Enhanced lateral drainage in pavement systems
table of contents
01
02
background information
basics of drainage
03
04
Mirafi® H2Ri
enhanced drainage applications
2
background
information
history & functions of geotextiles
3
history
the origins
Mirafi Inc. brought the first nonwovens
to the United States in the 1970’s
Geotextiles were originally intended to be an alternative to
granular soil filters. There is history dating back to the
1950’s of geotextiles being used behind precast concrete
seawalls, under precast concrete erosion control blocks,
beneath large stone riprap, and in other erosion control
situations.
roads, beneath railroad ballast, within embankments and
earth dams. ICI Fibres was a major influence in the use of
nonwoven, heatbonded fabrics. The first nonwovens used in
the United States were imported in the late 1970’s from ICI
Fibres by Mirafi Inc.
Geotextiles are manufactured from several polymers. 95% of
geotextiles manufactured are polypropylene-based, while
polyester, polyethylene and polyamide (nylon) make up the
other 5%.
In the late 1960’s, Rhone-Poulenc Textiles in France began
working with nonwoven needle-punched fabrics for unpaved
Worldwide geotextile sales exceeded
US $1 billion in 2012
section 01
4
functions of geotextiles
separation
Without separation
Separation is defined as “the placement of a flexible porous
textile (geotextile) between dissimilar materials so that
integrity and functioning of both materials can remain intact
or be improved”. *
10 lbs of stone placed on 10 lbs of mud
results in 20 lbs of mud
When placing stone aggregate on fine-grained soils, there
are two simultaneous mechanisms that tend to occur over
time. (1) The fine soils attempt to enter into the voids of the
stone aggregate thereby ruining its drainage capability.
(2) The stone aggregate attempts to intrude into the fine soil,
thereby ruining the stone aggregate’s strength. This results
in aggregate lost into the underlying subgrade.
With separation
section 01
(*Koerner, 2012)
5
function of geotextiles
confinement
Confinement usually applies in more
competent subgrades ( 3 ≤ CBR ≤ 8)
When placed at the bottom of or within the base course, a
geotextile can provide reinforcement through lateral
confinement of the aggregate layer. Lateral confinement
arises from the development of interface shear stresses
between the aggregate and the reinforcement. This
confinement occurs during placement, compaction and traffic
loading. This phenomenon is known as base reinforcement.
Base reinforcement improves the long-term structural
support for the base materials and reduces permanent
deformation in the roadway section. Industry research has
shown that confinement provided by reinforcement
geosynthetics can provide significant improvement in long
term pavement performance.
Geotextiles provide confinement through
friction. Geotextiles with higher coefficient
of interaction provides better confinement.
section 01
6
functions of geotextiles
reinforcement
Without reinforcement
Reinforcement usually applies in less
competent subgrades (CBR < 3)
High strength geotextiles possess tensile strength. They can
nicely complement materials that are good in compression
but weak in tension, such as fine-grained silt and clay soils.
Geotextile reinforcement is defined as “the improvement of a
total system’s strength created by the introduction of a
geotextile (that is good in tension) into a soil(that is good in
compression but poor in tension)”. *
surface can develop within the subgrade, causing it to
deform. This can lead to permanent rutting of the road
surface. Including a reinforcement geotextile at the
subgrade/base interface interrupts the shear plane, moving it
away from the weaker subgrade. This has the effect of
improving the subgrade’s bearing capacity.
When a wheel load is applied, an unreinforced shear
With reinforcement
section 01
(*Koerner, 2012)
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function of geotextiles
filtration & drainage
Filtration and drainage are not the same
thing
The geotextile function of filtration involves the movement of
liquid through the geotextile itself. The permittivity of a
geotextile defines its ability to transport water through
filtration.
Filtration
Filtration serves an additional purpose –
that of retaining soil on the upstream side
The geotextile function of drainage involves the movement of
liquid within the plane of its structure to provide a
drainage function. The transmissivity of a geotextile defines
its ability to transport water through drainage.
section 01
Drainage
8
basics of
drainage
keeping water out of roads
9
drainage
why is it important?
