Outer protective system are widely used in foundation pit

whose reinforcement quality has an important effect on the stability of foundation pit

surroundings around foundation pit. Real-time and on-line monitoring of outer protective system and surroundings around foundation pit will be useful for obtaining the deformation evolution and early-warning the foundation pit failure in time. In comparison with the routine monitoring method

distributed fiber optic sensing offers a number of attractive features

for example

distributed monitoring

long distance

real-time monitoring

long-term stability

and so on. So it fully meets the demand of the health monitoring of foundation pit and early-warning of foundation pit failure. In this paper

the measurement principle of Brillouin Optical Time-Domain Reflectometer （BOTDR） is introduced

and a novel distributed fiber optic sensor-based monitoring system for foundation pit engineering is introduced. The relative topics about application of BOTDR in foundation pit engineering are discussed in details

which include installation methods of optical fiber

optical fiber protection and temperature compensation method. Then taking a project as example

the authors analyzed the deformation monitoring data. The monitoring results show that BOTDR-based distributed monitoring system for foundation pit engineering can exactly reflect the states of deformation and has obvious advantages in terms of foundation pit deformation monitoring and real-time foundation pit failure prediction.