Concept Design of Sedhiou Bridge and Roads Network

Background

The Sedhiou Bridge and Roads Network project in Senegal represents a transformative infrastructure initiative designed to improve regional connectivity and stimulate local economic development. Beta Design Consultants were commissioned to provide an initial technical proposal that would serve as a blueprint for transitioning from a strong concept design to a tender-ready package, with the aim of developing the detailed design for construction during the Design and Build stage. This case study examines the approach, challenges, methodologies, and outcomes derived from the project’s initial technical proposal.

The proposal was developed after a comprehensive review of the concept design, benchmarking against similar projects, and an internal workshop to align design approaches with the unique site requirements, including:

• Geotechnical challenges due to variable soil conditions.
• The bridge had 30 spans with most of the piers in the Casamance river bed.
• Environmental and social considerations stemming from the local context.
• Choosing the construction methods especially for the piers to result in cost-effective solutions and reasonable programme.

Scope of Work

BDC’s proposal encompasses a comprehensive scope of works that covers the entire project lifecycle, from initial assessments to detailed design and support during construction.

The key elements of the scope include:

1.      Geotechnical Investigations:

• Extensive borehole drilling (e.g., pressure meter and core drilling up to 40 m) with SPT tests.
• Laboratory testing including particle size analysis, Atterberg limits, water content, Proctor tests, CBR tests, Los Angeles, and Micro Deval tests.

2.      Hydrological and Hydraulic Studies:

• Hydrological analysis of the catchment area, incorporating historical rainfall data (30 to 100 years) with climate change considerations.
• 2-Dimensional hydraulic modeling to simulate flood scenarios, evaluate scour risks, and determine protective measures for bridge piers.

3.      Traffic Studies:

• Manual counts and origin-destination surveys to establish current traffic patterns.
• Traffic projections using a macroeconomic model with various growth scenarios.
• Traffic allocation modeling on the planned road network.

4.      Environmental and Social Studies:

• Desktop and field studies including stakeholder interviews to assess and mitigate environmental and social impacts.
• Integration of mitigation measures into the project design.

5.      Concept Design Endorsement:

• Adoption and refinement of the current concept design with adjustments based on field investigations.

6.      Phased Detailed Design:

• Phase 1: Immediate design work including structural analysis of the bridge, hydraulic structures, and enabling works design alongside concurrent field studies.
• Phase 2: Detailed design adjustments based on the outcomes of geotechnical, bathymetric, topographic, and traffic surveys.

7.      Temporary Works and Construction Methods:

• Development of construction method consulting services to decide on the optimal bridge installation method (e.g., direct launch, movable scaffolding, or alternative segment dropping).
• Design of temporary works, including cofferdam design, sheet pile specifications, shoring systems, and temporary load analyses.

8.   Supply Chain Integration:

• Early involvement of key subcontractors (piling, steel fabrication, steel erection, bridge deck teams) to align design with practical construction approaches.

9.   Tender Technical Evaluation Support:

• Providing technical support during tender evaluations, including the development of evaluation matrices and selection questionnaires.

10.  Health and Safety Policy:

• BDC operates under ISO 45001 and holds the SSIP Acclaim Accreditation, ensuring robust safety management.

11.  Environmental Management:

• Accredited under ISO 14001, ensuring sustainable environmental practices are integrated throughout the project lifecycle.

12.  Quality Management:

• Operating in compliance with ISO 9001, ensuring that all deliverables meet high-quality standards.

13.  Social Policy:

• Policies addressing Equality, Diversity, Inclusion, and adherence to the Modern Slavery Act.

14.  Inspection and Maintenance Reports:

• Proposals include two additional reports focusing on the inspection and maintenance of both the road network and the bridge, ensuring long-term sustainability.

15.  Consultation and Coordination:

• Coordination with ASGC UK, Innovo, and other stakeholders to ensure that design and construction phases are tightly integrated and responsive to emerging challenges.

Methodology:

Beta Design Consultants (BDC) employed a structured and systematic approach to deliver the conceptual structural design for Sedhiou Bridge and Roads Network Project. The methodology focused on ensuring that all structural components were designed efficiently, considering sustainability, local regulations, and cost-effectiveness. Below is the detailed methodology applied throughout the project:

1.   Phased Design Approach

BDC’s proposal divides the design work into two distinct phases:

• Phase 1:
  • Finalizing design activities that are not highly dependent on field study outcomes, such as structural and hydraulic design.
  • Initiating field studies concurrently (e.g., geotechnical, topographical, and traffic surveys).
• Phase 2:
  • Refining critical design elements (e.g., pier design and reinforcement details) based on data from field studies.
  • Finalizing the construction drawings and detailed design for both the bridge and road network.

