Comparative Analysis of the Slope Stability Using Slide and Plaxis 2D Software: A Case Study of Tombel Pozzolan Quarry (South-West Cameroon)

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Introduction
Slope stability is a worldwide issue that can occur not only due to natural conditions but also often triggered by human activities.It can be represented in a vast range of sizes and time scales and with a variety of possible movements.Regardless of the design approach used, a full understanding of the problem and what it entails requires accurate knowledge of its likely causes and an awareness of the diferent instability mechanisms that may occur.Simultaneously, slope stability assessment requires understanding the relevant geological and geotechnical properties of soils and rocks that govern resisting (shearing) forces [1].Moreover, slope stability analysis is one of the most important subjects in geotechnical engineering [2,3].Slope failures depend on slope geometry, soil type, soil stratifcation, groundwater, and seepage.Calculating the safety factor is the general procedure in the slope stability analysis [4].Furthermore, the instability phenomenon may present diferent particularities for distinct ground conditions and is of major signifcance in large-scale geotechnical works, such as highways/railways, canals, open-pit mines, tunnels, and even embankment dams [1].Te slopes of mines and quarries resulting from the extraction activities constitute geotechnical work of mining operations.Te mine operators must be sure that the slopes are stable or that the unsafety factors are manageable for the long-lasting of the mines or quarry.Te diferent problems related to the creation of a quarry, the removal of a large quantity of overburden and waste, and the construction dump require that many strategies should be put in place in other to minimize the displacement of mining infrastructures.Among these strategies, one of the most important consists of minimizing the slope angle [5].Te geometry of a slope in an open-cast mine is directly related to the proftability of the mine.Te steeper the slope, the lower the cost of production with the risk of abandoning more ores in the mining site.On the other hand, the lower the slope, the higher the overburden removal and production costs.Te higher the height of the overall angle of the slope, the higher the risk of slope failure generating ground movements (landslides) at the edge of the mines [4].Te slope stability of a mine or quarry remains the frst principal question that should be asked when it comes to open-cast mineral exploitation.Te safety factors of a quarry under exploitation have a direct infuence on the slope stability, the principal techniques of exploitation, the total depth of the quarry, and the drainage problem.Technical solutions to slope stability problems require a good understanding of analytical methods, investigation tools, and stabilization measures [6].Tere are diferent methods for analyzing the stability of slopes and calculating safety factors, including the limit equilibrium method, the fnite element method, and the fnite diference method [7].So far, various stability assessment techniques have been developed, which include a range of simple evaluations, planar failure, limit state criteria, limit equilibrium analysis, numerical methods, and hybrid and high-order approaches, which are implemented in twodimensional (2D) and three-dimensional (3D) space [8].Numerical modeling is considered as a dominant tool for solving complex engineering problems and has become increasingly popular in geotechnical engineering analysis [9].In fnite element analysis of slopes through numerical modeling, prior assumption of the critical surface is not necessary, unlike hand calculation.Te fnite element method of calculating the safety factor is based on the strength reduction method.In this method, also called the phi-c-reduction method, the strength parameters of the soil are simultaneously reduced until failure occurs [8].Several authors have also investigated slope stability using diferent methods.Grifths and Lane used the fnite element method to solve several examples of slope stability analysis [10].Tey compared the fnite element method with other solution methods including the infuence of a free surface on slope and dam stability.Tey demonstrated that the fnite element method is a more powerful alternative to the limit equilibrium methods when assessing stability in their study of unreinforced slopes and embankments [10].Deliveris and Zevgolis conducted a comparative study on the simulation of a slope of an open-pit lignite mine by the fnite element method (FEM) and fnite diference method (FDM) using Plaxis and Flac software [11].Ali et al. [12] coupled numerical and analytical stability analysis charts for earth-fll dams under rapid drawdown conditions.Yaser et al. [13] conducted a comparative analysis for slope stability by using machine learning methods.Mohammad et al. [14] investigated on the discontinuous rock slope stability under blocky structural sliding by fuzzy key-block analysis method.In addition, Yaser et al. [15] for the estimation of the safety factor in slope stability analysis apply a technique of machine learning.Yimin et al. [16] conducted a fuzzy-based intelligent model for rapid rock slope stability analysis using Q slope .Ten, Kenmoe et al. [17] undertook studies on stability analysis of the cut slopes in the locality Limbe using numerical modeling.In addition, of all this former work, no author approached yet the study of the stability of the slopes in quarry on pozzolanas.Tey are materials rather porous and very much used as secondary components in the manufacturing process of made-up Portland cement, from where the particularity of this study.In this work, numerical analyses were carried out using Slide and Plaxis 2D software, implementing the limit equilibrium method and the fnite element method, respectively, to investigate the slope stability of the pozzolan quarry located in the Tombel locality in the South-West region of Cameroon.Te safety factors were frst calculated from these two software types and then compared.In addition, the mode of slope failure was investigated, and the efect of overload on the stability of the slope was also examined.

