7/28/2019 STABILTY ASSESSMENT OF HEADRACE TUNNEL SYSTEM FOR
PUNATSANGCHHU II HYDROPOWER PROJECT, BHUTAN
2/4
6/12/13 12 STABILTY ASSESSMENT OF HEADRACE TUNNEL SYSTEM FOR
PUNATSANGCHHU II HYDROPOWER PROJECT, BHUTAN Karma Tsheri
www.orgsun.com/2/4/21175-12-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.php
rock mass, the support material will be subjected to high
stresses and sometimes when the
support fails to sustain the large deformation caused by high
tangential stresses, the tunnelssqueezes inward reducing the size
of opening. In extreme cases, new equilibrium are reachedafter the
complete closure of tunnel, eg Kovari in 1998 and Steiner 1996
(Panthi, 2006). Manyauthors have developed different approaches to
predict tunnel squeezing. Hoek and Marinosapproach is discussed
below.
Hoek and Marinos (2000) Over burden alone is not responsible for
squeezing. The changingstrength and deformability properties of the
rock mass over time have far greater consequenceson squeezing
(Kovari, 1998).
In Hoek and Marinos approach, rock mass strength and over burden
are the two parameters
considered responsible for squeezing. With this view, Hoek and
Brown (2000) have suggested arelation that gives total strain
(ratio of tunnel closer to tunnel diameter), which is a function
ofrock mass strength and in-situ overburden pressure. The criterion
is based on iso-static circularstress condition.
The support pressure can be calculated using different
equations. The RMR method andUnal method are used here.
The rock support pressure from the RMR relation.
Norwegian University of Science and Technology, Trondheim Page
Stability Analysis 100RMR P * *
Dt.................................................................5(24)
The support pressure can alsobe calculated using equation proposed
by Unal (1983) as shown below.
B Pi (100 RMR) *
*.............................................................5(25)
Where is rock density int/m3, and B is tunnel width in m.
accordingly the deformation in the tunnels were calculated
firstwithout support pressure and later with support pressure. The
rock support pressure is tabulatedin table 5.13.
Figure 5.11 Tunnel convergence and degree of difficulties
associated with tunnel squeezing(Hoek & Marinos, 2000) Hoek and
Marinos defined the plastic zone (R) and total tunnel strain (t)by
following equations.
....5(26) 5(27) Where t is total inward deformation and t
istotal inward strain. Pi is the support pressure in MPa. When the
support pressure is taken aszero, the squeezing condition in the
rock mass may be rewritten as.5(28) ..5(29)Norwegian University of
Science and Technology, Trondheim Page Stability Analysis Hoek
ansMarinos have assumed that weak rock mass are incapable of
sustaining significant differentialstress and failure will occur
till in-situ horizontal and vertical stresses are equalized.
This justifies why they considered over burden instead of
tangential stresses, which isalways greater than over burden
pressure for estimating tunnel squeezing. For defining
theapproximate degree of difficulty at different level of
tunneling, the figure 5.11 right is used.
The squeezing results from the Hoek and Marinos relations for
the different reaches alongthe HRT alignment is given in table
5.13. The squeezing chart states that, degree of squeezingwill be
with few support problems when strain is less than 1%. Minor
squeezing problem whenstrain is between 1 %and 2.5%. When the
strain exceeds 2.5% but less than 5% there can besevere squeezing
problem in the rock mass. The tunnel will face extreme squeezing
when thestrain exceeds 10%.
