## 4 Conclusions  
The current study proposes a wide range of smear effect parameters for utilisation in practical design, while no comprehensive method has been proposed thus far in order to estimate the properties of smear zones accurately. Therefore, several factors that influence  
Figure 10: Settlement behaviour performance between two locations.  
the behaviour of the vertical drains were investigated by numerical methods as well as back-analysis of field performance data. Based on the results of this study, the following conclusions were derived:  
1. The permeability in the smear zone is one of the main factors affecting vertical drain behaviour. Accordingly, Equation (1) should be utilized in numerical analysis;
2. The smear effect parameter has a significant effect on drain rate consolidation. A value of \(\eta=6\) was suggested for accurate and reliable predictions in order to determine the equivalent horizontal permeability of embankment settlements despite the fact that the combination of equivalent horizontal and vertical permeability is not significant in numerical analysis; \(\eta=300\) is still recommended in this case. However, all numerical models developed in this study were found to have a total of settlement quite similar to when \(\eta=100\) was employed;
3. According to the performance analysis of the developed numerical model, the total settlement was approximately similar to the increasing \(\eta\) values for the model with equivalent horizontal permeability. In contrast, the model developed with the combination of equivalent horizontal and vertical permeability revealed that increasing the \(\eta\) values tends to reduce the magnitude of predicted settlements;
4. Location observations affect magnitude settlement. In the identification of the settlement profile, it was observed that the total of the settlement was higher when located near the centre than when near the embankment toe;
5. The finite element software was observed to be very useful in predicting the settlement of embankment stabilized with PVDs. The settlement simulated by Plaxis 2D produced considerably accurate representations of settlement during the consolidation process.  
A methodology was also recommended in order to predict the behaviour of PVD-improved subsoils. The first step was to evaluate the \(\eta\) by back-analysis based on an existing case history. Next, Equation (1) with \(\eta=6\) was determined. Lastly, the behaviour of soft soil stabilized with PVDs could be predicted using Plaxis 2D.  
Conceptualization, R.C.M. and N.L.M.Y.; methodology, R.C.M. and A.R.; software, R.C.M.; validation, A.R., N.L.M.Y. and A.R.; formal analysis, A.R.; investigation, R.C.M.; resources, S.H.K.; data curation, A.R.; writing--original draft preparation, R.C.M. and A.R.; writing--review and editing, N.L.M.Y. and S.H.K.; visualization, R.C.M. and A.R.; funding acquisition, S.H.K. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available upon request from the corresponding authors.  
The authors would like to thank the Centre of Green Technology for Sustainable Cities, Politeknik Ungku Omar and Universiti Kebangsaan Malaysia for providing the facilities. The authors would like to acknowledge the support of Prince Sultan University for paying the article processing charges (APC) of this publication.  
The authors declare no conflict of interest.