Figure 4-14 - uploaded by Krishna Kanta Panthi
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Rock mass conditions at Middle Marsyangdi: thinly foliated and fracture quartzite (left) and siliceous phyllite in intercalation with thin bands of metasandstone and micaceous phyllite (right).
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The need for tunnelling in Nepal, as in the Himalayan region in general, is enormous, particularly for hydropower development. Due to active tectonic movement and dynamic monsoon, the rock mass in the Himalaya is relatively weak and highly deformed, schistose, weathered and altered. Predicting rock mass quality, analyzing stress induced problems, i...
Citations
... In the Himalayan region, accumulated stresses are released due to active tectonic movement. This process causes rock mass to shear leading formation of faults, folds, and weakness zones [3]. Moreover, this activity leads to an increase in the anisotropic condition of rock mass where the geo-mechanical parameters are significantly changed within the short range. ...
... Moreover, this activity leads to an increase in the anisotropic condition of rock mass where the geo-mechanical parameters are significantly changed within the short range. Thus, tunneling in the Himalayan region is challenging and often encounters tunnel instabilities [3][4]. The natural condition of the ground is highly influenced by the excavation of underground structures. ...
... Thus, the extent of deformation depends on the rock mass strength, mechanical properties of rock mass, and in-situ stress [3][4][5]. Stress-induced instability is fundamentally classified into rock spalling/rock burst and large plastic deformation or tunnel squeezing [5]. According to Cai and Kaiser [6], rock spalling/ rock burst happens if the deep tunnel passes through the unjointed hard rock mass. ...
The instability in tunnels is mainly affected by geological anomalies, rock mass quality, complex geological structures, active tectonics, and stress anisotropy. This review article presents challenges associated with stability and applied remedial measures prevailing in hydropower tunnels in the Himalayas. The review covers nine hydropower tunnels located in different parts of the Himalayas. The review found that rock bursting/spalling frequently occurs when the tunnel passes through a high overburden with good rock mass quality. On the other hand, plastic deformation (squeezing) occurs when a tunnel passes through the weak and schistose rock mass. It has been found through the review that the tunnel crew was able to successfully solve instability challenges. Effective planning, design, and selection of appropriate construction techniques help to complete tunneling projects in the Himalayas.
... Hence, the pursuit of empirical rock mass classification is crucial for effectively assessing and addressing the support requirements of tunnels, guaranteeing their safe construction, operation, and overall stability (Panthi 2006;Ullah et al. 2018). These recent developments in rock mass characterization and support assessment techniques are crucial for ensuring the safe and efficient construction and operation of underground excavations in the future (Madlener & Specht 2020). ...
The study for the design of tunnels in similar geological settings, providing insights into potential challenges that may arise during excavation and offering strategies for mitigating risks in District Kalam on the Ushu River, Khyber Pakhtunkhwa, Pakistan. The methodology involved geological mapping, rock sampling, discontinuity surveys, and laboratory testing for empirical analysis of tunnel parameters at the Weir House, Powerhouse, and tunnel alignment locations. Empirical analysis of tunnel parameters using three rock classification systems, rock mass rating (RMR), rock quality tunneling index, and rock mass index (RMi). Based on the classification, the rock quality was found to be fair, indicating favorable rock properties. The Q-system rated the rock as poor to fair, suggesting low discontinuity intensity, medium rock strength, or medium deformation modulus. According to the RMi, rock was rated as medium to strong, indicating low discontinuity intensity, high rock strength, or low deformability. The support design for the tunnel is based on empirical analysis, it recommends support design for the tunnel reinforcement elements such as rock bolts, wire mesh, and shotcrete lining. Overall, the tunnel is stable and does not have complex structure and weak zones.
... Project-specific characteristics like size, shape, location, and orientation influences the design of caverns and tunnels. (Panthi, 2006). Further, the stability is dependent on the rock mass quality, in-situ stress, and groundwater conditions. ...
