Performance Evaluation of Geometric Modification on the Stability of Road Cut Slope Using FE Based Plaxis Software

*Fentahun Ayalneh Mekonnen*

#### **Abstract**

Slope failures are among the common geo-environmental natural hazards in the hilly and mountainous terrain of the world. Specially it is the major difficulty for the development of construction as it causes considerable damage on the infrastructure, human life and property. Different causes of slope failure and stabilization methods are proposed by different scholars. In this study the performance of geometric modification in slope stability was investigated using numerical method. The study uses slope height, slope angle and slope profile i.e. single slope, multi slope and bench slope as a governing parameter in the performance evaluation of geometric modification on the slope stability. The evaluation was conducted on a newly constructed road cut slope using a finite element based plaxis software. The result from performance evaluation of slope profiles show that geometric modification provides better and economical slope stability. The stability of slope decreases with increase in slope height and slope angle leading to an uneconomical design of high slopes in a single slope profile. However, the use of benching improves the stability of cut slope (i.e. the use of 2 m and 3 m bench improves the factor of safety by 7.5% and 12% from single slope profile). The method is more effective in steep slopes. Similarly, the use of a multi slope profile improves the stability of slope in stratified soil with varied strength. The performance is more significant when it is used in combination with benches. The study also provides comparison of slope profiles based on different criteria's and recommend the selection profile based on site-specific considerations.

**Keywords:** slope profile, bench slope, multi slope

#### **1. Introduction**

A slope is an inclined ground surface formed naturally or by excavation for different human activities. Its stability is the major consideration in civil engineering infrastructural projects such as open-pit mining operations, road cut or embankment slopes as its failure causes considerable damage on the infrastructure, human life and property.

Instability of slope can be occurred due to internal or external factors which causes failure either by reducing the shear strength of slope material or by

increasing the shear stress on the slope [1]. Different processes such as increased pore pressure, cracking, swelling, decomposition of clayey rock fills, creep under sustained loads, leaching, weathering, and cyclic loading are responsible to a reduction in shear strengths [2]. In contrast to this, the shear stress in slopes may increase due to additional loads at the top of the slope, increase in water pressure, increase in soil weight due to saturation, excavation at the bottom of the slope, and seismic effects [1]. Also, it must be noted that, slope geometry, state of stress, and erosion contributes to the failure of slope. The mechanism of slope failure varies and takes place as speed or slow rate, depending on the type of material, slope geometry, and types of triggering factors. Slide, fall, earth flow, debris flow, topple, planar and wedge failure are the common methods of slope failure.

As both natural and human activities are responsible for the failure of slopes, it is difficult to avoid the problem entirely. However, the level of damage can be significantly reduced by assessing the stability condition and adopting different preventive measures on it. There are various remedial measures applied during and after construction to reduce the impact of slope failure and these can be grouped into four general classes i.e. geometric modification, drainage control, slope reinforcement, and retaining structure [3].

Now a day slope stability studies have been attracted researcher's attention as their understanding on the impact of slope failure in human life and infrastructural development increases. Numerous slope stability studies were carried around the world so far and better understandings are established about causes of failure, mechanisms of failure, methods of analysis, and possible remedial measures. However, the damages due to slope failure are increasing from year to year and still the major difficulty for the development of infrastructural constructions in Ethiopia. A review of previous slope stability assessments [4–6] indicates that slope failures are the main constraint for road and railway construction in Ethiopia. To overcome this problem and acquire better solutions a continuous effort is needed. Hence, this study was carried to evaluate the performance of geometric modification i.e. slope profiles (single slope, multi slope and multi slope) on slope stability using numerical methods.

#### **2. Description of the study area**

The study area is located at Adama city in Ethiopia on a newly constructed ring road project. The area is in the east African refit valley system which is dominated by escarpments of various landscapes and bordering. The slope is formed by excavation of volcanic ridges and its height extends up to 40 m with 3 m bench every 10 m. Reddish to brownish color residual soils formed by a physical and chemical process from parent rock and volcanic rocks of different degree of weathering are the major type of materials found in the cut slope (**Figure 1**).

#### **3. Geometry of slope**

Geometry is among the most critical factors controlling the stability of the slope [7, 8]. Generally, slope height, slope angle and slope profile are the major parameters in geometric modification. Cut and embankment slopes can be formed using one of the three profiles i.e. single slope, multi slope and bench slope. But depending on the composition of slope material, height of the slope, and hydrological conditions these profiles have different performance in the stability of slope.

*Performance Evaluation of Geometric Modification on the Stability of Road Cut Slope Using FE… DOI: http://dx.doi.org/10.5772/intechopen.99633*

**Figure 1.** *Location of the study area and slope section of the road.*

Single slope profile is used in cut and embankments of dense soils with enough resistance against failure with a limited height [9]. Increasing height (h) and angle of slope (α) will increase the shear stress and decrease normal stress on the potential rupture plane [2]. As a result, h and α are major parameters control the performance of single slope profile.

Multi-sloped profiles are provided in cuts where the stratigraphy of soil consists of two or more layers with different strength characteristics [9]. The method allows the use of both steep and gentle slopes in stiff and weaker layer of the slope section respectively.

**Figure 2.** *Geometric profiles of cut slope.*

#### *Landslides*

Bench slope profile is a technique in which the overall slope is divided into multiple small slopes. It reduces the driving forces above the failure surface by reducing the weight of slope [8]. Bench slope, bench height and bench width are the major parameters control the performance of bench slopes (**Figure 2**).

#### **4. Methodology**

To investigate the performance of slope profiles a newly constructed road cut slope in Adama city was used. Under this investigation the effect of slope profiles and its parameters (slope height, slope angle, bench width, no of bench, and bench angle) on the stability of slope was evaluated interims of FS and deformation. The performance of multi-slope and bench slope profiles was evaluated with respect to single slope profiles and further comparison was made between them interims of construction difficulty, appearance or esthetic value, drainage control, and accessibility for maintenance.

#### **4.1 Numerical modeling**

The numerical modeling was carried using finite element method (FEM). The method discretizes a continuum into elements to describe the behavior or actions of individual pieces and reconnecting them to represent the behavior of the continuum [10–12].

#### **5. Material parameters for modeling**

For this FE modeling an elastic perfectly plastic Mohr-Coulomb material model was used. The model uses material stiffness (E and v) as elasticity parameter, material strength (, and c) as soil plasticity and as angle of dilatancy [10]. The slope section used for this investigation has both soil and rock layers, hence to determine the parameters both field and laboratory tests were carried. The soil shear strength parameters were obtained from direct shear test and its stiffness parameters were correlated with SPT data. Similarly, the strength and deformation parameters of rock layers were determined by correlating field and laboratory tests with rock data software. The geometric and material data used for this investigation were summarized in **Figure 3** and **Table 1**.

