3 PROJECT DESCRIPTION 3.1 Scope of the Project 3.2 South Apron
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3 PROJECT DESCRIPTION 3.1 Scope of the Project 3.1.1.1 Further to the recommendations of the Option Assessment and subsequent alignment developments detailed in Section 2 of this report, the preferred Trunk Road T2 is shown in Figure 3.1 and will comprise: • a dual two-lane trunk road of approximately 3.0km long with about 2.7km of the trunk road in form of tunnel; • ventilation and administration buildings and a traffic control and surveillance system; and • associated civil, electrical, mechanical, landscaping and environmental protection and mitigation works. 3.1.1.2 The works for the Trunk Road T2 project are grouped under the following major geographical headings: a) The South Apron Section – all works for the Trunk Road T2 Project located at the South Apron of the former Kai Tak Airport, including a ventilation building, a section of at-grade road, a section of depressed road, a section of cut and cover tunnel, a vertical launching shaft for the tunnel boring machines (TBM), a section of twin TBM tunnel and ancillary works. b) The Subsea Tunnel Section – all works for the Trunk Road T2 project in the sea between the South Apron and Cha Kwo Ling, including twin subsea TBM tunnels. c) The Cha Kwo Ling Section – all works for the Trunk Road T2 project located at the former Cha Kwo Ling Public Cargo Works Area (PCWA), including a section of cut and cover tunnel, a vertical receiving shaft for the TBMs, a section of twin TBM tunnels, a ventilation building and an administration building located inside the Lam Tin Interchange. The site formation and road works required to form the Lam Tin Interchange including the administration building, are under the scope of the Tseung Kwan O –Lam Tin Tunnel (TKO-LTT) project. 3.1.1.3 Details of the various elements of the selected Trunk Road T2 alignment are described in the sections below. The general horizontal layout of the preferred alignment is shown in Figure 3.1 while the vertical profile is show in Figure 3.2 – 3.2b. 3.2 South Apron 3.2.1 Site Clearance 3.2.1.1 Site clearance for the works in the South Apron will include the removal of small trees and shrubs, removal of fences and gates across the site. At the location of the proposed Final EIA Report – Section 3: Project Description (F0127-EB000560-MIEL-HKR-02) July 2013 Page 3-1 l:\environ\91164e trunk road t2\reports\public inspection\final eia report\03 project description.doc Barging Point there is an existing temporary structure to be removed at the commencement of the Trunk Road T2 project works. 3.2.2 At-grade Road 3.2.2.1 The proposed Trunk Road T2 starts at an interface with the Central Kowloon Route (CKR) at Chainage 5758m and is a dual 2-lane road. The trunk road continues at-grade for approximately 100m along the South Apron until it passes over the existing Jordan Valley Box Culvert (JVBC). 3.2.2.2 The construction of the at-grade section of road will generate small quantities of excavated materials from the, typically 2 to 3 metre deep, trench works and excavation works for the construction of the drainage network, the roads and the foundations for sign gantries. Small amounts of the material excavated for their construction will be temporarily stockpiled and used to backfill the trenches and sign gantry foundations. 3.2.2.3 The layout of the at-grade section, along with the depressed road section, can be seen in Figure 3.3 and a typical section of the at-grade road given in Figure 3.5a . 3.2.3 Depressed Road Section 3.2.3.1 After the Trunk Road T2 passes over the JVBC it begins to descend, within a depressed road section, for approximately 170m. This allows the level of the road to lower from the existing South Apron ground level of approximately +5mPD to -3.3mPD, at which point the road achieves sufficient depth for the road to be fully enclosed and the depressed road section connects to a tunnel section. 3.2.3.2 The depressed road section of the Trunk Road T2 will be contained within a reinforced concrete “u-shaped” section, consisting of a slab under the road and retaining walls on both sides of the road section. The layout of the depressed road section can be seen in Figure 3.3 and a typical section of the depressed road is shown in Figure 3.5b . The retaining walls will vary in height from 2m high to 10m high, as the road lowers in level, to retain the surrounding South Apron ground level. Tubular or sheet pile walling will be used to support the excavation to allow the construction of the open trough section. The selection of each type of steel pile walling is related to the method adopted by the contractor. It is anticipated that the sheet piles will be extracted and removed from site by the contractor for re-use on other projects or left in place and not require disposal. 