Archive:Hong Kong Mass Transport Study/Chapter 9

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Chapter 8 — Route Location and Right of Way

Hong Kong Mass Transport Study, Chapter 9 Design and Construction

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DESIGN AND CONSTRUCTION

1. The entire rapid-transit system and its components were designed in sufficient detail for cost estimating purposes. Limited investigations of soil conditions and underground utilities were made at all locations and intensive investigations were made at selected places to establish unit costs. All known construction methods were considered for use in the design, and two of the project engineers visited Tokyo to observe underground construction in progress. Functional design criteria were established by railway operating specialists before beginning the structural design phase of the work.

FUNCTIONAL DESIGN

2. The first step in the process of translating the lines and stations, established in other phases of the project, into a physical structure for operating trains and serving passengers, is to establish the criteria for the functional design. It is possible to determine the best methods of construction and to carry out the structural design and costing only when the functional design of running track and stations has been prepared.
3. Running Track — To allow for clearance, the minimum width of tunnel required for the rapid-transit car when travelling on a straight section of track is 13 feet. On curved sections of track, extra width must be allowed according to the length of the cars, the radius of the curve and the cant of the track. For design purposes it was assumed that a 14-foot width was required for each track in cut and cover construction. For bored tunnels a 15-foot 6-inch internal diameter was assumed; a clear width between parapets of 26 feet was used in the design of overhead structures.
4. The height of the recommended rail car is 11 feet 6 inches. Allowing for clearance above the car and for ballast, sleepers and rails below the car a minimum height of 13 feet 6 inches is required. For design purposes a headroom of 14 feet was assumed.

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   Figure 60 — Running Track Cross Sections

   Figure 60 shows cross-sections of running track on the surface, on overhead structure and in cut-and-cover tunnel. There is great variation in design throughout the system and these are only typical sections.
6. Station Mezzanine — The principal function of the mezzanine is to provide for the movement of people to and from the trains and for the activities associated with that movement. The main activity is that of paying the fare, so the mezzanine must house booking offices and ticket vending machines and also the control barriers to enable the tickets to be checked as passengers enter and leave the platforms. It must also accommodate numerous other facilities, so it will usually be several hundred feet in length. In view of its size, therefore, the headroom in the mezzanine should be at least 10 feet and extra height should always be provided where the additional cost is small.
7. The other facilities required in the mezzanine divide into two main categories; those required in connection with the operation of the rapid-transit system in general and the station in particular, and those provided for the convenience of the public. Of the first category, perhaps the most important is the station master's office. This will contain public address equipment for both the mezzanine and the platforms and means of communication with the control centre at Kowloon Bay Depot. Also, at interchange stations and at other heavily loaded stations, closed circuit television should be installed to ensure adequate station supervision.
8. Space must be provided in the mezzanine for a rest room for station staff and, at selected stations, staff rooms and canteen facilities for train crews. Many stations will need space for a small operational and clerical staff and all will need store rooms for items ranging from cleaning equipment to tickets. At many stations, space for escalator or lift machinery and rooms for the housing of train control apparatus must be incorporated into the design, and at some, accommodation will be required for ventilation equipment and electrical substations.
9. The facilities required for the convenience of customers include illuminated direction signs, information booths, concession counters for the sale of newspapers and other selected commodities, lavatories and first-aid facilities. The direction signs and information booths are, of course, also necessary for the efficient operation of the station.

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    Figure 61 — Typical Mezzanine Plans