**Figure 3.** *Cross-section of the newly constructed road cut slope.*

*Performance Evaluation of Geometric Modification on the Stability of Road Cut Slope Using FE… DOI: http://dx.doi.org/10.5772/intechopen.99633*


**Table 1.**

*Material properties used in numerical modeling.*

#### **5.1 Stability analysis**

To evaluate the stability of slope in different profiles first initial stress and pore water pressure distribution was generated using 0 procedure and phreatic water level respectively. Then the deformation and safety analysis were carried with plastic calculation and phi-c reduction method for the same loading conditions. Phi-c reduction is a method where the shear strength parameters (c and tan∅) are successively reduced until the failure occurs [13]. During the process the strength reduction factor (∑ ) is increased start from 1. The global safety factor is equal to the total multipliers ∑ at the point of failure which is expressed as the ratio of initial and reduced strength parameters [10].

$$\text{FS} = \sum \text{MSF} = \frac{\tan \mathcal{Q}\_{\text{input}}}{\tan \mathcal{Q}\_{\text{reduced}}} = \frac{\mathbf{C}\_{\text{input}}}{\mathbf{C}\_{\text{reduced}}} \tag{1}$$

#### **6. Numerical validation**

To validate the numerical model a slope section for this study was evaluated using Fellenius method (analytical solution) and the result was compared with numerical value both in FEM (plaxis) and LEM (slide) software's (**Figure 4**).

Validation also made using slope section first introduced by Zhang [14] and later used by numerous investigators i.e. Ferdlund and Krahn [15], Chen et al. [16], Griffiths and Marquez [17], Zhang et al. [18], and Chaowei et al. [19] to validate their 2D and 3D slope stability evaluations (**Figure 5**). The section was modeled using a slide, Plaxis-2D, and Plaxis-3D software with the same material and boundary condition. The result in **Figure 6** shows a drift of ± 5% from previous investigators. Generally, from both validations the result from numerical modeling shows good agreement with the analytical solution and the previous works.

**Figure 4.** *FS determination using analytical solutions.*

*Performance Evaluation of Geometric Modification on the Stability of Road Cut Slope Using FE… DOI: http://dx.doi.org/10.5772/intechopen.99633*

**Figure 5.**

*Modeling of slope section used for validation in slide, Plaxis-2D, and Plaxis-3D.*

**Figure 6.** *FS from different researchers and this study on Zhang [14] slope section.*

**Figure 7.** *Effect of slope angle and slope height on the performance of single slope profile.*

#### **7. Effect of slope height and slope angle**

Increasing angle and height of slope affects the stability by increasing the shear stress and decreasing shear strength on the potential rupture plane. To examine the effect of these parameters numerical models on **Figure 3** was made for different slope height and slope angles.

**Figure 7A** shows FS of slope for 27°, 34°, 45°, 63°, and 73° (i.e. increasing slope angle reduces the FS). Similarly, **Figure 7B** shows the effect of slope height on FS

#### *Landslides*

in an ideally sandy lean clay slope for different slope heights (i.e. increasing slope height increases the deformation and decrease the FS of the slope). Hence it is recognized that both slope height and slope angle reduce the FS of slope in the same principle i.e. increasing self-weight (driving force) above the failure surface and decreasing the normal force on the failure surface.

#### **8. Performance of bench on slope stability**

Bench width, cut angle and no bench are the major parameters which control the performance of bench slope profile. To examine the performance of benching and its parameters on the stability of slopes a typical slope section given in **Figure 3** was used. **Figure 8A** shows the FS of slope for 1, 2, 3, 4, 5 and 6 m bench width with a constant 10 m bench height. As the figure indicates stability increases with increasing bench width (i.e. FS increases in 3.5%, 7.7%, and 12% from single slope profile in 1:1 slope ratio for 1 m, 2 m and 3 m bench widths respectively). The percentage change of FS from equivalent single slope profile is 1.7%, 3.6%, 7.7% and 17.4% for 27°, 34°, 45° and 63° respectively in a constant 2 m bench width as shown in **Figure 8B**. Hence the use of benching is more effective in steep slopes.

Similarly, the effect of bench height was evaluated using uniform clayey sand soil in two cases (i.e. case 1, when the overall cut varies with constant slope within bench. Case 2, when overall cut is constant with varied slope within bench as shown in **Figure 8C**). Accordingly, decreasing bench height (increasing no of bench) increases the FS of slope in case 1. However, it has no significant effect in case 2. Generally, benches improve stability of slope in the opposite principle of slope

*Performance Evaluation of Geometric Modification on the Stability of Road Cut Slope Using FE… DOI: http://dx.doi.org/10.5772/intechopen.99633*


**Table 2.**

*FS for different combination multi-slope profiles (a= stronger slope & b= weaker slope).*

**Figure 9.** *FS and its change from single slope in % for d/t combination of multi-slope profiles.*

height and slope angle by decreasing the driving force of the slope above the failure surface. The method is effective to avoid the use of gentle and high slopes in the design of cut slope.

#### **9. Performance of multi slope profile**

To assess the performance of multi slope profile in stratified soils a layered slope section shown in **Figure 3B** is evaluated for different combinations of slope angle (i.e. in the weaker and stronger section). **Table 2** and **Figure 9** shows FS for different combination of weaker and stiffer slope section. Accordingly, FS is improved up to 30% from a single slope profile by adjustment of cut angle (i.e. decreasing weaker section and increasing stiffer section). But it should be reminded that the amount of change in FS depends on the strength characteristics of the slope section. Generally, multi slope profile allows the use of steep and gentle slope in stiff and loses materials respectively in stratified soil.

#### **10. Comparison of slope profiles**

Further comparison was made on the performance of profiles by evaluating the slope section in **Figure 10A** for single, multi, bench slope and combination both. **Figure 10B** shows the result of the comparison i.e. FS changes in 13%, 22.7%, and 37.5% from single slope profile in bench, multi-slope, and the combinations of both methods respectively. Hence the use of bench slope, multi slope and combination them provide effective stability in high and stratified slope.

**Figure 10.** *FS and deformation for different slope profiles.*

From the above evaluation, it is recognized that modification of slope geometry is one and the very first economical alternative of slope stability improvement. Although this investigation is made in a specific type of slope material there is no doubt in the role of geometric modification in slope stability. However, the selection of these slope geometry should depend on site-specific parameters i.e. susceptibility of the slope to erosion and infiltration, the variability of slope material, the height of slope, and adjacent area of the slope.

