Creep damage model of rock with varying-parameter under the step loading and unloading conditions

The creep characteristics of rock under step loading and unloading conditions were investigated in this study. Based on the generalized Burgers model, the total strain of rock was decomposed into elastic, viscoelastic, varying-parameter viscoelastic, and viscoplastic strains considering the damage. The four strains were connected in series to establish a new varying-parameter creep damage model that can characterize the creep characteristics of rock under step loading and unloading conditions as well as identify and verify the model parameters. The study results showed that the varying-parameter creep damage model could better describe the creep characteristics of rock under step loading and unloading conditions, significantly the non-linear both the strain and time of attenuation creep and accelerated creep. The model fitting curve was highly consistent with the experimental data, and the correlation coefficient R2 was greater than 0.98, which thoroughly verified the accuracy and rationality of the model. These findings can provide theoretical support for analyzing the deformation and long-term stability of rock and soil.

Optimization of Burgers creep damage model of frozen silty clay based on fuzzy random particle swarm algorithm

The creep characteristics of frozen rock and soil are crucial for construction safety in cases of underground freezing. Uniaxial compression tests and uniaxial creep tests were performed at temperatures of − 10, − 15, − 20, and − 25 °C for silty clay used in Nantong metro freezing construction to investigate the effect law of the stress–strain curves and creep curves. However, owing to the complex effects of factors such as temperature and ground pressure, the mechanical properties of underground frozen silty clay are uncertain. The Burgers creep damage model was established by using an elastic damage element to simulate the accelerated creep stage. The traditional particle swarm optimization algorithm was improved using the inertia weight and the fuzzy random coefficient. The creep parameters of the Burgers damage model were optimized using the improved fuzzy random particle swarm algorithm at different temperatures and pressure levels. Engineering examples indicated that the optimized creep model can more effectively characterize the creep stages of frozen silty clay in Nantong metro freezing construction. The improved fuzzy random particle swarm algorithm has wider engineering applicability and faster convergence than the traditional algorithm.

Creep damage model considering unilateral effect based on bimodulus theory

Based on the continuous damage mechanics (CDM) theory, Ambartsumyan bimodulus theory and creep damage theory, a bimodulus creep damage constitutive model is proposed in this paper. The model is able to describe the damage-induced unilateral behaviour related to the microdefect closure effect. The unilateral behaviour is considered a special bimodulus property. By judging the tension or compression state in bimodulus theory, different elasticity properties matrixes are selected according to signs of principal stresses. Then, an elasticity properties matrix is linearly converted to a general stress space. The model effectively solves the difficulty of determining tension or compression in complex stress states when the unilateral effect of damage is considered in the analysis of actual structures. The tangent elasticity matrix is used to improve the convergence of the proposed algorithm. In this study, a numerical simulation of the proposed model is achieved by writing subroutines in the FORTRAN language. A numerical example of a hole-in-plate structure under uniaxial stress is analysed. By comparing the results with those obtained by the traditional model, which does not consider the unilateral effect of damage, it is demonstrated that the proposed model is capable of describing the damage-induced unilateral behaviour related to microcracked closure effects. The numerical example validates the effectiveness and realizability of the proposed model.