A Review on the Characteristics of the Smear Zone: Field Data Back Calculation Compared with Laboratory Testing

Background: The so-called smear zone is a disturbed zone developed in soil during prefabricated vertical drainage (PVD) installation using a mandrel. There are 2 main parameters typically used to characterize the smear zone. First, the extent ratio signifies the extent of the soil damage due to mandrel penetration; and second, the permeability ratio κ represents the degree of disturbance to the soil permeability within the smear zone. Objectives: This study reviews 2 methods employed by various researchers to obtain the values for the 2 aforementioned parameters, i.e. 1) field data back calculation and 2) laboratory testing. It is found that the s’ values vary between 2.0 – 5.0 and between 2.0 – 6.3 based on field data back calculation and laboratory testing, consecutively. On the other hand, the κ values vary between 2.0 - 13.8 and 1.03 – 3.13 based on field data back calculation and laboratory testing, consecutively. Results and Conclusion: With regard to the previous studies, three causes of the variation are suggested in this study: 1) the laboratory testing’s inability to model the complexity of field conditions, 2) the absence of standardized laboratory methods that can be used as references and 3) the level of disturbance in the field which is considerably greater than that in the laboratory and differs at each research location. In addition to the review, historical data of a trial embankment at the embankment of the multi-purpose container yard in Kuala Tanjung, North Sumatra, Indonesia, are exhibited to illustrate the estimation of the s’ and κ values.