... The subdivisions are separated by the boundaries of the main frontal thrust (MFT), main boundary thrust (MBT), and main central thrust (MCT). These tectonic zones are all characterized by special lithology, tectonics, geological structures, and geological history and are made up of different rock types (Panthi, 2006). Figure 1 shows the simplified geological map of Nepal with the geological and tectonic boundaries. ...
... The value of the deformation modulus obtained from the empirical relationship is illustrated in Figure 6. It is observed that the relationship provided by Bieniawaski (1978) provides the highest value of the deformation modulus and the relationship by Hoek et al (2002) and Panthi (2006) provides almost similar values. In this article, the deformation modulus obtained from Equation 8 proposed by Panthi (2006) is considered. ...
Underground structures like tunnels and caverns have major advantages in hydropower projects. Tunnels are used for transporting the water from the intake to the tailrace outlet through the turbines whereas caverns primarily serve the purpose of powerhouse, transformer caverns, and settling basins. The site selection of the underground cavern is an important task to be considered to optimize the rock support and cost. Design aspects regarding stability and functionality are governed by the location, orientation, shape, and size of the caverns. Similarly, the choice of support for a particular geological condition and type and quality of rock mass needs to be carefully assessed during planning and implemented during the construction. This article discusses the location design and rock support requirement of the underground powerhouse cavern of the Super Dordi Hydropower Project in Nepal. The project lies in the lower boundary of the Higher Himalayan rock formation. The powerhouse cavern has a length of 39 m and has width (span) and height of 14.5 m × 28 m, respectively. The rock support measures predicted during planning are modelled using 2D numerical modelling tools. The study on monitored data and numerically modelled data are compared and discussed.
... The tunnel construction in the Himalayan region faces severe tunneling challenges due to the complex geological conditions characterized by a higher degree of jointing, high degree of faulting, folding, weathering, and the presence of weakness/shear zones within the rock mass (Panthi 2006). These complex geological conditions are due to the consequence of active tectonic activities in the region. ...
... These conditions significantly increase rock mass permeability and make headrace tunnels of hydropower projects susceptible to water leakage. Thus, groundwater inflow and leakage are the most common and challenging issues in hydropower tunnelling projects in the Himalayan region (Panthi 2006). Water ingress into these tunnels not only affects the stability of the tunnel but also poses operational and safety risks, which could lead to project delay and huge economic loss (Panthi and Nilsen 2010). ...
In the Himalayan region, tunnels are often constructed through complex and varying geological formations having rock mass with higher degree of jointing, faulting, folding, and weakness/shear zones. Such rock mass condition significantly increases the rock mass permeability which enables a higher possibility of water leakage into and out of the headrace tunnels built for hydropower projects and is a challenging situation for tunnel stability. Therefore, comprehensive leakage assessment and effective pre-and post-grouting application are essential in hydropower tunnels. In this research, the water leakage was predicted by using three machine learning approaches such as Support Vector Regression (SVR), Decision Tree (DT) regression, and K-Nearest Neighbors (KNN) models. The water leakage/inflow was predicted in one of the hydropower tunnels based on the geological condition of rock mass, rock mass quality, and hydro-geological conditions. The effective post-grouting method was applied to mitigate the potential water leakage and to enhance the rock mass quality and stability of the hydropower tunnel. It was observed that the injection grouting technique helps to make tunnels less permeable, reduces instability conditions, and ensures the long-term safety and structural integrity of the hydropower tunnels.
... Analysis and design of underground structures requires the reliable estimation of strength and deformation behaviors of rock mass [2]. The stability of underground excavation depends upon the rock mass quality and mechanical processes by which the rock is formed [3]. The stability of underground excavation basically depends upon the combined effect of rock mass quality and mechanical processes. ...
... Decomposition and dissolution causes chemical weathering, which depend upon the environmental and climatic region [4]. The intact rock mass is considered homogeneous, even few discontinuities does not represent the strength of rock mass [3]. The mislead interpretation of rock mass classification provides uneconomical support system [5], hence reliable estimation of strength and deformation is prerequisite for the analysis and design of underground structure. ...
