Application of a Thermal-Mechanical-Biological Model to Assess Landfill Airspace Utilization under Seasonal Waste Placement in Cold Regions

Landfill settlement consists of mechanical compression and biodegradation-induced settlement, with the latter strongly controlled by waste temperature. In cold climates, waste placed in winter at subzero temperatures suppresses microbial activity, reducing stabilization until the waste reaches temperatures that support biodegradation. Cold initial temperatures, combined with insulation from subsequently placed lifts, may leave waste frozen for years depending on the thermal history of the lifts. Although sequencing of lifts is routinely planned for logistical reasons, practitioners rarely consider lift thermal history, an oversight critical in cold climates. This study evaluates how sequential placement of waste lifts under different seasonal conditions influences thermal response, biodegradation-induced settlement, and airspace utilization. Two sequencing strategies were examined: a switchback strategy, where filling alternates direction between successive lifts, and a restart strategy, where filling always proceeds from the same side of the cell. These strategies produced 12 scenarios simulated with a validated thermal–mechanical–biological (TMB) model developed by the authors. Model outcomes were assessed using the biodegradation ratio (BR), defined as the ratio of the achieved biodegradation-induced settlement across all lifts to the maximum possible biodegradation-induced settlement. Four groups illustrate the range of outcomes: winter-only ( BR = 0 % ), summer-only ( BR = 53 % ), winter–summer alternating ( BR = 28 % ), and summer–winter alternating ( BR = 27 % ). While summer-only placement across an entire landfill cell is not feasible in practice, the findings demonstrate that performance can still be maximized by sequencing lifts in a way that avoids sections of the cell where all lifts are placed in winter. Such planning enhances airspace utilization and offers environmental and economic benefits.