Table 5/5 - Classification of Soil and Groundwater Corrosion Properties
8.13 PROVISION FOR FUTURE DEVELOPMENT
The items in the following Clauses shall be addressed in the design and shall be shown clearly and comprehensively on drawings and in supporting narrative in the Development Interface Report.
8.13.1 Knockout Panels for Access to Future Developments
Where access is required to future developments, appropriate provisions for the future openings (generally described as “knockout panels”) shall be made in the structure. In particular the analysis, design and detailing of the structure shall allow for the opening being provided in the future. In addition appropriate trimming reinforcement shall be provided. When such knock out panels are provided, they are to be designed to facilitate future removal as far as practical without compromising the structural integrity or watertightness of the structure before and after the development is constructed. Where possible
other than for structural integrity and serviceability, for future breaking out of openings through diaphragm walls, secant pile walls or similar works constructed from ground level, which are required to have continuous reinforcement to resist lateral ground loading.
8.13.2 Fire Separation for Railway Structures
A four-hour fire separation shall be provided between railway and development areas unless specified otherwise in the Land Transport Authority’s Standard for Fire Safety in Rapid Transit Systems. The minimum thickness of reinforced concrete walls or slabs separating railway and development areas shall be 200mm provided that the area of steel relative to that of concrete exceeds 1%.
8.13.3 Future Development Loads, Structural Capacity and Settlement / Deflection
In developing and completing the design, structural and foundation provisions for support of the future development above and adjacent to the underground structure shall be made.
Future development columns directly over the underground structure shall have their loads supported by the underground structure via column stumps or a suitable transfer structure. Otherwise, the future development columns shall have their loads supported by piled foundations.
Unless indicated otherwise in the Particular Specification, cut off level of all piles and column stumps shall be 2.5m below finished ground level. Pile/column stump reinforcement shall protrude from the cut off level for a lap length and be protected by grade C20 capping concrete.
Alternatively where cover is not available, suitably protected reinforcement couplers may be used, in which case the cut off level shall be 1m below finished ground level.
Where the future development façade fronts a road, all columns provided along the building façade shall be located immediately behind the road reserve (making due allowance for finishes) such that no part of the future column infringes upon the road reserve. Similarly all structural and foundation provisions for support of the columns shall be located behind the road reserve line (making due allowance for construction tolerances) such that no part of the foundation support infringes upon the road reserve.
The minimum characteristic horizontal loads to be designed for at each column shall be the higher of any specified load and 1.25% of the total characteristic dead load on the column. This load shall be assumed to act in any possible direction and therefore shall be designed for the most critical direction. The corresponding minimum characteristic moments to be designed for at each column shall be the higher of any
specified moment, and the moments due to the horizontal load as determined from the above. The horizontal load shall be taken to be acting at the higher of the pile/column stump cut-off level or a level of 4 metres above the top of roof slab, again acting in the direction giving the worst effect.
Column loads from future developments (both characteristic and ultimate) that are to be designed for and their final locations shall be reviewed as part of design development, and agreed with relevant authorities, and shall be recorded on a detailed column loading plan, all to the acceptance of the Engineer.
The structural capacity and predicted settlement/deflection of piles and column stumps at the cut off level corresponding to the appropriate limit state shall be calculated and shown on pile/column stump capacity plans. The design shall demonstrate that the settlement limits specified in Chapter 6 will not be exceeded. Structural capacity shall be specified in terms of maximum horizontal force, vertical force and moment that can be applied at the cut off level of the pile or column stump.
Unless indicated otherwise in the Particular Specification, underground structures shall be designed for development loads together with fill (including water pressure) between the roof of the underground structure and the development ground/base slab (no additional surcharge need be considered over the plan area of the development).
Unless indicated otherwise in the Particular Specification, where the future development includes basements to be excavated below existing ground level, the underground structure shall also be designed for the above mentioned loading without the basements. That is, development loads (minus basement loads) together with fill (including water pressure) between the roof of the underground structure and existing ground level.
These design loads shall be developed onto a roof loading plan for the underground structure.
8.13.4 Design Assumptions and Construction Constraints
An envisaged method and sequence of construction of the future development shall be determined and considered in the design. In this respect, the construction method and sequence should be practicable, cost effective, safe and should cause no disruption to the operation of the railway. In determining an envisaged method items such as those listed in Clause 8.1.2(b) shall also be taken into account.
The envisaged monitoring plan (including the location, type and details
stability and integrity during construction of the future development shall also be considered in the design.
Provisions shall be made in the design to complement the assumptions made in the envisaged method and sequence of construction for the future development.
Where the future development will include basements, the design shall determine safe limits and methods of excavation, restrictions on dewatering, minimum strut loads and permitted strut movements that must be observed to ensure the stability of the underground structure and the safe operation of the railway during the construction of future development, etc.
Any other restrictions to be placed on the future developer in order to preserve the stability and integrity of the station structure and the safe operation of the railway during construction of the future development shall also be determined.
All restrictions to be placed on the future developer shall be practicable and not cause undue additional cost to the future developer.
The effect of the future development on the architecture and electrical and mechanical services shall also be investigated and all necessary provisions made in the design. This interface shall be co-ordinated with the architect and System-wide Contractors.