VERTICAL ELLIPTICAL ACCESS-SHAFTS Geometrical optimisation through FE-modelling
(2020) In TVGT-5000 VGTM01 20201Geotechnical Engineering
Department of Construction Sciences
- Abstract
- Urbanisation is causing densification of cities and more and more facilities are being placed in
the underground to utilise the urban space as efficiently as possible. Access to the underground
is obtained by constructing vertical access shafts. By constructing the shaft with a circular plan
geometry, an effective construction is obtained which can carry large earth pressure loads by
utilising the arching effect in the construction. In this way, the walls do not need to be supported
with struts and the shaft is given a free opening from above. In tunneling projects, tunnel boring
machines may need to be lowered into the shaft, which requires a large radius of the circular
shaft. By instead constructing the shaft with an elliptical... (More) - Urbanisation is causing densification of cities and more and more facilities are being placed in
the underground to utilise the urban space as efficiently as possible. Access to the underground
is obtained by constructing vertical access shafts. By constructing the shaft with a circular plan
geometry, an effective construction is obtained which can carry large earth pressure loads by
utilising the arching effect in the construction. In this way, the walls do not need to be supported
with struts and the shaft is given a free opening from above. In tunneling projects, tunnel boring
machines may need to be lowered into the shaft, which requires a large radius of the circular
shaft. By instead constructing the shaft with an elliptical plan geometry, the ground surface can
be utilised more efficiently, while long objects can still be transported up and down from the shaft.
The purpose of this thesis is to investigate the behavior of elliptical retaining structures and to
seek an optimised elliptical shape where the arching effect can be utilised as far as possible in
the structure. The study is linked to a tunneling project between Lund and Malmö, where a new
sewage tunnel will be built to transport wastewater from Lund to an expanded sewage treatment
plant at Sjölunda in Malmö. In addition to the shape of the shaft, the foundation depth of the
retaining structure is also assessed on the basis of predetermined water inflow requirements in
the shaft. The study is based on drilling data from a previous project where geotechnical surveys
were carried out at Sjölunda.
From the given survey data, a geo-model with known geotechnical parameters is defined. The
tunnel will connect to Sjölunda at a depth of 30 m, meaning that the shaft bottom will be at
a depth of 30 m. Also a requirement for a free opening of 11 m was predefined for the shaft.
Groundwater related problems, such as the foundation depth of the retaining structure, are
investigated in the finite element software SEEP/W. The soil-structure interaction is modelled by
using the finite element software PLAXIS. A simplified method, which does not take into account
the soil-structure interaction, is also used and modelled in the FE-software Robot.
With a requirement to allow a maximum groundwater inflow in the shaft of 0.5 l/s, the foundation
depth of the retaining structure is determined to 10 m below the shaft bottom, i.e. 40 m
below ground surface. The shape of the shaft is investigated by starting from a circular shaft
that was modeled in both PLAXIS 2D and PLAXIS 3D. The models are verified by analytical
calculations of the soil pressure and the corresponding horizontal normal forces from the arching
effect in the structure. After verifying the model in PLAXIS 3D, a parameter study is performed
in which three elliptical geometries, with increasing elongation, are investigated. For one of these
geometries, a model is also built in Robot, where the load is applied as a uniformly distributed
radial load corresponding to the soil pressure at different depths taken from PLAXIS. By comparing
the obtained forces in the structure from both PLAXIS and Robot, it is found that PLAXIS
is better at simulating the real behaviour, where the retaining structure’s interaction with the
ground generates lower load effects in the wall. Based on the results, PLAXIS is considered to
give a more realistic result and these models are further on used to define an optimised geometry.
The resulting forces in the structure, obtained for three different geometries in PLAXIS, are
compared with the capacity of a predefined cross-section of a diaphragm wall. The comparison
showed that the optimum elliptical geometry, given the predetermined requirements of the shaft
and the geological conditions in the area, was obtained as a relation between the short and long
diameters of an ellipse of 0.45. (Less) - Popular Abstract (Swedish)
- Då städerna förtätas blir det alltmer aktuellt att förlägga anläggningar under marken.
För att få åtkomst till underjorden, vid t.ex. ett tunnelbygge, så konstrueras vertikala
åtkomstschakt, se Figur 1. För att förhindra att schaktet rasar samman så används någon
form av stödkonstruktion för att hålla emot det horisontella jordtrycket. Den geometriska
utformningen av stödkonstruktionen kan på olika sätt optimeras för att klara väldigt
stora jordtryck. En cirkulär geometri ger en stabil konstruktion, men kan också kräva
mycket markyta vid anläggandet. Genom att istället använda en elliptisk geometri kan
flera av cirkelns fördelar gällande stabilitet utnyttjas, samtidigt som konstruktionen
kräver mindre markyta.
