A mechanical method is proposed for deformation measurement of tunnel structures on the concept of the "On Site Visualization" of which the key point is the simultaneous visualization of measured results for those most concerned in the construction project.

A relative displacement between two arbitrary points is an important quantity during construction and service time after completion of tunnel. Measurement of tunnel convergence during construction or any facility attached to a completed tunnel, such as lighting or roofing can be conducted by this relative displacement measurement. For this purpose, this paper proposes a new mechanical device which can measure a relative displacement and show the result visually to workers or tunnel users without using electricity.

The proposed device is made of two components. The first component is a stiff and flexible thread which can mobilize a pulley to rotate when relative displacement of two points connected by the thread occurs. The second component is a plastic needle, which is attached on the side of the pulley for visualization of the measured displacement. The pulley can translate the linear displacement into rotations and its diameter determines how sensitive the needle rotates with respect to displacement. The method is usually adapted for the measurement of triangle convergence of tunnel during constructions. The same principle can also be applied for monitoring of cracks of linings of the tunnel by some necessary improvements. Some related laboratory and field experiments are introduced in this paper. Finally, the prospect of the mechanical methodology regarding its cost and application is discussed briefly.

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