JP7705589B2 - Pavement structure design method and interlocking block pavement structure - Google Patents

Description

Article 30, paragraph 2 of the Patent Act September 10, 2020, Japan Port Consultants Co., Ltd.

The present invention relates to a pavement structure design method for interlocking block pavement in heavy load areas and to an interlocking block pavement structure.

The "multilayer elastic theory" and "fatigue analysis" are used in combination in the structural design of pavements in heavy load areas such as container yards. When using the multilayer elastic theory for design, the most important factor is the numerical setting of the elastic coefficient of the ILB (Inter Locking Block) and the laying sand. If this value is set too low, the stress and strain generated in the pavement will be large, shortening its service life. On the other hand, if this value is set too high, the stress and strain will be small, lengthening its service life. In Japan, there have been no cases where the "multilayer elastic theory" and "fatigue analysis" have been applied to ILB pavements constructed in container yards.

For example, the Kawasaki Port Container Terminal, which was constructed about 24 years ago (1996), applied a design method proposed by the British Port and Harbour Association, while Osaka Nanko and Kobe Port Island have been constructed by cutting out 12 cm of severely damaged semi-flexible pavement and modified asphalt layers and replacing them with 100 mm of ILB and 20 mm of sand. As it is planned that 100 mm ILB will be adopted in container yards in Tokyo in the future, there is an urgent need to consider roadbed design.

In 1982, Professor Miura of Nihon University reported on the elastic modulus of the ILB and bedding sand, reporting that the value obtained by analyzing the ILB and bedding sand as one layer using a DC meter was 1648 MPa, and that the ILB alone was about 4335 MPa. Later, in 1989, Professor Kasahara et al. of Hokkaido Institute of Technology (now Hokkaido University of Science) reported that the elastic modulus of the ILB and bedding sand was 98-392 MPa based on the results of measuring the deflection at four points on the ILB pavement at the construction site using a towed FWD (Falling Weight Deflectmeter) device. In 1998, Professor Murai et al. of Tohoku Institute of Technology reported that the elastic modulus of the ILB alone was 1960 MPa, and that of the bedding sand alone was 29 MPa based on the results of tests using a vehicle-mounted FWD.

Patent Document 1 proposes a method for predicting the lifespan of pavement at the time of pavement design, using the multi-layer elastic theory, while taking into consideration the differences between the two-layer elastic theory and the multi-layer elastic theory, when predicting the lifespan of pavement at the time of pavement design for pavement structurally designed using the two-layer elastic theory. In this technology, the pavement is divided into upper and lower layers, the design cross section of each layer is determined based on the two-layer elastic theory, and the determined layer thickness of each layer and the design elastic coefficient corresponding to the material used in each layer are given, and the pavement lifespan caused by tensile strain occurring on the underside of the surface and base layers, and the pavement lifespan caused by compressive strain occurring on the upper surface of the roadbed are calculated from a given failure criterion formula based on the multi-layer elastic theory.

JP 2002-371503 A

The healthy value of the elastic modulus for asphalt pavement is generally considered to be 6,000 MPa, and in winter it can exceed 10,000 MPa. Compared to these values, the values from the previous research results mentioned above are far too small, so if these values are used to design the structure of heavy load areas, it will be necessary to reinforce the roadbed and subgrade structure, resulting in higher costs.

Furthermore, compared to asphalt pavements and semi-flexible pavements, a major feature of ILB pavements in heavy load areas is that, because the material is concrete, it does not undergo flow deformation during the high temperatures of summer like asphalt pavements, and the numerous regular joints make it less susceptible to the cracks that occur in asphalt pavements. However, the results of research to date cannot be considered to reflect the characteristics of ILB pavements. The low elastic modulus in previous research results is thought to be due to the pavement diagnostic equipment and analysis methods.

The present invention was made in consideration of these circumstances, and aims to provide a pavement structure design method and an interlocking block pavement structure that can maintain good road surface properties in heavy load areas for a long period of time by applying multi-layer elasticity theory and fatigue analysis.

