A turbomachine casing assembly including: a first casing element arrangeable adjacent to one or more rotating aerofoil structures of a turbomachine; a second casing element provided at a radially outer position with respect to the first casing element; and an infill member disposed between the first and second casing elements, wherein an end of the infill member is set back from an end of the first casing element such that a void is provided between the first and second casing elements.