According to the evaluation result, the use of a single slope profile is effective in homogenous stiff slope material when the height of the slope is low. Otherwise, the method may not be safe and economical choice as weak and high slope sections need very gentle slopes. Multi slope profiles are suitable in slopes where there is material strength variability. It provides a very economical slope design without extra excavation by making adjustments only within the slope section. Especially the method is ideal in slopes comprise both rock and soil. The use of bench is an effective geometric measure when the height of the slope is large. It increases FS by reducing the driving force above the failure surface. In addition to this the use of bench slope can provide

**Figure 11.**

*Advantages and limitations of slope profiles.*

*Performance Evaluation of Geometric Modification on the Stability of Road Cut Slope Using FE… DOI: http://dx.doi.org/10.5772/intechopen.99633*

the following advantages. (1) It reduces the area of the slope exposed to rainfall infiltration as it allows the use of steep slope between every benching. (2) It provides effective drainage control by collecting the rainwater from each slope profile and draining it laterally to ditches. (3) It provides access to side slopes for maintenance, plantation of vegetation, and decoration. (4) It uses for collection of debris falls above it. (5) It provides esthetic value and better appearance for slopes especially when it located around towns. In general slope profiles have advantages and limitations depending on site specific conditions as shown in **Figure 11**.

#### **11. Conclusion**

The performance evaluation of slope profiles in this study was made for the objective of creating awareness on the effect and its suitable condition of different geometric profiles on slope stability. The effect of geometric parameters like slope height, slope angle, bench width, no of bench and bench angle on slope stability were evaluated interims of FS and deformation on selected critical slope sections from the newly constructed road cut slope. From the result, it has been seen that geometric modification will provide better and economical slope stability compared to other structural remedies.

Accordingly, the stability of slope decreases with an increase in slope height and slope angle in single slope profile leading to an uneconomical design of high slopes in a single slope profile. Benching provides an important stability for cut slope especially for slopes having larger height and its performance is more effective in steep slopes. Bench width and bench height also parameters which affect the performance of benching. Multi-slope profile provides an effective slope stability in a stratified soil of varied strength. It allows economical slope design without extra excavation by making adjustments only within the slope section. In addition to its direct effect on the FS, slope profiles have different performance on drainage control, access to maintenance, and its esthetic value. Therefore, the selection of slope profiles during design should be based on site-specific considerations.

#### **Author details**

Fentahun Ayalneh Mekonnen Adama Science and Technology University (ASTU), Adama, Ethiopia

\*Address all correspondence to: fantahunayalneh@gmail.com; irccd@astu.edu.et

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **References**

[1] Searom, G. (2017). Landslide Hazard Evaluation and Zonation in and Around Hagereselam Town. A Thesis Submitted to School of Earth Sciences Addis Ababa University, Ethiopia.

[2] Prasad, N. (2017). Landslides – Causes and Mitigation Technical Report Centre for Water Resources Development and Management, India.

[3] Popescu, M. (2001). A Suggested Method for Reporting Landslide Remedial Measures International Union of Geological Sciences Working Group on Landslides, Commission on Landslide Remediation.

[4] Eleyas, A., Li Jian Lin, Costas I. Sachpaz, Deng Hua Feng, Sun Xu Shu, and Anthimos Anastasiadis (2016). Discussion on the analysis, prevention, and mitigation measures of slope instability problems: A case of Ethiopian railways. Electronic Journal of Geotechnical Engineering (21.12), pp. 4101-4119.

[5] Woldearegay, K. (2013). Review of the occurrences and influencing factors of landslides in the highlands of Ethiopia with implications for infrastructural development. Momona Ethiopian Journal of Science 5(1), 3-31.

[6] Samuel, A. (2017). Slope Stability Analysis of Rainfall Induced Landslides. A Case Study on Gohatsion – Dejen Road Abay Gorge. Masters Thesis in Addis Ababa Science and Technology University.

[7] Navya, B., and Hymavathi, J. (2017). Stability Analysis of Slope with Different Soil Types and Its Stabilization Techniques. Department of Civil Engineering, Institute of Aeronautical Engineering, Dundigal.

[8] S. Alfat, L. M. Zulmasri, S. Asfar, and M. S. Rianse. (2019). Slope stability

analysis through variational slope geometry using Fellenius method. Journal of Physics: Series 1242.

[9] ERA (2013). Geotechnical Design Manual: Ethiopian Roads Authority Series of Road and Bridge Design Documents. Addis Ababa, Ethiopia.

[10] Burman, A., Acharya, S. P., Sahay, R. R., and Maity, D. (2015). A comparative study of slope stability analysis using traditional limit equilibrium method and finite element method. Asian Journal of Civil Engineering.

[11] Plaxis (2013). Finite Element Program Developed for the Analysis of Deformation, Stability, and Ground Water Flow in Geotechnical Engineering. Ground Water Flow in Geotechnical Engineering Bv, Netherlands.

[12] Raghuvanshi, T. K. (2017). Plane Failure in Rock Slopes – A Review on Stability Analysis Techniques. Journal of King Saud University-Science.

[13] Chen, B. (2018). Finite element strength reduction analysis on slope stability based on ANSYS. Environmental and Earth Sciences Research Journal 4(3), 60-65.

[14] X. Zhang (1988). Threedimensional stability analysis of concave slopes in plan view. Journal of Geotechnical Engineering 114(6), 658-671.

[15] Fredlund, D.G., and Krahn, J. (1977). Comparison of slope stability methods of analysis. Canadian Geotechnical Journal 14(3):429439. DOI:10.1139/t77-045

[16] Chen, J., Yin, J.-H., and Lee, C.F. (2003). Upper bound limit analysis of slope stability using rigid finite elements *Performance Evaluation of Geometric Modification on the Stability of Road Cut Slope Using FE… DOI: http://dx.doi.org/10.5772/intechopen.99633*

and nonlinear programming. Canadian Geotechnical Journal 40(4):742752. DOI:10.1139/t03-032

[17] Griffiths, D., and Marquez, R. (2007). Three-dimensional slope stability analysis by elasto-plastic finite elements. Geotechnique 57(6):537-546.

[18] Zhang, Y., Chen, G., Zheng, L., Li, Y., and Zhuang, X. (2013). Effects of geometries on three dimensional slope stability. Canadian Geotechnical Journal 50(3):233-249.

