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Utilization of underground spaces in urban areas: Urban geo-grid plan
Engineering Geology, 35 (1993) 175-181
175
Elsevier Science Publishers B.V., Amsterdam
Utilization of underground spaces in urban areas: Urban geo-grid plan Noriharu Miyake and Atsushi Denda
Underground and Geoteehnieal Engineering Department, Shimizu Corporation, Shibaura 1-2-3, Minato, Tokyo, Japan (Revised manuscript accepted April 15, 1993)
ABSTRACT Miyake, N. and Denda, A., 1993. Utilization of underground spaces in urban areas: Urban geo-grid plan. In: M. Langer, K. Hoshino and K. Aoki (Editors), Engineering Geology in the Utilization of Underground Space. Eng. Geol., 35: 175-181. The Urban Geo-grid Plan aims for a systematic and better coexistence of above-ground and underground areas through the utilization of underground space presently not in use, without interfering with existing urban functions. There would be "base points" supporting regional functions which are laid out in a grid connected by "lines". Base points would consist of "grid points" and "grid stations", which serve as control centers for grid points, the grid points and grid stations being interconnected by tunnels to form an "underground network". Normally, a base point would be used for multiple purposes to supplement regional functions which are inadequate, as well as urban functions, and in emergencies, such as earthquake disasters, it would demonstrate information and evacuations functions.
Introduction For about four years, there is a shortage of office space in Tokyo. This is caused by the concentration of business and administrative functions in Tokyo, as the national capital of Japan and as an international metropolis. Transportation by roads and railways has become saturated. Disaster prevention functions have deteriorated. On top of all this, there has been an unprecedented escalation of land prices, and the urban problem has abruptly come to the fore. A clarifying example is the history of the construction of a subway line in Tokyo. Construction had been decided on in city planning as far back as 1971, however, much time was required for acquisition of land in certain areas and it was 16 years later that the land needed was finally acquired completely. The line was opened for service two years later. Because of such problems, deep underground space at more than 50 m depth, which is normally not used, has been the object of intense attention as a new frontier, that is, space which can be newly developed along with outer 0013-7952/93/$06.00
space and the oceans. At the same time, there is much expectation for this to serve as the trump card in resolving various urban problems. Under these circumstances, with the distressed international city of Tokyo as the model, a systematic underground development scheme - - Urban Geo-grid Scheme - - was formulated, and simulations were made toward realization of the scheme. The scheme was made public in April 1988 (Shimizu Corporation, 1988). This paper describes the concept of the scheme, the functions of facilities, and also the outlines of transportation and disaster prevention facilities, utilization of energy with groundwater as the heat source, and measures against buoyancy caused by groundwater.
Concept As shown in Figs. 1 and 2, "grid points", "grid stations", and an "underground network" connecting these points and stations are the component elements of the plan. This scheme makes a simulation using the overcrowded city of Tokyo
© 1993 - - Elsevier Science Publishers B.V. All rights reserved.
176
N. M I Y A K E A N D A. D E N D A
Fig. 1. Grid station and grid point group laid out in grid form and connecting underground network.
---.
;.....! .....i
I
IT
~id point ,[
f ~km* ¢ T Underground network " Grid station
10km
,, ,, ,, l
J
10km
J
1 Unit' 1 Grid station, 24 Grid points Fig. 2. System structure of 1 unit.
as the model for the realization of a systematic plan for cities. It would make use of "underground space", the only space not used. The concept of the scheme consists of the factors below. (1) The development and construction are to
proceed in co-existence with existing urban functions. (2) Use should be made normally in accordance with the situation in the district; inadequate district communications should be restored. (3) The facility is to be used as a temporary shelter for 500,000 persons in case of emergency such as an earthquake disaster. (4) Multi-purpose urban infrastructure functions (such as in commodity distribution and communications) should be collected in an underground network. (5) The grid stations/points should be located at parks and schoolyards where underground space had not been previously utilized. (6) The systems should be built simultaneous with the expansion and growth of urban functions. Structural factors
The outlines of the various facilities of the plan are as described below. Details are given in Table I.
