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International Journal of Advanced Science and Technology Vol. 28, No. 18, (2019), pp. 01-26 Landslide Occurrences in Malaysia Based on Soil Series and Lithology Factors Mohd Sofiyan Sulaiman1*, Amir Nazaruddin2, Noorbaya Mohd Salleh3, Roslan Zainal Abidin4, Nirwani Devi Miniandi5 and Abdul Hafidz Yusoff6 1,5Faculty of Ocean Engineering Technology and Informatics, University Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia 2Faculty of Civil Engineering, Universiti Teknologi MARA Cawangan Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia 3Infrastructure University Kuala Lumpur, 43000 Kajang, Selangor, Malaysia 4 Nilai University, 71800 Nilai, Negeri Sembilan, Malaysia 6Faculty of Bioengineering and Technology, Universiti Malaysia Kelantan, Jeli Kampus, Locked Bag No. 100, 17600 Jeli, Kelantan, Malaysia Abstract Past researchers have created various techniques to analyse landslide occurrences. Those techniques utilize qualitative, quantitative or semi-quantitative approaches. Each technique poses advantages and disadvantages depending on the available information, landslide inventory or area of interest. In Malaysia, landslides have become an alarming issue and fatalities are increasing in every event. These fatalities can be reduced if the landslide prone areas are mapped using zonation techniques. The main aim of this research is to produce a hazard risk map using the susceptibility index based on soil series and strata lithology in the state of Selangor, Malaysia. Over the past 20 years, this state has developed rapidly, and many housing schemes have been developed to accommodate high market demand. Moreover, this state has contributed the largest number of landslide tragedies in the past compared to the other states. Susceptibility index based on soil series and strata lithology provides high reliability after validation with past tragedies. Analytical Hierarchal Index (AHP) has been deployed to find the ranking and susceptibility index for those two factors. It was found that urban land soil series and acid intrusive lithology provide higher weightage of landslide susceptibility compared to other series or lithology. Any locations with those series and lithology will pose a critical level of landslide vulnerability. The overlaying of various series and lithology on the state of Selangor map reveals that three provinces, namely Gombak, Petaling and Hulu Langat should be given special attention should future development is to be carried out in these territories. Keywords: landslide, soil series, stratigraphy, risk, analytical hierarchal index 1. Introduction Past researchers have made four fundamental assumptions pertaining to landslide assessment and occurrence [4], [15], [34]. The assumptions are as such: a) landslides will always occur in the same geological, geomorphological, hydrogeological and climatic conditions as in the past; b) the main conditions that cause landslides are controlled by identifiable physical factors; c) the degree of hazard can be evaluated; d) all types of slope failures can be identified and classified. The first assumption is emphasized in this paper. Those four assumptions have led to the development of qualitative and quantitative landslide hazard assessments by researchers. Zonation approach or landslide susceptibility map has been applied to indicate areas where landslides are likely to occur in the future, by correlating some of the factors that contribute to landslides with historical distributions of slope failures [3]. To do so, a few techniques have been proposed, which can be grouped under two broad categories: quantitative and qualitative. In-depth discussion by ISSN: 2005-4238 IJAST 1 Copyright ⓒ 2019 SERSC International Journal of Advanced Science and Technology Vol. 28, No. 18, (2019), pp. 01-26 [4] revealed that qualitative technique has the same approach as geomorphological approach, where the degree of stability is determined by the provision of the needed information. On the other hand, quantitative approach deals with weightage and statistical measures. The latest approaches make full use of the logical-analytical model and neural network technique to assess landslide occurrences. In [22] however provides another discussion on the quantitative and qualitative approach by naming the techniques for each approach. As such, quantitative approaches include fuzzy logic, analytic hierarchy process, analytic network process, logistic regression, multivariate statistical approach and weighted linear combination. The qualitative models are derived from expert views or integration of ranking and weighting. In [3] added a new concept of heuristic approach in qualitative model. The heuristic method uses expert opinions to categorize