Cornerstone R100 Segmental Retaining Wall Unit and SRW Products SRW5, SRW7, and SRW9 Series Geogrids Connection Strength Testing

Transcription

1 Cornerstone R100 Segmental Retaining Wall Unit and SRW Products SRW5, SRW7, and SRW9 Series Geogrids Connection Strength Testing Prepared for Synteen Technologies, Inc. 816 Quality Drive Lancaster Business Park Lancaster, SC Prepared by National Concrete Masonry Association Research and Development Laboratory 2302 Horse Pen Road Herndon, Virginia Tel: Fax:

2 December 29, 2000 NATIONAL CONCRETE MASONRY ASSOCIATION The National Concrete Masonry Association (NCMA) is a non-profit organization whose mission is to support and advance the common interests of its members in the manufacture, marketing, research, and application of concrete masonry products. The Association is an industry leader in providing technical assistance and education, marketing, research and development, and product and system innovation to its members and to the industry. NCMA Technical Staff Robert D. Thomas, Director of Engineering and Research Jason J. Thompson, Structural Engineer R. Lance Carter, P.E., Manager of Engineered Landscape Products Dennis W. Graber, P.E., Director of Technical Publications Jeffrey H. Greenwald, P.E., Director of Codes and Standard Robert S. Zobel, Ph.D., Manager of Research and Development NCMA RESEARCH AND DEVELOPMENT LABORATORY The NCMA Research and Development Laboratory is exclusively devoted to the scientific research and testing of concrete masonry products and systems. The Laboratory is staffed by professional engineers and technicians with many years of experience in the concrete masonry industry. The Laboratory is equipped to perform nearly any physical research or testing of concrete masonry units and assemblages. The Laboratory performs research and development work for both the Association and individual companies. NCMA Research and Development Laboratory Staff Robert S. Zobel, Ph.D., Manager of Research and Development Donald L. Breeding, Laboratory Supervisor Douglas H. Ross, Senior Laboratory Technician Joynul Kahn, Laboratory Technician Jeffrey Johnson, Laboratory Technician NATIONAL CONCRETE MASONRY ASSOCIATION 2

3 2302 Horse Pen Road Herndon, Virginia (703) TABLE OF CONTENTS 1.0 INTRODUCTION CONNECTION STRENGTH TEST PROCEDURES CONNECTION TEST RESULTS ALLOWABLE CONNECTION STRENGTH NCMA METHODOLOGY 7 Appendix A Load Deformation Plots for SRW Products SRW5 Series 10 Appendix B Load Deformation Plots for SRW Products SRW7 Series 11 Appendix C Load Deformation Plots for SRW Products SRW9 Series 12 3

4 1.0 INTRODUCTION The connection between the geogrid reinforcement and segmental retaining wall (SRW) unit is a critical component of any SRW. Measurement of the strength of the connection through connection testing has been performed for almost a decade. The National Concrete Masonry Association (NCMA) has developed a standard method for testing the connection strength: NCMA Test method SRWU-1 Determination of Connection Strength between Geosynthetics and Segmental Concrete Units. The American Society of Testing and Materials (ASTM) has developed a draft standard, Draft Test Method Z4278Z " Determining the Connection Strength between Geosythetic Reinforcement and Segmental Concrete Units," which is based on the NCMA test method. Using either of these procedures, the connection between any geosynthetic reinforcement and SRW can be evaluated. A testing program was developed to evaluate the connection strength of Cornerstone Series 100 SRW units and Synteen geogrid reinforcement. The Cornerstone SRW units used for the tests referenced herein are dry cast concrete blocks. The Cornerstone Series 100 unit is 18 inches wide at the front split face, 8 inches high, 12 inches deep with a hollow core (Figure 1). The Cornerstone Series 100 unit has an approximate weight of 75 lbs., and the approximate weight for the Cornerstone Series 100 unit with core fill is 110 lbs. (all dimensions and weight are nominal). SRW Products geogrid reinforcement consists of high molecular weight, high tenacity polyester (PET) yarns woven into a dimensionally stable network of high modulus tensile members. SRW Products geogrid is coated with polyvinyl chloride (PVC) for additional dimensional stability. The testing program consisted of testing three different geogrid reinforcements (SRW5, SRW7, SRW9 Series) connected to Cornerstone Series 100 units. The tests were performed at normal loads between 140 lb/ft and 1560 lb/ft. A total of six (6) tests were conducted for each geogrid type resulting in a total of eighteen (18) individual tests. 2.0 CONNECTION STRENGTH TEST PROCEDURES The connection tests were performed in accordance with NCMA Test method SRW U-1 Determination of Connection Strength between Geosynthetics and Segmental Concrete Units. The configuration of the test specimens for each connection strength test is shown in Figures 2 through 3 and is described from the bottom to the top of the test chamber as follows: Lower course of Cornerstone Series 100 units placed with the 18-inch nominal dimension parallel to the wall face (12-inch nominal dimension perpendicular to the wall face (Figure 2). Granular infill placed and compacted to density as in field. 4

