MESA Cornerstone Segmental Retaining Wall Unit and Tensar Geogrid Connection Strength Testing

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1 MESA Cornerstone Segmental Retaining Wall Unit and Tensar Geogrid Connection Strength Testing Prepared for Tensar Earth Technologies, Inc Glenridge Drive, Suite 2 Atlanta, GA 3328 Prepared by National Concrete Masonry Association Research and Development Laboratory 232 Horse Pen Road Herndon, Virginia 2171 Tel: Fax: July 19, 2

2 TABLE OF CONTENTS 1. INTRODUCTION 2 2. CONNECTION STRENGTH TEST PROCEDURES 2 3. CONNECTION TEST RESULTS 3 4. ALLOWABLE CONNECTION STRENGTH NCMA METHODOLOGY 6 Appendix A Load Deformation Plots for Series MESA1 1 Appendix B Load Deformation Plots for Series MESA2 2 Appendix C Load Deformation Plots for Series MESA3 3 Appendix D Load Deformation Plots for Series MESA4 4 Appendix E Load Deformation Plots for Series MESA5 5 Appendix F Load Deformation Plots for Series MESA6 6 1

3 1. 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 MESA Cornerstone SRW units and Tensar MESA reinforcement. MESA grid reinforcement consists of an open polymer grid structure specifically developed to interact with the soil. MESA grid is manufactured using high density polyethylene. The MESA Cornerstone segmental retaining wall units used for the tests referenced herein are dry cast concrete blocks. The standard unit is 18 inches wide at the front split face, 8 inches high, and 12 inches deep with a hollow core (all dimensions are nominal). Figure 1 shows the geometry of a standard unit. The testing program consisted of testing six different Tensar grids (MESA1, MESA2, MESA3, MESA4, MESA5, and MESA6) connected to standard MESA Cornerstone units. The tests were performed at normal loads between 35 and 14 lb/ft. A total of 6 tests were conducted for each grid type (with the exception of MESA3 for which 7 tests were performed) resulting in a total of 37 individual tests. 2. 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, with exception as described herein. The service state connection strength is not reported in the Summary of Test Results (Tables 1 through 6) nor is it summarized on the Connection Strength versus Normal Load Plots (Figures 4 through 9). The configuration of the test specimens for each connection strength test is shown in Figures 2 and 3 and is described from the bottom to the top of the test chamber as follows: Lower course of Mesa Cornerstone segmental units placed with the 18- inch nominal dimension parallel to the wall face (12 inch nominal dimension perpendicular to the wall face. 2

4 Gravel placed inside the unit cells and between the units to the top of the first course and compacted by rodding. The geogrid was placed on top of the gravel-filled 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 grid was placed such that the first transverse rib was positioned just to the inside surface of the faceshell of the back of the units (Figure 3). Second course of MESA Cornerstone segmental units placed on top of the gravel-filled first course and the installed geogrid. The second course was then filled with gravel both inside the unit cells and between the units. The gravel was then rodded to compact. 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. After application of the normal load, each geogrid specimen was subjected to a seating load, to remove slack from the sample, not to exceed 1% of the peak connection strength or 2 lb/ft, whichever is smaller. Each geogrid specimen was subjected to a pullout load by displacing the geogrid at a rate of 1% of the gage length per minute. 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. 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 force at.75 inches horizontal displacement, as measured at the back of the Mesa Cornerstone segmental unit, is defined as the connection force at this displacement. The results of each series of 6 tests are summarized in Tables 1 through 6 (MESA1 through MESA6 respectively). 3

