Matakuliah
Tahun
Versi
: S0522/ Aplikasi Geosintetik Dalam Teknik Sipil
: Juli 2005
: 01/01
Pertemuan 12
APLIKASI DAN PEMILIHAN
MATERIAL GEOSINTETIK
Learning Outcomes
Pada akhir pertemuan ini, diharapkan
mahasiswa akan mampu :
 Mahasiswa mampu membedakan
pemakaian geosintetik sesuai kebutuhan
desain di lapangan  C6
Outline Materi
•
•
•
•
Pertimbangan desain
Kondisi tanah
Analisa pemilihan material
Perbandingan penggunaan
geosintetik sesuai kebutuhan dan
kondisi lapangan
• Aplikasi geosintetik sesuai kondisi
lapangan
Sebagian dari materi ini dikutip dari IGS Lecturer notes
No. 17 of 19
Geosynthetics in Dams
By Daniele Cazzuffi
ENEL Hydro, Milan, Italy
No. 18 of 19
Geosynthetics in Asphalt Pavements
By Prof. S.F. Brown FEng
University of Nottingham
No. 12 of 19
Geosynthetics in Erosion Protection
By Dr David Elton, P.E
Auburn University
Geosynthetics in Sediment and Erosion
Control
• Introduction and Applications
• What is it?
• Erosion control is a means of keeping a soil in
place or catching a soil after it has been
displaced but before it moves into surface
waters.
Why Is It Needed?
There are public laws that :
• preclude the polluting of surface waters with
sediments
• preserve topographic integrity
• preserve soil for farming
• preserve foundation integrity for structures
founded on soil.
Rill and Gully Slope Erosion
Riverbank Erosion, Including
Sapping (Formation of Caves)
Where Is It Needed?
• It is needed on construction and
agricultural sites and natural places
where water causes soils to displace.
• In short: where soil and moving water
interact at the ground surface
Factors Influencing Types of
Erosion
• Rainfall-induced erosion factors:
–
–
–
intensity and duration of rainfall
slope of land
soil type
• All affect the amount of erosion and
the erosion control measures selected.
Factors Influencing Types Of Erosion
(Continued)
• Shoreline erosion factors:
–
–
–
soil type
wave height
beach slope
–
duration and intensity of storm
• All affect the amount of erosion.
Factors Influencing Types Of Erosion
(Continued)
• Scour:
–
The amount of scour, around bridge piers for
example, is affected by pier shape, depth of
stream, storm duration and channel shape, in
addition to soil type.
Hard Armor Erosion Control on
Riverbank
Concrete cast
in a geotextile
former;
geotextile
filter
underneath
(not visible)
Design Approach
• Slopes and Channels
Channel erosion damage caused by
inadequate filter beneath hard armor
Strategy
• Choose least costly erosion control measure and
evaluate:
– LOW cost
nothing (fallow ground)
plants
degradable RECPs
permanent RECPs
permanent TRMs
soft armor
– HIGH cost
hard armor w/geotextile filter
• In conjunction with these choices, consider:
– reducing flow in any manner
– flattening slopes
– widening channels
Design Procedures for Erosion Control in
Slopes and Channels
Slopes
• There are several methods of estimating soil loss. The most
commonly used in the US is:
• USLE - Universal Soil Loss Equation:
A = R  K  LS  C  P
where: A = computed soil loss (tons/acre or kg/hectare) for a
given storm period or time interval
R = rainfall factor
K = soil erodibility value
LS = slope length and steepness factor
C = vegetation or cover factor
P = erosion control practice factor
• All factors, except C, do not vary more than one order of
magnitude. C changes several orders of magnitudes.