177
UTILIZATION OF UNDERGROUND SPACES IN URBAN AREAS: URBAN GEO-GRID PLAN
TABLE 1 Facilities in the outline of the Urban Geo-grid Plan Grid point Scale Diameter 30 m Height 25 m Stories: 3 underground stories Overburden 10 m Projection area 700 m2 Total floor area 2100 m2 Construction interval 2 km
Location Under a schoolyard or park
Method Continuous underground diaphragm wall method Open cut method
Construction period 20 months/point
Grid station
Underground network
Diameter I00 m Height 50 m Stories: 8 underground stories Projection area 7500 m2 Total floor area 40,000 m2
Trunk network (connecting grid stations)
Construction interval 10 km
Diameter: 3m, span: 2 km
Under re-developed areas such as former factory sites or under large parks
50 m underground
Shield tunneling method
40 months/station
Trunk: 24 months/km Branch: 12 months/km
Standard function Community facility: Meeting hall, chil- Station concourse, platform ren's center, public bath, exhibition hall Education and cultural facility: Business facility, large-scale parking lot Gymnasium, library Sports facility: Swimming pool, physical Energy facility, shopping center fitness center
Emergency function District disaster control center Capacity: 1000 to 1500 people Information collection and transmission
District evacuation and guidance District monitoring
Diameter: 10m, span: 10 km Branch network (connecting grid points)
Area disaster control center Capacity: 5000 to 10,000 people Information dispatching, area evacuation and guidance Energy supply
1. Gridpomt A grid p o i n t w o u l d be the m i n i m u m u n i t o f space used, with a d i a m e t e r o f 30 m a n d depth o f 25 m for a cylindrical shape. T h e grid p o i n t s are located at intervals o f 2 to 3 k m in grid form. The necessary facilities for c o m m u n i t y functions, edu-
Trunk: new transportation system Communications, energy network Branch: communications, energy network
Trunk, branch Evacuation route to safety zone Information network Commodity transportation
c a t i o n - c u l t u r e / s p o r t s are to be provided by the district.
2. Grid station A grid s t a t i o n w o u l d serve as a c o n t r o l center for a g r o u p o f grid p o i n t s o f a given n u m b e r o f
178
b i M I Y A K E A N D A. I ) E N I ) A
units. The station would have a diameter of about 100 m and a depth of 50 m. The grid stations would be located at intervals of approximately 10 km. They would be constructed underground at large-scale urban parks giving consideration to above-ground facilities and functions, as with grid points. A huge atrium for receiving sunlight is located at the center, with offices, a shopping center, and a large-scale parking garage. The grid station would serve as a key station for a new transportation system (Fig. 3).
for utilization for multiple purposes. This is the trump card of urban infrastructure facilities and much is expected of it as a medium for carrying on every day life.
3. Underground networks
l. Transportation facilities
The lifeline of this scheme consists of networks. Grid stations would be connected by a network of trunk lines, 10 m in diameter, and grid points by networks of branch lines about 3 m in diameter,
The main feature of the underground network is that it can be used for multiple purposes, in normal situations for transportation, communications, and energy supply, but in emergencies, for
Outlines of the facilities
The outlines of the transportation and disaster control facilities are described (with reference to Fig. 3 and Table 1, giving an example of a grid station).
Fig. 3. Model of a grid station.
UTILIZATIONOF UNDERGROUNDSPACESIN URBANAREAS: URBANGEO-GRIDPLAN
179
transportation of commodities which are in short supply and as an evacuation route in case of danger. Transportation would be by magneticallylevitated train, communication transmissions and energy supplies would be of underground multipurpose duct type. Inside a grid station, transportation from an underground train station to the ground surface would be a problem and emergency staircases would be provided besides highspeed elevators/escalators.
ature, can be considered as unutilized energy and the effective utilization of this will be examined. In effect, the groundwater temperature (stabilized at approximately 15°C) is to be the heat source for a grid station/grid point, with the water used as cooling water for heat pumps in the summertime (Fig. 4) and as a heat source in the wintertime. Through these, the efficiency (cop) of the heat pump can be improved by 10-15% in the summertime, and by 40-50% in the wintertime.
