Analysis of design choices for a slope stability scenario in the humid tropics

Abstract

Prediction of the conditions under which landslides may occur is essential for designing sustainable risk-mitigation measures and cost-effective geotechnical structures. Slope stability analyses typically account for slope geometry, soil mechanical properties and groundwater conditions to determine the performance of a slope with respect to a specified factor of safety. These properties vary both spatially and over time; geotechnical design codes require the use of factored design parameter values to account for possible worst-case conditions. Furthermore, standard geotechnical analyses typically exclude the dynamic hydrological processes of rainfall infiltration and loss of matric suction that often trigger landslides. Slope stability assessment is particularly challenging in developing countries with limited resources for acquiring slope data, meeting conservative design standards and mitigating landslide risk. This study applied a combined slope hydrology and stability model to address these issues for a residual soil slope in the tropics. This paper presents a method for maximising stability information from limited data, disaggregating the effects of three different design parameter sets and factor of safety threshold choices, as well as diagnosing the dominant geotechnical and dynamic landslide-triggering factors. This modelling approach provides a more transparent basis for sustainable slope-management decisions.

On the variability of the effective friction angle of Saint Lucian soils: investigations through a laboratory database

“…The modelled slope is identical to that studied in Shepheard et al (2018) with a height of 67m, a length of 130m, and an angle of 28°. The uppermost 8m are separated into two 4m deep layers of residual soil (0-4m depth) and decomposed bedrock (4-8m) with properties corresponding to the Hong Kong weathering grades (GEO 1988) ( Table 1).…”

“…This study employs the Combined Hydrology and Stability Model (CHASM) to illustrate an example envelope of the factor of safety (F) for a modelled slope, in which the angle of friction is changed according to the corresponding upper and lower bounds plotted in Figs 2 and 3 to the mean measured friction angle value of 24.2°. The input parameters used in this paper are given in Table 1, and are based on 'Case B' from Shepheard et al (2018).…”

“…(2) is 1.11; a reduction of 0.23 in uncertainty. Shepheard et al 2018) * Grade refers to weathering grades from fresh rock (Grade I) to residual soil (Grade IV) (see GEO 1988, for example).…”

“…Landslide hazard risk assessments allow engineers to quantify the stability of slopes in particular regions. Recent studies by Holcombe et al (2016), Beesley et al (2017) and Shepheard et al (2018) have simulated the response of a modelled slope to changes in a number of mechanical and geometric properties and showed that relatively small changes in some parameters can create large fluctuations in the calculated slope factor of safety. The slope stability has been shown to rely to a large degree on the estimate of the effective friction angle within the model.…”

Geodatabases to improve geotechnical design and modelling

“…Many such countries are in the humid tropics and are prone to rainfall-triggered landslides and this coincides with areas that are 'data-poor'. The Combined Hydrology And Stability Model, CHASM, has been extensively used for slope stability analysis in such locations (e.g., Anderson et al 1997, Holcombe et al 2016, Shepheard et al 2018a, Beesley et al 2017). Geodatabases at these locations could augment landslide modelling and sensitivity analysis and help better understand and manage current and future hazards associated with natural and engineered slopes.…”