3 Ngong Ping 360 John Batchelor, Suresh Tank 15 Waste as ... - Arup

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13. Roof structure at angle stations. For the roof structure, three alternative schemes were compared to identify the most economic solution, as opposed to the large portal frame structures originally proposed, which formed the basis of the target cost contract during Stage 2 for both the AIAS and the NLSAS. The final scheme adopted is a trussed frame (Fig 13), which simplified connection details and only amounted to about half the steelwork weight of the Stage 2 scheme. Columns and bracing along the central gridline were limited to locations agreed with the ropeway designer. Towers General There are eight towers in all, five of them in the country park (Towers 3, 4, 5, 6, and 7). The building and civil engineering contract 5201 included construction of the foundations and pilecaps within Arup’s scope of works. Arup also took over all natural terrain hazard assessment and mitigation works associated with the foundation design in the country park, including identification of hazards, boulder surveys, rock joint mapping, design of mitigation measures like soil nailing and boulder stabilization, and regulatory approval processes. Foundations Vertical pre-bored H-piles were adopted for Towers 1 and 2B, and a combination of vertical and raking minipiles for Towers 2A and 3-7, with rock sockets to resist tension and compression. Minipiles were the preferred option for works in the country park as they could be installed with small rigs. A typical tower foundation comprises a series of vertical and raking minipiles in two directions under a single pilecap supporting each tower leg. The ropeway designer supplied data on the most critical loads for each support, including the effects of dead load, imposed loads, wind, and earthquake loads (as required by MTRCL) from both the tower steel superstructure and the cable car system. The maximum and minimum loads in each of the three axes, together with co-existing loads, were analyzed to give all possible load combinations from the superstructure and the cable car above. Hundreds had to be assessed so as to determine the loads in the piles and for the design of the pilecaps. 14. Tower 2B. 492.0m Tower 4 49m Table 1: Tower and station distances Tung Chung terminal Tower 1 Tower 2A Airport Island angle station Tower 2B Tower 3 Tower 4 Tower 5 Nei Lak Shan angle station Tower 6 Tower 7 Ngong Ping terminal Table 2: Tower heights Horizontal distance Tower 1 37 12 2.5 Tower 2A 21 7 2.5 Tower 2B 50 16 2.5 Tower 3 17 7 7 Tower 4 49 16 2.5 Tower 5 44 13 2.5 Tower 6 27 9 2.5 Tower 7 46 16 4 * Below tower head Tower height in the axis Inclined distance 1 16 117 355 355 51 52 86 88 1490 1512 1048 1063 83 3 838 29 30 161 161 96 9 974 38 6 388 Tower width at base Tower width at top* The Arup Journal 1/2008 9
10 The design of Tower 7 proved the greatest challenge to the project team in devising a solution, taking it through the BD approvals process, and obtaining consents for construction over a fault zone. Based on the ground investigation provided by MTRCL (three boreholes and trial pits near the Tower 7 location), Arup’s foundation design comprised vertical and raking minipiles socketed in rock a few metres below ground level. This was approved by the BD and consent was granted. After BD approval and consent of the foundation pre-drilling, however, some of the early pre-drill holes revealed a rockhead level significantly lower than that anticipated from the original ground investigation holes. A total of 29 more holes were then drilled on a plan area of 45m x 45m to provide additional information for reviewing the ground conditions at the tower location. A 3-D geological model for the tower was developed using data from all the boreholes and drill holes. The depth to the grade III rockhead was found to be extremely variable (7.6m to more than 60m), which was interpreted as being due to the presence of a fault zone at the tower. The Arup Journal 1/2008 15. Tower 2A. Tower 7: foundation design 17. Geological model showing transfer beams spanning across the fault with minipiles (red) founded in grade IV or better rock. 16. Tower 4. 838m 18. The completed Tower 7 showing the extent of slope stabilization, and the tower plinths. Relocating it was not an option, as this would have had huge impact on cost and programme: the changed alignment would have meant the redesign by the ropeway designer of the towers, a requirement for additional land for the tower, further ground investigation and submission to the BD, a redesign of the tower foundations and stabilization measures, and further approvals. A raft spanning across the fault was also considered, with minipiles beneath it for stability. However, this option was ruled out due to the requirement for a large volume of concrete in a remote area with difficult access, the extra cost and programme implications, and impact on the stability of the existing slope due to the additional load of the raft. The solution adopted, therefore, was a fourbeam transfer structure spanning across the fault zone and supporting the four plinths of the steel tower (Fig 17). The transfer beams are supported on raking minipiles (18.4° to the vertical) and carefully located away from the fault zone in grade IV/III or better rock. With a lot of effort from the design and construction team and the MTRCL, the geological model was agreed with the appropriate approval departments. 19. Towers, the rescue trail and Nei Lak Shan angle station. 20. Tower 3.
Page 1 and 2: 2 The Arup Journal 1/2008 Contents
Page 3 and 4: 4 Background Ngong Ping is an impor
Page 5 and 6: 6 7. Tung Chung terminal building a
Page 7: 8 11. Nei Lak Shan angle station an
Page 11 and 12: 12 25. Detail of rescue trail timbe
Page 13: 30. Ngong Ping Village. Conclusion

3 Ngong Ping 360 John Batchelor, Suresh Tank 15 Waste as ... - Arup

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