properly installed silt fence is the most effective temporary sediment control device available 100...
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Properly installed silt fence is the most effective temporary sediment control device availableProperly installed silt fence is the most effective temporary sediment control device available
100 ft. of effective silt fence can retain 180 tons of sediment.100 ft. of effective silt fence can retain 180 tons of sediment.
Properly installed silt fence detains waterfor sedimentation to occur
Properly installed silt fence detains waterfor sedimentation to occur
Sediment control devices
primarily collect larger particles
of soil because clays and silts are
very small. Large particles cause
further erosion – thus a
multiplying effect - once
introduced into a stream.
Sediment control devices
primarily collect larger particles
of soil because clays and silts are
very small. Large particles cause
further erosion – thus a
multiplying effect - once
introduced into a stream.
Goal of silt fenceGoal of silt fence
Silt fence, for maximum efficacy, should
detain water for sedimentation to occur.
Occasionally it may be used to divert
stormwater to a storage area.
Silt fence, at a minimum, should retain large
soil particles and prevent loss from the site.
Silt fence, for maximum efficacy, should
detain water for sedimentation to occur.
Occasionally it may be used to divert
stormwater to a storage area.
Silt fence, at a minimum, should retain large
soil particles and prevent loss from the site.
Two most common problemsTwo most common problems
Placement issues – won’t pond water or
insufficient quantity for the area
Installation issues - inadequate backfill
and/or compaction – one weak area
allows the fence to fail
Placement issues – won’t pond water or
insufficient quantity for the area
Installation issues - inadequate backfill
and/or compaction – one weak area
allows the fence to fail
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Placement
Quantity
Installation
Compaction Attachment
Support
A failure on any segment
of the system makes the
entire silt fence a complete
waste of money!
A failure on any segment
of the system makes the
entire silt fence a complete
waste of money!
PLACEMENT
refers to specific locations on
each construction site, and to
specific designs (layouts)
at each location.
PLACEMENT
refers to specific locations on
each construction site, and to
specific designs (layouts)
at each location.
The ends of a “smile” must always be longenough to pond water and sediment.
The ends of a “smile” must always be longenough to pond water and sediment.
Designs called
J-hooks insure
water & sediment
pond behind
each silt fence.
Designs called
J-hooks insure
water & sediment
pond behind
each silt fence.
CorrectCorrect IncorrectIncorrect
Silt Fence PlacementSilt Fence Placement
Correct Silt Fence Placement
Incorrect Silt Fence Placement
Streets that have
been excavated,
but not paved,
are prime areas
for sediment
discharge.
Recommend
silt fence to
control sediment
and velocity.
Streets that have
been excavated,
but not paved,
are prime areas
for sediment
discharge.
Recommend
silt fence to
control sediment
and velocity.
Silt fence should pond water to be considered effective.
Silt fence should pond water to be considered effective.
Myth – flat sites do not need protection
Myth – flat sites do not need protection
Stop sediment before it reaches the pavement.
Stop sediment before it reaches the pavement.
Ditch checks Ditch checks
Do not install silt fence in a continuous flow
situation, or on the discharge of an outlet.
Install on the inlet side of a culvert.
A properly installed, compacted, and
supported silt fence will retain
significant sediment in a ditch situation.
Shallow posting (wood posts?) and poor
compaction will not be effective.
Do not install silt fence in a continuous flow
situation, or on the discharge of an outlet.
Install on the inlet side of a culvert.
A properly installed, compacted, and
supported silt fence will retain
significant sediment in a ditch situation.
Shallow posting (wood posts?) and poor
compaction will not be effective.
25 tons of sediment captured per fence in a ditch situation
25 tons of sediment captured per fence in a ditch situation
Concentrated flow is standard on many SWPP’s.
Concentrated flow is standard on many SWPP’s.
Proper installation can withstand concentrated flows
Proper installation can withstand concentrated flows
Leave room for sediment storage at toe of slope
Leave room for sediment storage at toe of slope
Protect area intakes with larger silt fence structures, if possible
Protect area intakes with larger silt fence structures, if possible
Proper placement should insure sedimentation.
Proper placement should insure sedimentation.
On-site adjustment is mandatoryOn-site adjustment is mandatory
Grading plans and PPP’s are often drawn in an
office many months prior to disturbance.
