EVALUATION OF THE GABI BLOCK SYSTEM FOR USE AS FREE-DRAINING SOIL RETAINING WALLS - SUBMISSION TO ROAD AND MARITIME SERVICES (RMS)

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1 EVALUATION OF THE GABI BLOCK SYSTEM FOR USE AS FREE-DRAINING SOIL RETAINING WALLS - SUBMISSION TO ROAD AND MARITIME SERVICES (RMS) Report Reference: EMS-RW AustRoads Subm - Final Prepared for Retaining Walls NSW Pty Ltd Stefan Bernard BEHons, PhD Head of Research Michael Van Koeverden BE, M.I.E Aust, CPEng, NPER Director Joanne Portella BEHons, BSc, MEngSc Specialist Engineering Consultant - Concrete November 2012 Daksh Baweja Michael van Koeverden Stefan Bernard M E M E M E

2 TABLE OF CONTENTS SUMMARY INTRODUCTION THE GABI BLOCK SYSTEM THE GABI CONCRETE MIX DESIGN, DENSITY AND STRENGTH TEST RESULTS CONCRETE DENSITY RESULT STRENGTH TESTING RESULTS APPLICATION EXAMPLES FEATURES AND BENEFITS TESTIMONY AND COMPARISON OF GABI BLOCKS WTH GABION BASKETS BY BELLINGEN SHIRE COUNCIL INVESTIGATION OF THE GABI BLOCK SYSTEM PERFORMANCE TESTING RESULTS DESIGN ASSUMPTIONS EXPERIMENTAL PROGRAM RESULTS AND DISCUSSION WATER INFILTRATION FRICTION BETWEEN BLOCKS FATIGUE CAPACITY PULL-OUT TESTS ON TENSAR CONCLUSIONS REGARDING PERFORMANCE TESTING APPENDIX 1 - DENSITY TEST RESULT APPENDIX 2 - COMPRESSION TEST RESULT APPENDIX 3 - FLEXURAL TEST RESULT APPENDIX 4 - INDIRECT TENSILE TEST RESULT APPENDIX 5 - TESTIMONY BY BELLINGEN CITY COUNCIL (BY DAVID FOWLER) APPENDIX 6 SOIL PRESSURE CALCULATIONS

3 SUMMARY Evaluation of the Gabi Block System - Retaining Walls NSW The Gabi Block retaining wall system (Gabi Block) is manufactured and distributed by Retaining Walls NSW Pty Ltd and provides an alternative to the traditional Rock filled Gabion Basket application. The report that follows here is the result of an investigation undertaken by Engineered Material Solutions (EMS) to assess the suitability of the Gabi Block System in soil retaining structures, specifically to assist Roads and Maritime Services (RMS) in providing in principal approval of the system for use in national road and bridge infrastructure. The Gabi Block system consists of precast concrete blocks which are dry-stacked and interlock, via a dedicated key joint mechanism, to form a pervious retaining wall structure. The Blocks are constructed using a special no-fines concrete mix which provides strength and a free-draining solution. From case study examples provided by Retaining Walls NSW, it can be seen that the Gabi Blocks offer an effective, attractive and convenient retaining wall solution. A testimony from the Bellingen Shire Council, who had been successfully using this system since 2010, provides strong endorsement for its use. The testimony indicates that the Gabi Block system compares favourably over Rock filled Gabion Baskets with respect to a number of aspects including: 35% saving on construction cost (per linear metre) construction time reduced by 50% ease of placement, with respect to labour and plant less traffic disruptions safer as no manual handling of rocks (gabion baskets are hand packed) Another important feature of the Gabi Blocks reported by Retaining Walls NSW is that given that they do not contain steel reinforcement or wire elements, they are resistant to the potentially detrimental effects of corrosion and fire. Gabi Blocks are lighter than conventional concrete, though they display good strength characteristics as summarised below: Table 1. Summary of Density and Strength Testing Results Test Result Australian Standard Test Method Density 2140kg/m 3 AS Compressive Strength 23.7MPa AS & 9 Flexural Strength 4.3MPa AS Indirect Tensile Strength 2.2MPa AS & 10 3

