ASTM D6638-01
(Test Method)Standard Test Method for Determining Connection Strength Between Geosynthetic Reinforcement and Segmental Concrete Units (Modular Concrete Blocks)
Standard Test Method for Determining Connection Strength Between Geosynthetic Reinforcement and Segmental Concrete Units (Modular Concrete Blocks)
SCOPE
1.1 This test method is used to determine the connection properties between a layer of geosynthetic reinforcement and segmental concrete block units used in construction of reinforced soil retaining walls. The test is carried out under conditions determined by the user that reproduce the connection system at full-scale. The results of a series of tests are used to define a relationship between connection strength for a segmental unit-geosynthetic connection system and normal load.
1.2 This is a performance test used to determine properties for design of retaining wall systems utilizing segmental concrete units and soil reinforcing geosynthetics, either geotextiles or geogrids. The test is performed on a full-scale construction of the connection and may be run in a laboratory or the field.
1.3 The values stated in SI units are regarded as the standard. The values stated in inch-pound units are provided for information only.
1.4 This standard may involve hazardous materials, operations, and equipment. 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.
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Designation:D6638–01
Standard Test Method for
Determining Connection Strength Between Geosynthetic
Reinforcement and Segmental Concrete Units (Modular
Concrete Blocks)
This standard is issued under the fixed designation D 6638; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This test method is used to determine the connection 3.1 Definitions:
properties between a layer of geosynthetic reinforcement and 3.1.1 displacement criteria, n—a user prescribed maximum
segmental concrete block units used in construction of rein- movement, mm (in.), of the geosynthetic reinforcement out
forced soil retaining walls. The test is carried out under from the back of segmental concrete units.
conditions determined by the user that reproduce the connec- 3.1.2 geosynthetic, n—a planar product manufactured from
tionsystematfull-scale.Theresultsofaseriesoftestsareused polymeric material used with soil, rock, earth, or other geo-
to define a relationship between connection strength for a technical engineering related material as an integral part of a
segmental unit-geosynthetic connection system and normal man-made project, structure or system. (D 4439)
load. 3.1.3 granular infill, n—coarse grained soil aggregate used
1.2 This is a performance test used to determine properties to fill the voids in and between segmental concrete units.
for design of retaining wall systems utilizing segmental con- 3.1.4 peak connection strength, n—the maximum tensile
crete units and soil reinforcing geosynthetics, either geotextiles capacity of the connection between geosynthetic reinforcement
or geogrids. The test is performed on a full-scale construction and segmental concrete units.
of the connection and may be run in a laboratory or the field. 3.1.5 segmental concrete unit (modular concrete block),
1.3 The values stated in SI units are regarded as the n—a concrete unit manufactured specifically for mortarless,
standard. The values stated in inch-pound units are provided dry-stack retaining wall construction.
for information only. 3.1.6 segmental concrete unit width, n—the segmental con-
1.4 This standard may involve hazardous materials, opera- crete unit dimension parallel to the wall face and coincident
tions, and equipment. This standard does not purport to with the geosynthetic reinforcement test specimen width.
address all of the safety concerns, if any, associated with its 3.1.7 service state connection strength, n— the connection
use. It is the responsibility of the user of this standard to tensile capacity at a service state displacement criterion be-
establish appropriate safety and health practices and deter- tween geosynthetic reinforcement and segmental concrete
mine the applicability of regulatory limitations prior to use. units.
3.2 For definition of other terms relating to geosynthetics,
2. Referenced Documents
refer to Terminology D 4439.
2.1 ASTM Standards:
4. Summary of Test Method
D 448 Classification for Sizes of Aggregate for Road and
Bridge Construction 4.1 One end of a wide geosynthetic reinforcement test
D 4354 Practice for Sampling of Geosynthetics for Testing specimen is attached to dry stacked segmental concrete block
D 4439 Terminology for Geosynthetics units assembled as specified by the user. The other end of the
D 4595 Test Method for Tensile Properties of Geotextiles test specimen is attached to a clamp, which is part of a constant
by the Wide-Width Strip Method rate of extension tensile loading machine. The top course of
segmental concrete block units is then loaded vertically to a
constant normal load and the geosynthetic is then tensioned
This test method is under the jurisdiction of ASTM Committee D35 on
under constant rate of displacement until a sustained loss of
Geosynthetics and is the direct responsibility of Subcommittee D35.01 on Mechani-
connection capacity and/or excessive movement (greater than
cal Properties.
150 mm) of the reinforcement out from the connection.
Current edition approved Feb. 10, 2001. Published April 2001.
Annual Book of ASTM Standards, Vol 04.03.
