Refer to hierarchy abovementioned in Section 1, a further explanation of the hierarchy of waste management on site is detailed below.
3.1.1 Hierarchy of Waste Management
Key to waste management is to reduce the amount of waste generated from the work site. Waste management options would be exercised in accordance with the hierarchy stipulated in the following table:
|
Avoidance and Minimization |
Avoid and minimize waste through careful planning and design works. |
|
Reuse |
Reuse construction waste such as excavated material, used wooden plants and ferric materials. |
|
Recovery and Recycle |
Undertake on-site or off-site waste recycling. |
|
Treatment and Disposal |
Properly treat and dispose of waste in accordance with legislative requirements, guidelines and good practices. |
Table 3.1: Hierarchy of Waste Management
In the context of waste reduction, environmentally responsible purchasing would involve the introduction of practices that discourage unnecessary purchases and encourage the purchase of products with reduced packaging, increased durability and materials with high recycled content, such as, recycled paper, steel and other raw construction materials.
Waste minimization is best achieved through careful planning, design and supervision. Good management practices would reduce and prevent large amount of waste generated. Raw materials would be managed from the first instance before they are ordered and delivered to the site. Good estimation and planning would minimize the amount of raw materials wasted. The generation of waste would be controlled at source.
Specific measures will be implemented to reduce the generation of waste materials, and thus minimize the amount of waste disposal to landfills. The measures will include:
Sorting on site to recover the inert portion of C&D materials;
Recover all metallic waste for recycling;
Recover all cardboard and paper packaging, and properly stockpile them in dry and covered condition to prevent cross contamination;
Use of the materials (such as formworks and hoardings) in the construction would be calculated before purchasing in order to minimize waste generation.
Use of metal formworks and hoardings, and they would be recycled after demolition on site as far as it can before disposal.
Construction & Demolition (C&D) materials will be generated from excavation and construction of bored pile foundation and substructures. Most of the C&D materials will be sorted and reused; however, the marine mud, estimated at about 22,450m3 has very limited usage on site. In order to recycle and reuse of the marine mud, a Cement Solidification/ Stabilization of Marine Mud technique will be applied.
For conserving transportation costs and environmental concerns, the cement S/ S process will be taking place on site in a specified contamination zone. Special safety and environmental control measures will be implementing in the stockpiling and treatment area of marine mud.
At the early stage, pilot trial will be carried out to determine an optimum mix proportion with considerations of actual field operations, workmanship, compliance with quality control test, maximization of the use of marine mud and the mechanical property. To maximize cost effectiveness and environmental conservation, the optimum mix should contain minimum content of Portland cement, maximum content of marine mud and adequate content of granular material. Furthermore, it should be workable by conventional mechanical compaction method while backfilling.
In the operation stage, initial screening of the excavated marine mud should be taken place at the anticipated generation area. Corresponding arrangement of supervision, handling and transportation should be also in place. For the sake of minimizing the contaminated zone, only 2 metal tanks and a conventional backhoe will be used to achieve an approximate daily production of 300m3 cement S/ S marine mud : in a mixing ratio of 5% cement, 15% granular fill and 80% marine mud. In case of the marine mud generation rate > the treatment rate, this production rate could be increased by a mass production approach.
Post production stage, for the quality control purpose, one sample per 100m3 of materials will be taken for making test cubes for analysis of at least 7-day UCS, plasticity index, and liquefied TCCP. Besides, for the quality control of workmanship of compaction, test for relative density in a sampling rate of 3 nos. per 100m2 should be carried out as normal backfilling practice. The compacted material will be tested for 7-day SPT. One drill hole per 100m3 of backfilled materials will be sunk and tests were conducted at 1.5m deep interval inside the backfilled material.
Refer to our past experience, all test results were “Passed”. It demonstrated the CSMM treatment and the application were practical in fulfilling both of the environmental and works related requirements.