Improved Surface Drainage of Pavements Final Report (1998) / Chapter Skim
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Chapter 2 Literature Review and Current Practice and Techniques for Improved Surface Drainage
Chapter 2 Literature Review and Current Practice and Techniques for Improved Surface Drainage
Pages 11-44
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From page 11... ...
The models identified during this study provide He tools needed to calculate the depth of sheet flow as a function of four general pavement characteristics: pavement geometry, location and capacity of drainage appurtenances, surface texture of the pavement surface, and any internal drainage 11
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From page 12... ...
The term open-graded asphalt concrete is used in this study to indicate either open-graded asphalt friction courses (OGAFC) or porous asphalt.
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From page 13... ...
METHODS FOR CONTROLLING WATER FILM THICKNESS A literature survey and a questionnaire were used to establish He current state~f-the art methods for pavement surface drainage. Implementable techniques for improving surface 13
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From page 14... ...
Controlling Water Film Thickness Through Pavement Geometry Highway geometric design criteria have evolved over many years and are designed to ensure He safe and efficient movement of vehicles. State agencies and many other transportation agencies use the guidelines issued by the American Association of Highway and Transportation Officials (AASHTO)
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From page 15... ...
Therefore, this discussion covers all Free areas of the pavement system. Maximum grades have been established based on vehicle operating characteristics, particularly, the operating performance of larger vehicles such as tractor semitrailers.
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From page 16... ...
J is to design vertical curves using a ~K-value." The K-value is defined as Me horizontal distance in feet (meters) required to effect a I-percent change in the gradient of Me grade.
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From page 17... ...
are used, special attention should be given to the selection of pavement geometry to ensure adequate drainage. This is critical in sag vertical curves since water tends to collect at the bottom of these curves.
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From page 18... ...
J o a, · o a, co · c)
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From page 19... ...
Pavement Type Cross-slope High Intermediate Low 1.5-2 1.5-3 2-6 On longitudinal curved sections of highways, the pavement is typically superelevated. A limit is placed on the rate of superelevation for driver comfort and safety.
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From page 20... ...
Consequently, when considering pavement surface drainage, special attention should be paid to these transition areas. After Me water has drained from the traveled lanes, the shoulders or parking lanes must either convey the water to an inlet or drain the water to ditches.
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From page 21... ...
Controlling Water Film Thickness Through Use of Appurtenances Drainage appurtenances are a very effective means for removing water and shortening the distance that water must flow in order to be removed from the pavement surface. Shortened flow paws imply reduced water film thickness.
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From page 22... ...
Figure 5. Typical sloped drain.
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From page 23... ...
Slotted drains in particular offer considerable potential as a means for shortening the length of the water flow path by simply reducing the distance that the water must flow before it is removed from the surface as illustrated in figure 4. Comprehensive analyses of Me interception capacity and spacing recommendations for drainage appurtenances have been performed in many studies (7,8)
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From page 24... ...
In the event of plugging, severe ponding could develop on the pavement surface, creating a safety hazard. Retrofitting existing pavements to accommodate slotted drains within or between We traveled lanes would be costly except, during major rehabilitation if the pavement cross-slope must be modified to accommodate the drains.
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From page 25... ...
Controlling Water Film Thickness with Internally Dmining Asphalt Surfaces (OGAC) Another technique for reducing water film Sicknesses on a roadway surface is We use of internally draining or open-graded asphalt concrete.
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From page 26... ...
This is determined by placing mixes with differing asphalt contents on a plate in an oven and measuring the amount of asphalt Hat drains from the mix. These mixes offer increased skid resistance and allow interns drainage of surface water from He pavement surface (109.
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From page 27... ...
Porous asphalt surfaces offer high values of skid resistance and contribute to the removal of water from the pavement surface. A summary of the mixture characteristics for different porous pavements as used in the United States and Europe is provided in table 4 (1~17920)
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From page 28... ...
