Kripamoy Sarkar

A numerical simulation of landslide-prone slope in Himalayan region—a case study

Stability of slope will always a problem due to its geodynamic nature of Himalayan region. The area investigated belongs to the Lower Siwalik formation, which is prone to failure due to presence of various weak planes or structures present in the rock mass. Frequent landslides causing loss of life, property, disturbance of morphological, surface and subsurface water flow pattern. A huge landslide in the Amiyan area occurred in 1999 and blocked the Gaula River which caused loss of agricultural land and other properties as well as waterlogged upstream side. The debris of Amiyan slope contains soil and sandstones of various types. This article deals with instability analysis of slopes of the Amiyan area, near Kathgodam, Nainital, Uttarakhand. This area experiences a number of local as well as regional slides. Extensive field surveys have been carried out to understand the geological detail. Laboratory experiments have been conducted to determine the various physicomechanical properties of rock mass. These properties have been used as input parameters for the numerical simulation. A number of researchers have used two-dimensional numerical models to simulate the slide area. Three-dimensional slope stability studies provide a better understanding of the mechanism of failure as well as zone of influence. The computed deformations and stress distribution, along the failure surface, have been compared with the field measurements and found to be in good agreement with field observations. In this case, finite difference method has been applied on the stability analysis of Amiyan slope. The study indicates that the slope is vulnerable and needs proper protection.Abstractاستقرار المنحدر دائما مشكلة نظرا الى الطبيعة الديناميكية الجغرافية للمنطقة الهيمالايا. في مجال التحقيق ينتمي إلى تشكيل Siwalik السفلى ، التي هي عرضة للفشل بسبب وجود طائرات ضعيفة أو مختلف الهياكل الحالية في كتلة صخرية. الانهيارات الارضية المتكررة تسبب خسائر في الأرواح والممتلكات ، والتشويش على سطح المورفولوجية ، ونمط تدفق المياه الجوفية. ادى انهيار ارضى ضخم في منطقة Amiyan قعت في عام 1999 وسدت نهر Gaula التي تسببت في فقدان الأراضي الزراعية وغيرها من الممتلكات ، وكذلك غمرتها المياه يصل الى جنب الدفق. حطام Amiyan المنحدر يحتوي على التربة والرمل من مختلف الأنواع.تتناول هذه الورقة تحليل لحالة عدم الاستقرار في منطقة السفوح Amiyan ، بالقرب من Kathgodam ، Nainital ، أوتار براديش. هذا المجال عدد من الخبرات المحلية ، فضلا عن الشرائح الإقليمية. مسوح ميدانية واسعة النطاق نفذت في فهم التفاصيل الجيولوجية. التجارب المختبرية التي أجريت لتحديد الخصائص الفيزيائية مختلف الخصائص الميكانيكية للكتلة صخرية. هذه الخصائص قد استخدمت على النحو معلمات الإدخال لالمحاكاة العددية. وهناك عدد من الباحثين استخدموا ثنائي الأبعاد لمحاكاة النماذج العددية في منطقة الشريحة. ثلاثي الأبعاد المنحدر دراسات الاستقرار تقديم فهم أفضل للآلية من الفشل ، وكذلك منطقة نفوذ. التشوهات حسابها وتوزيعها الإجهاد ، وعلى طول السطح الفشل ، وقد تم مقارنة القياسات الميدانية ، وجدت لتكون في اتفاق جيد مع الملاحظات الميدانية. في هذه الحالة ، فرق محدد الأسلوب (بشركة) وقد طبقت على تحليل استقرار المنحدر Amiyan. وتشير الدراسة إلى أن المنحدر هي الضعيفة واحتياجات الحماية الملائمة.

Static and dynamic analysis of a landslide

Slope failure is a recurrent phenomenon in hilly regions. It is hazardous because of the accompanying rapid mass movement of soil and rock mass. To alleviate the damage caused by landslide, slope-stability analyses and stabilization techniques require in-depth understanding and appraisal of the process that govern the failure behaviour of slopes. Once the instability behaviour is understood, remedial measures such as retaining walls, rock bolts, anchoring, etc., can be recommended to stabilize the slope.  This article deals with a comparative study used for the analysis of the stability of slopes of Amiyan area, near Kathgodam, Nainital, Uttarakhand assuming that the rock mass follow the Mohr–Coulomb failure criterion under static and dynamic loading conditions. The area constantly experiences local as well as regional slides along the river bank. A field study was carried out in the landslide area to collect the representative samples to determine the various physio-mechanical properties of rock as well as debris samples. These properties have been used as input parameters after converting it into the rockmass properties using a joint weakening coefficient for the numerical simulation. The computed deformations and the stress distributions, along the failure surface, have been compared with the field measurements/observation and found to be in good agreement. The global factor of safety (FOS) calculated by finite difference, finite element and dynamic analysis was found to be 1.57, 1.144 and 0.84, respectively. This indicates that the slope is critically stable in case of any small local/global disturbance which may further reduce the FOS and cause failure.

