Analysis of rainfall induced debris flows

Landslides are natural hazards that cause severe casualties and financial losses. There are various methods used to analyze landslides; among these, geotechnical and geophysical methods are widely used due to their accuracy and low cost, respectively. In this study, 2D electrical resistivity tomography (ERT) surveys, geotechnical, and field data are used to define the subsurface structure and the geometry of the Nargeschal landslide. To determine the most appropriate array, ERT measurements were performed by Wenner-alpha (Wa), Wenner-Schlumberger (WS), and dipole-dipole (DD) arrays. Furthermore, the relationship between electrical resistivity with change in the degree of saturation and landslide hydrology was investigated by completing multiple surveys at the same location, at different times. Landslide 3D geometry and hydrology were identified by ERT results. Moreover, geotechnical data was used to investigate the Nargeschal landslide and to interpret the ERT pseudo sections. The data from boreholes were used to constrain the depth and consequently the resistivity range that characterize the basal slip surface of the landslide in the ERT pseudo sections. The results of geotechnical investigations indicated that the landslide material had moisture content very close to the plastic limit, with a higher clay fraction and low shear strength at the slip surface. Finally, it must be noted that the simultaneous use of the ERT survey, geotechnical methods, and field investigations led to a complete and accurate characterization of the Nargeschal landslide.

Reconstruction of landslide model from ERT, geotechnical, and field data, Nargeschal landslide, Iran

Rainfall-Induced Landslides: Case Study of the Marappalam Landslide, Nilgiris District, Tamil Nadu, India

Field reconnaissance, geological mapping and photographic interpretation are utilized to study the failure mechanisms of July 2 catastrophic debris slide in 2017. The results suggested that...

Characteristics and mechanisms of coupled road and rainfall-induced landslide in Sichuan China

This study aims to demarcate landslide susceptible zones using methods of analytical hierarchy process (AHP) and frequency ratio (FR) to find the most influencing factors and to compare their prediction capability. Ten causative factors (slope angle, elevation, lithology, land use/land cover types, normalized difference moisture index, road buffer, normalized difference built-up index, water ratio index, stream power index, and soil) are used in the study. The area of the landslide susceptibility was grouped into five classes. According to the landslide susceptibility maps prepared using the AHP and FR methods, 11.14% and 6.57% of the area are very highly susceptible to landslides. Finally, the receiver operating characteristic (ROC) curves for the landslide susceptibility maps prepared using both AHP and FR methods were plotted, and the area under the ROC curve (AUC) values were estimated to validate the results. AUC values of 0.69 and 0.81 were estimated for the landslide susceptible zone maps prepared using AHP and FR, respectively. From the AUC values, it is confirmed that the FR method is more effective in predicting the landslide susceptible zones in Idukki district. The landslide susceptibility maps are helpful for land use planners and policy makers in adopting suitable mitigation measures to minimize the impacts of landslides and thereby reduce loss of life and property.

Landslide Susceptibility Zonation of Idukki District Using GIS in the Aftermath of 2018 Kerala Floods and Landslides: a Comparison of AHP and Frequency Ratio Methods

Landslides are frequently occurring natural hazards in Nilgiris district of Tamil Nadu, India, particularly during monsoon season The present study describes the geotechnical characterization and analysis of rainfall-induced landslide that occurred at Marappalam location of Nilgiris district on November 10, 2009 The detailed investigation comprises mapping of landslide, topographical survey, field and laboratory investigations, characterization of soil and rock, and numerical analysis Field study comprises borehole and geophysical investigations Detailed laboratory investigation was performed to identify index and engineering properties of soil and rock Based on the results obtained from field and laboratory investigations, the generalized subsoil profile of Marappalam slope has been plotted The investigations revealed that loose and soft soil layer with low permeability and plasticity interspersed with boulders could be the main source of debris flow Scanning electron microscopic analysis and x-ray diffraction analysis were performed to study the influence of weathering on slope failure Failure mechanism of Marappalam 2009 landslide was identified from the numerical analysis performed using landslide simulation program LS-RAPID The analysis revealed that the 5-day antecedent rainfall (303 mm) and intense rainfall on 10th November 2009 (405 mm) saturate the slope due to infiltration of rainwater This leads to a decrease in the matric suction and subsequent development of positive pore water pressure, which in turn reduces the shear resistance of the soil along with shear displacement, and resulted in a progressive failure

Geotechnical characterization and analysis of rainfall—induced 2009 landslide at Marappalam area of Nilgiris district, Tamil Nadu state, India

Landslide is a major natural hazard, which possesses serious threat to human population and various other infrastructures such as road, rail routes and other structures in the hilly terrain Nilgiris district, located in southern state of Tamil Nadu in India, is basically a hilly region, lying at an elevation of 1000–2600 m above Mean Sea Level (MSL) The district regularly receives rainfall during both the southwest and the northeast monsoons The average rainfall in this region is between 1500 and 3000 mm Due to the steep slopes and heavy rainfall during monsoons, the district is highly prone to landslides In recent times, occurrence of landslides in Nilgiris is increased due to sudden burst of development activities in the region The present study gives an overview of landslide events and remedial options practiced so far in Nilgiris and emphasises the importance of geotechnical investigation in that region The history of landslide events has been collected and soil samples have been taken from the places where, major landslides have occurred in the past to characterise them The rainfall data have been collected to understand the influence of rainfall on landslide occurrence From this study, it is observed that the main triggering factor for landslide in Nilgiris is heavy intense rainfall Though the rainfall is main triggering factor, many causal factors are also involved in triggering of landslides It is also observed that, the remedial measures practiced in this area was not site specific and mainly concentrated on construction of retaining walls and small gabion walls To understand the failure mechanism of landslides, various effects of pore water pressure and to suggest suitable site specific remedial measure to prevent the recurrence of such failures in the future, detailed geotechnical investigations are required

Overview of Rainfall Induced Landslide Events and Importance of Geotechnical Investigations in Nilgiris District of Tamil Nadu, India

Landslide is a major natural hazard which affects 15% land area of the country. Himalayas and Nilgiris are most affected locations due to landslides in India. Rainfall is the major triggering factor for landslides in Nilgiris, whereas some of the Himalayan regions experienced landslides due to combination of rainfall and earthquake. Though the rainfall is a major triggering factor, some of the other causative factors are also responsible for triggering of landslides in Nilgiris. The present study gives an over view of the various causal factors involved in triggering of landslides in Nilgiris. It is found that, cutting of slope at toe, heavy loading on slope at crest, blocking of surface drainage system and choking of weep holes in retaining structures, improper planning and design/implementation of remedial measures, vegetation removal and dumping are possibly the main causal factors for most of the landslides in Nilgiris during heavy rainfall. The study also suggest, though the retaining walls are commonly adopted as remedial measures, cost effective subsurface drainage systems together with slope reinforcement might be effective solution to control the landslides in many locations. Present study also gives an over view on the use of numerical analysis pertaining to landslides in Nilgiris together with on-going detailed site specific geotechnical investigation.

V. Senthilkumar

Papers

Rainfall-Induced Landslides: Case Study of the Marappalam Landslide, Nilgiris District, Tamil Nadu, India

Geotechnical characterization and analysis of rainfall—induced 2009 landslide at Marappalam area of Nilgiris district, Tamil Nadu state, India

Overview of Rainfall Induced Landslide Events and Importance of Geotechnical Investigations in Nilgiris District of Tamil Nadu, India

Landslides in Nilgiris: Causal Factors and Remedial Measures