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Tham khảo tài liệu 'systematic drilling and blasting for surface excavations part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EM 1110-2-3800 1 Mar 72 Release of high pressure gases to the atmosphere by exposed detonating fuse lying on the surface of the rock. Of these four processes the last three contribute the most energy to the airblast waves. a. Damage from Airblast. For residential structures cracked plaster is the most common type of failure in airblast complaints. However research has shown that windowpanes fail before any structural damage to the building occurs.30 Airblast pressures of only 0.03 psi can vibrate loose window sashes which may be a source of annoyance complaints but do not represent damage. Windowpanes that have been stressed by poor mounting or house settlement may fail when subjected to pressures as low as 0.1 psi. Airblast pressures of 1.0 psi will break windowpanes and as pressures exceed 1.0 psi plaster cracking which depends on wall flexibility will start to develop. Thus it is recommended that air pressures exerted on structures resulting from blasting be kept below 0.1 psi. b. Propagation of Airblasts. 1 Extensive research has been conducted on the determination of the airblast pressure generated by the detonation of explosives on the surface of the ground.31-34 From the data given by Perkins 33 34 the airblast pressure as a function of distance D and charge size w for the explosion of spherical charges at the ground surface under normal atmospheric conditions is given by p 175 D W1 3 where p airblast pressure psi D distance ft w charge size lb For surface excavation the explosives are placed in drill holes and confined by stemming which reduces the amount of airblast considerably. 2 Fig. 7-1 shows the airblast to be expected for different depths of burial DOB for buried spherical charges. In this figure both depth of burial in feet and distance from charge in feet are scaled by the cube root of the charge weight in pounds. The plotted points in Fig. 7-1 7-2 EM 1110-2-3800 1 Mar 72 Fig. 7-1. Propagation laws for airblast pressure from spherical charges for .
