EXCAVATION METHOD OF GROOVE HOLE FOR UNDERGROUND THICK WALL FORMATION

PROBLEM TO BE SOLVED: To provide a method of precisely excavating a groove hole for underground thick wall formation by use of a small-sized clamshell bucket without using a reaction material in which the use of a clamshell bucket having the same shell thickness as the width of a groove hole to be excavated is dispersed with. SOLUTION: A bucket having an opening shell width (c) corresponding to a width dimension W of a unit groove hole 10 is prepared, and the bucket is directed so that the opening and closing direction is turned to the width direction of the unit groove hole. Both the longitudinal end parts of the unit groove hole 10 are first excavated to a prescribed depth, projections formed by the claw part of the shell on the wall surfaces on the bucket opening and closing directional side of two holes 21, 22 formed by this excavation are shaven to flat the wall surfaces, and a width dimension larger than the designed width of the unit groove hole by the length (k) of the projections is formed. The opening and closing direction is changed 90 deg. to change the direction of the bucket, the remaining part between the two holes is excavated to a prescribed depth one side by one side with a virtual boundary line 25 for laterally halving the unit groove hole.