A Field Investigation to Improve Soft Soils Using Prefabricated Vertical Drain

Abstract

This paper presents a case history of soft ground improvement technique using prefabricated vertical drain (PVD) with application to a railway track in Bangladesh. The method with preloading and staged construction was used for the construction of a 32.4-km-long new railway track at Kashiani–Gopalganj section. The soil profile at the site consisted of a 5m to 16m thick silty clay layer having water content between 20 and 24%. The shear strength of soft soil varied between 12 kPa and 38 kPa. The estimated consolidation of soil was between 1 and more than 5 years. Soil treated with PVD having 1.0 and 1.5 m spacing of triangular grid resulted in accelerated settlements as observed from the measured data. Through field monitoring, 524 to 731 mm settlement was observed. The observed time at the field was long compared to the estimated time due to three main reasons such as creation of a smear zone, not applying the surcharge load, and not having the exact soil data for settlement estimation.