5 TABLE 1 SUMMARY OF TEST RESULTS MESA Cornerstone Units with MESA1 Geogrid TEST NUMBER NORMAL LOAD (lb/ft) EQUIVALENT WALL HEIGHT (ft) PEAK CONNECTION STRENGTH (lb/ft) LIMIT STATE CONNECTION STRENGTH T cl (lb/ft) TABLE 2 SUMMARY OF TEST RESULTS MESA Cornerstone Units with MESA2 Geogrid TEST NUMBER NORMAL LOAD (lb/ft) EQUIVALENT WALL HEIGHT (ft) PEAK CONNECTION STRENGTH (lb/ft) LIMIT STATE CONNECTION STRENGTH T cl (lb/ft) TABLE 3 SUMMARY OF TEST RESULTS MESA Cornerstone Units with MESA3 Geogrid TEST NUMBER NORMAL LOAD (lb/ft) EQUIVALENT WALL HEIGHT (ft) PEAK CONNECTION STRENGTH (lb/ft) LIMIT STATE CONNECTION STRENGTH T cl (lb/ft)

6 TABLE 4 SUMMARY OF TEST RESULTS MESA Cornerstone Units with MESA4 Geogrid TEST NUMBER NORMAL LOAD (lb/ft) EQUIVALENT WALL HEIGHT (ft) PEAK CONNECTION STRENGTH (lb/ft) LIMIT STATE CONNECTION STRENGTH T cl (lb/ft) TABLE 5 SUMMARY OF TEST RESULTS MESA Cornerstone Units with MESA5 Geogrid TEST NUMBER NORMAL LOAD (lb/ft) EQUIVALENT WALL HEIGHT (ft) PEAK CONNECTION STRENGTH (lb/ft) LIMIT STATE CONNECTION STRENGTH T cl (lb/ft) TABLE 6 SUMMARY OF TEST RESULTS MESA Cornerstone Units with MESA6 Geogrid TEST NUMBER NORMAL LOAD (lb/ft) EQUIVALENT WALL HEIGHT (ft) PEAK CONNECTION STRENGTH (lb/ft) LIMIT STATE CONNECTION STRENGTH T cl (lb/ft)

7 4. 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 = long-term allowable connection strength T ultconn = ultimate connection strength determined in accordance with NCMA Test Method SRW U-1 FS cs = 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 = long-term connection strength based on serviceability T conn@3/4 = connection strength at 2 mm (3/4 inch) deformation The limit state connection strength of the connection is provided in Tables 1 through 6 for each different type of grid tested at each level of normal load. The serviceability connection strength has not been determined per the request of Tensar Earth Technologies. A plot of the peak connection strength verses applied normal is shown in Figures 4 through 9 for each different grid type respectively (MESA1 through MESA6). In addition, individual load deformation plots for each test can be found in Appendices A through F. 6

Normal Load Segmental Retaining Wall Connection Test Setup Figure 2

8 12 " Nominal 18 " Nominal Figure 1 MESA Cornerstone Segmental Retaining Wall Unit Geometry Cornerstone Unit with TENSAR MESA Grid Dual Ram Normal Load Segmental Retaining Wall Connection Test Setup Figure 2 Connection Strength Test Setup MESA Cornerstone SRW Unit with Tensar MESA Grid 7

9 Cornerstone Unit with TENSAR MESA Grid spacer grid grid test specimen (35.5 inches) spacer grid Segmental Retaining Wall Connection Test Setup - Grid Placement Figure 3 - Connection Strength Test Setup MESA Grid Placement 8

10 Peak Connection Strength (MESA1) 25 2 Connection Strength (lb/ft) y = x tan(λ cs ) + a cs λ cs = 47.2 o a cs = 562 (lb/ft) Normal Load (lb/ft) Figure 4 - Variation of Peak Connection Strength for MESA1 Grid 9

11 25 Peak Connection Strength (MESA2) 2 Connection Strength (lb/ft) y = x tan(λ cs ) + a cs λ cs = 44. a cs = 522 (lb/ft) Normal Load (lb/ft) Figure 5 - Variation of Peak Connection Strength for MESA2 Grid 1

12 Peak Connection Strength (MESA3) Connection Strength (lb/ft) y = x tan(λ cs ) + a cs λ cs = 38.5 o a cs = 765 (lb/ft) Normal Load (lb/ft) Figure 6 - Variation of Peak Connection Strength for MESA3 Grid 11

13 Peak Connection Strength (MESA4) Connection Strength (lb/ft) y = x tan(λ cs ) + a cs λ cs = 57.2 o a cs = 54 (lb/ft) Normal Load (lb/ft) Figure 7 - Variation of Peak Connection Strength for MESA4 Grid 12

