Biochar implications for the engineering properties of soils: A review

Use of biochar as a soil amendment for climate change mitigation and environmental remediation has been intensively studied over the past decade, yet the growing interest in biochar for geo-environmental applications is primarily motivated by its active interactions with soil in terms of engineering properties. The addition of biochar can significantly alter the physical, hydrological, and mechanical properties of soils, but the diverse biochar characteristics and soil properties lead to the fact that a generalized conclusion on the impact of biochar on soil engineering properties is difficult to reach. Considering that the effects of biochar on soil engineering properties could also potentially affect the applications of biochar in other fields, this review intends to provide a comprehensive and critical overview of biochar implications for soil engineering properties. Based on the physicochemical properties of biochar pyrolyzed from varying feedstocks and pyrolysis temperatures, this review analyzed the physical, hydrological, and mechanical performances of biochar-amended soils and the underlying mechanisms. Among others, the analysis releases that the initial state of biochar-amended soil requires special attention when evaluating the effect of biochar on soil engineering properties, yet it is usually neglected in the current studies. The review closes with a brief overview of the potential impacts of engineering properties on other soil processes, and future needs and opportunities for further development of biochar in geo-environmental engineering from academia to practice.