ASTM D7499/D7499M-09(2014)

Standard Test Method for Measuring Geosynthetic-Soil Resilient Interface Shear Stiffness

SIGNIFICANCE AND USE
5.1 This test method is intended as a performance test to provide the user with a set of design values for the test conditions examined.  
5.1.1 The test method is applicable to all geosynthetics and all soils when loaded in a cyclic manner.  
5.1.2 This test method produces test data, which can be used in the design of geosynthetic-reinforced pavement structures or in applications where geosynthetics are subjected to cyclic loads.  
5.1.3 The test results may also provide information related to the in-soil stress-strain response of a geosynthetic under confined loading conditions.  
5.2 Information derived from this test may be a function of soil gradation, plasticity, as-placed dry unit weight, moisture content, length and surface characteristics of the geosynthetic and other test parameters. Therefore, results are expressed in terms of the actual test conditions. The test measures the net effect of a combination of interface shear mechanisms, which may vary depending on type of geosynthetic specimen, embedment length, relative opening size, soil type, displacement rate, normal stress, and other factors.  
5.3 Information between laboratories on precision is incomplete. In cases of dispute, comparative tests to determine if there is a statistical bias between laboratories may be advisable.
SCOPE
1.1 This test method details how cyclic loading is applied to geosynthetics embedded in soil to determine the apparent stiffness of the soil–geosynthetic interface.  
1.2 Resilient interface shear stiffness describes the shear stiffness between a geosynthetic and its surrounding soil under conditions of small cyclic loads.  
1.3 This test method is intended to provide properties for design. The test method was developed for mechanistic empirical pavement design methods requiring input of the resilient interface shear stiffness. The use of this parameter from this test method for other applications involving cyclic loading should be evaluated on a case-by-case basis. It can also be used to compare different geosynthetics, soil types, etc., and thereby be used as a research and development test procedure.  
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. This standard may involve hazardous materials, and equipment.

General Information

• Status: Historical
• Publication Date: 31-Aug-2014
• ICS: 59.080.70 - Geotextiles
• Technical Committee: D35 - Geosynthetics
• Drafting Committee: D35.01 - Mechanical Properties

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D7499/D7499M − 09 (Reapproved 2014)
Standard Test Method for
Measuring Geosynthetic-Soil Resilient Interface Shear
Stiffness
This standard is issued under the fixed designation D7499/D7499M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D653 Terminology Relating to Soil, Rock, and Contained
Fluids
1.1 This test method details how cyclic loading is applied to
D3080/D3080M Test Method for Direct Shear Test of Soils
geosynthetics embedded in soil to determine the apparent
Under Consolidated Drained Conditions
stiffness of the soil–geosynthetic interface.
D4439 Terminology for Geosynthetics
1.2 Resilient interface shear stiffness describes the shear
D4354 Practice for Sampling of Geosynthetics and Rolled
stiffness between a geosynthetic and its surrounding soil under
Erosion Control Products(RECPs) for Testing
conditions of small cyclic loads.
3. Terminology
1.3 This test method is intended to provide properties for
3.1 For definitions of other terms used in this test method
design. The test method was developed for mechanistic em-
refer to Terminologies D123, D653, and D4439.
pirical pavement design methods requiring input of the resilient
interface shear stiffness. The use of this parameter from this
3.2 Definitions of Terms Specific to This Standard:
test method for other applications involving cyclic loading
3.2.1 apertures, n—the open spaces in geogrids which
should be evaluated on a case-by-case basis. It can also be used
enable soil interlocking to occur.
to compare different geosynthetics, soil types, etc., and thereby
3.2.2 atmosphere for testing geosynthetics, n—air main-
be used as a research and development test procedure.
tained at a relative humidity of 60 6 10 % and a temperature
1.4 The values stated in either SI units or inch-pound units of 21 6 2°C [70 6 4°F].
are to be regarded separately as standard. The values stated in
3.2.3 cross-machine direction, n—the direction in the plane
each system may not be exact equivalents; therefore, each
of the geosynthetic perpendicular to the direction of manufac-
system shall be used independently of the other. Combining
ture.
values from the two systems may result in non-conformance
3.2.4 failure, n—an arbitrary point at which a material
with the standard.
ceases to be functionally capable of its intended use.