Study of Strain Rate and Thermal Damage of Dholpur Sandstone at Elevated Temperature

With the increasing demand of natural resources and its existence at higher depth, rock mechanics is facing a completely new challenge of rock mass behavior at higher temperature. The majority of rock masses for instance found in nuclear waste burial sites, geothermal energy extraction, enhanced and natural geothermal system and underground development of deep mine, oil and gas storage cavern encounters high temperatures and therefore rock strength and deformation characteristics under high temperature need to be studied in detail. During the last few years, some investigations have been carried out in this field (Alm 1985; Brede 1993; Alshayea et al. 2000; Xi 1998; Chen et al. 2005; Liu et al. 2001; Verma et al. 2010, 2013). Under the influence of high temperature below melting point of sandstone, its micro-structures may be re-arranged, consequently new micro-cracks develop due to the pre-existing ones which become widespread and widen. Meanwhile, various physical and petrographic changes take place in the boundary of minerals matrix. After cooling down to air dried temperature, thermally induced changes become permanent to some part of matrix of sandstone. The effect of temperature on the physical and mechanical properties of rock like sandstone has become an important area in rock mechanics. The results of this study will be helpful for restoration and redesign of fire-damaged sandstone buildings and monuments. Wide scale application of building sandstone material can be seen indifferent monuments, temples, and buildings in India, i.e., the Red Forts of Delhi and Agra, Places and buildings in Fatehpur Sikri (Cramer 1986; Anna et al. 2013; Shi and Jinyu 2014; Qiu-hua et al. 2007; Yang et al. 2015). In recent years, however, the behavior of rock is very complex under thermo-mechanical (TM) coupling (Dwivedi et al. 2008; Hudson et al. 2005; Zhou et al. 2011) with measurements of basic physicomechanical parameters; including modulus of rock deformation, Poisson’s ratio, tensile strength, compressive strength, cohesion, internal friction angle, viscosity and thermal expansion coefficients etc. with temperature(Heuze 1983; Lau et al. 1995; Du et al. 2004; Wu et al. 2005; Zhang et al. 2007; Johnson et al. 1978; Malkowski et al. 2012; Vishal et al. 2011). In this paper, the mechanical properties of Dholpur sandstone from upper Bhander subgroup has been cooled down after heating and then variation of mechanical and thermal damage with temperature have been carried out. Therefore, these results do not always replicate the necessary characteristics of rock masses at high temperature. In this paper, sandstones were collected from five locations Fig. 1. Rock samples were cored and & A. K. Verma amitvermaism@gmail.com

The assessment of slope stability along NH-22 in Rampur-Jhakri Area, Himachal Pradesh

The present paper demonstrates the assessment of slope stability analysis between Rampur to Jhakri road section along National Highway (NH-22), Himachal Pradesh, India. The different types of slope failures have affected most part of slopes which causes considerable loss of life and property, inconveniences such as disruption of traffic along highways. The poorly designed rock slopes for road widening or construction purposes may weaken the stability of the slopes. A detail field investigation has been carried out to collect the representative rock samples for determination of physico-mechanical properties of rock and joint data for kinematic analysis. The rocks exposed in the area are highly jointed quartzite and quartz-mica schist of Rampur-Larji Group of Palaeoproterozoic age. The continuous slope mass rating (CSMR) technique has been applied for the assessment of slope stability analysis at five vulnerable locations and the results shows slopes are partially stable to unstable. Kinematic analysis mainly shows wedge type of failure along with few toppling and planar failures. The existing slope required immediate treatment to prevent the failure for its long term stability.

Dump Slope Stability Analysis – A Case Study

In opencast mining operation, the stability of waste materials stands at high priority from the safety and economic perspective. Poor management of overburden (OB) dump results the instability of slope in an opencast mine. The present paper deals with the stability analysis of dump material of an opencast coal mine at Talcher coal field, Angul district, Odisha, by means of different geotechnical parameters and mineralogical composition affecting the dump slope. The prolonged rainfall in the mining area causes dump failure and loss of valuable life and property. A recent dump failure that occurred in 2013 at Basundhara mines of Mahanadi Coalfields Limited (MCL), Odisha, took 14 lives, and created problems for the mining industry. Most of the dump failure that occurs in the study area are mainly due to increase in pore water pressure as a result of rainfall infiltration. The stability of the waste dump was investigated using the limit equilibrium analysis to suggest an economical, sustainable and safe disposal of the dump in the study area.

Rock slope stability analysis along NH-44 in Sonapur area, Jaintia hills district, Meghalaya

Occurrences of landslide are most common and critical issue in North-East India. The various types of slope failures have been affected most part of slopes and road section between Malidor to Sonapur area (approx 30 Km) along NH-44 within Jaintia hills district, Meghalaya, India. These slope failures causes considerable loss of life and property along with many inconveniences such as disruption of traffic along highways. The unscientific excavations of rock slopes for road widening or construction purposes may weaken the stability of the slopes. The rocks exposed in the area are highly jointed sandstone and shale of Barail Group of Oligocene age. The Sonapur landslide is most dangerous and destructive rock fall-cum debris flow. The present study includes the kinematic analysis of the slope to assess the potential failure directions as the rocks are highly jointed in some parts of road cut sections. The continuous slope mass rating (CSMR) technique has been applied for slope stability analysis at five vulnerable locations. Kinematic analysis indicates mainly wedge type of failure along with few toppling and planar failures. These failure required immediate treatment to prevent the slide and long term stability of the slope.

