Unstable road cut slopes and design of retaining structures in the Rwandan context

Valentino, Roberto; Sobio, Yvan; Mizero, Jules; Safari, J.; Nsengiyumva, F.

doi:10.1007/s12517-021-07819-4

Cited by 6 publications

(4 citation statements)

References 20 publications

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“…Mountain reliefs with heights of up to 4486 m above sea level mostly dominate the western and northern areas of Rwanda. Due to the steep topographic gradient, associated with the construction of extensive road cut slopes, landslides in Rwanda are very frequent phenomena [12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Combined Effect of the Microstructure and Mechanical Behavior of Lateritic Soils in the Instability of a Road Cut Slope in Rwanda

Valentino,

Pizzati,

Mizero

2024

GeoHazards

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A very common hazard in Rwanda is represented by the instability of steep road cut slopes in lateritic soil. In its natural state, this material appears as a fine-grained weak and altered rock, generally in unsaturated conditions. Steep cut slopes made by this material could remain stable for a long time unless weathering weakens its mechanical behavior and heavy rainfall provokes a rapid landslide. This paper presents the results of an experimental investigation on the microstructural, petrophysical, and geotechnical properties of lateritic soil from a road cut slope located in Kabaya (Ngororero District—Rwanda), which was recently subjected to a landslide. The mechanical properties of the material are strictly related to the geological origin and history of the deposits, their formation environment, and weathering processes. These characteristics were revealed by peculiar microstructural features (micro-texture, porosity, and degree of alteration of original mineral paragenesis). The experimental investigations included identification and classification tests, direct shear tests on saturated samples, and swelling tests. This multidisciplinary approach provided insights into the relationship between geotechnical properties and the microstructural, petrophysical, and chemical characteristics of the altered rocks. This study showed how different levels of chemical alteration operated by weathering processes, in conjunction with brittle deformation related to the tectonic history, formed in the same site two shallow rock layers with similar macro-scale features and mechanical behaviors but markedly different microstructural and chemical properties. The innovative aspect of this research suggests an integrated multidisciplinary approach to considering microstructural aspects in addition to mechanical behavior in the slope stability analyses in lateritic soil. In particular, this study demonstrates the importance of such an approach since the failure mechanism is better explained if it is based on microstructural observations instead of considering the soil shear strength parameters only. This research helped to explain the formation of the landslide failure mechanism in a specific road cut slope, which could be assumed as representative of many other similar slopes subjected to landslides in Rwanda.

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Section: Introductionmentioning

confidence: 99%

Combined Effect of the Microstructure and Mechanical Behavior of Lateritic Soils in the Instability of a Road Cut Slope in Rwanda

Valentino,

Pizzati,

Mizero

2024

GeoHazards

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“…These materials may initially appear stable shortly after construction or excavation but eventually become prone to instability over time (Miščević and Vlastelica, 2014). In some cases, particularly for cut-slopes, failures can be attributed to design miscalculations, such as improper slope angles, excessive slope heights, and underestimated soil strength (Valentino et al, 2021;Singh et al, 2020). There exist varieties of numerical methods to analyze the stability of natural and cut-slopes that include the slice method, rigid body limit equilibrium method, plastic limit analysis method, etc.…”

Section: Introductionmentioning

confidence: 99%

Numerical modelling of cut-slope stability in the Lesser Himalayan terrain of west-central Nepal

Shrestha,

Paudyal,

Thapa

2023

Journal of Nepal Geological Society

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Area development without due consideration of geological factors has led to recurrent slope failures within the Lesser Himalayan Zone thereby rendering socio-economic impacts. This issue is well exemplified by cut-slopes in major highways of Nepal traversing through a diverse range of rocks and soils. The study has focused on addressing the stability challenges posed by highly vulnerable excavated cut-slopes with particular attention given to a debris cut-slope considered as a model for this study is located in the Lesser Himalayan terrain of west-central Nepal. The cut-slope model is analyzed by numerical modellings through both the limit equilibrium method (LEM) and finite element method (FEM). The study further evaluated the underlying causes of these failures to recommend the options for remedial measures. Data acquired from two-dimensional electrical resistivity tomography (2D-ERT), multi-channel analysis of surface waves (MASW), and laboratory testing were integrated into numerical modelling and simulation. The results showed that the lower slope below the natural benching is stable whereas the upper failed slope is unstable due to reduced gravitational loading. In LEM, factors of safety (FoS) range from 0.77 to 0.89 for cut-slope angles of 70° and 60° whereas the FoS in modified slopes (50° and 40°) were slightly greater than 1 which ranged from 1.01 to 1.18 and indicated marginal stability. Application of 25 mm diameter soil nails, each measuring 6 m in length and spaced at 2 m intervals with tensile and plate capacity of 125.6 kN, bond strength of 75.4 kN/m, and 80% of nail length have produced FoS of 1.30 or greater in LEM and FEM which is acceptable values specified by EM 1110-2-1902 and IS 456 2000 for end-of-construction and multistage loadings.

