How will the blanket be **stabilized **at the toe of the bank

How will the blanket be **tied into the bank **at its upstream and downstream ends

Stability Factors For Riprap. In the absence of waves and seepage, the stability of rock riprap

particles on a side slope is a function of: (1) the magnitude and direction of the stream velocity

in the vicinity of the particles; (2) the angle of the side slope; and (3) the characteristics of the

rock including the geometry, angularity and density. The functional relations between the

variables are developed below. This development closely follows that given by Stevens and

Simons (1971).

Consider flow along an embankment as shown in Figure 6.13. The fluid forces on a rock

particle identified as P in Figure 6.13a result primarily from fluid pressure around the surface of

the particles. The lift force F4 is defined herein as the fluid force normal to the plane of the

embankment. The lift force is zero when the fluid velocity is zero. The drag force Fd is defined

as the fluid force acting on the particle in the direction of the velocity field in the vicinity of the

particle. The drag force is normal to the lift force and is zero when the fluid velocity is zero.

The remaining force is the submerged weight of the rock particle Ws.

Figure 6.13. Diagram for riprap stability conditions.

Rock particles on side slopes tend to roll rather than slide, so it is appropriate to consider the

stability of rock particles in terms of moments about the point of rotation. In Figure 6.13b the

direction of movement is defined by the vector R . The point of contact about which rotation in

the R direction occurs is identified as point "0" in Figure 6.13c.

6.21

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