Apparatus and method for providing negative buoyancy for tunnel forms

Abstract

A method and apparatus for eliminating the necessity of providing hold-down devices, such as spuds and anchors, for opposing buoyancy in tunnel forms. The method comprises providing a movable counterweight car which preceeds the flow of fluid concretes, as it slopes from the crown of the tunnel forms downward and thus provides negative buoyancy at that area where there is the most fluid concrete and in that area where the most uplift occurs as well as the natural area where there are no forces of the crown helping to prevent flotation. The movable counterweight car is a hollow container curved to match the curvature of the excavated tunnel and clearing the movement of the forms. It has wheels that run on single track rails carried on the inside of the tunnel forms, the container being wholly or partly filled with steel scrap or punchings. The counterweight car has a fixed distance relationship to the discharge point of the concrete pump which generally precedes the discharge point of the slick line over the crown. A light cable connects the counterweight car to the slick line carrier or pump carrier and causes movement of the counterweight car at the same rate of speed as the slick line is withdrawn, thus synchronizing the movement of the counterweight car to the concrete pumping operation.