Retaining Walls, Roads and Erosion Control Systems Constructed from Recycled Tyres

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, Ecoflex has the expertise to efficiently build these systems.

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.

Gravity Retaining Wall

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 wit h 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.

When completed, the wall in Figure 1 will have a height of about 20 ft. A completed wall with shotcrete facing is shown in Figure 2.

E Wall System Design

E Wall Systems can be designed in accordance with typical U.S. practices and 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.

E Wall System at Kembla Grange

Figure 1. E Wall System at Kembla Grange

Split E Wall System with shotcrete facing

Figure 2. Split E Wall System with shotcrete facing

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.

Engineering Benefits

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 semi-trailers.

Energy Australia has constructed an access road as part of an 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 Figure 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 6. Although rutting was observed, the road was performing its intended function.

Completed Ecoflex E Pave - Energy Australia Project

Figure 3. Completed Ecoflex E Pave - Energy Australia Project

Ecoflex E Pave through swamp for Energy Australia Project

Figure 4. Ecoflex E Pave through swamp for 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 5ft/sec. The performance of each variation of the system was satisfactory. The stone size used for infilling should be appropriate for the anticipated velocities.

The Newstan coal mine has a stone-filled E Rosion Control System. The project had been in place for approximately 14 months at the time of the photographs in Figures 7 and 8. The E Rosion Control System appeared to be performing its intended function of scour protection. 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.

E Rosion Control System at Newstan Mine -Scour Protection Mats & Drainage Channels

Figure 5. E Rosion Control System at Newstan Mine -Scour Protection Mats & Drainage Channels

E Rosion Control System at Blandford - Scour Protection Mats & E Wall

Figure 6. E Rosion Control System at Blandford - Scour Protection Mats & E Wall

Environmental Considerations

The potential effect of Ecoflex Units on ground and surface water have been considered. Studies considering 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, 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 a case-by-case basis for environmental compatibility.

This information has been sourced, reviewed and adapted from materials provided by Ecoflex International.

For more information on this source, please visit Ecoflex International.

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