# Modelling the Structure and Anisotropy of London Clay Using the SA_BRICK Model
## 7 Conclusions  
With the further development of the built environment, the accurate numerical prediction of the deformation field around a tunnel excavation becomes increasingly important as more traffic routes require the use of underground space. Predictions of ground deformations caused by tunnel excavations with increased accuracy are important to assess, prevent, and mitigate possible damage of existing structures caused by tunnelling. It was demonstrated in the paper that the SA_BRICK model can be used to advance numerical modelling of such boundary value problems with increased accuracy. Based on the good agreement between laboratory results and numerical predictions, it can be concluded that the SA_BRICK model presents a complete kinematic hardening model by exhibiting the ability to model the main manifestations of the mechanical behaviour of natural clays, including the non-linear stress-strain response of soil, the recent stress history effect, the effect of structure, and the effect of anisotropy. In addition to London clay, the model SA_BRICK was successfully validated against the behaviour of other natural soil, i.e., Pappadai clay, as demonstrated by [PERSON] [63] and [PERSON] et al. [64]. Numerical analyses of the excavation of the Jubilee Line tunnels at St. James's Park comprised modelling of the west and east tube. For the modelling of the west tube, all kinematic hardening models predicted a maximum settlement of some 10 mm, which was twice less than that observed. This discrepancy was attributed [27] to excess unsupported tunnel heading and to local geological conditions affected by sand and silt partings giving potential for loosening and softening above and in front of the tunnel heading. However, when comparing the normalized data of the predicted settlement trough with the Gaussian distribution, the prediction of the SA_BRICK and M3-SKH models were the most accurate. In particular, a distinctive difference of the SA_BRICK model giving a much narrower settlement trough than BRICK was observed. It should be noted that the SA_BRICK model was calibrated against \"new data\", which, in comparison to the M3-SKH model, illustrated a much stiffer behaviour of soil. In the modelling of the east tube, the SA_BRICK model gives the most accurate prediction of the settlement trough in comparison with other models and is in fair agreement with the observed data. This is attributed to the fact the east tube was excavated in initially undisturbed ground, so that the numerical analyses were within the range of expected ground behaviour and gave better predictions overall. Finally, it can be concluded that the results presented in this research demonstrate that the main features of the behaviour of natural overconsolidated clays can be captured reasonably well to include the effects of structure and anisotropy by following a thorough and comprehensive process of the development of the kinematic hardening model and the appropriate calibration of input parameters. When compared to other kinematic hardening models, the improvements in SA_BRICK predictions presented in this paper confirm the adequate implementation of structure and anisotropy in the BRICK model, which resulted in more accurate and realistic simulations of the mechanical behaviour of a natural overconsolidated clay. The obvious advantage of the SA_BRICK model is completeness of the phenomena that can be accounted for to model the behaviour of natural clays using a single formulation. As a superposition of BRICK, A_BRICK and S_BRICK, the SA_BRICK model contains all the previous phases of the BRICK development and can be used for modelling a wide area of soils. As for the other kinematic hardening models, the preconditions for the appropriate use of the SA_BRICK model are high quality laboratory data needed for the selection of input parameters.