• NOTE: many of these factors are described in USDA (1997)
Cover Index factor (C) for Different Ground Cover Conditions
Type of Cover
None (fallow ground)
Temporary seedings (90% stand)
Ryegrass (perennial type)
Ryegrass (annuals)
Small grain
Millet or sudan grass
Field bromegrass
Permanent seedings (90% stand)
Sod (laid immediately)
Mulch
Hay, rate of application, tons/ac:
0.5
1.0
2.0
Small grain straw
2.0
Wood chips
6.0
Wood cellulose
1.5
Fiberglas
1.5
Factor
C
Percent
Effectiveness
1.0
0.0
0.05
0.10
0.05
0.05
0.03
0.01
0.01
95
90
95
95
97
99
99
0.25
0.13
0.02
0.02
0.06
0.10
0.05
75
87
98
98
94
90
95
Source: primarily HEC-15 (1988)
percent soil loss reduction as compared with fallow ground
Proposed C-Factors for RECPs
Update of RUSLE Equation
RECP
Category
ECN
ECB
Approximate
Proposed
Mass/Unit
Area
g/m2
(oz/ yd2)
34 to 100
(1 to 3)
400 to 880
(12 to 26)
270 to 340
(8 to 10)
270 to 370
Reported
Range of
C-factors
C-factors
100% Woven
Polypropylene
100% Woven
Coir/Jute
100% Straw
0.02
0.01
0.002 to 0.003
0.01 to 0.1
0.002 to 0.30
0.01
Straw/Coconut
0.002 to 0.11
100% Coconut/
Excelsior
100% Synthetic
0.003 to 0.09
0.01
TRM
0.01
(8 to 11)
270 to 400
(8 to 12)
270 to 490
0.01
0.003 to 0.11
(8 to 14)
NOTES/REFERENCES
All terminology consistent with the Erosion Control Technology Council approved terms.
“ECN” indicates temporary degradable erosion control net. Values assumes slope is flatter than 2H:1V.
“ECB” indicates temporary degradable erosion control blanket. Values assumes slope is flatter than 2H:1V.
“TRM” indicate permanent nondegradable turf reinforcement mat. Values assumes slope is flatter than 1H:1V.
Procedure
• Calculate A with the C value of a given permanent erosion control
solution (usually vegetation)
• Compare A with an acceptable A (e.g. 44 kN/ha/year (2
tons/acre/year))
• If A is acceptable*, check effectiveness of the temporary
(degradable) erosion control (RECP) measure used to establish
the permanent erosion control solution over the life of the RECP.
Choose a temporary solution with a small enough C to satisfy
regulations.
• *typically, acceptance is based on government regulations.
If A is unacceptable for permanent solution (vegetation), try
vegetation plus turf reinforcement mat for long term solution. C
values available from test or manufacturers.
• If that combination produces a satisfactory A, check A for
temporary erosion control solution used while permanent
solution is taking hold.
Channel Linings
• Two Common Methods of Analysis:
–
Permissible velocity in channel
–
Permissible shear stress in channel
• Velocity Calculation
149
.
V 
R 2/ 3
n
Sf
where:
V - velocity of flow (ft/sec)
n - Manning's roughness coefficient (see Table 3)
R - hydraulic radius ( A / wetted perimeter) (ft)
Sf - slope of channel, for uniform flow conditions.
• In SI units, this equation becomes:
V
VnRSf -
R
2/ 3
Sf
n
velocity of flow (m3/sec)
Manning's roughness coefficient (see Table 3)
hydraulic radius ( A / wetted perimeter) (m)
slope of channel, for uniform flow conditions.
• Compare calculated V with an acceptable V
from standard tables or manufacturer's
literature
Table 3. Manning’s Roughness Coefficients.
n - value1
Depth Ranges
0.5-2.0 ft
>2.0 ft
(15-60 cm)
(> 60 cm)
Lining
Category
Rigid
Lining type
0-0.5 ft
(0-15cm)
Concrete
Grouted riprap
Stone masonry
Soil cement
Asphalt
0.015
0.040
0.042
0.025
0.018
0.013
0.030
0.032
0.022
0.016
0.013
0.028
0.030
0.020
0.016
Unlined
Bare soil
Rock cut
0.023
0.045
0.020
0.035
0.020
0.025
Temporary
Woven paper net
Jute net
Fiberglass roving
Straw with net
Curled wood mat
Synthetic mat
0.016
0.028
0.028
0.065
0.066
0.036
0.015
0.022
0.021
0.033
0.035
0.025
0.015
0.019
0.019
0.025
0.028
0.021
Gravel Riprap
1-inch (2.5-cm) D50
2-inch (5-cm) D50
0.044
0.066
0.033
0.041
0.030
0.034
Rock Riprap
6-inch (15-cm) D50
12-inch (30-cm) D50
0.104
--
0.069
0.078
0.035
0.040
1Based
on data primarily from HEC-15 (Chen and Cotton, 1988)
Notes:
• Values listed are representative values for the
respective depth ranges.
