## 1 Introduction  
Soil is a complex porous three-phase material in which many phenomena take place simultaneously. Because of the complexity a lot of soil mechanics problems have to be solved numerically or by laboratory investigation [1]. For numerical calculations, mainly using the finite element method (FEM), appropriate material models have to be implemented. As there are many kinds of soil types, differing in particle size fractions, geological origin and the conditions of loading, there is no universal solution. Many commercial FEM software packages provide their own material models [2]. However, they also allow for extending the models as there is often a need to analyse some less typical soil mechanics problems or soil types more thoroughly. In case of porous media, constitutive equations are generally formulated in the effective stress and applied for coupled pore pressure--stress numerical calculations of geotechnical problems [3].  
Consolidation and settlement calculations are very important aspects of geotechnical design. The settlement of soil can be divided into three parts: (i) Elastic response, (ii) primary consolidation settlement related to the drainage of water, (iii) secondary settlement, related to the creep of the soil skeleton. In most cases only the primary consolidation is considered as it causes the largest settlement for the majority of soils. However, for organic or soft clay soils, the secondary compression can be also large and has to be taken into account [4]. Consolidation of the soft soil layer is also important in the case of column supported embarnkments, where the load transferred to the column and geosynthetic layer strongly depends on the settlement of the soft layer [5, 6].  
Rheological schemes provide a flexible tool for creating complicated constitutive relationships of various materials. By applying rheological schemes to model the behaviour of the soil skeleton and coupling them with the equation of pore water flow, it is possible to describe the transient (time-dependant) response of soil taking into account secondary consolidation of viscoelastic soils [7; 8; 9; 10; 11; 12]. In the study, a method of modelling the transient process of primary and secondary consolidation of soil based on Burgers rheological scheme is presented. The Burgers structure is commonly used to model the behaviour of asphalt mixtures [13; 14]. Here, it will be applied for the soil skeleton in order to simulate the transient process of consolidation of an organic soil layer. It should be noted that the presented procedure can be applied for any viscoelastic rheological structures. This shows that the great potential of constitutive models developed in different research fields can be straightforwardly utilized to solve geotechnical problems. An example of such a problem is the modelling of secondary consolidation. The 1D constitutive equations derived using rheological schemes can be implemented as a part of the evolution law of the Cap yield surface of the Modified Drucker-Prager/Cap model available in commercial FEM codes.  
On the other hand, the behaviour of soil in the effective stress space (\(e-\log\sigma^{\prime}\) curve) can be modelled by using non-classical rheological schemes as will be demonstrated in this paper. To do this, the non-classical Kepes element [15] will be introduced in a rheological scheme of the soil skeleton in effective stress, and based on that scheme a system of algebraic-differential equations will be formulated. This system of equations has not been presented previously in the geotechnical literature. Moreover, it should be emphasised that the Kepes element has not been applied to the geotechnical problem either. A detailed description of the Kepes rheological model for both 1D and 3D cases can be found in the monograph by [PERSON] [16].