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This study describes the behavior of embankments stabilized with prefabricated vertical drains installed in soft clay foundations, based on several fully instrumented case histories selected from Thailand and Malaysia. A multidrain analysis is conducted based on an equivalent, plane strain model developed by the authors. The deformation of soft clay beneath an embankment (i.e., along and away from the centerline) is predicted and compared with the available field measurements. The effects of both smear and well resistance are incorporated in the analytical formulation, which is used in conjunction with the modified Cam-clay theory. It is demonstrated that the installation of vertical drains significantly increases the rate of settlement, improves the dissipation of pore-water pressure, and decreases the lateral deformation of the soft clay foundation. To obtain better predictions, especially of pore pressures and lateral displacements, the equivalent discharge capacity of the drains needs to be modeled appropriately. The inclusion of the effects of smear and well resistance in the analysis of vertical drains improves the accuracy of predictions significantly, in comparison with the field measurements.Key words: clay, consolidation, embankment, finite element method, settlement, smear zone, vertical drain.

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The selection of aquifers based on Geoelectric Method data in constructing drilling wells was discussed in the present study. The research was conducted at the International Hospital Project in Nyitdah Tabanan Bali. The research position was around 8,5736 LS 115,1215 LE. Before the study was conducted, a well drill (well 1) has been made. The results showed that there were two types of aquifers, namely unconfined aquifers and unconfined aquifers. Related to this study, well 1 took water in the unconfined aquifers of 4 m depth. If the water kept taken for a long period, the quality and quantity of the water would be worse since well 1 was unconfined aquifers that took surface water. This would adversely affect the hospital building being built. The land around the building would be hollow due to the water loss, and the building would become unstable. Another drill well (well 2), based on geoelectricity data, can be made on 5,25 m -18,75 m. In-depth 23 m, it was suspected that unconfined aquifers would have been found in well 2. After being drilled, aquifers were found in 23 m depth. Drilling was kept doing to 55 m depth. The new well (well 1) had TDS 205 mg/l and well 1 had TDS 350 mm/g. The number was still under the recommendation of Health Minister Regulation. The Minister recommendation was TDS 500 mg/I. However, well 1 had a hazardous state of pollution because it used water that seeps into the soil. A well 1 still had good water condition since there was fields rice around it while the aquifers of well 2 were not polluted because it was shrouded by hard layers. This means the quality of well 2, in a longer period, was better than the quality of well 1.

This study describes the effect of smear on the settlements of soft clay foundations which have been improved by installation of vertical drains. The smear zone propagation around a band-shaped drain was monitored using a large, radial drainage consolidometer. The test results reveal that a significant reduction in the horizontal permeability takes place towards the central drain, whereas the vertical permeability remains relatively unchanged. The estimated smear zone was about 3–4 times the cross-section area of the band-shaped drain (mandrel). In the analysis, the classical axisymmetric solution for consolidation by vertical drain has been converted into an equivalent 2D plane strain analysis. The plain strain model is subsequently applied to a number of embankments stabilized with vertical drains. It is revealed that the inclusion of smear effects improves the settlement prediction significantly.

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