landslide- prone areas by terms such as “very low,” “low,” “moderate,” “high,” and “very high.” This method is considered useful for producing qualitative landslide susceptibility maps for large areas [7]. Table 1 shows a summary of the available approaches to produce landslide susceptibility zoning that have been practiced worldwide. Landslide susceptibility zoning using lithology as key parameters has been deployed widely by past researchers [3], [6], [10], [17]-[18]. In [6], [10] pointed out that stratigraphy played a key role in the spatial and temporal evolution of pore water pressure during rainfall, and the onset of local instabilities. Thus, stratigraphy is an important parameter in determining landslide susceptibility. In general, factors causing landslides can be grouped into two: external and internal factors. It is widely recognized that geological factors greatly influence the occurrence of landslides, because lithological and structural variations often lead to a difference in strength and permeability of rocks and soils [29]. Among other factors (such as slope angle, slope aspect, distance to roads and faults, land use and land cover), lithology with respect to type, physical and chemical characteristics, and mineralogy play a significant role. There are two reasons for the increasing international interests in landslides: the awareness of the socio-economic significance, and the increasing pressure of development and urbanisation on the environment [4]. As development increases on sloping urban areas, more incidences of deep and shallow landslides have been reported. Over the past decade, there have been dramatic increase in cases of erosion induced landslides in Malaysia. Soil erosion, a natural process that continuously occurs without any symptoms or warning signs, has been identified as a serious issue for decades, and might become even more critical in the future as a result of uncontrolled developments [2]. Table 1. Various Techniques of Landslide Susceptibility Zoning After [3], [28] No. Broad Technique Sub-Technique Sub-Sub Category Technique 1 Qualitative Distribution (inventory) - - approach Heuristic method - - 2 Quantitative Statistical approach Bivariate statistical Weights of analysis evidence model Weighted overlay method Frequency ratio approach Information value method Multivariate statistical Logistic analysis regression model ISSN: 2005-4238 IJAST 2 Copyright ⓒ 2019 SERSC International Journal of Advanced Science and Technology Vol. 28, No. 18, (2019), pp. 01-26 Discriminant analysis Multiple regression models conditional analysis Artificial Neural Networks (ANN) Probabilistic Bayesian probability - approach Certainty factor - Favourability function - Multi criteria Analytical Hierarchy - decision making Process Rainfall threshold - model - 3 Semi- GIS-based heuristic Analytical hierarchy - quantitative approaches process (AHP) and Weighted linear - combination models According to the National Slope Master Plan (NSMP) 2009-2023, Selangor and the Federal Territory of Kuala Lumpur have experienced the most landslides since the 1970s, followed by Pahang, Penang and Sabah. Until November 2011, 600 deaths have been recorded since 1961. The highest fatality for a single landslide event was recorded on Dec 26, 1996, involving 302 people in Keningau, Sabah. Economic losses from landslides totalled almost RM 3 billion (S$1.2 billion) from 1961 to 2007 [30]. Having a tropical climate, Malaysia is prone to soil erosion due to its hot and humid condition throughout the year. The average annual rainfall in Malaysia exceeds 2,000 mm, which is above the global average. The highest annual rainfall ever recorded in the history of Malaysia was 5,293 mm [25]. Heavy rainfall can have adverse effects on soil particles because it amplifies the ability of raindrops to detach soil particles. Soil resistance against erosion is termed as soil erodibility, and its value depends on several factors such as soil structure, infiltration level and organic matter content. It is important to measure soil susceptibility to water erosion, as it is an essential parameter needed for soil erosion prediction. In [11] had produced a diagram for the determination of soil erodibility factor (K). Obtaining the soil erodibility factor (K) is crucial for the calculation of soil loss and sediment yield computation. The K factor makes full use of the soil percentage (% sand, % silt, % clay) and soil type. However, soil erodibility formula (K) is a continuous type of formula and is not meant for predicting the probability of landslide occurrence. In [1] have made the efforts of creating a binary approach by converting the soil erodibility into the probability of landslide occurrence (known as “ROM” scale). Many studies have benefited from this “ROM” scale.