Importance of ground strain in predicting blast-induced strain and stress in pipelines

Abstract

This paper compares measured ground motions and strains in welded, steel pipelines, which were induced by blasting at unusually small-scaled distances. All three studies involved field measurement of the blast response of large (20 to 36 in. or 500 to 900 mm) diameter, pipelines trenched into or placed immediately above rock. Motions were induced by detonations of 5 to 15 lbs (2 to 7 kg) per delay trenching shots and 800 to 900 lbs (360 to 400 kg) per delay surface mining shots. Some of the blasts were detonated as close as 4 ft (1.3 m) from the pipeline. All of these field-scale blasts were detonated at scaled distances less than 30 ft/(lb1/2) or 13.5 m/(kg1/2). More than 30 of the blasts produced peak strains greater than 10 micro mm/mm, and peak particle velocities greater than 1 ips (25 mm/s); some of which were higher than 10 ips (250 mm/s). These measurements demonstrate the importance of absolute distances between pipe and blast, depths of blast hole, proper measurement of propagation and particle velocity, measurement of both hoop and longitudinal strains, equality of ground and pipe strains, and conservativeness of typical regulatory particle velocity control limits.