Ground classification systems have been widely used to characterize the soil or rock mass for the analysis and design of underground structures. Deformation characteristics of rock mass around the underground excavation boundary varies according to types of rock and their properties, in situ stress condition and types of support used. Broadly used classification systems for underground structures are Rock Mass Rating (RMR) and Rock Quality Index (Q- Systems) but in-case of the Nagdhunga-Naubisea road tunnel Nippon Expressway Company Limited used NEXCO-System. Literally, the NEXCO classification is based on the velocity of elastic wave, geological condition, boring core condition, competence factor, stability of tunnel face and convergence. However, in-case of Nagdhunga-Naubisea road tunnel, grade point is computed using the similar parameters that are used in RMR- System and Q-System. This research focuses about comparison between ground classification from RMR, Q-system and NEXCO system. The geological descriptions obtained from project office at chainages (0+497 to 0+502), (0+508 to 0+513), (0+581.8 to 0+587.8) and (0+584.2 to 0+590.2) were used to correlate the relationship between RMR, Q-system and NEXCO system of rock mass classification systems. Results showed that from RMR, the ground classification is “poor” at all the chainages whereas from Q-system is “very poor” at chainage (0+508 to 0+513) and “poor” at other chainages. Similarly, from NEXCO- system it was found that “DII” at chainages (0+497 to 0+502) and (0+508 to 0+513) and CII for chainages (0+581.8 to 0+587.8) and (0+584.2 to 0+590.2). These results revealed that the ground classification from NEXCO as DII is similar to poor from RMR and poor or very poor from Q system where as CII from NEXCO is similar to poor from both RMR and Q system.
... A rockmass is a complex geometrical and mechanical Pages: 1 -6 assemblage resulting from a long history of tectonic forces and other natural environmental effects. The intact rock specimen is usually strong and homogeneous, with few discontinuities and therefore doesn't represent the strength of the total rockmass [3]. The displacement, strength and failure properties of a rockmass are determined by the mechanical properties of the intact rock, the geometrical properties of the discontinuities, and the mechanical properties of the discontinuities. ...
Rock engineering involves the comprehensive examination of both rock mechanics and engineering geology. Evaluating the various parameters of rock engineering plays a crucial role in effective planning, design, and construction of subterranean structures. Two primary parameters, strength and deformability, are pivotal in understanding the mechanical properties of the rock mass. These properties are typically determined using a range of commonly employed empirical methods. Additionally, rock engineering delves into engineering geological factors such as the characteristics of rock joints and in-situ stress conditions, all of which are meticulously studied to ensure the success of underground projects.This paper describes about the interaction of rockmass and support applied after the excavation is made in the rockmass. The geological conditions in the project area have been thoroughly examined through a combination of literature review and on-site surface mapping. These investigations have revealed that the project site is situated within the Augen Gneiss unit, which is part of a meta-sedimentary rock sequence equivalent to the Nuwakot group rocks from the Paleoproterozoic era. Support estimation using Q-chart and Numerical Modelling with Phase-2 software is carried out and compared with the support used in the project.
... The rock masses are composed of the rock material and discontinuities that have been identified since the first geological studies [19] proved that the description and classification of the variables that control or influence the behavior of the rock mass is the process of rock mass characterization, and the outcomes of the characterization process will be used to evaluate the rock mass quality. A structural or geological feature known as a discontinuity changes the homogeneity of a rock mass indicated by [20]. Discontinuities in the physical continuity of the rocks include bedding surfaces, joints, faults, and foliations. ...
... Figure 4 illustrates pillar strength based on diverse empirical relationships for both 2 m and 5 m pillar widths. This analysis yields pillar strength ranging from (2-12) MPa for a smaller tunnel (4.2 m) and (1-12) MPa for a larger tunnel (6.5 m) within the 2 m wide pillar zone, as shown in Fig. 4. Similarly, in the case of a 5-m-wide pillar, the smaller tunnel exhibits a strength capacity spanning (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) MPa, while the larger tunnel ranges from (3-15) MPa, as depicted in Fig. 4. ...