    Although design of the mezzanines must primarily be geared to the efficient operation of the rapid-transit system, they can often serve a secondary function as a pedestrian subway. With this feature in mind, most of the underground mezzanines have been designed so that there is free movement between all access points. Figure 61 shows two layouts for the mezzanine of an underground station, one for a station with side platforms and the other for a central-platform station.
11. Access to Station Mezzanine — Most underground stations have been designed with a mezzanine level under a major road and above the station platform. Access to the mezzanine should be provided from both sides of the road. Where there is a road junction above, then access should be provided from all corners of the junction.
12. All underground mezzanines have been designed to have at least four major access points and many of the high-load stations have more. In addition to the main entries, the owners of neighbouring properties should be given the opportunity and even encouraged to provide their own entries wherever this does not conflict with the design and operation of the ticket facilities. In Tokyo, many large commercial establishments have a basement on the same level as the station mezzanine with direct access to it.
13. In most areas of Hong Kong, the footpaths are too narrow to accommodate the main accesses to the mezzanine. At Central Station, which is located under Des Voeux Road Central, some access on the south side can be provided in Chinese Street, Li Yuen Street, Douglas Street, Chiu Lung Street and Theatre Lane which are largely pedestrian ways linking Queen's Road and Des Voeux Road. However, on the north side it will be necessary to locate most of the main entries in the adjacent buildings. This solution will have to be applied at many other stations and should be considered whenever redevelopment of a site adjoining a station is proposed.
14. The access from surface streets to an underground station mezzanine will normally be by stairways. Escalators, especially for upward movements, should be considered either where the depth of the mezzanine is greater than usual, or as a convenience to the public at heavily used stations. In the preliminary design it was impossible to carry out a detailed analysis of the accesses to each station, and so for the purpose of making cost estimates, it was assumed that all access to the mezzanine from the surface streets would be by stairway. At overhead stations the ticket halls will normally be located below the station platform and as they will usually be at ground level, efficient access can easily be provided.

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    Access to Station Platforms — Access from the mezzanine to the station platforms may be by stairway or by escalator, depending on the vertical separation of the two levels. For all upward movements of more than 12 feet, escalators have been assumed. Escalators for downward movements of more than 12 feet have also been allowed for unless the expected passenger load is small. At some stations, where exceptionally large passenger loads are expected, escalators may be desirable where the rise is less than 12 feet.
16. For design purposes the capacity of an escalator, of about three feet in width, was assumed to be 8,000 people per hour. The theoretical capacity is greater than this, but it is necessary to assume a lower figure in order to allow for surges in passenger demand. The number of escalators and the number and width of stairways at each station was determined according to the estimated passenger loads. Three widths of stairway were used; 6 feet, 10 feet and 12 feet. At Tsz Wan Shan, the depth of the station requires high-speed lifts.
17. Platforms — All stations have 600-foot long platforms of 12-foot clear width to accommodate eight-car trains. Although some lines will be operating with six-car trains in the design year, it is expected that the full-length trains will be required eventually. The structural headroom on the platforms should be at least 10 feet so that signs can be installed at sufficient height to be visible to passengers.

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Figure 62 — Typical Side Platform Station Cross Sections

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Figure 63 — Side Platform Stations

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Figure 64 — Typical Central Platform Station Cross Sections

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Figure 65 — Typical Tunnel Station Cross Section

18. Figure 62 shows cross-sections of typical side-platform stations for underground and overhead construction. The side platform is the simplest station design; access is provided from the mezzanine to the back of the platform. Thirty-one of the fifty stations for the recommended system are of side-platform design. Their locations are shown in Figure 63. Seventeen of these stations are underground, thirteen on overhead structure, and one, at Hung Hom, at surface level.
19. In order to maintain regularity of train headways when the maximum train service is being operated, the terminal stations must be designed to allow some make-up time in the train schedules. With present signalling techniques, two tracks must be provided at one terminus of each line and three at the other. Island platforms are chosen to facilitate the management of passenger movements at these locations.
20. In addition to the end of line terminus, it is sometimes necessary to reduce the level of service near the extremities of a line by turning back trains at an intermediate station. The ideal layout for such turnback facilities involves a three-track station, but an alternative arrangement with a reversing siding beyond a two-track station can be used where the right of way is of limited width, provided the frequency of the service is not too close.
21. Figure 64 shows the cross-sections of underground and overhead central platform stations. These sections are applicable both to a two-track terminus and to a two-track turnback station. For both forms of construction access stairs are located in a central stairwell.
22. Underground central platform stations are located at Kennedy and North Point on Hong Kong Island, Shek Kip Mei and Choi Hung on the Kwun Tong Line and at Lai Chi Kok and Tsuen Wan on the Tsuen Wan Line. The station at Shek Kip Mei has a central platform because the approach at each end of the station is in tunnel. Choi Hung and Lai Chi Kok Stations have a central platform because they have been used as temporary terminals in the stage develop ment plan. The overhead central-platform design should be used at Chai Wan Central Station on the Island Line and at Kwun Tong and Ma Yau Tong Stations on the Kwun Tong Line. At Wo Liu Hang the central-platform station is at ground level.
23. At Lo Fu Ngam and Tsz Wan Shan, the stations will be constructed in bored tunnel. Figure 65 shows a cross-section of these stations which have a form of central platform. At Lo Fu Ngam the access to the platform will be by escalator, and, at Tsz Wan Shan, by lift.

