Diseo de SubdrenesFuentes de humedad a drenarInfiltracinAgua SubterrneaLos sistemas actuales principalmente direccionan el agua que se infiltra en la estructura del pavimento.

ClasificacinDrenaje longitudinalDrenajes de bordeSubdrenesDrenes transversales y horizontalesBases PermeablesSistemas de pozos

Cunetas Longitudinales, Diseo Tpico (USA) Base Granular Losa Ho.18.5 m0.02 m/m0.04 m/m1 : 41 : 6Sub-rasanteBase Tratadacuneta1.9 m3.7 m

Otras posibilidades para redudir el dao por humedad en pavimentos de Asfalto

Pavimentacin en ancho completo (proteccin de bermas)Mayor espesor de asfalto en superficie y el uso de base asfltica.Terraplenes granulares de mayor espesor.

Uso de Barras pasajuntas (Dovelas)Bermas de hormign atadasSobreancho en los carrilesTerraplenes granulares de mayor espesor

Otras posibilidades para redudir el dao por humedad en pavimentos de Hormign

Terrapln Granular

Base PermeableCapa drenante de granulometra abierta.Puede ser tratada o no tratada.Puede ser drenada por los bordesBase Permeable tratada con cemento

Capa SeparadoraUna capa de granulometra cerrada o una capa de geotextil con baja permeabilidad.Se usa en conjunto con una base permeable.Mantiene una separacin entre la subrasante y la base permeable.Dirige la infiltracin superficial hacia los drenajes longitudinales.

Drenajes Longitudinales por TuberaTubera circular metlica, plstica o de hormign perforada.Corre a lo largo de la longitud del pavimentoIntercepta el agua que sale de la estructura del pavimento Ubicado en una cuneta al lado del pavimentoTubera longitudinal

Drenajes de Borde Prefabricados Geocompuestos (PGED)Tambin llamado drenaje panel o fin Corazn rgido de plstico recubierto con un geotextilMenor capacidad hidrulica que una tuberaUsado en aplicaciones limitadas (ya construdas)Seccin PGED

Tuberas Transversales de SalidaTuberas cortas, circulares, conectadas a los drenajes longitudinales.Perpendicular a la carreteraEspaciada a intervalos regularesTransporta el agua desde los drenajes longitudinales a las cunetas o a las quebradas

Cunetas Laterales, Alcantarillado PluvialTransportan agua desde las tuberas de salida alejndolas de la estructura del pavimento. Deben tener profundidad adecuadaEn zonas urbanas, se usa tuberas de alcantarillado pluvial en lugar de cunetas.

Tipos de Subdrenes

Sistemas de Drenaje TpicosSistema de Base PermeableBase PermeableCapa de SeparacinDrenajes Longitudinales / base permeableTuberas de salida y cunetas / alcantarillas

Sistema de Base Permeable con Drenaje Longitudinal

Base Permeable, Salida Directa

Otros Sistemas de SubdrenajeSistemas de drenaje longitudinal conBases no erosionables o erosionablesTuberas de drenaje o drenes geocompuestosTuberas de salida y cunetas / alcantarillasBases no erosionables con bermas de hormign poroso (pav. Rgidos)Bases permeables con salida directa

Seccin con Drenaje Longitudinal GeocompuestoRelleno de arenaDrenajeGeocompuesto Base GranularSubbase/Subrasante25 mm100 mmBermaPavimento

Bases no erosionables con hombrera de hormign poroso

Materiales Envolventes > 1.2 D85 = Dimetro equivalente a pasa 85%> 1.0De este modo no se colmata la tubera de drenaje> 2

Capa de Separacin< = 5Usar el mismo criterio para base y capa de separacinEvitar que los finos de la subrasante colmatenla base permeableSi es difcil conseguir materiales adecuados, usar Geotextil< = 25

Los datos para el diseo son el tiempo en el que la estructura del pavimento est sometida a niveles cercanos a la saturacin y la Calidad del DrenajeMtodos de Diseo de DrenajeEstado de Flujo ConstanteTiempo de Drenaje(Recomendado)

Consideraciones para el DiseoDurante una lluvia, el agua se infiltra en la base permeable hasta que la misma se satura. El agua en exceso corre por una cuneta lateral. Criterio clave para el diseo: Tiempo requerido para drenar una cierta cantidad de agua de la capa drenante una vez que la lluvia ha parado.

