Authors :
Bikram Bhusal; Dr. Chhatra Bahadur Basnet; Ghan Bahadur Shrestha; Samrat Poudel
Volume/Issue :
Volume 8 - 2023, Issue 4 - April
Google Scholar :
https://bit.ly/3TmGbDi
Scribd :
https://bit.ly/3LPo4ny
DOI :
https://doi.org/10.5281/zenodo.7888723
Abstract :
The upstream section of the headrace tunnel
(HRT) of the Setikhola Hydropower Project passes
through calcareous and silicious phyllite with scant
foliation which is weak and deformable rock mass.
Bands of quartzite and metasandstone are intercalated
locally within phyllite. These weak rocks may undergo
plastic deformation. In such rock mass, there is a high
chance that the tunnel might experience squeezing.
Approximately 92 percent of the tunnel alignment has an
overburden greater than 100 meters, with a maximum
overburden above the tunnel of more than 500 meters.
The portion from chainage 1+100 to 1+600 m along the
tunnel alignment due to substantial overburden and
intercalation of silicious phyllite and meta-sandstone, is
critical in terms of tunnel squeezing. The tunnel at this
section is analyzed for squeezing phenomenon using
empirical techniques such as Singh et al. (1992), Goel et
al. (1995), semi-analytical techniques such as Hoek and
Marinos (2000), and Shrestha and Panthi (2015),
analytical techniques such as the Convergence
Confinement Method (Carranza Torres and Fairhurst,
2000) as well as numerical programs such as Phase2
and
RS3
. According to the empirical and semi-analytical
squeezing prediction criteria, there is high chance of
significant squeezing particularly in the selected
headrace segment at chainage 1+580 m. The numerical
analysis was carried out at the section where maximum
deformation was anticipated from the prediction
criteria. Numerical model also shows considerable
deformation at this section to cause heavy squeezing. The
support system estimated primarily using empirical
methods are applied in the numerical modeling. The
support system is inadequate because the model shows
considerable deformation even after the application of
the support and also failure occurs at the support. To
overcome this effect either a heavy support system needs
to be applied, reducing the pull length and adopting top
heading and benching tunneling method or strengthen
the rock mass by pre-injection grouting.
Keywords :
Weak And Deformable Rock Mass, Stability Analysis, Empirical Relations, Semi-Analytical Technique, Analytical Technique, Numerical Modeling, Support System.
The upstream section of the headrace tunnel
(HRT) of the Setikhola Hydropower Project passes
through calcareous and silicious phyllite with scant
foliation which is weak and deformable rock mass.
Bands of quartzite and metasandstone are intercalated
locally within phyllite. These weak rocks may undergo
plastic deformation. In such rock mass, there is a high
chance that the tunnel might experience squeezing.
Approximately 92 percent of the tunnel alignment has an
overburden greater than 100 meters, with a maximum
overburden above the tunnel of more than 500 meters.
The portion from chainage 1+100 to 1+600 m along the
tunnel alignment due to substantial overburden and
intercalation of silicious phyllite and meta-sandstone, is
critical in terms of tunnel squeezing. The tunnel at this
section is analyzed for squeezing phenomenon using
empirical techniques such as Singh et al. (1992), Goel et
al. (1995), semi-analytical techniques such as Hoek and
Marinos (2000), and Shrestha and Panthi (2015),
analytical techniques such as the Convergence
Confinement Method (Carranza Torres and Fairhurst,
2000) as well as numerical programs such as Phase2
and
RS3
. According to the empirical and semi-analytical
squeezing prediction criteria, there is high chance of
significant squeezing particularly in the selected
headrace segment at chainage 1+580 m. The numerical
analysis was carried out at the section where maximum
deformation was anticipated from the prediction
criteria. Numerical model also shows considerable
deformation at this section to cause heavy squeezing. The
support system estimated primarily using empirical
methods are applied in the numerical modeling. The
support system is inadequate because the model shows
considerable deformation even after the application of
the support and also failure occurs at the support. To
overcome this effect either a heavy support system needs
to be applied, reducing the pull length and adopting top
heading and benching tunneling method or strengthen
the rock mass by pre-injection grouting.
Keywords :
Weak And Deformable Rock Mass, Stability Analysis, Empirical Relations, Semi-Analytical Technique, Analytical Technique, Numerical Modeling, Support System.