[19] Chaowei, S., Junrui, C., Bin, M., Tao, L., Ying, G., and Huanfeng, Q. (2019). Stability Charts for Pseudo-Static Stability Analysis of 3D Homogeneous Soil Slopes using Strength Reduction Finite Element Method.

#### **Chapter 7**

## Assessment of Landslide Risk in Ethiopia: Distributions, Causes, and Impacts

*Getnet Mewa and Filagot Mengistu*

#### **Abstract**

The complex geological and geomorphological settings of Ethiopia, consisted of highland plateaus, escarpments, deeply dissected valleys, and flat lowlands, are results of multiple episodes of orogenesis, peneplanation, crustal up-doming, faulting, and emplacement of huge volumes of lava. The broad elevation contrast raging from about −125 m to 4550 m Above Mean Sea Level (AMSL) is an important factor in determining the climate regimes, vegetation types, and even populations' lifestyles. In Ethiopia landslides, mostly manifested as rockfall, earth slide, debris, and mudflow, are among the major geohazard problems that immensely affects life, infrastructures, and the natural environment. They widely occur in the central, S-SW, and N-NW highland regions. This study discusses the distributions, causes, and impacts of landslides and presents a susceptibility zoning map produced applying the weighted overlay analysis method in the ArcGIS environment. For this purpose, key parameters (lithology, elevation, rainfall, slope angel, land use-land cover, and aspect) were selected and assigned weights by considering their contributions to slope failures. Correlations with inventory data have shown very good matching, where more than 90% of the observed data fall in areas categorized either as moderate, high, or very high susceptible zones, where appropriate risk assessments could be mandatory before approval of major projects.

**Keywords:** orogensis, landslide susceptibility, plateau, rockfall, earth slide

#### **1. Introduction**

Landslide is a phenomenon that represents the downward movements of a wide range of slope-forming materials (soils/rocks) due to gravitational and other driving forces [1, 2]. Considering the characteristics of the sliding materials and mechanisms of movements they can be classified as falls, topples, slides, flows, spreads, or any mixture of these and occur either slowly or suddenly. Situated in the horn of Africa between 33 and 48°E longitude and 3.40 and 14.85°N latitude, Ethiopia is the second African nation with a population of about 115 million (www.worldometers.info) and a surface area of 1.122 million km<sup>2</sup> . The landscape constitutes highlands plateaus, dissected valleys, escarpments, gentle slopes, and flat plains. These land features are results of geodynamic processes associated with the establishment of the East African Rift System (EARS), which is a narrow

North-west - South-east (NE-SW) elongated rift with thin continental lithosphere. This rift dissects Ethiopia diagonally into western and eastern plateaus that represent the Nubian and Somalian plates, respectively (**Figure 1**) [3–5]. Active rifting processes combined with local and global drivers (like seismicity, hydrometeorological events, and demographic factors) have created a suitable environment for the widespread effects of landslides. It occurs in the mountainous regions of Ethiopia dominantly in the North-Northwest (N-NW), central and South – Southwest (S-SW) highlands, and rift-margins, usually following intensive precipitations and brings variable impacts on life, built infrastructures, and natural environment [6–9].

In this work, the distributions, probable causative factors, and impacts of landslides are described with more emphasis on infrastructures using few selected case studies. Applying different secondary sources, a landslide inventory map is compiled and relationships between the natural attributes (lithology, slope height, slope angle, rainfall, and land use-land cover) and spatial distributions of landslides are assessed. Moreover, a susceptibility zoning map is generated involving the mentioned parameters to which weights were assigned considering their significance to slope failure. Such a map serves as an input to delineate areas according to their importance to various developmental activities and also helps to identify risk

#### **Figure 1.**

*Generalized map of the East African Rift System (the dotted lines show boundaries of the East African Rift System, while the triangles represent volcanic centers (from Riftvolc consortium, 2013).*

potential ones that demand more evaluations and implementation of mitigation measures before major projects are supported.

#### **2. Geomorphology, climate, and general geology**

Ethiopia's land surface is characterized by wide elevation contrast that varies from about 125 m below sea level to 4550 m above mean sea level which represents the lowest point in the world, Danakil Depression, and Ras-Dashen mountains (**Figure 2c**). The elevation is the key determinant that defines the climatic conditions of Ethiopia. Accordingly, the country is divided into five climatic zones (**Figure 2a**) that locally known as *Wurch* (very cold), *Dega* (cold), *Weyinadega* (moderate), *Kola* (hot), and *Breha* (very hot temperature zone) [10]. They are distinguished by distinct precipitation and temperature regimes, vegetation and crop types, and even lifestyles of the populations. *Wurch*, *Dega*, and *Weyinadega* climatic zones typically represent the northern, central, and SW highlands as well as rift neighboring plateaus (**Figure 2b** and **c**). They are described by mediumhigh altitudes (mainly above 1500 m amsl), moderate-high precipitation (above 1000 mm/year), and low-moderate average temperatures (below 25°C). Areas like Tarmaber, Meket, Gashena, Semen Mountains, Arsi, and Bale mountains with elevations above 3200 m amsl that intermittently receive snow and hail (personal communications with local people in 2019; World Institute of Conservation & Environment) constitute this category. Meanwhile, *Kola* and *Bereha* climatic zones, representing the NE (Afar), western (Humera-Metema), S-SW (Gambela, southern Omo), and eastern Ethiopia, show low altitudes, high-very high temperature (above 30–50°C), and very low precipitation (<500, rarely up to 750 mm/year).

The rifting process has defined not only the geomorphology but also the geological settings of Ethiopia, which are discussed in many works [3, 6, 11, 13, 14]. Hence, the formations that underlay the Ethiopian territory differ in composition and age, which ranges from Quaternary to Precambrian (**Figure 2c**). The oldest Precambrian basement rocks are represented by high-grade ortho- and paragneisses and migmatites as well as low-grade volcano-sedimentary—ultramafic assemblages and granitoids [13]. These Precambrian rocks constitute part of the Pan-African Mozambique belt and are distributed in the northern, western, and southern parts of Ethiopia. These formations have undergone prolonged erosion and denudation during Paleozoic that resulted in undulated terrain over which thick Mesozoic sediments (mainly sandstone and limestone) were deposited. The Jurassic sediments cover wide areas of eastern and some places in central and northern Ethiopia. Uplifting of the Afro-Arabian block during Tertiary has resulted in the eruption of a large volume of lava through fractures and covers a substantial part of the country

#### **Figure 2.**

*Climatic zones (a), average annual rainfall distribution (b), and simplified geological (overlain on the topographic) maps of Ethiopia (c). Sources: [10–12].*

forming elevated terrains. During this period, sediments deposition took place that cover eastern Ethiopia. Meanwhile, the quaternary period is known for the placement of volcanic lava in areas from Afar depression up to the Lakes Region in the central main Ethiopia rift. Thick Quaternary sediments are distributed in Gambela, Borena, Metema, and few other flat lowland areas (**Figure 2c**).

