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NYSDOT Geotechnical Page 20-1 October 3, 2013
Design Manual
GEOTECHNICAL DESIGN MANUAL
CHAPTER 20
INFILTRATION FACILITY DESIGN
AND SUBSURFACE DRAINAGE
NYSDOT Geotechnical Page 20-2 October 3, 2013
Design Manual
(Intentionally left blank)
Table of Contents
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20.1 OVERVIEW ............................................................................................................... 20-4
20.1.1 Recharge.......................................................................................................... 20-4
20.2 GEOTECHNICAL INVESTIGATION FOR INFILTRATION FACILITIES ........... 20-4
20.3 GEOTECHNICAL DESIGN OF INFILTRATION FACILITIES .............................. 20-4
20.3.1 Parameters for Geotechnical Design of Infiltration Facilities ......................... 20-9
20.3.1.1 Subsurface Explorations and Permeability Tests ................................ 20-9
20.4 FILTER DESIGN FOR GROUNDWATER DRAINS ............................................. 20-11
20.4.1 Basis for the Use of Granular Filters ............................................................ 20-11
20.4.2 Design of Granular Filters ............................................................................. 20-11
20.4.3 Filter Criteria ................................................................................................. 20-12
20.4.4 Granular Filters at Pipe Joints, Holes, and Slots ........................................... 20-12
20.5 SUBSURFACE DRAINAGE ................................................................................... 20-13
20.5.1 Underdrains ................................................................................................... 20-13
20.5.2 Edge Drains ................................................................................................... 20-14
20.5.2.1 Preformed Composite Edge Drains................................................... 20-16
20.6 REFERENCES ......................................................................................................... 20-19
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Infiltration Facility Design and Subsurface Drainage
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20.1 OVERVIEW Infiltration facility design includes the design of basins, trenches and other water quality best
management practices (BMP’s) designed to encourage infiltration and pollutant removal of
stormwater runoff before it enters back into the subsurface water supply. Geotechnical design of
infiltration facilities not only includes assessment of the groundwater regime, soil stratigraphy,
and hydraulic conductivity of the soil as it affects the functioning of the infiltration facility, but
also involves an evaluation of the geotechnical stability of the facility (e.g., slope stability, affect
of seepage forces or soil piping at adjacent structures and slopes, and design of fills that control
the retention, diversion, or discharge of the collected stormwater).
20.1.1 Recharge
Allowing precipitation to replenish the groundwater supply, via infiltration or percolation, is an
important phase in the natural hydrologic cycle. The groundwater levels and hence, groundwater
supplies, generally increase in relationship to the amount of precipitation and the hydraulic
conductivity of the subsurface materials. The hydrologist or groundwater geologist refers to
water entering the aquifer as “recharge” bringing rise to the commonly used term “recharge
basin”.
20.2 GEOTECHNICAL INVESTIGATIONS FOR INFILTRATION FACILITIES The requirements of a geotechnical field investigation, the evaluation of the soil properties, and
groundwater quality requirements, and the necessary design elements for an infiltration practice
are discussed in the Geotechnical Design Procedure (GDP-8) Design, Construction, and
Maintenance of Recharge Basins and in the NYS DEC’s Stormwater Management Design
Manual (2010).
For geotechnical stability, the site investigation and design requirements provided in NYSDOT
GDM Chapters 2, 10, 12, and 13 are applicable.
20.3 GEOTECHNICAL DESIGN OF INFILTRATION FACILITIES
Unsaturated Flow vs. Saturated Flow
Since stormwater infiltration systems are designed to completely drain within 48 hours,
groundwater replenishment by means of recharge basins, as shown in Figure 20-1, or other
infiltration practices, generally takes place through unsaturated flow conditions in the soil zone
above the groundwater level. The process of water flow through an unsaturated soil is termed as
infiltration. Infiltration is an unsteady-state process of flow, meaning that the flow rate varies
with time under a constant head of water (e.g. infiltration flow rate will change even if the basin
remains full of water). When a stormwater infiltration basin experiences very long rain events
that will keep water in the basin for several days, the infiltration flow rate below will actually
decrease until the rate of flow approaches what occurs within a saturated soil condition. At soil
saturation, the flow is called percolation, and the rate of flow reaches its slowest value. However,
CHAPTER 20
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soil saturation below an infiltration practice is rarely achieved since an extraordinarily long rain
event is required.
