SITES SOFTWARE APPLICATION SEMINAR

1. STABILITY DESIGN SITES SOFTWARE APPLICATION SEMINAR __________________________ SITES 2005.1.4 INTEGRATED DEVELOPMENT ENVIRONMENT for WATER RESOURCE SITE ANALYSIS

2. SEMINAR OBJECTIVES • Basic understanding of stability Design for earth auxiliary spillways

3. SITES STABILITY ANALYSIS TECHNOLOGY OPTIONS PERMISSIBLE VELOCITY - not for TR60 ALLOWABLE STRESS 3

4. STABILITY • For the stability design the tractive stress of the earth or vegetated earth spillway is computed from the peak discharge of the 6 hour SDH storm.

5. TR60 Requirements

6. Old TR-60 Table 7-1 had corrections for Permissible Velocities (which are now not included in the new version). 10% for not more than once in 50 years and 25% for not more than once in 100 years. To make stress on an equal footing as velocity the same type of correction was made. Stress is proportional to the square of the velocity. So these values were added for stress. 1 in 50 (1.10)2 = 1.21 say a 20% increase 1 in 100 (1.25)2 = 1.5625 say a 50% increase 6

8. SITES AUXILIARY SPILLWAY STABILITY ANALYSIS • BASED ON PEAK OF SDH • APPLIED TO EXIT CHANNEL • VELOCITY OR STRESS calculations • Second Ed of TR60 only allows STRESS 8

9. Agriculture Handbook 667

10. EFFECTIVE STRESS • BARE EARTH • e=ds 10

11. EFFECTIVE STRESS • Maintenance code effect • e= dS(1-Cf) (ns/n)2 If MC=2, Cf0 If MC=3, Cf0 and n ns

12. EFFECTIVE STRESS • VEGETATION • e= ds (1-Cf) (ns/n)2 12

13. Note: If Cf = 0.9 then (1-Cf) = 0.1 and if Cf = 0.8 then (1-Cf) = 0.2 ===> this is a 100% increase in effective stress. From soil grain roughness if ns = 0.0156 & n = 0.040 D75 = 0.05” (ns/n)2 = 0.1514 A 100% increase from a change in soil roughness requires a D75 = 0.40” a 800% increase in grain size. 13

14. 0.341

16. Effective Stress = 0.314 psf

17. The allowable stress for a 1” grain size is 0.4 psf. A grain size of about 0.9” would meet the stability requirements for this example. .85

19. END OF PRESENTATION 19