The excavation speed of pilot shaft is one of the key difficulties for the excavation of shaft, high ones in special, of hydropower works.
水电工程竖井特别是高竖井开挖，主要难点体现在竖井导井开挖的速度上。
The spoiling is a key factor influencing the advance speed for the shaft excavation, especially for the excavation of large cross section and deep shaft.
对于竖井开挖 ，尤其是大断面 深竖井开挖 ，出碴这一环节 ，往往是决定掘进速度快慢的关键因素。
Excavation in frozen gravel with air picks has the shortage of high labor intensity, low speed, and low efficiency.
在立井冻结砾石层段施工中，人工风镐掘进劳动强度高、速度慢、效率低。
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