4 A detailed investigation was recently conducted by EMS to determine the potential suitability and performance characteristics of the Gabi Block system for use in soil retaining applications. The investigation involved two stages. Stage 1 focused on gaining a better appreciation of the system, its benefits and any potential concerns that would need to be addressed before the Gabi system could be used more extensively. It involved a number of discussions with independent design professionals and government authorities to fully understand what would be expected of the system in terms of design and application requirements. The most relevant of question and answers are summarised within this report. Stage 2 involved a detailed testing regime to determine performance characteristics and establish design data for the Gabi Block system. Stage 2 testing confirmed the following properties: The water permeability of the Blocks was very high, reported as 12.4m/hr (approx. ~8680 litres/hr). This high flow rate of water through the blocks is seen as a tremendous benefit as the build-up of moisture behind a soil retaining structure can significantly increase the in-service loads and influence the life of the structure. With no geogrid and the Blocks resting concrete on concrete, the friction coefficient was 0.75 (This indicates a high level of static friction which provide significant resistance to potential sliding of the blocks one surface relative to another). This sliding resistance together with the action of the keyway encourage the blocks to remain in position even if exposed to sudden or unexpected impact loading. With Tensar 520 Geogrid present between the Blocks, the friction coefficient averaged 0.45 (which is considered by the report authors to still provide significant static friction despite the presence of the geogrid material). Note: Consideration of the appropriate geogrid to be used within a soil layer should form part of the retaining structure design and it should be noted that the Tensar geogrid used in this research was not the strongest or stiffest available but was considered the most appropriate for the scale of testing undertaken. It is expected that higher loads may be developed in other grid materials. As demonstrated in this research it should also be highlighted that the Gabi block system easily incorporates the use of geogrid material and allows termination of the ends to develop higher tensile capacity in the soil layers. This overcomes the existing problem with other systems where the geogrid is folded up or down at its edges and as a result a loss of tensile capacity results within the soil layer at its edges. Fatigue testing of the concrete blocks confirmed the keyway remained visibly undamaged after 10,000 cycles. If each cycle represents a daily moisture / temperature differential, this equates to about a 30 year design loading with no apparent effect to the performance of the male or female keyway joint or Block surface under design loads. Note: Testing was ceased after 10,000 cycles, however the in-service design life of this system is expected to far exceed this 30 year life given the good condition of the blocks after this loading. 4

5 In pull-out tests undertaken on the TENSAR 520 Geogrid it was noted that the grid itself failed before being pulled out from between the individual Gabi Block units. Therefore the termination of the geogrid between the Blocks and across the keyway appears to provide adequate end fastening to develop tensile capacity in the geogrid. This potentially could resolve some of the end effects with geogrid soil layers that are not terminated correctly. Based on the available information, the test findings, the case studies and testimony all presented within this report, it is the opinion of the EMS authors that RMS should consider in principal approval of the Gabi Block System by Retaining Walls Pty Ltd for soil retaining walls and other related structures along Australian roadways as an alternative to the traditional Gabion Basket solution. 5

