Dana N. Humphrey, Ph.D., P.E. Consulting Engineer

Transcription

1 Dana N. Humphrey, Ph.D., P.E. Consulting Engineer November 19, 2004 Mr. Garry Callinan Ecoflex Australia Pty Ltd Annie Street Wickham NSW 2293 Australia RE: Technical review of E Wall, E Pave, and E Rosion Control Systems Dear Mr. Callinan: At your request I have performed a technical review of the Ecoflex E Wall, E Pave, and E Rosion Control Systems. This review included: a site visit to view installations in Australia on September 28 through October 3, 2004, a review of technical information provided by Ecoflex, and a comparison to typical United States design practices. The site visit included visiting several completed E Wall projects, one E Wall project that was under construction, one E Pave project that was under construction, one completed E Pave project, and one completed E Rosion Control project. The core of the Ecoflex systems is a tire with one sidewall removed. This is termed an Ecoflex Unit. In most applications the Ecoflex unit is filled with crushed stone or recycled concrete aggregate. The Ecoflex systems were developed by Ecoflex Australia Pty Ltd, which holds patents on the systems. Ecoflex has compiled an array of documentation regarding the systems and has engaged consultants to evaluate several aspects of the systems. Moreover, I observed that Ecoflex has the expertise to efficiently build these systems. My evaluation of the individual systems is given in the following sections. E Wall System The E Wall System consists of Ecoflex Units filled with stone or recycled concrete aggregate with a nominal size of about 3 in. In some cases the units are faced with shotcrete, pressure treated wood, or sheet metal panels. The E Wall System is analyzed as a gravity retaining wall using conventional geotechnical principles. It is possible to obtain adequate factors of safety against overturning, sliding, bearing capacity, and internal stability for a range of foundation, backfill soil, and surcharge conditions. Ecoflex has developed software to assist with stability analyses of the E Wall System. Moreover, a 9-ft high test wall with a 1H:5V batter was subjected to a surcharge of 1,740 psf and remained stable with lateral deflections slightly greater than 2 in.

2 I had the opportunity to visit an E Wall System that was under construction. When completed, this wall will have a height of about 20 ft. A completed wall with shotcrete facing is shown in Figure 1. Overall, I conclude that E Wall Systems can be designed in accordance with typical U.S. practices. Moreover, it is my opinion that the E Wall System is a relatively mature technology as evidenced by a large number of successful field installations in addition to useful design aids. In areas that experience frost penetration in excess of 2 ft a facing system that can tolerate differential movement should be used. Alternately, in some installations it may be possible to have no external face. For cases when the E Wall System is founded on compressible soils, the inherent tolerance of the E Wall System for differential movement would be an important advantage. For this case, the facing system should be chosen with due consideration to expected movements. Figure 1. E Wall with shotcrete facing Page 2

3 E Pave System The E Pave System typically consists of one or two layers of Ecoflex Units with the interior cavities filled with stone or recycled concrete aggregate with a size range of ¾ to 3 in. (typical). In many cases a separation geotextile is placed on the original ground surface prior to placing the Ecoflex Units. Typical applications involve construction of access roads and parking lots over weak subgrade soils. In concept, the E Pave Units used in this application provides two primary engineering benefits. First, the relatively large contact area of the tire side wall with the subgrade soil would reduce the contact stresses with subgrade soil and increase the resistance of the road to bearing capacity failure. Second, the confinement provided by the units would be expected to increase the stiffness of the contained aggregate. This limits rutting within the aggregate layer and aids in distribution of the applied wheel load to the underlying subgrade soil. Verification of the performance of the E Pave System is largely based on observation of field installations. Ecoflex provided documentation that the system had been used successfully for access roads and parking areas constructed on soft ground applications. The units have performed successfully when subjected to repeated loadings with loaded tandem axle dump trucks and semitrailers. When in Australia, I observed construction of an access road that was part of an Energy Australia power line construction project. The road cross section consisted of a single layer of Ecoflex Units placed on a layer of geotextile. The road was constructed directly on the underlying vegetation. Construction of the road is illustrated in Figures 2 and 3. The primary loading was the truck traffic required to construct the road. A section of the road that had been subjected to frequent applications of loaded semitrailers is shown in Figure 4. Although rutting was observed, the road was performing its intended function. Overall, I conclude that the E Pave System is a promising technology for construction of roads on weak subgrade soils. To enhance application of this system, I suggest that engineering guidelines be developed to aid in selection of one and two layer E Pave systems as a function of subgrade strength, anticipated traffic loading, and allowable rut depths. Page 3

