ASTM D6638-18

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Designation: D6638 − 11 D6638 − 18
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 D6638; 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 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. 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 safety, health, and healthenvironmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D448 Classification for Sizes of Aggregate for Road and Bridge Construction
D4354 Practice for Sampling of Geosynthetics and Rolled Erosion Control Products (RECPs) for Testing
D4439 Terminology for Geosynthetics
D4495 Test Method for Impact Resistance of Poly(Vinyl Chloride) (PVC) Rigid Profiles by Means of a Falling Weight
D6637D6637/D6637M Test Method for Determining Tensile Properties of Geogrids by the Single or Multi-Rib Tensile Method
3. Terminology
3.1 Definitions:
3.1.1 displacement criteria, n—a user prescribed user-prescribed maximum movement, mm (in.), of the geosynthetic
reinforcement out from the back of segmental concrete units.
3.1.2 geosynthetic, n—a planar product manufactured from polymeric material used with soil, rock, earth, or other geotechnical
engineering related engineering-related material as an integral part of a man-mademanmade project, structure, or system. (D4439)
3.1.3 granular infill, n—coarse grained coarse-grained soil aggregate used to fill the voids in and between segmental concrete
units.
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 1, 2011July 15, 2018. Published July 2011August 2018. Originally approved in 2001. Last previous edition approved in 20072011 as
D6638 – 07.D6638 – 11. DOI: 10.1520/D6638-11.10.1520/D6638-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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
D6638 − 18
3.1.4 peak connection strength, n—the maximum tensile capacity of the connection between geosynthetic reinforcement and
segmental concrete units.
3.1.5 segmental concrete unit (modular concrete block), n—a concrete unit manufactured specifically for mortarless, dry-stack
retaining wall construction.
3.1.6 segmental concrete unit width, n—the segmental concrete unit dimension parallel to the wall face and coincident with the
geosynthetic reinforcement test specimen width.
3.1.7 service state service-state connection strength, n—the connection tensile capacity at a service state service-state
displacement criterion between geosynthetic reinforcement and segmental concrete units.
3.2 For definitiondefinitions of other terms relating to geosynthetics, refer to Terminology D4439.
4. Summary of Test Method
4.1 One end of a wide geosynthetic reinforcement test specimen is attached to dry stacked dry-stacked segmental concrete block
units assembled as specified by the user. The other end of the test specimen is attached to a clamp, which is part of a constant 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 under constant rate of displacement until a sustained loss of connection
capacity and/oror excessive movement (greater than 150 mm) 150 mm) of the reinforcement out from the connection.connection,
or both.
4.1.1 Peak connection capacity, and and, when required, tensile capacity after a user prescribed user-prescribed displacement
criteria has occurred, is used to define connection strength based on peak and service state criteria and, when required, 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 (lb/ft). Generally, a series of tests areis
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 reinforcement and segmental concrete block units is used in design of
reinforced soil retaining walls.
5.2 This test is used to determine the connection strength for the design of the connection system formed by segmental concrete
block units and geosynthetic reinforcement layers in reinforced soil retaining walls. Performing a series of these connection tests
at varying normal loads permits development of a relationship between connection strength and normal load. This relationship may
be linear, bi-linear,bilinear, or some other complex mathematical expression.
5.3 This connection strength test is meant to be a performance test (laboratory or field),field); therefore, it should be conducted
using full-scale system components. The conditions for the test are selected by the user and are not for routine testing.
5.4 As a performance test on full-scale system components, it accounts for some of the variables in construction procedures and
materials tolerance normally present for these types of retaining wall systems.
6. Apparatus
6.1 Testing System—An example of a test apparatus and setup is illustrated in Figs. 1 and 2. The principal components of the
test apparatus are:
6.1.1 loading frame,Loading Frame.
6.1.2 normal load piston/actuator, Normal Load Piston/Actuator.
6.1.3 Vertical Loading Platen, vertical loading platen,with stiff rubber mat or airbag to apply uniform vertical pressure to top
of concrete blocksblocks.
