Table 2.

Analysis of TST advance forecast results.

Chainage mileage	Length (m)	Wave velocity of rock mass (m/s)	Grade of surrounding rock	Forecast results
K2 + 022 ~ K2 + 032	10	3800	IV	Affected by unloading, the integrity of surrounding rock is poor, relatively broken, and joints are relatively developed
K2 + 032 ~ K2 + 052	20	4400	III	The surrounding rock has good integrity, slightly developed joint fissures and no obvious adverse geological phenomena
K2 + 052 ~ K2 + 122	70	3900–4100	IV	There are many weak structural planes developed and distributed. The surrounding rock is poor in integrity, with fault fracture zone and rich in groundwater