2014年-世界发展银行全球_Improving_Vietnams_Sustainability___Rural_Road_Pavement_and_Surfacing_Design_Options_12页_1mb

Summary of Improving Vietnam's Sustainability: Rural Road Pavement and Surfacing Design Options

Core Content

This document outlines the findings and recommendations from the Rural Road Surfacing Research (RRSR) programme in Vietnam, focusing on improving the sustainability and performance of low volume rural roads (LVRRs). It highlights the importance of designing roads that are compatible with their local environment and task, and the need for updated standards, specifications, and maintenance practices.

Main Points

• Sustainability of Pavement Options: Unsealed gravel wearing course (GWC) is not a sustainable option in many Vietnamese road environments, especially in high rainfall and steep gradient areas. Gravel loss rates exceed the 20mm/yr sustainability threshold in over 60% of the assessed road sections.
• Design and Construction: Roads should be designed with local materials, considering the road environment factors such as climate, terrain, traffic, and sub-grade conditions. The use of appropriate construction techniques and ensuring compliance with specifications is essential for long-term performance.
• Whole Life Costs: While unsealed roads may have lower initial costs, they often result in higher maintenance and rehabilitation expenses over time, making them less cost-effective in the long run.
• Maintenance Challenges: Lack of routine maintenance leads to poor performance and increased vulnerability to climate impacts. Maintenance should be integrated into the design process and tailored to local resources and community arrangements.
• Drainage Importance: Effective drainage is a critical component of sustainable rural roads. Poor drainage significantly impacts pavement performance and increases whole life costs.

Key Actions

1. Final assessments of trial pavements, particularly with respect to climate impacts.
2. Upgrade of Vietnamese rural road standards and specifications to reflect current research and climate threats.
3. Increased focus on funding and implementing effective rural road maintenance.

Research Background

• The RRSR programme, supported by the World Bank and DFID since 2003, has evaluated various pavement and surfacing options for LVRRs in Vietnam, Laos, and Cambodia.
• The research has identified the importance of the "Road Environment" in pavement selection and design, including construction materials, climate, hydrology, terrain, sub-grade, traffic, and construction regime.

Pavement Selection and Design

• A two-phase approach is recommended: Phase I for identifying suitable options based on the road environment, and Phase II for detailed design considering engineering requirements.
• The selection process should filter out unsuitable or unsustainable options and prioritize those that align with local conditions and resources.

Pavement Performance

• Unsealed Granular Pavements: Perform poorly in high rainfall and steep gradient areas, requiring frequent re-graveling. They are more sustainable in low rainfall, flat regions with adequate gravel supply.
• Concrete Pavements: Generally perform well, especially when constructed with proper procedures and materials. However, poor construction and curing can lead to premature cracking.
• Sealed Flexible Pavements: Perform as well or better than traditional options when using emulsion double chip seal on dry-bound macadam base. However, they are vulnerable to heavy traffic and axle loads.
• Stone Block and Brick Pavements: Low maintenance options, with mortared joints performing better in high erosion areas. However, joint and surface deterioration are common issues.

Key Recommendations

1. Design and construction of rural roads should be based on four key principles: suitability for function, local environment, use of local materials, and whole life cost considerations.
2. Adoption of research-based solutions by regulatory authorities is necessary for effective implementation.
3. A proper classification system for rural roads is essential to guide pavement selection.
4. Use of local materials should be prioritized, and the question should be: "What roads can I build with locally available materials?"
5. Technical standards and specifications should be updated to reflect regional and national research outcomes.
6. Unsealed GWC roads are not sustainable in many environments and should be phased out.
7. Composite construction and spot improvements can be effective in budget-constrained scenarios.
8. Effective drainage systems are vital for long-term road performance and should be incorporated into design.
9. Whole Life Asset Cost (WLAC) assessment must be integrated into the design process to ensure cost-effectiveness.

Practical Outcomes

• Strategic shift from unsealed to sealed pavements in Vietnam's rural road projects (RT2 to RT3).
• Adoption of RRSR outcomes in design manuals for Ethiopia and South Sudan.
• Integration of RRSR findings into Cambodian and Lao PDR standards and specifications.
• Use of RRSR content in teaching and research modules at the University of Transport and Communications (Vietnam).

What Needs to Be Done?

• Mainstream research outcomes into formal standards and operational manuals.
• Work closely with the Ministry of Transport (MoT) and relevant departments to update practical guidelines and manuals.
• Incorporate climate resilience into pavement design and construction standards, with a flexible and regionally focused approach.

Authors

• Jasper Cook: Geotechnical and Road Engineering Short Term Consultant, World Bank, Hanoi, Vietnam and Vientiane, Lao PDR.
• Pham Gio Tuan: Road Engineering Short Term Consultant, World Bank, Hanoi, Vietnam.

Acknowledgements

• Contributions from DFID's Peter O'Neill and Simon Lucas.
• Support from the Ministry of Transport and the Steering Committee.
• Vital contributions from Tran Thi Minh Phuong and various project teams including Intech-TRL, ITST, TDSI, and OTB Engineering.