Fig. 1. Test system of BOTDR. (a) Experimental setup of BOTDR; (b) photo of the test system

Fig. 2. Test site of the pile foundation

Fig. 3. Arrangement of the distributed optical fiber sensors on the test pile. (a) Cross section; (b) detailed arrangement of the optical fibers; (c) pretreatment of the test pile surface; (d) photo of the test pile with installed sensing fibers

Fig. 4. Horizontal loading system

Fig. 5. Strain distribution of the sensing fibers under different loads

Fig. 6. Relationship between the maximum strain and the horizontal load

Fig. 7. Schematic of pure bending deformation

Fig. 8. Displacement distribution of the test pile under different loads

Fig. 9. Relationship between the maximum displacement and the horizontal load