Stability analysis of a recurring soil slope failure along NH-5, Himachal Himalaya, India

The repetitive soil slope failure along the National Highway (NH)-5 in Jhakri region of Himachal Pradesh, India draws frequent concern due to heavy damage and traffic disruption almost every year. Being only linking route from border district to the nearby land area, stability of the road-cut slopes along this highway is of major concern in regard to safe transportation. Absence of any previous stability investigation of this recurring slope failure calls for an integrated geotechnical and numerical approach in order to understand the instability factors. The geotechnical analysis has been performed to determine the inherent properties of soil materials which affect the stability of existing slope. An event-specific antecedent rainfall threshold has been suggested to quantify the relationship between rainfall and slope failure. A two-dimensional limit equilibrium method has also been executed to visualize the scenario of pre- and post-failure stability of the slope. On the basis of limit equilibrium analysis, it has been inferred that slope geometry is a major affecting parameter that influences the failure pattern. Moreover, preventive measures through benching and soil nailing have also been proposed and validated through limit equilibrium analysis for long-term stability and safe transportation.

Comparative analysis of limit equilibrium and numerical methods for prediction of a landslide

Landslides that occur due to the rapid motion of a rock-mass are a primary risk in mountainous terrains and are a danger to human life and civil infrastructure. The application of geotechnical engineering methodologies for remedial purposes is to assess unpredictable behavior and the stability of the slope, and for analysis and design. The aim of the study is to quantify the global factor of safety (FOS) and describe a correlative and comparative assessment of the conventional Limit Equilibrium Model as compared with the advanced Numerical Model for the rock slopes of Amiya, Nainital, Uttarakhand in India utilizing Mohr-Coulomb failure criterion. The rock-mass characteristics were determined as a result of an estimation of the physio-mechanical properties of rock and debris from collected field samples with the help of the joint weakening coefficient for limit equilibrium (LE) and the numerical solution. Global FOS estimated by means of stability analysis procedures, such as Swedish slip circle, Ordinary method of slices, Modified Bishop, Janbu method, Finite difference static analysis, Finite element static, and Finite difference dynamic analysis, was found to be 0.65, 1.34, 1.38, 1.29, 1.57, 1.144, and 0.84, respectively. The results helped to deduce that the slope remains substantially stable and failure may only occur in the case of a down slope movement of rock debris (clastic mass of rocks) with a small local/global tremor. Combination of the LE technique and numerical approach (hybrid approach) has been found to be a better method for critical slip surface and FOS determination.

Qualitative stability assessment of cut slopes along the National Highway-05 around Jhakri area, Himachal Pradesh, India

Several deformation phases in tectonically active Himalayas have rendered the rock masses very complex in terms of structure, lithology and degree of metamorphism. Again, anthropogenic activities such as roads, tunnels and other civil engineering constructions have led to a state of disequilibrium which in many cases, results in failure of rock masses. National Highway-05 around Jhakri area in India is a major connecting route to the China border in the hilly terrains of the state Himachal Pradesh. It cuts through the Himalayan rocks and has a hazardous history of landslides destroying human lives and interrupting communication very frequently. As a contribution towards the mitigation process, a study has been carried out along the highway to analyse kinematic stability and qualitative estimation of rock mass condition through rock mass classification systems. The kinematic analysis shows that the rock slopes are prone to planar and wedge failure. Rock mass rating for most of the locations lies between 7 and 34, representing a poor rock mass quality (Class IV), whereas slope mass rating is more disperse and ranges from 11 to 52 for most of the slopes (Class III, IV and V).

The Effect of Lineation on Anisotropy in Dry and Saturated Himalayan Schistose Rock Under Brazilian Test Conditions

The paper presents experimental observations of the anisotropic effect of dry and saturated lineated schistose rock on deformational behaviour and fracture patterns under indirect tensile loading conditions. Dry mylonitic quartz–mica schist (M-QMS) shows strength minima in between lineation orientation of 20°–30° with loading direction, whereas dry crenulated quartz–mica schist (C-QMS) shows strength minima in between 45° and 60°. Water saturation significantly reduces the failure strength and shifts the strength minima towards a higher angle. In addition, the water saturation effect induces plasticity along the lineation direction. P-wave velocity is found to be maximum along lineation direction, which continuously decreases to a minimum value across the lineation. Three types of fracture patterns, namely layer activation, central and non-central, are observed for both the rock types. For both the rock types, tensional fractures occur when the lineation is inclined at 0° and 90° to the loading direction, whereas shear and mixed-mode fractures occur at all other orientations. Fracture through the layer activation is prominent in saturated specimens compared to the dry specimens for β angle range of 15°–60° and 15°–45° in the case of M-QMS and C-QMS, respectively.