Location of the Study Area.
Te study area is located in Tombel, 100 km North of Douala (Cameroon) and 4.0 km West of Loum town (Cameroon) as shown in the location map below (Figure 1).Te company has been granted a mining concession over an area of 27.2990 hectares at Custom-Mbonzie, Tombel Subdivision in the South-West region of Cameroon for pozzolan mining [3].It lies between latitudes 4 °30′and 4 °50′ of the Northern Hemisphere and between longitudes 9 °35′ and 9 °50′ East.Te spatial location of the Dangote quarry site is on the outskirts of Tombel town and precisely defned with the Universal Transverse Mercator (UTM) coordinates of 576430m and 522307 m within zone 32N of the Global Positioning System (GPS) Zoning Grid.Te elevation in the concession area varies from 452 to 565 m.Te hydrography network is meaningful: a permanent stream (Mungo River) that crosses many villages and seasonal streams (Toow, Ngese, Ebulle, Childe, Metobe, Edibana, Kola, and Esemze).Te pozzolan deposit is highly permeable due to its very high porosity.Moreover, it exhibits a radial drainage system, where the streams radiate outward from a central high point or circular mountains of volcanic origin [18].Te climate of the study area is a tropical monsoon climate with constant temperatures throughout the year.Tombel and its adjoining areas have warm and humid conditions with an average annual temperature of 27 °C and an average humidity of about 85%.

Climatic Conditions.
Figure 2 shows the ombrothermic diagram of the study area plotted from the data of the weather station of Njombe (Littoral-Cameroun).We note that the entire Tombel Graben benefts from an equatorialtype climate with two seasons, namely, a rainy season from March to November, and a dry, energetic season from December to February.Te rainiest months are July, August, and September with an average annual precipitation of 1.289 mm, while December, January, and February remain  Te indigenous people (Bonkeng, Abbo, and Bafoung) only represent less than 10% of the population.Te schooling rate here is relatively low, and the language best shared by all is "Pidgin English" due to the strong linguistic diversity.Te most represented religion is animism, followed by Christianity and fnally Islam.Economic activity is marked by the exploitation of the gneiss quarry by SOCARIC and pozzolans by CIMENCAM.However, cash crop agriculture constitutes the basis of the economy because it employs nearly 85% of the active population.It is represented by vast plantations of banana trees, rubber trees, cocoa trees, papaya trees, mango trees, pineapples, oil palms, avocado trees, fowers, and pepper trees, which set up by the companies: PHP, SPM, CAPLEME, and by individuals.A good number of inhabitants are proletarians in these diferent societies.However, the rest of the population works on their plantations where they sell food products.Tese populations also trade, particularly in market garden products.

