Distinct analysis of fully grouted bolts around a circular tunnel considering the congruence of displacements between the bar and the rock

This paper presents a new calculation procedure for the analysis and dimensioning of fully grouted radial bolts in tunnels. This procedure is based on the principle of congruency of the displacements, imposing the conditon that the lengthening of the bolt, added to the displacements due to the shear strains in the bolt–rock interface, is equal to the expansion in the radial direction of the reinforced rock annulus. A comparison of the results obtained using this procedure with those obtained using the traditional numerical modelling method, which is more costly in computational terms, has led to satisfactory results. The application of the procedure to a real case has given results that are comparable with the in situ measurements. The proposed instrument is able to analyse the stress and strain state in rock in detail, in the presence of a bolting intervention, and to proceed with its correct dimensioning with the objective of improving the degree of stability of the rock around the tunnel.