(1) In order to achieve the above object, the present invention has taken the following measures. That is, the pavement structure design method of the present invention is a pavement structure design method for interlocking block pavement in a heavy load area, and is characterized by including at least the steps of: calculating the elastic modulus of the sand laid on the upper roadbed and the block layer integrating the interlocking blocks laid on the sand using the measurement results obtained by performing deflection measurements on an interlocking block pavement consisting of a roadbed, a lower roadbed, an upper roadbed, sand, and interlocking blocks; calculating the elastic modulus of the sand alone and the interlocking block alone laid on the sand; and applying the elastic modulus of the block layer, the elastic modulus of the sand alone, and the elastic modulus of the interlocking block alone to the multilayer elasticity theory to calculate the deflection, stress, or strain of the interlocking block pavement in a heavy load area.

(2) The pavement structure design method of the present invention is also characterized in that it further uses the interlayer slippage between the interlocking blocks and the bedding sand, and the interlayer slippage between the bedding sand and the upper roadbed to calculate the deflection, stress, or strain of the interlocking block pavement in the heavy load area.

(3) The pavement structure design method of the present invention is also characterized by further setting the allowable deflection amount of the interlocking block pavement.

(4) The interlocking block pavement structure of the present invention is an interlocking block pavement structure in a heavy load area, designed using the pavement structure design method described in any one of (1) to (3) above, and characterized in that the roadbed, subbase, upper base, bedding sand, and interlocking blocks are layered.

According to the present invention, it is possible to maintain good road surface properties in heavy load areas for a long period of time. It is also possible to realize a pavement structure that is highly durable, reliable, and safe. Furthermore, as a result of the improved durability, it is possible to reduce the life cycle cost (LCC).

1 is a flowchart showing the steps of a pavement structure design method according to an embodiment of the present invention. FIG. 1 is a diagram showing an example of deflection (d) and strain (εr _{, εz} ) that occurs in a pavement composed of a roadbed, a lower subgrade, an upper subgrade (asphalt mixture), a sand layer, and an ILB, in that order. FIG. 1 is a diagram showing examples of deflection (d), stress (σ _r ), and strain (ε _z ) that occur in a pavement composed of a roadbed, a subbase, an upper base (cement-based, concrete-based), a sand layer, and an ILB, in that order. This figure shows examples of deflection (d), stress (σr), and strain (εr, εz) that occur in a pavement composed of a roadbed, a lower subgrade, an upper subgrade (cement-based, _concrete -based), an upper subgrade ( _{asphalt-based mixture), a sand layer} , and an _ILB , in that order. FIG. 1 is a diagram showing an example of a fatigue curve of a material. This figure shows the correlation between joint width, damage rate, and deflection amount in interlocking block pavement.

[Multilayer elasticity theory and fatigue analysis]
The multilayer elastic theory is a method of calculating the displacement (deflection d), stress (σ r ), and strain (ε _{r ,} ε _z ) that occur at any point on the pavement, assuming that the material of each layer that makes up the pavement is elastic, as shown in Figures 2A to 2C. FIG. 2A is a diagram showing an example of deflection (d) and strain (εr _{, εz} ) that occurs in a pavement composed of the roadbed, lower roadbed, upper roadbed (cement-based, concrete-based), sand, and ILB, in that order. FIG. 2B is a diagram showing an example of deflection (d), stress (σr), and strain ( _εr ) that occurs in a pavement composed of the roadbed, lower roadbed, upper roadbed (cement-based, concrete-based), sand, and ILB, in that order. FIG. 2C is a diagram showing an example of deflection ( _d ), stress (σr), and strain (εr, _εz ) that occurs in a pavement composed of the roadbed, lower roadbed, upper roadbed (cement-based, concrete-based), upper roadbed (asphalt-based mixture), _{sand, and ILB} , in that order. On the other hand, fatigue analysis involves calculating the allowable number of load cycles by applying the material fatigue curve and fatigue failure criteria shown in Figure 3 to the obtained stress and strain. From the results of this calculation, it is essential to satisfy the following formula:
(Permissible number of loaded wheels) ≧ (Design traffic volume)
[About elastic modulus]
The elastic modulus of a material can be calculated by dividing the stress obtained from indoor tests by the strain. For pavements, the higher this value, the higher the bearing capacity. When applying multi-layer elasticity theory, the most important factor is the value of the elastic modulus of each layer of the pavement. For asphalt and concrete pavements, values of the elastic modulus have been proposed based on previous research results, including the roadbed and subgrade. For ILB pavements, as mentioned above, the values in previous research results are small, so it is inappropriate to apply these values.

