Doha South Sewage Infrastructure project – Main Trunk Sewer

 

CEEQUAL Good – Design & Construction Award
Version 5, June 2019  | Qatar

Client: Ashghal – Public Works Authority
Designer: AECOM Ltd and Bouygues
Contractor: Bouygues

Assessors: Aza Elnimah and Timothy Bell (KEO International Consultants)

This slideshow requires JavaScript.

Project Summary

The Doha South Sewage Infrastructure project is a world class solution to upgrade and expand the sewerage infrastructure in Doha’s oldest area-the south catchment. The purpose of this is to accommodate the projected population growth for an additional one million people. The project is strategic in nature and was developed to change the entire approach to foul sewer drainage in the Doha South catchment from a pumped network to a gravity sewer network. The aim is to address, amongst other things, serious environmental and health issues resulting from undersized and aged sewerage drainage infrastructure in the Doha South catchment.

The Main Trunk Sewer (MTS) is a major element of the Doha South Sewage Infrastructure project. The MTS is a gravity-based sewage system that conveys the sewage to the Doha Sewage Treatment Plant (STW). It is designed conservatively to assure that it can adequately convey low flows without accumulation of solids, which could otherwise become a maintenance issue. MTS is also sized to meet projected flows for its 100-year design life. MTS is designed in such a way that it is self-cleaning. MTS has no pumps, valves or any other mechanical or electrical components within the sewer or associated structures. MTS was constructed using Tunnel Boring Machines (TBMs) that required a limited number of shafts, ultimately limiting adverse impacts to the environment.

By addressing and resolving serious environmental and health issues resulting from undersized and aged sewerage drainage, the Doha South Sewage Infrastructure Project both supports and contributes to achieving the Qatari National Vision (QNV) 2030. The Qatar National Vision 2030 aims to transform Qatar into an advanced country capable of sustaining its own development and providing a high standard of living for its people.

Project Management

Both the Designer (AECOM) and the Contractor (Bouygues) had their own sustainability procedures implemented into their code of practice. This documented commitment supported the implementation of sustainability throughout the cycle of the project. Furthermore, both the Designer and Contractor are ISO14001 certified meaning they each have their own effective environmental management system which lent itself to managing the design and construction of MTS. At the project management level environmental risk and opportunities were identified, recorded, and prioritized according to their significance throughout the course of the project. Finally, the project team understood the innovativeness of this project to the region in terms of ‘sustainability management on mega-projects’. In so, the team actively participated in sharing best practices and lessons learned with fellow members of the civil engineering sector. This was carried out through various mediums such as news paper articles, presentations in conferences, and published research papers.

Land Use and Landscape

Due to the nature of the project being a tunnel, the surrounding land uses had a tremendous influence on the route and construction methodology of MTS. An optioneering report was developed for the client whereby 10 different route options were presented. The report included a ‘Multi Criteria Decision Making analysis (MCDM)’ which looked at the environmental and social implications of each of the 10 routes. Factors assessed included the characterization of the areas, environmental setting, sensitive receptors, historic land uses, social sustainability aspects, land use efficiency, as well as effects on neighbours. These factors were compiled on a scoring sheet, the scores for each option were assessed by multiple reviewers and the best performing route was selected. Subsequently, a geotechnical investigation was carried out for the selected route. The site-specific subsurface geo-investigation and report ensured the client about the suitability performance of the chosen route. The land use and site selection for the route were rigorously assessed and the best-case scenario route in terms of environmental and social performance was selected. In so, land use efficiency was maximized for the Doha South Sewage Infrastructure project MTS project.

Ecology and Biodiversity

The Environmental Impact Assessment as well as the Pre-Construction Ecological survey both concluded that the site was of low ecological value. The CEMP provided a plan to prevent any further harm to the ecological environment and protect any existing trees.

The Water Environment

The design of MTS takes particular measures to protect groundwater from any potential contamination. The MTS tunnel is designed with three layers of redundancy to prevent leakage including grouting on the outside of the pipe, the pipe itself and an HDPE membrane inside the pipe. The EIA concluded that based on these design features the risk of potential leakage was of ‘no significance’.

In terms of construction, the protection of the groundwarer is embedded into the contract. The contract states that ‘active dewatering is not permitted’. This condition had a tremendous impact on the project because it obliged the Contractor to use efficient construction methodologies such as D-wall, VSM, and grouting in the shaft construction. This significantly decreased the amount of dewatering required for the project ultimately minimizing groundwater depletion.

Physical Resources – Uses and Management (Energy, Water, Materials, Waste)

Energy
In terms of design, MTS requires no pumping because it is a completely gravity based system meaning it uses zero energy in operation.

During the construction process the Contractor maximized opportunities to use energy efficiently. A Carbon Footprint Management plan (CFM) was produced and incorporated into the CEMP. The CFM included strategies to reduce overall energy consumption such as the selection and maintenance of efficient generators on site. Other strategies that were implemented were, the use of lithium ion batteries for the TBMs, the use of solar panels to operate all cameras on site, and the use of LED lighting in tunnel. Futhermore, fuel was tracked and reported on a monthly basis in order to benchmark the project and study trends.

