surface layer shear stress, the asphalt mixture layer bottom tensile strain, the inorganic binder stable base layer bottom tensile stress and the roadbed top surface vertical compressive strain of the inorganic binder stable base layer asphalt pavement, the surface layer shear stress and the asphalt layer bottom tensile strain are greatly influenced by the surface layer modulus gradient change, and under the condition that the two indexes are controlled not to be too large, the surface layer modulus gradient group b is recommended to be the optimal combination scheme
And 5, researching the influence degree of the modulus of the base layer surface layer to the typical inorganic binder stable asphalt pavement structure combination design index through sensitivity analysis, thereby guiding the selection of the key pavement structure design modulus during the inorganic binder stable asphalt pavement structure combination design.
5.1, firstly inputting the optimal modulus combination and the modulus ratios of different base layer surface layers into finite element software to obtain the numerical values of the design indexes under the modulus ratios of the different base layer surface layers;
inputting the modulus gradient group b and the six groups of base layer surface layer modulus ratios into finite element software to obtain the numerical values of the design indexes under different base layer surface layer modulus ratios, as shown in table 6:
TABLE 6 different design index values for different bedding layer modulus ratios under modulus gradient set b
| Ratio of modulus of base layer to surface |
1 | 1.3 | 1.5 | 1.8 | 2 | 2.5 |
| Maximum shear stress/MPa | 0.194 | 0.1986 | 0.204 | 0.21 | 0.2121 | 0.2286 |
| Asphalt layer bottom tensile strain/mu epsilon | 3.517 | 1.749 | 1.973 | 2.268 | 2.469 | 2.958 |
| Inorganic bond bed bottom tensile stress/MPa | 0.2279 | 0.2538 | 0.2688 | 0.2889 | 0.301 | 0.3276 |
| Vertical compressive strain/mu epsilon of roadbed top surface | 55.44 | 49.69 | 46.79 | 43.33 | 41.42 | 37.6 |
5.2, utilizing a sensitivity index formula to the numerical value of the design index to obtain the influence of the base layer surface layer modulus ratio on the design index, and sequencing the influence degree to obtain the final optimal base layer surface layer modulus ratio:
the numerical value of the design index obtained in table 3 is substituted into formula 4-3 to obtain the influence of the base layer surface modulus ratio on the design index, as shown in fig. 20.
Carry out sequencing analysis with the influence degree of base course surface course modulus ratio bituminous paving structure design index through sensitivity analysis, can see from figure 20 that base course surface course modulus ratio is the biggest to the vertical compressive strain influence degree of the top surface of the roadbed of these two kinds of typical bituminous paving structures, and secondly is the bituminous layer bottom tensile strain, consequently need pay attention to the thickness and the modulus of base material when bituminous paving structure combination design, chooses for use better base material. The modulus of the base material needs to be larger than that of the surface layer material, and the optimal ratio of the modulus of the surface layer of the base layer of the inorganic binder stabilized base asphalt pavement is 1.3-1.5.
By the method, the optimum modulus combination of each structural layer of the asphalt pavement with the inorganic binder stable base layer can be determined through abaqus software analysis, the cracking of the inorganic binder stable base layer and the reflective cracks of the asphalt pavement caused by the cracking are reduced, and the service life of the pavement structure is prolonged.
Claims (10)
1. The method for determining the optimal modulus combination of the asphalt pavement structure layer is characterized by comprising the following steps of:
step 1, according to the structural combination of the existing asphalt pavement, an upper surface layer, a middle surface layer and a lower surface layer are regarded as a whole, according to the requirement of a specification on the value range of the elastic modulus of an inorganic binder stable material at 20 ℃, the modulus median is taken as the uniform modulus of the surface layer, and n groups of base layer surface layer modulus ratios are selected;
step 2, inputting the surface layer modulus, the n groups of base layer surface layer modulus ratios and the thicknesses of the structural layers into finite element software to obtain the mechanical response influence of the design indexes of the asphalt pavement under different base layer surface layer modulus ratios, and determining the optimal base layer surface layer modulus ratio according to the mechanical response result;
step 3, changing modulus gradients of the upper surface layer and the lower surface layer, adjusting the moduli of the upper surface layer and the lower surface layer, and combining m groups of upper surface layer modulus groups, middle surface layer modulus groups and lower surface layer modulus groups according to the requirement of the specification on the value range of the elastic modulus of the inorganic binder stable material, and under the condition of ensuring that the average value of the upper surface layer, the middle surface layer and the lower surface layer is the median value of the modulus of the whole surface layer;
and 4, inputting the thickness of each structural layer and m groups of dynamic moduli into finite element software to obtain the mechanical response of the inorganic binder stable base asphalt pavement under different surface layer modulus gradients of the upper surface layer, the middle surface layer and the lower surface layer, and determining the final optimal modulus combination of the upper surface layer, the middle surface layer and the lower surface layer and the base layer according to the influence degree of the modulus gradients on control indexes.
