Spring Folder Type Bireflection Target(스프링 폴더형 내공변위타겟)

The most important item in the “A” measurement out of the tunnel measurement is the convergence measurement.
The purpose of the crown and the convergence measurement is to verify the stability of the ground surrounding the tunnel and the data is important to verify its conditions due to the tunnel excavation, and for predicting the ultimate displacement and determining whether or not the lining should be added. However, despite the fact that engineers reside in the field of tunnels and install various instruments for measurement, tunnel collapsing accident is still going on due to different reasons.
In order to verify the effect of the primary strut and tunnel stability in tunnel excavation, it is necessary to install measuring instruments for measurement as soon as possible in the vicinity of the tunnel blind end, but the initial displacement is often lost due to missing of the installation timing because of laying the shortcrete.
Normally, it is not easy to determine the stability entirely because of the lack of the data on and on when the measurement instrument is damaged by scattered debris in case of working combined with excavation by machine and blasting at the same time.

In the field of tunnels, the conventional fixed type crown and the bi-reflection target can not resist the scattered debris made during the blasting work and the loss ratio of the target reaches about 20~30%.
Moreover, using the conventional way delays the installation timing to reduce the loss ratio or it often measures by separating the target and then mounting again one by one according to the blasting work time. On the contrary, the spring-fold type bi-reflection target adopted a simple method that it becomes recovered to the original position by a fixing device and the spring connected with prism in case when it is hit by scattered debris when blasting.

Model Name	SJ-1402 (Patent No. 10-0951811)
Target material	Reflection sheet: Polyvinyl chloride. Body: Steel
Target Dimension	Reflection plate (45 X 50mm), Fixing plate (50 X 60mm) & Thickness 4mm
Target rotation angle	110° (1 way), Recovered to original position
Spring Pin material	Special steel
Spring Pin dimension	Spring Cavity Pin(400X25mm), Target coupling (50X25mm) Anchor Bolt(45X10mm), Total length for coupling: Approx. 470mm
Spring Pin rotation angle	180° (Front/Rear, Left/Right), Recovered to original position

This is subject to change without prior notice in order to improve the product’s quality.

Type	Tape Extensometer	Fixed type Convergence Meter	Spring folder type Convergence Meter
Measurement / Installation timing	Hang a ring on the convergence pin to maintain the tape tensile force for measurement using dial gauge Installation: After laying 1st and 2nd S/C	Prism target is installed on the convergence pin and then measure using electro-optical wave measuring instrument. Installation: After laying 1st and 2nd S/C	Same as left Installation: Immediately after drilling the blind end. Possible to find position displacement
Advantage	Good precision: 0.01mm	Possible to find position displacement Possible for 3-D analysis	Possible to find position displacement Possible for 3-D analysis Minimum loss rate for blasting Minimum loss of displacement in the beginning of drilling
Disadvantage	Excessive individual error during measurement time	Excessive loss rate for blasting Lack of data continuity due to the loss	–
Economic condition	No efficiency	Excessive cost for re-installation	Good economic condition