The elastic modulus of the new material can be calculated from the results of non-destructive tests such as the Falling Weight Deflectmeter (FWD) and repeated load tests conducted indoors. The FWD is a device that drops a weight onto the pavement to apply an impact load and measures the deflection shape of the pavement surface that occurs at that time. From the deflection shape measured by this device, it is possible to estimate the elastic modulus of the pavement constituent layers using a dedicated program (for example, the dynamic back analysis program Wave BALM).

[Measurement of elastic modulus]
In order to measure the elastic modulus of the ILB and the bedding sand to be applied to the structural analysis, the inventors, with the cooperation of a major road company, performed deflection measurements on the ILB pavement at the Osaka Nanko Container Yard in September 2018 using the latest diagnostic device (vehicle-mounted FWD) at that time. As a result of analyzing the deflection amount obtained by this measurement, the elastic modulus when the ILB and the bedding sand are one layer was "3000 to 8000 MPa", and the average value was "5100 MPa". In addition, according to an analysis by Professor Kawana et al. of Tokyo University of Agriculture, the elastic modulus of the ILB alone was "5000 to 12000 MPa", and the average value was "8200 MPa". In addition, the elastic modulus of the bedding sand alone was "10 to 50 MPa", and the average value was "20 MPa".

In this invention, the elastic modulus applied to the structural design is the value for the ILB alone, the value for the laid sand alone, and the value for the ILB and laid sand combined into one layer (hereafter referred to as the "block layer"). This is because it has been confirmed that there are differences in deflection, stress, and strain between the "ILB alone and laid sand alone" and the "block layer" depending on the pavement structure.

In ILB pavement, when the bedding sand becomes finer and hardens, "interlayer slippage" occurs at the interface between the blocks and the hardened bedding sand, which increases the movement of blocks and the loss rate of joint sand, and also tends to increase the damage of blocks, as reported by Yanuma et al. in a paper (Yoshida and Yanuma, "Evaluation of the durability of cushion sand in interlocking block pavement by loaded vehicle running experiment": "Pavement" April 2001 issue, pp. 26-31). Therefore, interlayer slippage between the ILB and bedding sand is an important factor in structural analysis. The value of interlayer slippage applied to the multilayer elastic theory is generally "0 to 0.99". "0" means that slippage is not taken into consideration. The value of interlayer slippage applied to ILB pavement is the maximum value of "0.99". In this embodiment, the interlayer slippage is set as follows. For asphalt, analysis is performed without considering interlayer slippage, and for concrete pavement, slippage is considered only between the concrete slab and the roadbed, and analysis is performed without considering slippage for other layers. In contrast, analysis is performed both with and without considering interlayer slippage between the ILB and the laying sand, and between the laying sand and the roadbed layer. This is because taking slippage into consideration results in larger values for deflection, stress, strain, etc., resulting in a safer design.

[Setting the allowable deflection on ILB pavement]
In heavy load areas, the wheel load is high, so the deflection that occurs on the ILB pavement is also large. If the deflection becomes too large, the blocks will compete with each other, causing chipped corners. To prevent this, the allowable deflection is set using the results of previous research. According to "Hata and Yanuma: Application of Interlocking Blocks to Roadway Pavements: Pavement 27-9, 1992," where the block damage rate is B, the deflection amount (mm) is W, and the joint width is J, then "B = 6.097 + 3.775W - 3.267J" holds, and if the block damage rate exceeds 3%, a complaint will occur. In addition, according to the description on page 7 of "Yaninuma, Sumioka, Kirihara, and Harimoto: Five-year survey results of interlocking block pavement and semi-flexible pavement test-constructed in a container yard: Pavement 55-9, 2020", the damage rate after five years is "semi-flexible pavement (41.4%) > 100 mm ILB pavement (8.3%) > 80 mm ILB pavement (5.5%)". This damage rate was calculated by classifying the ILBs in the measurement section into chips (mild and severe) and cracks and investigating all of them, while for semi-flexible pavement, it was calculated using a mesh method that divides the section into squares of 0.5 m in length and width. Figure 4 is a table showing the correlation between joint width, damage rate, and deflection amount in interlocking block pavement calculated from the proposed formula. Based on the above knowledge and this correlation, it is preferable to set the allowable deflection amount to "1.0 mm to 4.0 mm" depending on the traffic volume.