14 Peak Connection Strength (MESA5) Connection Strength (lb/ft) y = x tan(λ cs ) + a cs λ cs = 55.3 o a cs = 85 (lb/ft) Normal Load (lb/ft) Figure 8 - Variation of Peak Connection Strength for MESA5 Grid 13

15 Peak Connection Strength (MESA6) Connection Strength (lb/ft) y = x tan(λ cs ) + a cs λ cs = 6.6 o a cs = 1118 (lb/ft) Normal Load (lb/ft) Figure 9 - Variation of Peak Connection Strength for MESA6 Grid 14

16 Appendix A Load Deformation Plots for Series MESA1

17 Transverse Load (lb/ft) Figure A-1 - Transverse Load Deformation Response (MESA1) Normal Load = 349 lb/ft Peak Load = 866 lb/ft A-1

18 16 Figure A-2 - Transverse Load Deformation Response (MESA1) Normal Load = 72 lb/ft 14 Peak Load = 135 lb/ft 12 Transverse Load (lb/ft) A-2

19 25 Figure A-3 - Transverse Load Deformation Response (MESA1) Normal Load = 155 lb/ft Transverse Load (lb/ft) Peak Load = 1933 lb/ft A-3

20 18 Figure A-4 - Transverse Load Deformation Response (MESA1) Normal Load = 148 lb/ft Peak Load = 169 lb/ft Transverse Load (lb/ft) A-4

21 18 16 Figure A-5 - Transverse Load Deformation Response (MESA1) Normal Load = 146 lb/ft Peak Load = 1618 lb/ft Transverse Load (lb/ft) A-5

22 Figure A-6 - Transverse Load Deformation Response (MESA1) Normal Load = 141 lb/ft 25 Transverse Load (lb/ft) Peak Load = 1954 lb/ft A-6

23 Appendix B Load Deformation Plots for Series MESA2

24 1 9 Figure B-1 - Transverse Load Deformation Response (MESA2) Normal Load = 347 lb/ft Peak Load = 92 lb/ft Transverse Load (lb/ft) B-1

25 14 Figure B-2 - Transverse Load Deformation Response (MESA2) Normal Load = 77 lb/ft Transverse Load (lb/ft) Peak Load = 115 lb/ft B-2

26 Figure B-3 - Transverse Load Deformation Response (MESA2) Normal Load = 152 lb/ft Transverse Load (lb/ft) Peak Load = 1568 lb/ft B-3

27 Figure B-4 - Transverse Load Deformation Response (MESA2) Normal Load = 155 lb/ft 16 Peak Load = 1498 lb/ft Transverse Load (lb/ft) B-4

28 Figure B-5 - Transverse Load Deformation Response (MESA2) Normal Load = 158 lb/ft Transverse Load (lb/ft) Peak Load = 1637 lb/ft B-5

29 Figure B-6 - Transverse Load Deformation Response (MESA2) Normal Load = 146 lb/ft 25 2 Peak Load = 1915 lb/ft Transverse Load (lb/ft) B-6

30 Appendix C Load Deformation Plots for Series MESA3

31 Figure C-1 - Transverse Load Deformation Response (MESA3) Normal Load = 367 lb/ft 12 1 Peak Load = 984 lb/ft Transverse Load (lb/ft) C-1

32 Figure C-2 - Transverse Load Deformation Response (MESA3) Normal Load = 378 lb/ft 1 9 Peak Load = 914 lb/ft 8 Transverse Load (lb/ft) C-2

33 Figure C-3 - Transverse Load Deformation Response (MESA3) Normal Load = 345 lb/ft 12 Peak Load = 1133 lb/ft 1 Transverse Load (lb/ft) C-3

34 Figure C-4 - Transverse Load Deformation Response (MESA3) Normal Load = 344 lb/ft Transverse Load (lb/ft) Peak Load = 131 lb/ft C-4

