Norwegian hydropower industry has more than 100 years of experiences in constructing more than4000 km-long unlined pressure shafts and tunnels with maximum static head of 1047 m（equivalent to almost 10.5 MPa） reache...Norwegian hydropower industry has more than 100 years of experiences in constructing more than4000 km-long unlined pressure shafts and tunnels with maximum static head of 1047 m（equivalent to almost 10.5 MPa） reached at unlined pressure tunnel of Nye Tyin project. Experiences gained from construction and operation of these unlined pressure shafts and tunnels were the foundation to develop design criteria and principles applied in Norway and some other countries. In addition to the confinement criteria, Norwegian state-of-the-art design principle for unlined pressure shaft and tunnel is that the minor principal stress at the location of unlined pressure shaft or tunnel should be more than the water pressure in the shaft or tunnel. This condition of the minor principal stress is prerequisite for the hydraulic jacking/splitting not to occur through joints and fractures in rock mass. Another common problem in unlined pressure shafts and tunnels is water leakage through hydraulically splitted joints or pre-existing open joints. This article reviews some of the first attempts of the use of unlined pressure shaft and tunnel concepts in Norway, highlights major failure cases and two successful cases of significance, applies Norwegian criteria to the cases and reviews and evaluates triggering factors for failure.This article further evaluates detailed engineering geology of failure cases and also assesses common geological features that could have aggravated the failure. The minor principal stress is investigated and quantified along unlined shaft and tunnel alignment of six selected project cases by using threedimensional numerical model. Furthermore, conditions of failure through pre-existing open joints by hydraulic jacking and leakage are assessed by using two-dimensional fluid flow analysis. Finally, both favorable and unfavorable ground conditions required for the applicability of Norwegian confinement criteria in locating the unlined pressure shafts and tunnels for geotectonic environment different from that of Norway are highlighted.展开更多
Unexpected,serious deformation failures have occurred during construction of a main shaft. A study of con-struction parameters of the main shaft is required. First,the stability of the shaft and wall-rock is investiga...Unexpected,serious deformation failures have occurred during construction of a main shaft. A study of con-struction parameters of the main shaft is required. First,the stability of the shaft and wall-rock is investigated by nu-merical methods. The modeling results are as follows: The convergence of shaft liner is greater than 60 mm at a depth of 650 m; the maximum principal stress in the liner approaches 190 MPa,which exceeds the strength of the liner,so it is inevitable that the liner deform locally. Second,stability analysis of shafts with different liner thicknesses has been completed. The results have the following features: If the depth where the liner thickness is increases from 400 mm to 500 mm is 650 meters,the convergence deformation of the liner is reduced by 3.4 mm while the maximum principal stress is reduced by 5 MPa. At a depth of 250 m if the liner thickness is increased from 400 mm to 500 mm the conver-gence of the liner is reduced by 1.5 mm while the maximum principal stress is reduced by 10 MPa. Therefore,increasing the liner thickness has little effect on liner convergence but can reduce the maximum principal stress in the liner. The thickness of the liner can be increased to reduce the maximum principal stress and increase the capacity for shear defor-mation. Finally,construction techniques employing releasing-displacements have been numerically simulated. The con-clusions are that as the releasing displacement is increased the convergence of the surrounding rock increases linearly while the convergence of the lining decreases linearly. The plastic zone in the surrounding rock mass at first increases linearly but then,at a release-displacement of 95 mm,expands rapidly. These conclusions show that use of suitable re-leasing displacement can increase the self-supporting capacity of the surrounding rock. But when the releasing dis-placement exceeds 95 mm the plastic zone rapidly enlarges and stability rapidly decreases. The maximum principal stress of the lining also decreases as the release-displacement increases. There is a definite inflection point in the rela-tionships involving releasing displacement. When the releasing displacement passes this point the effect on principal stress decreases. In conclusion,a reasonable releasing displacement value when lining the shaft is 95 mm.展开更多
文摘Norwegian hydropower industry has more than 100 years of experiences in constructing more than4000 km-long unlined pressure shafts and tunnels with maximum static head of 1047 m（equivalent to almost 10.5 MPa） reached at unlined pressure tunnel of Nye Tyin project. Experiences gained from construction and operation of these unlined pressure shafts and tunnels were the foundation to develop design criteria and principles applied in Norway and some other countries. In addition to the confinement criteria, Norwegian state-of-the-art design principle for unlined pressure shaft and tunnel is that the minor principal stress at the location of unlined pressure shaft or tunnel should be more than the water pressure in the shaft or tunnel. This condition of the minor principal stress is prerequisite for the hydraulic jacking/splitting not to occur through joints and fractures in rock mass. Another common problem in unlined pressure shafts and tunnels is water leakage through hydraulically splitted joints or pre-existing open joints. This article reviews some of the first attempts of the use of unlined pressure shaft and tunnel concepts in Norway, highlights major failure cases and two successful cases of significance, applies Norwegian criteria to the cases and reviews and evaluates triggering factors for failure.This article further evaluates detailed engineering geology of failure cases and also assesses common geological features that could have aggravated the failure. The minor principal stress is investigated and quantified along unlined shaft and tunnel alignment of six selected project cases by using threedimensional numerical model. Furthermore, conditions of failure through pre-existing open joints by hydraulic jacking and leakage are assessed by using two-dimensional fluid flow analysis. Finally, both favorable and unfavorable ground conditions required for the applicability of Norwegian confinement criteria in locating the unlined pressure shafts and tunnels for geotectonic environment different from that of Norway are highlighted.
基金Project 2004-01D supported by Jinchuan Group Ltd of Gansu Province, China
文摘Unexpected,serious deformation failures have occurred during construction of a main shaft. A study of con-struction parameters of the main shaft is required. First,the stability of the shaft and wall-rock is investigated by nu-merical methods. The modeling results are as follows: The convergence of shaft liner is greater than 60 mm at a depth of 650 m; the maximum principal stress in the liner approaches 190 MPa,which exceeds the strength of the liner,so it is inevitable that the liner deform locally. Second,stability analysis of shafts with different liner thicknesses has been completed. The results have the following features: If the depth where the liner thickness is increases from 400 mm to 500 mm is 650 meters,the convergence deformation of the liner is reduced by 3.4 mm while the maximum principal stress is reduced by 5 MPa. At a depth of 250 m if the liner thickness is increased from 400 mm to 500 mm the conver-gence of the liner is reduced by 1.5 mm while the maximum principal stress is reduced by 10 MPa. Therefore,increasing the liner thickness has little effect on liner convergence but can reduce the maximum principal stress in the liner. The thickness of the liner can be increased to reduce the maximum principal stress and increase the capacity for shear defor-mation. Finally,construction techniques employing releasing-displacements have been numerically simulated. The con-clusions are that as the releasing displacement is increased the convergence of the surrounding rock increases linearly while the convergence of the lining decreases linearly. The plastic zone in the surrounding rock mass at first increases linearly but then,at a release-displacement of 95 mm,expands rapidly. These conclusions show that use of suitable re-leasing displacement can increase the self-supporting capacity of the surrounding rock. But when the releasing dis-placement exceeds 95 mm the plastic zone rapidly enlarges and stability rapidly decreases. The maximum principal stress of the lining also decreases as the release-displacement increases. There is a definite inflection point in the rela-tionships involving releasing displacement. When the releasing displacement passes this point the effect on principal stress decreases. In conclusion,a reasonable releasing displacement value when lining the shaft is 95 mm.