2. Disaster control facilities
2. Water supply
Those places where fire can be considered to occur inside a grid station would be the underground train station including the railway and the underground mall. Thorough consideration must be given to emergency passages and entries for fire-fighting. Besides conventional disaster-control facilities, it will be necessary to secure shelter space at the underground train station as a temporary safe area. It may be necessary to install a smoke control technique based on overall pressurized smoke containment.
It is desirable that groundwater should be used as effectively as possible, in this specific case also. Since a stable supply may be expected, it should be possible to use the water for miscellaneous purposes. It may be necessary for utilization to raise the efficiency through improvement of water quality or an organic combination with the abovementioned energy facilities.
Outline of environmental planning Because this scheme is planned to be executed in the near-future, an outline will be given below with emphasis on the utilization of groundwater in connection with energy and water supply. In both cases, however, it will be necess/ary for continuing studies prior to the executiorr of the plans, in order to avoid any adverse effects on the surrounding environment.
1. Energy The energy consumption of an underground, manned space is supposed to be more than double that of an above-ground facility with similar functions, and it is desirable that this consumption is minimized. In the capital area, the groundwater table, which had been considerably lowered, has risen as a result of a pump-up regulation, and it may be expected that the groundwater level will rise further in the future. The groundwater temperature which may be the mean annual air temper-
Problems and outlooks Problems and outlooks have been summarized for work execution and environmental technologies, respectively.
f I
~
~
Itank, 5 t o , I 5 ~C 1 I Power
~ ~ - ~
Water injection ,
i_
I
Pump-u~ II'
-
I
i
I II I I1:::i::21:9:
'"'.1.1
II I lS:r=°i!
"
Fig. 4. Example of a system using groundwater as unutilized energy (summertime).
180
1. Work execution technology
It is possible for all facilities to be constructed with present-day available technologies. It is, however, required that the work will be executed in shorter periods of time and in narrower spaces, and, moreover, the effects on the surrounding environment should be minimized and costs should be reduced. Various technologies related to these demands, such as automation of the shield tunnelling method, are now under development. 2. Uplift acting on structure
The lowlands of Japan, where Tokyo is situated, consist of comparatively unsolidified soil deposited during Pleistocene and Holocene times, with a high groundwater level. Underground constructions are built at present up to depths of more than 30 m, and techniques to control the upward force of the groundwater acting on the bottoms of these constructions are becoming more and more important (Fujita et al., 1992). Present-day techniques to control uplift acting on the bottom of constructions after completion, are given in Table 2. Uplift counteracting techniques have to function during the complete life of the structure. It is, therefore, necessary to make an acurate estimation of the degree of uplift, cost, construction period, etc. giving consideration to future head variation, running cost, and other factors. Of these techniques, the method which would be promising in the future is that of pumping up and utilizing the groundwater, acting to produce uplift at the base slab within limits given by environmental aspects. 3. Environmental and disaster control technologies
The aspects of the psychology and physiology of people living in underground spaces have not been as adequately studied compared with work execution techniques. Research is presently going on regarding the influence of variations in light/sound/heat/scenery/air environment. It is clear that among all related technologies the greatest problem is that of disaster control, with the emphasis on smoke control and evacuation as previously
N. MIYAK~:AND .a. J~Nt~A TABLE 2 Uplift countermeasures presently adopted Uplift countermeasure
Frequency
Problem
(1) Increasing of weight
High
Space required for increasing weight
(2) Large weight through overlaysoil (overlay soil at top of structure)
Low
Unit weight small compared with (1)
(3) Permanent anchor (countered by tensile force)
Medium Largenumber required in case of high buoyancyfor high cost
of structure (framework of base slab, beams, columns, etc.)
