Panel Placement
Establish Starting Point & Alignment Lines
- It is custom to work from upstream to downstream
- Prevents construction flows from undermining or bunching fabric
- String lines are set both parallel and perpendicular to the slope in an offset manner
Placement of first fabric panel
- Panels are identified for placement according to fabrication drawings
- Panels are accordion folded and then rolled
- Panels should be extended into position by pulling the leading side of the panel
- Panels should be placed loosely, and extra form contraction should be gathered into temporary tucks at each seam and the top of the slope
Placement of remaining fabric panels
- If panels are sewn together in the field, the succeeding panel is placed atop the last mil width
- Panels are then joined together edge-to-edge by sewing the top layers and bottom layers independently
- If panels are joined together with pre-installed zippers, the succeeding panel is placed adjacent to the last mil width
Fine Aggregate Pumping
- Fine aggregate concrete is pumped into the forms by inserting a 2” Ø grout hose through a small slit in the top layer of fabric
- In order to control the position and prevent sliding, concrete is either pumped into the portion of the panel that has been placed into the anchor trench or is secured with sandbags
- A tight seal is made by wrapping non-woven fabric around the pipe, as well as closing the slit once pumping has discontinued
- The first section of the panel is left unpumped to prevent fabric from sliding into the flank trench
- Starting in the second section, the injection pipe should be inserted inside the first baffle and at a distance from the toe as determined by slope angle and fabric type
- The flow of concrete should always be directed toward the toe of the slope
- The spacing of injection ports is also determined by slope angle and fabric type
- As the fabric is being pumped, the panel will contract, causing a tightening of the form
- As one baffled section is fully inflated, the contractor will repeat these steps along the alignment of the plans until the entire lining has been pumped
- Each individual baffle sewn into the fabric form will act as a cold joint, allowing the contractor to control the workflow
- Once concrete has cured (approximately 24 hours), toe and flank trenches can be backfilled and compacted
Mix-Design
Typical Range of Mix Proportions
| Cement | 750–850 | 810–920 |
| Sand | 2030–2120 | 2195–2290 |
| Water | 485–555 | |
| Fly Ash | Up to 25% of Cement |
Fabric-formed fine aggregate concrete possesses superior physical properties. The compressive strength of fine aggregate concrete pumped into fabric forms is typically 1.5 to 1.75 times greater than companion samples taken from conventional concrete test cylinders. In addition, the fine aggregate concrete has less than 5% water absorption. This, combined with a "case-hardening" effect, produces a concrete that is abrasion resistant, durable under freeze-thaw action, resistant to "breakup caused by thermal cracking, highly impermeable, and resistant to acid, alkali salt, organic solvents, biological organisms and petrochemicals and permits FFC revetments to be constructed without reinforcement steel.
Installation Tips
- Always maintain appropriate slack throughout the fabric to prevent fabric stretching, pinching, over-stressing, and non-uniform thicknesses
- Average pumping speed is 15 yd3/hour
- Standard pumping distance from worksite is 500 linear feet, with as much as 2,500 linear feet possible with sufficient pump(s) set-up
- Concrete line pumps are the choice pump for ease of installation. They are portable, towable, small, and can pump various mix designs. Boom trucks are NOT recommended
- Proper mix design is critical to a smooth, efficient, and successful installation
- Pumping procedures and sequence is key to preventing installation malfunctions
- Typical crew size includes four laborers, one pump operator, and one superintendent