From the demographic perspective, areas categorized as *Wurch*, *Dega*, and especially *Weynadega* zones, are the most ideal and preferred for settlement due to the availability of sufficient water, fertile lands, and suitable climate for life. But the spread, frequency, and severity of landslides in these areas are more than in *Kola* and *Breha zones*, where the climates are more hostile and flatness of terrain and scarcity of waster do not favor mass movements.

#### **3. Objectives**

The basic objective of this study is to examine the distributions, causative factors, and impacts of landslides and acquire a fundamental understanding enabling to develop effective mitigation measures that help to save life and the economy. Accordingly, its specific objectives are: (a) conduct inventory of landslide occurrences across the nation; (b) map links between the spatial distributions and natural attributes that trigger and/or aggravate landslides; (c) assess impacts of landslides on life and infrastructures; d) produce landslide susceptibility zoning map of Ethiopia.

#### **4. Methods and materials**

The methodology used in this study comprises—(a) collection and analyses of geological, engineering geological, and geo-hazard data from published and unpublished reports and research publications [11, 15–23]. All data are compiled in the geographic coordinate system using WGS84 datum; (b) collection of rainfall data the Chirps gridded data for the year 2015 available online was used after comparing it with the National Meteorological Agency (NMA) data, which was found almost alike; (c) download land use-land cover map from National Aeronautics and Space Administration (NASA) web page; (d) data about past landslides events and their impacts. This includes information about the date and time of occurrences, deaths, injuries, forced resettlements, damages to infrastructure, and possible causes; Government offices, non-governmental organizations (NGOs), private firms, research publications, mass media, and local communities, including elder people with knowledge previous events, have served as sources; (e) 30 m resolution DEM data—important inputs about slope height (elevation), slope gradient, and slope direction (aspect) are extracted. These data are closely linked to rainfall and temperature distributions, soil humidity, soli thickness, vegetation types, and density as well as hydrological features of sloppy areas that determine the scale/rates of mass movements; (f) applying a multi-class scoring system based on assigning of weights to selected parameters contributing to slope failure, produce landslide susceptibility zoning map [24, 25].

#### **5. Inventory, distribution, and impacts of landslide**

This landslide inventory has identified more than 600 locations across the nation, where landslides occurrences are clearly observed, very few of them are

#### *Assessment of Landslide Risk in Ethiopia: Distributions, Causes, and Impacts DOI: http://dx.doi.org/10.5772/intechopen.101023*

even known with a history of repeated events. Moreover, it reflects localities, where potential landslide risks are imminent [7–9, 15–23, 26–29]. The distribution of inventory data well correlates with lithology, elevation, structural, rainfall, and seismicity maps. Only considering the patterns, landslides occurrences are tentatively classified into four blocks, Block A–D (**Figure 3**). *Block A* represents the N-NE parts of the country, including the eastern part of the western plateau, western rift escarpments, and some places on the rift floor. It stretches from north of Mekele through Michew, Woldiya, Dese, Kombolcha, Kemisse, Shewarobit and continues to the south of Debrebirhan. Major parts of this block are underlain by Tertiary and Quaternary volcanic, whereas Mesozoic sediments are distributed at the NE part of the block covering limited areas of SE Tigray.

Dese and its surrounding are the most well-known areas, where recurrent landslides cause impacts on settlements, roads, and other properties (**Figure 4a** and **b**). At many places, emerging springs from near surfaces are observed which indicate shallow groundwater. So, steep terrain, undercutting of stream banks, slope erosion, and shallow groundwater are key factors that trigger/aggravate displacement of slope materials. Meanwhile, huge volcanic blocks that are almost detached from the parent rocks are observed at the southern end of the block, in Mushmado village, Say-Debir district, about 8 km from Lemi town (**Figure 4c**). The probability that these blocks would crumble into the valley side is very high if triggered by extreme hydrometeorological, seismic, or other events and will put life, infrastructures, and farmlands in the valley under very high rockfall risk.

*Block B* encompasses areas between 8 and 13°N latitude and 36.5 and 39°E longitude. Many zones in East and West Gojam (Gozamin, Gonch-Siso Ense, Hulet-Ej-Ense, Shebel-Berenta, Awabel, Aneded, Machakil, Dejen, Adet, Sekela), East Wollega (Ambo, Gedo, Weliso), and Gonder (Lai-Armachoho, Ebinat, Guangua, Quarit) are found here. Moreover, such rivers like Abay, Tekeze, Beshilo, and their main tributaries that formed deep valleys are also among the risk vulnerable areas. The dominant landslide types are rockfall and rock/soil slides, to some extent mudflows. Their impacts on infrastructures and farmlands are quite significant.

The landslides in the Abay gorge, between Dejen and Gohatsion main road, have long and repeated histories, and this economically vital route passes through the 40 km wide Abay (Nile) valley (**Figure 5**). Subsurface investigations carried out within this valley revealed the depths to the slip planes mainly vary are the range of 14–25 m [22]. Even though deaths are not reported, unofficial sources disclosed that the cost of monitoring and road maintenance exceeds 1.5 million USD/year.

**Figure 3.** *Landslide inventory map (left) and landscape of NE part of Ethiopia (right).*

#### **Figure 4.**

*Panoramic views of landslides: (a) partial settlement of house foundation, in Dese town; (b) debris slide threatening the Addis Ababa-Dese main road, Kewet district, Debresina town; (c) rockfall risk in Mushmado village, Saya-Debir district, North Shewa zone.*

#### **Figure 5.**

*View of landslide occurred in Kurar village, Dejen side (a), the same route, but on the Gohatsion side (b–d): road under maintenance in June 2010 (b), rockfall and debris slide damaged it in August 2010 (c), the site was visited in September 2019 (d).*

*Block C* represents south-southwestern Ethiopia and the landslide occurrences are identified within 36–39°E longitude and 5–8°N latitude. It includes Ziway, Shashemene, Hawasa, Hosaina, Adami-Tulu, Jima, Dila, Sodo, Agremariam, Koso Jinka, Sawla, Arbaminch Zuria, Chincha, Gofa, Gidole, Konso, Bako-Gazer, Basketo, and many others places. Along the rift margins, where slope gradients are relatively high, the landslides are manifested by rockfall, debris, and mudflows. A massive landslide that occurred in Gidole, about 55 km SE of Arbaminch town, is a good example that demonstrates how severe is the economic, social, and environmental impacts of landslides in the region (**Figure 6**).