35 Figure C-5 - Transverse Load Deformation Response (MESA3) Normal Load = 713 lb/ft 16 Peak Load = 1474 lb/ft Transverse Load (lb/ft) C-5

36 Figure C-6 - Transverse Load Deformation Response (MESA3) Normal Load = 155 lb/ft Transverse Load (lb/ft) Peak Load = 1721 lb/ft C-6

37 Figure C-7 - Transverse Load Deformation Response (MESA3) Normal Load = 148 lb/ft Transverse Load (lb/ft) Peak Load = 1762 lb/ft C-7

38 Appendix D Load Deformation Plots for Series MESA4

39 12 Figure D-1 - Transverse Load Deformation Response (MESA4) Normal Load = 35 lb/ft Peak Load = 167 lb/ft Transverse Load (lb/ft) D-1

40 Transverse Load (lb/ft) Figure D-2 - Transverse Load Deformation Response (MESA4) Normal Load = 75 lb/ft Peak Load = 162 lb/ft D-2

41 25 Figure D-3 - Transverse Load Deformation Response (MESA4) Normal Load = 157 lb/ft Peak Load = 2165 lb/ft Transverse Load (lb/ft) D-3

42 25 Figure D-4 - Transverse Load Deformation Response (MESA4) Normal Load = 153 lb/ft Transverse Load (lb/ft) Peak Load = 1971 lb/ft D-4

43 25 Figure D-5 - Transverse Load Deformation Response (MESA4) Normal Load = 932 lb/ft Peak Load = 21 lb/ft Transverse Load (lb/ft) D-5

44 3 Figure D-6 - Transverse Load Deformation Response (MESA4) Normal Load = 145 lb/ft Peak Load = 2744 lb/ft Transverse Load (lb/ft) D-6

45 Appendix E Load Deformation Plots for Series MESA5

46 Transverse Load (lb/ft) Figure E-1 - Transverse Load Deformation Response (MESA5) Normal Load = 345 lb/ft Peak = 1237 lb/ft E-1

47 Transverse Load (lb/ft) Figure E-2 - Transverse Load Deformation Response (MESA5) Normal Load = 73 lb/ft Peak Load = 1953 lb/ft E-2

48 Transverse Load (lb/ft) Figure E-3 - Transverse Load Deformation Response (MESA5) Normal Load = 149 lb/ft Peak Load = 2219 lb/ft E-3

49 Transverse Load (lb/ft) Figure E-4 - Transverse Load Deformation Response (MESA5) Normal Load = 15 lb/ft Peak Load = 2227 lb/ft E-4

50 3 Figure E-5 - Transverse Load Deformation Response (MESA5) Normal Load = 15 lb/ft 25 Peak Load = 2444 lb/ft Transverse Load (lb/ft) E-5

51 3 Figure E-6 - Transverse Load Deformation Response (MESA5) Normal Load = 1395 lb/ft Transverse Load (lb/ft) Peak Load = 2817 lb/ft E-6

52 Appendix F Load Deformation Plots for Series MESA6

53 2 18 Figure F-1 - Transverse Load Deformation Response (MESA6) Normal Load = 359 lb/ft Peak Load = 186 lb/ft 16 Transverse Load (lb/ft) F-1

54 Transverse Load (lb/ft) Figure F-2 - Transverse Load Deformation Response (MESA6) Normal Load = 7 lb/ft Peak Load = 2347 lb/ft F-2

55 35 Figure F-3 - Transverse Load Deformation Response (MESA6) Normal Load = 152 lb/ft Peak Load = 2914 lb/ft Transverse Load (lb/ft) F-3

56 Transverse Load (lb/ft) Figure F-4 - Transverse Load Deformation Response (MESA6) Normal Load = 152 lb/ft Peak Load = 2741 lb/ft F-4

57 Transverse Load (lb/ft) Figure F-5 - Transverse Load Deformation Response (MESA6) Normal Load = 145 lb/ft Peak Load = 3154 lb/ft F-5

58 Transverse Load (lb/ft) Figure F-6 - Transverse Load Deformation Response (MESA6) Normal Load = 1399 lb/ft Peak Load = 3692 lb/ft F-6

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