The large deformation mechanical properties of slip zone soil play an important role in the stability evolution of landslide. The traditional landslide stability evaluation method can only be used to calculate a single stability factor, which cannot dynamically evaluate the landslide stability as it evolves. The large deformation mechanical properties of slip zone soil from Outang landslide in the Three Gorges Reservoir area are investigated by the indoor repeated direct shear test. Based on the damage theory, the shear damage behavior of slip zone soil with large shear displacement is analyzed, and a mechanical model describing the relationship between shear stress and shear displacement in accordance with the mechanical mechanism of landslide is established. Then, the stability of Outang landslide is dynamically evaluated by skillfully combining the mechanical model and the residual thrust method. The results show that the slip zone soil has obvious softening behavior and constant residual strength under the condition of large deformation. The model with clear physical meaning can reflect the large displacement shear mechanical properties of slip zone soil, which is consistent with the test results. The stability factor of Outang landslide gradually decreases and tends to be constant as landslide moves. The mechanical mechanism of the landslide stability evolving with deformation is the strain softening behavior of the slip zone soil, and the mechanical mechanism of the landslide stability evolving with water level is the reduction of effective stress in anti-sliding section under the influence of reservoir water. It is suggested that active measures should be taken in time in the prevention and control of landslide, and the construction of drainage engineering should be paid attention to for large-scale bank landslides. 

https://www.researchsquare.com/article/rs-819772/latest.pdf

Evaluating the stability of Outang landslide in the Three Gorges Reservoir area considering the mechanical behavior with large deformation of the slip zone

Slope instability triggered by rainfall is common in tropical countries like India, where the soil of hill slopes are generally in unsaturated condition, having higher strength than in the saturated condition due to matric suction. This study aims to investigate the change in pore water pressure (PWP) with rainfall infiltration into the slope and the corresponding effect of the slope stability on different hill slopes from different regions of India. By applying rainfall on the surface of slope as a flux boundary condition, a transient seepage analysis is performed using SEEP/W, and the corresponding results in the form of PWP distribution within the slope are used as input for SLOPE/W program of Geostudio 2018 R2, to check the stability of slope. This study involves the use of CMIP5 (Coupled model intercomparision project phase 5) simulations for rainfall data of different regions for the duration of 2015–2050, 2051–2075 and 2076–2100; which is completely based on non-stationary approach (i.e., the statistics of extremes changes with time) rather than the conventional methods of extracting rainfall data that are based on stationary approach. The stability of different slopes is checked for 95 percentile rainfall intensity as well as for maximum rainfall intensity for a period of 2015–2100, and the analysis is performed for 5 days for which the duration of rainfall is considered to be 24 h. It is concluded that due to climate change, slopes which may be marginally stable under historical and present rainfall events can fail under projected precipitation estimates, and this can be understood by the results of Haflong slope stability analysis as the 30° slope, which is marginally stable under maximum rainfall intensity for the period 2015–2050 having factor of safety (FOS) value 1.0013, will fail under the maximum rainfall intensity for the period 2051–2075 and 2076–2100 having FOS value 0.9935 and 0.9989, respectively. A continuous decrease in FOS with increasing rainfall intensity is observed for all the study areas under consideration. 

/pdf/rainfall-triggered-slope-instability-analysis-with-changing-l3aid9sz.pdf

Rainfall Triggered Slope Instability Analysis with Changing Climate

https://link.springer.com/content/pdf/10.1007/s40098-021-00581-0.pdf

The main objective of the study is to estimate the shear resistance mobilized on the slope surface under large deformation and to identify the failure mechanism of the landslide through the simulation model. The field investigations were carried out using Geophysical tests, and the laboratory tests were conducted to identify the engineering properties of the soil with weathering characteristics of the parent rock. The residual shear strength parameters from Torsional ring shear tests were used in LS-RAPID numerical simulation software to study the mechanism of the landslide. The critical pore water pressure ratio (ru = 0.32) required for the initiation of a landslide was obtained. The increase in pore water pressure reduces the soil matric suction and thereby results in the reduction of the shear strength of the soil. The progressive failure mechanism and the three landslide processes (initiation, run out and deposition) are investigated. The velocity of the moving landslide mass in the role of demolishing the building is studied and helps in finding suitable remedial measures for the nearby building. The empirical rainfall threshold based on the antecedent rainfall was developed and revealed that either a high daily rainfall intensity of 142 mm without any antecedent rainfall, or an antecedent rainfall of 151 mm for a cumulative period of 5 days with even continuous normal rainfall can initiate landslide.

Investigation on the Failure Mechanism of Rainfall-Induced Long-Runout Landslide at Upputhode, Kerala State of India

Rainfall-induced landslide is one of the major natural disasters in the Western Ghats of India. Kerala state in southern India received unprecedented heavy rainfall from July to August 2018. The rainfall received was higher than the average for the past 100 years. The present study discusses the investigation of vertical cut failure at Kaithakunda, located in Malappuram district, Kerala, India. It was due to the series of medium rainfall followed by a short period of extremely heavy rainfall. The heavy rainfall triggered the slope failure, which led to the damage of the building and the death of three residents of the building. The index and engineering properties of the soil were evaluated from the laboratory tests. The tests revealed that the soil was silty sand (SM) with low permeability. Tests on the mineral composition and microstructure fabric nature of the soil revealed that the soil was formed due to the weathering action of the parent charnockite rock. The finite element analysis of the slope was carried out using PLAXIS 3D. The analysis was carried out in two stages. The original slope before the vertical cut was modelled as the first stage. The vertical cut was modelled in the second stage to study the actual site condition before failure. The failure occurs due to the increase in pore water pressure in the soil, thereby reducing the matric suction and shear strength of the soil. The vulnerability of the building located near the cut slope is studied using the Support Vector Method to investigate the effect of material on the failure. The results showed the importance of the material properties in the increase of building resistance to 20%.

/pdf/finite-element-and-vulnerability-analyses-of-a-building-bhp76t43.pdf

Finite Element and Vulnerability Analyses of a Building Failure due to Landslide in Kaithakunda, Kerala, India

The present study investigates the rainfall-induced long-runout landslide that occurred in the Achanakkal area of the Nilgiris district in the Tamil Nadu state of India on November 11, 2009...

Chandrasekaran Sembulichampalayam Sennimalai

Papers

Failure Mechanism of Long-Runout Landslide Triggered by Heavy Rainfall in Achanakkal, Nilgiris, India