The 3 most important aspects of good
road design are drainage, drainage &
drainage
Everyone connected with the design and construction of
highways recognizes the importance of good drainage. No
other single feature is as important in determining the ability
of a pavement to withstand the effects of weather and
traffic.
The pavement structural section may be designed with
sufficient strength to support traffic loads even over soil with
a moisture content well above optimum. Accumulation of
water in the base or subbase, however, may cause distress
section 02
regardless of the structural section used. Water trapped in
any element of the pavement structure reduces the internal
friction and lowers the shear strength of the material. It may
cause cracking or disintegration of the pavement or pumping
of fine grained soil into the base.
Poor drainage is the major cause of
potholes and cracks. Undrained water on
roads can cause vehicles to hydroplane
at speeds over 45 mph.
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drainage
sources of water infiltation
The sources of water in a pavement structure are
mainly surface infiltration or groundwater. The
majority of surface infiltration takes place through
cracks in the pavement. Infiltration also occurs
through granular shoulders and mainly contributes to
pavement edge distress. Groundwater seepage into
the subgrade or pavement structure can result from a
natural spring, a high water table rising to pavement
level, or capillary action.
drainage
section 02
11
drainage
at the design stage
Surface drainage
Internal Drainage
Efficient surface drainage improves the removal of water
from the pavement surface to minimize surface water
infiltration into the structure and to reduce the risk of
hydroplaning. On most road sections this is accomplished by
providing a crossfall of 2% from the pavement centerline
towards the pavement edge. Fully paved shoulders are
typically sloped at 4% towards the edge while granular
shoulders, and partially paved shoulders, should be
constructed at a 6% slope to prevent edge curl and ponding.
The function of internal pavement drainage is to collect and
discharge water which may enter the pavement structure
through the surface course, surface cracks, granular
shoulders or from the subgrade. Internal drainage prevents
the build-up of moisture which could adversely affect the
strength and stability of the granular layers and subgrade.
The drainage system may also include subdrains, French
drains or open-graded drainage layers to improve water
collection and discharge.
section 02
12
effects of water on pavement structures
frost action
Frost action is worse in fine-grained
silty soils and silty granular materials
Distress manifestations associated with frost action include
frost heaving and frost boils. Fine-grained silty soils and silty
granular materials are subject to frost action in the presence
of moisture and freezing temperatures. Water can be drawn
up to the freezing front by thermodynamic forces and
capillary action to form ice lenses in frost-susceptible soils.
These conditions are aggravated when the water table is at a
shallow depth.
Pavement structures are generally weakest in the spring,
irrespective of the subgrade soils type, due to the higher
section 02
moisture regime that is generated by the melting of ice
lenses and increased precipitation and infiltration rates. The
higher moisture regime results in reduced strength properties
in the granular layers and subgrade.
The weakest pavement condition normally occurs when all
layers are thawed and the subgrade is saturated and has low
support properties.
The greatest potential for damage in flexible pavements
occurs in a partially frozen pavement when the granular base
is thawed and saturated and overlies a frozen subgrade.
Lack of proper drainage is one of the most
significant contributors to frost heave
distresses
13
effects of water on pavement structures
flexible pavements
Excess water can cause permanent cracking and deformation of a flexible pavement
The presence of water within the pavement structure reduces the strength of both the granular layers and the subgrade. The loss
of strength is caused by the generation of excess soil pore water pressures when a moving wheel loads the pavement.
The development of high pore water pressures prevents the full frictional capacity of the granular or subgrade from being
mobilized as it would be if it were in a dry or moist condition.
Additional asphalt cracking due
to deflection under load
Deflection of granular base and
buildup of hydrostatic pressure
Subgrade deflection
section 02
14
effects of water on pavement structures
rigid pavements
Water contributes to stepping of joints in a rigid pavement structure. The action of a wheel passing from one slab to the next
results in a slurry of water and soil fines initially being forced out from the edge of the approach slab. As the wheel transfers from
the approach slab to the leave slab, soil fines and water from under the leave slab are moved by suction forces to fill the void
under the approach slab. Continued wheel load repetitions in the presence of water result in the edge of the approach slab
progressively heaving as the leading edge of the leave slab settles, which results in a stepped joint or crack, and eventual loss of
support and slab cracking.