... The project is situated in the eastern region of Nepal, in the Himalayan range, where the tectonic stress is likely to affect the horizontal stress. According to a study from author Panthi [16], the tectonic stress direction in the project location is oriented at 5 degrees North-East. In another study from authors Shrestha and Panthi [17], tectonic stress was found to be 3 MPa in a project located in the western part of Nepal, while in the eastern region, it was found to be 5 MPa through in-situ stress measurements. ...
This research investigates the utilization of tunnel junctions in underground design, focusing on accessibility, connectivity, and safety considerations. The study specifically examines tunnel junctions within hydropower tunnels in eastern Nepal, employing the Rocscience Phase2 finite element model (FEM) with a post-peak failure approach. The generalized Hoek–Brown method, complemented by the strain-softening method and incorporating the residual Geological Strength Index (GSI) proposed by Cai et al. (Int J Rock Mech Min Sci 44:247–265, 2007), is applied in the model. The resulting analysis encompasses volumetric strain, shear strain, and stress distribution, facilitating the comprehensive evaluation of tunnel intersections, corroborated by on-site geological verification. Findings indicate a direct correlation between stress distribution in tunnels, overburden increments, and tunnel openings for specific pillar dimensions, as vertical stress is inherently tied to overburden. Smaller pillars exhibit heightened vulnerability to increasing overburden and excavation sequences, with notable impacts extending to the periphery of the pillar section. Moreover, the study underscores that 2D numerical modeling, using software such as Phase2, falls short in illustrating stress unloading commonly associated with conventional drill blast excavation methods. As a recommendation, the adoption of other explicit or implicit FEM models capable of accurately capturing dynamic unloading and failure conditions is advised. Ultimately, a comprehensive understanding of the stress path proves imperative in ensuring the effective performance of project components within the desired factor of safety.
... The primary factor influencing these stability problems is associated with rock mass quality. The major factors that influence the rock mass quality in the underground opening are rock mass strength, rock deformability, strength anisotropy, discontinuities in the rock mass, and degree of weathering (Panthi 2006). Some of the other stability problems are linked to water inflow and rock swelling. ...
The rock mass is heterogeneous and makes underground space construction a challenge to engineers. The rock formation, mineralogical composition, degree of schistosity, and weathering, are the major factors that determine the stability condition and rock support requirements. This manuscript deals with the stability situation of the underground settling basin caverns of Super Dordi Hydropower Project (SDHP) in Lamjung district of Nepal which is located at the lower boundary of the Higher Himalayan rock formation. The two parallel underground settling basins are 120m long and have an approximate cross-sectional area of 113 sq. m. The manuscript further discusses geological and rock mass quality conditions and evaluates the stability of the underground settling basins using 2D numerical modeling. The outcomes of the analysis presented in the manuscript have been helpful for the optimization of applied rock support.
... In the Himalaya, slope cutting in highly deformable and fractured rock mass is one of the challenging tasks in the infrastructure development activities such as road cuts, cut slopes for hydropower projects, portals to the tunnels and so forth (Panthi, 2006). The failure criterion in such slopes is hard to define as the failure is governed by the joints, fractures, frequent shear bands, and highly schistose and deformed rock mass which may act as soil like material. ...
Stability of a cut-slope at the headworks area of the hydropower projects is very important for smooth operation of hydropower plant. Underestimation during construction period may bring a catastrophic consequence. This manuscript presents overall assessment results of the rock cut slope excavated to accommodate two settling basins of Seti Khola Hydropower Project (22 MW) located at Lekhnath, Kaski, Nepal. The height of the cut slope is about 50 m and is among the most challenging part of the construction work. The cut slope is excavated in a highly schistose and deformed phyllite with interbedding of metasandstone layers. The evaluations are made on the overall rock mass and discontinuity characteristics. The results of detailed stability assessment using software program SLIDE in consideration with both normal and seismic loading conditions are presented. Final rock support measures are proposed to ascertain long-term stability of the cut-slope.