In this invention, the structural design of ILB pavement in heavy load areas is carried out based on the following concept. That is, to apply the multilayer elastic theory, a safe and reliable structural design is realized by analyzing the ILB and bedding sand as one layer (block layer) and by separating the ILB and bedding sand alone. A safer and more reliable structural design is also possible by examining interlayer slippage based on whether or not it occurs. In addition, by setting an allowable value for the amount of deflection that occurs on the ILB pavement, it is possible to prevent excessive corner chipping of the blocks.

Figure 1 is a flow chart showing the procedure of the pavement structure design method according to an embodiment of the present invention. First, the deflection of the interlocking block pavement is measured using a vehicle-mounted FWD (step S1). Next, the elastic modulus of the sand laid on the upper roadbed and the block layer integrated with the interlocking blocks placed on the sand are calculated using the measurement results obtained in step S1 (step S2). As described above, the elastic modulus calculated here is 3000 to 8000 MPa, with an average value of 5100 MPa. Next, the elastic modulus of the sand alone and the elastic modulus of the interlocking block alone placed on the sand are calculated (step S3). As described above, the elastic modulus of the interlocking block alone is 5000 to 12000 MPa, with an average value of 8200 MPa. Also, the elastic modulus of the sand alone is 10 to 50 MPa, with an average value of 20 MPa, as described above.

Next, the interlayer slippage between the interlocking blocks and the sand, and between the sand and the upper roadbed are set (step S4). Next, the allowable deflection of the interlocking block pavement is further set (step S5). As described above, the allowable deflection is set to 1.0 mm to 4.0 mm depending on the traffic volume. Next, the elastic modulus of the block layer, the elastic modulus of the sand alone, and the elastic modulus of the interlocking blocks alone are applied to the multilayer elastic theory to calculate the deflection, stress, or strain of the interlocking block pavement in the heavy load area (step S6). Finally, it is confirmed that all the deflection, stress, and strain items are on the safe side (step S7), and the process is terminated.

According to this embodiment, it is possible to maintain good road surface properties in heavy load areas for a long period of time. It is also possible to realize a pavement structure that is highly durable, reliable, and safe. Furthermore, as a result of the improved durability, it is possible to reduce the life cycle cost (LCC).

Claims (4)

A pavement structure design method for interlocking block pavement in a heavy load area, comprising:
A step of measuring deflection of an interlocking block pavement in which a roadbed, a lower subgrade, an upper subgrade, bedding sand, and interlocking blocks are layered, and using the measurement results obtained, calculating the elastic modulus of the bedding sand laid on the upper subgrade and the block layer in which the interlocking blocks placed on the bedding sand are integrated;
A step of calculating the elastic modulus of the single layer of the sand and the elastic modulus of the single interlocking block placed on the single layer of the sand;
A pavement structure design method comprising at least a step of applying the elastic modulus of the block layer, the elastic modulus of the laying sand alone, and the elastic modulus of the interlocking blocks alone to multi-layer elasticity theory to calculate the deflection, stress or strain of the interlocking block pavement in the heavy load area. The pavement structure design method according to claim 1, further comprising calculating the deflection, stress or strain of the interlocking block pavement in the heavy load area by further using the interlayer slippage between the interlocking blocks and the bedding sand, and the interlayer slippage between the bedding sand and the upper roadbed. The pavement structure design method according to claim 1 or 2, further comprising setting the allowable deflection amount of the interlocking block pavement. An interlocking block paving structure in a heavy load area, comprising:
4. An interlocking block pavement structure designed using the pavement structure design method according to any one of claims 1 to 3, characterized in that a roadbed, a subbase, an upper base, sand and interlocking blocks are layered on top of each other.

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