The most critical variable in potential failure of an ACB system is block protrusion (when one block sticks up relative to another in the direction of flow). Enviroflex® eliminates block protrusion with a vertically overlapping edge that locks the blocks together. Enviroflex® is also tapered at the block interface and holes to eliminate any sharp edges. Most other horizontally interlocking blocks, especially when installed in large mats, have significant gaps between blocks that result in no interlock and the blocks are free to move up and down relative to each other. Even a tightly spaced horizontally interlocking block has the ability to move up and down relative to other blocks.
No. All systems are flume tested without the use of cables or connection devices. Enviroflex® does not need to have all the blocks cabled together because the vertical interlock eliminates the ability to remove one block from a matrix. Enviroflex® is a palletized product that is either placed with a grappling machine or by hand. In other systems, cables are mostly used for installation of large mats and to keep the blocks together due to lack of interlock. In case of terminal ends or sections butting up to existing or proposed structures, Enviroflex® is cast with holes to allow for cables or pins to tie off into a closure pour of concrete.
Generally, an experienced, licensed general engineering contractor can easily install Enviroflex®. Further, a contractor with experience in fine grading and construction of revetment systems is best suited.
Enviroflex® is fiber reinforced to add tensile strength to the block for driving, impacts from large debris, and to hold the block together in cases of minor cracks. Fiber Reinforcement also adds a greater resistance to abrasion and wear.
The thickness of Enviroflex® is chosen based on shear stress and velocity. A thicker block has a higher critical shear stress. Other considerations include vehicle traffic, loading, etc.
A drainage layer (ie. 4″ layer of crushed rock) is very economical and will greatly improve the performance of the system a channel environment. Testing in the lab and field has proven much higher critical values with a drainage layer. The drainage layer relieves pressures from ground water pumping and provides a relief between the filter fabric and ACB.
Enviroflex® has an opening of 21.5% and dictates the permeability of the product itself. The permeability of the system will depend on other factors such as slope of installation, infill in the product, drainage layer, filter fabric, and the sub grade.
Generally, woven geotextiles are preferred over non-woven geotextiles because of their high hydraulic conductivity and durability. However, in all cases, the soil’s particle size, disbursement and cohesiveness (among other factors) will determine fabric selection. In general, if a fabric exhibits too tight of a weave (or clogs up) sub-structural hydrostatic pressure will build up and force the blocks up. If the fabric weave is too loose, soil particles will migrate up and through the ACBs causing sub-structural erosion and consequential ACB failure. Mirafi and other manufacturers offer guides for geotextile selection.
Yes. The vertical interlocking feature makes Enviroflex® a one-directional block. This means the block has to be installed in a certain direction relative to upstream and downstream. Enviroflex® is typically installed in a diagonal pattern with the longest axis across the block in the direction of flow. However, depending on design needs, it can be placed +/- 45 degrees from the longest axis.
In cases where you transition from an ACB to existing ground, concrete cut off walls are common. A minimum section of 6″ is left between the ACB and the cut off wall to allow for a cable connection and closure pour of concrete between the two. In cases where you transition from solid concrete to an ACB, eyebolts are often drilled or cast into the concrete and the ACB is cabled to the structure and finished off with a closure pour. The closure pour should be reinforced with rebar or fiber and be of similar concrete strength as the ACB (ie. two inches of grout is not a good solution). See our typical details for more information.
We recommend a maximum of a 2:1 slope. In steeper applications there is risk of the product becoming undermined and the application may be best suited for a retaining wall. For steeper applications, seek help from a qualified soils engineer.
Yes, when the block, filter fabric, base, and sub grade have been designed for the proposed frequency and load to be supported. In wet conditions, the ACB section must also be analyzed for pore pressure development and potential for loss of fines in the subgrade or sub-base.
In cases where the upstream area of the ACB will carry sediment onto the installation you may choose to have the cells naturally fill in with soil. Other times, depending on project needs the product may be filled in with crushed rock or soil. Planting can be done with seeding or hand planting depending on project needs.