6 1 INTRODUCTION Evaluation of the Gabi Block System - Retaining Walls NSW Retaining Walls NSW Pty Ltd are designers and manufacturers of the patented Gabi Block retaining wall system. The system consists of precast concrete blocks that interlock to create a retaining structure. The blocks are constructed using a special no-fines concrete mix to provide a free-draining solution. The system provides an alternative to the traditional Rock filled Gabion Basket solution. Gabi Block (and Gabi Mat) solutions have been used in a number of applications including mass gravity walls, bridge abutments, stream channels, coastal protection, sea and canal walls, riverine walls, revetments, erosion prevention, landslip rehabilitation and wing walls. Figure 1. Typical roadside retaining wall application of the Gabi Block system Retaining Walls NSW engaged Engineered Material Solutions (EMS) to report on the suitability of their Gabi Block system to provide a strong, durable, free-draining retaining wall solution. This was undertaken with the view of obtaining in principal approval from AustRoads for the use of the Gabi Block system in soil retaining walls and other road related structures across Australia. This report provides a detailed description of the Gabi Block system and the benefits it has to offer while some of the queries relating to design and application requirements are considered and addressed. Test findings relating to the performance of the blocks when they are used to retain soil are presented, including permeability to water, load capacity in shear, coefficients of friction in shear, and fatigue resistance as tested by EMS in a previous investigation. This data provides useful design parameters and performance validation of the Block system. 6

7 Also provided is a testimony from Bellingen Shire Council who have been successfully using the Gabi Block system for a number of years and have identified numerous advantages over the use of Rock filled Gabion Baskets. 2 THE GABI BLOCK SYSTEM The Gabi Block system is manufactured and distributed by Retaining Walls NSW, an Australian owned Company and includes the Gabi Block and the Gabi Mat products (see The products are manufactured in fixed height and width of 1200mm and 600mm respectively and varying depths as described in Figure 2 below. Half Blocks and corner blocks are also available to suit design and application requirements. The Gabi Blocks range in weight from 1 tonne to 4 tonne and the Gabi Block system typically comes in a vertical wall arrangement as shown in Figures 2, though potentially, the Gabi products can be designed and tailor made to accommodate sites with alternative requirements. Figure 2. Typical Vertical Gabi Block arrangement 7

8 The Blocks are precast, dry-stacked and interlock via a key-joint mechanism as can be seen from the above arrangements. Construction of a Gabi Block retaining wall does not require mortar. In this way, the system is flexible, can tolerate some movement and settlement, as well as being fast and convenient. 2.1 The Gabi concrete mix design, density and strength test results The Gabi concrete mix is a patented no-fines concrete mix that enables the Gabi Blocks to be permeable enough to act as a drainage system. The concrete mix also incorporates polypropylene fibres for added strength. Figures 3 and 4 show the Gabi concrete mix and the free-draining capacity of the Blocks respectively. Figure 3. The Gabi no-fines concrete mix, incorporating polypropylene fibres 8

9 Figure 4. Demonstration of free-drainage capacity Concrete Density Result Concrete density (Mass per Unit Volume) was determined using the Rapid Measuring Method according to AS The test certificate is provided in Appendix 1. Two cores were taken and tested; the density result was 2140 kg/m 3 for both specimens. This is approximately 200kg/m 3 lighter than would be expected of a normal density concrete mix and 140 kg/m 3 heavier than the maximum density generally nominated for a light weight concrete Strength Testing Results The following concrete strength tests were undertaken: Compressive strength test, according to AS & 9 (conducted on core specimens) Flexural strength test (modulus of rupture), according to AS (conducted on saw cut specimens) Indirect Tensile Strength, according to AS & 10 (conducted on core specimens) Test certificates are included in Appendix 2-4 and test results were summarised and presented previously in Table 1. With regard to compression strength testing, the average result of 23.7MPa for the three cores is higher than what might be expected for a no-fines concrete, normally between 10 and 20MPa. In addition the two flexural strength (modulus of rupture) 9

10 results of 4.3MPa (beams cut from blocks) are reported here, are high and suggest a strong bond between the aggregate and paste in the concrete. The indirect tensile strength averaged at 2.3MPa for the two specimens tested and it correlates as expected with the compressive strength; indirect tensile strength is typically approximately 10% of the compressive strength (and 2.3MPa is approximately 10% of 23.7MPa). 2.2 Application Examples The following section shows examples of retaining wall applications of the Gabi Block System. More information regarding some of these projects and others is available from the Gabi System website (see Particular attention is drawn to Figure 7 which shows the use of the Gabi Block system to rehabilitate a section of a creek embankment which supports a 2 lane roadway above. The creek embankment had been repeatedly subject to flood waters and was severely scoured during the 2009 QLD floods. Gabion baskets were previously used to rehabilitate this particular site, however as observed by a representative of Retaining Walls NSW, on both occasions that they were used, they were literally washed away by the floods. Gabi Blocks were subsequently installed in 2011 and no issues have been reported since. Figure 5. Esk Duck Creek Bridge Abutment (for Esk Shire Council) 10

