Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good underst...Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good understanding for prediction of tunnel deformation and surface settlement during the engineering life of the structure. The deformational behaviour, design of sequential excavation and support of any jointed rock mass are challenging during underground construction. We have raised several commonly assumed issues while performing stability analysis of underground opening at shallow depth. For this purpose, Kainchi-mod Nerchowck twin tunnels(Himachal Pradesh, India) are taken for in-depth analysis of the stability of two asymmetric tunnels to address the influence of topography, twin tunnel dimension and geometry. The host rock encountered during excavation is composed mainly of moderately to highly jointed grey sandstone, maroon sandstone and siltstones. In contrast to equidimensional tunnels where the maximum subsidence is observed vertically above the centreline of the tunnel, the result from the present study shows shifting of the maximum subsidence away from the tunnel centreline. The maximum subsidence of 0.99 mm is observed at 4.54 m left to the escape tunnel centreline whereas the maximum subsidence of 3.14 mm is observed at 8.89 m right to the main tunnel centreline. This shifting clearly indicates the influence of undulating topography and inequidimensional noncircular tunnel.展开更多
The stochastic finite element equations for random temperature are obtained using the first-order per-turbation technique taking into account the random thermal properties and boundary condition, based on heat transfe...The stochastic finite element equations for random temperature are obtained using the first-order per-turbation technique taking into account the random thermal properties and boundary condition, based on heat transfer variational principle. The local average method for 2-D is used to discretize random fields. Then, the random temperature fields of embankment in cold regions are investigated on condi-tion that the thermal properties and boundary condition are taken as random fields, respectively, by using the program, which is written by the methods. The expected value of temperature field and the standard deviation of the temperature field of embankment in cold regions are obtained and analyzed.展开更多
It is becoming possible to do detailed numerical analyses for the various mechanical behavior of braced excavation by researching and developing the numerical analysis technique such as the finite element method (FEM)...It is becoming possible to do detailed numerical analyses for the various mechanical behavior of braced excavation by researching and developing the numerical analysis technique such as the finite element method (FEM). However, the mechanical behavior of braced excavation has not been clarified fully both in theory and in experience. Therefore, improving the prediction accuracy during the prior design is very important for making the observational method of braced excavation more effective. In this paper, FEM analyses were performed for a model of braced excavation by using Geotechnical Finite Element Elasto-plastic Analysis Software, GeoFEAS (2D). As the constitutive law of ground, MC-DP model, and Duncan-Chang model were applied. The results were compared and discussed with that of a site measurement, and the effects of the constitutive law of ground on the analyzed result were verified. For the difference between the results, the reason was investigated by the analyses adjusting the elastic modulus of ground, and the appropriate application of the constitutive law was researched.展开更多
The neutron shielding component of ITER （International Thermonuclear Experimental Reactor） vacuum vessel is a kind of structure resembling a wall in appearance. A FE （finite element） model is set up by using ANSYS...The neutron shielding component of ITER （International Thermonuclear Experimental Reactor） vacuum vessel is a kind of structure resembling a wall in appearance. A FE （finite element） model is set up by using ANSYS code in terms of its structural features. Static analysis, thermal expansion analysis and dynamic analysis are performed. The static results show that the stress and displacement distribution are allowable, but the high stress appears in the junction between the upper and lower parts. The modal analysis indicates that the biggest deformation exists in the port area. Through modal superposition, the single-point response has been found with the lower rank frequency of the acceleration seismic response spectrum. But the deformation and the stress values are within the permissible limit. The analysis results would benefit the work in the next step and provide some reference for the implementation of the engineering plan in the future.展开更多
基金financial support from Indian Institute of Technology Bombay, India
文摘Tunnelling related hazards are very common in the Himalayan terrain and a number of such instances have been reported. Several twin tunnels are being planned for transportation purposes which will require good understanding for prediction of tunnel deformation and surface settlement during the engineering life of the structure. The deformational behaviour, design of sequential excavation and support of any jointed rock mass are challenging during underground construction. We have raised several commonly assumed issues while performing stability analysis of underground opening at shallow depth. For this purpose, Kainchi-mod Nerchowck twin tunnels(Himachal Pradesh, India) are taken for in-depth analysis of the stability of two asymmetric tunnels to address the influence of topography, twin tunnel dimension and geometry. The host rock encountered during excavation is composed mainly of moderately to highly jointed grey sandstone, maroon sandstone and siltstones. In contrast to equidimensional tunnels where the maximum subsidence is observed vertically above the centreline of the tunnel, the result from the present study shows shifting of the maximum subsidence away from the tunnel centreline. The maximum subsidence of 0.99 mm is observed at 4.54 m left to the escape tunnel centreline whereas the maximum subsidence of 3.14 mm is observed at 8.89 m right to the main tunnel centreline. This shifting clearly indicates the influence of undulating topography and inequidimensional noncircular tunnel.
基金the "National Science Fund of Distinguished Young Scholars of China" (Grant No. 40225001)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX3-SW-351)+3 种基金the CAS Special Fund for the National Excellent PhD Dissertation Author (to Dr. Lai, Y.M.)the Foundation of "Hundred People Plan" of Chinese Academy of Sciences (to Dr. Lai Y M)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX1-SW-04)the National Natural Science Foundation of China (Grant No. 40640420072)
文摘The stochastic finite element equations for random temperature are obtained using the first-order per-turbation technique taking into account the random thermal properties and boundary condition, based on heat transfer variational principle. The local average method for 2-D is used to discretize random fields. Then, the random temperature fields of embankment in cold regions are investigated on condi-tion that the thermal properties and boundary condition are taken as random fields, respectively, by using the program, which is written by the methods. The expected value of temperature field and the standard deviation of the temperature field of embankment in cold regions are obtained and analyzed.
文摘It is becoming possible to do detailed numerical analyses for the various mechanical behavior of braced excavation by researching and developing the numerical analysis technique such as the finite element method (FEM). However, the mechanical behavior of braced excavation has not been clarified fully both in theory and in experience. Therefore, improving the prediction accuracy during the prior design is very important for making the observational method of braced excavation more effective. In this paper, FEM analyses were performed for a model of braced excavation by using Geotechnical Finite Element Elasto-plastic Analysis Software, GeoFEAS (2D). As the constitutive law of ground, MC-DP model, and Duncan-Chang model were applied. The results were compared and discussed with that of a site measurement, and the effects of the constitutive law of ground on the analyzed result were verified. For the difference between the results, the reason was investigated by the analyses adjusting the elastic modulus of ground, and the appropriate application of the constitutive law was researched.
基金the National 973 program of China(No.2004CB720704)
文摘The neutron shielding component of ITER （International Thermonuclear Experimental Reactor） vacuum vessel is a kind of structure resembling a wall in appearance. A FE （finite element） model is set up by using ANSYS code in terms of its structural features. Static analysis, thermal expansion analysis and dynamic analysis are performed. The static results show that the stress and displacement distribution are allowable, but the high stress appears in the junction between the upper and lower parts. The modal analysis indicates that the biggest deformation exists in the port area. Through modal superposition, the single-point response has been found with the lower rank frequency of the acceleration seismic response spectrum. But the deformation and the stress values are within the permissible limit. The analysis results would benefit the work in the next step and provide some reference for the implementation of the engineering plan in the future.