Applied and Environmental Soil Science
Te touristic aspect of this area is not negligible despite the very poor condition of the roads.It is worth noting here a beautiful landscape composed of a succession of volcanic cones, vast orderly plantations, parks, and foral spaces.Tis touristic aspect is also marked by the small Boubou Park, the Lake Granny toilets, and the spectacular emergence of springs in the volcanic formations.Applied and Environmental Soil Science 2.5.Geological Setting.Te area falls along the Cameroon Volcanic Line and exhibits a fat topography with scattered isolated pozzolan hills all over the area.Te soil in Tombel is extremely fertile, which is composed of volcanic ashes, and favorable for agricultural activities.Tis fertility is also quite encouraging as many credits go to valley bottoms where the annual production of food crops is abundant.As far back as the 19 th century, soil erosion by water was a critical problem, which greatly afected the economic life of the population.Most of the hills were afected; most of the farmlands and roads were destroyed massively.Te study area falls within the Cameroon Volcanic Line (CVL) tectonic structure with the consequence of a series of parallel fssures oriented N30 and some transversal events [19].Tis line is made of 12 main volcanic centers with ages ranging from 51.8 Ma to now.Te regional map of the cones shows two major tectonic axes that control volcanic activity, the Te entire area is covered by volcanic basaltic rocks and falls within the Cameroon Volcanic Line, which is trending in a NE-SW direction.Te study area consists of black, red, and reddish brown soft pozzolan with scoria/pumice along the hard lava.Pumice is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or not contain crystals.Te pozzolan is formed when superheated, highly pressurized molten rock is violently ejected from a volcano.Te unusual foamy confguration of pumice happens because of simultaneous rapid cooling and rapid pressurization.Te high pressure creates bubbles by lowering the solubility of gases (including water and CO 2 ) that are dissolved in the lava, causing the gases to rapidly escape.Figure 3 shows the geological settings of the study area.

. Materials and Methods
3.1.Field Analysis.Two types of geological formations are observed in the study area, namely, pozzolan and basalt.Te color of the basalt was obtained from the Munsell soil classifcation chart.Te pozzolan deposits are characterized by red color at the top, reddish brown color at the middle, and black color at the back with an intrusion of basalts that cuts the dome.Landslide scars were recognized in the feld by sharp changes in vegetation type, the presence of bare crescent-shaped scarps, sharp depressions in the landscape, and the presence of displaced material at the foot of the scar (jumbled-up mixture of subsoil and topsoil).Te geometric parameters (width of rupture, length of rupture, and scarp height) were measured with a graduated surveyor tape.6 Applied and Environmental Soil Science Cleaning and sampling were done by a shovel and a core cutter and then stored in sealed and labeled sample plastics.
In addition, a torvane meter was used to determine the in situ shear strength of the materials.Te slope orientation (direction of movement) was obtained using a compass.Te mode of movement was determined following the procedure proposed by Davies et al. [21].Samplings were done at the top, at the middle, and sometimes at the foot of the slide following the variation of colors of the materials [22].Figure 4 shows the sketch of a plan view of the debris slide at Tombel quarry indicating where and how various parameters were measured in the feld.

Field Landslide Characteristics.
Te characteristics of the diferent landslide types observed are summarized in Table 1.
Figure 5 shows feld landslide characteristics at the Tombel quarry.

Physical and Mechanical
Analyses.Physical analyses including natural water content, bulk density, porosity, particle size distribution, unit weight, and mechanical analyses such as direct shear tests were performed at the Chemistry Laboratory of Dangote (Douala-Cameroun) and the National Civil Engineering Laboratory of Cameroon (Labogenie).
Te natural water content (ω) of soil is an important parameter as it gives information on the amount of water within the pores between the soil grains.It is removable by oven-drying at a temperature not exceeding 110 °C.It was determined according to the NF P 94−050 (1996) [24] standard.Te natural water content is determined by the following equation: Very good Equal to 25 Compact    where ω the natural water is content, m 1 is the initial mass of the sampled material, and m 2 is the mass of the sampled material after drying at 110 °C for 24 hours.Te bulk density is determined for porous materials when pores within the material particles are included in the volume measurement.Tis is determined using parafn and the hydrostatic balance method.Furthermore, a specifc weight was obtained when the volume measured excluded the pores as well as the void spaces between particles within the bulk sample.It was determined using the pycnometer method according to the NF P 18-554 and NF P 18-555 (1995b) [25] standards.Te dry density, porosity, void ratio, and saturation ratio were determined using the following formulas:    Applied and Environmental Soil Science where c d is the dry unit weight of soil, c s is the absolute unit weight, s r is the saturation ratio, n is the porosity, ω is the natural water content, e is the void ratio, c h is the humid unit weight, and c ω is the unit weight of water.Te grain size analysis was performed according to the NF P 94-056 (1996) [26] standards.Based on this specifcation, the grain size distribution curves were plotted with size fractions greater than 80 µm, obtained by wet sieving through a series of sieves of decreasing mesh sizes, while the size fractions less than 80 µm were obtained by sedimentation.Furthermore, the shear strength tests were done on specimens according to the French standard Norm NF P94-071-2 (1994) [27] enabling the determination of the friction angle (φ) and cohesion (c) of the studied slide materials.
Finally, the unit weight of the studied slide materials is obtained by multiplying values of the bulk density with the acceleration due to gravity g � 9.8 m/s 2 .According to [28], the unit weight of materials is classifed as follows (Table 2).