11 Figure 6. Bushby Creek Road Bridge (Richmond Valley Council) Figure 7. Gabi Block system used to rehabilitate a flood scoured creek enbankment. 11

12 Figure 8. Pottsville Holiday Park Foreshore, installed along the river edge Figure 9. Scenic Drive, Tweed Shire, Gabi Bock System under construction to rectify landslip 12

13 Figure 10. Coffs Harbour 2.3 Features and benefits As seen in the previous section, the Gabi Block products present many opportunities for application including bridge abutments and retaining structures along roadways. According to Retaining Walls NSW, in their experience the main benefits of using Gabi Blocks for retaining walls are identified as follows: As the blocks are highly permeable, this corresponds to a reduction in potential damage and/or collapse of the retaining structure due to improved drainage characteristics. Unlike Gabion Baskets, Gabi Blocks are not affected by fire. If a fire passes over Gabion's, the plastic or galvanised coating on the wires is likely to be removed and rust initiated. In some cases the baskets have been known to disintegrate, leaving a pile of rock. Gabi Blocks do not contain any wire elements and thus are not subject to such risk. Construction time is dramatically reduced especially on large retaining walls. Traditional systems use small blocks or bagged products (gravel, sand) which are relatively labour and time consuming in the construction process. 13

14 Efficient and safe handling, transport and installation. Large size blocks are able to be safely lifted into position leading to a dramatic reduction in construction time compared to traditional systems. Efficiency and time saving leads to cost savings Can be installed in difficult areas where access is limited and/or dangerous Gabi Blocks are replaceable and reusable Maintenance is envisaged to be minimal Corrosion of embedded steel reinforcement is not an issue (normally the most detrimental concrete problem) as no steel reinforcement is present within the Blocks. 3 TESTIMONY AND COMPARISON OF GABI BLOCKS WTH GABION BASKETS BY BELLINGEN SHIRE COUNCIL A testimony regarding successful use of the Gabi Blocks is provided in Appendix 5 from David Fowler, Manager of the Bellingen Shire Council- Works Section, who had been using the Gabi Block system since 2010 and was very supportive of its use in retaining wall construction. In particular the council had used the Gabi Block system for the repair of numerous land slip failures within their region which were repaired quickly and efficiently with this system. As users of both conventional Rock filled Gabion Basket system and the new Gabi Block technology comparisons were drawn between the construction and financial benefits of the two systems. As detailed in Appendix 5, David suggests that the Gabi Blocks compare very favourably over the Rock filled Gabion Baskets in a number of aspects. For an example retaining wall of 50 metres in length and 2 metres high adjacent to a 2 lane roadway, the following was deduced: 35% saving in construction cost; Gabion Baskets cost approximately $1840/metre, Gabi Block system approximately $1200/metre construction time reduced by 50% flexible design (particularly with respect to bends in wall) ease of placement, with respect to labour and plant no need to stockpile or double handle aggregates less traffic disruptions due to reduced plant movements Better Workplace safety as there is no manual handling of rocks required (gabion baskets are hand packed) and also, the issue of aggregate loaded plant buckets coming in close vicinity to labourers packing the baskets is avoided. 14

15 Also included here are some photos supplied by Bellingen Shire Council- Works Section showing examples where the Gabi Block system has been successfully used to replace traditional gabion baskets. Figure 11. Kalang Rd 15