Annual Book of ASTM Standards, Vol 04.13.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6638–01
4.1.1 Peak connection capacity, and tensile capacity after a
user prescribed displacement criteria has occurred, is used to
define connection strength based on peak and service state
criteria respectively. Both these values may be obtained from
each test that measures geosynthetic displacement. Tensile
loads and strengths are reported per unit width of geosynthetic
sample, kN/m (lb /ft). Generally a series of tests are performed
to establish a mathematical relationship between connection
strength and normal load on the connection.
5. Significance and Use
5.1 The connection strength between geosynthetic rein-
forcement and segmental concrete block units is used in design
FIG. 2 Connection Test Apparatus (Plan View)
of reinforced soil retaining walls.
5.2 Thistestisusedtodeterminetheconnectionstrengthfor
the design of the connection system formed by segmental
6.2 Loading Frame—The loading frame shall have suffi-
concrete block units and geosynthetic reinforcement layers in
cient capacity to resist the forces developed by the horizontal
reinforced soil retaining walls. Performing a series of these
and vertical loading pistons/actuators.
connection tests at varying normal loads permits development
6.3 Tensile Loading Clamp and Loading Assemblies—The
of a relationship between connection strength and normal load.
geosynthetic is gripped at its free end with a clamp extending
This relationship may be linear, bi-linear, or some other
the full width of the specimen. The clamp shall be capable of
complex mathematical expression.
applying a uniform force across the full width of the test
5.3 This connection strength test is meant to be a perfor-
specimen. A roller grip assembly may be used to apply the
mance test (laboratory or field), therefore, it should be con- tensile load. For some geosynthetics it may be necessary to
ducted using full-scale system components. The conditions for
epoxy bond the geosynthetic to, or within, the clamp in order
the test are selected by the user and are not for routine testing. toobtainauniformstressdistributionacrosstheentirewidthof
5.4 As a performance test on full-scale system components
the test specimen.
itaccountsforsomeofthevariablesinconstructionprocedures 6.3.1 The tensile loading unit will generally be a constant
and materials tolerance normally present for these types of
rate of extension screw jack or hydraulic actuator that can be
retaining wall systems.
displacementratecontrolled.Theloadingequipmentshallhave
a capacity that is at least equal to 120 % of the wide strip
6. Apparatus tensile strength of the geosynthetic (Test Method D 4595)
multiplied by the specimen width. The piston shall be capable
6.1 Testing System—An example of a test apparatus and
ofatleast150mm(6inches)ofmovementinordertofacilitate
setup is illustrated in Figs. 1 and 2. The principal components
test set up and to ensure that there is adequate stroke to achieve
of the test apparatus are:
failure of geosynthetic reinforcement specimens.
6.1.1 loading frame,
6.1.2 normal load piston/actuator,
NOTE 1—Some systems (that is, modular concrete units with a depth
6.1.3 vertical loading platen, with stiff rubber mat or airbag
greater than 0.5 m) may need more than 150 mm of movement to achieve
to apply uniform vertical pressure to top of concrete blocks failure of the connection.
6.1.4 vertical load cell, to measure normal load
6.3.2 The orientation of the tensioning force shall be hori-
6.1.5 geosynthetic loading clamp,
zontal and perpendicular to the back of the segmental units and
6.1.6 horizontal piston/actuator, to load geosynthetic rein-
shall be applied at the elevation where the geosynthetic exits
forcement in tension
the back of the segmental units.
6.1.7 horizontal load cell to measure geosynthetic tensile
6.4 Load Cells—A calibrated load cell shall be used to
force, and
measure the tensile connection force and normal load during
6.1.8 two (2) horizontal displacement measurement de-
the test. The load cell used for measuring tension shall have a
vices,to record displacement of the geosynthetic at the back of
capacity that is greater than or equal to 120 % of the wide strip
the segmental concrete blocks.
tensile strength of the geosynthetic (Test Method D 4595)
multiplied by the specimen width. The load cell used for
measuring the normal surcharge load shall have a capacity that
is greater than or equal to 100 % of the maximum anticipated
normalload.Theloadcellsshallbeaccuratewithin 60.5 %of
its full-scale range.
6.5 Displacement Measuring Devices—Two linear variable
displacement transducers (LVDTs) or similar electronic dis-
placement measuring devices are recommended to continu-
ously monitor the displacement of the geosynthetic out from
FIG. 1 Connection Strength Test System the back of the concrete units. Alternatively, dial gauges may
D6638–01
be read and recorded manually at regular intervals not greater multiple of the segmental retaining wall unit width totaling
than one minute. LVDTs, dial gauges or similar measuring closest to, but exceeding 750 mm (29.5 in.) in width. For
devices shall be accurate to 6 0.1 mm (60.005 in.). segmentalretainingwallunitwidthsgreaterthan500mm(19.7
in.) a geosynthetic specimen width of 1000 mm (39.4 in.) may
be used.