The ESC contractor must adjust the plan to
properly control the site, or at a minimum notify
the site managers of potential problems.
Grading plans and PPP’s are often drawn in an
office many months prior to disturbance.
The ESC contractor must adjust the plan to
properly control the site, or at a minimum notify
the site managers of potential problems.
Do not use silt fence:Do not use silt fence:
Where you can not create a storage area for runoff, such as on steep slopes, on small areas, or in short segments.
Where you can not prevent water running around the end
In a V-shaped or shallow channel
Where you can not create a storage area for runoff, such as on steep slopes, on small areas, or in short segments.
Where you can not prevent water running around the end
In a V-shaped or shallow channel
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Placement
Quantity
Installation
Compaction Attachment
Support
QUANTITY relates to area of control.
The volume of water from a large site
can not be controlled in one run of silt
fence. Multiple locations or storage
areas are often required.
QUANTITY relates to area of control.
The volume of water from a large site
can not be controlled in one run of silt
fence. Multiple locations or storage
areas are often required.
Large areas often
need additional
runs installed in
the interior to
reduce the volume
of water reaching
the perimeter fences.
Large areas often
need additional
runs installed in
the interior to
reduce the volume
of water reaching
the perimeter fences.
Long runs should be avoided. They tend to
accumulate sediment in one area,
causing premature overflow.
Long runs should be avoided. They tend to
accumulate sediment in one area,
causing premature overflow.
Long runs often concentrate water and then overflow
Long runs often concentrate water and then overflow
Breaking up a run more than doubles storage area
Breaking up a run more than doubles storage area
Multiple runs slow runoff velocity and add storage area on site.
Multiple runs slow runoff velocity and add storage area on site.
Proper QuantityProper Quantity
100 ft. of silt fence per 10,000 sq. ft.
of disturbed area seems to be an
adequate rule of thumb for sediment
control and economics.
100 ft. of silt fence per 10,000 sq. ft.
of disturbed area seems to be an
adequate rule of thumb for sediment
control and economics.
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Placement
Quantity
Installation
Compaction Attachment
Support
INSTALLATION relates to how the
fabric is placed in the soil, appropriate
depth of placement, and appropriate
backfill for an effective silt fence.
INSTALLATION relates to how the
fabric is placed in the soil, appropriate
depth of placement, and appropriate
backfill for an effective silt fence.
Improper installation often leaves silt fence blowing in the wind.
Improper installation often leaves silt fence blowing in the wind.
No compaction = washoutsNo compaction = washouts
DOT job with inspector does not insure proper installation.
DOT job with inspector does not insure proper installation.
Mechanical installation
reduces many labor-related
installation problems.
Mechanical installation
reduces many labor-related
installation problems.
Mechanical installation
provides consistent,
dependable silt fence.
Mechanical installation
provides consistent,
dependable silt fence.
The slicing method disturbs,
but does not excavate soil,
creating an optimal condition
for compaction.
The slicing method disturbs,
but does not excavate soil,
creating an optimal condition
for compaction.
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Placement
Quantity
Installation
Compaction Attachment
Support
COMPACTION
relates to soil permeability. Loose or
trash-filled backfill is easily saturated
with water and washed out under the
silt fence. Compacted soil resists
saturation, and thus washouts.
COMPACTION
relates to soil permeability. Loose or
trash-filled backfill is easily saturated
with water and washed out under the
silt fence. Compacted soil resists
saturation, and thus washouts.
Silt Fence StudySilt Fence Study
EPA co-sponsored research has shown compaction is the critical factor in silt fence effectiveness.
EPA co-sponsored research has shown compaction is the critical factor in silt fence effectiveness.
Trenches must be over-backfilled and
mechanically compacted –
BEFORE installing posts
Slicing installation must be mechanically
compacted before installing posts
Trenches must be over-backfilled and
mechanically compacted –
BEFORE installing posts
Slicing installation must be mechanically
compacted before installing posts
Poor compaction means washoutsPoor compaction means washouts
EPA co-sponsored research ASTM
and ASHTO specifications are
vague on backfill, compaction,
and chronological order of posting
- resulting in poor performance.
EPA co-sponsored research ASTM
and ASHTO specifications are
vague on backfill, compaction,
and chronological order of posting
- resulting in poor performance.