16 Figure 12. Billings Rd Dorrigo Figure 13. Waterfall Way Bellingen 16

17 4 INVESTIGATION OF THE GABI BLOCK SYSTEM A detailed investigation was recently conducted by EMS to determine the potential suitability and performance characteristics of the Gabi Block system for use as a soil retaining system(i). The investigation involved two stages. Stage 1 focused on gaining a better appreciation of the system, its benefits and any potential concerns. It involved a number of discussions with independent design professionals and government authorities to fully understand what would be expected of the system in terms of design and application requirements. The most relevant of question and answers are summarised in Table 2. Stage 2 involved a detailed testing regime to determine performance characteristics and establish design data for the Gabi Block system. Stage 2 was able to provide important data and information about the performance of the blocks with regard to permeability to water, load capacity in shear, coefficients of friction in shear, and fatigue resistance when these blocks are used to retain soil. The experimental program and results are presented in section 5 of this report. Table 2. Design and Application Requirements: Questions and Answers. Design and Application Requirements Q: What is the permeability of the Gabi block (pervious) blocks? A: The water infiltration of the blocks was measured to ASTM C1701 and confirmed to be 14.7seconds on average across the block tested, at a flow rate of 12.4 m/hr, under a very low 50mm head of water. This equates to approximately 8.68m 3 /hr or 8680litres/hr. This is a very high rate of infiltration and indicates the very high permeability of the pervious concrete used in the present blocks. Note: Pervious concrete is very well developed in the USA and there are numerous ASTM standards for the testing of this material. ACI and ASTM sub-committee C9.49 has information on test methods. Pervious concrete is not new, it has been around for 20 years and a lot of research data is available on what minimum levels of permeability are required to avoid clogging and it is unlikely that clogging will occur in the Gabi block system due to this high flow-rate of water infiltration. Q: How can the permeability over time be assured? A: The use of a suitable geotextile below and behind the wall, a suitably granular backfill and clay-free secondary fill. When used in combination with a geotextile, pervious concrete slabs on grade have demonstrated very good performance if the permeability and voids ratio exceed a certain level. Making sure that potential clogging material is not close to the wall, and the use of geotextiles, has been shown to work in slabs on grade which are subject to greater pumping action than a vertical wall. Given the very high water infiltration rates of the Gabi Block system is unlikely that clogging of the concrete will be an issue if construction of the wall follows the manufacturers recommendations. 17

18 Q: Is the cementitious paste within the no fines concrete sound and resistant to soil chemicals? A: The pervious blocks are unreinforced other than polyfibres and galvanized lifting inserts. Carbonation or sorptivity are not expected to be an issue with the pervious concrete as it is unreinforced and fast fluid transfer is likely due to the very high permeability of the blocks. The presence of any chlorides within the concrete is also not seen as an issue, due to the absence of embedded steel reinforcement, and may assist in the acceleration of the binder hydration rate and subsequent development of the aggregate / paste bond strength at the point-to-point contact regions. To address the issues of acid or sulfate attack on the concrete mix the cementitious binder is to comply with relevant standards including AS3972 and AS3582. Sulfate resisting requirements and low ph acid/sulfate soil conditions should be addressed in line with relevant existing guides and specifications. Q: How does the lightweight nature of the blocks affect the mass retaining effect of the retaining structure A: The weight of the individual blocks within the Gabi Block system should be taken into consideration when designing a specific retaining wall solution. The manufacturer has validated the system with independent Chartered Professional Engineers and has many examples of structural applications where these blocks are in use and performing well. Note: The Gabi Block system is modular and each individual Block is locked into place via a dedicated keyway and can be stacked on top another as required as part of a structural solution. Q: If something crashes into the wall can it be fixed? A: Due to the independent nature of each Gabi Block in the interlocking retaining wall they are easily lifted (embedded lifting inserts are present) and removed should damage occur due to collision or otherwise. Retaining walls NSW have cited projects where they have removed blocks temporarily to assist in running of services etc and re-instated the same blocks back within the wall upon completion. 5 PERFORMANCE TESTING RESULTS 5.1 Design Assumptions Since there are a very large number of possible design permutations, and the performance of the blocks is likely to change as a result of changes in design, a few assumptions have been made to allow representative laboratory testing to be undertaken that reflects the likely design of retaining walls incorporating these 18

