STRENGTH REQUIREMENTS FOR ROUND CONDUIT 



741 



The test equipment used is shown in Fig. 2. Each tube was laid length- 

 wise on the trench bottom between two pieces of plastic conduit of the 

 same outside diameter. The tubes were oriented so that one of the strain 

 gages was at the top of each tube. The trench was then filled with the 

 backfill material. The loads at the surface of the fill were applied by 

 using trucks with various measured wheel loads. The trucks were either 

 moved slowly to a stop in position over each tube, or driven at moderate 

 speed across the trench. Additional impact tests were made with a 

 Hydrahammer, which consists of a 500-pound-weight dropped from 

 different heights onto the surface of the fill. Each tube was subjected, 



4000 

 3 800 



3600 

 3400 

 3200 

 3000 

 *Q 2800 



X 



C 2600 



2400 



z 



a 22001- 



\- 



2000 ■ 



STRAIN MEASUREMENTS TAKEN 

 AT THE INSIDE SURFACE OF 

 THE CONDUIT 



STRAIN GAGE 



CONDUIT 



X =1 

 O r2 



i =3 

 • =4 



STRAIN MEASUREMENTS VS. APPLIED LOAD 



CONDUIT OUTSIDE DIAMETER 

 CONDUIT WALL THICKNESS 

 HEIGHT OF COVER 

 WIDTH OF TRENCH 

 CONDUIT MATERIAL 

 BACKFILL MATERIAL 



4.5 IN. 

 0.065 IN. 

 30 IN. 

 22 IN. 

 ALUMINUM 

 CLAY 



j_ 



2000 4000 6000 8000 10000 



APPLIED LOAD [lBS] 



12000 14000 



Fig. 3 — Strain measurements versus applied load. 