This recent occurrence within the deeply excavated zone (up to 25 m) started in 2009 following intensive rainfalls that saturate the subsurface. The road construction intended to connect Gidole with the Arbaminch-Konso main road has affected the toe parts of the old landslide zone and resulted in the release of shallow groundwater that triggered that landslide. To prevent mass movement slope regarding, about 250 m long retaining walls and drainage ditches were constructed. But due to the large extent of the sliding zone these measures did not change the situation, rather doubled the project cost. So, construction across the failed was abandoned in 2013.

The landslide observed in Alem village, Dodota district, in September 2019 has severely damaged a section on the Dera-Asela main road (**Figure 7a**). The mudflow occurred on May 28, 2018 (**Figure 7a** and **b**) following heavy rainfalls has triggered the sudden movement of a huge volume of earth mass from the head of the landslide and buried houses with 22 people in Western Arsi Zone, Tulu-Gola village, of which 14 were from the same family (May 30, 2018, the Ethiopian reporter).

*Block D* mainly constitutes the eastern part of the Main Ethiopian Rift, such as different districts of East Shewa, Arsi, Harage, Diredawa, and Jigjiga zones. Accordingly, Adama, Chole, Cheleleka, Merti, Fentale, Golelcha, Mechara, Lome, Asebe-Teferi, Bedeno, Kersa, Deder, Chiro, Haromay, Melka-Jilo, Fedis, Gursum, and the areas with landslide records. Rockfall, rock slide, and debris flows are the

*Assessment of Landslide Risk in Ethiopia: Distributions, Causes, and Impacts DOI: http://dx.doi.org/10.5772/intechopen.101023*

#### **Figure 6.**

*Panoramic view of a landslide body in Welaite village, 2 km NE of Gidole town observed in March 2011 (a), and the same body observed in March 2016 (b). Note that in 2011 its width was about 40 m whereas in 2016 it expanded to about 200 m.*

**Figure 7.**

*Road collapse at Alem village, Dodota district, along with the Dera-Assela road (a) and mudslide that killed 22 people and domestic animals in Tulu-Gola village, Western Arsi zone (b and c).*

widely observed landslide phenomena. At many places, the landslides are associated with highly weathered and fractured volcanic (ignimbrites and basalts) with steep slope gradients (up to 75°).

In general, this inventory survey has provided tangible information about the spatial distribution, main causative factors, and impacts of landslides. Meanwhile, lack of well-organized records about the types and extents of damages, at this stage it is impossible to give any credible estimations of the economic and environmental losses caused by landslides. Abay A. [30] estimated the losses from 1998 to 2003 to be 135 death, 3500 displaced households, and 1.5 million USD worth of property damages. B. Abebe, et al. [8] stated that landslides that occurred between 1993 and 1998 have claimed hundreds of human lives, damaged over a hundred kilometers of asphalt roads, destroyed many houses, farmlands, and natural vegetations. Similarly, a compilation of data from mass media, newspapers, different reports, and affected communities, (including Fana Broadcasting Corporation; Ethiopian Broadcast Corporation (EBC); Walta Information Center; GSE unpublished technical reports published in 2003–2019) revealed that only between 2016 and 2020 more than 302 people and 1500 domestic animals were killed (**Table 1**).

The landslide in different parts of the country is associated related with three distinct geological setups—(a) landslides developed within the Territory volcanic environment where saturated pyroclastic materials and clay are present as intercalations within the volcanic flows that cover a wide area of the Ethiopian highlands; (b) landslides formed within the sedimentary terrain and the presence of siltstone, shale, and marl as intercalations within the limestone sequence. These are common in the Abay (Nile) valley, in areas south of Mekele (Northern Ethiopia); (c) presence of unstable colluvial materials (silt and clay with gravel and boulder matrix) in areas of relatively gentle terrain covering different formations. Overall, the intercalation within the volcanic and sediments acts as rupture surfaces that aggravate easily displacement of landmasses whenever absorb more fluid in the rainy season.


**Table 1.**

*Summary of landslide inventory showing affected districts and death and injury reported from 2016 to 2020.*

#### **6. Landslide causative factors**

The root causes that initiated or accelerated landslide observed at various locations could be associated with the following factors—(a) presence of physically incompetent (soft) earth materials that make up slope surfaces or elevated terrains and also effects of structural discontinuities in areas; (b) intensity and duration of rainfall and effects flooding, erosion a well as groundwater level fluctuations; (c) slope heights and (elevation) and slope angles, which favor mass movements; (d) poor earthwork practices during infrastructure developments (constructions of roads, bridges, dams/ reservoirs), and quarrying for mine exploitations. These works involve the removal of earth masses from one place and dumping it into another place which causes either mass deficiency or excess load or both; the effects destabilize slop balances; (e) demographic factor expressed by fast population growth that accompanied by a continuous struggle for resource share. Such struggles put too much pressure on the natural environment and aggravate slope movements; (f) passiveness to enforce code of land-use practices and make accountable those who violate norms; (g) lack of awareness (illiteracy) among rural communities about the influence of landslides in their livelihoods; (h) absence of alternative means of subsistence for rural youth community who have little access to land ownership. So, they rely on over-using of the natural environment that leads to intensive land degradation. Except the natural factors, the human-related ones seem to be fully manageable if better awareness is created, job opportunities are improved and extreme poverty is reduced, land use and land administration codes and practices are enforced, and traditional community practices on land and forest preservations are fully respected. These measures play their role to improve communities' resilience to cope up with the impacts of landslides. The spatial associations between landslide and seismicity are explained in different works [4, 31–33]. In the Ethiopian context, the occurrences of landslides and earthquake epicenters that are practically concentrated within the rift system and surrounding plateaus are found to have very close correlations. But no instrumental records are available that justify the contribution of ground vibrations to triggering landslides.