~) 25.0 mm 99-100 - - - 19.0 85-96 100 - - 14.0 - - - 100 100 12.5 60-71 - 11.2 - 90-95 10.0 - - 100 9.5 8.0 - 28-40 6.3 17-31 5.0 4.75 2.75 2.36 2.0 18-23 7-19 10-12 710, ~- 6-8 250 - 4-6 90 - 2-4 74 1-6 17 5 55 23 14 Air Voids (%)
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From page 29... ...
Surface water can quickly infiltrate into porous asphalt, greatly reducing the amount of free surface water, which causes splash and spray from the vehicle tires. This reduction in splash and spray provides greater visibility, resulting in safer roadway conditions than on Portland cement concrete or conventional dense-graded asphalt pavements (23-25~.
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From page 30... ...
Porous asphalt surfaces have a tendency to develop black ice more quickly than conventional dense-graded pavements. Black ice can occur suddenly at the onset of a light rainfall when the internal pavement temperature is near or above freezing, and the air temperature is at or below freezing.
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From page 31... ...
Porous asphalt surfaces also reduce tire noise and minimize splash and spray, thereby increasing driver visibility (11,18,25,26,28)
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From page 32... ...
Grooving is generally ineffective on asphalt concrete surfaces because the grooves close quickly under the action of traffic. The grooves in Portland cement concrete act as subsurface channels that drain water from the pavement surface.
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From page 33... ...
6.4 mm Figure 6. Typical grooving patterns for Portland cement concrete pavement (30)
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From page 34... ...
However, unless grooves are parallel to the slope of the pavement, their ability to conduct flow is reduced and their effectiveness minimized. In summary, grooving Portland cement concrete pavements can reduce water film thickness and thus increase the speed at which hydroplaning will occur.
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From page 35... ...
Predicted water film thickness, WFr, for grooved portland cement concrete pavement, rainfall iritensity 75 mm/in (309.
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From page 36... ...
. The importance of macrotexture for asphalt surfaces is discussed in a previous section on the use of porous asphalt to control water film thickness.
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From page 37... ...
The guidelines are complemented by an interactive computer program, PAVDRN, which allows the pavement engineer to predict water film thickness and the propensity for hydroplaning (Appendix A)
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From page 38... ...
The guidelines also recommend other control methods such as slotted drains between traveled lanes. For superelevated sections the guidelines suggest the use of a maximum recommended superelevation to minimize water film thickness on horizontal curves and the use of other methods, such as increased mean texture depth or grooving, if superelevation does not reduce the potential for hydroplaning to desired levels.
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From page 39... ...
Drainage appurtenances are typically necessary to control water film thickness, especially on large, multilane facilities where the flow path length spans more Man two travel lanes. The most promising technology for multilane highways is Be use of slotted drains placed between the Gavel lanes.
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From page 40... ...
The mean texture depth is subtracted from He depth to determine the water film Sickness. The water film thickness, computed in this manner, is used to determine the speed at which hydroplaning will occur.
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From page 41... ...
of Planes Length of Each Plane Longitudinal Slope Width of Each Plane Pavement Type Mean Texture Depth Cross-Slope of Plane ~ Cross-SIope of Plane 2 Cross-Slope of Plane 3 3 300 m 0.02 m/m 4m PCC 0.50 mm 0.015 m/m 0.025 m/m 0.035 m/m 41
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From page 42... ...
However, as the drainage length increases across the second and third lanes of travel, the water film thickness increases to a point where the hydroplaning speed for the third, outermost lane of travel is significantly below the design speed of 90 1an/h. One solution for increasing the hydroplaning speed could be to install a longitudinal slotted drain between the second and third lanes of travel In the direction of travel (see figure 5~.
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From page 43... ...
From the analysis, ache flow at the end of the second plane needs to be reduced to a value that will eliminate the hydroplaning potential for the system. A slotted vane grate is selected and placed between the second and third lanes.
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