Diameter-adjustable deformation measuring magnetic ring device

A diameter-adjustable deformation measuring magnetic ring device is characterized by comprising 4-8 circular-arc structure units, wherein each circular-arc structure has a radian of 45-90 degrees and has a length of 40-60 mm, the 4-8 circular-arc telescopic structure units form a circular ring after splicing, the minimum inner diameter of the circular ring is smaller than the outer diameter of a matched settling tube by 2-3 mm, and the 4-8 circular-arc telescopic structure units after complete stretching have an inner diameter being larger than the outer diameter of the settling tube by 80-100 mm and have an outer diameter being larger than the diameter of a borehole by 20-40 mm. It can be effectively guaranteed that the gap between the diameter-adjustable settling magnetic ring and the settling tube does not become small with the hole shrinkage of the borehole, thus the influence of the settling tube on the settling magnetic ring can be eliminated.