THE EFFECTS OF RAINFALL INTENSITY, PAVEMENT CROSS SLOPE, SURFACE TEXTURE, AND DRAINAGE LENGTH ON PAVEMENT WATER DEPTHS

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1 THE EFFECTS OF RANFALL NTENSTY, PAVEMENT CROSS SLOPE, SURFACE TEXTURE, AND DRANAGE LENGTH ON PAVEMENT WATER DEPTHS " :".., r.. r '('., SUMMARY REPORT.... of Research Report Number Study Cooperative Research Program of the Texas Transportation nstitute and the Texas Highay Department n Cooperation ith the U. S. Department of Transportation and the Federal Highay Administration May, 1971 TEXAS TRANSPORTATON NSTTUTE Texas A&M University College Station, Texas

2 The Effects of Rainfall ntensity, Pavement Cross Slope, Surface Texture, and Drainage Length on Pavement Water Depths by Bob M. Gallaay. Robert E. Schiller. Jr.. and Jerry G. Rose Abstract Reported herein are the results of a study concerned ith determining the amount of ater hich can be expected to exist on various pavement types under normal ranges of pavement cross slopes, rainfall intensities, pavement textures, and drainage lengths. Equations are developed hich relate these variables and their relative e ffects to ater depth. Results are presented in both tabular and graphic form. Background information and pertinent past research pertaining to hydraulics of ater flo over paved surfaces are given. Nine different type surfaces ere tested. The surfaces ere placed on individual 28 feet long b y 4 feet ide, double tee, prestressed, concrete beams. Rainfall or uniform intensity as applied to the surface. Water depth measurements ere taken at regularly spaced drainage lengths for various combinations of rainfall intensity and pavement cross slope. Multiple regression analyses ere used to determine the best fit of the data. Pavement cross slope as found to affect ater depths significantly. For a rainfall intensity of 1.5 in/hr, a surface texture of.3 inches, and a drainage length of 24 feet, increasing the cross slope from 1/ 16 in/ ft (1 / 192) to 1/ 4 in/ ft (1/48) decreased ater depths by 62 percent in the outside heel path (approximately 21 feet from the top of the drainage area). Correspondingly, increases in surface texture decreased ater depths; hereas, increases in rainfall intensity and drainage length increased ater depths. The over-all experimentally obtained equation is d = [3.38 x 1 - a (1 / T) -.ll (L)-43 () -5 (l / S) -42] _ T here d T L S average ater depth above top of texture (in.), average texture depth (in.), drainage-path length (ft), rainfall intensity (in/ hr) and cross slope (ft/ft). The findings and conclusions contained herein ill be useful to the highay engineer in determining proper geometric designs a nd paving materials commensurate ith acceptable pavement friction characteristics and service demands. Suggestions for further research are also included.

3 .8 RANFALL NTENSTY = 1.5 N / HR SURFACE TEXTURE =.3 N RURAL HGHWAYS HGH SPEED TRAFFC C ROSS SLO PE ( N FT).6 " :: -.4 a::.2. 1;2 Top f _2ere PROBABLY JUSTFED ON PAVED SHOULDERS ONLY -. 2L J L LENGTH OF DRANAGE PATH, L (FT) Figure 1. Pavement ater depth vs. length of drainage path for different cross slopes. Objectives The objectives of this research ere: 1. To examine the relative effects of various rainfall intensities, pavement cross slopes, drainag e lengths, and surface textures on resultant pavement ater depths. 2. To develop an equation relating rainfall intensity, pavement cross slope, drainage length, and surface texture to pavement ater depth, and 3. To recommend means by hich the findings and conclusions contained herein can be implemented by the highay engineer in determining proper geometric designs and paving materials commensurate ith acceptable pavement ater depths and service demands. Summary of Findings and Results 1. The experimentally determined equation relating ater depth to surface texture, length of drainage path, rainfall intensity, and pavement cross slope is d = [3.38 X lq-r (l / T) - 11 (L)AR ()-' 19 (l / S).4 2 ] - T

4 .2 DRANAGE LENGTH =24FT SURFACE TEXTURE =.3 N HGH SPEED RURAL HGHWAYS CROSS SLOPE (N/ FT) z. 1 6 'U : a.. a::.8 1- <l.4 SUGGESTED TENTATVE MNMUM.!'2E..._ Texture _ -o. o4l l l RANFALL NTENSTY, (N/ HR) Figure 2. Pavement ater depth vs. rainfall intensity for different cross slopes. here d T L S average ater depth above top of texture (in.), average texture depth (in.), drainage-path length (ft). rainfall intensity (in/hr), and cross slope (ft/ft). 2. ncreasing surface texture resulted in a decrease in ater depth for a given rainfall intensity, cross slope, and drainage length. This effect as more pronounced a t the flatter cross slopes and loer rainfall intensities. 3. Greater drainage lengths increased ater depths, hoever, the rate of increase in ater d epth became smaller as drainage lengths increased.

5 .6 RANFALL NTENSTY = 1.5 N/HR CROSS SLOPE = 1/4 N / FT RURAL HGHWAYS SURFACE TEXTURE (N) " J: t- Cl. a:: i- <{ :;: Top or-re xt ure- VALUE SUGGESTED - -- FOR HGH SPEED TRAFFC L 6L------,2-----, LENGTH OF DRANAGE PATH, L (FT) Figure 3. Pavement ater depth vs. length of drainage path for different surface textures. 4. Greater ater depths ere associated ith higher rainfall intensities; notithstanding, the adverse effect of rainfall intensity as quite pronounced, even at the loer rainfa ll intensities. 5. ncreases in pavement cross slope resulted in reduced ater depths. This effect as very significant at the flatter cross slopes he re a slight increase in cross slope resulted in a pronounced reduction in ater depth. The reader is referred to Table 8 and Figure 18 in the full report for a more detailed account of findings 2 through Surface texture, rainfall intensity, and pavement cross slope ere found to affect the average d etention ater* on the surfaces similar to the manner in hich these variables affected ater depth. ncreases in surface texture and pavement cross slope resulted in decreased d e tention; hereas, increases in rainfall intensity increased detention. The reader is referred to *The ater in question is that ater above a calculated median datum line refere nced from an average of the tops of the asperity peaks.

6 _ z.8.6 SUGGESTED RANGE OF SLOPE!_...--SUGGESTED TENTATVE MNMUM CROSS SLOPE (N/ FT) " a.. a::.2 3:. -.2!of Text + HGH SPEED RURAL HGHWAY RANFALL NTENSTY= 1.5 N/HR DRANAGE LENGTH =24FT AVERAGE TEXTURE DEPTH, T (N) Figure 4. Pavement ater depth vs. average texture depth for d ifferent cross slopes. Table 9 and Figure 19 in the full report for more d etailed information. The experimenta lly determined equation as here Det = [ 11.8 X lq - R (l / T) - 11 () 57 (l / S) 31 ] - T Det average ater depth d etention (in.), T S average texture depth (in.), rainfall intensity (in/hr). a nd cross slope (ftjft). 7. Detailed plots of the findings are contained in Fig ures through 4.

7 The published version of the complete report of hich this is a summary may be obtained by addressing your request as follos: R. L. Leis, Chairman Research & Development Committee Texas Highay Department- File D-8 ll th and Brazos Austin, Texas 7871 (Phone 512/ )