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    Figure 66 — Central Station Cross Section

    Special Stations — Central Station has platforms at two levels, since the Island Line is located immediately above the Kwun Tong Line. The central-platform layout has been used because the flow in and out of the station is likely to be relatively unidirectional in the peak hours, and more efficient use can be made of escalators with this design. Also, Des Voeux Road is too narrow to allow the use of side platforms without considerable demolition of property. Figure 66 shows a cross-section through Central Station. This same cross-section also applies at Mong Kok Station where the Kwun Tong Line is located immediately above the Tsuen Wan Line. Here, a central platform arrangement is needed to permit easy transfer between the two lines. Figure 67 is a longitudinal section of Mong Kok Station, showing the arrangement of entries and exits and also the escalators for the transfer movement between the two levels.

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Figure 67 — Mong Kok Station Cross Section

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    Figure 68 — Western Market Station Cross Section

    Western Market Station is the southern terminus of the Kwun Tong Line and is also a turnback station for the Island Line trains. A three-track layout is required for the Kwun Tong Line terminus and also for the Island Line turnback. Figure 68 shows a cross-section of this Station; the intermediate mezzanine caters for the transfer movement between the two levels.
26. Admiralty Station is the southern terminus of the Tsuen Wan Line where passengers may transfer to the Island Line. The station for the Island Line has side platforms, while three tracks are needed to reverse the Tsuen Wan Line service. As at Western Market, the transfer between the two lines is by way of an intermediate mezzanine level.
27. At the Tsim Sha Tsui Station the track arrangement at the lowest level is designed so that passengers may transfer between the Kwun Tong and Tsuen Wan Lines by merely walking across a central platform; a three-track terminating arrangement is adopted at the Sha Tin Line level. Detailed design study may, however, show advantages in providing the three-track terminus at Sha Tin instead of at Tsim Sha Tsui.
28. Similar layouts were designed for Kowloon Tong and Diamond Hill stations, where side platforms were used at all levels. The layouts were designed to cater for the anticipated traffic in or out of the station and also for the transfer movements.

CONSTRUCTION METHODS

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Figure 69 — Relationship of Lines to Ground Level

29. Construction of a railway line falls into three basic categories: overhead, underground and surface, the last-named term including lines in cutting and on embankment. Surface construction has limited application within an urban area because of the severance problems in respect of other means of communication. Similarly, it is seldom practical to make much use of overhead structures in dense urban development, such as exists along the north shore of Hong Kong Island and in most of the urban area of Kowloon. The use of overhead construction must usually be limited to low density areas and to areas where development is only just beginning. Figure 69 indicates the extent to which surface, overhead and underground construction methods have been adopted for the recommended system.
30. Most of an urban railway network must be constructed underground, either by bored tunnelling or by cut-and-cover methods. The use of bored-tunnel methods causes much less dis ruption to surface traffic and underground utilities. However, if construction is below the water table, as is quite often the case in Hong Kong, the cut-and-cover method will be cheaper unless the depth of construction is unusually great.
31. Investigations suggest that cut-and-cover will be the more suitable for the greater part of the recommended system. The various cut-and-cover methods are discussed in detail in the appendix, which also contains a more detailed discussion of surface, overhead and tunnel construction.

