ANALYSIS AND DESIGN OF UNDERGROUND METRO STATION
K.Anitha1, M.Santhiya
2
Assistant Professor1,2
,Department of Civil Engineering 1,2
BIST, BIHER, Bharath University
Sri Sairam Engineering College2
,Chennai.
[email protected] [email protected]
ABSTRACT
India is a developing country, new infrastructure is been developing in the major cities of
India such as Delhi, Bangalore, Chennai, Hyderabad, Kolkata, Mumbai etc. The new rapid transit
system called metro is been introduced in this major cities which include both overhead metros
and underground metros. This project deals with the analysis and design of typical underground
metro station structures.Analysis and design of underground metro station consists of two types of
analysis. One is construction stage analysis and other one is permanent stage analysis.
Construction stage analysis is carried out by WALLAP software and permanent stage analysis is
carried out by STAAD Pro software. In this project the retaining structure used is Diaphragm
wall. Calculate the maximum moment and shear force in active and excavated face of the
diaphragm wall in both construction and permanent analysis results. Taken the maximum moment
from the two results design diaphragm wall. The load combinations are provided as per
IS:456(2000) ultimate limit state and Serviceability stage.Designing the roof slab, concourse slab
and base slab use STAAD Pro software.
1.INTRODUCTION
Infrastructure plays a vital role in metropolis. Explosive growth of cities in developing
countries and, thus the demand for improved livability and environmental protection has created a
strong demand for new underground development. The population of India in urban areas keeps
increasing year by year due to urbanization. In 1950 as many as 357 million people live in urban
areas and the number increased to 1009 million in 2000 (UN 2002 Report).It is expected that the
number will reach 1409 million in 2030.As many mega cities show, there is a limit of how far
cities can sprawl. One way of dealing with the problems of urban space scarcity is by building
upwards. Indeed, high-rise buildings have for years been the manifesting example of how to
create more space on a limited amount of land[1-7]. However, office space or living space is not
the only demanded space in cities. Other than that, we can go deeper into discussing underground
space. Underground space refers to a space that is situated below the ground level. Underground
land can also be defined as land which lies below the surface of the earth. It means anything
below the surface land can be considered as underground land. Underground development will
create more space above ground for many purposes especially for recreation and social activities
also development of new green fields and residential area. Looking back, the underground space
has been exploited for thousands of years, for strategic and military purposes, for religious
building, for water and sanitation conveyance and military purposes. It is only later than that the
underground has been deeply used for transportation, commercial building and other
infrastructure[8-14], such as tunneling and integrated railway transport. India is also not excluded
from urbanization issues. Based on the number of urban density and urbanization the urban
development in India is growing rapidly. It means the consideration for using urban underground
International Journal of Pure and Applied MathematicsVolume 119 No. 12 2018, 9749-9759ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu
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space for development must be given a full attention. Underground utilization pattern varies in
different urban contexts, depending on the local culture, geographical situation, social
environment and economic needs. The underground metro system was introduced in major cities
to relief the pressure from the surface, provide more efficient and encourage more extensive use
of public transport. Underground metro system is having very high investment cost but the overall
life cycle cost of underground metro system is very less.India is a developing country, new
infrastructure is been developing in the major cities of India such as Delhi, Bangalore, Chennai,
Hyderabad, Kolkata, Mumbai etc[15-21].
1.2 COMPONENTS OF UNDER GROUND METRO STATION
The various components of underground metro station box is as follows.
Diaphragm wall
Roof slab
Concourse slab
Base slab
1.2.1 Diaphragm wall
Diaphragm wall is generally a reinforced concrete wall constructed in the ground using
under slurry technique. These structures can be used for larger depths and as for both temporary
and permanent structures[22-26]. The primary advantage of this wall from other pile is it has less
number of joints than other piles and can go for greater depths. It improves the water tight. They
can be designed to take the high structural loads. Typical view of diaphragm wall with strut as
shown in Figure 1.2
Figure 1.2 Diaphragm Wall with Struts
1.2.2 Roof slab
The roof slab is just below the ground level. This is the top most layer of the underground
station box. Above the roof slab the soil back fill is placed. Station will be 200m long and about
20m deep.
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1.2.3 Concourse slab
The concourse slab is placed below the roof slab. This is where passengers will come to
buy tickets. The amenities like Stairs, escalators and lifts facilities are available in this concourse
level. Station will be 200m long and about 20m deep[27-32].
1.2.4 Base slab
This is the bottom most layer of underground metro station box. Base level the tracks are
laid and passengers will come board trains. Stairs, escalators and lifts will be provided at base
levels. Each station will be 200m long and about 20m deep. Below the base slab the barrette is
constructed. Sometimes barrette structure is removed after the whole structure is constructed.
