A prefabricated vertical drain (PVD)-improved ground under embankment surcharge loading at the Second Bangkok International Airport was modelled using a three-dimensional finite difference program and proposed matching schemes. The matching schemes used an equivalent well radius and an equivalent permeability to account for the cross-section of band-shaped drains and the smear effect, respectively. The well resistance of the PVD was taken into account by imposing a finite discharge capacity throughout the consolidation process. The numerical method incorporating the matching schemes satisfactorily simulated the drainage behaviour of the PVD unit cell and of the full-scale PVD improved ground. The three-dimensional numerical modelling also showed that the degree of consolidation of the PVD-improved ground in terms of settlement rate was higher than that in terms of excess pore pressure dissipation rate. In addition, after the PVD improvement, the undrained shear strength of the clay layers below the centre of the embankment was numerically estimated to be approximately twice the value before the improvement.

Soil-liquefaction-related hazards can damage structures or lead to an extensive loss of life and property. Therefore, the stability and safety of structures against soil liquefaction are essential for evaluation in earthquake design. In practice, the simplified liquefaction analysis procedure associated with numerical simulation analysis is the most used approach for evaluating the behavior of structures or the effectiveness of mitigation plans. First, the occurrence of soil liquefaction is evaluated using the simplified procedure. If soil liquefaction occurs, the resulting structural damage or the following mitigation plan is evaluated using the numerical simulation analysis. Rational and comparable evaluation results between the simplified liquefaction analysis procedure and the numerical simulation analysis are achieved by ensuring that the liquefaction constitutive model used in the numerical simulation has a consistent liquefaction resistance with the simplified liquefaction analysis procedure. In this study, two frequently used liquefaction constitutive models (Finn model and UBCSAND model) were calibrated by fitting the liquefaction triggering curves of most used simplified liquefaction analysis procedures (NCEER, HBF, JRA96, and T-Y procedures) in Taiwan via FLAC program. In addition, the responses of two calibrated models were compared and discussed to provide guidelines for selecting an appropriate liquefaction constitutive model in future projects.

This paper presents a field monitoring study with emphasis on the design and construction of a subsurface drainage system and evaluation of its stabilization efficiency on the slope of You-Ye-Lin landslide using a three-dimensional finite element method program (Plaxis 3D) for the groundwater flow and slope stability analyses. The subsurface drainage system consists of two 4-m diameter drainage wells with multi-level horizontal drains and was installed to draw down the groundwater level and stabilize the unstable slope of the landslide. Results demonstrate that the subsurface drainage system is functional and capable of accelerating the drainage of the infiltrated rainwater during torrential rainfalls during the typhoon season. The large groundwater drawdown by the subsurface drainage system protects the slopes from further deterioration and maintains the slope stability at an acceptable and satisfactory level.