Table 5-13Support pressure and deformation along the HRT
alignment Description Ch.0 toAdit I Adit I to Adit II Adit II to
S/shaft Support pressure MPa 6.23 6.68 7.Deformation withoutsupport
0.1 0.33 0.pressure % Deformation with support 0.003 0.06
0.pressure % From theresults, very less squeezing problems is
expected along the HRT. All the possible squeezing canbe solved by
adopting simple flexible support measures. However, since all these
inputparameters are calculations based on rock mass parameters on
the surface, it should not be areason to relax. There should be
adequate readiness for any worsening squeezing problem
Permanent Magnets
www.univastmagnetics.com
High quality and low lead time TS16949 certified
http://www.google.com/url?ct=abg&q=https://www.google.com/adsense/support/bin/request.py%3Fcontact%3Dabg_afc%26url%3Dhttp://www.orgsun.com/2/4/21175-12-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.php%26gl%3DNP%26hl%3Duk%26client%3Dca-pub-9894471784993021%26ai0%3DCRt4zlFu4UaDjCeuEmwXm-oGwC6Ly29MC2sXPiDbAjbcBEAEgzOXwGlC2ma3d-_____8BYI0EyAEBqQIZ3HmvqsOqPqgDAcgD0wSqBLYBT9DpBhXrZCs9MC76qSY3iWv4vkrYqCF71_ckw5RpkCNQnkxMOD_cN_HkojseA5IBZ6JEOSne_01XxwE7hdNd5Emt7G3u8OKmYJ4U-sCOA9xjyqv-B4STiKKzpBAbagl9PTzTfeXM2V3M37vkzOnlSl9UCFlKJk4j8EPbHlXspB1oF78qJsUHziwZkS0Yf7D9i9Ee5KaDfglUJ5wX2j4s0QRG4sE2aEiSPUQsVODouN8T4XonUziAB7Ky4DQ&usg=AFQjCNEYLsCrTSYsrKgkbgPtZaCTdzARvghttp://googleads.g.doubleclick.net/aclk?sa=L&ai=CRt4zlFu4UaDjCeuEmwXm-oGwC6Ly29MC2sXPiDbAjbcBEAEgzOXwGlC2ma3d-_____8BYI0EyAEBqQIZ3HmvqsOqPqgDAcgD0wSqBLYBT9DpBhXrZCs9MC76qSY3iWv4vkrYqCF71_ckw5RpkCNQnkxMOD_cN_HkojseA5IBZ6JEOSne_01XxwE7hdNd5Emt7G3u8OKmYJ4U-sCOA9xjyqv-B4STiKKzpBAbagl9PTzTfeXM2V3M37vkzOnlSl9UCFlKJk4j8EPbHlXspB1oF78qJsUHziwZkS0Yf7D9i9Ee5KaDfglUJ5wX2j4s0QRG4sE2aEiSPUQsVODouN8T4XonUziAB7Ky4DQ&num=1&sig=AOD64_3fuQp5U1ZsZ-qhrBxg3_UzlpEltQ&client=ca-pub-9894471784993021&adurl=http://www.univastmagnetics.com
7/28/2019 STABILTY ASSESSMENT OF HEADRACE TUNNEL SYSTEM FOR
PUNATSANGCHHU II HYDROPOWER PROJECT, BHUTAN
4/4
6/12/13 12 STABILTY ASSESSMENT OF HEADRACE TUNNEL SYSTEM FOR
PUNATSANGCHHU II HYDROPOWER PROJECT, BHUTAN Karma Tsheri
www.orgsun.com/2/4/21175-12-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.php
Different types of support are adopted based on the nature of
stability problems. Therecannot be a single standard support for
any stability problem. It has to be customized dependingon rock
mass parameters, technology, time and money available. The best
support system canbe one which provides reasonably best stability
within minimum time and cost. Some of thecommonly adopted support
systems in tunnel stability problem are discussed below.
6.1.1 Scaling Scaling involves removal of disintegrated loose
hanging rock fragmentstriggered by vibration impact of blasting
around the tunnel periphery. It is carried outimmediately after
every cycle of blast at the face of the tunnel. Normally 20-30
minutes isrequired to remove the loose fragments rocks. Different
methods of scaling are Manual scalingManual scaling is one of the
oldest methods of scaling. The scaling is done from the piles
of
blasted material or from wheel loaders as a platform. It is
risky and has poor safety standards. Itis not much in use these
days except in small drifts and shafts where machines cannot be
used.
Figure 6.1 and 6.2 illustrates manual scaling.
Figure 6.1 Mannual scaling from muck pile (L) & from scissor
plateform (R) NorwegianUniversity of Science and Technology,
Trondheim Page Rock Support Estimation Mechanicalscaling The
scaling is done using the tunneling rig machines. This has improves
safetystandards and consumes less time. In Bhutan, mechanical
scaling is most widely practiced.Figure 5.2 illustrates how
mechanical scaling is done.