(4) Pump-up of
Extremely
Combined use with
groundwater (groundwater under base slab constantly pumped up)
low
cut-offwall effective; maintenance required; environmental problems required to be considered.
mentioned. Research and development works are going on regarding these items. Results
The greatest advantages of the scheme, as previously described, are that the system can be used for multiple purposes with the combination of "base points" and "lines", and further, that it possesses functions for normal situations and also for emergencies such as needed at times of earthquake disasters. A discussion concerning priorities in the use of specific functions of the system, and from which area construction should be started, should be settled hereafter. As previously pointed out, present-day construction technologies are adequate, but a shortening of the construction time and economizing of space are required, and nurturing of safety and comfort technologies is desirable. For about four years a discussion is going on in Japan, to use underground space at depths of more than 50 m (space which normally had not been
UTILIZATIONOF UNDERGROUNDSPACESIN URBANAREAS:URBANGEO-GRIDPLAN
used in the past) for building purposes and tunnel structures "Deep Underground". Arguments have arisen aiming for an effective infrastructure in the future. The arguments are that such underground space could be used without charge as a rule. If this were to be made possible through legislation, the construction of this scheme would be hastened.
Acknowledgements The fundamental principles of this scheme were set up by a team named "Group Chaos" with Mr. S. Tohma as representative, which was established
181
independently within the Shimizu Corporation in 1987. The group consisted of six young engineers coming from various sectors in the company such as design, technological development and research. The sincerest gratitude is owed the members of this group.
References Shimizu Corporation, 1988. Urban Geo-grid Plan. Shimizu Bull., 56:14-17 (in Japanese). Fujita K., Okahara, M., Naemura, S., Tamura, M., Takahasi, K., Nakamura, Y., Suzuki, Y. and Miyake, N., 1992. Discussion: Current state and outlook of foundation construction methods. Found. Eng. Equipm., 20-1:2-21 (in Japanese).
175
Elsevier Science Publishers B.V., Amsterdam
Utilization of underground spaces in urban areas: Urban geo-grid plan Noriharu Miyake and Atsushi Denda
Underground and Geoteehnieal Engineering Department, Shimizu Corporation, Shibaura 1-2-3, Minato, Tokyo, Japan (Revised manuscript accepted April 15, 1993)
ABSTRACT Miyake, N. and Denda, A., 1993. Utilization of underground spaces in urban areas: Urban geo-grid plan. In: M. Langer, K. Hoshino and K. Aoki (Editors), Engineering Geology in the Utilization of Underground Space. Eng. Geol., 35: 175-181. The Urban Geo-grid Plan aims for a systematic and better coexistence of above-ground and underground areas through the utilization of underground space presently not in use, without interfering with existing urban functions. There would be "base points" supporting regional functions which are laid out in a grid connected by "lines". Base points would consist of "grid points" and "grid stations", which serve as control centers for grid points, the grid points and grid stations being interconnected by tunnels to form an "underground network". Normally, a base point would be used for multiple purposes to supplement regional functions which are inadequate, as well as urban functions, and in emergencies, such as earthquake disasters, it would demonstrate information and evacuations functions.
Introduction For about four years, there is a shortage of office space in Tokyo. This is caused by the concentration of business and administrative functions in Tokyo, as the national capital of Japan and as an international metropolis. Transportation by roads and railways has become saturated. Disaster prevention functions have deteriorated. On top of all this, there has been an unprecedented escalation of land prices, and the urban problem has abruptly come to the fore. A clarifying example is the history of the construction of a subway line in Tokyo. Construction had been decided on in city planning as far back as 1971, however, much time was required for acquisition of land in certain areas and it was 16 years later that the land needed was finally acquired completely. The line was opened for service two years later. Because of such problems, deep underground space at more than 50 m depth, which is normally not used, has been the object of intense attention as a new frontier, that is, space which can be newly developed along with outer 0013-7952/93/$06.00
space and the oceans. At the same time, there is much expectation for this to serve as the trump card in resolving various urban problems. Under these circumstances, with the distressed international city of Tokyo as the model, a systematic underground development scheme - - Urban Geo-grid Scheme - - was formulated, and simulations were made toward realization of the scheme. The scheme was made public in April 1988 (Shimizu Corporation, 1988). This paper describes the concept of the scheme, the functions of facilities, and also the outlines of transportation and disaster prevention facilities, utilization of energy with groundwater as the heat source, and measures against buoyancy caused by groundwater.
