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Effect of the cross-sectional shape of tunnels on the distribution of contact pressures
Conclusions 1. When determining the earth pressure on timbering of tunnels constructed by the cut-and-cover method it is necessary to distinguish two cases of the joint action of the structure and enclosing soil: in a trench and in made ground. Structures for which the condition $ H_{f} $/$ B_{t} $≥0.5 can be referred to the first case and $ H_{f} $/$ B_{t} $<0.5 to the second (where $ H_{f} $ is the height of the fill over the ceiling and $ B_{t} $ is the width of the trench at the level of the tunnel ceiling). For structures in a trench the vertical pressure on the ceiling from the weight of the fill soil and uniformly distributed load on the ground surface should be determined for the stage of the limiting state with consideration of the friction of the fill on the trench walls. In this case it is permissible to take the surfaces of sliding in the form of vertical planes passing through the slope of the trench at the level of the tunnel ceiling. The pressure from the weight of the fill on a tunnel in made ground when $ H_{f} $≤0.5 B (where B is the tunnel width) can be considered equal to the weight of the column of soil, but when $ H_{f} $>0.5 B it is necessary to take into account the concentration of pressure caused by the different deformability of the structure and enclosing soil. In calculations of vertical pressure from clay fill it is necessary to take into account cohesion which is restored as the soil is compacted. 2. The distribution of stresses along the foot of the tunnel in the case of weak soils can be taken in calculations in the form of a rectangular diagram. For bases having high values of shear resistance it is necessary to take into account the concentration of pressure on the edge portions of the bottom and take the distribution of pressure on the foot to be saddle-shape in accordance with the recommendations given in [3]. 3. The horizontal pressure on the walls of tunnels in a trench can be assumed uniformly distributed over the height with an intensity equal to 0.25–0.3 of the acting vertical pressure on the ceiling in the case of layerwise compaction of the fill in the pockets and 0.2 of the acting vertical pressure in the case of loose fill; for structures in made ground it is taken as the active pressure according to Coulomb's theory. 4. The indices of the physical and me chanical properties used in calculations of the pressure of soil fills should be designated on the basis of engineering-geologic investigations of the disturbed soil carried out with consideration of the conditions and methods of placing the fill.
Effect of the cross-sectional shape of tunnels on the distribution of contact pressures
Conclusions 1. When determining the earth pressure on timbering of tunnels constructed by the cut-and-cover method it is necessary to distinguish two cases of the joint action of the structure and enclosing soil: in a trench and in made ground. Structures for which the condition $ H_{f} $/$ B_{t} $≥0.5 can be referred to the first case and $ H_{f} $/$ B_{t} $<0.5 to the second (where $ H_{f} $ is the height of the fill over the ceiling and $ B_{t} $ is the width of the trench at the level of the tunnel ceiling). For structures in a trench the vertical pressure on the ceiling from the weight of the fill soil and uniformly distributed load on the ground surface should be determined for the stage of the limiting state with consideration of the friction of the fill on the trench walls. In this case it is permissible to take the surfaces of sliding in the form of vertical planes passing through the slope of the trench at the level of the tunnel ceiling. The pressure from the weight of the fill on a tunnel in made ground when $ H_{f} $≤0.5 B (where B is the tunnel width) can be considered equal to the weight of the column of soil, but when $ H_{f} $>0.5 B it is necessary to take into account the concentration of pressure caused by the different deformability of the structure and enclosing soil. In calculations of vertical pressure from clay fill it is necessary to take into account cohesion which is restored as the soil is compacted. 2. The distribution of stresses along the foot of the tunnel in the case of weak soils can be taken in calculations in the form of a rectangular diagram. For bases having high values of shear resistance it is necessary to take into account the concentration of pressure on the edge portions of the bottom and take the distribution of pressure on the foot to be saddle-shape in accordance with the recommendations given in [3]. 3. The horizontal pressure on the walls of tunnels in a trench can be assumed uniformly distributed over the height with an intensity equal to 0.25–0.3 of the acting vertical pressure on the ceiling in the case of layerwise compaction of the fill in the pockets and 0.2 of the acting vertical pressure in the case of loose fill; for structures in made ground it is taken as the active pressure according to Coulomb's theory. 4. The indices of the physical and me chanical properties used in calculations of the pressure of soil fills should be designated on the basis of engineering-geologic investigations of the disturbed soil carried out with consideration of the conditions and methods of placing the fill.
Effect of the cross-sectional shape of tunnels on the distribution of contact pressures
Mal'ginov, S. I. (author)
1972
Article (Journal)
English
Local classification TIB:
770/6545/8000
BKL:
56.20
Ingenieurgeologie, Bodenmechanik
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