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9027292
- author
- Elfving, Björn LU and Sandström, Aron
- supervisor
-
- Ola Dahlblom LU
- Erika Tudisco LU
- Mats Svensson LU
- organization
- course
- VGTM01 20201
- year
- 2020
- type
- H3 - Professional qualifications (4 Years - )
- subject
- keywords
- Access-shafts, FE-modelling, Plaxis, Robot, Elliptical, Circular, Optimisation, Geotechnical, Engineering, Retaining, Structures, Tunnel, Soil, Interaction
- publication/series
- TVGT-5000
- report number
- TVGT-5068
- ISSN
- 0349-4977
- language
- English
- id
- 9027292
- alternative location
- http://www.geoteknik.lth.se/fileadmin/geoteknik/publications/tvgt5000/web_tvgt_5068.pdf
- date added to LUP
- 2020-08-28 12:45:13
- date last changed
- 2020-08-28 12:45:13
@misc{9027292,
abstract = {{Urbanisation is causing densification of cities and more and more facilities are being placed in
the underground to utilise the urban space as efficiently as possible. Access to the underground
is obtained by constructing vertical access shafts. By constructing the shaft with a circular plan
geometry, an effective construction is obtained which can carry large earth pressure loads by
utilising the arching effect in the construction. In this way, the walls do not need to be supported
with struts and the shaft is given a free opening from above. In tunneling projects, tunnel boring
machines may need to be lowered into the shaft, which requires a large radius of the circular
shaft. By instead constructing the shaft with an elliptical plan geometry, the ground surface can
be utilised more efficiently, while long objects can still be transported up and down from the shaft.
The purpose of this thesis is to investigate the behavior of elliptical retaining structures and to
seek an optimised elliptical shape where the arching effect can be utilised as far as possible in
the structure. The study is linked to a tunneling project between Lund and Malmö, where a new
sewage tunnel will be built to transport wastewater from Lund to an expanded sewage treatment
plant at Sjölunda in Malmö. In addition to the shape of the shaft, the foundation depth of the
retaining structure is also assessed on the basis of predetermined water inflow requirements in
the shaft. The study is based on drilling data from a previous project where geotechnical surveys
were carried out at Sjölunda.
From the given survey data, a geo-model with known geotechnical parameters is defined. The
tunnel will connect to Sjölunda at a depth of 30 m, meaning that the shaft bottom will be at
a depth of 30 m. Also a requirement for a free opening of 11 m was predefined for the shaft.
Groundwater related problems, such as the foundation depth of the retaining structure, are
investigated in the finite element software SEEP/W. The soil-structure interaction is modelled by
using the finite element software PLAXIS. A simplified method, which does not take into account
the soil-structure interaction, is also used and modelled in the FE-software Robot.
With a requirement to allow a maximum groundwater inflow in the shaft of 0.5 l/s, the foundation
depth of the retaining structure is determined to 10 m below the shaft bottom, i.e. 40 m
below ground surface. The shape of the shaft is investigated by starting from a circular shaft
that was modeled in both PLAXIS 2D and PLAXIS 3D. The models are verified by analytical
calculations of the soil pressure and the corresponding horizontal normal forces from the arching
effect in the structure. After verifying the model in PLAXIS 3D, a parameter study is performed
in which three elliptical geometries, with increasing elongation, are investigated. For one of these
geometries, a model is also built in Robot, where the load is applied as a uniformly distributed
radial load corresponding to the soil pressure at different depths taken from PLAXIS. By comparing
the obtained forces in the structure from both PLAXIS and Robot, it is found that PLAXIS
is better at simulating the real behaviour, where the retaining structure’s interaction with the
ground generates lower load effects in the wall. Based on the results, PLAXIS is considered to
give a more realistic result and these models are further on used to define an optimised geometry.
The resulting forces in the structure, obtained for three different geometries in PLAXIS, are
compared with the capacity of a predefined cross-section of a diaphragm wall. The comparison
showed that the optimum elliptical geometry, given the predetermined requirements of the shaft
and the geological conditions in the area, was obtained as a relation between the short and long
diameters of an ellipse of 0.45.}},
author = {{Elfving, Björn and Sandström, Aron}},
issn = {{0349-4977}},
language = {{eng}},
note = {{Student Paper}},
series = {{TVGT-5000}},
title = {{VERTICAL ELLIPTICAL ACCESS-SHAFTS Geometrical optimisation through FE-modelling}},
year = {{2020}},
}