Evaluation of Curve Fitting Techniques for Estimating Time of Surcharge Release in Embankment Construction over Soft Soils

Constructing embankments over soft soils can be problematic due to the magnitude and time associated with subsurface compression. Determining the end of primary consolidation is greatly exacerbated for layered soils that compress at varying rates. This paper discusses the use of magnet extensometer instrumentation to isolate compression within specific subsurface layers and associated techniques for estimating the time of construction induced settlement. Field data is used during construction to estimate the end of construction induced subsurface compression, which greatly affects the project schedule. This case study briefly summarizes instrumentation installation, data gathering, and the challenges associated with projecting the time of construction settlement. Two different curve fitting techniques were evaluated in this research: using standard primary consolidation equations and finite difference equations for estimating the end of primary consolidation settlement. For the site investigated, the curve fitting techniques proved to be somewhat problematic because the soil layers had small magnitudes of settlement and the transition between primary and secondary settlement was not readily apparent during the evaluation of real time field data. Using the finite difference equations also proved somewhat problematic trying to fit the full record of field data based on all of the different stages of loading. Additional lessons learned include the need for effective project communication between contractors, designers, and owners and a corresponding open discussion regarding practical settlement risk.