DESIGN AND COSTING

32. The procedure adopted for estimating was to design a number of basic units for underground and overhead construction and cost all of them. All sections of the proposed routes were then examined, and the basic unit most suitable to the location and ground conditions was selected for each section. The cost of the basic unit being adjusted to allow for particular conditions at each location.
33. Preliminary Investigations — A considerable number of bore hole logs and other soil records were examined to determine the ground conditions over each section of route. These records were supplied largely by the Buildings Ordinance Office of the Public Works Department and by local contractors specialising in ground investigation work. Further information on ground conditions was obtained by visits to sites on the proposed routes where open excavation or piling was in progress. Old maps of the Colony and records of reclamation were examined to assess the likely location of old sea walls, which constitute major underground obstructions, particularly in Central District.
34. It was not possible in the time available to obtain full details of all underground utilities. However, details of all utilities which might affect the type of construction or the vertical alignment of the proposed routes were obtained from the relevant authorities. Also full details were obtained of all the utilities in a section of Des Voeux Road Central; this section contained storm and foul water drains, water and gas mains and electricity, telephone, telegraph and Rediffusion cables and was considered to be representative of the more congested conditions likely to be encountered during construction.
35. Discussions were held with the Traffic Engineering Division of the Public Works Department in order to assess the extent to which roads could be closed to facilitate construction.
36. Surface Construction — Where surface construction is proposed, preliminary designs of earthworks, retaining structures and drainage were drafted and an estimate of cost, taking into account the effect on existing utilities, was prepared for each individual section.
37. Overhead — Most of the overhead sections of the proposed routes are in areas of reclamation where the ground is flat, so there is little need for variation in the height of the structure to obtain the required clearance of 16 feet 6 inches at road crossings. At this height, long spans with correspondingly large depths of superstruc ture would be aesthetically undesirable. In view of the poor founda tion conditions in reclaimed areas, very short spans would not be economic. Designs for running-line structures were therefore based on a span of 80 feet.
38. Preliminary foundation designs were drafted using reinforced concrete piles and assuming ground conditions typical of reclaimed areas. Alternative designs for the T-columns, using reinforced concrete and steel, were prepared and costed. Based on present day prices, the former proved cheaper. For the superstructure, alternative designs incorporating precast, prestressed concrete box girders (one for each track) and composite steel/concrete construction were considered; with the latter, the weight of the superstructure and the cost of the columns and foundations were less but these savings were more than offset by the higher cost of the superstructure.
39. To assess the effect of shorter spans, preliminary designs were drafted for 40-foot spans using similar foundations and substructure but with the superstructure designed as reinforced concrete T-beams; there was no significant difference in cost between this design and that using 80-foot span, precast, prestressed, concrete box girders.
40. Preliminary structural designs were also prepared for two typical overhead stations with reinforced concrete piled foundations, reinforced concrete portal frame supports and precast, prestressed concrete box girders for the superstructure. Spans were reduced to 60 feet, a convenient module for station and mezzanine layout, but a uniform depth of construction was maintained.
41. From these preliminary designs, the costs of overhead construction were estimated on a linear basis for running line and station platforms and on an area basis for mezzanines. In applying these rates to the overhead sections of the proposed routes, allowances were of course made for any variations from the normal superstructure height and span.
42. Underground—Cut and Cover — Preliminary designs were prepared for running line structures with H-pile, sheet-pile and diaphragm wall methods of cut-and-cover construction for various widths and depths below ground level. For each design, various soil conditions were considered but only within the range of conditions for which each method is suitable. Varying amounts were added to the resultant basic costs to allow for the following conditions within each section.
    1. Presence of utilities.
       The problems of construction in Des Voeux Road Central were studied in detail. Methods of supporting the utilities during and after construction and, where necessary, diverting them prior to construction, were examined, discussed with the relevant authorities and costed. The probable extent of this problem in each section of route was assessed and appropriate additional costs were allocated.
    2. Maintenance of Traffic.
       On the basis of discussions held with the Traffic Engineering Division of the Public Works Department, the extent to which traffic would have to be maintained during construction was assessed and the additional costs were estimated. On Hong Kong Island, it was assumed that the trams would continue in operation throughout construction of the Island Line.
    3. Breaking-up and reinstatement of paved surfaces.
       The cost was assessed on the basis of the type of pavement, whether concrete or bituminous; allowance being made for the material required for reinstatement.
    4. Adverse ground conditions.
       The allowance for adverse ground conditions was based on the available borehole information on each section; it took into account the likely presence of boulders and old sea walls.
    The same procedure was adopted in estimating the cost of underground station structures; designs were prepared for side and central-platform stations, both with and without mezzanines.
43. Underground—Bored Tunnelling — In each section where this method of construction appeared to be economic, detailed studies of the costs of construction were made. Where tunnelling in free air and without shields is proposed, costs were estimated on a linear basis since they are largely independent of length and of the time available for the work. However, in the case of shield-driven tunnels, particularly in compressed air, the shields and compressed air equipment form a substantial part of the cost. The estimates were therefore based on the most economic size of contract in relation to the time available for construction.
44. Immersed Tube — Studies showed that this method of construction would be the most economic for the crossing of the harbour, but was unlikely to be competitive elsewhere. The design, method of construction and estimates of cost have been based on those for the proposed cross-harbour road tunnel.
45. Stations — For most stations the basic structural cost, including stairways, was estimated as indicated above. However, individual designs were prepared and costed for Western Market, Central, Admiralty, Tsim Sha Tsui, Mong Kok, Kowloon Tong, Diamond Hill and Ma Yau Tong. The stations at Lo Fu Ngam and Tsz Wan Shan, which must be constructed in tunnel, also required special consideration.
46. At all stations, allowance was made for adequate numbers of access ways between mezzanine and street level, but no attempt was made to locate the exact position of the entrances in relation to surrounding property. At specific stations, allowance was also made for the cost of providing pedestrian subways connecting to bus stations or similar facilities.
47. In addition to the structural costs, estimates were prepared for the cost of station finishes. Finishes in stations would need to be of pleasing appearance, hard wearing and easily maintained. In the mezzanines, a high standard of finish was assumed with quarry tile floors, ceramic tile walls and acoustic tile ceilings. In platform areas, a slightly lower standard of finish, with concrete floors, and painted ceilings, is appropriate. Allowance was made for special treatment below platform level to reduce train noise.
48. Maintenance Depots and Storage Sidings — At a number of locations, underground or overhead storage sidings are required. The necessary structures, site works and buildings have been designed and costed for these and for the four maintenance depots, including the main depot, control centre and administration block at Kowloon Bay.