If infiltration practices are chosen to address stormwater runoff, the Designer will need to
evaluate the probability of soil saturation below the practice. Therefore, the Designer will need
reliable information on the seasonal, high groundwater elevation or the presence of a protected
aquifer, the possibility of a temporary, perched water level or a deep frost layer, the soil gradation
for an extended depth below the bottom of the infiltration facility and the presence of any
shallow bedrock or impermeable soil layers at the proposed site.
Infiltration flow is complex and encompasses gravity flow and flow enhancements through
capillary suction and diffusion. This combination of flow methods explains why unsaturated flow
is faster than saturated flow. In design computations, the average rate of flow in unsaturated soil
conditions is represented by use of a hydraulic conductivity factor and a hydraulic diffusivity
factor. Although the flow is more complex, the same engineering principles can be applied to
unsaturated flow as is used for saturated flow. Therefore, the hydraulic conductivity factor and
the hydraulic diffusivity factor can be reliably estimated after first determining a soil’s coefficient
of permeability under saturated conditions.
Therefore, an essential element to be determined in the geotechnical investigation is the
coefficient of permeability (ks) of the soils underlying an infiltration practice. Permeability (ks)
represents the capacity of a saturated, porous material for transmitting a fluid without damage to
the structure of the medium (also known as saturated hydraulic conductivity).
The coefficient of permeability (ks) in a soil layer is best determined by performing percolation
tests or “rising head” tests near the proposed base elevation(s) of the stormwater infiltration
practice. The accuracy of the permeability value is dependant on saturated soil conditions being
ensured through soaking of the soil, or by utilizing a drill hole for a “rising-head” test that
extends below the water table. However, for soils with very high infiltration flow rates and very
deep water tables, soil saturation during the percolation test may be difficult to achieve. Under
such conditions, the designer may be able to obtain a reasonable value of the soil’s coefficient of
permeability by use of a laboratory procedure or by performing a “falling-head” test in a shallow
drill hole.
Design Methods for Infiltration Practices
The NYSDOT makes use of two design procedures to develop stormwater infiltration practices.
One procedure allows design of an infiltration practice that can address the stormwater runoff
from multi-year storm events. The alternate procedure allows design of an infiltration practice
that can address only the annual stormwater runoff event and incorporates by-pass outlets for
multi-year storm events.
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An infiltration practice capable of handling multi-year storm events is often used at sites which
display very high infiltration flow rates (generally an infiltration flow rate of 15 in./hr, or greater)
and which have soils with less than 10% fines and a relatively deep water table. This design
procedure is presented in the Geotechnical Design Procedure (GDP-8) Design, Construction, and
Maintenance of Recharge Basin is used.
For sites which display moderate to low infiltration flow rates, the infiltration practice is
developed to handle the annual stormwater runoff event using the procedure given in NYS
DEC’s Stormwater Management Design Manual (2010). This design procedure is used at sites
where the coefficient of permeability can be accurately measured in the field (typically 15 in./hr
> ks > 0.5 in./hr), and have soils with no more than 40% fines and a moderately deep water table.
Infiltration practices cannot be used when the infiltration flow rate is less than 0.5 in./hr. The
designer must consider that an infiltration practice is intended to provide a recharge of the
groundwater and also act as a sediment and pollutant filter of the stormwater. To accomplish the
filtering requirement, a pre-treatment fore bay is generally required upslope of the infiltration
practice.
Figure 20-1 Groundwater Replenishment Through a Recharge Basin
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Multi-Year Storm Infiltration Practice - Feasibility and Preliminary Design
When considering an infiltration practice that can handle a multi-year storm event, two types of
recharge methods may be proposed - surface or subsurface.