1.5 This standard does not purport to address all of the
3.2.5 geosynthetic, n—a planar product manufactured from
safety concerns, if any, associated with its use. It is the
polymeric material used with soil, rock, earth, or other geo-
responsibility of the user of this standard to establish appro-
technical engineering related material as an integral part of a
priate safety and health practices and determine the applica-
man-made project, structure, or system.
bility of regulatory limitations prior to use. This standard may
3.2.6 geosynthetic-soil resilient interface shear stiffness,
involve hazardous materials, and equipment.
n—a parameter that describes the apparent stiffness of the
interface between the soil and the geosynthetic determined by
2. Referenced Documents
calculating the slope of the shear stress, shear displacement
2.1 ASTM Standards:
curve as the embedded geosynthetic is subjected to a cyclic
D123 Terminology Relating to Textiles
load.
3.2.7 junction, n—the point where geogrid ribs are intercon-
nected in order to provide structure and dimensional stability.
This test method is under the jurisdiction of ASTM Committee D35 on
Geosynthetics and is the direct responsibility of Subcommittee D35.01 on Mechani- 3.2.8 machine direction, n—the direction in the plane of the
cal Properties.
geosynthetic parallel to the direction of manufacture.
Current edition approved Sept. 1, 2014. Published September 2014. Originally
3.2.9 pullout, n—the movement of a geosynthetic over its
approved in 2009. Last previous edition approved in 2009 as D7499/D7499M–09.
DOI: 10.1520/D7499_D7499M-09R14.
entire embedded length, with initial pullout occurring when the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
back of the specimen moves, and ultimate pullout occurring
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
when the movement is uniform over the entire embedded
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. length.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7499/D7499M − 09 (2014)
3.2.10 pullout force, (kN), n—force required to pull a 5.1.3 The test results may also provide information related
geosynthetic out of the soil during a pullout test. to the in-soil stress-strain response of a geosynthetic under
confined loading conditions.
3.2.11 pullout resistance, (kN/m), n—the pullout force per
width of geosynthetic measured at a specified condition of
5.2 Information derived from this test may be a function of
displacement.
soil gradation, plasticity, as-placed dry unit weight, moisture
content, length and surface characteristics of the geosynthetic
3.2.12 rib, n—the continuous elements of a geogrid which
and other test parameters. Therefore, results are expressed in
are either in the machine or cross-machine direction as
terms of the actual test conditions. The test measures the net
manufactured.
effect of a combination of interface shear mechanisms, which
3.2.13 wire gage, n—a displacement gage consisting of a
may vary depending on type of geosynthetic specimen, em-
non extensible wire attached to the geosynthetic and monitored
bedment length, relative opening size, soil type, displacement
by connection to a dial extensometer, or electronic displace-
rate, normal stress, and other factors.
ment transducer.
5.3 Information between laboratories on precision is incom-
plete. In cases of dispute, comparative tests to determine if
4. Summary of Test Method
there is a statistical bias between laboratories may be advis-
4.1 In this test method, a horizontal layer of geosynthetic is
able.
embedded between two layers of soil. Six prescribed levels of
horizontal cyclic force are applied to the geosynthetic at five
6. Apparatus
specified levels of normal stress confinement. The maximum
6.1 Test Box—An open rigid box consisting of two smooth
and minimum forces and corresponding displacements are
parallel sides, a back wall, a horizontal split removable door, a
recorded for the last ten cycles of each combination of normal
bottom plate, and a load transfer sleeve. The door is at the front
stress and cyclic force (loading sequence).
as defined by the direction of applied cyclic force. A typical
4.2 The resilient interface shear stiffness (kPa/m or psi/in)
box is shown in Fig. 1.
of the test specimen can be calculated for any loading sequence
6.1.1 The box should be square or rectangular with mini-
by dividing the cyclic shear stress by the corresponding net
mum dimensions 457 mm [18 in.] long by 457 mm [18 in.]
recoverable horizontal displacement of the embedded geosyn-
wide by 305 mm [12 in.] deep, if sidewall friction is
thetic
minimized, otherwise the minimum width should be 760 mm
[30 in.]. The dimensions should be increased, if necessary, so
5. Significance and Use
that minimum width is the greater of 20 times the D85 of the
5.1 This test method is intended as a performance test to soil or 6 times the maximum soil particle size, and the
provide the user with a set of design values for the test minimum length greater than 5 times the maximum geosyn-
conditions examined. thetic aperture size. The box shall allow for a minimum depth
5.1.1 The test method is applicable to all geosynthetics and of 150 mm [6 in.] above and below the geosynthetic. The depth
all soils when loaded in a cyclic manner. of the soil in the box above or below the geosynthetic shall be
5.1.2 This test method produces test data, which can be used a minimum of 6 times the D85 of the soil or 3 times the
in the design of geosynthetic-reinforced pavement structures or maximum particle size of the soil, whichever is greater. The
in applications where geosynthetics are subjected to cyclic box must allow for at least 305 mm [12 in.] embedment length
loads. beyond the load transfer sleeve.
