Site-specific geological and geotechnical studies on the Lanta Khola landslide, North Sikkim Highway, India

Anbarasu, K.; Gupta, Saibal; Sengupta, A.

doi:10.3328/ijge.2009.03.03.361-376

Cited by 10 publications

(6 citation statements)

References 21 publications

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“…The water content in the debris at depth decreases in a northwesterly direction; however, at each level, the movement of water within the debris parallels the geological contact. As suggested by Anbarasu et al (2009), this soggy zone at the contact becomes saturated with water following a particular minimum threshold precipitation ). This reduces the shear strength within the soggy zone, ultimately leading to its failure and triggering of slide activity.…”

Section: Vesmentioning

confidence: 93%

“…Monitoring of slide activity over an entire year indicates that all movement of debris material during sliding occurs from immediately below the soggy zone. According to Anbarasu et al (2009), this indicates that the water-saturated, relatively impermeable soggy zone near the head plays a pivotal role in activating the Lanta Khola slide.…”

Section: Geological Backgroundmentioning

confidence: 97%

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Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India

et al. 2009

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Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important to identify the subsurface structures that channel water below the landslide surface in order to understand the triggers of slide activity. This can only be accomplished by geophysical survey; however, an appropriate geophysical technique that can be applied in such terrains must be identified. Very low-frequency (VLF) electromagnetic survey was performed over the Lanta Khola landside in order to delineate subsurface structures. Although a very limited number of VLF transmitters are available worldwide, it was possible to pick up VLF signals from a number of VLF stations even in this highaltitude mountainous terrain. VLF measurements along five profiles perpendicular to the geological strike were recorded, and a high conducting zone was delineated from the VLF observations. This conducting zone correlates with the low resistive zone identified from gradient resistivity profiling. The anomalies confirm that there is a water-saturated zone (soggy zone) even in the subsurface of the slide parallel to the geological gneiss-schist contact within the Lanta Khola slide. This indicates that the conductive feature correlates with a weak water-saturated debris layer that lies along the slide and is parallel to the geological contact. Resistive structures on either side of the landslide zone can thus be correlated with the stable ground. It is necessary to drain out water from the soggy zone to minimize slide activity since this zone appears to penetrate into the body of the slide.

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Section: Vesmentioning

confidence: 93%

Section: Geological Backgroundmentioning

confidence: 97%

Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India

et al. 2009

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“…Due to such reasons the mechanism and induced parameters behind rainfall induced landslide is being studied extensively all round the world and especially in the Himalayan region (Nandy et al 2015;Upgupta et al 2015;Dimri et al 2017). Such studies have been able to quantify few relationships between rainfall precipitation and local landslide characteristics parameters (Anbarasu et al 2009). Intensity and duration of the rainfall are two controlling factors of the rainfall-induced landslides (Rahardjo et al 1995;Bhambri et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Site-specific geological and geotechnical investigation of a debris landslide along unstable road cut slopes in the Himalayan region, India

Prakasam

Aravinth

Nagarajan

et al. 2020

Geomatics, Natural Hazards and Risk

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The present research work investigates the slope instability along NH-05 near Jhakri, Himachal Pradesh, India. Initially, field investigation has been conducted to study the slope morphometry and characteristics. The studied landslides trends along NW-SE direction with height 27.26 m from the road surface and at an angle of 63 vertically post failure. Parameters responsible for slope stability such as particle size distribution, Atterberg Limit and shear strength parameters were collected through direct shear plot using soil samples collected from field. The results reveal that the soil coarse to fine loamy with no surface vegetation long the landslide areas. The absence of vegetation exposes the soil for erosion during high monsoon rainfall. Based on the shear test results the value of c and Phi is 10.28 kPa and 18.8 . 2 D limit equilibrium model has been used using Rocscience software for slope stability assessment. LEM model reveals a safety factor value 0.43 which is less than the value considered for stale slopes. Reenforced bench slope with soil nailing has been suggested as a suitable stabilization measure with a FOS value of 1.2 which reveals the slope can be stabilized with the mentioned approach.

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“…Along the selected transect both units are multiply deformed, but are separated by an intervening ductile shear zone dominated by a single penetrative fabric that consistently strikes NW-SE and dips north-east (Fig.3). The fabric is associated with S-C structures that preserve a top-to-the-southwest sense of movement (Anbarasu et al 2009). This zone incorporates components of both units, and the presence of a common fabric along the contact zone can be attributed to pervasive transposition of the earlier foliation along the zone of thrusting.…”

Section: The Hhcs Lhs and The Mct In This Studymentioning

confidence: 99%

Evidence for structural discordance in the inverted metamorphic sequence of Sikkim Himalaya: Towards resolving the Main Central Thrust controversy

et al. 2010

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Inverted metamorphism in the Himalayas is closely associated with the Main Central Thrust (MCT). In the western Himalayas, the Main Central Thrust conventionally separates high grade metamorphic rocks of the Higher Himalayan Crystalline Sequence (HHCS) from unmetamorphosed rocks of the Inner sedimentary Belt. In the eastern Himalayas, the Inner sedimentary Belt is absent, and the HHCS and meta-sedimentary Lesser Himalayan Sequence (LHS) apparently form a continuous Barrovian metamorphic sequence, leading to confusion about the precise location of the MCT. In this study, it is demonstrated that migmatitic gneisses of the sillimanite zone in the higher structural levels of the HHCS are multiply deformed, with two phases of penetrative fabric formation (S 1HHCS and S 2HHCS ) followed by third folding event associated with a spaced, NW-SE trending, north-east dipping foliation (S 3HHCS) . The underlying LHS schists (kyanite zone and lower) are also multiply deformed, with the bedding S 0 being isoclinally folded (F 1LHS ), and subsequently refolded (F 2LHS and F 3LHS ). The contact zone between the HHCS and LHS is characterized by ductile, top-to-the southwest shearing and stabilization of a pervasive foliation that is consistently oriented NW-SE and dips northeast. This foliation is parallel to the S 3HHCS foliation in the HHCS, and the S 2LHS in the LHS. Early lineations in the HHCS and LHS also show different dispersions across the contact shear zone, implying that pre-thrusting orientations of the two units were distinct. The contact shear zone is therefore interpreted to be a plane of structural discordance, shows a shear sense consistent with thrust movement and is associated with mineral growth during Barrovian metamorphism. It may well be considered to represent the MCT in this region.

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Site-specific geological and geotechnical studies on the Lanta Khola landslide, North Sikkim Highway, India

Cited by 10 publications

References 21 publications

Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India

Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India

Site-specific geological and geotechnical investigation of a debris landslide along unstable road cut slopes in the Himalayan region, India

Evidence for structural discordance in the inverted metamorphic sequence of Sikkim Himalaya: Towards resolving the Main Central Thrust controversy

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