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Abstract:The field of infrastructure rehabilitation and development requires a better understanding of soil-structure interactions. The interaction behaviour between soil and structures has mostly been investigated through theoretical and/or numerical analysis. This paper presents a series of experiments performed on an intermediate-scale physical model made of an instrumented silo. In contrast to most reported laboratory tests, both the horizontal and vertical stresses were monitored during backfilling operations realised by wild pouring. Drop tests were performed to investigate the density variation with respect to the drop (or falling) height of the soil, which were introduced in the pressure interpretation. The results showed that horizontal stress in the direction parallel to the pouring plane is larger than that perpendicular to the pouring plane. Apparently, the vertical stress is well-described using the arching solution by considering the backfill in an active state, whereas the horizontal stress perpendicular to the pouring plane is better described with the arching solution by considering the backfill in an at-rest state. An estimate of the earth pressure coefficients based on the measured vertical and horizontal stresses indicates, however, that the backfill was closer to an at-rest state in the direction perpendicular to the pouring plane, whereas in the direction parallel to the pouring plane, it was in a state between at-rest and passive. These results indicate that it is important to measure both the horizontal and vertical stresses to obtain a whole picture of the state of the backfill. The results showed also that the horizontal stresses can be larger than those calculated by the overburden solution, probably due to dynamic loading by drop mass during the filling operation and stress lock.

The geomechanical behavior of rock salt has been investigated extensively over the years. Experimental studies have identified distinctive features associated with non-linear inelastic response that shows strong time and loading history dependencies. In this paper, a relatively simple constitutive model is presented and implemented into the numerical code FLAC, and then applied to analyze the time-dependant behavior of excavations in salt mines. The unified creep-plasticity model includes an internal state variable (ISV) with an evolution law that induces progressive strain hardening (SH) until a steady-state is reached. Numerical analyses are performed with the proposed ISV-SH model to evaluate material parameters, based on creep tests results on a natural rock salt, and to simulate the response of a circular opening and of rectangular mining excavations created in sequence. The results are analysed and compared with those obtained with the well-known Norton power law equation, commonly used in salt mines engineering. The time-dependent calculation results illustrate key aspects of rock salt behavior and highlight the major influence of transient inelastic behavior and stress redistribution on the response of underground openings. The proposed modelling approach constitutes an advantageous alternative to analyses based on stationary creep laws, often used in rock salt mining operations.