title: Prediction of Rainfall-Induced Shallow Landslides in the South-East Queensland Region
Creators: name: Cogan, Jacob S
Publisher: name: Griffith University
Year: 2023
Subjects: subject: landslides
subject: rainfall
subject: flume

description: Landslides occur annually worldwide from natural and man-made influences with high levels of destruction. The prediction and mitigation of landslide occurrences can be largely beneficial in minimizing destruction and loss of life due to such occurrences. Observations on the causes of landslides, ranging from earthquakes, geological instabilities and human excavations and cuttings from slopes, have detailed rainfall of a prolonged or heavy nature has been deemed the primary cause, often occurring in mountainous terrain. Documented devastating occurrences of rainfall-induced landslides causing destruction to infrastructure and property, along with loss of human life, have occurred in many European countries, America, Taiwan, Japan, Hong Kong, Nepal and India. Australia is not free of landslide risk with a summarised cataloguing detailing over 114 known landslides causing injury or death and damage to infrastructure between 1842 to December 2011. One particularly devastating landslide in Australia occurred in Thredbo, New South Wales, in 1997, causing the death of 18 people as a result of heavy rainfall coupled with snowmelt. This historical evidence of landslide activity indicates a need for the monitoring of landslides within Australian mountainous regions. The mountainous regions between Mudgeeraba and the Currumbin Valley of south-east Queensland are particularly susceptible to shallow landslides during large rainfall weather events, due to the general steepness of slopes and weathered top layers of soil overlaying bedrock. As roadways are limited through these mountain passes, rainfall-induced shallow landslides can leave people stranded either in dire need of resources or medical aid. A prime example of a weather event leading to rainfall-induced shallow landslides in south-east Queensland was ex-Tropical Cyclone Debbie, on the 31st of March, 2017. Local government reported an excess of some 25 major landslides along road corridors of the mountainous areas. Rainfall of the event saw in excess of 700 mm over 2 days. Though not always cyclonic in nature, weather patterns like these are exhibited in the region yearly, causing slope instabilities. Although landslides can occur annually in south-east Queensland, there has been limited investigation undertaken into the causes and effects of this phenomenon within the region. This means there is an ongoing risk to economy and human life, requiring the identification of key indicators of rainfall-induced shallow landslides in the region. This thesis presents a comprehensive investigation into the relationships between rainfall, slope and soil characteristics and the identification of the role they play for the initiation of rainfall-induced shallow landslides occurring in south-east Queensland. Through this thesis’ analysis, the development of predictive methods for future patterns in rainfall-induced shallow landslides for the south-east Queensland region is accomplished. The thesis scope is limited to the analysis of rainfall-induced shallow landslides occurring in the coarse-grained sandy soil typically observed between Mudgeeraba and the Currumbin Valley mountainous regions. Approaches to prediction of rainfall-induced shallow landslides are limited to the use of laboratory flume-based investigations, rainfall intensity-duration thresholds and limit equilibrium method for slope stability analysis of the region. A key mechanism finding for the onset of landslides in south-east Queensland is the observation of drastic reduction in shear strength due to increased moisture content of the soil tested. Knowing this, moisture content was found to be a suitable predictor of landslide initiation when monitored using appropriate measuring devices. From this study, it was identified that slopes in the region exhibiting slope angles between 45 to 55° are susceptible to failure when impacted by rainfalls in the range of 40 to 100 mm/h. This information aided in the development of simple predictive modelling techniques. The information obtained through the research of this thesis is beneficial for local government authorities and roadway contractors and engineers in the industry that can utilise simple tools for the prediction of rainfall-induced shallow landslides in south-east Queensland. Furthermore, from the observation of moisture content being a suitable predictor of landslide initiation, field monitoring setups could be put in place by government or researchers to further watch and study the phenomenon. These findings are applicable and can be extrapolated to other regions of the world potentially allowing for proactive risk management and reduction in destruction and damage to persons.