Concept As shown in Figs. 1 and 2, "grid points", "grid stations", and an "underground network" connecting these points and stations are the component elements of the plan. This scheme makes a simulation using the overcrowded city of Tokyo
© 1993 - - Elsevier Science Publishers B.V. All rights reserved.
176
N. M I Y A K E A N D A. D E N D A
Fig. 1. Grid station and grid point group laid out in grid form and connecting underground network.
---.
;.....! .....i
I
IT
~id point ,[
f ~km* ¢ T Underground network " Grid station
10km
,, ,, ,, l
J
10km
J
1 Unit' 1 Grid station, 24 Grid points Fig. 2. System structure of 1 unit.
as the model for the realization of a systematic plan for cities. It would make use of "underground space", the only space not used. The concept of the scheme consists of the factors below. (1) The development and construction are to
proceed in co-existence with existing urban functions. (2) Use should be made normally in accordance with the situation in the district; inadequate district communications should be restored. (3) The facility is to be used as a temporary shelter for 500,000 persons in case of emergency such as an earthquake disaster. (4) Multi-purpose urban infrastructure functions (such as in commodity distribution and communications) should be collected in an underground network. (5) The grid stations/points should be located at parks and schoolyards where underground space had not been previously utilized. (6) The systems should be built simultaneous with the expansion and growth of urban functions. Structural factors
The outlines of the various facilities of the plan are as described below. Details are given in Table I.
177
UTILIZATION OF UNDERGROUND SPACES IN URBAN AREAS: URBAN GEO-GRID PLAN
TABLE 1 Facilities in the outline of the Urban Geo-grid Plan Grid point Scale Diameter 30 m Height 25 m Stories: 3 underground stories Overburden 10 m Projection area 700 m2 Total floor area 2100 m2 Construction interval 2 km
Location Under a schoolyard or park
Method Continuous underground diaphragm wall method Open cut method
Construction period 20 months/point
Grid station
Underground network
Diameter I00 m Height 50 m Stories: 8 underground stories Projection area 7500 m2 Total floor area 40,000 m2
Trunk network (connecting grid stations)
Construction interval 10 km
Diameter: 3m, span: 2 km
Under re-developed areas such as former factory sites or under large parks
50 m underground
Shield tunneling method
40 months/station
Trunk: 24 months/km Branch: 12 months/km
Standard function Community facility: Meeting hall, chil- Station concourse, platform ren's center, public bath, exhibition hall Education and cultural facility: Business facility, large-scale parking lot Gymnasium, library Sports facility: Swimming pool, physical Energy facility, shopping center fitness center
Emergency function District disaster control center Capacity: 1000 to 1500 people Information collection and transmission
District evacuation and guidance District monitoring
Diameter: 10m, span: 10 km Branch network (connecting grid points)
Area disaster control center Capacity: 5000 to 10,000 people Information dispatching, area evacuation and guidance Energy supply
1. Gridpomt A grid p o i n t w o u l d be the m i n i m u m u n i t o f space used, with a d i a m e t e r o f 30 m a n d depth o f 25 m for a cylindrical shape. T h e grid p o i n t s are located at intervals o f 2 to 3 k m in grid form. The necessary facilities for c o m m u n i t y functions, edu-
Trunk: new transportation system Communications, energy network Branch: communications, energy network
Trunk, branch Evacuation route to safety zone Information network Commodity transportation
c a t i o n - c u l t u r e / s p o r t s are to be provided by the district.
