Abstract: A racket string 10 of the present invention includes a synthetic fiber. The cross section is flattened by heating, compressing, and deforming the string after it has been formed, and an indentation is made in any part of the string. The flattened string is wound in a substantially non-twisted state. A method for producing the racket string includes heating the string at a temperature of Tg (° C.) or more and Tm ?10 (° C.) or less, where Tg (° C.) represents a glass transition point and Tm (° C.) represents a melting point of a main synthetic fiber constituting the string, compressing and deforming the string between rollers 7a and 7b that are arranged with a predetermined clearance therebetween; and then cooling and winding up the string.

Abstract: The object of the present invention is to provide a monofilament which has sufficient mechanical strength to be practically used also as a string for rackets and which is excellent in workability. Disclosed is a monofilament which is formed by extruding a material prepared by blending mainly a polylactic acid type polymer (A) and an aliphatic polyester (B) other than polylactic acid, and drawing the extruded material. This could be used as a racket string which has a tenacity-elongation curve similar to that of natural gut and is excellent in water resistance and heat resistance.

Abstract: There are disclosed a method and a machine for constructing a shaft having a substantially circular cross-section. According to the present invention, the shaft having a shotcrete formed on a peripheral wall thereof can be easily constructed. The shotcrete can be promptly formed on the peripheral wall by spraying concrete on the wall above the water level of the water in the shaft before the wall is damaged. Also, muck excavated from a working face of the shaft can be efficiently conveyed therefrom to outside of the shaft even if the shaft has a depth of more than hundreds of meters.