The need for urban growth and development has been driving man to occupy areas once considered improper or of low interest, due to the presence of low-resistance and highly compressive soft soil. Nowadays it is possible to improve soil by installing prefabricated vertical drains (PVD) with geosynthetics. These drains can also be assisted by applying vacuum, equivalent to the pressure of an embankment up to 4m high, but with less need for earth movement to mobilize and demobilize the temporary overload. This technology is being applied in a highway construction in an alluvial soft soil deposit extending for over 100 km, currently in progress in Latin America. Several undisturbed samples were extracted and tested in laboratory to determine soil compressibility and consolidation time. To assess the efficiency of the methods employed for sampling and molding specimens, quality indexes of consolidation tests carried out in the highway construction site are presented. Given the variable nature of this soil formation, back analyses were carried out to assess the compressibility and consolidation time of the alluvial soft soil.