[Retracted] Optimal Defect Detection and Sensing System of Railway Tunnel Radar considering Multisensor System Combined with Active Interference Suppression Algorithm

Table 1

Tunnel defect classification table.

Defective item	Defect level	I	II	III	IV
		Slight defect length (m)	More serious defect length (m)	Severe defect length (m)	Very serious defect length (m)
There is a cavity behind the lining	There is a hole	≤1	1 ≤ L ≤ 3	3 ≤ L ≤ 5	>5
Backfill is not dense	Not dense	≤3	3 ≤ L ≤ 9	9 ≤ L ≤ 15	>15
The base is not dense	Not dense	≤3	3 ≤ L ≤ 9	9 ≤ L ≤ 15	>15