Conventional time-of-failure estimated from slope surface displacement over time, ignores the crucial geotechnical and environmental causative factors that lead to slope instability. The instrumentation and monitoring are expensive, labour-intensive, and often not feasible for large number of hill slopes. This paper focuses on the physics-based determination of time-of-failure charts for laterite soil slopes prevalent in the Western Ghats of India, under rainfall infiltration. The finite element model was first validated by performing coupled flow deformation analysis of Kondavi soil cutting situated in the Ratnagiri district of Maharashtra, India. The soil samples were collected from the site for basic geotechnical characterisation in the laboratory. In addition, the soil water characteristics curve (SWCC) was determined using the filter paper method, and the unsaturated parameters were obtained using the van Genuchten model. Following the validation of numerical model with the failed Kondavi cutting, the factor of safety (FOS) and time-of-failure (TOF) were studied for varying rainfall intensity, and permeability of the soil. The FOS and TOF charts were then established for varying slope angles (30°, 45°, 60°), effective cohesion (10 kPa, 18 kPa, 25 kPa), effective friction angle (22°, 25°, 28°), water table depth (25 m, 28 m, 30 m, 35 m) and height of slope (15 m, 25 m, 35 m). Results indicate that if rainfall intensity is lower than soil permeability, TOF depends on both the intensity and duration of the rainfall. Higher rainfall intensity leads to a shorter time of failure, and vice versa. Conversely, when rainfall intensity exceeds soil permeability, TOF is determined by the duration of rainfall and the permeability of soil, as the rainfall infiltrates at the saturated permeability rate regardless of its intensity. It is also observed that friction is the dominant parameter for initial FOS, while cohesion is the dominant parameter for the TOF of a rainfall-induced landslide. Finally, charts are proposed that shall serve as a preliminary guide for the determination of the TOF for rainfall-induced instability in the lateritic soil slopes of India. The performance of the charts is further evaluated by comparing the observed and predicted TOF of two other failed laterite cuttings. The implications of these findings are profound, as the proposed TOF charts can be integrated into early warning systems, contributing towards improved disaster mitigation and preparedness with timely decision making for adequate management of landslide associated risks.

中文翻译：

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基于物理的红土土质边坡降雨引起的失稳确定


根据边坡表面位移随时间推移估计的传统破坏时间忽略了导致边坡失稳的关键岩土工程和环境因素。仪器和监测成本高昂、劳动强度大，并且通常不适用于大量山坡。本文重点介绍了在降雨渗透下印度西高止山脉普遍存在的红土土质边坡的失效时间图的基于物理的确定。有限元模型首先通过对位于印度马哈拉施特拉邦 Ratnagiri 区的 Kondavi 土壤切割进行耦合流变形分析来验证。从现场收集土壤样本，用于在实验室进行基本的岩土工程表征。此外，采用滤纸法测定土壤水分特性曲线 （SWCC），并使用 van Genuchten 模型获得非饱和参数。在用失败的 Kondavi 切割验证数值模型之后，研究了不同降雨强度和土壤渗透性的安全系数 （FOS） 和失效时间 （TOF）。然后针对不同坡度角（30°、45°、60°）、有效黏聚力（10 kPa、18 kPa、25 kPa）、有效摩擦角（22°、25°、28°）、地下水位深度（25 m、28 m、30 m、35 m）和坡高（15 m、25 m、35 m）建立 FOS 和 TOF 图表。结果表明，如果降雨强度低于土壤渗透性，TOF 取决于降雨的强度和持续时间。降雨强度越高，失效时间越短，反之亦然。 相反，当降雨强度超过土壤渗透性时，TOF 由降雨持续时间和土壤渗透性决定，因为降雨以饱和渗透率渗透，而不管其强度如何。还观察到，摩擦力是初始 FOS 的主要参数，而内聚力是降雨诱发的滑坡 TOF 的主要参数。最后，提出了一些图表，这些图表将作为确定印度红土边坡降雨引起的不稳定性的 TOF 的初步指南。通过比较其他两个失败的红土切割的观测和预测 TOF 来进一步评估图表的性能。这些发现的意义是深远的，因为拟议的 TOF 图表可以整合到早期预警系统中，有助于改进减灾和准备，并及时做出决策以充分管理滑坡相关风险。