*Assessment of Landslide Risk in Ethiopia: Distributions, Causes, and Impacts DOI: http://dx.doi.org/10.5772/intechopen.101023*

#### **7. Landslide risk susceptibility zoning**

Landslide susceptibility zoning maps are useful tools to differentiate areas that are suitable for agriculture, infrastructure development, national parks, or other purposes as well as delineate risk-prone areas that should be either protected or rehabilitated before approval of any developmental projects [24, 34, 35]. In Ethiopian landslide, mapping and risk zonation were

carried out in specific hazard affected areas, mostly in the highlands and rift regions, using ground survey and remote sensing data [8, 22, 27, 28, 30, 36–40]. However, in this work attempt is made to produce a landslide susceptibility zoning map of the country and correlated with the inventory data acquired through extensive fieldworks mainly by the Geological Survey of Ethiopia, where the lead author has been working for a long time. The field observation data was also used for validation purposes. Thus, the parameters for analyses were selected based on the expert's decision to which weighted values were assigned according to their contributions or influence to slope instabilities [24, 25]. The weights given to involved parameters are as follows: For lithology, elevation, and rainfall—20% each, for slope angle and land use-land cover—15% each, and for aspect—10%. Initially, each of these parameters was sub-divided into five categories, which represent the very low, low, moderate, high, and very high landslide susceptibility zones.

Then using the weighted overlay method in the ArcGIS environment, the map displayed in **Figure 8** is generated. The spatial coverage of each class was calculated by multiplying the corresponding raster counts by the grid pixel sizes and dividing a single class value by the total areal coverage and then multiplying by 100%. Accordingly, about 49.1% of Ethiopia's land surface is susceptible to landslides, of which 39% moderate, 10% high, and 0.1% very high-risk zones. Similarly, 50.9% of the territory is categorized either as very low (5.9%) or low (45%) susceptible zones (**Table 2**).

**Figure 8.** *Landslide susceptibility zoning map of Ethiopia and known landslide occurrences.*


**Table 2.**

*Landslide susceptibility zoning.*

#### **8. Conclusions**

This assessment clearly indicated that landslides are major threats to life, infrastructures, and the natural environment. Natural and human-induced factors (existences of poorly consolidated, easily erodible, saturated and soft earth materials, high slope gradients, intensive or continuous precipitations with subsequent flooding and erosion, scarcity or absence of vegetation cover in sloppy terrains, ground vibrations or seismicity, and continuous growth of population with poor land-use practices) are among the key causes that exposed about 49% of the country to landslide risks. Unfortunately, until the road sector sensed the real challenges posed by a landslide and the ever-increasing rates of fatalities and environmental losses became evident, the issue has never been taken seriously. Hence, it is quite important to proceed with landslide risk assessments to identify and prioritize areas based on their extents, frequency of occurrences, the severity of consequences, as well as nature of different elements exposed to risk. This could be possible through careful considerations of updated landslide inventory data/maps and introducing varieties of risk susceptibility models based on integrated analyses of high-resolution remote sensing and ground observation data, which represent distributions of natural and human-related factors. Ultimately, such comprehensive assessments will play a positive role to ease consequences on life, infrastructures, and the natural environment. It is important to underline that the existing trends of land-use practices are completely inadequate to manage impacts of human-induced landslides that occur very widely. Therefore, implementing zero tolerance for improper land uses through stringent monitoring and enforcement of relevant policies, guidelines, directives, and respecting important social norms must be taken as fundamental tasks of all concerned bodies.

#### **Acknowledgements**

We are very grateful to geoscientists of the Geological Survey of Ethiopia (Leta Alemayehu, Habtamu Eshetu, Yewunesh Bekele, Biruk Abel, Abaynesh Mitiku, Tekaligene Tesfaye, Yekoye Bizuye, Debebe Nida, and many others), Addis Ababa University, Ethiopian Roads Authority, National Disaster Risk Management Commission (NDRMC), and other who put tremendous efforts to travel to various parts areas of the country and collect invaluable data used in this assessment. We also extend our sincere appreciation to those who put direct or indirect contributions to this piece of work.

*Assessment of Landslide Risk in Ethiopia: Distributions, Causes, and Impacts DOI: http://dx.doi.org/10.5772/intechopen.101023*

## **Author details**

Getnet Mewa\* and Filagot Mengistu Institute of Geophysics, Space Science and Astronomy, Addis Ababa University, Ethiopia

\*Address all correspondence to: getmewa@gmail.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **References**

[1] Varnes DJ. Slope movement: Types and process. In: Schuster RL, Krizek RJ, editors. Landslides: Analysis and Control, Special Report No. 176. Washington D.C.: Transportation Research Board, National Research Council; 1978. pp. 11-33

[2] Hungr O, Leroueil S, Picarelli L. The Varnes classification of landslide types, an update. Landslides. 2014;**11**:167-194

[3] John BS. Synopsis of Geology of Ethiopia. Search and Discovery Article #70215. 2016

[4] Mazzarini F, Keir D, Isola I. Spatial relationship between earthquakes and volcanic vents in the centralnorthern Main Ethiopian Rift. Journal of Volcanology and Geothermal Research. 2013;**262**:123-133

[5] Chorowicz J. The East African rift system. Journal of African Earth Sciences. 2005;**43**:379-410

[6] Abbate E, Bruni P, Sagri M. Geology of Ethiopia: A review and geomorphological perspectives. In: Landscapes and Landforms of Ethiopia. 2015. pp. 33-64, World Geomorphological Landscapes book Series (WGLC)

[7] Woldearegay K. Review of the occurrences and influencing factors of landslides in the highlands of Ethiopia: With implications for infrastructural development. Momona Ethiopian Journal of Science (MEJS). 2013;**5**(1):3-31

[8] Abebe B et al. Landslides in the Ethiopian highlands and the rift margins. Journal of African Earth Sciences. 2010;**56**(2010):131-138

[9] Ayenew T, Barbieri G. Inventory of landslides and susceptibility mapping in the Dessie area, northern Ethiopia. Engineering Geology. 2004;**77**(1-2): 1-15. DOI: 10.1016/j.enggeo.2004.07.002

[10] Kidanewold BB, Seleshi Y, Melese AM. Surface Water and Groundwater Resources of Ethiopia: Potentials and Challenges of Water Resources Development. 2004

[11] Tefera M, Chernet T, Haro W, Teshome N, Woldie K. Geological Map of Ethiopia. Bulletin/The Federal Democratic Republic of Ethiopia, Ministry of Mines and Energy, Ethiopian Institute of Geological Surveys. No. 3; 1996

[12] Fazzini M, Bisciet C, Billi P. The climate of Ethiopia. In: Landscapes and Landforms of Ethiopia. Edition: World Geomorphological Landscapes. 2010. DOI: 10.1007/978-94-017-8026-1\_3

