Predicting landslides probabilities along mountain road in Taiwan

Abstract

This paper gives a brief introduction on the background and current status of landslides along mountain roads in Taiwan and presents a detailed analysis based on the Gaussian Process model for predicting locations and occurrence times of future landslides using historical data. Based on in- herent and man-made features of failed and not-failed slopes, locations of possible future landslides are predicted. Together with historical rainfall data, a rainfall fragility graph is established. The analy- sis results show that the Gaussian Process model is effective in predicting landslide potentials and probabilities. Comparisons of the Gaussian Process analysis and the discriminant function analysis are made, which show that the former outperforms the latter in many aspects. The results are valuable for predicting where and when landslides would occur in future heavy rainfalls. The island of Taiwan was formed by the collision action of Eurasia plate and Philippine sea plate. It is relatively young in geological age. For the total area of 36000 km 2 , mountains cover more than two thirds of Taiwan. The area percentages of mountains are about 28.40% for elevation of 0~100m, 39.48% for 100~1000m, 20.22% for 1000~2000m, 10.73% for 2000~3000m, and 1.17% for 3000~4000m, respectively. To accommodate population of more than 23 million, a large portion of the lower mountain area has already been intensively developed for cultivation and tourism. To keep up with the development, an extensive mountain road network has been built over the past decades. The total length of roads with elevation above 100m in Taiwan is more than 67,000 km. Some of them were built with high engineering standards, but a large number of them were built with low en- gineering standards. Even worse, some were built along river valley with cut-slope methods and suf- fered from both river scouring problems on the down-slope and stability problems on the up-slope. Therefore, landslides in different failure types are not unusual along mountain roads when the slopes are experiencing long period of rainfalls or torrential rain accompanied with typhoons. When a landslide occurs, it may cause traffic interruption, damage vehicles and injure personnel. Therefore, it is desirable to predict where and when landslides may happen to provide a safe traffic condition for the public. Although research results on landslide prediction have been reported, those focusing on landslides along mountain roads are rare. Landslides along mountain roads are somewhat different from other types of landslides: they are affected by numerous features, especially manmade features. Due to this nature, landslide prediction for slopes along mountain roads is by no means a straightforward matter but it is an interesting topic to work with. In this study, Route T-18 in central Taiwan is chosen to demonstrate the suitability of landslide prediction using Gaussian Process model. Two main questions are of concern: (a) Given the historical landslide data along the demonstrative mountain roads in Taiwan, where are the locations along the roads with high landslide potential in the future? (b) Given the historical landslide and rainfall data, what are the landslide probabilities of the slopes along the roads in a future heavy rainfall? The former mainly concerns with the locations of future landslides, while the latter concerns with the time of landslide occurrence in future rainfalls. Note that the concept of probability is highlighted in this study due to the complexity of slope sta- bility problems: it can never be certain where and when a slope will fail because there are numerous