Direction of Travel
Approach
slab
Leave
slab
Water & fines displaced
under leave slab
Buildup of
hydrostatic pressure
section 02
15
effects of water on pavement structures
capillary action
Water can travel up to 30 feet vertically
in silty soils because of capillary action
Two forces affect water movement through soils, gravity and
capillary action. Capillary action refers to the attraction of
water into soil pores; an attraction which makes water move
in the soil. Capillary action involves two types of attraction:
adhesion and cohesion. Adhesion is the attraction of water
to solid surfaces, while cohesion is the attraction of water to
itself.
capillary conductivity of the larger pores is greater. The clay
has small pores and attracts water more strongly than the
sandy soil, but transmits it more slowly. This means that the
water will eventually rise higher in clay than silty sand
because the pores are smaller and closer together.
Soil pore size is a significant factor in how water moves
through soil. If a column of sandy silt is placed by a column
of clay and both columns are placed in water, the water will
rise more rapidly in the column of sandy silt because the
The rate of water movement and the
amount of water retention are related to
pore sizes in a soil
section 02
16
effects of water on pavement structures
capillary barriers
A capillary barrier forms and restricts water flow when two
porous materials with differing hydraulic conductivities are in
contact. Different material interfaces have different
breakthrough suctions. An important factor in the design of
capillary barriers is that the thickness of the capillary barrier
should exceed the height of water rise within it.
As shown in the example below, several feet of sand may be
required in order to construct capillary barriers. This can be
cost prohibitive, especially in areas where there is a lack of
affordable materials. This had led to the use of
geosynthetics for capillary barriers as an economical
alternative.
4” of 1” minus crushed aggregate
Geosynthetic reinforcement
14” of 3” minus crushed aggregate
Common fill from cut or borrow
5’
min
4
3.5’ capillary barrier (sand)
1
Horizontal Scale 1:100
Vertical Scale 1:20
Geosynthetic reinforcement
section 02
Example of haul road design with
a granular capillary barrier
17
effects of water on pavement structures
geosynthetic capillary barriers
Current geosynthetic capillary barriers
can be problematic in unsaturated soils
Soil
Geotextile
Geotextiles can act as capillary barriers because the suction
in fine grained soils prevents water flow to larger geotextile
pores. As moisture accumulates in the overlying soil, the
suction decreases. When the suction decreases to the
“breakthrough suction,” water freely flows into the
geotextile.
While awaiting the decrease in suction, water can be stored
in the overlying soils beyond levels that would normally drain
under gravity. This could cause the granular base or subbase
layers to weaken due to the additional moisture having
accumulated. This could cause a problem with geotextilegeonet geocomposites in unsaturated conditions.
section 02
Water in
soil pore
r2
Soil
particles
r2
Air in geotextile pore
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®
Mirafi
H 2R i
a better drainage solution with the
benefit of reinforcement &
confinement
19
the history of Mirafi® H2Ri
Alaska DOT&PF
In 2007, a TenCate representative posed this question to a
senior member of Alaska’s Department of Transportation &
Public Facilities. The answer was “differential frost heaving”
and this response led to the development of Mirafi® H2Ri.
Frost heaving results from ice forming beneath the surface of
soil during freezing conditions in the atmosphere. The ice grows
in the direction of heat loss (vertically toward the surface),
starting at the freezing front or boundary in the soil. Frost heave
requires three components to be simultaneously present: (1)
Water must be present to feed the ice crystal growth, (2)
Extended periods of freezing temperatures must exist in the
area of concern, (3) Soils must be frost susceptible.
