Tsuen Wan Drainage Tunnel

to meet current and future needs a flood protection strategy was chosen by the drainage Services Department this will avoid disruption to the highly populated urban areas of chunan and minimize interferences with existing infrastructure the storm water transfer strategy is to intercept and convey surface runoff from the copper catchments before it enters the lower urban areas and direct it through a tunnel to discharge into the sea a rambler channel the 5.2 km long drainage tunnel stretches from woi hop in the East to Yao camt to the West the 6 and 1/2 M diameter drainage tunnel will be constructed using a double shield Hard Rock Tunnel boring machine or TBM the tunnel Drive will pass through three geological interfaces 18 identified fall zones the tunnel will be constructed predominantly in hard rock with the majority of the alignment between 30 and 200 M below ground level at intake I3 there will be relatively Low cover the tunnel will be only 15 M below the existing stream course the tunnel Drive will run concurrently with the site formation works at the intake sites the added to the tunnel breakthrough will be completed after the TBM has passed to minimize potential water Ingress during the construction of the tunnel forward probing and pre-excavation grouting will be carried out the TBM will operate for 20 hours a day 7 days a week with an average production of 13 m per day the spoil generated by the tunnel excavation will be approximately 225,000 cubic M the tunnel spoil handling system is a continuous conveyor system which will extend from the portal to the backup decks of the TBM the outfall at yaam toau forms the point at which the drainage tunnel will discharge the storm water into ramler Channel the site is on a slope of partly natural and partly mad main terrain immediately adjacent to Castle Peak Road the site has several significant constraints such as the gradient limited Works area and proximity to existing residential structures including green View Terrace drainage facilities and Highway [Music] structures The Works consist of the tunnel portal outfall structure and Associated slope Works a box Culvert and access ramp seabed protection works and the construction of infrastructure to support tunneling operations the tunnel portal will be constructed by open cut method to the tunnel invert level following the completion of soil nail slope stabilization works and the pipe pile walls due to the constrainted site and its proximity to Castle Peak Road it will be necessary to assemble the TBM in stages on a working platform outside the tunnel portal the tapered open Channel forming the the site formation work will be used as a TBM assembly area with additional space provided by an elevated steel [Music] structure the provision of a full noise enclosure is envisaged to screen the tunnel portal activities from sensitive receivers adjacent to the site the tunnel spoil handling conveyor system will also be housed within acoustic enclosure at the portal spoil generated during the evening and nighttime will be stored in an overnight spoil storage [Music] area the Box culbert will be formed under Castle Peak Road by means of horizontal pipe pile [Music] methods intake I3 Works involve the construction of the 8 m deep Vortex chamber an Associated approach Channel a 5 m deep drop shaft added deoration chamber maintenance access shaft and air vent shaft and a temporary River diversion wall for the construction Works an open cut method will be used for the excavation of the shafts maintenance access Vortex structure and the Eastern portion of the deoration chamber the Western ption of the deoration chamber will be excavated in a heading and bench sequence using mechanical tling methods the connecting added to the drainage tunnel will also be excavated in a heading and bench sequence as the addit is located below the existing stream bed and the rock cover is expected to be low pre-excavation gring may be necessary to control water inflow and to increase stability of the excavation temporary support including Rock bolts and shock crate will be installed as required for the ground conditions encountered during the excavation the inlet channel will be constructed in the dry [Music] season intake I2 is located on an existing stream course adjacent to an elevated Bridge along loway Road and next to Hong Chi Hong Temple an old masonary wall is located at the Western embankment of the river Channel works at I 2 involve Channel modification works construction of a retaining wall on the western side of the channel a Vortex chamber and its Associated approach channel the drop shaft and underground duration chamber and the maintenance access shaft and tunnel a temporary steel deck will be erected for the construction of the H pile wall to enable Channel widening since the construction of the drop shaft and Associated Works cannot be completed in a single dry season the existing stream channel will be widened to provide sufficient weight for water flow in the wet season Rock excavation inside the drop shaft man access shaft and other underground elements will be by mechanical excavation techniques the maintenance access shaft will require excavation in both soft BR and rock pip piles will be installed to provide lateral support for the excavation in soft ground the soil will be excavated using a grab the excavated rock material from the lower section of the shaft will be removed by a crane using a Muk skip the inclined man access tunnel will be excavated from the bottom of the access shaft on completion of the drop shaft the deoration chamber will be excavated in three stages with a heading and two benches the connecting added to the drainage tunnel will be excavated as full face the permanent concrete lining of the adders man access tunnel man access shaft and drop shaft will start after the completion of the underground excavations the construction of the intake structure and approach Channel requires temporary and partial diver version of the existing stream course The Works will be carried out in stages with the necessary Channel FL diversion Works in place intake i1 is located on a steep natural slope in close proximity to the shingun and woi hop channels Works in intake i1 involve construction of a temporary copper Dam a spiral access ramp Ranch access between the spiral ramp and the Box Culvert a Cascade and a 21 1/2 M long box Culver to connect to the main tunnel the temporary access road to the works area will allow installation of the pipe pile copper Dam on the fill slope further piling will be installed from a temporary steel deck excavation for both the spiral ramp and box culber will be in the soft CR and rock lateral support will be formed by the pipe pile walls with struts and wailings a grout curtain will be required around the perimeter of the pipe pile wall to prevent the Ingress of water during excavation the position of the struts in the Box culbert will be designed to suit retrieval of the TBM at completion of the tunneling site access will be maintained from woi Hop road to the Box cul area via steel deck over the existing y hop drainage channel the construction of the intake will begin with the concrete spir ramp followed by the construction of the stepped Cascade box Culvert and linking access concrete will be placed by a concrete pump truck from the elevated working [Music] platform