FIG. 1 Side View of Typical Test Device
D7499/D7499M − 09 (2014)
NOTE 1—To remove side wall friction as much as possible a high
6.4 Displacement Indicators—Horizontal displacement of
density polyethylene (HDPE) geomembrane should be bonded to the
the geosynthetic is measured at the entrance of the box and at
inside surfaces of the pullout box. The sidewalls may also be covered with
several locations on the embedded portion of the specimen.
a layer of silk fabric, which has been shown to eliminate adhesion and has
Measurements outside the door at the box entrance are made by
a very low friction value. Alternatively, a lubricant can be spread on the
sidewalls of the box and thin sheets of polyethylene film used to minimize
electronic displacement transducers (for example, linear vari-
the side wall friction. It should be also noted that the effect of sidewall
able differential transformers (LVDTs) can be used) mounted to
friction on the soil-geosynthetic interface can also be eliminated if a
the box frame to read against a plate attached to the specimen
minimum distance is kept between the specimen and the side wall. This
near the door.
minimum distance is recommended to be 150 mm [6 in.].
6.4.1 Displacement measurements within the box may em-
6.1.2 The box shall be fitted with a pair of metal sleeves
ploy any of several methods, which place sensors or gauge
(load transfer sleeves) at the entrance of the box to transfer the
connectors directly on the geosynthetic and monitor their
force into the soil to a sufficient horizontal distance so as to
change in location remotely. One such device utilizes wire
significantly reduce the stress on the door of the box. The
gages, which are protected from normal stress by a surrounding
sleeves shall consist of two tapered (illustrated in Fig. 3) or
tube, which runs from a location mounted on the specimen to
non-tapered (no more than 13 mm [0.5 in.] thick) plates
extending the full width of the pullout box and into the pullout the outside of the box where displacements are measured by
displacement transducers.
box a minimum distance of 150 mm [6 in.], but it is
recommended that this distance equal the total soil depth above
6.4.2 All electronic measurement devices must be accurate
or below the geosynthetic. Both design types must possess
to 60.01 mm. Locations of the devices must be accurately
tapered edges at the point of load application in the soil that are
determined and recorded. Minimum extension capabilities of
no more then 3 mm [0.12 in.] thick. The plates shall be rigidly
50 mm [2 in.] are recommended.
separated at the sides with spacers and be sufficiently stiff such
6.4.3 Determine the displacement of the geosynthetic at the
that normal stress is not transferred to the geosynthetic between
front (leading end) and the rear (embedded end) of the
the plates.
geosynthetic at several locations along its width; suggested
6.2 Normal Stress Loading Device—Normal stress applied
layout is shown in Fig. 2.
to the upper layer of soil above the geosynthetic must be
6.5 Geosynthetic Clamping Devices—Clamps which con-
constant and uniform for the duration of the load step. To
nect the specimen to the cyclic force system without slipping,
maintain a uniform normal stress, a flexible pneumatic or
causing clamp breaks or weakening the material may be used,
hydraulic diaphragm-loading device which is continuous over
see Note 2. The clamps shall be swiveled to allow the cyclic
the entire test box area should be used and capable of
forces to be distributed evenly throughout the width of the
maintaining the applied normal stress within 62 % of the
sample. The clamps must allow the specimen to remain
required normal stress. Normal stresses utilized will depend on
horizontal during loading and not interfere with the interface
testing requirements; however, stresses up to 250 kPa [35 psi]
shear surface. Gluing, bonding, or otherwise molding of a
should be anticipated. A recommended normal stress-loading
geosynthetic within the clamp area is acceptable and recom-
device is an air bag.
mended whenever slippage might occur. Thin metal rods or
6.3 Cyclic Force Loading Device—Horizontal cyclic force
tubes may be used to reduce friction between the geosynthetic
must be supplied by a device with the ability to apply cyclic
clamp/sample and the top edge of the lower load transfer sleeve
load in the direction of the opening of the box. The force must
(Fig. 3).
be at the same level with the specimen.