ESTIMATES

49. The method, and therefore the cost, of construction is largely dependent on the nature of the ground, so the available information on ground conditions was carefully examined. Although extensive soil information was obtained, it was seldom available directly on the rapid-transit route, so it was necessary to interpolate from information in the general vicinity. Also, in some undeveloped areas, there was a complete lack of detailed information. Thus, while it has been necessary to assume a particular method of construction, detailed investigations may prove other methods to be preferable. Where there was doubt as to the best method of construction, the more expensive method was generally chosen.
50. Where more than one method of construction is considered equally suitable, the method with the lowest construction cost is assumed. The exception to this rule is in Nathan Road where more expensive compressed air tunnelling techniques have been assumed for construction between the stations at Waterloo Road and Jordan Road.
51. In the estimate of right-of-way cost an allowance was made for disruption of surface traffic during construction. This includes claims due to unavoidable restriction of access to property as well as less tangible costs which would affect the community as a whole. Should these costs become excessive in a particular area, it could lead to the more extensive adoption of bored tunnelling methods which, while more expensive than cut-and-cover methods at shallow depths, greatly reduce interference with surface traffic and underground utilities.
52. Basis of Estimates — The estimates of civil engineering construction cost include, besides the lines and stations, underpinning and demolition of buildings, ventilation shafts and chambers, drainage, electrical substations, site preparation for maintenance depots, maintenance and workshop buildings, the administration building and station finishes. Costs of track (ballast, sleepers and rails), mechanical, electrical and signalling equipment, rolling stock, maintenance equipment and station furnishings, are given in Chapter 10. The estimates have been based on present day prices and allowances of 2 per cent for site investigations, 8 per cent for engineering charges and 20 per cent for contingencies, have been included in the summaries.
53. Typical Costs — The cost of running line varies considerably according to the method of construction. Surface construction may vary from less than $2,000 per linear yard of double track to over $6,000 depending on the depth of cut or height of fill, the extent to which retaining walls are required and the nature of the ground. Little variation is expected in the cost of overhead construction and it will normally be close to $4,500 per yard. The construction of underground running line will normally vary between $7,000 and $30,000 per yard but, for short lengths, particularly adverse conditions may more than double the cost. These typical costs are net and do not allow for investigations, engineering fees or contingencies.
54. Typical costs excluding investigation, engineering and contingencies, for various types of construction, and different site conditions, are given in the appendix. These tables are included for information only and should not be used to assess the cost of construction for any particular section of route. At first glance it might appear that compressed air tunnelling is cheaper than the diaphragm wall method of construction. However, if tunnels are used where the route is located under a roadway, the cost of stations is considerably increased because of the added depth. The overall cost including stations is less with diaphragm wall construction.
55. Summary of Cost — Table 66 summarises the construction cost by lines. Where a facility, such as a station, is shared by more than one line, the cost has been shared equally between the lines.

