Topic 7 Pavement Drainage Instructor: Shih-Hsien Yang N674300 Pavement Analysis & Design
Topic 7
Pavement Drainage
Instructor: Shih-Hsien Yang
N674300 Pavement Analysis & Design
Objectives
vImpact of moisture on pavement distress
vDefine drainage factors
vList properties that influence drainability
vDescribe principle behind drainage timev DRIP
How Much Water Gets into PavementvRain: dry-wet; freeze-thawvPavement design, age, and conditionvSurface drainage: longitudinal and transverse
slopes, ditches, and storm drain.
Sources of Moisture
SeepageThrough Permeable Surface
Water Table
Capillary Vapor
Water Table
Pavement Infiltration
Water in Pavements
vStripping in HMAvLoss of subgrade supportvReduction of granular layer
stiffnessvErosion of cement-treated
base layersvReduction in the pavement
service life if base is saturated for sometime
vDebond between layers
How to Address the Problem?
v Pavement geometry (slopes and ditches)v Crack sealingv Treated Layerv Thicker Layersv Full Widthv Subsurface Drainage
0.02 m/m0.04 m/m
Subgrade
Treated base
HMA
Aggregate base
Pavement Slopes
Sx SRS
W LR
( )S S SR x= +2 2 0 5.
LR W SSX
= +12 0.5
Tan A SSX
( ) =
( )
)(
Pavement Slopes
vSurface and subsurface slopes
vAlways positive SR
vRecommended slopes:v 0.01 – 0.025 m/m (spec range)v 0.02 m/m (normal conditions)v 0.025 m/m (high rainfall)
Drain Requirements
vSufficient stiffness to support traffic without significant permanent deformation under dynamic loading
vSufficient transmissivity to rapidly drain the pavement section and prevent saturation of the base
vSufficient air void to provide a capillary break
Permeable Base System
Rigid outlet pipe
Longitudinalpipe edgedrain
10-yearflow
Ditch
PavementPermeable baseBase layer
Shoulder
Shoulder
Permeable base
Base layer
Pavement
SubgradeDitch
Fabric
Embankment
Geocomposite Edgedrains
Sand Backfill
Prefabricated Geocomposite Edge Drain (PGED)
Aggregate base
Subbase/Subgrade
25 mm
100 mm
ShoulderPavement
Subsurface Drainage
OGDL EDGE DRAIN
PGED
Pavement Design Equations (AASHTO 1993)
SN = a1D1 + a2D2m2 + a3D3m3
log10W18 = (ZR)(S0) + (9.36)(log10(SN+1) - 0.20 + log10[ΔPSI/(4.2-1.5)]/[0.40 + (1.094/(SN+1)5.19)] + (2.32)(log10MR) - 8.07
Drainage - mi
Adjust layer coefficients to account for effects of certain levels of drainage on untreated materials
Quality of Drainage Water Removed WithinExcellent 2 hours
Good 1 day
Fair 1 week
Poor 1 month
Very poor Water will not drain
Quality of Drainage
Percent of Time Pavement Structure is Exposed to Moisture Levels Approaching
SaturationLess Than
1% 1-5% 5-15% Greater Than 25%
Excellent 1.40-1.35 1.35-1.30 1.30-1.20 1.20
Good 1.35-1.25 1.25-1.15 1.15-1.00 1.00
Fair 1.25-1.15 1.15-1.05 1.00-0.80 0.80
Poor 1.15-1.05 1.05-0.80 0.80-0.60 0.60
Very Poor 1.05-0.95 0.95-0.75 0.75-0.40 0.40
* Quality of drainage is a function of permeable base quality of drainage and effectiveness of drainage system
Permeabilityv Ability of materials to
carry waterv Coefficient of permeability
(k)v Measure of permeability v Rate of flow through a unit area
with a unit hydraulic gradientv Affected by
v Porosityv Effective grain size, D10v Percent passing #200 sieve
v Measured in the lab:v Falling head testv Constant head test
v Field testing:v Field permeability testing devicev Tipping buckets
Air
Water
Solid
Wt of waterWw=
Weight—Volume Relationship
Ws= Wt of solids
WT= Total wt
VA= Air vol.
VW= Water vol.
VS= Solid vol.
VV= Voids vol.
VT Total vol.