6.3.1 The cyclic force system must be able to apply multiple
NOTE 2—A suggested method of clamping is shown in Fig. 4 and
load repetitions using a haversine-shaped load pulse consisting
includes a simple clamp consisting of two pieces of 22 gauge sheet metal
glued to both sides of the geosynthetic sample. The sheet metal plates
of a 0.2 s load followed by a 0.80 s rest period. The loading
should be at least the same width as the geosynthetic being tested. Special
system must also be able to simultaneously maintain a mini-
precautions should be taken to ensure that geotextile samples adhere to the
mum seating load on the material during cyclic loading.
sheet metal–such as making holes for the epoxy to flow through the fabric,
6.3.2 Also, a device to measure the cyclic force (that is, a
however; all such modifications to the fabric to facilitate bonding should
load cell) must be incorporated into the system and shall be
not interfere with the remainder of the geosynthetic protruding from the
accurate within 60.5 % of its full-scale range. front edge of the sheet metal.
FIG. 2 Example Instrumentation Layout
D7499/D7499M − 09 (2014)
FIG. 3 Side View of Load Transfer Sleeve Arrangement
FIG. 4 Geosynthetic Clamping Detail
6.6 Soil Preparation Equipment—Use equipment as neces- 7.3 Test Specimens—For each unit in the laboratory sample,
sary for the placement of soils at desired conditions. This may remove the required number of specimens.
include compaction devices such as vibratory or “jumping-
7.3.1 Remove the minimum of specimens for testing in a
jack” type compaction, or hand compaction hammers. Soil
required direction, see Not
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7499/D7499M − 09 D7499/D7499M − 09 (Reapproved 2014)
Standard Test Method for
Measuring Geosynthetic-Soil Resilient Interface Shear
Stiffness
This standard is issued under the fixed designation D7499/D7499M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method details how cyclic loading is applied to geosynthetics embedded in soil to determine the apparent stiffness
of the soil–geosynthetic interface.
1.2 Resilient interface shear stiffness describes the shear stiffness between a geosynthetic and its surrounding soil under
conditions of small cyclic loads.
1.3 This test method is intended to provide properties for design. The test method was developed for mechanistic empirical
pavement design methods requiring input of the resilient interface shear stiffness. The use of this parameter from this test method
for other applications involving cyclic loading should be evaluated on a case-by-case basis. It can also be used to compare different
geosynthetics, soil types, etc., and thereby be used as a research and development test procedure.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. This standard may involve hazardous materials, and equipment.
2. Referenced Documents
2.1 ASTM Standards:
D123 Terminology Relating to Textiles
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D3080D3080/D3080M Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions
D4439 Terminology for Geosynthetics
D4354 Practice for Sampling of Geosynthetics and Rolled Erosion Control Products(RECPs) for Testing
3. Terminology
3.1 For definitions of other terms used in this test method refer to Terminologies D123, D653, and D4439.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 apertures, n—the open spaces in geogrids which enable soil interlocking to occur.
3.2.2 atmosphere for testing geosynthetics, n—air maintained at a relative humidity of 60 6 10 % and a temperature of 21 6
2°C (70[70 6 4°F). 4°F].
3.2.3 cross-machine direction, n—the direction in the plane of the geosynthetic perpendicular to the direction of manufacture.
3.2.4 failure, n—an arbitrary point at which a material ceases to be functionally capable of its intended use.
3.2.5 geosynthetic, n—a planar product manufactured from polymeric material used with soil, rock, earth, or other geotechnical
engineering related material as an integral part of a man-made project, structure, or system.
This test method is under the jurisdiction of ASTM Committee D35 on Geosynthetics and is the direct responsibility of Subcommittee D35.01 on Mechanical Properties.
Current edition approved June 15, 2009Sept. 1, 2014. Published September 2009September 2014. Originally approved in 2009. Last previous edition approved in 2009
as D7499/D7499M–09. DOI: 10.1520/D7499_D7499M-09.10.1520/D7499_D7499M-09R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7499/D7499M − 09 (2014)
3.2.6 geosynthetic-soil resilient interface shear stiffness, n—a parameter that describes the apparent stiffness of the interface
between the soil and the geosynthetic determined by calculating the slope of the shear stress, shear displacement curve as the
embedded geosynthetic is subjected to a cyclic load.
3.2.7 junction, n—the point where geogrid ribs are interconnected in order to provide structure and dimensional stability.
