Ground strain measuring system using optical fiber sensors

It is widely recognized that the dynamic behavior of the soil is essential to discuss the characteristics of ground behavior during earthquakes, and many research has been conducted for a long period. Many problems, however, remain unsolved about the dynamic property, which is usually treated as stress-strain relationship, of the soil. One of the reasons for this. is lack of a means to measure the strain in the real ground. This paper presents a system to measure the ground strain using the fiber Bragg grating (FBG) sensors. Employment of optical fiber sensor makes the device simple in mechanism and highly durable. Two types of prototypes of the ground strain measuring device are made and their applicability are examined in the dynamic shaking table experiments. Displacement values measured by the displacement meter and the presented system are compared. The experimental results indicate that it is possible to measure the ground strain by the presented system, although necessity to improve the accuracy is also recognized.