drainage system of pavements

PAVEMENT DRAINAGE

PRESENTED BY :KAZIM KHAN (05-CTE-26)SYED ABID MASOOD (05-CTE-07)

CONTENTS

Related Terms & Definitions

Why is road drainage so importants ?

Factors Affecting the drainage system in road construction

Sources of Moisture in Pavements

Moisture-Related and Accelerated Distresses

Purpose of Subsurface Drainage

Components of a Pavement Drainage System

Types of drainage systems

Geocomposite Drainage Layers

Design of Pavement Drainage

PART 1

Water in the

Pavement

Structure

Primary Cause

of Distres

s


Pavement:

All elements from the wearing surface of a roadway to the subgrade.

Permeable base:

A free draining layer in the pavement designed to rapidly remove free water from most elements of pavement.

Base crossdrain: A subsurface drain, generally perpendicular to the roadway alignment,

designed to drain infiltrated water.

Dense-graded aggregate base (DGA): Mixture of primarily sand and gravel, well-graded from coarse to fine

(usually unstabilized, but sometimes asphalt or cement stabilized)


Drainage aggregate: Open-graded aggregate with high permeability.

Drainage pipe:

Rigid or flexible pipe conduit designed to collect and/or transport water out of the pavement section (usually perforated).

Edgedrain:

A subsurface drain usually located at the edge of the pavement.

Headwall:

A protective structure at a edgedrain outlet.


Infiltration:

Free water in the pavement structural elements entering through cracks, joints, or permeable paving.

Outlet:

The point of discharge of an edgedrain.

Outlet pipe:

The lateral connection from the edgedrain to the outlet.

Usually a solid pipe and usually strong to prevent damage.


Prefabricated geocomposite edgedrain (PGED):

An edgedrain consisting of a drainage core covered with geotextile. Usually 1 to 2 in. thick by 1 to 3 ft high, placed in a narrow trench. It may include drainage aggregate or sand as a part of the installation.

Separator/filter layer (aggregate or geotextile):

A geotextile or aggregate (subbase) layer separating a permeable base layer from an adjacent soil (or aggregate) containing fines to prevent the fines from contaminating the drainage aggregate. Must meet the filter criteria for drainage filters.

Underdrain:

A deep subsurface drain located at a sufficient depth to intercept and lower the ground water to a required design level


Capillary action The flow of liquids through porous media & movement of liquids in

thin tubes.

Vapor movement

The process by which the entire body of fluid moves in responses to differences in hydraulic potentials.

Seepage

The process by which a liquid leaks through a porous substance.

WHY IS ROAD DRAINAGE SO IMPORTANTS ?

A road’s infrastructure is an engineering work, aiming the establishment of a platform, on which vehicle circulation is possible under safety conditions, proper traffic flow, commodity, and economy, independently of the region’s climate conditions;

Water, along with heavy traffic, is one of the greatest causes of road ruin.

Subsurface Drainage Importance

Reduction of the pavement’s load capacity

Premature

deterioration of the pavement

Diminish of the road’s useful

life

Soil’s resistance to compression may drop from

0.15 MPa to0.07 MPa (about half) if its

water content increases from 25 to 30%.

Factors Affecting the drainage system in road construction

Sensitivity of groundwater

Importance of road

Area (rural or populated)

Amount of traffic

Sensitivity of streams, rivers, lakes


Vapor movement

Seepage

Capillary action

Surface infiltration

Groundwater


Flow of existing sub-surface water, from higher terrain near the road

Elevation or drop of the water table

Water infiltration by joints or badly sealed cracks (concrete pavement) or by porous and fissured areas

Moisture movement on the soil

Successive frost/defrost cycles, increase cracks and therefore water infiltration on the pavement

Sources of Moisture

PCC Pavement Water Infiltration

Moisture-Related and AcceleratedDistresses

Pumping/erosion.

Faulting.

Corner cracking.

Transverse cracking.

Fatigue (alligator)

Rutting

Stripping

Frost heave.

Potholes

Purpose of Subsurface Drainage

Subsurface drainage is intended to remove water that infiltrates into a pavement.

Surface water is primarily removed through proper geometric design.

Water can enter the pavement in numerous ways,

only some of which can be effectively drained by a subsurface drainage system.

The basic idea is that water in the pavement drives certain types of distress.

Fac Purpose of Subsurface Drainage

Amount of free water that infiltrates into the pavement structure.

Potential for moisture-related damage to pavement.

Ability to design, construct, and maintain the drainage system.

Other general factors (e.g., topography, soil types,etc.).


