Abstract
The initial of debris flow can be classified into two types based on their triggering positions, that is, debris flow from slope and debris flow from gully or channel. For the former, great progress has been achieved on the mechanisms of soil failure and liquefaction. The framework established by a series of theories or laws, such as the Mohr–Coulomb criteria, the unsaturated soil mechanics, and the critical state of soil mass, has been used widely in industry and research. However, the details and discrimination basis for the transformation process from landslide into debris flow still need to be further clarified. Relatively, debris flow from gully or channel is more complex due to its various mass sources and the diversity of processes. Nevertheless, through a great number of case studies and experimental statistics, people have gradually recognized the influential rule and critical condition of factors from landform, hydrology, and other aspects on debris flow initiation. Furthermore, based on the theories of granular flow, continuum mechanics, and rheological law, some typical event-based scenarios can also be reproduced by different single-/two-phase depth integral/average numerical models. However, some key knowledge on mechanism and application level is still insufficient, such as the erosion and entrainment mechanism of materials from different sources, the boundary tractions and materials exchange, as well as the selection of prediction indicators. Three current discriminated methodologies for debris flow initiation, that is, the safety factor method, the rainfall indicator method, and the comprehensive assessment method, were summarized in this article. Considering the technical limitation of each methodology, it is believed that the establishment or improvement of a unified, stable, and open-access database system for event registration and query, as well as the development of large-scale and high-precision rainfall monitoring, is still regarded as the important aspect of debris flow prevention in the future. In addition, as an economic and efficiency means for obtaining information on potential threats and real-time hazard messages, the multielement method for debris flow is recommended as a long-term reference.
Highlights
The term “debris flow” is a cage name for the torrent that occurs in mountainous areas and carries a large amount of sediment, stones, and other debris materials
The results showed that the accuracy of related models, that is, area under the receiver operating characteristic curve (ROC) curve (AUC), could reach over 0.7 (Kern et al, 2017; Staley et al, 2017; Addison et al, 2019; Cui et al, 2019)
The research on initial mechanism of debris flow is the basis of related disaster prevention and mitigation, which is of great significance to improve the performance of debris flow monitoring and early warning
Summary
The term “debris flow” is a cage name for the torrent that occurs in mountainous areas and carries a large amount of sediment, stones, and other debris materials. Iverson’s work indicated the critical influence of pore water pressure on the formation of landslide debris flow in different mechanisms and soil types on mathematical and physical level and strongly promoted the application of relevant indicators in debris flow prediction and early warning research. Some process details, especially the issues on soil liquefaction, are still needed to be addressed, such as how to establish the mathematical relationship between vibration energy and soil cohesion, the relationships between different soil properties and liquefaction vibration, and the corresponding critical phenomena If these issues cannot be discussed sufficiently, it is difficult to break through the framework of safety factor method on slope debris flow initiation. The model assumed a scenario that in an infinite gully slope, the loose material reached the state of saturation after being
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