5 The geogrid was placed on top of the first course of units. Beyond the width of geogrid test specimen, additional pieces of geogrid were installed as spacers in order to maintain a level top surface of the second course of units. The geogrid was placed such that the first transverse rib was positioned just to the inside surface of the face of the front of the units (Figure 2). Second course of Cornerstone Series 100 units placed on top of first course and the installed geogrid. Granular infill placed and compacted to density as in field. For each connection test, once the connection was set up in the test chamber the test was conducted as follows: Normal load was applied to the wall specimen through a dual ram hydraulic loading system to steel spreader beams, bearing plates and a layer of hard neoprene bearing pads placed on the top course of the units. The magnitude of normal load for each hydraulic ram was maintained at a constant level and monitored using electronic load cells throughout each test. Figures 2 and 3 show the connection test configuration. After application of the normal load, each geogrid specimen was subjected to a pullout load by displacing the geogrid at a rate of 10% of the gage length per minute (Figure 3). The test was continued until a constant or decreasing pullout load was recorded. The normal load was maintained at a constant magnitude throughout each test. All of the geogrid specimens used in this testing program were loaded in the machine direction. 3.0 CONNECTION TEST RESULTS Connection force is defined as the connection load divided by the initial width of the geogrid specimen. The peak connection strength is defined as the peak value of connection force. The connection strength at 0.75 inches horizontal displacement, as measured at the back of the Cornerstone Series 100 unit, is defined as the connection force at this displacement. The results of each series of 6 tests are summarized in Tables 1 through 3 (SRW5, SRW7, SRW9 Series, respectively). 5

6 TABLE 1 SUMMARY OF TEST RESULTS Cornerstone Series 100 Units with SRW5 Series TEST NUMBER NORMAL LOAD APPROXIMATE WALL HEIGHT (ft) PEAK CONNECTION STRENGTH 0.75-inch CONNECTION STRENGTH TABLE 2 SUMMARY OF TEST RESULTS Cornerstone Series 100 Units with SRW7 Series TEST NUMBER NORMAL LOAD APPROXIMATE WALL HEIGHT (ft) PEAK CONNECTION STRENGTH 0.75-inch CONNECTION STRENGTH TABLE 3 SUMMARY OF TEST RESULTS Cornerstone Series 100 Units with SRW9 Series TEST NUMBER NORMAL LOAD APPROXIMATE WALL HEIGHT (ft) PEAK CONNECTION STRENGTH 0.75-inch CONNECTION STRENGTH

7 4.0 ALLOWABLE CONNECTION STRENGTH NCMA METHODOLOGY Several procedures exist today for determining the allowable connection strength of SRWs. The NCMA Design Manual for Segmental Retaining Walls has adopted a procedure for determining the allowable connection strength that considers both a limit connection strength and a serviceability connection strength. The procedure is presented below: The ultimate strength of the connection is evaluated using the limit state connection strength: T cl = T ultconn FS cs Where: T cl T ultconn FS cs = long-term allowable connection strength = ultimate (peak) connection strength determined in accordance with NCMA Test Method SRW U-1 = factor of safety against connection failure, typically equal to 1.5 Limiting movement of the wall face over the life of the structure is also considered. T cs = T conn@3/4 Where: T cs T conn@3/4 = long-term connection strength based on serviceability = connection strength at 20 mm (3/4 inch) deformation The limit state connection strength and serviceability state connection strength of the connection are provided in Tables 1 through 6 for each different type of geogrid tested at each level of normal load. A plot of the peak connection strength and connection strength at 0.75 inches horizontal displacement verses applied normal load is shown in Figures 4 through 6 for each different geogrid type, respectively. In addition, individual load deformation plots for each test can be found in Appendices A through C. 7

8 12 " Nominal 18 " Nominal Figure 1 Cornerstone Series 100 Segmental Retaining Wall Unit Geometry Dual Ram Normal Load Segmental Retaining Wall Connection Setup Figure 2 Connection Strength Test Setup 8

9 Figure 3 - Connection Strength Test Setup 9

10 Appendix A Load Deformation Plots for SRW Products SRW5 Series

11 Appendix B Load Deformation Plots for SRW Products SRW7 Series

12 Appendix C Load Deformation Plots for SRW Products SRW9 Series