19 blocks. It was assumed that the blocks are stacked two high and are subject to a lateral force resulting from soil pressure. It has been assumed that the soil pressure will vary with moisture content, and thus resistance to a varying load has been assessed. The soil pressure loads for the subsequent testing of the blocks was determined by independent structural engineers Northrop Engineers and are summarised here and included in full as Appendix 6 of this report. Case 1: Assuming Soil backfill as Sandy Gravel to Stiff Clay (with Cohesion), the active pressure on the wall P a = kN/m wall Case 2: Assuming Soil backfill as Cohesion less, the active pressure on the wall P a = 35.2kN/m wall 5.2 Experimental Program Several tests were performed on the pervious concrete blocks provided by Retaining Walls NSW Pty Ltd. These included permeability to water as measured using ASTM C1701, friction in response to a shearing force both longitudinally and perpendicular to a wall, and fatigue resistance under a sinusoidal shearing force. Further testing was also undertaken incorporating a commercially available polypropylene geogrid (Tensar 520) which is used in soil applications to provide additional tensile capacity to a soil layer. This geo-grid material was placed between the two Gabi-blocks under test and any changes in frictional and fatigue properties of the blocks were recorded when the Tensar 520 is in place straddling the Gabi Block keyway. A perpendicular pull-out test on a sample of Tensar 520 was also conducted to estimate the likely load to dislodge this in-service. 5.3 RESULTS AND DISCUSSION Water Infiltration The water permeability of pervious concrete is related to the rate at which water can infiltrate into the surface of these blocks. Water is expected to originate from within the soil being retained by the blocks. Water infiltration tests in accordance with ASTM C1701 were therefore conducted with two blocks resting on their sides to simulate lateral transmission of water from the soil into a block. This test involves the placement of a 300 mm diameter ring at least 50 mm in height on the surface of the block. Plasticine was used to produce an impervious boundary between the base of the ring and the surface of the block. Water was then poured in at a constant rate and the time taken for the water to penetrate into the Block and 19

20 disappear from the surface was recorded. In this way the permeability of the pervious Block is estimated under a very small 50mm water head pressure. The above tests were conducted at four separate locations on the surface of the blocks to determine an average Infiltration rate. Two tests were carried out at each location, and the results are listed in Table 1. The mean time for infiltration was 14.7 seconds. Using the measured diameter of the container, the infiltration rate I was determined, using Section 9 of ASTM C1701, to be 12.4 m/hr. As the blocks were tested on their side the surface open to infiltration is approximately 1.2m x 0.6m = 0.7m m/hr x 0.7 m 2 = 8.68m 3 /hr (~8680 litres/hr) This is a very high rate of infiltration and indicates the very high permeability of the pervious concrete used in the present blocks. Location Time for Infiltration (s) Mean 14.7 seconds Table 3. Time to infiltrate surface of pervious blocks by ASTM C1701, seconds Friction Between Blocks The principal force likely to be applied to these pervious blocks in a retaining wall application is a lateral force that induces a shear stress at the boundary between stacked blocks. A test method involving bi-axial force application was therefore developed to obtain the coefficient of friction for one Block sliding relative to an underlying Block in response to a lateral force. Tests were conducted both for the case of a Block resting directly on another Block, and for one Block resting on another with Tensar 520 geogrid placed in between. In addition, these tests were repeated for both loading in the longitudinal and perpendicular directions. In all tests a surcharge of 8 kn was applied to the upper surface of the mobile Block to simulate the presence of an additional block, (800kg). A schematic representation of the test configuration is shown in Figure 14, and photographs of the tests are shown in Figure

