Evaluation of Paper Sludge Landfill Cover Settlement: Fid-Bau Portal

Evaluation of Paper Sludge Landfill Cover Settlement

Quiroz, Juan D. / Simpson, Pickett T. / Zimmie, Thomas F.

A study of field settlement was conducted for the Hubbardston, MA paper sludge landfill cover, and two paper sludge landfill cover test plots constructed by NCASI (National Council for Air and Stream Improvement). The compression behavior was examined using the Casagrande logarithm of time graphical method such that primary and secondary compression rates could be evaluated. Back-calculated field values were then substituted into Terzaghi's theory of one-dimensional consolidation modified for secondary compression to observe any deviation of actual measurements from that predicted by theory. The prediction model curves followed the consolidation trends but failed to model the field data accurately. In general, secondary compression was observed in all the field cases with the NCASI plots exhibiting tertiary, quaternary and even quinary compression phases. Secondary compression accounted for 17.9% to 69% of the total settlement for the case histories. Extended-single load laboratory consolidation tests (lasting about sixteen days) were performed to evaluate the secondary compression characteristics of two paper sludges. These tests revealed a varying secondary compression rate similar to the field observations presented herein. Varying secondary compression rates for paper sludges are most likely due to various creep mechanisms and temperature. The results of this study indicate that secondary compression accounts for a large portion of the total settlement and the presence of varying secondary compression rates should be recognized in design, as well as the laboratory evaluation of consolidation characteristics.