Soils are considered to be frost susceptible when their levels
of sensitivity to capillarity action and permeabilities are at
optimum levels. Silty clays, silts, silty sands and very fine
sands tend to be the most frost susceptible of soils.
Capillarity
“What problem do you have today that
can’t be solved with geosynthetics?”
Permeability
section 03
20
Mirafi® H2Ri
how it works
Mirafi® H2Ri is a unique reinforcement
geotextile that also wicks water away
from roadways
Mirafi® H2Ri is manufactured using the same patented weaving
technology and polypropylene yarns as the Mirafi® RSi-series.
In addition, TenCate has combined deep grooved nylon yarns to
allow for the transportation of water away from a road
structure.
The patented wicking yarns in
Mirafi® H 2Ri are hygroscopic.
The black polypropylene yarns are hydrophobic and tend to repel
water. The blue nylon yarns are hygroscopic, meaning that they
attract and wick water. Together, these products provide
reinforcement and drainage through wicking.
Clogging of the nylon yarn is minimized by the groove spacing
which is between 5 and 10 μm.
section 03
21
Mirafi® H2Ri
excellent reinforcement option
Past research has demonstrated that geosynthetics containing
the combination of high tensile modulus, high permittivity, high
coefficient of interaction and the ability to provide separation of
the subgrade from the base aggregate, will result in superior
performance in roadway reinforcement applications.
Mirafi® RS380i, RS580i and H2Ri were tested by GeoTesting
Express (Alpharetta, GA) in a large cyclic box apparatus. The
Mirafi® RS580i has a higher modulus and coefficient of
interaction than the Mirafi® RS380i, therefore, providing better
roadway performance.
Mirafi® H2Ri, however, showed the best performance although
the modulus and permittivity are not as high as Mirafi® RS580i.
The superior performance of Mirafi® H2Ri can be attributed to
the wicking yarns that wick excess moisture out of the subgrade
and base course, thereby strengthening those layers.
section 03
22
1. mitigation of frost boils & frost
heaving
enhanced
drainage
applications
2. protection of roadways against
swelling & shrinkage of
expansive subgrades
3. lateral drainage in pavements
with high water tables
4. minimization of moisture
accumulation within base course
and/or subgrade materials
23
mitigation of frost boils & frost heaving
enhanced drainage applications
Test Installation of Mirafi® H2Ri at Mile
110 – Dalton Highway (AK)
The Dalton Highway was made famous by the reality
television show “Ice Road Truckers”. It is a remote 414 mille
highway through the Alaskan wilderness. It begins 80 miles
north of Fairbanks and ends at Deadhorse, AK, the industrial
camp for the oil fields in Prudhoe Bay. The narrow highway
runs parallel to the Trans-Alaska Pipeline and a large amount
of truck traffic travels the road throughout the year. Along
the highway lies a spot called Beaver Slide, which is located
at mile 110.5 approximately eight km south of the Arctic
Circle. Like most of the Dalton Highway, Beaver Slide
consists of a gravel surface and is prone to frost boils.
It is a downhill section of road cut into the side of a hill with
a gradient of approximately 11%. Each spring, there is
shallow groundwater seepage from the slope, which then
comes up into the road embankment causing the frost boils
and subsequent road damage. Soft spots also developed on
the Beaver Slide after lengthy rainy events during warmer
temperatures.
Mirafi® H 2Ri wicks water away from a
pavement by either daylighting (exposing)
the edge of the fabric in a ditch , or by
dropping the edge into a road’s subdrain.
section 04
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mitigation of frost boils & frost heaving
enhanced drainage applications
The original road was built directly on the original tundra,
with a degraded granite backfill that contained greater than
6% silt. Alaska Department of Transportation & Public
Facilities defines non-frost susceptible soils as having less
than 4% fines; this means the backfill soil was frost
susceptible. Water was also plentiful at the site. Ground
water was found approximately six inches below the tundra
and was encountered during the pit excavation for sensor
location 20.
Location of sensors
In August 2010, the general contractor built a 60-foot test
section at the Beaver Slide and installed two layers of
Mirafi® H2Ri. Researchers monitored the test section with
22 moisture and temperature sensors to measure
temperature and moisture changes over a three-year period.
