PSI - Issue 5

H Hammoum et al. / Procedia Structural Integrity 5 (2017) 69–76 H Hammoum et al./ StructuralIntegrity Procedia 00 (2017) 000 – 000

72 4

thickness. The test results obtained in 1983 at Fort Collins, Colorado (Simons et al., 1983) show that, given the same stone sizes, the Reno mattress tolerates a much greater velocity than the loose rock and, given the same velocity, the stone size that will be stable in a Reno mattress revetment is much smaller than that required for a loose-stone revetment. The performance function G 3 associated with this limit state is represented by the following stability condition:

3 C G : V-V

(8)

3.4. Estimation of deformation effects

When the shear stress reaches the critical value of the condition of "initial movement", part of the stone fill moves downstream inside each compartment of the Reno mattress (Fig. 1). To evaluate the degree of deformation three parameters (Δ z, t and d m ) are used, which are respectively the height difference between the highest and lowest rock surface within a mattress compartment, the thickness of the mattress and the average size of the stone fill. For the efficiency of the protection it must therefore be that: Δz t 2. 1 dm dm         (9)

Fig. 1. General pattern of stone movement within the mattress compartment (France Gabion, 1985)

The same procedure for evaluating the acceptability of deformations is followed also for the Reno mattress on the banks. The performance function G 4 associated with this limit state is represented by the following stability condition:

m        t 2. 1 d 

Δz

4 G :

(10)

d

m

3.5. Residual velocity at the underside of the revetment

The water velocity at the interface with the stone layer and the base soil must therefore be slow enough not to move the particles that form the soil. Since the velocity of the water under the revetment depends mainly on the slope of the channel and on the size of the voids between the stones, that is, on the size of the stones themselves, assuming that the predominant direction of flow is parallel to the surface of the Reno mattress, the velocity will remain practically constant in the face of varying hydraulic conditions and thicknesses of the Reno mattress (Simons et al., 1983). The