Vv = Volume of voids
VT = Total volume
= Unit dry weight, kN/m3
Gsb = Bulk specific gravity
Porosity
v Porosity: indicates aggregate’s ability to store or give up water
γd
𝑁 =𝑉$𝑉%
= 1 −Υ)
9.81𝐺./
Effective Porosity
where, N = PorosityWL = Water loss, %
v Effective porosity indicates the amount of drainable water (how strong the soil will hold water)
𝑁0 =𝑉𝑜𝑙𝑢𝑚𝑒𝑜𝑓𝑤𝑎𝑡𝑒𝑟𝑑𝑟𝑎𝑖𝑛𝑒𝑑
𝑇𝑜𝑡𝑎𝑙𝑉𝑜𝑙𝑢𝑚𝑒= 𝑁×𝑊𝐿
Saturation
where,
Drained water = Ne x U = Vv - Vw
Ne = Effective porosity
U = Percentage drained
v Saturation: Measure of the amount of water in the soil; Vw = Vv% Saturation
𝑆 =𝑉D𝑉$
×100
MOVEMENT OF WATER
vGravity, capillary action, vapor pressuresvFine-grained soil ⇒ capillaryvGranular materials ⇒ gravity
v = ki (Darcy’s law)v = discharge velocity (not actual seepage velocity)k = coefficient of permeabilityi = hydraulic gradient
Q = vA (Discharge = volume of flow per unit time):A = cross-sectional area normal to the direction of flow
Darcy’s Law Assumptions
vSteady-state flowvSoil is porous and homogenousvLaminar flow
Surface Inflow
vTwo ApproachesvSteady-State Flow
v Rainfallv Percentage of rainfall that enters the
pavement
vTime-to-Drain
Time-to-Drain Design Assumptions
vDuring a rainfall event water infiltrates into the permeable base until it is saturated
vExcess rainwater runs off to a side ditchvTime required to drain certain amount of water
from the drainage layer after a rain event
Time-to-Drain
PavementPermeable baseBase layer
Shoulder
qi
qd
Q
Pavement Discharge Rate, qd
vqd is based on time-to-drain analysis
where:qd = pavement discharge, m3/day/mW = width of the permeable base, mH = base thickness, mNe = effective porosity of base materialU = percent drained in decimaltd = time to drain, hrqi = pavement infiltration, m3/day/m2
HMA pavements: 0.10 to 0.15 m3/day/m2
PCC pavements: 0.15 to 0.20 m3/day/m2
𝑞) = 24𝑊𝐻𝑁0𝑈1𝑡)= 𝑞K𝑊
Excellent 2 hoursGood 1 dayFair 7 daysPoor 1 monthVery Poor Does not drain
For Pavement: Time required to drain 50% of the drainable water
Design Standards
For Freeways: 50% drained in 2 hrsIf heavy traffic, in 1 hr
Excellent < 2 hoursGood 2 to 5 hoursFair 5 to 10 hoursPoor > 10 hoursVery Poor >>> 10 hours
For pavement rehabilitation, 85% saturation
Design Standards
Effect of Degree Saturation on Deformation for Granular Material
t = T x m x 24
Time-to-Drain Calculation
m-factor (days)Time factor
Time to drain (hrs)
How to Estimate Time to Drain (t)
vInput: v S and Sx
v W, H, k, γd, Gsb, WL (for permeable base)vInterim Output:
v SR, LR, S1 {S1 = (LR x SR)/H}v T for a desirable degree of drainage (U)v N and Ne
v N = [1- {γd / (9.81 x Gsb)}]v Ne = N x WL
v “m” factor: m = (Ne x LR2) / (k x H)
vOutput: t = T x m x 24
Transmissivity
U-T Relationship
Deg
ree
of D
rain
age
-U
.01 .05 .2 1 5 201
.7
.3
0
Time Factor - T
10 8 6 4 2 1 .6.8S1 = .4 0
1
2
3
5
7
0.01 .03 .10 .30 .60
Slop
e Fa
ctor
(S1)
Time Factor (T50)
T for U = 50% Drained
Time-to-Drain and Permeability Relationship
Time to Drain, hrs
Perc
ent D
rain
ed
0 1 3 5 7100
20
0
k = 305 m/day
k = 610 m/dayk = 915 m/day
40
60
80
k = 153 m/day H = 0.15 mNe = 0.25LR = 7.6 mSR = 0.02 m/m
Base DrainabilitiesA
AcceptableM
MarginalU
Unacceptable
Subg
rade
Soi
l D
urab
ility
Fair
Poor
EXC G F to P
F to P P to VP VP
G F P to VP
EXC - ExcellentG - GoodF - FairP - PoorVP - Very Poor
Combining Base and Subgrade Drainage
PERFORMANCE
Good
Time to drain
For two lane road - Lane width = 24 ft, Slope = 0.01
Base k (ft/day) time to drain Quality
OGB 1000 2 hrs to drain Excellent
DGAB 1 1 week Fair
DGAB w/ fines 0.1 1 month Poor
Reality no drains does not drain Very Poor
Aggregate Gradations
1 0
Percent Passing
Sieve Sizes, mm
20
40
60
80
100
12.5 25.4 37.50 9.54.752.075
AASHTO No. 67 AASHTO No. 57
Pea gravel
Dense Agg. base Sand
Fine Sand MediumSand
CoarseSand Gravel
010
50
7060
403020
8090
100
.075 .180 .300 .600.850
1.182.00
2.36 4.759.525.012.5
19.0 37.5 63.0
K (ft. / day)
Sieve Sizes
Perc
ent P
assi
ngInternal Drainage Factors - Permeability
Aggregate Gradation Importance
vEffective grain size, D10v Sieve size corresponding to 10% passing (by wt)v Affects permeability
vCoefficient of uniformity (indicates stability),