They analyzed the data to evaluate the effectiveness of this
geosynthetic to mitigate the frost boils in Alaskan
pavements.
section 04
25
mitigation of frost boils & frost heaving
enhanced drainage applications
The data collected clearly showed that the Mirafi® H2Ri
removed water from the roadway. Moisture contours taken
in June 2011 (below) also indicates that the moisture content
of the soil parallels the wicking geosynthetic, a further
indication of its effectiveness at removing water.
section 04
26
protection of roadways against swelling & shrinkage of expansive subgrades
enhanced drainage applications
Field Study – State Highway 21
One of the concerns related to excess water in pavements is
the moisture migration into the subgrade which may cause
differential settlement in expansive clays soils. Pavements
founded on expansive clays are exposed to noticeable heave
during the wet season and shrinkage in the dry season.
Moisture generally seeps into the shoulder of the pavement
which causes the soil below the shoulders to swell more
than under the center of the road. Infiltration of precipitation
through pavement layers and subgrade soils not only
weakens the road structure, but also exacerbates the
differential deformations induced by swelling and shrinkage
of the subgrade. Significant longitudinal cracks are
developed when the subgrade dries and settles unevenly.
This induces tensile stresses in the flexible pavement.*
As part of the Texas Department of Transportation State
(*Zornberg et al 2012, Roodi and Zornberg 2012)
Highway Improvement Plan, a stretch of approximately 6
miles of State Highway 21 was planned to be rehabilitated.
This portion of SH21 has shown poor performance for many
years. Despite several maintenance operations over this
time, the road continued to suffer from various distresses
over many areas, suggesting very poor ride quality. The main
distresses observed were major longitudinal and edge
cracking, vertical deformation, rutting and faulting.
section 04
27
protection of roadways against swelling & shrinkage of expansive subgrades
enhanced drainage applications
The road was founded on a highly plastic subgrade soil with
a plasticity index value in excess of 35%, indicating a highly
expansive clay.
Since the lateral drainage and seasonal swelling and
shrinkage of the expansive subgrade were of significant
concern in this area, the University of Texas at Austin
proposed an evaluation involving eight test sections
constructed with four different types of separator
geotextiles. The selected geotextiles included: (1) Mirafi®
140NC, (2) Mirafi® HP570, (3) Mirafi® RS580i, (4) Mirafi®
H2Ri.
The performance of the road will be evaluated with a
comprehensive monitoring program including (1)
precipitation and environmental data, (2) moisture
Types of distresses on SH21
monitoring, (3) visual conditions surveys, (4) TxDOT Annual
Pavement Management Information System data, (5) Falling
weight deflectometer testing, and (6) laboratory pullout
testing.
section 04
28
protection of roadways against swelling & shrinkage of expansive subgrades
enhanced drainage applications
Potential Control Sections
500
500
500’
500’
140NC
H2Ri
500
500
500
500
500
500
500’
500’
500’
500’
500’
500’
RS580i
HP570
H2Ri
HP570
RS580i
140NC
Reinforcement
Separation
Separation
Length
Type
Repeats
Types of distresses on SH21
Reinforcement
Separation
Hydraulic
After a site visit in September 2012, TxDOT chose the worst
sections and subsequently installed the sensors and
geosynthetics in January 2013. Site inspection visits took
place in May, October and December 2013. More
Reinforcement
Separation
(Control)
information and data analysis are expected shortly.
section 04
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lateral drainage in pavements with high water tables
enhanced drainage applications
Daniel Boone Bridge – Interstate 64 (MO)
The Daniel Boone Bridge upgrade is a $117 million project
undertaken by the Walsh-Alberici Joint Venture. This designbuild project includes a new bridge on I-64 over the Missouri
River between St. Louis and St. Charles Counties, replacing the
deteriorating bridge built in 1935. This project also includes a
shared-use path connecting the Katy Trail with the Monarch
Daniel Boone Bridge (artist’s rendition of upgrade)
Levee Trail and the addition of a fourth travel lane. The new
bridge will measure 2,615 feet with a main navigational span
of 510 feet and two intermediate back spans of 370 feet. It is
a parallel flange plate girder design with flexibility to add a
fifth vehicular lane in the future. Construction began in 2013
and will be completed by the end of 2015.