21 a) b) Figure 14. Elevation of friction test set up in which a mobile Block is displaced: a) longitudinally relative to a lower restrained block, or b) perpendicularly relative to the restrained block. Note: The restrained Block has a reduced height in order to fit in the test rig and avoid roll-over. The lateral force was applied using a hydraulic actuator under displacement control at a rate of 1.0 mm/min. The displacement of the mobile Block was measured relative to the restrained Block using a 5 mm LVDT with a precision of mm. a) b) Figure 15. The friction test set up in which a mobile Block is displaced: a) longitudinally relative to a lower restrained block, or b) perpendicularly relative to the restrained block. 21

22 Figure 16. Friction coefficient for longitudinal friction tests on blocks with and without Tensar 520 Geogrid in place. Total normal load on geogrid was 16 kn (1600kg) including 8 kn (800kg) surcharge. Figure 17. Friction coefficient for perpendicular friction tests on blocks with and without Tensar 520 Geogrid in place. Total normal load on geogrid was 16 kn (1600kg). Tests were conducted in two parts; plot represents movement of upper Block relative to lower block. The tests were stopped at 75 kn (7500kg) due to the risk that the blocks and foundations might break rendering them unavailable for the subsequent fatigue tests. The friction coefficient for the longitudinal friction tests depended on the presence of the Tensar 520. With the Tensar 520 present between the blocks, the friction coefficient averaged 0.45 (Figure 17). When the blocks were tested with concrete resting on concrete the friction coefficient was When the blocks were tested in a perpendicular configuration (Figure 15b) the presence of the Tensar 520 did not alter the total load resistance during the test but changed the compliance of the boundary (Figure 18). It is believed that the concrete-on-concrete test appeared softer than when Tensar 520 was included between the blocks because of crushing of aggregate fragments at the boundary. Both tests were stopped at 75 kn 22

23 (7500kg) because of concern that the restraining Block would break if the test proceeded any further. This was undesirable because these same blocks were required for the fatigue tests. This load capacity also appeared to be well in excess of the loads likely to be encountered in practice Fatigue Capacity A fluctuation in moisture content within the retained soil will lead to possible swelling and contraction of the soil mass or a change in the pressure applied by the soil to the retaining wall. A series of tests were therefore undertaken to determine whether the wall elements can withstand cyclic loading associated with a change in moisture content. The test configuration was the same as used for the perpendicular friction test shown in Figure 14b). The load was applied as a sinusoidal cyclic load with a minimum magnitude of 5 kn (500kg) and a maximum magnitude of 43 kn (4300kg). A total of 10,000 cycles of load were applied after which the wearing surface was inspected for damage. Two tests were conducted, the first included Tensar 520 geogrid between the blocks, while the second involved one Block placed directly over another with no geotextile in between. a) b) Figure 18. Fatigue Testing Results a) Fatigue tests on Block with geogrid present between blocks. Graph shows upper and lower loads sustained on every fifth cycle, the maximum load was 43 kn (4300kg) and minimum was 5kN (500kg). The test started on the right and the Block progressively bedded in as it moved to the left. The boundary between the blocks was much softer than for the concrete-on-concrete test because of the high compliance of the Tensar 520 geogrid. b) Fatigue tests on Block with no geogrid present between blocks. There was no apparent damage to the Block by the end of the test. The results of the tests indicated that the keyway between the blocks could withstand 10,000 cycles of the full design load of 43 kn (4300kg) without damage. This was true both with and without the Tensar 520 present at the boundary. Inspection of the key and geogrid indicated that no damage was evident to either suggesting that the fatigue capacity of the wall system was very large. 23