6.1.4 Vertical Load Cell, vertical load cell,to measure normal loadload.
FIG. 1 Connection Strength Test System
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FIG. 2 Connection Test Apparatus (Plan View)
6.1.5 geosynthetic loading clamp,Geosynthetic Loading Clamp.
6.1.6 Horizontal Piston/Actuator, horizontal piston/actuator,to load geosynthetic reinforcement in tensiontension.
6.1.7 Horizontal Load Cell, horizontal load cellto measure geosynthetic tensile force, and force.
6.1.8 Two (2) Horizontal Displacement Measurement Devices, two (2) horizontal displacement measurement devices,to record
displacement of the geosynthetic at the back of the segmental concrete blocks.
6.2 Loading Frame—The loading frame shall have sufficient capacity to resist the forces developed by the horizontal and
vertical loading pistons/actuators.
6.3 Tensile Loading Clamp and Loading Assemblies —Assemblies—The geosynthetic is gripped at its free end with a clamp
extending the full width of the specimen. The clamp shall be capable of applying a uniform force across the full width of the test
specimen. A roller grip assembly may be used to apply the tensile load. For some geosynthetics, it may be necessary to epoxy bond
the geosynthetic to, or within, the clamp in order to obtain a uniform stress distribution across the entire width of the test specimen.
6.3.1 The tensile loading unit will generally be a constant rate of extension screw jack or hydraulic actuator that can be
displacement rate controlled. The loading equipment shall have a capacity that is at least equal to 120 % of the wide strip wide-strip
tensile strength of the geosynthetic (Test MethodsMethod D4495 or D6637D6637/D6637M) multiplied by the specimen width.
The piston shall be capable of at least 150 mm (6 inches)in.) of movement in order to facilitate test set up setup and to ensure that
there is adequate stroke to achieve failure of geosynthetic reinforcement specimens.
NOTE 1—Some systems (that is, modular concrete units with a depth greater than 0.5 m) may need more than 150 mm of movement to achieve failure
of the connection.
6.3.2 The orientation of the tensioning force shall be horizontal and perpendicular to the back of the segmental units, and shall
be applied at the elevation where the geosynthetic exits the back of the segmental units.
6.4 Load Cells—A calibrated load cell shall be used to measure the tensile connection force and normal load during the test.
The load cell used for measuring tension shall have a capacity that is greater than or equal to 120 % of the wide strip wide-strip
tensile strength of the geosynthetic (Test MethodsMethod D4495 or D6637D6637/D6637M) 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 normal load. The load cells shall be accurate to within 6 0.5 % 60.5 % of its full-scale range.
6.5 Displacement Measuring Devices—Two linear variable displacement transducers (LVDTs) or similar electronic displace-
ment measuring devices are recommended to continuously monitor the displacement of the geosynthetic out from the back of the
concrete units. Alternatively, dial gauges may be read and recorded manually at regular intervals not greater than one minute.
1 min. LVDTs, dial gauges, or similar measuring devices shall be accurate to 6 0.1 60.1 mm (60.005 in.).
7. Sampling
7.1 Segmental Concrete UnitsUnits:
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7.1.1 Segmental concrete units shall be full-size blocks and meet the manufacturer’s material and dimensional specifications.
Model or prototype units shall not be used unless it can be demonstrated that they are equivalent to production units.
7.1.2 The user shall specify and/oror collect (or both) a sufficient sample of representative segmental units, from a standard
production lot, to construct the anticipated number of test configurations for the connection system within the testing agency’s load
frame and testing system.
7.1.3 The wall for connection testing shall be constructed using randomly selected full-size (that is, full width) full-width)
segmental units from the usersuser’s sampling of a standard production lot,lot; see section 7.1.2. A maximum of two half width
half-width segmental concrete units may be used on only one course of the units being tested in a confined width test apparatus.
Segmental concrete units may be re-usedreused in testing if there is no cracking, abrasion, or wearing of the concrete surfaces
between tests.
7.1.4 Wall Width—The wall for testing shall be constructed to a minimum of 750 mm (29.5 in.) in width and contain at least
one typical segmental concrete unit running bond joint. The segmental wall width for testing shall be at least as wide as the
geosynthetic test specimen width (see 7.2.3). Testing of segmental concrete unit widths greater than 500 mm,mm may be
represented in this test by limiting the test wall to 1000 mm (39.4 in.) in width.
