ASTM D6916-18

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Designation: D6916 − 06c (Reapproved 2011) D6916 − 18
Standard Test Method for
Determining the Shear Strength Between Segmental
Concrete Units (Modular Concrete Blocks)
This standard is issued under the fixed designation D6916; 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 shear strength between two layers of 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
facing system at full-scale. full scale. The results of a series of tests are used to define a relationship between shear strength
developed between segmental concrete units 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
facing system 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
D4595 Test Method for Tensile Properties of Geotextiles by the Wide-Width Strip Method
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 top segmental concrete
unit out from the back of lower 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.
3.1.4 peak shear strength, n—the maximum shear capacity between segmental concrete units.
3.1.5 segmental concrete depth, n—the segmental concrete unit dimension perpendicular to the wall face.
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 Oct. 1, 2011July 15, 2018. Published October 2011August 2018. Originally approved in 2003. Last previous edition approved in 20062011 as
D6916D6916 – 06c (2011).–06c. DOI: 10.1520/D6916-06CR11.10.1520/D6916-18.
For referenced ASTM standards, visit the ASTM Web Site, 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 web site.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6916 − 18
FIG. 1 Shear Test Apparatus (Cross Section View)
3.1.6 segmental concrete unit (modular concrete block), n—a concrete unit manufactured specifically for mortarless, dry-stack
retaining wall construction.
3.1.7 segmental concrete unit width, n—the segmental concrete unit dimension parallel to the wall face.
3.2 For definitiondefinitions of other terms relating to geosynthetics, refer to Terminology D4439.
4. Summary of Test Method
4.1 In this test method, segmental concrete units are assembled in two rows (layers). The bottom row is laterally restrained. The
top row is loaded vertically to a constant surcharge load, and the interface is sheared at a constant rate of displacement until a drop
of load after the peak load occurs. The test may be run with the geosynthetic reinforcement sandwiched between the two rows of
segmental concrete units to determine the shear strength between segmental concrete units at the connection between the units and
the geosynthetic reinforcement.
5. Significance and Use
5.1 The shear strength between segmental concrete units (with and without geosynthetic reinforcement) and is used in design
of reinforced soil retaining walls.
5.2 This test is used to determine the shear strength for the design of the facing stability of segmental retaining walls.
Performing a series of these shear tests at varying normal loads permits development of a relationship between shear strength and
normal load. This relationship may be linear, bi-linear,bilinear, or some other complex mathematical expression.
5.3 This shear 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 Fig. 1. The principal components of the test
apparatus are:
6.1.1 Loading Frame.
6.1.2 Normal Load Piston/Actuator . Piston/Actuator.
6.1.3 Vertical Loading Platen, with stiff rubber mat or airbag to apply uniform vertical pressure to top of concrete blocks.
D6916 − 18
6.1.4 Vertical Load Cell, to measure normal load.
6.1.5 Horizontal Piston/Actuator , Piston/Actuator, to apply horizontal load on the top segmental concrete unit.
6.1.6 Horizontal Load Cell, to measure applied force on the top segmental concrete unit.
6.1.7 Two (2) Horizontal Displacement Measurement Devices, to record displacement of the top segmental concrete unit.
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 Shear Loading Plate—The shear loading plate must be sufficiently rigid to apply a uniform force across the full width of
the top course. For some segmental units, it may be necessary to apply the load through a deformable material (that is, stiff rubber)
which will conform to an irregular block surface, thereby allowing for a uniform load distribution.
6.4 Restraining Box/Plate—A rigid restraining box/plate is required to prevent horizontal movement of the lowermost
segmental concrete units during shear testing. The restraining box/plate area shall be of sufficient width and depth to accommodate
the full scale “as manufactured” full-scale “as-manufactured” segmental concrete units being tested.
6.5 Shear Loading Assembly—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 anticipated shear strength of the segmental concrete units. The piston shall be capable of at least 150 mm (6 in.) of movement
in order to facilitate test set up setup and to ensure that there is adequate stroke to achieve peak load. The orientation of the
tensioning force shall be horizontal and perpendicular to the back of the segmental units. The horizontal loading arrangement must
not permit rotation of the top concrete unit during shear.
6.6 Load Cells—A calibrated load cell shall be used to measure the shear force and normal load during the test. The load cell
used for measuring shear shall have a capacity that is greater than or equal to 120 % of the anticipated shear force between units.
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.
6.7 Displacement Measuring Devices—Two (2) Linear Variable Displacement Transducerslinear variable displacement
transducers (LVDTs) or similar electronic displacement measuring devices are recommended to continuously monitor the
displacement of the top segmental concrete unit out from the back of the lower segmental 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 (0.005 in.).
7. Sampling
7.1 Segmental Concrete Units:
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 shear system within the testing agency’s load frame
and testing system.
7.1.3 The shear interface must be constructed with full-size or modified (see 7.1.4) segmental concrete units randomly selected
from the usersuser’s sampling of a standard production lot,lot; see 7.1.2.
7.1.4 Test Width—The width of the shear interface for testing shall be constructed to a minimum of 750152.4 mm (29.5(6 in.)
in width. The test section shall consist of at least two bottom course segmental concrete units, with at least one top course
segmental unit placed on top of the lower segmental concrete units. The shear interface shall include at least one typical segmental
concrete unit running bond joint. The top unit must be the full width of the unit. The bottom units may be adjusted to fit into the
test apparatus. Testing of segmental concrete unit widths greater than 500 mm (19.7 in.),in.) may be represented in this test by
limiting the test wall to 1000 mm (39.4 in.) in width.
NOTE 1—Any modification to the width of bottom units should maintain the integrity of the test shear interface and insureensure that a representative
(repeatable) test shear interface is maintained.
7.1.5 Test Height—The height of the segmental concrete unit may be reduced to facilitate handling and safety issues. Any
modification to the segmental concrete unit height shall not alter the geometry of the test shear interface and shall be clearly stated
in the test report (see 10.2).
7.1.6 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 Geosynthetic (if required) : (If Required):
7.2.1 If the segmental concrete units are to be used for a geosynthetic reinforced geosynthetic-reinforced segmental retaining
wall, then a layer of a specified geosynthetic material shall be placed between the segmental concrete units.
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7.2.2 Sampling Requirements—The latest version of ASTM sampling protocol for geotextiles (Practice D4354) shall be used for
the geosynthetic reinforc
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