2. Grid station A grid s t a t i o n w o u l d serve as a c o n t r o l center for a g r o u p o f grid p o i n t s o f a given n u m b e r o f
178
b i M I Y A K E A N D A. I ) E N I ) A
units. The station would have a diameter of about 100 m and a depth of 50 m. The grid stations would be located at intervals of approximately 10 km. They would be constructed underground at large-scale urban parks giving consideration to above-ground facilities and functions, as with grid points. A huge atrium for receiving sunlight is located at the center, with offices, a shopping center, and a large-scale parking garage. The grid station would serve as a key station for a new transportation system (Fig. 3).
for utilization for multiple purposes. This is the trump card of urban infrastructure facilities and much is expected of it as a medium for carrying on every day life.
3. Underground networks
l. Transportation facilities
The lifeline of this scheme consists of networks. Grid stations would be connected by a network of trunk lines, 10 m in diameter, and grid points by networks of branch lines about 3 m in diameter,
The main feature of the underground network is that it can be used for multiple purposes, in normal situations for transportation, communications, and energy supply, but in emergencies, for
Outlines of the facilities
The outlines of the transportation and disaster control facilities are described (with reference to Fig. 3 and Table 1, giving an example of a grid station).
Fig. 3. Model of a grid station.
UTILIZATIONOF UNDERGROUNDSPACESIN URBANAREAS: URBANGEO-GRIDPLAN
179
transportation of commodities which are in short supply and as an evacuation route in case of danger. Transportation would be by magneticallylevitated train, communication transmissions and energy supplies would be of underground multipurpose duct type. Inside a grid station, transportation from an underground train station to the ground surface would be a problem and emergency staircases would be provided besides highspeed elevators/escalators.
ature, can be considered as unutilized energy and the effective utilization of this will be examined. In effect, the groundwater temperature (stabilized at approximately 15°C) is to be the heat source for a grid station/grid point, with the water used as cooling water for heat pumps in the summertime (Fig. 4) and as a heat source in the wintertime. Through these, the efficiency (cop) of the heat pump can be improved by 10-15% in the summertime, and by 40-50% in the wintertime.
2. Disaster control facilities
2. Water supply
Those places where fire can be considered to occur inside a grid station would be the underground train station including the railway and the underground mall. Thorough consideration must be given to emergency passages and entries for fire-fighting. Besides conventional disaster-control facilities, it will be necessary to secure shelter space at the underground train station as a temporary safe area. It may be necessary to install a smoke control technique based on overall pressurized smoke containment.
It is desirable that groundwater should be used as effectively as possible, in this specific case also. Since a stable supply may be expected, it should be possible to use the water for miscellaneous purposes. It may be necessary for utilization to raise the efficiency through improvement of water quality or an organic combination with the abovementioned energy facilities.
Outline of environmental planning Because this scheme is planned to be executed in the near-future, an outline will be given below with emphasis on the utilization of groundwater in connection with energy and water supply. In both cases, however, it will be necess/ary for continuing studies prior to the executiorr of the plans, in order to avoid any adverse effects on the surrounding environment.
1. Energy The energy consumption of an underground, manned space is supposed to be more than double that of an above-ground facility with similar functions, and it is desirable that this consumption is minimized. In the capital area, the groundwater table, which had been considerably lowered, has risen as a result of a pump-up regulation, and it may be expected that the groundwater level will rise further in the future. The groundwater temperature which may be the mean annual air temper-
Problems and outlooks Problems and outlooks have been summarized for work execution and environmental technologies, respectively.
f I
~
~
Itank, 5 t o , I 5 ~C 1 I Power
~ ~ - ~
Water injection ,
i_
I
Pump-u~ II'
-
I
i
I II I I1:::i::21:9:
'"'.1.1
II I lS:r=°i!