1. Surface recharge basins should be designed in accordance with Geotechnical Design
Procedure (GDP-8) Design, Construction, and Maintenance of Recharge Basins. GDP-8 is
intended to serve as a guide for determining feasibility, design, basin size, construction, and
maintenance requirements for high infiltration flow rate facilities. Pre-treatment of 100% of
the stormwater runoff volume must be addressed by methods discussed in NYS DEC’s
Stormwater Management Design Manual (2010).
Basin recharge is feasible wherever the following conditions exist:
• The soils, excluding the top 5 ft. of surface soil, are relatively permeable, and contain
less than 5% of fine grained soils. Obtaining an accurate coefficient of permeability
from percolation tests at these sites is often difficult and the use of a “rising-head”
drill hole permeability test can also be difficult since the water table is typically
located far below the base of the infiltration practice,
• Unsaturated conditions exist to a considerable depth below the surface. Infiltration
cannot occur if a soil is already saturated by permanent groundwater. For a design to
be valid, a good rule-of-thumb is that the depth of unsaturated soil below the
proposed basin floor is greater than 25 percent of the peak basin operating head with a
minimum separation of 5 feet from the seasonally high water table or any shallow
bedrock. The peak basin operating head, H, is defined as the maximum depth of water
permissible for the proposed basin,
• Unsaturated soils are not laterally confined, i.e. they have the capacity for water to
move and store horizontally. It is very helpful if sufficient space is available for
placing multiple basins in the project vicinity. Maximum use should be made of the
surrounding natural terrain, interchange loop channels between infiltration practices
and other project site depressions. This can allow substantial runoff volumes to be
disposed of by infiltration in a very small space,
• The infiltration flow rate of the underlying soils is sufficiently high to allow full
drainage of the basin within 48 hours,
• The basin will be located at least 100 feet away from water supply wells, and
• Cannot be located within a fill layer.
2. Subsurface recharge can be accomplished through the use of leaching basins. "Design of
Leaching Basins", Research Report 157, should be used as a source of information regarding
leaching basin design.
Leaching basins resemble isolated pits more than recharge basins, and are designed to
function differently than recharge basins. Leaching basins are usually cylindrical and deep,
often 10 to 20 ft. deep, with a 4 to 10 ft. internal diameter (see Figure 20-2). The walls are 4
in. thick concrete with rectangular windows cut in them below 5 ft. to allow water passage.
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The basin’s lower portion is surrounded by 2 ft. thick aggregate. This aggregate is covered by
a filter material to prevent overlying soil outside the basin from washing down into the
gravel. The bottom of the basin has no concrete floor, but is open to an underlying 2 ft. of
aggregate. Pre-treatment of 100% of the stormwater runoff volume must be addressed by
methods discussed in NYS DEC’s Stormwater Management Design Manual (2010).
Leaching Basin recharge is feasible wherever the following conditions exist:
• Unsaturated soils are not laterally confined, i.e. they have the capacity for water to
move horizontally and vertically,
• The permeability of the underlying soils is sufficiently high to allow full drainage of
the basin within 48 hours,
• The leaching basin will be located at least 100 feet away from water supply wells and
at least 10 feet from any structures,
• Typically will not be used to drain a surface area larger than one acre,
• Minimum separation of 4 feet from the seasonally high water table or any shallow
bedrock, and
• Cannot be located within a fill layer.
Figure 20-2 Leaching Basin
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Annual Storm Runoff Infiltration Practice - Feasibility and Preliminary Design
Stormwater infiltration practices designed to handle the annual stormwater runoff volume should
be designed in accordance with NYS DEC’s Stormwater Management Design Manual (2010).
This manual is intended to serve as a guide for determining the feasibility, design, type and size,
construction, and maintenance requirements for moderate to low infiltration flow rate facilities.