2. The method for determining the optimal modulus combination of the asphalt pavement structure layer according to claim 1, wherein the design indexes comprise the maximum shear stress of the base asphalt pavement, the maximum asphalt layer bottom tensile strain, the maximum inorganic binder layer bottom tensile stress and the maximum roadbed top surface vertical compressive strain.
3. The method for determining the optimal modulus combination of the asphalt pavement structure layers according to claim 1, wherein n is greater than or equal to 3, and m is greater than or equal to 3.
4. The method of claim 1, further comprising the step of determining the optimal modulus combination of the asphalt pavement structure layers,
and 5, firstly inputting the optimal modulus combination and different base layer modulus ratios into finite element software to obtain the numerical values of the design indexes under different base layer modulus ratios, obtaining the influence of the base layer modulus ratio on the design indexes by using the sensitivity index formula on the numerical values of the design indexes, and sequencing the influence degrees to obtain the final optimal base layer modulus ratio.
5. The method for determining the optimal modulus combination of the asphalt pavement structure layers according to claim 4, wherein a local sensitivity analysis method is adopted, each design index is used as an evaluation index, and the sensitivity index S isηThe calculation formula is as follows:
let ηi＝f(Xi)
Then:
in the formula:
(xi) -each design index function expression;
Sη-sensitivity index for each index;
Δ Xi-amount of parameter change;
Δηiand the variation of each design index corresponding to the delta Xi.
6. The method for determining the optimal modulus combination of the asphalt pavement structure layer according to claim 1, wherein in step 1, the median modulus 10000 is taken as the uniform modulus of the surface layer, and the thicknesses of the upper layer, the middle layer, the lower layer, the base layer and the subbase layer are respectively 40mm, 60mm, 80mm, 360mm and 200 mm; n is 6; the modulus ratios of the base layer and the surface layer are respectively 1.0, 1.3, 1.5, 1.8, 2.0 and 2.5.
7. The method for determining the optimal modulus combination of the asphalt pavement structure layers according to claim 6, wherein m is 4; the modulus of the upper, middle and lower surface layers are four groups: (7000, 10000, 13000), (9000, 10000, 11000), (11000, 10000, 9000), (13000, 10000, 7000).
8. The method for determining the optimal modulus combination of the asphalt pavement structure layer as claimed in claim 7, wherein the optimal modulus ratio of the base layer to the surface layer is 1.2, and the optimal modulus combination is (9000, 10000, 11000).
9. The method for determining the optimal modulus combination of the asphalt pavement structure layer according to claim 1, wherein in step 1, the median modulus 10000 is taken as the uniform modulus of the surface layer, and the thicknesses of the upper surface layer, the middle surface layer, the lower surface layer, the base layer and the underlayer are respectively the same, and in step 1, the median modulus 10000 is taken as the uniform modulus of the surface layer, and the thicknesses of the upper surface layer, the middle surface layer, the lower surface layer, the base layer and the underlayer are respectively 20mm, 80mm, 360mm and 200 mm; n is 6; the modulus ratios of the base layer and the surface layer are respectively 1.0, 1.3, 1.5, 1.8, 2.0 and 2.5.
10. The method for determining the optimal modulus combination of the asphalt pavement structure layers according to claim 9, wherein m is 4; the modulus of the upper, middle and lower surface layers are four groups: (7000, 10000, 13000), (9000, 10000, 11000), (11000, 10000, 9000), (13000, 10000, 7000).
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