1.3ANALYSIS OF UNDERGROUND STATION BOX
1.3.1GENERAL
The underground metro station analysis and design consists of two parts. The first one is
construction stage analysis and the second one is permanent stage analysis. The construction
stage analysis is the retaining system analysis doing this use WALLAP software. Using the
WALLAP software calculates the maximum moments and shear force in soil and excavated face
of the diaphragm wall. For underground metro station design two types of load combinations has
to be considered. One is based on ultimate strength conditions and the other one is ultimate
serviceability conditions. For ultimate strength conditions consider the multiplication load factor
is 1.5 based on IS: 456(2000). For ultimate serviceability conditions consider the multiplication
load factor is one based on IS: 456(2000).
Permanent stage analysis is made by using STAAD Pro software.. Form the load
combinations based on IS: 456(2000) calculate the maximum bending moment and shear force
based on ultimate strength and serviceability conditions. For analyze the diaphragm wall divide
the entire length of the diaphragm wall in to small parts. Each part has to be analyzed by both
construction and permanent stage. Finally compare the maximum moments and shear force from
the above two results[33-37]. Find the maximum bending moment in both soil and excavation
sides. The reinforcement detail has to be prepared in the form of drawing. For analysis and
design of roof slab, concourse slab and base slab use STAAD Pro software. The reinforcement
detail has to be prepared in the form of drawings.
1.3.2 CONSTRUCTION STAGE ANALYSIS
In this analysis the structure has to retain the load of construction stage and thus taking in
to consideration of all the geotechnical details and thus incorporating in the software called
WALLAP to find the embedment depth and the envelop moments on the wall by giving the
proper commands to the software. Thus the bending moment behavior of the elements is studied
through this software, and then the moments for each member are noted down for comparison of
moments in permanent analysis. The embedment depth for this project is found to be 5m below
the base slab[38-42].
1.3.3 Case study details of the section
In this project a typical case is considered for the analysis and design of underground
metro station. The geotechnical details of this case is given in Table 1.3
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Table 1.3 Geotechnical profile of the section
Stratum
No
Elevation of
top of
stratum
Soil Type
Active side Excavation side
1 116.98 Silty Sand with Clay Silty Sand with Clay
2 106.82 Sand Sand
3 104.02 Completely
Weathered Rock
Completely Weathered
Rock
4 101.92 Highly Weathered
Rock
Highly Weathered Rock
5 99.82 Medium Weathered
Rock
Medium Weathered Rock
The following soil properties are assumed for that section
Assuming that the water table is at the surface, for the analysis and the design.
Saturated unit weight of the soil γsat = 21kN/m3
Submerged unit weight of the soil γsub = 11kN/m3
Unit weight of water γw = 10 kN/m3
Lateral earth pressure at rest condition Ko = 0.5
Lateral earth pressure at active condition Ka = 0.3
1.3.4 ANALYSIS OF DIAPHRAGM WALL
Compare maximum bending moment and shear values from STAAD Pro and WALLAP
analysis results. Taken the maximum moments and shear force values from that result, based on
that values design diaphragm wall[43-46]. The diaphragm wall design is based on IS: 456(2000).
Maximum shear force values are tabulated in the Table 4.10.
Table 4.10 Maximum bending moment value for the cross section
S.No Y-
Coordinate
Differ
(m)
Bending moment KN.m
Ultimate strength Ultimate serviceability
Soil Excava
te
Soil Excavate
1. 116.98 0.00 0.00 0.00 0.00 0.00
2. 116.09 0.89 9.00 9.00 6.00 6.00
3. 115.20 0.89 46.00 46.00 31.00 31.00
4. 114.59 0.61 96.00 96.00 64.00 64.00
5. 113.98 0.61 173.00 173.00 116.00 116.00
6. 112.99 0.99 366.00 366.00 244.00 244.00
7. 112.79 0.20 417.00 417.00 278.00 278.00
8. 112.69 0.10 445.00 445.00 297.00 297.00
9. 112.39 0.30 533.00 533.00 356.00 356.00
10. 112.09 0.30 1729.00 1729.00 1153.00 1153.00
11. 111.94 0.15 1620.00 1620.00 1080.00 1080.00
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12. 110.94 1.00 978.00 978.00 652.00 652.00
13. 110.07 0.87 614.00 614.00 410.00 410.00
14. 109.20 0.87 342.00 342.00 228.00 228.00
15. 108.05 1.15 109.00 109.00 73.00 73.00
16. 106.89 1.16 429.00 429.00 286.00 286.00
17. 106.82 0.07 459.00 459.00 306.00 306.00
18. 106.69 0.13 472.00 472.00 315.00 315.00
19. 106.59 0.10 565.00 565.00 377.00 377.00
20. 105.59 1.00 200.00 200.00 134.00 134.00
21. 104.81 0.78 601.00 601.00 401.00 401.00
22. 104.02 0.79 852.00 852.00 568.00 568.00