The infiltration practice is sized based on an assumption that saturated flow (the slowest rate of
water flow in a soil) will occur. Therefore, the coefficient of permeability, rather than the
hydraulic conductivity factor, is used in the design of the infiltration practice. This approach
allows for a slightly conservative capacity of the infiltration practice and helps ensure that the
practice will fully drain within 48 hours.
Pre-treatment of between 25% to 100% of the stormwater runoff volume, and the by-pass of
larger storm volumes, must be addressed by methods discussed in NYS DEC’s Stormwater
Management Design Manual (2010).
Feasibility of recharge at sites with moderate to low infiltration flow rates:
• Underlying soils must have an infiltration flow rate of at least 0.5 in./hr,
• Soils should have a clay content of less than 20% and clay/silt content of less than
40%,
• Infiltration practice cannot be located in fills or in areas with slopes greater than 15%,
• The base of the infiltration practice (basin, trench, or dry well) should have a
minimum separation of 3 feet above the seasonally high water table or a bedrock layer
(4 feet separation if over a sole source aquifer), and
• The infiltration practice will be designed to infiltrate between 90 to 100% of the
annual stormwater runoff event and have an overflow by-pass capacity for at least a
10-year storm event.
20.3.1 Parameters for Geotechnical Design of Infiltration Facilities
20.3.1.1 Subsurface Explorations and Permeability Tests
Permeability Tests
The following test procedures provide the Designer with an estimation of the coefficient of
permeability that can also be used to develop the hydraulic conductivity factor and the hydraulic
diffusivity factor:
• Specific Surface Analysis: Geotechnical Test Procedure (GTP-5) Test Procedure for
Specific Surface Analysis describes the method for determining the specific surface of soil
solids from grain size distribution data. It also describes the use of the specific surface in
calculating the coefficient of permeability and other soil properties.
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Specific surface is the particle surface area contained in a unit volume of soil solids. The
particle surface area includes only the external particle surface (the internal porosity of
individual particles is neglected). The estimated, saturated permeability of the cohesionless
granular material can be determined from the specific surface of solids.
The soil samples obtained from the subsurface exploration is tested. The test method
involves:
• Performing a grain size analysis of the soil specimen,
• Examining the shape characteristics of the grains contained in each sieve interval,
and
• Calculation of the specific surface.
Limitations: There is a limitation on the test procedure. If the soil sample contains more
than 5% passing the No. 200 sieve, the specific surface analysis is not performed.
• Drill Hole Infiltration Test: A drill hole infiltration test is detailed in Appendix D of the
NYS DEC Stormwater Management Design Manual. Additional information on drill hole
permeability tests are described in NAVFAC Design Manual DM-7.1 Soil Mechanics.
The drill hole infiltration test shown in the NYS DEC’s Stormwater Management Design
Manual (2010) is a “falling-head” drill hole test that provides a reliable estimation of the
saturated permeability when the infiltration flow rates are moderate to moderately low
and the soils contain more than 5% fine grained particles. The test is intended for
relatively shallow infiltration practices where excavation to the testing level is practical.
For sites with very high infiltration flow rates, the measured rates may be unreliable for
determining the coefficient of permeability (ks) due to the surrounding soil being unable
to become saturated prior to and during testing. For very low infiltration rates, the
coefficient of permeability will be too low to allow adequate infiltration flow.
Additional drill hole permeability tests presented in NAVFAC Design Manual DM-7.1
make use of a “rising-head” test that is performed below the water table. This approach
provides more accurate results than the “falling-head” test, but the soil must also be
moderately permeable and the water table located within soil conditions similar to the
base of the infiltration practice.
The factors affecting the performance and applicability of the drill hole permeability test
include:
• Depth of the water table level,
• Type of material (rock or soil),
• Depth of the test zone,
• Permeability of the test zone, and
• Heterogeneity and anisotropy of the test zone.
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To account for these factors, it is necessary to isolate the test zone at various depths.