2.   Early Stakeholder and Supply Chain Engagement

• Consultation Sessions:
  BDC organized early consultation workshops with supply chain partners, including piling, steel fabrication, and installation teams.
• Construction Method Evaluation:
  Two primary methods were identified for bridge installation, with additional alternatives explored based on site conditions and logistical feasibility.

3.   Integration of Field Studies

• Geotechnical and Hydraulic Assessments:
  These studies ensure that design assumptions are validated and that appropriate measures are taken to address potential issues such as scour, settlement, and structural loading.
• Traffic and Environmental Studies:
  Data from these studies feed directly into design modifications, ensuring the final package is robust, sustainable, and aligned with local conditions.

Technical Challenges and Solutions

• Robust Design Foundation:
  The comprehensive scope ensured that the strong concept design was effectively translated into a detailed and responsive engineering package.
• Risk Mitigation:
  Early identification of geotechnical and construction risks allowed for proactive planning and design flexibility.
• Enhanced Collaboration:
  Early engagement with key stakeholders and subcontractors resulted in a more integrated and efficient design process.
• Sustainability Focus:
  Incorporating detailed environmental, social, and quality management systems reinforced the long-term viability of the project.

Lessons Learned

• Value of Early Consultation:
  Involving specialists and key stakeholders at the outset can significantly reduce the risks of rework and delays.
• Adaptability in Design:
  A phased approach that accommodates iterative updates based on field data enhances the overall robustness of the project.
• Comprehensive Impact Assessment:
  A holistic view that integrates technical, environmental, and social considerations is essential for large-scale infrastructure projects.

Experience

Beta Design Consultants (BDC) has a proven track record of successfully managing and delivering complex structural engineering projects, particularly within the public sector. With over 20 years of experience in the industry, we have built a strong reputation for providing high-quality, cost-effective, and sustainable solutions for a wide range of projects. Our expertise spans various sectors, including heritage buildings, educational institutions, and public infrastructure, where our technical knowledge and innovative approach have consistently resulted in successful project completions.

Key Project Highlights:

• Public Sector Support: BDC has played a key role in several major public and international development projects. We had just completed the Concept Design for Administrative City in Koloma  (Guinea) and the Construction Services support for Brentford Waterfront Project (UK). Our work often involves integrating new technologies and materials with established traditional methods to create cost-effective and sustainable solutions.
• Surveys, Investigations and Field Studies: With a keen eye for detail, BDC excels at conducting comprehensive assessments for sites, buildings, infrastructure assets and energy installations. We assess the integrity of both new and existing structures, providing clients with a clear understanding of potential risks and actionable recommendations for repair or strengthening. These assessments help to identify the need for maintenance, refurbishment, or full structural upgrades.
• Cost-Effective Refurbishments: Our approach to refurbishments focuses on delivering cost-effective solutions that maximize the value of existing structures while minimizing disruption and unnecessary costs. Whether it's a structural upgrade or an aesthetic enhancement, BDC’s designs aim to ensure that every aspect of the project is efficient and sustainable.

Sector Expertise:

• Public Infrastructure: We have managed projects for public sector organizations involving structural assessments, upgrades, and refurbishments of civic buildings, transport infrastructure, and public spaces. This includes our work on high-traffic sites and historic public structures, where maintaining safety and accessibility is paramount.
• Specialist Structural Design: Whether it's a difficult soil condition, a complex foundation requirement, or the need for sustainable material choices, BDC brings specialist knowledge to every project. Our engineers are skilled in addressing challenging and unique design criteria, often achieving outstanding results where others may face difficulties.

Why Choose Beta Design Consultants?

• Proven Success in Complex Projects: Our team has demonstrated its ability to handle complex structural issues across a range of project types and sectors. We have consistently delivered high-quality work on time and within budget.
• Tailored Solutions: At BDC, we pride ourselves on delivering bespoke solutions that are tailored to the specific needs of each client and project. We understand that no two projects are alike, and we ensure that our structural designs are customized to meet the unique challenges presented.
• Collaboration with Clients: We work closely with our clients from project inception to completion, ensuring that their vision is realized and their objectives are met. Our collaborative approach fosters transparency and trust, ensuring that we always deliver results that exceed expectations.
• Innovation and Sustainability: BDC is committed to incorporating the latest technologies and sustainable practices into all our projects. From the use of BIM for better project coordination to sustainable design strategies, we ensure that our structural solutions not only meet immediate project goals but also contribute to long-term environmental goals.

By choosing Beta Design Consultants, clients gain a reliable partner that brings both technical expertise and a commitment to delivering successful outcomes on every project.