Basic Components Variable ComponentsSurface Pavement Rigid: Portland Cement

ConcreteFlexible: Asphaltic Concrete

Permeable Base Unstablilied GranularAsphalt Stabilized GranularCement Stabilized Granular

Separator/Filter Layer Dense-Graded Granular (Subbase)Geotextile

Subgrade Strength of Subgrade SoilLocation of Water TableFinal Grade

Edgedrains (including outlets with headwalls)

Aggregate Trench Drain w/ Geotextile Filter & PipePrefabricated Geocomposite Edgedrain (PGED)

Stress distribution Pattern

Stress distribution in dry pavement

layer

Stress distribution in

saturated pavement layer

PART 2

TYPES OF DRAINAGE SYSTEMS

DRAINAGE

Surface drainage

Transversal drainage

Longitudinal drainage

Subsurface drainage

Transversal Drainage

Transversal Drainage

Slab culverts

Pipe culverts

Cause ways

Longitudinal Drainage

Gutters, ditches and channels;

Galleries, collectors and drains;

Connection and Collecting Accessory organs, namely visit and cleaning chambers;

Reception chambers, connection or derivation boxes.

Longitudinal Drainage

Sub-surface drainage Main types of devices

1. Longitudinal interception drains

2. Longitudinal water table lowering drains

3. Transversal drains

4. other devices

Drainage layers Draining spurs Draining masks Sub-surface drainage Longitudinal drains in ½ hillsid Christmas tree drain Cutting drain

1. Longitudinal interception drains

Longitudinal Edgedrains

Runs parallel to the traffic lane

Collect water that infiltrates the pavement surface and drains water away from the pavement through outlets

Types of edgedrains systems

1. Pipe edgedrains in an aggregate filled trench,

2. Pipe edgedrains with porous concrete (i.e., cement treated permeable base) filled trench,

3. Prefabricated geocomposite edgedrains in a sand backfilled trench, and

4. Aggregate trench drain ("French" drain).

Longitudinal Edgedrains

Typical AC pavement with pipe edgedrains

Typical PCC pavement with geocomposite edgedrains

Figure 7-6. Typical edgedrains for rehabilitation

Typical edgedrains for rehabilitation projects

2. Longitudinal water table lowering drains

3. Transversal drains

Drainage layers

Longitudinal drains in ½ hillside

Cutting drain

Christmas tree drain

Draining Spurs

A small ridge that projects sharply from the side of a larger hill or mountain

Draining masks

Horizontal Geocomposite Drainage Layers

Drainage in PCC Pavement System

Pre-pave installation

Post-pave installation

Comprehensive Drainage SystemComponents

CONTAMINATION/ PUMPING

AGGREGATE PENETRATION

AASHTO Drainage Definitions

Quality of Drainage Water Removed Within*

Excellent 2 Hours

Good 1 Day

Fair 1 Week

Poor 1 Month

Very Poor Water will not Drain

*Based on time to drain

AASHTO Guide for Design of Pavement Structures

Design of Pavement Drainage

The hydraulic requirements for the permeable layer to achieve the required time-to-drain.

The edgedrain pipe size and outlet spacing requirements.

Either the gradation of requirements for a graded aggregate separation layer or the opening size, permeability, endurance, and strength requirements for geotextile separators.

The opening size, permeability, endurance, and strength requirements for geotextile filters, or the gradation of the granular filters (to be used in the edgedrain).

Sub-surface drainageHydraulic calculation for drains (QL)

QL = q . B . L

QL - water flow through the pipe (m3/s)

q - surface run-off water flow (m3/s/m) L - sect ion's length [m] B - width calculation's [m]


In cases where the drainage is used not only as interception drainage but also to lower the water level, dimensioning should consider specific calculations for the underground flow in

to the drain. In this situation the projected flow should be the sum of the aforementioned value and the estimate through the application of Darcys’ Law.

In order to simplify dimensioning, some authors consider that the in-flow to the drain amounts to about 35% of the total flow generated in banks added by 20% for flow originated in the road platform, i.e.:

QL = 0.35×QT + 0.20×Qp

QL– water flow to de pipe (m3/s);QT – surface run-off water in slopes (m3/s);Qp – surface run-off water in platform (m3/s).


As to the depth of installation of the drains, one can estimate, in a first approach, by the formula:

D – drain depht (m)

d – depth that groundwater level should stabilize(m)

b – distance between drains(m)

i – infiltration soil rate (m/s)

K – soil permeability (m/s)

0.50.5

0.5


The capacity of a circular pipe flowing full can be determined by Manning's equation:

Q = (53.01/n) D8/3 S1/2

where, Q = Pipe capacity, cu ft/day D = Pipe diameter, in. S = Slope, ft/ft n = Manning's roughness coefficient

Refrences

http://www.usroads.com/journals/rmej.htm

http://pavementinteractive.org/index.php?title=Surface_Drainage

www.fhwa.dot.gov/.../geotech/pubs/05037/07a.cfm

http://en.wiktionary.org/wiki/seepage

http://books.google.com/

http://en.wiktionary.org/wiki/seepage

http://books.google.com/

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drainage system of pavements

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