• Manning’s roughness coefficients, n, vary
with the flow depth.
• n-values for vegetative linings are found in
Chen and Cotton (1988) (HEC-15) on pages
42 - 46.
• Another method is to evaluate the shear
stress on the ground surface caused by the
running water. (Method follows).
Shear Stress Calculation
• maximum shear stress on channel
base:
   w d Sf
where:  w dSf -
shear stress
unit weight of water
depth of flow
gradient of channel for uniform flow
conditions
• Calculate the expected shear stress and
compare with acceptable shear stress
Design Variables
• increasing the width/depth ratio of channel
reduces 
– channel slope: flatter reduces  (note: 10% is
considered a "steep Channel". Sf > 10% usually
requires hard armor)
Design Procedure for Sf < 10%
Channels
Shear stress approach :
• calculate the maximum 
   w d Sf
• Note: this requires d. If Q is known, and the
gradient and lining material are known, d can be
found from Chart 3.
If Q is unknown, use Manning's equation to get Q
2 /3
149
.
Q
AR
n
Sf
where: Q = flow (cfs)
n - Manning's roughness coefficient (see Table 3)
A - cross-sectional area of channel (ft2)
R - hydraulic radius ( A / wetted perimeter) (ft)
Sf - slope of channel for uniform flow conditions.
• Then, knowing Q, use Chart 3 to get d. With d,
calculate maximum shear, , and compare with
tabulated values of  for RECPs (Tables 1 and
2 from HEC-15) or with manufacturer's data.
In SI units, this equation is:
A 2/3
Q
R Sf
n
where:
Q = flow (m3/sec)
n - Manning's roughness coefficient (see Table 3)
A - cross-sectional area of channel (m2)
R - hydraulic radius ( A / wetted perimeter) (m)
Sf - slope of channel for uniform flow conditions.
Design Chart / Nomogram
ref: Chen, Y.H. and G.K. Cotton (1988)
Table 1. Classification of Vegetal Covers as to Degree of Retardance.
Retardance
Class
A
B
Cover
Condition
Weeping lovegrass
Yellow bluestem
Ischaemum
Excellent stand, tall (average 30") (76 cm)
Kudzu
Bermuda grass
Native grass mixture.
(little bluestem, bluestem,
blue gamma, and other long
and short midwest grasses)
Weeping lovegrass
Lespedeza sericea
Alfalfa
Weeping lovegrass
Kudzu
Blue gamma
Very dense, growth, uncut
Good stand, tall (average 12") (30 cm)
Excellent stand, tall (average 36") (91 cm)
Good stand, unmowed
Good stand, tall (average 24") (61 cm)
Good stand, not woody, tall (average 19")
(48 cm)
Good stand, uncut (average 11") (28 cm)
Good stand, unmowed (average 13") (33 cm)
Dense growth, uncut
Good stand, uncut (average 13") (28 cm)
Table 1. Classification of Vegetal Covers as to Degree of Retardance.
Retardance
Class
C
D
Cover
Condition
Crabgrass
Bermuda grass
Common lespedeza
Grass-legume mixture-summer (orchard grass,
redtop, Italian ryegrass,
and common lespedeza
Centipedegrass
Kentucky bluegrass
Fair stand, uncut (25 to 120 cm)
Good stand, mowed (average 15 cm)
Good stand, uncut (average 28 cm)
Bermuda grass
Common Lespedeza
Buffalo grass
Grass-legume mixture
fall, spring (orchard grass,
redtop, Italian ryegrass,
and common lespedeza)
Lespedeza sericea
Good stand, headed 15 to 30cm
Good stand, cut to 6 cm
Excellent stand, uncut (11 cm)
Good stand, uncut (8 to 15 cm)
Good stand, uncut (10 to 13cm)
After cutting to (5 cm) Very good
stand before cutting
Good stand, uncut (15 to 20cm)
Very dense cover (average 15 cm)
Table 1. Classification of Vegetal Covers as to Degree of Retardance.