Numerical Methods of Slope Stability Analysis
3.4.1.Slide 2D Software.Slide 2D is a software used for the analysis of slope stability of soils and rocks as well as for circular and noncircular failure surfaces [29].It is very simple to use and was developed by Rocscience Inc., Toronto, Canada.In addition, complex models such as external loading, groundwater, and support can be modeled in a variety of ways and analyzed quickly and easily.Tis software uses the limit equilibrium method of analysis.Tis method evaluates the safety factor and gives an idea of the equilibrium state of the studied slope concerning the limit equilibrium (see Figure 6).Te precision of the calculations depends not only on the quality of the determination of the shear parameters but also on the methods of calculations implemented.Te slide allows analyzing the stability of slip surfaces using vertical slice limit equilibrium methods.Individual slip surfaces can be analyzed, or search methods can be applied to locate the critical slip surface for a given slope [31].

Plaxis 2D
Software.Plaxis 2D is a special-purpose two-dimensional fnite element program used to perform strain, stability, and fow analyses for diferent types of geotechnical applications.It was developed by PLAXIS BV corporation with several universities including DUT in the Netherlands and NTNU in Norway [32].Real situations can be modeled by a plane strain or an axisymmetric model.Tis program uses a graphical interface allowing users to quickly generate fnite element geometry and mesh models based on a vertical cross-section representing the situation.Te objective of soil modeling is to determine a behavior model that shows the evolution of its physical and mechanical characteristics.Te model is thus a complete description of the behavior of the soil.Te general presentation of the modeling program is illustrated in Figure 7.

Physical and Mechanical Characteristics.
Te physical and mechanical characteristics of the studied slide materials are summarized in Table 3.

Natural Water Content.
Figure 8 shows a variation of natural water content in the studied slide materials.

Bulk Density.
Figure 9 shows the distribution of the diferent samples versus their bulk density values.

Porosity.
Figure 10 shows a variation of pore spaces in the diferent slopes.4.
As shown in Table 4, the studied slide materials are made up of a high gravelly fraction (71.2-74.2%),an average sandy fraction (23.8-25.7%),and a weak silty fraction (0.1-0.9%) and clayey fraction (1.3-4.1%).Figure 11 exhibits the cumulative distribution curve of the diferent fractions obtained from values of Table 4   Applied and Environmental Soil Science 11 from 19 to 51 °.Te direct shear test allowed obtaining the following results in Table 5 and drawing the direct shear linear graph as shown in Figure 12.