Typically, to identify the subsurface strata, two subsurface explorations should be
progressed within 5 ft. of each other. The first subsurface exploration would identify the
soil strata by obtaining continuous samples. The exploration (usually a test hole
progressed with continuous Standard Penetration Testing) should be progressed to a
sufficient depth to locate and determine the extent and properties of all soil, water, and
rock strata that could affect the performance of the feature. Typically, the minimum depth
of the exploration should be at least 10 ft., or to a depth equal to the basin’s full height,
whichever is greater, below the proposed base elevation of the infiltration practice. The
second subsurface exploration would be progressed to perform the permeability test.
If subsurface explorations are not proposed and the appropriate equipment is obtainable, a more
common way of determining the coefficient of permeability at the site is a percolation test.
Percolation Test: Percolation is defined as the gravity flow of groundwater through the
fully saturated pore spaces in rock or soil. A percolation test is typically used as a test to
determine the suitability of a soil for the installation of a domestic sewage-disposal
system, in which a hole is dug and filled with water and the rate of water-level decline is
measured. The Department utilizes percolation test data to determine infiltration rates.
Percolation tests are described in NYSDOT GDM Chapter 4.
20.4 FILTER DESIGN FOR GROUNDWATER DRAINS
20.4.1 Basis for the Use of Granular Filters
Water seeping through a soil produces seepage pressures which can dislodge soil particles in the
direction of seepage, when the force is sufficient. If the soil does not have sufficient cohesion or
the individual soil particles are not sufficiently heavy or encircled to resist the seepage force, they
can be displaced. If the soil is well graded and contains a sufficient proportion of particles that
are too large for the seepage forces to move, a natural filter layer may develop as some of the
smaller particles are trapped between the larger particles and thus, erosion due to seepage should
stop. In the absence of coarse particles erosion may start near the ground surface and work its
way progressively back along the path of the seepage flow. Examples of this occurrence are some
types of cut-slope sloughs and piping under or through dams. Criteria have been developed for
the determination of the required particle distribution of a granular filter material, which when
placed over, or adjacent to, a soil with a known problematic grain size distribution, will prevent
erosion of the soil.
20.4.2 Design of Granular Filters
A filter material must meet two basic requirements:
1. The filter material must be fine enough to prevent infiltration of the material from which
drainage is occurring, and
2. The filter material must be much more permeable than the material being drained.
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20.4.3 Filter Criteria
• Retention or Stability Criterion – see NYSDOT GDM Chapter 7.
The 15% size (D15) of a filter material must be not more than four or five times the 85% size
(D85) of a protected soil. The ratio of D15 of a filter to D85 of a soil is called the piping ratio. This
criterion prevents the migration of fines and clogging.
• Permeability Criterion – see NYSDOT GDM Chapter 7.
The 15% size (D15) of a filter material should be at least four or five times the 15% size (D15) of
a protected soil.
The intent of criterion 2 is to guarantee sufficient permeability to prevent the buildup of large
seepage forces and hydrostatic pressures in filters and drains.
The two criteria are expressed as follows:
Equation 20-1
)(
)(54
)(
)(
15
15
85
15
soilD
filterDto
soilD
filterD
An additional criterion required by the US Army Corps of Engineers to ensure that the gradation
curve of a filter aggregate will be somewhat parallel to the curve for a soil is:
Equation 20-2
25)(
)(
50
50
soilD
filterD
20.4.4 Granular Filters at Pipe Joints, Holes, and Slots
When pipes are embedded in granular filter material, the ends of the pipe backfill should be
sealed by lower permeability soils and the filter materials in contact with pipes must be coarse
enough to not enter joints, holes or slots. The US Army Corps of Engineers and the US Army et
al. use the following criteria for gradation of granular filter materials in relation to slots and holes
along the pipe:
For circular holes:
Equation 20-3
0.1)(85
diameterhole
filterD
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For slots:
Equation 20-4
2.1)(85
widthslot
filterD
20.5 SUBSURFACE DRAINAGE
20.5.1 Underdrains
Underdrains are narrow trenches filled with clean aggregate filter material having a gradation that
is both pervious to water and capable of protecting the trench from infiltration by the surrounding
soil. Commonly, the flow capacity of the underdrain is enhanced by including a perforated or
slotted pipe within the aggregate filter material.
