Blinding struts — Part 1: Buckling response

The term ‘blinding’ is used to describe the thin layer of unreinforced over-site concrete which is used to protect the base of excavations from construction traffic and to provide a clean surface for the construction of the base slab. Blinding is not generally seen or exploited as a structural element even though it clearly provides some temporary lateral support to the retaining walls of cut-and-cover excavations. This paper shows that enhanced blinding can be used to prop retaining walls in cut-and-cover excavations during construction prior to the completion of the base slab. An experimental program is conducted on 1/41/4 scale specimens, which demonstrates that the failure load of blinding struts is governed by upheaval buckling, and which is employed for the validation of nonlinear finite element models. The main parameters governing the buckling load are shown to include: i) the amplitude of the geometrical imperfection, ii) the thickness of blinding, and iii) the eccentricity of the applied load with respect to the centroid of the strut.

► Blinding is a layer of over-site concrete used to protect the base of excavations.
► Blinding can be used to provide temporary lateral support to retaining walls.
► Laboratory tests show that blinding struts typically fail in upheaval buckling.
► The strength of the tested struts is predicted with finite element analysis.