(HEC - 15)
Retardance
Cover
Condition
Bermuda grass
Bermuda grass
Good stand, cut 4cm height
Burned stubble
Class
E
Note: Covers classified have been tested in experimental channels. Covers
were green and generally uniform.
Table 2. Permissible Shear Stresses for Lining Materials
Permissible
Unit Shear Stress1
(lb/ft2)
(kg/m2)
Lining Category
Lining Type
Temporary
Woven Paper Net
Jute Net
Fiberglass Roving:
Single
Double
Straw with Net
Curled Wood Mat
Synthetic Mat
0.15
0.45
0.73
2.20
0.60
0.85
1.45
1.55
2.00
2.93
4.15
7.08
7.57
9.76
Vegetative
Class A
Class B
Class C
Class D
Class E
3.70
2.10
1.00
0.60
0.35
18.06
10.25
4.88
2.93
1.71
Gravel Riprap
1-inch
2-inch
0.33
0.67
1.61
3.22
(2.54 cm)
(5 cm)
Table 2. Permissible Shear Stresses for Lining Materials
Permissible
Unit Shear Stress1
Lining Category
Lining Type
(lb/ft2)
(kg/m2)
Rock Riprap
6-inch
(15 cm)
12-inch (30 cm)
2.00
4.00
9.76
19.52
Bare Soil
Non-cohesive
Cohesive
See Chart 1
See Chart 2
1ref:
HEC - 15
For fallow cohesionless soils, compare with Chart 1
note: if particle diameters are larger than 100mm (0.33 ft), use
 = 25.5 D50
with D50 being the mean rock size in meters, and  in kPa,
or
 = 4 D50
with D50 being the mean rock size in feet, and  in psf.
Ref. Chen and Cotton (1988)
Erosion Control Using Geosynthetics
Applications:
• Introduction
• Useful in scour, surface and shoreline
protection
• Geosynthetic functions include:
–
–
–
–
filtration
containment (bags)
protection
providing a medium for plant growth
Erosion Control Using Geosynthetics
Scour Applications
– Bridge pier footing
– Canal Lining
Surface Protection
Philosophy
• reduce the intensity of the raindrops impacting the soil,
reduce the speed of runoff, increase the amount of water
that soaks into the soil rather than running off.
Roving
• Roving is fine threads spread out on the ground surface,
tacked down with a spray that holds it in place while
vegetation takes hold.
• Roving is applied manually, with a light machine. The
method is slow, but useful in smaller areas with uneven
surfaces.
Roving Materials
• spools of
thread
• placed
using air
guns
Roving Being Applied
1. Roving (white)
being sprayed
on to the
ground surface,
2. Being tacked
down with
asphalt spray
Rolled Erosion Control Product
Being
installed
in a ditch
Permanent Installations
(Permanent Erosion and Revegetation Mats)
Soft PERMs
• Turf Reinforcement Mats (TRMs)
– TRMs are typically placed on the surface and then filled in
with soil. They reinforce the ground surface, making erosion
more difficult. The TERM holds the soil in place while
vegetation takes hold.
• Erosion Control and Revegetation Mats (ECRMs)
– These combine surface control and surface slope
stabilization at the same time.
Geocell Confinement Systems (GCS)
Geocellular
confinement
system on a
slope being
filled with soil
GCS – Soil Fill
GCS are an
expensive,
rugged way to
stabilize a slope
or roadbed.
These cellular
mats are filled
with soil. They
are very strong
and very
effective.
Hard Permeable System
• Gabions - wire baskets
filled with cobble-sized
rocks
• Hard armor: Gabion
channel lining (geotextile
filter underneath not
visible)
• Loose stone – riprap.
Random placement is
best. There are various
methods for estimating
how large these rocks
must be to avoid
displacement.
Hard Armor
• Riprap being installed
with geotextile filter
underneath
• Concrete or masonry:
Dolos (large concrete
objects), articulated
blocks (forming a mat),
concrete facings (cast in
place or precast)