tests were carried out to assess the load-bearing capacity of 900 mm diameter standard unreinforced drainage pipes bedded in 360 deg gravel surround. they had been extensively cracked longitudinally at the crown, springings and invert. static loads of up to 126 kn were applied to the ground surface above the pipes at cover depths ranging from 0.3 to 1.44 m above the pipe crown. the largest vertical deflection of the pipe measured was 6.6 mm (0.71 per cent) for a load of 100 kn at 0.3 m cover. an identical uncracked pipe section was subsequently installed with a similar granular bedding at 0.6 m cover depth in the trrl test pit and was deliberately cracked in situ by blows from a heavy excavator bucket. it was then subjected to a programme of static and repeated loading by means of a hydraulic jack and total collapse was induced by 30 cycles at 300 kn load. these results indicated that a rigid pipe which has cracked and thus has technically 'failed' in the ground can still support heavy external loads under some circumstances by mobilizing support from the bedding material when the pipe deflects.(a)

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