TRI Environmental, Inc. national field study of random installations
TRI Environmental, Inc. national field study of random installations
70% of trench installations had no backfill
or no compaction
The remaining 30% of trench installations
had an average compaction of only 45% of
the undisturbed soil strength
70% of trench installations had no backfill
or no compaction
The remaining 30% of trench installations
had an average compaction of only 45% of
the undisturbed soil strength
TRI Environmental, Inc. national field study of random installations
TRI Environmental, Inc. national field study of random installations
Less than 8% of sliced installations
were not compacted.
The remaining 92% of sliced
installations had an average compaction
of 86% of the undisturbed soil strength.
Less than 8% of sliced installations
were not compacted.
The remaining 92% of sliced
installations had an average compaction
of 86% of the undisturbed soil strength.
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Placement
Quantity
Installation
Compaction Attachment
Support
PROPER POST SPACING
AND POST DEPTH
relates to a support system that
will not fall over under the load
of a full silt fence.
PROPER POST SPACING
AND POST DEPTH
relates to a support system that
will not fall over under the load
of a full silt fence.
Support PostSpacingSupport PostSpacing
Post should be spaced
a maximum of 6 ft.
apart and driven
24 inches into
compacted ground.
Post should be spaced
a maximum of 6 ft.
apart and driven
24 inches into
compacted ground.
60" steel T-post (1.33# per foot)
24”aboveground
24”below
ground
EPA co-sponsored research EPA co-sponsored research
Trench installations were adversely
affected by the inability to compact
effectively when the posts were
installed first and when insufficient
backfill was placed in the trench.
Trench installations were adversely
affected by the inability to compact
effectively when the posts were
installed first and when insufficient
backfill was placed in the trench.
Properly supported silt fence will carry 24 inches of sediment.
Properly supported silt fence will carry 24 inches of sediment.
Wood post spacingWood post spacing
Wood posts may be more difficult to
drive an adequate depth into
compacted soil, requiring closer
post spacing to achieve adequate
silt fence support.
Wood posts may be more difficult to
drive an adequate depth into
compacted soil, requiring closer
post spacing to achieve adequate
silt fence support.
wood posts are difficult to install to a proper depth
wood posts are difficult to install to a proper depth
ATTACHMENT
Proper attachment is the glue of the
system, combing the strength of the
fabric and the support posts into a
unified structure. It must be adequate
to support 18 inches of sediment.
ATTACHMENT
Proper attachment is the glue of the
system, combing the strength of the
fabric and the support posts into a
unified structure. It must be adequate
to support 18 inches of sediment.
Attachment must be adequate to support a fully loaded silt fence
Attachment must be adequate to support a fully loaded silt fence
AttachmentAttachment
For steel posts, recommend 3 plastic
ties per post, located in the top 8
inches of the fabric, with each tie hung
on a post nipple, placed diagonally to
attach as many threads as possible.
For wood posts, recommend several
staples per post using a wood lath to
overlay the fabric for extra strength.
For steel posts, recommend 3 plastic
ties per post, located in the top 8
inches of the fabric, with each tie hung
on a post nipple, placed diagonally to
attach as many threads as possible.
For wood posts, recommend several
staples per post using a wood lath to
overlay the fabric for extra strength.
A properly installed silt fence can retain several tons of sediment, thus saving millions of tons across the country.
A properly installed silt fence can retain several tons of sediment, thus saving millions of tons across the country.
Tell-tale sign of a problemTell-tale sign of a problem
If there is minimal sediment or
water behind a silt fence, either
water is running around the
end, or there is a washout
needing repair.
If there is minimal sediment or
water behind a silt fence, either
water is running around the
end, or there is a washout
needing repair.
Wire-backed fence problemsWire-backed fence problems
Doubles the cost of silt fence
Creates voluminous, expensive disposal
Disposal creates environmental harm
Modern fabrics do not need wire support
Improper post spacing for fence
support is the real problem
Doubles the cost of silt fence
Creates voluminous, expensive disposal
Disposal creates environmental harm
Modern fabrics do not need wire support
Improper post spacing for fence
support is the real problem
Disposal pile of wire-backed silt fence from just one job
Disposal pile of wire-backed silt fence from just one job
Posts too far apart, wire no helpPosts too far apart, wire no help
Alternatives to wire-backed fenceAlternatives to wire-backed fence
Possibly more runs of silt fence to
reduce the potential volume/load
Use of steel posts spaced 4 feet
apart and 24 inches deep
Possibly more runs of silt fence to
reduce the potential volume/load
Use of steel posts spaced 4 feet
apart and 24 inches deep
Maintenance of silt fenceMaintenance of silt fence
Once the fabric is clogged with sediment, it no
longer functions as designed – so removing
sediment does not result in a performing fabric.
