Tunnel construction is a critical aspect of civil engineering projects in Kenya, especially for infrastructure development such as roadways, railways, water supply, and mining operations. Quantity Surveyors require precise tunnel drawings to accurately estimate costs, manage resources, and ensure compliance with design specifications. This chapter focuses on the types of tunnels encountered in the field and the essential features of tunnel drawings, equipping Quantity Survey professionals with the knowledge to interpret and prepare these technical documents effectively.

9.1 Types Of Tunnels

In Kenya, tunnels are constructed for various purposes including transportation, water conveyance, and mining. Understanding the different types of tunnels is vital for Quantity Surveyors to evaluate project scope, materials, and construction methods accurately. This section explores the classification of tunnels based on their function, construction method, and geological setting.

9.1.1 Classification by Purpose

Tunnels serve diverse functions in civil engineering projects, influencing their design and construction techniques.

• Transportation Tunnels: Used for roads, railways, and pedestrian pathways, these tunnels facilitate efficient movement through geographical obstacles such as hills and mountains. For example, tunnels in Nairobi’s urban road network help alleviate traffic congestion.
• Water Conveyance Tunnels: Designed to transport water for irrigation, hydroelectric power, or municipal supply, these tunnels must ensure watertightness and durability. The Thika Dam project includes water tunnels to channel water to treatment plants.
• Utility Tunnels: These house essential services such as electrical cables, telecommunication lines, and pipelines, protecting them from environmental damage and facilitating maintenance.
• Mining Tunnels: Created for access to underground minerals, these tunnels require specialized ventilation and safety considerations. The South Rift Valley mining operations use such tunnels extensively.
• Service and Escape Tunnels: Incorporated in large infrastructure projects, these tunnels provide emergency exits or service access to main tunnels, enhancing safety.

9.1.2 Classification by Construction Method

The method used to construct a tunnel depends on ground conditions, tunnel size, and available technology.

• Cut-and-Cover Tunnels: Constructed by excavating a trench, building the tunnel structure, then covering it back. This method is common for shallow tunnels such as underpasses in urban areas.
• Bored Tunnels: Created using Tunnel Boring Machines (TBM), these tunnels are circular and suitable for long distances and deep installations. The Nairobi Expressway project employs bored tunnels for underpasses.
• Drill and Blast Tunnels: Used in hard rock conditions, this method involves drilling holes, charging explosives, blasting, and removing debris. It is typical in mining and mountainous terrain.
• Immersed Tube Tunnels: Prefabricated tunnel sections are submerged and joined underwater, often used for river or lake crossings.
• New Austrian Tunneling Method (NATM): This technique uses the surrounding rock’s strength for tunnel support, employing shotcrete and rock bolts. It is adaptive to varying geological conditions.

9.1.3 Classification by Geological Setting

Geological conditions influence tunnel design, safety, and construction approach.

• Soft Ground Tunnels: Constructed in soils like clay, silt, or sand, requiring extensive support systems to prevent collapse. Groundwater control is a significant challenge here.
• Rock Tunnels: Excavated through solid rock formations, these tunnels are generally more stable but require blasting or mechanical excavation.
• Mixed Ground Tunnels: Pass through alternating layers of rock and soil, demanding flexible construction methods and support systems.
• Underwater Tunnels: Built beneath bodies of water, these tunnels require waterproofing and pressure-resistant design to withstand hydrostatic forces.

9.1.4 Relevance to Quantity Surveying

Accurate knowledge of tunnel types allows Quantity Surveyors to:

• Assess material requirements suited to tunnel type and ground conditions.
• Estimate labour and equipment costs based on construction methods.
• Evaluate risks related to geological challenges and incorporate contingencies.
• Coordinate with engineers to verify design assumptions affecting quantities and rates.

Chapter Summary

This chapter covered the various types of tunnels, highlighting their distinct structural purposes and construction methods. It explained the essential components and conventions involved in preparing accurate tunnel drawings, emphasizing clarity and adherence to relevant standards. The chapter detailed how to enhance tunnel drawings with precise annotations and sectional views to ensure comprehensive representation of the tunnel’s features. It also explored emerging technologies transforming tunnel drawing practices, starting with Building Information Modeling which integrates multidimensional data for improved design and coordination. Augmented Reality and Virtual Reality were discussed as tools for immersive visualization and on-site guidance. The use of cloud-based collaboration platforms was presented as a means to facilitate real-time teamwork and data sharing among project stakeholders. Finally, the chapter introduced drones and 3D scanning as innovative methods for capturing detailed site information to enhance drawing accuracy and project monitoring.