7. Sampling
7.1 Segmental Concrete Units
NOTE 3—Narrower geosynthetic reinforcement specimen widths may
7.1.1 Segmental concrete units shall be full-size blocks and be used for a specific concrete unit, provided that sufficient testing
demonstrates that narrower samples provide an evaluation of connection
meet the manufacturer’s material and dimensional specifica-
performance that is equivalent to the minimum 750 mm (29.5 in.) width
tions. Model or prototype units shall not be used unless it can
sample. This procedure may be appropriate for wall connections that are
be demonstrated that they are equivalent to production units.
primarily mechanical (non-frictional) in nature.
7.1.2 The user shall specify and/or collect a sufficient
sample of representative segmental units, from a standard 7.2.4 Specimen Length—The geosynthetic specimen shall
have sufficient length to cover the interface surface as specified
production lot, to construct the anticipated number of test
configurations for the connection system within the testing by the user. The specimen must be trimmed to provide
agency’s load frame and testing system. sufficient anchorage at the geosynthetic loading clamp and a
7.1.3 The wall for connection testing shall be constructed freelengthbetweenthebackoftheconcreteblocksandloading
using randomly selected full-size (that is, full width) segmental clamp ranging from a minimum of 200 mm (7.9 in.) to a
units from the users sampling of a standard production lot, see maximum of 600 mm (23.6 in.), The geosynthetic reinforce-
section 7.1.2. A maximum of two half width segmental ment specimen shall be placed between the stacked segmental
concrete units may be used on only one course of the units concrete units to cover the same area that will be used in field
being tested in a confined width test apparatus. Segmental construction of the connection or as determined by the user.
concrete units may be re-used in testing if there is no cracking, 7.2.5 Anew geosynthetic reinforcement test specimen shall
abrasion or wearing of the concrete surfaces between tests.
be used for each test.
7.1.4 Wall Width—The wall for testing shall be constructed
7.2.6 Number of Tests—Asufficient number of tests shall be
to a minimum of 750 mm (29.5 in.) in width and contain at
conducted to adequately define a relationship between connec-
least one typical segmental concrete unit running bond joint. tion strength and normal load applied to the connection. Tests
The segmental wall width for testing shall be at least as wide
shall be conducted at a minimum of three unique normal loads
as the geosynthetic test specimen width (see 7.2.3). Testing of within the range of loads typical of wall design, as directed by
segmental concrete unit widths greater than 500 mm, may be
the user. Additionally, at least two more tests at one normal
represented in this test by limiting the test wall to 1000 mm load will be necessary to verify repeatability (see section
(39.4 in.) in width.
7.2.7).
7.2.7 Repeatability of Test Results—The testing agency
NOTE 2—Narrower wall widths may be used for testing, provided the
shall provide evidence of test results repeatability by conduct-
connection strength is proven to be unaffected by this reduction (see
section 7.2.3). ing at least three tests at one normal load level for a specific
segmental concrete units and geosynthetic reinforcement sys-
7.1.5 Conditioning—Thesegmentalconcreteunittestspeci-
tem. The general range for repeatability of peak connection
men shall be brought to standard temperature and relative
strengthofthesethreenominallyidenticaltestsis 610 %from
humidityconditionsfortestinginalaboratory.Thetemperature
the mean of the three tests (see reference in X1.1). If the test
is to be 21 6 2°C (70 6 4°F) and the relative humidity of 65
results are outside of this range it shall be duly noted on the
6 10 %. For field-testing the specimen shall be brought to
report.
ambient conditions for not less than one hour. The temperature
and humidity at the start and end of the test shall be recorded
8. Test Procedure
for field-testing.
8.1 Install and brace lower course of concrete segmental
7.2 Geosynthetic
units. Place the units such that a running joint will be
7.2.1 Sampling Requirements—The latest version ofASTM
coincident with the center of pull for the geosynthetic rein-
sampling protocol for geotextiles (Practice D 4354) shall be
forcement test specimen, on either this course or the course
used for the geosynthetic reinforcement material.
above.
7.2.2 Conditioning—The geosynthetic reinforcement test
specimen shall be brought to standard temperature and relative 8.1.1 The connection shall be constructed using the geosyn-
thetic reinforcement, granular infill, full-scale segmental con-
humidityconditionsfortestinginalaboratory.Thetemperature
is to be 21 6 2°C (70 6 4°F) and the relative humidity of 60 crete block units and connectors specified by the user. The
number, type an
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