and can be useful for upgrading smaller riprap slope protections. The 

 following specific conclusions were also made: 



a. A 100-percent stone overlay coverage gives about the same stabil- 

 ity number, Ng, as a conventional two-layer armor stone thickness. 

 Overlay stone stability numbers for a 100-percent overlay can be computed 

 from the formula: 



2/9 

 Ng = 1.46 (cot Q) ' . 



b. A 67-percent overlay coverage gives stability numbers about 10 

 percent less than a 100-percent overlay coverage. 



c. The reserve stability of a 100-percent stone overlay coverage is 

 about one-half of a conventional two- layer armor stone thickness. 



d. Rounded boulders were about as stable as a stone overlay as 

 angular quarrystone; however, because of their shape, more boulders are 

 needed per unit area to obtain the same percent coverage. 



e. The stability numbers obtained in the prototype tests were 40 

 percent higher than those in small-scale (1:10) tests. However, this 

 apparent scale effect is based on only two prototype and two small-scale 

 tests. 



22 