What is to be done with the removed sediment
and how do you physically handle it?
Solution – leave the sediment in the silt fence
and build a new silt fence above or below to
collect additional sediment.
Once the fabric is clogged with sediment, it no
longer functions as designed – so removing
sediment does not result in a performing fabric.
What is to be done with the removed sediment
and how do you physically handle it?
Solution – leave the sediment in the silt fence
and build a new silt fence above or below to
collect additional sediment.
Cleaning simply creates a low volume sediment basin
Cleaning simply creates a low volume sediment basin
Fabric can not be restoredFabric can not be restored
Inspector ResponsibilitiesInspector Responsibilities
Inspectors must know proper placement
and installation concepts
Must not approve improper installations for
payment.
Improper installation includes silt fence that
does not pond water.
Inspectors must know proper placement
and installation concepts
Must not approve improper installations for
payment.
Improper installation includes silt fence that
does not pond water.
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Effective silt fence works
like a chain…
Each link must work;
if one link fails,
the system fails
Placement
Quantity
Installation
Compaction Attachment
Support
A Study of
Silt Fence Installation Techniques and
Associated Efficiency and
Performance Issues
A Study of
Silt Fence Installation Techniques and
Associated Efficiency and
Performance Issues
Silt Fence StudySilt Fence Study
EvTEC
Environmental Technology
Evaluation Center
EvTEC
Environmental Technology
Evaluation Center
Silt Fence StudySilt Fence Study
Verification of Performance
• The field evaluation included 51 test
segments reflecting different soil
types, installation methods, and
hydraulic conditions.
• Various amounts of backfill, degrees
of compaction, spacing of posts,
volumes of runoff, and types of soil
were evaluated.
Verification of Performance
• The field evaluation included 51 test
segments reflecting different soil
types, installation methods, and
hydraulic conditions.
• Various amounts of backfill, degrees
of compaction, spacing of posts,
volumes of runoff, and types of soil
were evaluated.
Silt Fence StudySilt Fence Study
Additionally, installation sequence, such
as installing posts before versus after
compaction, was evaluated.
Performance, as measured by water
retention, and efficiency, as measured
by installation time, were evaluated.
Additionally, installation sequence, such
as installing posts before versus after
compaction, was evaluated.
Performance, as measured by water
retention, and efficiency, as measured
by installation time, were evaluated.
Silt Fence StudySilt Fence Study
Nuclear Density Measurements
Silt Fence StudySilt Fence Study
Silt Fence StudySilt Fence Study
Indication of Piping Failure
Silt Fence StudySilt Fence Study
Typical High Volume Retention Test
Silt Fence StudySilt Fence Study
High Volume Water Application
Silt Fence StudySilt Fence Study
Piping failure
Silt Fence StudySilt Fence Study
The static slicing method was found to
provide storm water retention as good as
or better than the ‘Best’ trenched
installation and far superior to common
installations.
The static slicing method was found to
provide storm water retention as good as
or better than the ‘Best’ trenched
installation and far superior to common
installations.
Silt Fence StudySilt Fence Study
The ‘best’ installation far exceeded the
standard ASTM and ASHTO
specifications which are vague as to
backfill, compaction, and chronological
order of posting.
The ‘best’ installation far exceeded the
standard ASTM and ASHTO
specifications which are vague as to
backfill, compaction, and chronological
order of posting.
Silt Fence StudySilt Fence Study
The conclusion was clear that when the
enhancements of the ‘Best’ trenched
installations were not performed - the
trenched installation performed poorly.
The conclusion was clear that when the
enhancements of the ‘Best’ trenched
installations were not performed - the
trenched installation performed poorly.
Silt Fence StudySilt Fence Study
Trench installations were adversely
affected by the inability to compact
effectively when the posts were installed
first and when insufficient backfill
material was placed in the trench.
Trench installations were adversely
affected by the inability to compact
effectively when the posts were installed
first and when insufficient backfill
material was placed in the trench.