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“…About 43 % of its surface area is classified as having moderate to very high susceptibility to landslides, with 49 % of the local population exposed to landslide risks (Nsengiyumva et al, 2018). The long-term landslide-predisposing factors in Rwanda include its pronounced topographic profile, the inherent geological and lithological units, weathering processes, earthquakes, demographic pressure and the related anthropogenic activities such as deforestation, agriculture expansion and slope incision through road construction activities (Bizimana and Sönmez, 2015;Depicker et al, 2015Depicker et al, , 2021bMoeyersons, 1989;Monsieurs et al, 2018b;Nsengiyumva et al, 2018;Valentino et al, 2021). The development of mining sites and the connected feeder roads also changes the nature of the natural hillslope through excavation, thus exacerbating landslide susceptibility and risks of slope failures.…”

Section: Introductionmentioning

confidence: 99%

Potential of satellite-derived hydro-meteorological information for landslide initiation thresholds in Rwanda

Uwihirwe

Riveros

Wanjala³

et al. 2022

Nat. Hazards Earth Syst. Sci.

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Abstract. Satellite and hydrological model-based technologies provide estimates of rainfall and soil moisture over larger spatial scales and now cover multiple decades, sufficient to explore their value for the development of landslide early warning systems in data-scarce regions. In this study, we used statistical metrics to compare gauge-based and satellite-based precipitation products and assess their performance in landslide hazard assessment and warning in Rwanda. Similarly, the value of high-resolution satellite and hydrological model-derived soil moisture was compared to in situ soil moisture observations at Rwandan weather station sites. Based on statistical indicators, rainfall data from Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (GPM_IMERG) showed the highest skill in reproducing the main spatiotemporal precipitation patterns at the study sites in Rwanda. Similarly, the satellite- and model-derived soil moisture time series broadly reproduce the most important trends of in situ soil moisture observations. We evaluated two categories of landslide meteorological triggering conditions from IMERG satellite precipitation: first, the maximum rainfall amount during a multi-day rainfall event, and second, the cumulative rainfall over the past few day(s). For each category, the antecedent soil moisture recorded at three levels of soil depth, the top 5 cm by satellite-based technologies as well as the top 50 cm and 2 m by modelling approaches, was included in the statistical models to assess its potential for landslide hazard assessment and warning capabilities. The results reveal the cumulative 3 d rainfall RD3 to be the most effective predictor for landslide triggering. This was indicated not only by its highest discriminatory power to distinguish landslide from no-landslide conditions (AUC ∼ 0.72), but also the resulting true positive alarms (TPRs) of ∼80 %. The modelled antecedent soil moisture in the 50 cm root zone Seroot(t−3) was the most informative hydrological variable for landslide hazard assessment (AUC ∼ 0.74 and TPR 84 %). The hydro-meteorological threshold models that incorporate the Seroot(t−3) and RD3 following the cause–trigger concept in a bilinear framework reveal promising results with improved landslide warning capabilities in terms of reduced rate of false alarms by ∼20 % at the expense of a minor reduction in true alarms by ∼8 %.

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Unstable road cut slopes and design of retaining structures in the Rwandan context

Cited by 6 publications

References 20 publications

Combined Effect of the Microstructure and Mechanical Behavior of Lateritic Soils in the Instability of a Road Cut Slope in Rwanda

Combined Effect of the Microstructure and Mechanical Behavior of Lateritic Soils in the Instability of a Road Cut Slope in Rwanda

Numerical modelling of cut-slope stability in the Lesser Himalayan terrain of west-central Nepal

Potential of satellite-derived hydro-meteorological information for landslide initiation thresholds in Rwanda

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