vCoefficient of gradation/curvature,
Cu =D60
D10D60 = Sieve size corresponding to 60% passing (by wt) D10 = Sieve size corresponding to 10% passing (by wt)
Cz = D230
D10 * D60D30 = Sieve size corresponding to 30% passing (by wt)
* <4 may be unstable
Types of Current Permeable Bases
v Unstabilized permeable basevDevelops stability through aggregate interlock and
internal frictionvFiner gradation than stabilized bases
v Stabilized permeable basevStability is achieved by interlock and
cementation/binder (AC or PC)vMore open-graded than unstabilized layers
Construction of Permeable Bases
v Good and stable supporting layerv Stablev Avoid contaminationv No discontinuities in the flow pathv Placement is very important (consider a control
strip)v Over compaction can be a problem v Resultant permeability should meet or exceed the
design one
Factors Affecting The Design of Drainage Layer
vPavement slopesvAggregate gradationvPorosity and effective porosityvLayer saturationvPermeability
The Need for a Separator Layers
vDense-graded aggregatevDense-graded HMAvCement-treated base vGeotextilesvAsphalt chip sealsvTreated subgrade
Design of Aggregate Separator Layer: Gradation
vSatisfy filtration and uniformity requirements:v Subgrade/separator layer interface
v D15(separator layer) < 5*D85(subgrade)v D50(separator layer) < 25*D50(subgrade)v Practice:
v D15(separator layer) < 3.50 mm (filtration)v D50(separator layer) < 3.25 mm (uniformity)
v Permeable base/separator layer interfacev D15(permeable base) < 5*D85(separator layer) v D50(permeable base) < 25*D50(separator layer) v Practice:
v D85(separator layer) > 0.44mm (filtration)v D50(separator layer) > 0.24mm (uniformity)
v Percent passing #200 sieve should be <12%v CU > 20, preferably in the vicinity of 40
Physical Properties of the Aggregate Separator Layer
vMinimum CBR of 50% vLow permeability (< 5 m/day)vGood interlock through durable and angular crushed
stonevMinimum thickness of 100mm
Gradation of a Separator Layer (DGAB)
D60
D10
Dense-graded aggregate base
D10= 0.98 mm
Cu= 45.97Perc
ent P
assi
ng
Sieve Sizes, mm
20
40
60
80
100
12.5 25.4 37.50 9.54.752.075Max. 12% fines
Example of Separator Layer Gradation
Grain Size - mm
Separator layer gradation
20
40
60
80
100
01 5 100.50.10.050.01 50 100
Design EnvelopePerc
ent P
assi
ng
GeotextileSeparator Layer Design
vCheck forv Separation criteria (soil retention)v Survivability and endurance criteria v Clogging potential criteria* v Permeability criteria*
Time Domain Reflectometry
0
5
10
15
20
3/3/00 3/17/00 3/31/00 4/14/00 4/28/00 5/12/00 5/26/00
Date
Moi
stur
e C
onte
nt (%
)
0
5
10
15
20
25
30
35
40
45
50
Prec
ipita
tion
(mm
)
Precipitation
Moisture Content
0
5
10
15
20
3/14/00 3/28/00 4/11/00 4/25/00 5/9/00 5/23/00
Date
Moi
stur
e C
onte
nt (%
)
0
5
10
15
20
25
30
35
40
45
50
Prec
ipita
tion
(mm
)
Precipitation
Moisture Content
SECTION B
SECTION J
Degree of Saturation (%)
Def
lect
ion
(mm
)
60 70 80 90 100
2.5
5.0
7.5
10.1
12.6
15.1
6.2 % Fines9.1 % Fines
11.5 % FinesCrushed stoneGravel
Deflection vs. Saturation of Base
Monitoring Techniques
vPerformance monitoring can identify potential problems sooner and save moneyv Visual condition surveysv FWD testing (structural integrity)v Profile (ride quality)
vIf sub-drainage is present, can the outlets be found and are they clear of debris?
vAre inlets clear and functioning?vAfter a rain, is water flowingvAre the joints or cracks properly sealed?vAre ditches clear of standing water and/or
grass/weeds?vAre typical signs of pumping evident?
Visual Evaluation
Moisture Related Distresses-HMA
Moisture Related Distresses-PCC
Click to edit Master title style
PAVEMENT PERFORMANCE IS A TRUE REFLECTION OF DRAINAGE SYSTEM
OGDL Problems
OGDL Failure
Guide for Selecting m2
Quality of Drainage*
Excellent
Good
Fair
Climate Condition A
1.25 - 1.20
1.25 - 1.20
1.25 - 1.20
Climate Condition F
1.25 - 1.15
1.25 - 1.15
1.15 - 1.05
v Recommended drainage coefficient, m2
* Quality of drainage is a function of permeable base quality of drainage and effectiveness of drainage system
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