PROBLEM TO BE SOLVED: To prevent the separation of surface concrete by inhibiting force of vertical and lateral motion from being transmitted in the thin-walled direction of each of the upper, lower, right, and left plates of a concrete caisson body even if the force of lateral motion acts on a straight part and the force of the vertical motion acts on a curved part in the case where the front and back concrete caisson bodies are coupled together by a guide pin so as to resist the vertical motion in the straight part and the lateral motion in the curved part. SOLUTION: In an open shield tunneling method, a pin inserting hole 11 is formed in such a slim shape as to extend in the thin-wall directions of the right and left side plates 4a and 4b and the upper and lower floor boards 4c and 4d of the concrete caisson body 4. In the guide pin 12 inserted into the inserting hole 11, the width of one side is made narrower than longitudinal width in order to enable a movement in the longitudinal direction of the inserting hole 11, and the width of the other side is made approximately equal to lateral width. The guide pins 12 inserted into the inserting holes 11 formed in the side walls 4a and 4b allow the vertical motion of the caisson body 4 to undergo shearing resistance, and the guide pins 12 inserted into inserting holes 11 formed in the floor boards 4c and 4d permit the lateral motion thereof to undergo the shearing resistance.
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