Rock, especially rock salt, exhibits time-dependent behaviour. Creep of rock and rock salt is related to various applications in civil engineering, the mining industry or petroleum engineering, such as energy storages, wellbore stability in oil and gas extraction, radioactive waste facilities design, etc. (Cornet, Dabrowski & Schmida, 2018).
For instance, drilling a deep borehole (around 5000m of depth) for oil extraction could face a serious instability problem when going through a creeping salt layer (see Dusseault, Maury, Sanfilippo & Santarelli (2004)). Most of the underground applications are concerned with large time scales (tens to thousands of years or even longer) and thermal effects at great depth (hundreds to thousands of meters of depth). The Norton power creep law (Norton, 1929) is widely used for describing the steady state creep behaviour, which is relevant for those large time scales.
In this context, an enriched version of the Norton law, the Norton-based Double Power Creep (N2PC) model for Salt Rock, including temperature effects, was implemented in PLAXIS software. Although the model is particularly adapted for creep of rock salt, it can be used also for other types of rock which exhibit similar creep behaviour.
With the release of PLAXIS 2D/3D CONNECT Edition V20 Update 1 (January 2020), the PLAXIS User Defined Soil models are delivered with the PLAXIS installation. When enabling the Geotechnical SELECT Entitlement [GSE] when starting the PLAXIS application, this model becomes available in the Parameters tab when selecting "User defined" for the Material model. Note that the optional temperature dependency part of the model requires the PLAXIS 2D Thermal module, and if used in Fully coupled Thermo-Hydro-Mechanical analysis the PlaxFlow module is required as well.