24 5.3.4 Pull-out Tests on Tensar 520 One issue of importance in the design of retaining walls with reinforced earth behind the wall is the capacity of the geogrid anchorage within the wall and the mode of failure of that connection when stressed in tension. Two pull-out tests were therefore undertaken to determine the tensile load capacity of the Tensar 520 when pulled out from between two blocks. The upper Block had a surcharge of 8 kn (800kg) placed on it under load control. The tests resulted in tensile failure of the polypropylene strands; the load deflection curves for these tests are shown in Figure 20. The load resistance reached a plateau at about kn (1630kg to 1690kg) for a 600 mm wide strip as the strands stretched to breaking point. This represents an ultimate load capacity of 26.5 kn/m (2650)kg/m width). The geogrid failed through a ductile mode in which individual strands progressively ruptured leading to a wide plateau in load capacity. The Tensar 520 was quite compliant in loading with a rigidity of 0.6 kn/mm.m. (60 kg/mm.m) a) b) Figure 19. Pull-out Test a) Photograph of pull-out test in progress b) Tensar 520 after completion of the test showing ruptured strands of polypropylene. It was noticed during the Tensar 520 geo-grid pull-out tests that the overlying Block rose up relative to the lower block, possibly as the strands between them tightened. In addition, the strands hanging out from the front of the Block boundary pulled in to the space between the two blocks. It is suggested that some means be found to secure the Tensar geogrid more securely between the blocks so that it is prevented from pulling out should a significant horizontal force arise in the geogrid. The present tests were undertaken over a period of about 20 minutes. Slower loading of the geogrid may possibly lead to creep rupture of the strands between the blocks. 24

25 Figure 20. Pull-out tests on a 600 mm wide strip of Tensar Conclusions regarding performance testing A number of experiments were performed on pervious concrete blocks to generate engineering data on the performance of these blocks when used in a retaining wall application. The tests have shown that the water infiltration rate for these blocks is very high thereby providing a large margin of safety over the possibility of clogging should soil enter into the permeable voids between the aggregate particles in these blocks. The mechanical tests demonstrated that the coefficient of friction for concrete sliding over concrete along the longitudinal direction is about When Tensar 520 geogrid is placed between the blocks, the coefficient of friction is reduced to about When loads are imposed perpendicular to the keyway between the blocks, the coefficient of friction effectively exceeds 4. The key between the blocks is capable of resisting a perpendicular shear force of 75 kn (7500kg) per block. When the blocks are stacked two high, the fatigue capacity of the blocks has been found to equal at least 10,000 cycles of load at 100% of the design lateral load of 43 kn/block (4300kg/block). It is also expected to resist many more cycles than tested. In conclusion, it is the opinion of the report authors that the Gabi Block system provides a free-draining retaining wall system that has a significant frictional capacity between individual blocks in both the transverse and longitudinal directions. After 10,000 cycles of loading the fatigue resistance of the blocks appears sound and likely to provide a long design life in service when designed and installed as per recommendations. In addition it would appear that where the use of a Tensar geogrid is required to enhance soil tensile capacity the termination of the geogrid between the blocks, straddling the keyway, will provide significant tensile capacity to the grid before likely pull-out failure. It should be noted however from the above that the presence of the geogrid between individual blocks will reduce the friction coefficient at the interface by approximately 40% and should be considered in relevant design calculations. 25

26 APPENDIX 1 - DENSITY TEST RESULT 26

27 APPENDIX 2 - COMPRESSION TEST RESULT 27

28 APPENDIX 3 - FLEXURAL TEST RESULT 28

29 APPENDIX 4 - INDIRECT TENSILE TEST RESULT 29

30 APPENDIX 5 - TESTIMONY BY BELLINGEN CITY COUNCIL (BY DAVID FOWLER) 30

31 APPENDIX 5 (CONTINUED) 31

32 APPENDIX 6 SOIL PRESSURE CALCULATIONS 32

33 APPENDIX 6 (CONTINUED) 33

34 REFERENCES i Bernard, S. and van Koeverden M., "Mechanical Performance of the Gabi Block Pervious Concrete System - produced by Retaining Walls NSW Pty Ltd", EMS, Report Reference EMS-RW-July12. 34