Estimation of in situ viscoelastic parameters of a weak rock layer by time-dependent plate-loading tests

• We perform in situ large-scale compressive creep tests using rigid bearing plate.
• We propose a new visco-elastic creep model.
• We derive the visco-elastic deformation equation of rock in rigid-plate loading test.
• The new creep model is more accurately than the others.
• We discuss the sensitivity of each parameter in the model.

In order to study the deformation mechanism of the weak layer in diabase dikes under long-term loading at the Dagangshan hydropower dam foundation, in situ large-scale compressive creep tests using rigid bearing plate were performed. The plate was placed perpendicular to the weak rock layer in test galleries of the dam slope. The five-parameter generalized Kelvin model was identified to describe the creep behavior of the weak layer, which avoids the rapid convergence issue if using the three-parameter generalized Kelvin model. Based on the Boussinesq problem in elastic mechanics, mathematical equations were derived through Laplace transform and inverse transform to describe deformation-time history for the five-parameter generalized Kelvin model under three-dimensional stress–strain conditions. A finite difference model was used to validate the model. The sensitivity of each parameter in the model was analyzed, which indicates that E0 mainly influences the value of the instantaneous deformation; E1 and E2 mainly influence the value of the creep deformation; η1 and η2 mainly influence the time when the deformation rate becomes stable. Based on the derived equations, the rheological parameters were estimated. Reasonable agreement between the experimental results and model results is obtained. Results show that the five-parameter generalized Kelvin model is capable of representing the compressive creep test behavior more accurately than the three-parameter generalized Kelvin model or the standard Burgers model.