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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



hotwooii 18 and 30 inches. The majiiiiludc of the bending- niomenls 

 appeared to he only a function of the backfill nuiterial, the appHed load, 

 and the height of backfill over the conduit. 



b. For a trench width of 5 inches, the bending moments seemed to 

 be independent of the type of backfill material. The same results have 

 been obtained with a backfill of clay, sand, or gravel. This phenomenon 

 indicates that the applied load was carried mainly by the undisturbetl 

 soil but deformation of the trench walls together with friction between 

 the backfill material and the trench walls transmitted the load to the 

 conduit. The magnitude of the bending moments in 5-inch wide trenches 



e| = MEASURED STRAINS [iN/In] 



E= 10X10* PSI 



Fig. 7 — Moment distribution in ;i thin wnllcd tul)e, usiiij^ clay hnckfiil. 



