Tunneling in lesser Himalaya, Jammu and Kashmir, India with special emphasis on tectonic mélange

Abstract

Himalayan fold belt has full of geological surprises, 'mélange' is one of them which create difficulties during tunneling. Such mélange completely went unnoticed during surface mapping and geotechnical investigation preceding the construction of the Udhampur railway tunnel (URT). During the construction, the mélange zone has encountered across the tunnel, which occurs along the Tanhal thrust (equivalent to MBT) that separates the Murree Group and the Shiwalik Group. The mélange was characterized by a chaotic, heterogeneous geological mixture of stronger blocks (scale independence) and weaker sheared fine-grained matrix, often termed as "block-in-matrix rocks" or bimrocks, which enforced mixed face tunneling. The heterogeneity in a tectonic mélange led to stress concentrations in the rock blocks, and there were relatively high deformations within the matrix also. Release of stress from the blocks due to excavation, with unfavorable joint and thrust orientations enforced brittle failure of the blocks (face and crown collapses) while matrix deformation (time dependent) caused convergence of primary support later. Additionally, the clay minerals with high swelling potential within the matrix swelled and created pressure on the primary support. Due to the geomechanical heterogeneity in mélange, homogenizing the rock-mass by the commonly used quantitative systems might have lead to an inappropriate design and construction. The adopted New Austrian Tunneling Method (NATM) proved to be an useful tool for tunneling.

Forecast of Ground Deformation Caused by Tunnel Excavation Based on Intelligent Neural Network Model

“…e new Austrian Tunneling Method (NATM) adopted by Dhang proved to be a useful tunneling tool [6]. Due to the massive excavation and unloading of the ground surface, a large number of cracks and fractures appeared in the segments of the underlying shield tunnel.…”

3D Monitoring & its Significance in Tunneling: Special Emphasis on Tunnel T-74R of USBRL Project, India

“…1). However, because of the poor and unpredictable geological conditions, tunneling is a challenging activity in the Himalayan area [1][2][3]. The groundmass underwent multiple periods of deformation owing to the collision of the Indian and Eurasian plates, weakening the rocks of the sub-and lower Himalayas [4].…”

Structural and geochemical studies of the Palaeozoic granites from Dalhousie region of Himachal Himalaya: Implications on petrogenesis and deformation of strongly peraluminous S‐type granites

“…Cambro‐Ordovician (500 ± 25 Ma) granitic magmatism not only provides a comprehensive perspective of the heterogeneous melting of the crust but also the interplay between mafic and felsic magmas during this time (Kumar, Singh, et al, 2022). The intense mylonitization of the Palaeozoic granites is commonly associated with Himalayan Orogeny (Le Fort, 1983; Singh, 2003; Singh et al, 2002; Singh & Jain, 1996). Previous studies suggest that the granitic massif of Palaeozoic age from the Dalhousie–Chamba area belong to the LHGB and these granites occur as elongated/lenticular structures in the core of an antiform within the Chail metasediments of the Chamba Group (Kanwar & Bhatia, 1977; Kumar et al, 1983; Le Fort, 1983; McMahon, 1981; Thakur, 1998).…”

“…According to Singh and Jain (1996), the Palaeozoic and Proterozoic granites occurring within the Lesser Himalaya, either as large‐scale concordant sheets or as isolated elliptical‐shaped bodies reveal localized high ductile shear strains along their margins, where numerous shear indicators consistently reveal initial top‐to‐SW verging displacement showing overthrust geometry. Such granitic bodies are distinguished by post‐magmatic deformation, which gives rise to the development of mylonitic fabric on their marginal contact with undeformed massive to the porphyritic core.…”