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用建築廢料填海的規格限制

撰文:姚松炎



近日政府官員向區議會介紹東大嶼人工島填海工程的技術可行性問題時提到,可以用本地建築廢料 (技術文件稱為「惰性物料」,一般指拆樓時留下的混凝土物料及磚塊等建築廢料) 作為填海物料,減少用海砂,以解決近期海砂供應不足而且價格飊升等問題。


然而,今日有保育團體代表在報章反駁指,用建築廢料填海有不少缺點,而且技術上有嚴格規格限制。首先,有工程師指出只有60微米至250毫米的惰性物料適宜填海 [1],以確保填海區的穩定沉降,因此,須在本地就建築廢料進行分類和加工,確保尺寸規格協合規定,以現時香港的高工資情況,可以想像利用建築廢料填海的成本不一定比海砂便宜。


事實上,土木工程拓展署就使用建築廢料作填海物料在近年加入了詳細的規格限制,以下為大家介紹土木工程拓展署 (2006) 一般土木工程規格書[2] 中有關用建築廢料作填海物料的規格限制,


首先第6.01條規定填海工程須符合第21章的規定,除非第6章另有規定。而第21.03條有關填海料的規格則詳列於第6.09條。近年第6.09條加入了容許惰性建築及拆樓物料用作填海料的規定,第6.05條定義惰性建築及拆樓物料為建築及拆樓時所產生的石料、泥、石屎、瀝青、磚石等[3],但必須屬可以壓實至符合可填出穩定面積的要求 [4],而且不能含有會出現體積變化的物料、有機物、木材、危險、有毒或易燃物料、金屬、象膠、塑膠或合成物料。[5] 關於填料尺寸則在6.09(3)及表6.1有所規定,2009年4月加入了有關Grade 200的循環再用石填料的尺寸限制,規定須要100%不超過200毫米,詳見圖1。[6] 另外第6.09(6) 亦有石填料尺寸規定,最大塊石料不能比最細塊的尺寸大三倍。[7]

第7條對Grade 200的循環再用石填料作出定義,為循環再用的石材或惰性建築及拆樓物料,而必須堅硬、耐用及沒有裂痕、根脉及其他分解跡象。[8] 其他規格還包括填料的可溶性硫酸鹽含量 (6.09(9)),總硫酸鹽含量 (6.09(10)),均勻系數 (6.09(11)(12))。


換言之,並非任何的建築廢料均可用作填海物料,若須符合所有規格,必須經過多項分類及/或加工過程才可用作填海料,在香港進行這類工序所需的工資相信會非常昂貴,政府官員理應向區議會補充有關使用建築廢料填海所需的分類和加工成本,以免誤導區議員及公眾。


而且,本地的拆樓物料數量有限,除非把填海工程延期完成,否則短時間內難以滿足東大嶼人工島的填海體積需求。譬如2017年全年的建築廢料量只有154萬公噸 [9],即使全部可以用作填海,亦只夠填少量東大嶼人工島的填海量,如果全部用建築廢料填海,可能須要更長時間才能完成工程,令時間成本和利息成本大升,政府官員也應詳細向區議會解釋有關現時的廢料存量和相關的利息支出和存倉費用與海砂填海成本的差別,讓公眾作出最佳決定。


[1] Yam, T. (2019) Carrie Lam’s Lantau Tomorrow plan is shortsighted on cost and sources of fill material for reclamation, Letters, SCMP, 15 Mar. https://www.scmp.com/comment/letters/article/3001622/carrie-lams-lantau-vision-biggest-reclamation-world-and-we-are (“For this particular project, the team has looked into, apart from the primary and secondary consolidation, the behaviour of public fill material to achieve the ‘acceptable’ serviceable limit. Deformation behaviour includes the creep behaviour of the public fill which consist primarily of man-made fill, alluvium and CDG. The result is a sorted public fill material with a maximum size of 250mm and a minimum of 60 microns, to limit the settlement no larger than 500 mm over a period of 50 years.“ cited from Cheng, A.T.N., Bok, A.K.M., Lee, D. and Yin, K.K. (2010) Towards a Sustainable Reclamation for Hong Kong, Environmental Paper Award, HKIE Environmental Division, http://hzmb.hk/text/schi/doc/Envir_Paper.pdf)


[2] CEDD (2006) General Specification for Civil Engineering Works, HKSAR Government. https://www.devb.gov.hk/en/publications_and_press_releases/publications/standard_contract_documents/index.html


[3] “6.05 Inert construction and demolition material shall mean rock, rubble, earth, soil, concrete, asphalt, brick, tile and masonry generated from construction and demolition works.“ (CEDD, 2006)


[4]“Earth Works: Fill material 6.09(1) Fill material shall consist of naturally occurring or processed material, or inert construction and demolition material [italics are added in new edition], which at the time of deposition is capable of being compacted in accordance with the specified requirements to form stable areas of fill.“ (CEDD, 2006)


[5] ”6.09(2) Fill material shall not contain any of the following: (a) Material susceptible to volume change, including marine mud, soil with a liquid limit exceeding 65% or a plasticity index exceeding 35%, swelling clays and collapsible soils, (b) Peat, vegetation, timber, organic, soluble or perishable material, (c) Dangerous or toxic material or material susceptible to combustion, and (d) Metal, rubber, plastic or synthetic material.”(CEDD, 2006)


[6] “6.09(3) The different types of fill material shall have the particle size distributions within the ranges stated in Table 6.1.“ (CEDD, 2006)


[7] “6.09(6) Rock fill material shall consist of pieces of concrete or hard and durable rock of which the maximum size shall not be greater than three times the minimum dimension of individual pieces and in the opinion of the Engineer not more than 30% by mass is discoloured or shows evidence of decomposition.“ (CEDD, 2006)


[8] “6.09(7) Recycled rock fill material (Grade 200) shall be recycled rock or inert construction and demolition material which is hard and durable, and free from cracks, veins, and other evidence of decomposition.“ (CEDD, 2006)


[9] ”The quantity of overall construction waste disposed of at landfills in 2017 was 4,207 tpd (1.54 million tonnes), which has decreased by 4.9% compared to 2016. In recent years, the reuse rate of inert materials sorted out from construction waste has remained at above 90%, and was 92% in 2017. These materials were delivered to the public fill reception facilities and other outlets for beneficial direct reuse.” https://www.wastereduction.gov.hk/sites/default/files/msw2017.pdf