Conceptos BsicosQqiqdDrenaje de bordeSuperficieBase Permeable Subbase

AASHTO: Tiempo requerido para alcanzar: 50 % de 85% de saturacinsaturacin

Normas de Diseo

t=T x m x 24

Donde:t = Tiempo de drenaje, horasT = Factor de Tiempom = factor m, dasEcuacin del Tiempo de Drenaje

Procedimiento para obtener t1: Determinar la geometra de la carretera, S Pendiente LongitudinalSx, Pendiente Transversal2: Determinar datos de la base permeable: W Ancho de la baseH Espesor de la base k Permeabilidad baco, fig. 7-10 Gs Gravedad especfica de los slidos

Procedimiento para obtener t3: Calcular: SR, Pendiente ResultanteLR, Longitud Resultante S1, Factor de Pendiente (Slope factor) S1 = (LR x SR)/H4: Calcular el volumen de vacos y seleccionar la prdida de agua c

5: Calcular porosidad y porosidad efectiva (N y Ne)N = [1- {gd / (9.81 x Gsb)}]Ne = N x WL6: Calcular el factor m m = (Ne x LR2)/(k x H)7: Estimar el Factor T para un grado de drenaje dado, U. Fig. 7.118: Estimar tiempo de drenaje, tt = T x m x 24

Procedimiento para obtener t

Fig. 7-11 para la obtencin de T

Factor de tiempo T, para U = 0.5 (50 % drenado)

Dados:Pendiente Longitudinal S = 0.02 m/mPendiente Transversal, SX= 0.02 m/mAncho de Base, W = 7.315 mEspesor de Base, H = 0.1 mCoef. de permeabilidad, k= 1000 m/dayPorosidad Efectiva, Ne= 0.26

Determinar:Tiempo para drenar 50 % de aguaEjemplo ver Apuntes 7.6.5.

Respuesta (resumen)Pdte resultante, SR = 0.02828Longitud Resultante, LR = 10.345 mFactor de pendiente, S1 = 2.92Factor de tiempo, T = 0.12Factor m = 0.268 daysTiempo para drenaje, t = 0.77 hours

(1)Assigned(2)from Chart(3)T x m x 24(4)Ne x UDegree ofDrainageUTime Factor,TTime toDrain, hrs.tWaterdrained0.10.50.9Formulario para clculo de drenaje

Formulario para clculo de drenaje

Ejemplo de Grfico de Porcentaje Drenado

013572060100Tiempo para drenar, horasPorcentaje Saturacink = 305 m/dayEjemplo de Grfico de Porcentaje Saturacin246H = 0.15 mN = 0.3Ne = 0.25LR = 7.6 mSR = 0.02 m/m

Sensibilidad del tiempo de DrenajeFactores a considerarPorosidad efectivaCoeficiente de permeabilidadPendiente ResultanteLongitud ResultanteEspesor de la base permeable

AASHTO: Tiempo requerido para alcanzar: 50 % de 85% de saturacinsaturacin

Normas de Diseo

Porcentaje de SaturacinEliminar los das de congelamiento y lluvias eventuales en poca seca. P = S + R * 100 365P = Porcentaje del tiempo en que el pavimento est prximo a la saturacinS = Das de deshielo en primaveraR = Das con lluvia si el pavimento puede drenar hasta el 85% de saturacin en 24hrs o menos. Si el tiempo excede 24hrs debe multiplicarse por el tiempo de drenaje.

Valores mi Recomendados

Valores Cd Recomendados

Efectos del Coeficiente de Drenaje en el DiseoLos coeficientes de Drenaje mayores que 1.0 reducen la estructura del pavimentoCoeficientes menores que 1.0 incrementan la estructura del pavimentoIncrementar la estructura del pavimento no es una solucin para drenajes pobres.

Efectos de Hinchamiento y CongelamientoAASHTO recomienda la provisin de soluciones especiales para las zonas afectadas, alternativamente se provee un mtodo para determinar la prdida de serviciabilidad por hinchamiento o congelamiento.

ResumenLa infiltracin superficial representa una de las mayores causas de humedad en el pavimento.La humedad es perjudicial para el desempeo de los pavimentosLos sistemas de drenaje deben disearse para remover la humedad de los pavimentos antes de que se daen. Las diferentes alternativas de subdrenes pueden proveer una solucin efectiva. Es importante un anlisis econmico.