Daniel Boone Bridge (prior to upgrade)
section 04
30
lateral drainage in pavements with high water tables
enhanced drainage applications
There were several significant challenges regarding this
project: (1) There is significant downward pressure on
MoDOT construction spending. (2) Most of this funding is for
maintenance projects, with very few dollars available for
capital projects such as new roads and bridges. The
exception to this is in design-build projects such as the
Daniel Boone Bridge. (2) Subgrade soils on this site are
saturated and the water table is also very high. (3) Drainable
aggregate in this area is very expensive, ranging up to
$40/ton.
Concrete Pavement
Type V aggregate
Drainable aggregate
Original design
Concrete Pavement
The original design called for a 12” concrete pavement, 4”
type V (1 ½” minus) aggregate and 4” drainable aggregate.
After consultations between TenCate representatives and the
owner, the type V aggregate was increased to 6” and the
drainable aggregate was removed in favor of Mirafi® H2Ri,
which would offer reinforcement and drainage.
Type V aggregate
Mirafi® H2Ri
Alternative design with Mirafi® H2Ri
section 01
31
lateral drainage in pavements with high water tables
enhanced drainage applications
The first on-ramp was constructed in September 2013 and the remainder of the approaches should be completed by summer 2014.
In all, 90,000 yd2 of Mirafi® H2Ri will be installed to reinforce and drain the approaches and on-ramps by the end of construction
in 2015. The photo on the left shows the installation of Mirafi® H2Ri on October 17, 2013. The photo on the right shows how
Mirafi® H2Ri is wicking water away from the road on October 21, after a ¼” rainfall from October 18.
section 04
32
minimization of moisture accumulation within base course and/or subgrade materials
enhanced drainage applications
the 1993 AASHTO Flexible Pavement Design Methodology.
This methodology predicts the # of 18 kip Equivalent Single
Axle Loads a road can carry based on a number of factors.
The most significant of these factors is the structural number
that each layer (subbase, base, asphalt, etc) contributes to
the overall structure. It is well known that the structural
number of a layer is directly proportional to the drainage
coefficient of that layer (ie SN=a1D1 +a2D2M2 +a3D3M3+…),
where M is the drainage coefficient.
base course
According to the Federal Highway Administration’s
Geosynthetic Design & Construction Guidelines (FHWA NHI-0792), “Geosynthetics may also provide cost and
performance benefits when used in roadways with firm,
fairly competent subgrades (CBR ranging from 3 to 8)…
extending the design life or increasing structural support
through improved drainage when used for… or as part of
the roadway drainage systems”.
Previous full-scale testing has shown that geosynthetics can
improve the structural number of a granular base or subbase
by contributing a geosynthetic structural coefficient to this
layer. The goal of this joint research program is to quantify
the drainage benefit that Mirafi® H2Ri contributes.
In the spirit of this concept, TenCate Geosynthetics has
embarked on a joint research program with the University of
Kansas and the University of Alaska Fairbanks. The goal of this
program is to quantify the benefit that Mirafi® H2Ri brings to
.
.
.
.
section 04
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minimization of moisture accumulation within base course and/or subgrade materials
enhanced drainage applications
subgrade
According to Budhu (2010), “…the undrained shear strength of
fine grained soils can increase about 20% for 1% reduction in
the moisture content”. Based on the preliminary laboratory
testing performed by the University of Alaska Fairbanks, Mirafi®
H2Ri can increase the undrained shear strengths of such soils
by 45% to 90% when compared to soils treated with other
geosynthetics.
section 04
34
thank you
contact information
For more info, please go to our
website at
www.mirafi.com
www.miraspec.com
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