In the construction of Ningbo Bridge, Zhaobaoshan highway tunnels were designed as twin tunnels with large span and excessively small interval of 4 m, only 1/7-1/10 of ordinance in the norm. A series of measures should be adopted for the safety of tunnels. One of the crucial measures is the protection of the rock mass between the two tunnels, which includes the utilization of controlled blast to protect rock mass. The author used such techniques as sonic wave measurement, Landsonar method and vibration velocity measurement to measure the depth and condition of rock mass under blasting. In addition, the displacement, the strain and the pressure of the tunnels and the shotcreting or the lining were also measured to inspect the safety of the tunnels. With the help of the measuring data, the construction plan, construction procedures and blasting parameters were determined. The engineering is successful and the economic benefits are obvious.