Simple Methods Used to Estimate the Limit-State Axial Load Capability of Spillway Invert Slabs

Abstract

Invert spillway slabs provide an important contribution to the overall seismic stability of retaining walls, especially those earth-retaining L-walls and T-walls (sometimes referred to as cantilever retaining walls) that border spillway channels. Key to the seismic performance of spillway retaining walls is the stabihzing force that the channel invert slab exerts at tlie toe of the wall. The magnitude of this stabihzing force will depend on the limit state axial load capacity of the invert slab.Invert slabs can be founded on earth or rock. Types of construction used by the Corps include an independent block plan and a continuous reinforcing plan. Invert slabs when loaded axially can exhibit either short column or long column behavior with the latter term referring to slabs whose axial capacity is reduced by second-order deformations (i.e., P • A effects).Slab capacity in terms of axial load-moment interaction is determmed based on ultunate strength design principles and applied to both unreinforced (plain concrete) and remforced concrete sections. Influences from the subgrade reaction, slab dead load, and axial load eccentricity are considered in the analyses to develop an understanding of invert slab behavior and the influence, if any, second-order deformations may have m reducing the axial load capacity.