Underdrains lower or remove the subsurface water level below pavements or structures by means
of gravity flow. To function, they must be continuously sloped to an outlet, such as a drainage
channel or a closed drainage system. If designed and located appropriately, no intercepted water
is allowed to sit within the underdrain for long periods (more than 48 hours) and this helps to
ensure that any transported sediments do not settle out and block low points. The installation’s
effect on the adjacent site conditions depends on the surrounding area’s permeability and the
depth to which the groundwater level must be lowered. See NYSDOT GDM Chapter 7 for design
of underdrain filter material gradation. Installation details are provided on Standard Sheet 203-05
Installation Details for Corrugated and Structural Plate Pipe and Pipe Arches.
The Regional Geotechnical Engineer should be consulted to locate underdrains and their outlets
during design. Because underdrains are relatively expensive, good engineering requires
discriminate application. Ideally, the invert of the underdrain trench should be at least 4 ft. lower
than the nearest edge of pavement or ground surface. In areas where this can not be accomplished
due to shallow rock, water, or underdrain outlet elevations, considerations should be given to
constructing an underdrain trench as close to this depth as reasonably possible.
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Figure 20-3 Underdrain Installation Detail
(NYSDOT HDM Chapter 9)
20.5.2 Edge Drains
Edge drains are designed to remove water from the pavement section by means of gravity flow.
To function, they thus must be continuously sloped to an outlet, such as a drainage channel or a
closed drainage system, to ensure that no intercepted water is allowed to accumulate and that any
transported sediments do not settle out and block low points.
Edge drains for NYSDOT pavement designs extend 12 in. below the subgrade surface, thereby
also functioning as an underdrain.
Edge drain details and location depend on the highway geometry (e.g. superelevated, sag, etc.) as
well as pavement section (e.g. curbing, permeable base, etc). The edge drain should normally be
placed at the pavement's interface with the shoulder or curb since a change in the subbase
thickness at these locations often leads to subsurface water buildup and pavement damage.
Several studies had been performed by numerous State’s and the FHWA since the 1990’s to
determine how effective underdrain system were in minimizing damage to pavements and which
subsurface drainage systems performed better. The most comprehensive study was Project 1-34
by the National Cooperative Highway Research Program. In summary, the study revealed that:
1. both concrete and asphalt pavement systems, only a few years after construction, can
absorb up to 25 to 40% of a short rain event and underdrain and minor infiltration can
effectively remove most of this water within 24 hours,
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2. The more flexible a pavement system is, the more its performance relies on effective
subsurface drainage,
3. Connecting a permeable treated base layer to an underdrain significantly improves the
pavement’s long term performance,
4. Blocked underdrains can significantly contribute to the poor performance of a pavement,
5. Daylighting the outside edge of a subbase layer or a treated permeable base layer, in lieu
of connecting these layers to an underdrain, allows even better long term pavement
performance, and
6. Geotextiles wraps around an underdrain can impact its effectiveness within as little as 7
to 10 years.
Locations along the highway where concentrations of subsurface water may require underdrains
are sometimes difficult to predict during design, but some obvious locations for underdrains are:
1. Areas of existing surface seepage or saturation where a new highway is to be located,
2. Where the pavement parallels the base of a long or tall hill, or
3. On very long downhill grades where flow from infiltrated runoff and seepage zones tends
to follow the direction of the pavement. On long, downhill grades, transverse underdrains
cut diagonally across the travel lanes can improve the effectiveness of the underdrain
system.
