Slipforming method and apparatus for in situ lining of an upwardly open shaft with monolithic concrete

A slipform and method for lining upright shafts with monolithic concrete by pumping concrete downwardly through a "tremmie tube" to a slipform apparatus and simultaneously pulling the slipform apparatus upwardly within the shaft such that the delivered concrete is formed continuously into a monolithic lining within the shaft. The apparatus includes downwardly open outer and inner slipform members. The inner slipform or core member fits within a conical recess of the outer slipform member and includes a lower cylindrical portion for forming the open inside diameter of the lining. Concrete, in a wet condition, is delivered by the tremmie tube between the two slipform members and molded against the shaft wall. The tremmie tube is pulled upwardly from the shaft opening by a hoist mechanism that is also used during the previous drilling operation. The rate of ascent for the form members is timed in accordance with the setting time of the concrete so that the upwardly moving form members leave the formed concrete in a self-supporting state. The tremmie tube is made up of a plurality of interconnected tube sections. In the present method, individual tremmie tube sections are added at the hoist mechanism and then lowered to correspondingly lower the slipform assembly. After descending a desired distance, the steps are reversed and the tube is pulled upwardly at a relatively continuous rate while concrete is pumped down to the form members. Successive tubing lengths are removed as they clear the ground surface.