In traditional smooth blasting construction,soft cracked surrounding rock is prone to a series problems,such as difficulty to control the amount of overcutting and undercutting,serious damage of surrounding rock,and low half-hole preservation rate.Based on the blasting construction of Xiaobaiyan tunnel in Guizhou Province,a casing pipe charge blasting design with double-layer perimeter holes was designed for soft fractured surrounding rock.In this study,starting from the causes of overbreak and underbreak,the perimeter hole layout,charge structure and blasting sequence were optimized.The charge structure of the outermost auxiliary holes was adjusted to the same uncoupled charge as that of the perimeter holes,and a protection casing pipe was added to the side of the reserved rock mass in each perimeter hole.The perimeter holes in were designed to initiate first and then followed by the inner layers of holes.Through numerical simulation and field tests,it is determined that the circumferential spacing of the double-layer perimeter holes is 500 mm,and the radial spacing is 650 mm.The initiation delay interval of the inner and outer layers is 50 ms.After applying the presented blasting design,the amount of over-excavation in the field test section has been reduced by 40% to 60% compared with conventional smooth blasting,and the half-hole preservation rate has increased to 89%.Finally,22 kg explosive consumption is saved per cycle advance and the economic benefit is significantly improved,which has a good popularization and application value.