4 Figure 2. Ecoflex Units placed on a layer of geotextile for the Energy Australia project Figure 3. Ecoflex Units filled with aggregate for the Energy Australia project Page 4

5 Figure 4. Performance of Ecoflex Units for the Energy Australia project E Rosion Control System There are several variations of the E Rosion Control System that can be used as scour protection in ditches and swales, and as aprons the outlet of large size culverts. The variations include: Ecoflex units filled with 3 to 6 in. crushed stone or recycled concrete aggregate; in some cases the surface of the units are covered by wire mesh. Medium weight batter protection units consisting of three Ecoflex Units bolted together using tire tread; void within tire filled with tire side walls strapped together with UV resistant nylon strapping and coiled tire tread. Lightweight batter protection units consisting of overlapping elements of tire wall, interwoven with recycled conveyor belt strap, bolted to the end tire units. These designs were subjected to flow tests by the MacKay Hydraulic Laboratory at the University of Queensland (Chapman, 1999). Flow velocities ranged from 2 to 5 ft/sec. The performance of each variation of the system was satisfactory. The stone size used for infilling should be appropriate for the anticipated velocities. Page 5

6 I observed a stone-filled E Rosion Control System at the Newstan coal mine. The project had been in place for approximately 14 months at the time of my visit. Photographs of the installation are shown in Figures 7 and 8. The E Rosion Control System appeared to be performing its intended function of scour protection. Overall, I conclude that properly designed and installed E Rosion Control Systems can be used for erosion protection in swales and scour protection at the outlets of culverts and bridge structures. Stone size should be elected as appropriate for anticipated flow velocities. Figure 5. E Rosion Control System at Newstan Mine Page 6

7 Figure 6. Close up of E Rosion Control System at the Newstan Mine project Environmental Considerations I have considered the potential effect of Ecoflex Units on ground and surface water. The studies I conducted of 3-in. size tire derived aggregate (TDA; tire shreds) placed both above and below the water table (Humphrey and Katz, 2000, 2001) indicated that TDA releases negligible levels of metals that have a primary (health based) drinking water standard and low levels of manganese, iron, and in some cases zinc, which have secondary (non-health based) drinking water standards. Release of organic compounds was found to be negligible. Given that the release of metals is associated primarily with steel belts exposed on the cut edges of the TDA pieces and that Ecoflex Units have no exposed steel belts and a smaller overall surface area compared to TDA, Ecoflex Units would be expected to have an effect on water quality that is even lower than that of TDA. As such, it is my opinion that Ecoflex Units will have a negligible effect on water quality when used in locations with near neutral ph. Applications where the Ecoflex Units would be subjected to either highly acidic or basic conditions should be evaluated on case-by-case basis for environmental compatibility. Page 7

8 Closure Based on a site visit, review of information provided by Ecoflex, and my evaluation of the system, I conclude that the E Wall, E Pave, and E Rosion Control Systems can be designed in accordance with typical U.S. design practice. Designs for specific projects should be performed by a registered professional engineer. I look forward continuing to work with Ecoflex to implement your technology in the United States. Please contact me if I can provide any additional information. Sincerely, Dana N. Humphrey, Ph.D., P.E. Consulting Engineer REFERENCES Humphrey, D.N., and Katz, L.E. (2000), Five-Year Field Study of the Effect of Tire shreds Placed Above the Water Table on Groundwater Quality, Transportation Research Record No. 1714, Transportation Research Board, Washington, D.C., pp Humphrey, D.N., and Katz, L.E. (2001), Field Study of the Water Quality Effects of Tire Shreds Placed Below the Water Table, Proceedings of the International Conference on Beneficial Use of Recycled Materials in Transportation Applications, November 13, Arlington, VA. Page 8