Discussion
In Figure 8, it is seen that the values of the natural water content of the studied slide materials are low.Tese low values in water content can be attributed to the texture of the samples since sampling was done on degraded pyroclastic cones, which tend to have similar characteristics to sand and gravel.Te high values are observed in slide materials 3 and 4 and can be attributed to the high clay fraction in the samples collected in these two locations.Slide materials 1, 2, and 5 showed a low value due to the sandy and gravelly texture of these materials.So, water infltration could induce failure by  weakening slopes via the reduction in suction and strength [34][35][36].Tis strength reduction only becomes noticeable when the mobilized forces become lesser than the shear forces, and steep slopes are mainly afected on account of increasing shear stress against reducing shear strength, thereby causing a signifcant fall in the slope safety factor [37][38][39][40].Tis reduction in shear strength can trigger a landslide in a tailing dump slope along the weak planes [41].
Figure 9 shows the distribution of the diferent samples versus their bulk density values.According to these values, the studied materials are aggregates.Bulk density also gives an idea of the texture of the soil.A bulk density varying from 1.4 to 1.7 g/cm 3 represents sandy soils, a bulk density varying from 1.1 to 1.4 g/cm 3 corresponds to silts, and a bulk density of less than 1.1 g/cm 3 represents clay soils.Table 3 shows that the studied slide materials are found in the same range as silt soils.It shows a high value of 1.67 in studied slide 1 materials.Tis implies the samples collected in the frst slide were mostly sandy in texture; studied slides 2, 3, and 5 materials were silty in texture, while studied slide 4 materials were also sandy in texture.In Figure 10, the high values of bulk density of studied slide materials are also attributed to the texture of the samples since samples are mostly sandy Applied and Environmental Soil Science   14 Applied and Environmental Soil Science and gravelly, which explains why there is an increase in pore spacing in the samples.As seen in Table 2, the unit weight of studied slide materials is found between 11 and 16 kN/m 3 .Tey are considered peaty to very bad materials.So, good soils are not found in the study area.Te average of specifc gravity is high, ranging from 2.33 to 2.72 g/cm 3 with average values of 2.61 ± 0.14 g/cm³.According to [42], the studied materials are far from compressible to not very compressible.
Te studied materials are characterized by a low cohesion (0.21-0.41 bars) and low values of internal friction angle ranging from 19 to 51 °.Tese low values of cohesion can be related to the average void index (0.6-1.47) and high porosity (37.5-59.56%).Tese values are lower than those obtained by [43] on the In Amenas soils (1.25 bars) and those obtained by [43] on Algerois materials (0.07-0.47 bars).Te low shear strength parameter values could be the consequence of the presence of expansive minerals [42,44].Te reduction in shear strength can trigger a landslide in a tailing dump slope along the weak planes [42].Reference [44] noted that the slope geometry and the strength of materials on it ultimately determine the stability of a slope.
Te limitations of this study relate to the sampling points, which do not refect reality because the study area is anisotropic.Additionally, the number of sampling points was not representative enough to allow in-depth analysis.Te hydric aspect was not considered in this study, even though pozzolan is a water-breaking rock.Te tests on samples were not carried out in situ, and the study was done in 2D.In future work, it is intended to carry out many soil campaigns to supplement existing information, to conduct in situ tests to supplement those obtained at the laboratory,   Applied and Environmental Soil Science and to analysis of the slope's stability in 3D.Furthermore, other methods for slope stability such as artifcial neural networks, intelligent optimization, machine learning algorithms, Monte Carlo simulation, and direct coupling approach will be used.

Modeling
6.1.Modeling with Slide. Figure 13 shows the slope geometry plotted using Slide 2D software.Tis geometry is generated by the parameter values of the studied landslide measured on the feld.Also, the groundwater condition has been considered.
Te safety factor after calculation is given in Figure 14.
As shown in Figure 14, the safety factor is 0.87 (FoS � 0.87) and this value shows that the slope is unstable and is said to fall freely.Te characteristics of the support that can be used to stabilize the slope to avoid slope rupture are shown in Figure 15.
It is found from Figure 15 that geotextile support of 100% strip coverage, 100 kN/m tensile strength, the adhesion property of 4 kPa, and a frictional angle of 40 °are suitable to stabilize the slope.Te geotextile is anchored at the slope surface, and the new value of the safety factor obtained is shown in Figure 16.As seen in Figure 16, after the support characteristics have been introduced, the value of the safety factor has increased from 0.87 (unstable state) to 1.51 (very stable state).Tus, the geotextile of the calculated properties above should be used to stabilize the slope and fnally avoid the risk of accidents due to landslides that can occur at any level in the quarry.