CONSTRUCTION

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Figure 70 — Proposed Design and Construction Programme

56. Figure 70 shows the outline design and construction programme for the proposed scheme for stage development. It is based on a decision being taken no later than mid-1968 to proceed with the project. Any delay in reaching this decision would affect the completion date for the first stage but moderate delays to other stages could be avoided by increasing the design and construction effort.

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Figure 71 — Proposed Construction Scheme for Stage 1

57. Figure 71 gives a detailed construction programme for Stage 1. A construction period of about 36 months would be needed for the cross-harbour section. Compressed air tunnelling is recommended for running line between the northern end of the cross-harbour section and Waterloo Road Station and it has been assumed that this tunnelling work would form one contract. The intervening stations would be constructed by cut-and-cover and part of the station structures would need to be completed to provide access before the start of tunnelling.
58. The detailed programme for Stage 1 allows a period of three months for laying track and for the installation of signalling and power supply equipment on each section of running track and between six and ten months for these items plus finishes in stations. The laying of track and installation of signalling devices and power supply should be carried out from the maintenance depot at Kowloon Bay. Thus the depot must be in partial operation at least 18 months before the opening of Stage 1. The programme has been arranged so that, as far as possible, the contracts nearest to the depot are completed first. The section of track from the maintenance depot to Kowloon Tong Station would be completed six months before the start of passenger operations, to allow time for the training of staff.
59. Investigations and Design — The programme allows an absolute minimum period of 18 months, before the award of the first contract, for investigation, design and obtaining tenders. Ground surveys must be carried out before detailed design can start, to determine the nature of the soils along the proposed routes and the extent of underground obstructions. The exact location of all underground utilities must be determined and plotted. Where underground construction is to be carried out close to or beneath buildings, it may be necessary to carry out condition surveys before construction, as a basis for settlement of alleged damage claims.
60. Arrangements for traffic diversions to ease construction will need to be worked out well in advance since they could affect the method of construction as well as the order in which work is to be performed.
61. It may be desirable to invite tenders for alternative designs based on different methods of construction. During the progress of the work, it would be essential for design staff to maintain close liaison with the contractors so that, on later contracts, full advantage can be taken of improved techniques and methods of construction.
62. Contract Procedure — The rapid development of Hong Kong in recent years has encouraged a healthy and capable construction industry, so there is no reason why local contractors should not carry out most of the construction work. However, while there is considerable experience of rock tunnelling in Hong Kong, compressed air tunnelling is highly specialised work, of which little, if any, has been carried out in the Colony to date.
63. Research would be required to determine the optimum size of contract. While large contracts are usually simpler to administer and would attract international contractors, they do not necessarily lead to lower overall costs. Recent experience in the construction of the San Francisco rapid-transit system has shown that lower cost may sometimes be achieved by reducing the size of contracts. In Tokyo, construction of the underground railway system has been based on large numbers of small contracts. There is usually more competitive tendering for smaller contracts, though larger contracts should lead to greater efficiency.
64. Contracts would most probably be awarded on the basis of competitive tendering but consideration should be given to selective tendering and serial contracting, the latter system combining many of the merits of competitive tendering and negotiated contracts.
65. Many public utilities would be affected during construction and careful planning would be essential to maintain adequate services while they were being modified or diverted. Close liaison with the owners of the utilities will be essential at all times. The present system, whereby each company is responsible for variations to its own utilities, could prove to be extremely cumbersome in practice and could lead to higher costs. Critical examination of this problem in consultation with all concerned will be needed in order to devise an equitable solution.

66. Financial Requirements — Table 67 gives the construction cost of the system by stages and the estimated year-by-year financial requirements are set out in Table 68. Usually where parts of a facility, such as a station, come into operation in separate stages, the whole cost has been apportioned to the earlier stage.