An Isotropic Elastoplastic-viscoplastic Bounding Surface Soil Model With Consideration Of Damage

The analysis of the creep(rheological)mechanical properties of the clay is very important for ensuring engineering safety.Over the years,many scholars at home and abroad have done a lot of works on the creep analysis of clayKaliakin and Dafalias(1990)proposed a elastoplastic-viscoelastic boundary surface model with a significant effect on the simulation of clay creep triaxial tests when the stress loading level is low and the soil samples are not cracked.However,when the stress level is high,soil samples due to creep cracking,the model is difficult to accurately calculate the simulation of the deformation value.The difficulty of this simulation shows that it is necessary to consider the effects of damage in the model.Thus,Mosleh A.Al-Sharmarni and Stein Sture developed a damage formula in the theory of anisotropic clay boundary surface model.The computational study shows that the damage creep can be improved by using the damage formula compared with the damage formula,but this improvement is limited to the medium stress level,so the model with the damage formula still have some defects.That is,the model can not make a comprehensive and correct simulation of the undrained creep response under various stress levels,especially when the stress level is high and the creep cracking deformation is significant.In order to further solve these problems,the main work and related achievements of this paper,on the basis of the previous work,are as follows:(1)In this paper,an initial damage function is proposed by referring to Al-Shamrani and Sture’s article.The form of the function is more complex than that of Al-Shamrani and Sture’s article,and the damage function is introduced into the elastoplastic-viscoelastic boundary surface model,which has been proposed by Kaliakin and Dafalias(1990),a elastoplastic-viscoelastic boundary surface model considering damage is formed.The simulation results show that the initial damage function proposed in this paper has a significant effect on improving the elastoplastic-viscoelastic boundary surface model to simulate the large creep cracking of soil samples in Dankai soft clay and Vancouver Haney soft clay.Comparison of Al-Shamrani and Sture articles and the calculation of the simulation results in this paper can be seen,Al-Shamrani and Sture text and the axis of the relationship between the curve is the logarithmic coordinates,and this article is directly used in the natural number of coordinates,the accuracy is higher.(2)As the initial damage function formula is relatively complex,different parameter values need to be input at different load levels,which need to be improved.On the one hand,it is necessary to simplify the formula form,and on the other hand,it is necessary to unify the damage parameter values under different load levels.Therefore,according to the analysis of the relationship between the initial damage function and the time,we have theoretically expounded why the introduction of the damage function can effectively improve the simulation of the creep cracking deformation of the soft soil specimen.At the same time,the simplified two-parameter exponential damage function form is summed up from the initial damage function,and the rationality of its application in constitutive simulation is verified by combining the undrained creep test of Osaka soft clay and Vancouver Haney soft clay.(3)The two-parameter exponential damage function solves only the problem of simplifying the damage function formula and does not solve the problem that the input value of the damage parameter value is constant under different load levels.Therefore,the data of the two parameters under different loads are fitted with data,and the simplified four parameters and the five-parameter damage function are proposed to satisfy the uniformity of the input values of the parameters under different loads.Through the undrained creep test of Osaka soft clay and Vancouver Haney soft clay,it shows the rationality of simplifying the four parameters and the five parameter damage function.For the soft clay related engineering in practice,this adaptation from the low stress to the high stress of the soft soil loading process of continuous analysis of the damage function improvement,has important engineering significance.(4)In this paper,a elastoplastic-viscoelastic boundary surface model considering damage is proposed.The creep damage effect of soft soil is simulated by introducing the damage function.For the further time-dependent soil mechanics analysis,such as anisotropy,earthquake or dynamic action,and discontinuous loading creep simulation analysis,etc.The application of damage function and the way of analysis and derivation have good reference value for promoting the research progress in these fields..(5)In addition to the soft clay material,the initial simplified damage function proposed in this paper and the subsequent simplified damage function derivation have good reference value for the damage,creep cracking and large deformation numerical simulation of other engineering materials.