Multiscale mechanical behaviour of sand–steel structure interface for deep underground space

As shallow and intermediate-depth underground space development saturates, deeper space expansion becomes inevitable. Thus, assessing soil–structure interface behaviour under high stress is vital for deep underground structures. In this study, a self-designed multi-functional shear apparatus was used to conduct a series of interface shear tests between sand with different relative densities and steel structure under high normal stress. The shear displacement, shear stress, particle breakage, small-strain shear modulus, and the particle displacement field were monitored throughout the tests. The results indicate that as the normal stress increases, the small-strain shear modulus increases, the relative particle breakage initially rises rapidly until 1.5 MPa normal stress and then stabilizes, the horizontal particle displacement in the interface area tends to decrease, and the vertical particle tends to compress. With increasing relative density of sand, the relative particle breakage becomes more pronounced, the horizontal particle displacement decreases, but the small-strain shear modulus shows a slight variation. The present testing results can provide a technical reference for evaluating the soil–structure interface behaviour under deep underground space.