Water
Through its design the MTS completely eliminates the use of water during operation. The MTS replaces the exisiting sewage pumping stations with a gravity based sewage system. The MTS adequately conveys low flows without accumulation of solids and is simultaneously self-cleaning. The MTS has no pumps, or valves within the sewer or associated structures.

During the construction process specific and measurable requirements were implemented to minimize the projects impact on water resources. Within the site offices, flow and flush fixtures were all lowflow and plastic bottles were completely ban.

Water was efficiently used for construction activities. As per the Dewatering Management Plan and the Water Quality Control Plan, dewatered water was treated and reused in order to minimize the use of potable water. A primary and secondary lagoon were set up on site to facilitate the groundwater treatment, reuse, and disposal process. Treated dewatering effluent was mainly reused for dust suppression, concrete curing, soil compaction, cleaning, as well as tunnel boring and grouting.

Furthermore, in order to maximize the efficient use of water the contractor collected and reused rainwater onsite. Rainwater was also collected by gravity into two underground tanks which were equip with oil separators. The collected water was then pumped into a tanker and moved to the primary lagoon whereby it went through the same treatment process as groundwater. After this process the rainwater was reused on site.

Materials
The tunnel segments for MTS were all prefabricated and locally manufactured near the project site. Prefabrication provided precision in terms of material procurement and waste reduction. Furthermore, the material quantities used in the shaft design were optimized. The designer reduced the concrete thickness of the shaft walls from 200mm by alternating thickness based on soil/geotechnical conditions. Lastly material forecasts were carried out and reported on a monthly basis. The end of project report shows that the planned quantities and actual quantities for major materials were consistently aligned throughout the duration of the project. The CEMP included logistic plans to support the material management approach such as transportation, laydown areas, and waste management.

Transport

The project is completely below ground and will have no impact on traffic in the operational phase. Nonetheless measures were put in place during the construction phase to both minimize the traffic impacts on the local community and discourage car usage whilst commuting to work for staff.

The Contractor assigned specific routes and times of day for the transport of materials this was captured in the CEMP. Entrances to the project sites and diversion plans were arranged in a manner that they do not disturb the local community; this is captured in the Traffic Management Plan. From the onset of the project, site office staff were surveyed about their office commuting patterns and encouraged to carpool in groups based on the findings. Potential carpooling opportunities were identified and encouraged where possible. Lastly, during the winter months the Contractor launched a ‘Bike to Work’ initiative whereby staff were incentivized with helmets and bike lights if they cycled to work. Staff were also permitted access an on-site shower if they cycled to work. The ‘bike to work’ initiative was promoted through posters and emails.

What were the main challenges for the project and how were these overcome?

The main challenge in this case was that the CEEQUAL Assessor was engaged after the concept design was complete. Therefore, there were aspects in the design and the evidence documentation that the Assessor could not influence. This was overcome by being very selective with the credits targeted.

Another limitation in terms of ecology and biodiversity was that the project wasn’t permitted by the municipality to improve the landscape as part of the reinstatement plan, everything had to be restored to its exact preconstruction condition. The project team organized a meeting with leading figures of the Public Parks Department to discuss opportunities for improvement to the landscape in future projects and the potential benefits associated.

The final major challenge was benchmarking/setting targets for energy and water. This is a major part of the CEEQUAL assessment and required for some points. This was challenging because the stage at which the CEEQUAL Assessor was engaged and there were no comparable projects in the region with available metrics to be reference. The projects carbon data now serves as a benchmark for future projects.

What were the drivers and perceived benefits for undertaking a CEEQUAL assessment on this project?

Qatar is embracing sustainability in the built environment with schemes such as LEED, BREEM, and GSAS. There is a shift in attitude to adopt sustainability as a necessary practice. CEEQUAL was the most appropriate framework to manage a project of this typology and scale.

How did the use of CEEQUAL influence the outcomes of the project? What was done differently because of the CEEQUAL process?

CEEQUAL influenced the practice of reducing carbon emissions during construction. The Carbon Footprint Management plan which included various resource efficiency strategies integrated requirements from the CEEQUAL assessment (specifically in section 8 and 9). Had it not been for CEEQUAL material, water, fuel, and waste tracking would not so integral to the reporting process. The urgency to optimize resources and reduce waste would also not be as pressing if CEEQUAL was not used.

What elements of this project highlight best practice and innovation?

Elements of this project that highlight best practise were, optimized material efficiency, benchmarking for future projects in the region, and maximizing water efficiency.

MTS is successful in providing a safe, sustainable, innovative and best-in-class sewage infrastructure, resulting in a higher quality of life for Qatar’s future generations, in alignment with the Qatari National Vision 2030

Mahmoud Kamal, Environmental Manager
Contractor (Bouygues/UCC- KEO Consultants)

The project will provide advanced solutions for transferring sewage water in Doha. The programme is designed to serve the city of Doha and its surroundings, where 90% of Qatar’s population resides. The city has seen a rapid population growth over the last few years, which necessitated the expansion of its sanitation system. We’re glad to have delivered a project which speaks to Qatar’s investment in building a sustainable future.

Daniel Clert, Director of Construction
Contractor-Bouygues