Figure 20-4 Edge Drain in a Curbed Pavement Section
(NYSDOT HDM Chapter 9)
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The edge drain should intercept water from the highest water-bearing layer of the pavement
section. In flexible pavements, this water is usually encountered near the bottom of the asphalt
base course. In rigid pavements, it is usually found at the top of the subbase course. Also, since
the pavement’s subbase materials are often permeable, water can be located at the bottom of the
subbase layer. Typical edge drain installations for rehabilitation and restoration of conventional
pavements are shown in the see NYSDOT Comprehensive Pavement Design Manual.
In pavement sections that include a treated permeable base layer, the top of the edge drain should
be in full contact with the bottom of the permeable base at the lowest levels of its cross-section.
Again, the NYSDOT Comprehensive Pavement Design Manual provides edge drain details for
full-depth PCC over permeable base and edge drain details for full-depth HMA with permeable
base.
Edge drains must be provided with lateral outlets to the roadway ditch or to appropriate
structures in a closed storm-drain system. In practice, edge drains are normally placed in a trench
dug after subbase construction. This method requires removing subbase and subgrade material,
but it is used for ease of construction because it achieves uniform compaction of the roadway
section, and adequately confines the underdrain filter material.
20.5.2.1 Preformed Composite Edge Drains
Preformed edge drains are also available, usually consisting of a ribbon of corrugated or dimpled
plastic sheathed in an underdrain geotextile. The ribbons, referred to as Prefabricated Composite
Edge Drains (PCED) may be 2 ft. to 3 ft. taller, or taller, to ensure full contact with the pavement
subbase and subgrade layers. PCED are installed by a trenching machine that excavates a slit-
trench, places the edge drain, and backfills with fine, coarse aggregate, and compacts the trench
in one pass. PCED are particularly advantageous where an open trench is not wanted, or for very
long installations of pavement drains.
Although the installation process is rather quick and simple, inspection of the installation and
backfill operations are critical. To prevent cracking and settlement at the pavement surface above
the trench, the Prefabricated Composite Edge Drain must be placed tightly against one side of the
trench, without bends or folds, and the fine, coarse aggregate backfill must reach to the base of
the trench, be compacted in at least 2 lifts, and must be placed to match the subbase surface
above the top edge of the Prefabricated Composite Edge Drain. Since compaction of superpave
asphalt commonly requires a 4 foot wide placement, the installation of Prefabricated Composite
Edge Drains is now performed through the top of the exposed subbase layer. The asphalt
pavement is then placed afterwards.
See the NYSDOT Comprehensive Pavement Design Manual for complete guidance for PCED
installation and use.
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Figure 20-5 Preformed Composite Edge Drain: Installation with Stone Backfill
Adjacent to Full Depth Asphalt Pavement
(NYSDOT HDM Chapter 9)
Figure 20-6 Preformed Composite Edge Drain: Installation with Stone Backfill
Adjacent to Concrete Pavement
(NYSDOT HDM Chapter 9)
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Figure 20-7 Preformed Composite Edge Drain: Installation with Existing Suitable
Backfill Material Adjacent to Asphalt Pavement
(NYSDOT HDM Chapter 9)
Figure 20-8 Preformed Composite Edge Drain: Installation with Existing Suitable
Backfill Material Adjacent to Concrete Pavement
(NYSDOT HDM Chapter 9)
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20.6 REFERENCES
Cedergren, H.R., Seepage, Drainage, and Flow Nets, Third Edition, John Wiley and Sons, Inc.,
1989.
Department of Environmental Conservation, New York State Stormwater Management Design
Manual, Center for Watershed Protection, August, 2010.
Department of the Navy, Naval Facilities Engineering Command (NAVFAC), Soil Mechanics,
Design Manual 7.1, May, 1982.
Geotechnical Engineering Bureau, Design, Construction, and Maintenance of Recharge Basins,
Geotechnical Design Procedure GDP-8, New York State Department of Transportation, Office of
Technical Services,
https://www.dot.ny.gov/divisions/engineering/technical-services/technical-services-
repository/GDP-8b.pdf
Geotechnical Engineering Bureau, Test Procedure for Specific Surface Analysis, Geotechnical
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