NOTE 2—Narrower wall widths may be used for testing, provided the connection strength is proven to be unaffected by this reduction (see section
7.2.3).
7.1.5 Conditioning—The segmental concrete unit test specimen shall be brought to standard temperature and relative humidity
conditions for testing in a laboratory. The temperature is to be 21 6 2°C2 °C (70 6 4°F)4 °F) and the relative humidity of 65 6
10 %. For field-testing field testing, the specimen shall be brought to ambient conditions for not less than one hour. 1 h. The
temperature and humidity at the start and end of the test shall be recorded for field-testing.field testing.
7.2 GeosyntheticGeosynthetic:
7.2.1 Sampling Requirements—The latest version of ASTM sampling protocol for geotextiles (Practice D4354) shall be used for
the geosynthetic reinforcement material.
7.2.2 Conditioning—The geosynthetic reinforcement test specimen shall be brought to standard temperature and relative
humidity conditions for testing in a laboratory. The temperature is to be 21 6 2°C2 °C (70 6 4°F)4 °F) and the relative humidity
of 60 6 10 %. For field-testing field testing, the specimen shall be brought to ambient conditions for not less than one hour. 1 h.
The temperature and humidity at the start and end of the test shall be recorded for field-testing.field testing.
7.2.3 Specimen Width—The geosynthetic reinforcement test specimen shall be a minimum of 750 mm (29.5 in.) in width. For
tests that use two or more full segmental retaining wall units on the bottom course, the geosynthetic shall be an exact multiple of
the segmental retaining wall unit width totaling closest to,to but exceeding 750 mm (29.5 in.) in width. For segmental retaining
wall unit widths greater than 500 mm (19.7 in.) (19.7 in.), a geosynthetic specimen width of 1000 mm (39.4 in.) (39.4 in.) may
be used.
NOTE 3—Narrower geosynthetic reinforcement specimen widths may be used for a specific concrete unit, provided that sufficient testing demonstrates
that narrower samples provide an evaluation of connection performance that is equivalent to the minimum 750 mm (29.5 in.) width sample. This
procedure may be appropriate for wall connections that are primarily mechanical (non-frictional) in nature.
7.2.4 Specimen Length—The geosynthetic specimen shall have sufficient length to cover the interface surface as specified by
the user. The specimen must be trimmed to provide sufficient anchorage at the geosynthetic loading clamp and a free length
between the back of the concrete blocks and loading clamp ranging from a minimum of 200 mm (7.9 in.) to a maximum of 600
mm (23.6 in.),in.). The geosynthetic reinforcement specimen shall be placed between the stacked segmental concrete units to cover
the same area that will be used in field construction of the connection, or as determined by the user.
7.2.5 A new geosynthetic reinforcement test specimen shall be used for each test.
7.2.6 Number of Tests—A sufficient number of tests shall be conducted to adequately define a relationship between connection
strength and normal load applied to the connection. Tests shall be conducted at a minimum of five (5) unique normal loads within
the range of loads typical of wall design, as directed by the user. Additionally, at least two more tests at one normal load will be
necessary to verify repeatability (see section 7.2.7).
7.2.7 Repeatability of Test Results—The testing agency shall provide evidence of test results repeatability by conducting at least
three tests at one normal load level for a specific segmental concrete units and geosynthetic reinforcement system. The general
range for repeatability of peak connection strength of these three nominally identical tests is 6 10 % 610 % from the mean of the
three tests (see reference in X1.1). If the test results are outside of this range, it shall be duly noted on the report.
8. Test Procedure
8.1 Install and brace lower course of concrete segmental units. Place the units such that a running joint will be coincident with
the center of pull for the geosynthetic reinforcement test specimen, on either this course or the course above.
8.1.1 The connection shall be constructed using the geosynthetic reinforcement, granular infill, full-scale segmental concrete
block units, and connectors specified by the user. The number, type, and arrangement of mechanical connectors shall also be
specified by the user.
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8.1.2 A single course of segmental units shall be placed on a rigid base
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