The pile group foundation of Sutong bridge is the largest in the world. It is composed of 131 overlength cast-in place bored piles which are 117 m long. The sensors worked under this engineering environment must subject to large pressure

as well as construction factors

and they damage easily. In order to improve the installing survival rate of the sensors

some sensor protection techniques are put forward after several field tests

including concrete strain gauge

surface strain gauge

hydrostatic level and water pressure gauge. The installing survival rate of sensors can be ensured by implementation of sensor protection techniques. The average survival rate exceeds 96%. The rules of load mechanism and uneven settlement are analyzed by monitoring data. The results show that the load mechanism of overlength cast-in place bored piles is different with the piles in common. The uneven settlement of large-scale pile group foundation appears in the direction across bridge; and the uneven settlement in longitudinal direction can be ignored.