Effects of elastoplastic strengthening of gravel soil on rockfall impact force and penetration depth

Abstract

Gravel soil backfilled on the top of a rock shed serves as a cushion and protects structures in mountainous districts that are endangered by rockfalls. Strengthening effect under rockfall impact is one of the factors that can influence the properties of the backfilled gravel soil; therefore, this effect should be considered in studies on the mechanical behaviour of the structure protected by the gravel soil. This paper introduces a bilinear enhanced constitutive model considering the strengthening coefficient and proposes a theoretical calculation method for rockfall impact force and penetration depth based on the Hertz contact theory. Back analysis and mathematical statistical analysis of the results of rockfall experiments produced a range of strengthening coefficients for the gravel soil. Based on the obtained values of the strengthening coefficient and the proposed calculating method, ranges of values of impact force and penetration depth are predicted. Based on the comparisons with previous experimental results and the results calculated using other previous methods, the calculated upper and lower limits of impact force in this study prove to be in good agreement with the previous experimental results; however, the calculated medium values are lower than the test medium values. Furthermore, the predicted medium values of the penetration depth were, on average, 20% larger than the experimental values. This study shows that the effects of the strain rate and pressure dependencies produce a certain influence on the estimated results of rockfall impact force and penetration depth. It also shows that the effects of pressure dependencies are comparatively more distinct than those of the strain rate.