Pages: | 1 | ... | 10 | 11 | 12 | 13 | 14 | ... | 18 |
All scientific work >> Scientific work in english
back to top
| Home | Contacts |
2011 www.orgsun .com - "Free electronic library"
ASCE Online Library
www.ascelibrary.org
Free search 1,000,000 pages All areas of civil engineering
http://www.google.com/url?ct=abg&q=https://www.google.com/adsense/support/bin/request.py%3Fcontact%3Dabg_afc%26url%3Dhttp://www.orgsun.com/2/4/21175-12-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.php%26gl%3DNP%26hl%3Duk%26client%3Dca-pub-9894471784993021%26ai0%3DCdiHGlFu4UeuXDISvmgWBoYCYC-zKo64C1P6hrlPAjbcBEAEgzOXwGlDcoo7Z_P____8BYI0EyAEBqAMByAPTBKoEswFP0CmnMcFyvnJZ4WJwu0bkIWn44UV_PWzXMKIJfic_uTrII0BHq9upsopOLEX3cDpJ-1po8Gq0F3YS3SX9Az97qMMm-FaxFyrs64tjU2mVNCuWlIJqspvkV4-C7SYYYeHKeu-nBsJKgQe_TNaFmYwESQiiQ6H0q1qeewOKPz4jikbNNd6_mxwMpGYkFI7MiwE5KXCmvyiE3hcjsIF5RRV9on8KvehXBN3mue9zQb8_eximeoAH3vHgAQ&usg=AFQjCNHr1hyvNQZ_LsIMXVK2pd-KFT0L3ghttp://googleads.g.doubleclick.net/aclk?sa=L&ai=CdiHGlFu4UeuXDISvmgWBoYCYC-zKo64C1P6hrlPAjbcBEAEgzOXwGlDcoo7Z_P____8BYI0EyAEBqAMByAPTBKoEswFP0CmnMcFyvnJZ4WJwu0bkIWn44UV_PWzXMKIJfic_uTrII0BHq9upsopOLEX3cDpJ-1po8Gq0F3YS3SX9Az97qMMm-FaxFyrs64tjU2mVNCuWlIJqspvkV4-C7SYYYeHKeu-nBsJKgQe_TNaFmYwESQiiQ6H0q1qeewOKPz4jikbNNd6_mxwMpGYkFI7MiwE5KXCmvyiE3hcjsIF5RRV9on8KvehXBN3mue9zQb8_eximeoAH3vHgAQ&num=1&sig=AOD64_2ah1stCNenCny4rGXlxOmpCjb7mA&client=ca-pub-9894471784993021&adurl=http://www.ascelibrary.orghttp://www.orgsun.com/admin/contacts.phphttp://www.orgsun.com/http://www.orgsun.com/2/4/21175-12-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.php#tophttp://www.orgsun.com/2/http://www.orgsun.com/1/temi.phphttp://www.orgsun.com/2/4/21175-18-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.phphttp://www.orgsun.com/2/4/21175-14-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.phphttp://www.orgsun.com/2/4/21175-13-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.phphttp://www.orgsun.com/2/4/21175-12-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.phphttp://www.orgsun.com/2/4/21175-11-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.phphttp://www.orgsun.com/2/4/21175-10-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.phphttp://www.orgsun.com/2/4/21175-1-stabilty-assessment-headrace-tunnel-system-for-punatsangchhu.php
![Vehicle dynamics, stabilty and brake performance of ... dynamics, stabilty and brake performance of motorcycles ... ABS 1 (1988) FTE no 2 brake pressure modulators, ... [ABS] y-x max](https://img.dokumen.tips/doc/110x75/5aa0ce0c7f8b9a0d158eb93c/vehicle-dynamics-stabilty-and-brake-performance-of-dynamics-stabilty-and-brake.jpg)
![44161289 MSC Circ 456 Stabilty Criteria[1]](https://img.dokumen.tips/doc/110x75/577cc6061a28aba7119d87b1/44161289-msc-circ-456-stabilty-criteria1.jpg)
