Active isolation of steady-state surface vibrations by open and softer in-filled trenches in an elastic and homogeneous half-space is investigated in this study using PLAXIS 2D. Percentage isolation by barrier is estimated from amplitude reduction factors. Effects of in-fill material parameters are investigated in terms of impedance ratios against the case of a trench of definite geometry. Several cases of softer backfilled trenches with impedance ratios ranging from 0.08-0.42 are studied and their effectiveness is compared with that of an open trench of identical dimension. It is found that softer in-filled trench barriers of impedance ratios lying between 0.08-0.17 exhibit isolation effectiveness comparable to open trenches. Isolation efficiency of in-filled trenches increases with decrease in impedance ratio. Both open and in-filled trenches are found more effective in reducing the vertical vibration component than the horizontal. Keywords:vibration isolation, in-filled trench, impedance ratio, Rayleigh wavelength