Abstract: In the field of geology and geotechnical engineering, deformation monitoring has always been an important index to evaluate
stability. Its spatio-temporal evolution law can provide important reference for the optimization of design and construction parameters
of foundation engineering and the determination of early warning index of geological hazards. With the continuous development of
photoelectric sensing technology, its role in deformation monitoring of geological and geotechnical engineering is becoming more and
more important. However, the coupling performance between sensing optical fiber and rock-soil body has a significant impact on
monitoring results, and clarifying the mechanism between them has become a key part in the application of this technology. Based on
the comprehensive analysis of the current deformation monitoring technology of geology and geotechnical engineering, the pull-out test
of fiber-sand coupling performance based on distributed sensing technology was carried out. The coupling performance between
sensing fiber and sand, and the strain transfer law between them were analyzed from the test results and sensing fiber characteristics.
The experimental results show that except for the first stage pull-out, the R2 fitted by the data are all above 0.99, which shows that the
measured strain distribution of the optical fiber has better regularity; the elastic modulus of the optical fiber obtained by the back
calculation of the experimental data is about 0.35 GPa, which is basically consistent with the given value; by measuring the F-Shead and
F-Stail relationship of the optical fiber, it is concluded that the interaction process of the optical fiber-sand interface is mainly divided
into full-coupling, semi-coupling and relative sliding. The above research results provide guidance for the application of distributed
sensing technology in deformation monitoring of various geological and geotechnical engineering, and also provide important reference
for carrying out various model tests.

Key words: optical fiber-sand interface, coupling performance, distributed sensing, pull-out test