Issue 59

S. Anouar et alii, Frattura ed Integrità Strutturale, 59 (2022) 374-395; DOI: 10.3221/IGF-ESIS.59.25

In the description of the boundary conditions, there are two types of boundary conditions in PLAXIS 3D; Boundary conditions concerning groundwater flow and boundary conditions for displacement which use default fixities as follows in Fig 17. X min = horizontally fixed, X max = horizontally fixed, Y min = horizontally fixed, Y max = horizontally fixed, Z min = horizontally fixed, and Z max = horizontally fixed. For groundwater flow’s boundary conditions as the vertically upward (Zmin and Zmax and Xmax are open), swelling displacements are intended to be assessed as shown in Fig. 17.

Figure 17: the boundary condition. [53].

In this part, the results of the numerical model were validated by the analytic results. The consolidation settlements consist of two categories; primary consolidation settlements and secondary consolidation settlements. The former takes a long time until all excess pore pressure is dissipated. The latter consolidation, however, is a viscous behaviour of the soil-water system causing slow rate compression [54]. The primary settlements are calculated using the works of Terzaghi as is shown in Tab. 6. It is noticed that the primary consolidation has a higher value than the secondary consolidation. For this reason, we exclusively calculate the value of primary consolidation which itself is used for the sake of validating the numerical results. We compare the value of total settlements calculated by the analytic method (0,4517 m) which is shown in tab. 7, and the settlements from Plaxis (0,5112 m) as it is shown in Fig. 18, good accordance has been found. The characteristics of soils used for the analytic calculation of total settlements are explained in the experimental section. One meter underneath the original earth's surface is the phreatic level.

Stress history

Primary consolidation settlement

      ' ' i p

'

'

 p C e H

 0 ( / (1 )). . log(( s

     ) / )

i

i

           ' ' ' i p i

'

'

'

'

 p H C e

  0 0 .[(( / (1 )). log( / )) (( / (1 ) log(( S p i c C e   

    

) / ))]

i

p

   ' ' p i

'

'

 p C e H

 0 ( / (1 )). . log(( c

     ) / )

i

i

Table 6: Expressions for primary consolidation settlement with stress history [55].

  : Added pressure.  ' i : Average effective vertical stress on the clay layer.

386