Table 3 Ultrasonic test results of S1 section of test model with different control hole spacing.

From: Study on anti-reflection of deep soft and high gas coal seam floor by deep hole controlled blasting

Working condition

Wave velocity range(km/s)

Mean wave velocity(km/s)

Descend range

Background value

2.10 ~ 2.80

2.56

 

No control hole

1.79 ~ 2.30

2.17

0.15

d = 20 mm

1.84 ~ 2.33

2.13

0.17

d = 60 mm

1.75 ~ 2.20

2.08

0.19

d = 80 mm

1.62 ~ 2.16

2.00

0.22

d = 100 mm

1.68 ~ 1.97

1.91

0.35

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