Mitigating embankment frost heave with nano-ZnO in the Arctic

Abstract

Non-frost susceptible soils (e.g., gravel) are typically used as embankment fill to minimize the frost heave problem on the highways in the Arctic. However, accesses to the non-frost susceptible soils are limited in the remote regions, and the transportation costs for it are very high, thereby resulting that frost susceptible soils have to be used to fill the embankments. In this study, nano-ZnO was added to two types of frost susceptible soils, namely silty clay and clay, to reduce the frost susceptibility of soils and to mitigate the frost heave. Firstly, the unconfined compressive strengths of the soil samples whose the mass ratios of the nano-ZnO to the silty clays were 1.5 wt%, 3.0 wt%, 4.5 wt% and 6.0 wt% were tested. A series of isotropic freezing tests were then conducted to study the temperatures and frost heave deformations of the soil samples with the nano-ZnO of 0.0 wt%, 1.5 wt%, 3.0 wt% and 4.5 wt%, thereby verifying the effectiveness of the nano-ZnO in reducing the frost susceptibility of the soils. The optimal mass percentage of the nano-ZnO was determined by the mechanical and freezing tests. Finally, a clay embankment model with the nano-ZnO of the optimal mass percentage (defined as the nano-ZnO embankment model) during freezing-thawing cycles under various artificial rainfall conditions in the Arctic environment was tested. A clay embankment model without nano-ZnO was the control case, and defined as the control embankment model. Experimental results revealed that 1) with the increased nano-ZnO, the unconfined compressive strengths of the soil samples initially increased and subsequently decreased, and the maximum value corresponded to the mass percentage of 4.5 wt%; 2) the usage of the nano-ZnO can considerably reduce the freezing point and the frost heave deformations of the soil samples; 3) the optimal mass percentage of the nano-ZnO was 4.5 wt%. Compared with the soil sample without the nano-ZnO, the frost heave deformation of the soil sample with the nano-ZnO of 4.5 wt% was reduced by 71.98% and 78.44% using the rapidly cooling and step by step cooling method, respectively; 4) the usage of 4.5 wt% nano-ZnO was reduced the frost heave deformation of the clay embankment model by a maximum value of 74.06% under artificial rainfall, whereas the frost heave deformation of the embankment model reduced by a maximum value of 31.94% without artificial rainfall. Moreover, the mechanisms of the increase in the compressive strength and the decrease in the frost heave were analyzed. This study can provide considerable insights for mitigating the frost heave problems in highways in the Arctic when frost susceptible soil is used as embankment fill.