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A newsletter published by Projects Division, MTR Corporation

P. 5 - 6 The Application of RFID for XRL Contract 816A Environmental Control System無線射頻辨識於高鐵工程合約816A環境控制系統的應用

P. 7 - 8 WIL & SIL(E) - “In Case of Fire; Do Not Use the Lift” True or Not?在西港島綫及南港島綫(東段)新站「如遇火警，切勿使用升降機」是對是錯？

Dec 2013Issue No.33

P. 9 - 10 SIL(E) 3 Months Early Degree 1 Access for WCH and OCP南港島綫 (東段)黃竹坑站及海洋公園站提早3個月取得「進度一」

People Development Collaboration & Trusted Partnership Projects Delivery Effectiveness

SCL Contract 1106 Pillbox Relocation沙中綫工程合約1106 碉堡遷移

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Lee Blade Sr Construction Engr-Civil 高級建造工程師–土木

Background

A pillbox constructed during the Second World War and located in the Tai Hom Village site was found to be in conflict with the diaphragm wall works for the new SCL station at Diamond Hill. In order to preserve this structure, it was decided to relocate it in one piece to a storage location at the edge of the worksite boundary. From initial surveys it was found to be constructed from a weak concrete base of varying thickness and hollow concrete blocks forming the walls. The blocks were interlocked but without mortar in the joints. The roof is a lightly reinforced concrete dome found to be of very low grade weak concrete.

The Planning

A plan was developed between MTR, the contractor, design teams and Government departments to support the pillbox and transport the whole structure on a flatbed trailer. The structure was analysed to determine how much movement the structure could withstand without causing failure, and a series of monitoring trigger levels was established. Experts from the UK in the field of ground movement monitoring were consulted and it was agreed that further monitoring by fibre optic cable should be utilised for the safety of the structure. This is a relatively recent development, and a company from Switzerland were contracted to perform the measurements.

Fibre Optic Monitoring

A fibre sensor cable of up to 70m in length was installed around the inside of the structure, and at least 10mm of sensor was fixed to the inside wall with epoxy glue at intervals of 50mm to 100mm. At every location where the sensor is fixed the strain development is monitored to detect movement. Readings were taken hourly at first and more frequently at crucial moments of the construction and during the transportation.

Project Link Issue No.33December 2013

People Development Collaboration & Trusted Partnership Projects Delivery Effectiveness

3D model of the structure during the planning stage survey規劃階段測量時碉堡結構的立體模型

The pillbox before relocation works commenced遷移工程開始前的碉堡

Close up of the sensor cable showing the epoxy glued sensor locations感應線的近貌，顯示以環氧樹脂膠固定的感應器位置

Fibre optic sensor cable installed inside the pillbox安裝在碉堡內的光纖感應線

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Project Link Issue No.33December 2013

Support Work

A steel framework was constructed around the inside of the pillbox to support the dome roof. Eight steel H-Piles were driven down 12m into the ground, four on each side of the pillbox. These would eventually act as stilts that would support the pillbox before transportation.

A concrete retaining ring wall was cast around the pillbox base to a depth of 500mm to retain the soil the pillbox base is sitting on. The retained soil was grouted with microfine cement to bind it together and effectively strengthen the base. The grouting pressure was kept low and no movement in the structure was detected.

A continuous horizontal pipe pile raft was constructed under the pillbox with only 500mm of cover to the base slab. Drilling speed was kept low to prevent heave damaging the structure. During this time a steel plate wrap was formed around the outside of the pillbox to prevent the block work wall

construction from moving due to the lack of mortar in the joints.

The pipe piled raft was to be supported on four steel beams placed perpendicular to the pipe piles and welded to the H-piles at each end. The two ends were excavated and supported on the steel work with simple construction. For the two beams in the middle of the structure, two timber headings were constructed and the beams placed inside. This minimised the amount of excavation before all four beams were installed and welded to the H-piles. The structure was now supported on the raft and connected to the H-piles acting like stilts.

Bulk excavation under the pillbox could now commence, settlement by this point was approximately 7mm in uniform settlement across the structure. By the end of the bulk excavation this had stabilised at a maximum of 16mm. Again very little differential settlement was seen and the strain inside from the fibre optic was still showing no movement.

Once excavated a haul road was constructed under the structure all the way to the temporary storage location. A flatbed trailer was brought with the capability to individually adjust the suspension on each of its 36 wheel sets to ensure the pillbox structure was not put under stress during the move.

