Laserfiche WebLink
<br />Background <br /> <br />Some early installations of concrete fabric mats were completed on Spring Creek and Battle <br />Creek in South Dakota in the early 1970's (Brice and Blodgett 1978, Karim 1975). These <br />installations used much larger sections (1.9 m2), which made the mat more rigid and more <br />susceptible to undermining. The simplicity of construction and durability of these mats made <br />them an allractive erosion control alternative. Experience and technology have improved <br />the flexibility and performance of fabric formed concrete mats since the 1970s. <br /> <br />Hydraulic Design Procedure <br /> <br />The design procedure involves quantifying the hydraulic stability of the grout filled mattress <br />using a "continuum method" similar to the design approach presented in Chen and Cotton <br />(HEC-15) (1986). This approach is in contrast to the "discrete particle" approach introduced <br />by Stevens (1968) in Richardson et al. (HIRE) (1990) used for selecting riprap and for the <br />design of articulated concrete block systems (ACB's) as presented in Design Guideline 4. <br />The design procedure for grout filled mattresses involves computing the stability of the <br />revetment by comparing the ratio of the tractive forces caused by the flow to the resisting <br />forces of the protection system. The ratio of resisting to tractive forces is known as the <br />factor of safety against the initiation of sliding across the subgrade surface as described by <br />the following equation. <br /> <br />FS=~ <br />'to <br /> <br />where FS = factor of safety <br />'t, = the resistive stresses of the mattress and anchoring system <br />'to = the design hydraulic shear stress caused by the flow <br /> <br />The continuum method of design is unique in that it analyzes the frictional forces which <br />affect the initiation of sliding between the mattress and subgrade or filter material. This is in <br />contrast to the discrete particle approach which analyzes a single unit for the initiation of <br />overturning as with ACB's and the initiation of motion as with riprap using the Shields <br />equation. The ratio of tractive to resisting frictional forces (the "force balance" approach) is <br />analyzed based on the size and weight characteristics of each mattress, the angle of friction <br />with the supporting subgrade with or without a filter, and additional resistive forces provided <br />by anchoring systems. Forces are quantified on a per unit area basis and the design <br />parameter is the thickness of the mattress. <br /> <br />Reference to manufacturer's literature is necessary for a quantification of the resistive forces <br />supplied by proprietary grout filled mattresses and anchoring systems. A review of tractive <br />forces caused by flowing water in straight channels, at bends, on bed slopes and side <br />slopes, and on steep and mild gradient channels can be found in Chen and Cotton (HEC- <br />15) (1986). The quantification of hydraulic tractive forces is a common procedure for <br />hydraulic engineers. It is the manufacturer's responsibility to provide methods for computing <br />the resistive forces of proprietary products. <br /> <br />5.4 <br />