***The use of adequate cross slopes on the mainline and shoulders can help prevent moisture from entering the pavement. Transverse slopes are generally 1.5 to 2.0 percent on the traffic lanes but can be as high as 5 to 6 percent on superelevated curves. Shoulder cross slopes are typically around 4 percent. Longitudinal slopes of 0.20 to 0.30 percent are needed for sections with longitudinal edgedrains to maintain flow.

*Some of the other design features that have shown promise in minimizing moisture accelerated damage for AC pavements are full-width paving to eliminate lane-shoulder cold joints and cracks, and building the pavements on deep granular subbases to limit the potential for frost damage. If not full-width paving, then a widening of the AC layers will help eliminate edge loadings.*Some of the other design features that have shown promise in minimizing moisture accelerated damage for PCC pavements are dowels to reduce pumping, faulting, and erosion), tied shoulders (which keep the lane shoulder joint tight), and widened lanes to minimize edge deflections and stresses. A thick granular subbase layer also helps to remove water beneath the pavement structure.

**Modules 5 and 6 discuss permeable bases in detail.*Module 7 discusses separator layer design in detail.

*Module 8 discusses longitudinal pipe edgedrains in detail.*Module 9 discusses PGESs in detail.***This section of the presentation focuses on the different subsurface drainage systems available.

*A permeable base system has the following components: permeable base, separator layer, longitudinal pipe edgedrain, and outlet pipes and ditches.

*A permeable base is designed with an open gradation and few fines to rapidly remove moisture that infiltrates into the pavement surface. Permeable bases typically have a permeability in excess of 300 m/day. Pipe edgedrains are recommended with permeable bases in order to handle the high flow capacities.

*This is a sketch of a pavement with a permeable base daylighted directly into the side ditch. Some studies, such as NCHRP 1-34, have reported that well-maintained daylighted permeable bases can be as effective as permeable bases with edgedrains in reducing moisture accelerated damage.

*There are other types of subsurface drainage systems and methods of minimizing the effects of excess moisture in pavements. Not all these systems have the same performance.*Longitudinal edgedrains consist of a drainage system that runs parallel to the traffic lane. The edgedrains collect water, which is then discharged through outlet pipes. Edgedrains without a permeable base are not recommended on newly constructed sections. However, pipe and geocomposite edgedrains are suitable candidates where drainage requirements are misleading.

*This system consists of a nonerodible dense-graded base under the traffic lanes and a treated permeable base under the shoulder. The nonerodible base can consist of a LCB with at least 8 percent cement or an AC base with at least 6 percent asphalt. This design offers better support under the traffic lanes where it is needed most, while still providing a means to remove water from the pavement structure.

Mention that this design is a lot in Europe. California also uses porous concrete shoulders.

*Important points to be discussed here:Definition of the coefficient of uniformity.What it indicates (particle size spread in a material, how dense it is).Typical values (dense-graded20 to 50; open-graded2 to 6; uniformly graded1).

If CU is less than 4, the material may be unstable and may need stabilization using cement or asphalt.*Important points to be discussed here:Definition of the coefficient of uniformity.What it indicates (particle size spread in a material, how dense it is).Typical values (dense-graded20 to 50; open-graded2 to 6; uniformly graded1).

If CU is less than 4, the material may be unstable and may need stabilization using cement or asphalt.*Approaches to drainage designthe time-to-drain and depth-of-flow.

Emphasize that the recommended design method is the time-to-drain approach and that it will be discussed in this module. Depth-of-flow will not be discussed.

Point out that this module deals only with the hydraulic considerations of design.*The base is always assumed to be saturated at the end of a rainfall event; therefore, this is a conservative approach.

Further, it is also assumed that water from the permeable base is removed, either through edgedrains or by daylighting, to a side ditch.

Emphasize the most important output of the time-to-drain method is the time required to drain the base. Permeable base material selection will be based on this parameter.*Explain each flow quantity on the slide and how it is handled in the time-to-drain design.qi need not be calculated because we assume that the permeable base is always saturated.qd and Q are functions of the time required to drain the base (these will be discussed in module 8).

The key issue in this method is, therefore, the determination of the time to drain the pavement.*There are two design standards for determining the time to drain: AASHTO percent drained (50 percent, shown here) and percent saturation (85 percent).

The AASHTO percent drained approach does not consider the water retained by the effective porosity quality of the material. These must be used as guidelines for pavement drainage. A pavement with a higher classification will require a better quality of drainage.*Highlight the importance of this equation in the time-to-drain method. The constant 24 in the equation is to convert the units from days to hours.

