Geotechnical inclinometer system is widely used in field monitoring of the deformations of soils and structures. Its working principle is that the deformations of an inclinometer casing are measured to reflect the deformations of monitored objects

with which engineering stability and safety can be analyzed. While the engineering stability and safety is under threat

accompanying oversize localized deformations are of common occurrence. This may result in that inclinometer probe cannot be lowered into inclinometer casing

leading to failure of the casing and losing of key data. In order to predict the possibility of the failure of the casing

5 methods are proposed to determine the curvature or the deflection angle of localized deformation curves of the casing. By comparing the calculated curvatures or the deflection angles with their limiting values at failure

the possibility of casing failure is analyzed. A case of the failure of an inclinometer casing in a foundation excavation project is analyzed. The adaptability of the proposed methods is compared. Of the 5 methods

the method of biarc fitting of 5 data points with an end point constraint is recommended for detecting the failure of an inclinometer casing.