23. 102.97 1.05 914.00 914.00 610.00 610.00
24. 101.92 1.05 600.00 600.00 400.00 400.00
25. 100.87 1.05 345.00 345.00 230.00 230.00
26. 99.82 1.05 1464.00 1464.00 976.00 976.00
27. 98.98 0.84 2746.00 2746.00 1831.00 1831.00
28. 98.68 0.30 3278.00 3278.00 2186.00 2186.00
29. 98.38 0.30 3849.00 3849.00 2566.00 2566.00
30. 98.17 0.21 4051.00 4051.00 2701.00 2701.00
31. 97.17 1.00 2548.00 2548.00 1699.00 1699.00
32. 96.57 0.60 1845.00 1845.00 1230.00 1230.00
33. 95.97 0.60 1262.00 1262.00 842.00 842.00
34. 95.37 0.60 866.00 866.00 578.00 578.00
35. 94.77 0.60 476.00 476.00 318.00 318.00
RESULTS AND DISCUSSIONS
6.1 GENERAL
In this project underground metro station box is analyzed and designed. The entire
structure is modeled and analyzed. The diaphragm wall, roof slab, concourse slab and base slab
are designed and detail drawings are prepared. Taken the moment and shear force results from
WALLAP and STAAD pro software, compare the maximum value from the results based on
design diaphragm wall[47-50].
6.2 DIAPHRAGM WALL
Diaphragm wall is generally a reinforced concrete wall constructed below the ground level
which is used to retain the structure. The length of the diaphragm wall is around 22m. Designing
the diaphragm wall two typed of analysis has to be done. Bending moment, shear force and
envelope from WALLAP analysis is given shown in
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Shear force kN
Figure 6.1 Bending moment and shear force envelope from WALLAP
The above envelope diagram the centre line (0-0) shows the position of diaphragm wall.
Left side shows the soil side results the same way right side shows the results of excavation side.
The continuous line shows shear force values and dotted line shows the bending moment values.
Comparing the STAAD and WALLAP results at most of the places permanent analysis results
only govern the design. But the roof slab to base slab level construction stage results only govern
the design. The structure is analyzed by only permanent stage that roof slab to base slab level the
structure is failed by construction stage itself. So construction stage analysis is also very
important in underground station design. Example at roof slab level the Y co-ordinate values are
112.69m and 112.39m the bending moment value from permanent stage analysis is 445.00 kN.m
and 533.00 kN.m and the values from construction stage analysis is 665.21kN.m and
1617.46kN.m respectively[9-16]. So compare the above two result construction stage analysis is
important.
6.3 ROOF SLAB DESIGN
Roof slab is designed by using STAAD Pro software. Load combination Maximum
vertical up, Maximum vertical down, Maximum horizontal only govern the roof slab design. The
maximum moment from STAAD analysis result is 1740kN.m.Maximum moment is from beam
number14. 10 numbers of 25 mm diameter bars are used.
6.4 CONCOURSE SLAB DESIGN
Concourse slab is designed by using STAAD Pro software. Load combination Maximum
vertical up, Maximum vertical down, Maximum horizontal only govern the roof slab design. The
maximum moment from STAAD analysis result is 324kN.m.Maximum moment is from beam
number12. 6 numbers of 20 mm diameter bars are used.
6.5 BASE SLAB DESIGN
Base slab is designed by using STAAD Pro software. Load combination Maximum
vertical up, Maximum vertical down, Maximum horizontal only govern the roof slab design. The
maximum moment from STAAD analysis result is 900 kN.m. Maximum moment is from beam
number14. 6 numbers of 25 mm diameter bars are used.
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CONCLUSION
Studied about the construction methods and concept of underground metro station design.
Compare the bottom up construction method the top down construction method is efficient and
economical.Designing the diaphragm wall construction stage analysis is completed using
WALLAP software and permanent stage analysis is completed using STAAD Pro software.
Taken the maximum moment from two analyses designed diaphragm wall and the reinforcement
drawing are prepared. The permanent structures of roof slab, concourse slab and base slab are
designed using STAAD Pro software and then the reinforcement drawings are prepared.Retaining
structure used in this project is diaphragm wall . In diaphragm wall design the roof level bending
moment value from construction stage is 33.18% more than the permanent stage analysis. The
concourse slab level bending moment value from construction stage is 40.00% more than the
permanent stage analysis. The base slab level bending moment value from construction stage is
50.10% more than the permanent stage analysis. Below the base slab level permanent stage
analysis only governs the design.
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