[13] Yibas B et al. The tectonostratigraphy, granitoid geochronology and geological evolution of the Precambrian of southern Ethiopia. Journal of African Earth Sciences. 2002;**34**(2002):57-84

[14] Kazmin V. Geological map of Ethiopia 1:2,000,000, 1st ed. and explanatory notes. Geological Survey of Ethiopia, National Government Publication; 1973

[15] Eshetu H, et al. Engineering Geological & Geohazard Mapping of Dese Map Sheet. GSE Unpublished Technical Report. Addis Ababa: Geological Survey of Ethiopia; 2013

[16] Nida D, Bizuye Y. Geological Hazards and Engineering Geology Map of Hosaina Map Sheet. GSE Unpublished Technical Report. Addis Ababa: Geological Survey of Ethiopia; 2014

[17] Abel B, et al. Akakai Map Sheet Engineering Geological Mapping and Geo-Hazard Assessment. GSE Unpublished Technical Report. Addis Ababa: Geological Survey of Ethiopia; 2012

[18] Eshetu H, et al. Engineering Geological & Geohazard mapping of *Assessment of Landslide Risk in Ethiopia: Distributions, Causes, and Impacts DOI: http://dx.doi.org/10.5772/intechopen.101023*

Nazareth Map Sheet, GSE Unpublished Technical Report. Addis Ababa: Geological Survey of Ethiopia; 2012

[19] Negash T, Legesse F. Engineering Geological Mapping of Debrebirhan Map Sheet. GSE Unpublished Technical Report. Addis Ababa: Geological Survey of Ethiopia; 2014

[20] Mitiku A. Detail Engineering Geology and Geo-Hazard Investigation of Selected Areas in Jima Map Sheet. GSE Unpublished Technical Report. Addis Ababa: Geological Survey of Ethiopia; 2015

[21] Mitiku A. Engineering Geological and Geo-Hazard Distribution Mapping of Ageremariyam Map Sheet. GSE Unpublished Technical Report. Addis Ababa: Geological Survey of Ethiopia; 2016

[22] JICA-GSE. The Project for Development Countermeasures against Landslides in the Abay Gorge, Ethiopia. Final Report. Addis Ababa: Geological Survey of Ethiopia; 2012

[23] Eshetu H, et al. Geological Hazards and Engineering Geology Maps of Dilla (NB 37-6). GSE Unpublished Technical Report. Addis Ababa: Geological Survey of Ethiopia; 2014

[24] Fell R et al. Guidelines for landslide susceptibility, hazard and risk zoning for land-use planning. Engineering Geology. 2008;**102**(2008):99-111

[25] Soeters R, van Westen CJ. Slope instability recognition analysis and zonation. In: Turner KT, Schuster RL, editors. Landslides: Investigation and Mitigation, Special Report No. 247. Washington DC: Transportation Research Board National Research Council. pp. 129-177

[26] Feseha S, Mewa G. Road failure along the Dedebit-Adiremets road, Northern Ethiopia. Journal of African Earth Sciences. 2016;**118**:65-74

[27] Fubelli G, Guida D, Cestari A, Dramis F. Landslide hazard and risk in the Dessie town area (Ethiopia). In: Presented at the World Landslide Forum, Landslide Science and Practice. Vol. 6. Addis Ababa: Geological Survey of Ethiopia; 2013

[28] Ayalew L. The effect of seasonal rainfall on landslides in the highlands of Ethiopia. Bulletin of Engineering Geology and the Environment. 1999;**58**:9-19

[29] Varilova Z et al. Reactivation of mass movements in Dessie graben, the example of an active landslide area in the Ethiopian Highlands. Landslides. 2015;**12**:985-996. DOI: 10. 1007/s10346- 015-0613-2

[30] Abay A, Barbieri G. Landslide susceptibility and causative factors evaluation of the landslide area of Debresina, in the southwestern Afar escarpment, Ethiopia. Journal of Earth Science and Engineering. 2012;**2**(3)

[31] Nowicki Jessee MA, Hamburger MW, Allstadt K, Wald DJ, Robeson SM, Tanyas H, et al. A global empirical model for near-real-time assessment of seismically induced landslides. Journal of Geophysical Research: Earth Surface. 2018;**123**:1835-1859

[32] Tonnellier A, Helmstetter A, Malet J-P, Schmittbuhl J, Corsini A, Joswig M. Seismic monitoring of soft-rock landslides: The Super-Sauze and Valoria case studies. Geophysical Journal International. 2013;**193**:1515-1536

[33] Walter M, Schwaderer U, Joswig M. Seismic monitoring of precursory fracture signals from a destructive rockfall in the Vorarlberg Alps, Austria. Natural Hazards and Earth System Sciences. 2012;**12**:3545-3555

[34] Petschko H, Brenning A, Bell R, Goetz J, Glade T. Assessing the quality of landslide susceptibility maps—case study Lower Austria. Natural Hazards Earth System Science. 2014;**14**:95-118

#### *Landslides*

[35] Regmi NR, Giardino JR, Vitek JD. Modeling susceptibility to landslides using the weight of evidence approach: Western Colorado, USA. Geomorphology. 2010;**115**:172-187. DOI: 10.1016/ j.geomorph.2009.10.002

[36] Hamza T, Raghuvanshi TK. GIS based landslide hazard evaluation and zonation: A case from Jeldu district, Central Ethiopia. Journal of King Saud University—Science. 2017;**29**:151-165

[37] Mulatu E, Raghuvanshi TK, Abebe B. Landslide hazard zonation around Gilgel-Gibe-II hydropower project, SW Ethiopia. SINET: Ethiopian Journal of Science. 2009;**32**(1):9-20

[38] Mengistu F, Suryabhagavan KV, Raghuvanshi TK, Lewi E. Landslide hazard zonation and slope instability assessment using optical and InSAR data: A case study from Gidole Town and its surrounding areas Southern Ethiopia. Remote Sensing of Land. 2019;(3):1-14. DOI: 10.21523/gcj1.19030101

[39] Chimidi G, Raghuvanshi TK, Suryabhagavan KV. Landslide Hazard Evaluation and Zonation in and around Gimbi Town, Western Ethiopia—A GIS-Based Statistical Approach. Addis Ababa: Geological Survey of Ethiopia; 2017

[40] Ermias B, Raghuvanshi TK, Abebe B. Landslide hazard zonation (LHZ) around Alemketema Town, North Showa Zone, Central Ethiopia—A GIS based expert evaluation approach. International Journal of Earth Sciences and Engineering. 2017;**10**(01):33-44. DOI: 10.21276/ijee.2017.10.0106