Silt Fence StudySilt Fence Study
The ‘Best’ trenched installation requires
nearly triple the installation effort to achieve
similar effectiveness as static slicing.
Trenching techniques meeting only minimum
or marginally enhanced specification
requirements fared quite poorly.
The ‘Best’ trenched installation requires
nearly triple the installation effort to achieve
similar effectiveness as static slicing.
Trenching techniques meeting only minimum
or marginally enhanced specification
requirements fared quite poorly.
Silt Fence StudySilt Fence Study
Performance trends provide a clear
indication that a greater level of
compaction (i.e. higher density obtained)
corresponds to better performance (i.e.
greater water retention).
There was a significant correlation
between the cone penetrometer readings
and the nuclear density measurements.
Performance trends provide a clear
indication that a greater level of
compaction (i.e. higher density obtained)
corresponds to better performance (i.e.
greater water retention).
There was a significant correlation
between the cone penetrometer readings
and the nuclear density measurements.
Silt Fence StudySilt Fence Study Poorly performing test segments
experienced excessive seepage and, in the worst case, subsequent “blow-out” of soil in the trench.
Segments installed using slicing or the “best” trenching techniques experienced no blowouts.
Those segments installed using the minimum specification requirements experienced both excessive seepage and blowout.
Poorly performing test segments experienced excessive seepage and, in the worst case, subsequent “blow-out” of soil in the trench.
Segments installed using slicing or the “best” trenching techniques experienced no blowouts.
Those segments installed using the minimum specification requirements experienced both excessive seepage and blowout.
Silt Fence StudySilt Fence Study
Additionally, the static slicing method of
installation was found to be much more
efficient, and therefore, cost effective
technique for silt fence installation when
compared to a range of traditional
trench-based procedures.
Additionally, the static slicing method of
installation was found to be much more
efficient, and therefore, cost effective
technique for silt fence installation when
compared to a range of traditional
trench-based procedures.
Silt Fence StudySilt Fence Study
Static slicing ranged from 1.75 to 4
times faster than all trench-based
installation techniques.
As far as installation efficiencies go, the
static slicing method provided much
quicker installations than any trench
method installation attempted.
Static slicing ranged from 1.75 to 4
times faster than all trench-based
installation techniques.
As far as installation efficiencies go, the
static slicing method provided much
quicker installations than any trench
method installation attempted.
Silt Fence StudySilt Fence Study
The static slicing method offers practical
advantages over traditional trenching-
based methods, such as maneuverability,
minimal soil-handling and hand labor,
consistent depth and compaction, and
ease of installation in windy conditions, on
steep side slopes, through rocky soils,
and in saturated soils.
The static slicing method offers practical
advantages over traditional trenching-
based methods, such as maneuverability,
minimal soil-handling and hand labor,
consistent depth and compaction, and
ease of installation in windy conditions, on
steep side slopes, through rocky soils,
and in saturated soils.
Silt Fence StudySilt Fence Study
Mechanical installation by static slicing
minimizes the hand labor requirements,
as well as the potential backfill and
compaction problems associated with
trenching. As a result, static slicing can
be expected to provide uniform,
dependable installations.
Mechanical installation by static slicing
minimizes the hand labor requirements,
as well as the potential backfill and
compaction problems associated with
trenching. As a result, static slicing can
be expected to provide uniform,
dependable installations.
Silt Fence StudySilt Fence StudyConclusions
There appear to be two possible ways to
achieve maximum silt fence performance –
static slicing or the “best” trench-based
installation.
The combination of maximum performance
and maximum productivity can be achieved
in one method – static slicing. The static
slicing method is included in ASTM D 6462.
Conclusions
There appear to be two possible ways to
achieve maximum silt fence performance –
static slicing or the “best” trench-based
installation.
The combination of maximum performance
and maximum productivity can be achieved
in one method – static slicing. The static
slicing method is included in ASTM D 6462.
Silt Fence StudySilt Fence StudyConclusions
In all cases, static slicing produced silt
fence installations as good as or better
than the best trench-based installations.
Both static slicing and the best trench-
based installations substantially
outperformed “typical” trench-based
installations.
Conclusions
In all cases, static slicing produced silt
fence installations as good as or better
than the best trench-based installations.
Both static slicing and the best trench-
based installations substantially
outperformed “typical” trench-based
installations.