3.2.8 machine direction, n—the direction in the plane of the geosynthetic parallel to the direction of manufacture.
3.2.9 pullout, n—the movement of a geosynthetic over its entire embedded length, with initial pullout occurring when the back
of the specimen moves, and ultimate pullout occurring when the movement is uniform over the entire embedded length.
3.2.10 pullout force, (kN), , n—force required to pull a geosynthetic out of the soil during a pullout test.
3.2.11 pullout resistance, (kN/m), n—the pullout force per width of geosynthetic measured at a specified condition of
displacement.
3.2.12 rib, n—the continuous elements of a geogrid which are either in the machine or cross-machine direction as manufactured.
3.2.13 wire gage, n—a displacement gage consisting of a non extensible wire attached to the geosynthetic and monitored by
connection to a dial extensometer, or electronic displacement transducer.
4. Summary of Test Method
4.1 In this test method, a horizontal layer of geosynthetic is embedded between two layers of soil. Six prescribed levels of
horizontal cyclic force are applied to the geosynthetic at five specified levels of normal stress confinement. The maximum and
minimum forces and corresponding displacements are recorded for the last ten cycles of each combination of normal stress and
cyclic force (loading sequence).
4.2 The resilient interface shear stiffness (kPa/m or psi/in) of the test specimen can be calculated for any loading sequence by
dividing the cyclic shear stress by the corresponding net recoverable horizontal displacement of the embedded geosynthetic
5. Significance and Use
5.1 This test method is intended as a performance test to provide the user with a set of design values for the test conditions
examined.
5.1.1 The test method is applicable to all geosynthetics and all soils when loaded in a cyclic manner.
5.1.2 This test method produces test data, which can be used in the design of geosynthetic-reinforced pavement structures or
in applications where geosynthetics are subjected to cyclic loads.
5.1.3 The test results may also provide information related to the in-soil stress-strain response of a geosynthetic under confined
loading conditions.
5.2 Information derived from this test may be a function of soil gradation, plasticity, as-placed dry unit weight, moisture content,
length and surface characteristics of the geosynthetic and other test parameters. Therefore, results are expressed in terms of the
actual test conditions. The test measures the net effect of a combination of interface shear mechanisms, which may vary depending
on type of geosynthetic specimen, embedment length, relative opening size, soil type, displacement rate, normal stress, and other
factors.
5.3 Information between laboratories on precision is incomplete. In cases of dispute, comparative tests to determine if there is
a statistical bias between laboratories may be advisable.
6. Apparatus
6.1 Test Box—An open rigid box consisting of two smooth parallel sides, a back wall, a horizontal split removable door, a
bottom plate, and a load transfer sleeve. The door is at the front as defined by the direction of applied cyclic force. A typical box
is shown in Fig. 1.
6.1.1 The box should be square or rectangular with minimum dimensions 457 mm (18 in.)[18 in.] long by 457 mm (18 in.)[18
in.] wide by 305 mm (12 in.)[12 in.] deep, if sidewall friction is minimized, otherwise the minimum width should be 760 mm (30
in.).[30 in.]. The dimensions should be increased, if necessary, so that minimum width is the greater of 20 times the D85 of the
soil or 6 times the maximum soil particle size, and the minimum length greater than 5 times the maximum geosynthetic aperture
size. The box shall allow for a minimum depth of 150 mm (6 in.)[6 in.] above and below the geosynthetic. The depth of the soil
in the box above or below the geosynthetic shall be a minimum of 6 times the D85 of the soil or 3 times the maximum particle
size of the soil, whichever is greater. The box must allow for at least 305 mm (12 in.)[12 in.] embedment length beyond the load
transfer sleeve.
NOTE 1—To remove side wall friction as much as possible a high density polyethylene (HDPE) geomembrane should be bonded to the inside surfaces
of the pullout box. The sidewalls may also be covered with a layer of silk fabric, which has been shown to eliminate adhesion and has a very low friction
value. Alternatively, a lubricant can be spread on the sidewalls of the box and thin sheets of polyethylene film used to minimize the side wall friction.
It should be also noted that the effect of sidewall friction on the soil-geosynthetic interface can also be eliminated if a minimum distance is kept between
the specimen and the side wall. This minimum distance is recommended to be 150 mm (6 in.).[6 in.].