Transportation

Once the flatbed was in place under the structure the rear two H-piles were cut. Once this section of the structure settled, strain was detected in the entrance section of the pillbox by the fibre optic monitoring. The flatbeds hydraulic suspension was adjusted such that the pillbox structure was brought back up to the original position and the strain removed. The front two H-piles were then cut and the hydraulic suspension again adjusted to level the structure. The middle four H-piles were cut two at a time and the structure was ready to move.

Pillbox excavation and installation of supportive beams碉堡挖掘及安裝支撐結構樑

Timber heading under the pipe piles and the beam installed supported by H-piles

管樁之下的木材管道及由工字樁支撐的樑柱

Horizontal pipe piled raft under construction正在建造中的水平管樁筏

End beam in place under the pipe piles and supported by the H-piles at each end

管樁之下的尾樑，每端以工字樁支撐

4People Development Collaboration & Trusted Partnership Projects Delivery Effectiveness

Project Link Issue No.33December 2013

Pillbox showing the 4 beams supported on H-piles, concrete base for the flatbed under construction

碉堡坐落在以工字樁支撐的四條樑，平板拖車的混凝土板建造中

Flatbed in place ready for cutting the H-piles prior to transportation平板拖車已在位，準備好在運送前切斷工字樁

Pillbox being transported to the storage location via flatbed trailer碉堡以平板拖車運到儲存位置

Pillbox relocation complete and awaiting the protective shed to be constructed碉堡遷移工程完成，正等待建造保護棚

背景

一個位於大磡村在第二次世界大戰建造的碉堡，對沙中綫鑽石山站的隔牆工程造成阻礙。為了保留這個建築物，整個碉堡將遷移到近工地邊界的位置存放。初步測量顯示，碉堡的地基由厚度不一的低強度混凝土建成，牆身是空心混凝土塊。這些混凝土塊互相扣鎖，但在接口位置沒有使用灰泥。頂部是輕鋼筋混凝土圓拱頂，材料是極低強度混凝土。

遷移計劃

港鐵、承辦商、設計小組及政府部門共同制定了支撐及運送整個碉堡移到平板拖車上的計劃。小組分析碉堡結構，以決定其出現損毀之前可以承受多少移動，並訂出了一系列的監測戒備水平。來自英國的地面移動監測專家提供了意見，認為應使用光纖線作進一步的監測，以保護碉堡結構。這是新近發展的技術，一家瑞士公司獲聘進行量度。

光纖監測

小組在結構內部安裝一條長達70米的光纖感應線，最少有10毫米的感應器以環氧樹脂膠按50至100毫米的隔距固定在結構內牆。在裝有感應器的每個位置，其應變的增長都得到監測，以偵察其活動。起初儀器的讀數每小時讀取，其後在建造及運送階段的關鍵點則更為頻密。

支撐工程

小組在碉堡內部建造了一個鋼架以支撐圓拱頂。八支工字鋼樁分別在碉堡兩則，各四支樁打進地下12米深處。這些鋼樁最終會成為支柱，在運送前支撐着碉堡。

碉堡底部四周鑄了500毫米深的混凝土扣環牆，以保留碉堡地基之下泥土。保留的泥土以微粒混凝土灌漿，使其黏緊並有效地加固地基。灌漿的壓力維持在低水平，並偵察到結構沒有移動。

連續水平管樁筏在碉堡之下建造，距離底板只有500毫米。鑽挖以低速進行，避免結構受損。在這個階段，小組在碉堡外部建造了鋼板外罩，避免石塊牆的結構因接口沒有加上砂漿而移動。

管樁筏以四支鋼樑支撐，與管樁形成直角，兩端焊接在工字樁，然後兩端被挖掘起來，透過簡單的建造方式以鋼材結構支撐。結構中央的兩條鋼樑放置在已建造的兩條木材管道，這減少了四條樑於安裝及焊接在工字樁之前的挖掘工作。結構以筏支撐着，連接發揮支柱作用的工字樁。

在碉堡之下的大型挖掘階段，土地沉降為整個結構一致大約7毫米。大型挖掘完成後，沉降穩定為最大16毫米。不均勻沉降很少出現，來自光纖的應變仍沒有顯示任何移動。

碉堡挖掘出來後，在結構之下建造了運輸路綫，直通至臨時安置地方。小組使用36個輪組均可以獨立調校的平板拖車，確保碉堡結構在運送時不會受壓。

運送過程

平板拖車設置在結構之下後，末端的兩支工字樁就會被切斷，這部分的結構就會降下，光纖監測儀器在碉堡的入口部分偵察到應變。平板拖車的液壓懸掛系統會相應調整，令碉堡結構回復原本的位置。然後，前方的兩支工字樁會被切斷，液壓懸掛系統再次調整，令結構保持水平狀態。中間的四支工字樁同時被切斷後，結構就可以被運走。