3.2.3.3 The existing ground water level on the South Apron is at about +3.3mPD, which is based on the results of the ground water monitoring from KL/2009/02. Therefore, in order to construct the depressed road section in a dry working environment the ground water will be lowered by pumping out of the groundwater within the plan area of the depressed road section. The sheet pile walling will be driven down to a level to enable control of the ground water flow under the excavation such that dry construction conditions can be maintained. 3.2.3.4 The depressed road section will generate approximately 30,500m3 of excavated materials. Based upon a review of the geological profile in this area, all of the material Final EIA Report – Section 3: Project Description (F0127-EB000560-MIEL-HKR-02) July 2013 Page 3-2 l:\environ\91164e trunk road t2\reports\public inspection\final eia report\03 project description.doc excavated will be fill material. This section is proposed to be the last major section of the alignment to be excavated, with the excavated materials being exported off site via the barging point to a public fill site rather than placed in the stockpile works area. In order to handle this material, and the other materials to be exported form the Trunk Road T2 site, a platform will be constructed within the land of the proposed barging point to allow tipping of the material from trucks to barges. The platform will be adjustable to allow for the variation in tidal levels. Good practice dust control procedures for handling the materials will be applied including a 3–sided enclosure on the unloading ramp and water sprays to control dust as the materials are placed in the barges. 3.2.4 Cut and Cover Tunnel Section 3.2.4.1 From the connection with the depressed road section the Trunk Road T2 continues to descend at a gradient of about 5% within a fully enclosed twin cell rectangular tunnel section (refer to Figure 3.5c ), that will be constructed using the cut and cover method. This reinforced concrete cut and cover section is approximately 570m long (from chainage 6050 to 6620) and reaches a road level of approximately -28.6mPD. The chainage 6620 is close to the southern edge of the South Apron, at which point the cut and cover tunnel section connects to the subsea tunnel section. 3.2.4.2 The planned programme of works is such that the cut and cover section for the Trunk Road T2 will commence first with the excavated materials being stockpiled on site or directly removed to Public Fill Reception Facilities (PFRF). The planned stockpile area is for this material is at Works Area 4 (see Section 3.4 below) which has an anticipated capacity of 50,000m3. Once this capacity is reached further material will be exported off site for disposal at PFRF. Throughout the duration of the construction works, the materials within the stockpile will be used for backfilling over the completed sections of cut and cover tunnel and so provide a source of material to be managed by the Contractor to avoid importing fill materials for the project and minimise export of excavated materials from the site. 3.2.4.3 During excavation for the cut and cover sections of tunnel at both the South Apron and Cha Kwo Ling, it is anticipated that quantities of underlying marine muds will be excavated. As these materials are not suitable for disposal at a public fill reception facility (PFRF), they may have to be disposed of to East Sha Chau Contaminated Mud pits. The preferred alternative is that the marine mud is treated on site by mixing with sand and cement such that as much as possible can be used as fill materials for areas such as the future at-grade roads (e.g. under the at-grade Road D4, the location of which is shown in Figure 3.3) or landscaped areas such as in the promenade areas at the former Cha Kwo Ling Public Cargo Working Area (PCWA). 3.2.4.4 For the majority of the cut and cover sections between Chainages 6050 to 6620 (refer to Figures 3.2 & 3.2a ), it is anticipated that diaphragm walling will be used to support the excavation. However, for the section of tunnel in front of the Public Works Central Laboratory (PWCL) (Chainages 6480 to 6560), it is anticipated that contiguous large diameter bored piles will be used to support the excavation and further limit ground Final EIA Report – Section 3: Project Description (F0127-EB000560-MIEL-HKR-02) July 2013 Page 3-3 l:\environ\91164e trunk road t2\reports\public inspection\final eia report\03 project description.doc movement adjacent to the PWCL.