Modeling with Plaxis.
Te geometry of the slope obtained using Plaxis 2D is shown in Figures 17 and 18.
Moreover, when the intrinsic properties of the studied slide materials have been considered, the mesh obtained is shown in Figure 19.
Figure 20 is obtained when the pore water conditions have been considered.Tis shows that the water level is beneath the slide area since no water is observed to fow out from the studied slide materials.
In addition, the deformation seen in Figure 21 is obtained when the properties of each node have been introduced.
Figure 22 shows the surfaces (colored zone) that are more likely to slide down, and it is obtained when the safety factor is calculated.It is seen that the slope is at limited equilibrium means that the slope is more likely to slide at any moment under the infuence of both the internal and external factors that lead to landslides.
Figure 23 shows the calculation information that is used to calculate the safety factor, and from there, we can deduce that the slope is at limit equilibrium, which is unsafe.
Te characteristics of the support used to stabilize the unstable slope are shown in Figure 24.
From Figure 24, it is found that a geotextile support of 100% strip coverage, 100 kN/m tensile strength, the adhesion property of 10 kPa, and a frictional angle of 40 °are good to stabilize the slope in other to avoid slope rupture.Te geotextile is anchored at the slope surface, and the new value of the safety factor is obtained as shown in Figure 25.
As seen in Figure 25, after the support characteristics have been introduced, the value of the safety factor has increased from 1.0, which is said to be at a limit equilibrium state to 1.98, which is a very stable state.Terefore, the geotextile of the calculated properties above should be used to stabilize the slope and fnally avoid the risk of accidents due to landslides that can occur at any level in the quarry.Te advantages and disadvantages of these methods are shown in Table 6.Te results obtained using the two software types are compared as shown in Table 7.

Conclusion and Recommendations
Tis research was carried out on the comparative analysis of the slope stability using Slide and Plaxis 2D software at Tombel Dangote quarry (South-West Cameroon) to bring solutions against landslide-prone soils.Likewise, they are characterized by a low cohesion between 0.21 and 0.41 bars.Te slope analysis by the fnite element method implemented in Plaxis 2D software showed that the safety factor value using the Janbu method is 1.0 (FoS � 1.0), which indicates that the studied slope is at a limited equilibrium state and the slopes are likely to fall at any time under the infuence of factors that trigger landslides.In addition, the analysis of the slope by the limit equilibrium methods implemented in the Slide 2D software showed that "Janbu" underestimates the safety factor value, which is equal to 0.87 (FoS � 0.87), and this value indicated that the slope is very unstable and can slide down at any time even under the infuence of gravity.Te obtained results by the Slide 2D software showed that the characteristics of stabilizing the support are a geotextile of 100% strip coverage, a tensile strength of 100 kN/m, an adhesion property of 4 kPa, and a frictional angle of 40 °.With the introduction of the support, the safety factor increased from 0.87 (unstable state) to 1.51 (very stable state), corresponding with a percentage increase of 64%.Te same approach was done using the Plaxis software, and the support characteristics were found to be a geotextile support of 100% strip coverage, a tensile strength of 100 kN/m, an adhesion property of 10 kPa and a frictional angle of 40 °.Te results showed that the addition of the support increased the safety factor value from 1.0 (unstable equilibrium state) to 1.98 (very stable state), corresponding with a percentage increase of 98%.Terefore, the results of this work show that the proposed support (geotextile) with the given properties is suitable to reduce the risk of slides in this area.Te comparison of the two software types shows that Plaxis 2D is more efcient and has good precision on calculated values.Te limitations of this study relate to the sampling points, which do not refect reality because the study area is anisotropic.Additionally, the number of sampling points was not representative enough to allow indepth analysis.Te hydric aspect was not considered in this study, even though pozzolan is a water-breaking rock.Te tests on samples were not carried out in situ, and the study was done in 2D.In future work, it is intended to carry out many soil campaigns to supplement existing information, conduct in situ tests to supplement those obtained at the laboratory, and to analysis of the slope's stability in 3D.Furthermore, other methods for slope stability such as artifcial neural networks, intelligent optimization, machine learning algorithms, Monte Carlo simulation, and direct coupling approach will be used.

2. 4 .
Population and Economic Activity.Te population (around 70,000 inhabitants) generally concentrated along the Nkongsamba-Douala road axis (Ninetynine, Penja, and Njombe) is made up of people from various ethnic groups: Bamiléké, Bamoun, Haoussa, Mbos, Balong, Babong, Bayangui, Bonkeng, Abbo, and Bafoung.Most of the nonnatives are grouped either by village district or by tribe.All these ethnic groups live together and lead a community life.

Figure 1 :Figure 2 :
Figure 1: Location map of the study area.