D7499/D7499M − 09 (2014)
FIG. 1 Side View of a Typical Test Device
FIG. 2 Example Instrumentation Layout
6.1.2 The box shall be fitted with a pair of metal sleeves (load transfer sleeves) at the entrance of the box to transfer the force
into the soil to a sufficient horizontal distance so as to significantly reduce the stress on the door of the box. The sleeves shall consist
of two tapered (illustrated in Fig. 3Fig. 3) ) or non-tapered (no more than 13 mm (0.5 in.)[0.5 in.] thick) plates extending the full
width of the pullout box and into the pullout box a minimum distance of 150 mm (6 in.),[6 in.], but it is recommended that this
distance equal the total soil depth above or below the geosynthetic. Both design types must possess tapered edges at the point of
load application in the soil that are no more then 3 mm (0.12 in.)[0.12 in.] thick. The plates shall be rigidly separated at the sides
with spacers and be sufficiently stiff such that normal stress is not transferred to the geosynthetic between the plates.
6.2 Normal Stress Loading Device—Normal stress applied to the upper layer of soil above the geosynthetic must be constant
and uniform for the duration of the load step. To maintain a uniform normal stress, a flexible pneumatic or hydraulic
diaphragm-loading device which is continuous over the entire test box area should be used and capable of maintaining the applied
normal stress within 62%62 % of the required normal stress. Normal stresses utilized will depend on testing requirements;
however, stresses up to 250 kPa (35 psi)[35 psi] should be anticipated. A recommended normal stress-loading device is an air bag.
6.3 Cyclic Force Loading Device—— Horizontal cyclic force must be supplied by a device with the ability to apply cyclic load
in the direction of the opening of the box. The force must be at the same level with the specimen.
6.3.1 The cyclic force system must be able to apply multiple load repetitions using a haversine-shaped load pulse consisting of
a 0.2 seconds load followed by a 0.80 seconds rest period. The loading system must also be able to simultaneously maintain a
minimum seating load on the material during cyclic loading.
FIG. 3 Side View of Load Transfer Sleeve Arrangement
D7499/D7499M − 09 (2014)
6.3.2 Also, a device to measure the cyclic force (i.e., (that is, a load cell) must be incorporated into the system and shall be
accurate within 60.5 % of its full-scale range.
6.4 Displacement Indicators— — Horizontal displacement of the geosynthetic is measured at the entrance of the box and at
several locations on the embedded portion of the specimen. Measurements outside the door at the box entrance are made by
electronic displacement transducers (e.g., (for example, linear variable differential transformers (LVDTs) can be used) mounted to
the box frame to read against a plate attached to the specimen near the door.
6.4.1 Displacement measurements within the box may employ any of several methods, which place sensors or gauge connectors
directly on the geosynthetic and monitor their change in location remotely. One such device utilizes wire gages, which are
protected from normal stress by a surrounding tube, which runs from a location mounted on the specimen to the outside of the box
where displacements are measured by displacement transducers.
6.4.2 All electronic measurement devices must be accurate to 6 0.01 60.01 mm. Locations of the devices must be accurately
determined and recorded. Minimum extension capabilities of 50 mm (2 in.)[2 in.] are recommended.
6.4.3 Determine the displacement of the geosynthetic at the front (leading end) and the rear (embedded end) of the geosynthetic
at several locations along its width; suggested layout is shown in Fig. 2.
6.5 Geosynthetic Clamping Devices—Clamps which connect the specimen to the cyclic force system without slipping, causing
clamp breaks or weakening the material may be used, see Note 2. The clamps shall be swiveled to allow the cyclic forces to be
distributed evenly throughout the width of the sample. The clamps must allow the specimen to remain horizontal during loading
and not interfere with the interface shear surface. Gluing, bonding, or otherwise molding of a geosynthetic within the clamp area
is acceptable and recommended whenever slippage might occur. Thin metal rods or tubes may be used to reduce friction between
the geosynthetic clamp/sample and the top edge of the lower load transfer sleeve (Fig. 3).
NOTE 2—A suggested method of clamping is shown in Fig. 4 and includes a simple clamp consisting of two pieces of 22 gauge sheet metal glued to
both sides of the geosynthetic sample. The sheet metal plates should be at least the same width as the geosynthetic being tested. Special precautions should
be taken to ensure that geotextile samples adhere to the sheet metal – such metal–such as making holes for the epoxy to flow through the fabric, however;
all such modifications to the fabric to facilitate bonding should not interfere with the remainder of the geosynthetic protruding from the front edge of
...