"
Fig. 4. Example of a system using groundwater as unutilized energy (summertime).
180
1. Work execution technology
It is possible for all facilities to be constructed with present-day available technologies. It is, however, required that the work will be executed in shorter periods of time and in narrower spaces, and, moreover, the effects on the surrounding environment should be minimized and costs should be reduced. Various technologies related to these demands, such as automation of the shield tunnelling method, are now under development. 2. Uplift acting on structure
The lowlands of Japan, where Tokyo is situated, consist of comparatively unsolidified soil deposited during Pleistocene and Holocene times, with a high groundwater level. Underground constructions are built at present up to depths of more than 30 m, and techniques to control the upward force of the groundwater acting on the bottoms of these constructions are becoming more and more important (Fujita et al., 1992). Present-day techniques to control uplift acting on the bottom of constructions after completion, are given in Table 2. Uplift counteracting techniques have to function during the complete life of the structure. It is, therefore, necessary to make an acurate estimation of the degree of uplift, cost, construction period, etc. giving consideration to future head variation, running cost, and other factors. Of these techniques, the method which would be promising in the future is that of pumping up and utilizing the groundwater, acting to produce uplift at the base slab within limits given by environmental aspects. 3. Environmental and disaster control technologies
The aspects of the psychology and physiology of people living in underground spaces have not been as adequately studied compared with work execution techniques. Research is presently going on regarding the influence of variations in light/sound/heat/scenery/air environment. It is clear that among all related technologies the greatest problem is that of disaster control, with the emphasis on smoke control and evacuation as previously
N. MIYAK~:AND .a. J~Nt~A TABLE 2 Uplift countermeasures presently adopted Uplift countermeasure
Frequency
Problem
(1) Increasing of weight
High
Space required for increasing weight
(2) Large weight through overlaysoil (overlay soil at top of structure)
Low
Unit weight small compared with (1)
(3) Permanent anchor (countered by tensile force)
Medium Largenumber required in case of high buoyancyfor high cost
of structure (framework of base slab, beams, columns, etc.)
(4) Pump-up of
Extremely
Combined use with
groundwater (groundwater under base slab constantly pumped up)
low
cut-offwall effective; maintenance required; environmental problems required to be considered.
mentioned. Research and development works are going on regarding these items. Results
The greatest advantages of the scheme, as previously described, are that the system can be used for multiple purposes with the combination of "base points" and "lines", and further, that it possesses functions for normal situations and also for emergencies such as needed at times of earthquake disasters. A discussion concerning priorities in the use of specific functions of the system, and from which area construction should be started, should be settled hereafter. As previously pointed out, present-day construction technologies are adequate, but a shortening of the construction time and economizing of space are required, and nurturing of safety and comfort technologies is desirable. For about four years a discussion is going on in Japan, to use underground space at depths of more than 50 m (space which normally had not been
UTILIZATIONOF UNDERGROUNDSPACESIN URBANAREAS:URBANGEO-GRIDPLAN
used in the past) for building purposes and tunnel structures "Deep Underground". Arguments have arisen aiming for an effective infrastructure in the future. The arguments are that such underground space could be used without charge as a rule. If this were to be made possible through legislation, the construction of this scheme would be hastened.
Acknowledgements The fundamental principles of this scheme were set up by a team named "Group Chaos" with Mr. S. Tohma as representative, which was established
181
independently within the Shimizu Corporation in 1987. The group consisted of six young engineers coming from various sectors in the company such as design, technological development and research. The sincerest gratitude is owed the members of this group.
References Shimizu Corporation, 1988. Urban Geo-grid Plan. Shimizu Bull., 56:14-17 (in Japanese). Fujita K., Okahara, M., Naemura, S., Tamura, M., Takahasi, K., Nakamura, Y., Suzuki, Y. and Miyake, N., 1992. Discussion: Current state and outlook of foundation construction methods. Found. Eng. Equipm., 20-1:2-21 (in Japanese).