4
Debundscha axis (N60-150) and the Batoke axis (N30-40).Morphologically, Mount Cameroon is a stratovolcano, located on a horst with boundary faults that are expressed by slope breaks.It is bounded by the Tombel Graben to the North and the Douala basin to the South.It has an elliptical shape, is 50 km long, and is 35 km wide.Its basement (Pan-African granite and gneiss) is covered by cretaceous to quaternary sediments, observed in the Bomana maar at the NW of the Mount Cameroon massif appearing to be a rather complex edifce produced by three main types of volcanic activity (efusive eruptions, responsible for the lava fows covering parts of the stratovolcano; an explosive activity that has built about 140 strombolian cones; and a hydro-magmatic activity that formed the Debundscha and Bomana maars in the sedimentary basement at the North-West of the volcano).Mount Cameroon lavas are essentially basanites (60 vol.%), alkaline basalts (25 vol.%), hawaiites (10 vol.%), and rare mugearites (5 vol.%).Camptonite, a type of lamprophyre composed mainly of plagioclase and brown hornblende, recently has been found.Moreover, xenoliths (1-5 cm × 0.5-4 cm) of dunites, wehrlites, and clinopyroxenites have been observed in the basanites of the strombolian Batoke cone located in the South fank of the massif at 500m above sea level.Similar xenoliths of wehrlites and clinopyroxenites have been discovered in the basaltic tephra of a strombolian cone located at 3000 m elevation on the northwestern fank of Mount Cameroon [20].Te lease area of Tombel Pozzolan is located around Loum and Tombel in the South-West region of Cameroon.

Figure 4 :
Figure 4: Sketch of plan view of debris slide at Tombel quarry indicating where and how various parameters were measured in the feld [23].h: height; A (wr): width of depletion zone; B (Lr): length of depletion zone; C: total runout distance.

Table 1 :
Field landslide characteristics.the top of the pozzolan dome (i) Presence of reddish brown pozzolan (ii) Poorly materials are sorted with little vegetation the top of the pozzolan dome (i) Presence of black pozzolan (ii) Poorly materials are sorted and mixed with borders (iii) No water observed Wr: the top of the pozzolan dome (i) Presence of black pozzolan (ii) Poorly materials sorted with little vegetation Wr: 20.the top of the pozzolan dome (i) Presence of reddish brown pozzolan (ii) Poorly materials sorted with little vegetation Wrthe top of the pozzolan dome (i) Presence of black pozzolan (ii) Poorly materials sorted with dense vegetation (iii) No water observed Wr; Lr: Length; h: Scarp height.

Figure 8 :
Figure 8: Variation of natural water content in the studied slide materials.

Figure 9 :
Figure 9: Variation of bulk density in the diferent slide materials.

Figure 10 :
Figure 10: Distribution of bulk density in the studied slide materials.

4. 1 . 4 .
Particle Size Distribution.Te particle size distribution of studied slide materials is summarized in Table .

Figure 13 :
Figure 13: Geometry of the slope using Slide 2D.

Figure 14 :
Figure 14: Unstable slope showing the safety factor.

Figure 16 :Figure 17 :
Figure 16: Stabilized slope showing the support and the new safety factor.

Figure 22 :
Figure 22: Unstable slope showing the safety factor.

Figure 25 :
Figure 25: Stabilized slope showing the support and the new safety factor.

Table 3 :
Physical and mechanical characteristics of studied slide materials.
w: water content, c h : humid weight, c d : dry unit weight, c s : absolute unit weight, e: void ratio, n: porosity, S r : saturation ratio, e 0 : initial void ratio, C c : compression index, C g : swelling index, σ p ′: preconsolidation constraint, C: cohesion, φ: friction angle.

Table 4 :
Particle size distribution of studied slide materials.

Table 5 :
Direct shear test results.

Table 6 :
Advantages and disadvantages of geotextiles.

Table 7 :
Comparison between Plaxis and Slide 2D software.It uses the direct shear test data (cohesion, internal angle of friction) and bulk density It uses the fnite element method of slope analysis It uses the limit equilibrium method of slope analysis More complex and gives a more precise safety factor than slide software since it uses both the oedometric and the direct shear test data of a material Less complex than Plaxis 2D since it takes only the direct shear test data of a material 18 Applied and Environmental Soil Science 6.3.Comparison between Plaxis and Slide 2D Software.