The procedure to estimate the time-to-drain equation is explained in the next few slides.*Remind participants that, the water loss value, WL, in step 2 is a function the fines content and type. The pavement resultant slope, SR, and the resultant length, LR, in step 3 can be computed using equations presented earlier in the module. The slope factor S1 is computed using the equation shown.

Once the slope factor, S1, is known, the time factor (step 4), T, can be computed for any degree of drainage, U (it is the percent drained expressed in decimal). The degree of drainage is an assumed value based on the design standard chosen. For example, if the time to drain 50 percent of the base is being estimated, U = 0.5. Point out that with this chart, T can be estimated for a wide range of slope factors and degrees of drainage. *Remind participants that, the water loss value, WL, in step 2 is a function the fines content and type. The pavement resultant slope, SR, and the resultant length, LR, in step 3 can be computed using equations presented earlier in the module. The slope factor S1 is computed using the equation shown.

Once the slope factor, S1, is known, the time factor (step 4), T, can be computed for any degree of drainage, U (it is the percent drained expressed in decimal). The degree of drainage is an assumed value based on the design standard chosen. For example, if the time to drain 50 percent of the base is being estimated, U = 0.5. Point out that with this chart, T can be estimated for a wide range of slope factors and degrees of drainage. *Porosity and effective porosity are computed as shown. Remind participants that these quantities were computed previously as part of an example. The "m" factor can then be calculated. Remind participants that the units of m will depend upon the units used for other parameters.

The time to drain can finally be calculated using the equation shown. It is expressed in hours if the m factor is in days.*Walk through a specific example of determining T from this chart, say, with a slope factor S1 = 3 and U of 0.5.*This is a simplified version of the chart for determining the time factor. It is used to determine the time factor for a degree of drainage of 50 percent over a wide range of slope factors.

Repeat the example from the previous slide for determining T from this chart for S1 = 3 and U = 0.5. Contrast the simplicity of the chart with the previous chart.*Participants can compute t using the formulas provided. Note that U = 0.5. The instructor can use DRIP to illustrate the solution.

*Manual computations will need to use the charts to determine T for 50 percent drained. Then the m factor needs to be estimated. Finally, the time to drain can be computed.

*When designing pavements with the time-to-drain approach, the time to drain is calculated for different degrees of drainage instead of just one (as in the previous example). The form shown is used to tabulate the results. Using the data in the table, the time histories of percent drained or percent saturation are plotted. These plots are used for design verification.

Point out how each column is computed.*Once these quantities are computed, plots of percentage drained 100*(column 1) versus time to drain (column 3), or percentage saturation (column 6) versus time to drain (column 3) are obtained, depending on the design standard being used.*As the percent drained increases, the time to drain also increases. The time to drain can be reduced by increasing the permeability of the material. This plot can be used to check the time-to-drain design when the AASHTO percent drained standard is used.

Question:The drainage design recommendation states that 50 percent of the water should be drained in less than 2 hours for interstate highways. Which of the materials above meet the standard for the given conditions?

Answer:The materials with k of 305, 610, and 915 m/day.

*This is a plot of percent saturation versus time to drain. As the time to drain increases, the percent saturation decreases. This graph can be used to obtain the drainage history when 85 percent saturation is being used as the design standard.

Point out that the public domain FHWA program, DRIP, can perform the necessary calculations rapidly and accurately. Therefore, the use of this program is recommended.*If the designs fail to meet the standard, revisions need to be made. For this purpose, it is important that engineers understand the effects of the various parameters in the time-to-drain calculations through sensitivity analysis. This will be useful to adjust the base parameters to meet the design standard. Briefly state what is involved in a sensitivity analysis.

Point out that, for simplicity, the effect of each factor mentioned was studied individually.

*To perform the time-to-drain calculations, click on the Time-to-drain option under Permeable Base on the main screen.

The next step in the solution process will be to be to input roadway geometry information by clicking on Roadway Geometry button to the right.*There are two design standards for determining the time to drain: AASHTO percent drained (50 percent, shown here) and percent saturation (85 percent).

The AASHTO percent drained approach does not consider the water retained by the effective porosity quality of the material. These must be used as guidelines for pavement drainage. A pavement with a higher classification will require a better quality of drainage.****Much of the information from this module is essential to understanding the material in subsequent modules. Highlight the important points in this module and encourage questions from the participants.

Pavements with permeable bases and edgedrains typically cost 10 to 20 percent more than nondrained sections. Thus, they must extend the service life by at least the same amount to be cost-effective.