Building shores are essential temporary structures that provide support to walls, slabs, and other building elements during construction, ensuring safety and stability. In the role of a quantity surveyor in Kenya, understanding the foundation types for shores is critical for accurate cost estimation, planning, and risk management. Foundations for shores must be selected and designed to suit the soil conditions, load characteristics, and site constraints to prevent settlement or failure. This chapter begins with a comprehensive examination of the various types of foundations used for building shores, focusing on their application, advantages, and considerations in the Kenyan construction environment.

4.1 Types of Foundations

Foundations serve as the interface between the building shores and the ground, distributing loads safely to prevent structural failure or excessive settlement. In Kenya, variable soil conditions ranging from expansive clays in Nairobi to rocky terrains in Rift Valley require careful foundation selection for shores. Quantity surveyors must understand these foundation types to prepare accurate bills of quantities and advise on cost-effective and safe temporary works solutions. The following subtopics explore the primary foundation types used for building shores, their characteristics, and practical relevance.

4.1.1 Shallow Foundations for Building Shores

Shallow foundations are those constructed near the ground surface, typically within a depth equal to or less than their width. They are widely used for shores supporting light to moderate loads in firm soil conditions commonly found in urban areas like Mombasa and Kisumu. The choice of shallow foundation depends on soil bearing capacity, water table level, and the load from the building shore system.

Characteristics and Suitability of Shallow Foundations

• Load Distribution: Shallow foundations spread the load over a broad area near the surface, reducing pressure on the soil. This prevents excessive settlement especially when supporting lightweight shores.
• Cost-Effectiveness: Compared to deep foundations, shallow foundations are less expensive and quicker to construct, benefiting projects with tight budgets such as county government offices.
• Types of Shallow Foundations: Common types include strip footings, pad footings, and raft foundations, each suitable for different shore configurations and load intensities.
• Soil Conditions: Best suited for soils with adequate bearing capacity within 1.5 to 3 meters depth, such as well-compacted sandy or gravelly soils found in Nairobi’s upper zones.
• Limitations: Shallow foundations are not advisable in highly expansive clays or areas with high groundwater levels, as these conditions can cause differential settlement and instability.

In practice, a quantity surveyor working on a hotel renovation in Nakuru would specify pad footings under shores where the soil profile is firm, balancing cost and structural safety.

Suitability of Shallow Foundations

• Urban Construction Projects: Shallow foundations are particularly suitable for urban construction projects in cities like Nairobi and Mombasa, where soil investigations confirm adequate bearing capacity within the upper soil layers. For example, county government office buildings often utilize strip or pad footings due to predictable soil conditions and moderate loads.
• Low to Moderate Load Structures: These foundations are ideal for supporting temporary works with light to moderate loads, such as shoring for residential developments or small retail outlets. In Kisumu, timber shores for slab support often rest on shallow foundations because the imposed loads are within safe limits for the local soils.
• Sites with Low Water Table: Shallow foundations are best suited for areas where the water table is low, reducing the risk of water-related soil instability. For instance, in Eldoret, where groundwater is not a major concern, shallow foundations are commonly used for temporary works.
• Projects with Tight Schedules: Because shallow foundations are quick to construct, they are suitable for projects with tight timelines, such as emergency hospital expansions in Nakuru, where rapid shore installation is required to maintain progress.
• Sites with Minimal Underground Obstructions: Shallow foundations are advantageous where there are few underground utilities or obstructions, minimizing the risk of service disruptions. For example, in new developments on the outskirts of Nairobi, shallow foundations can be installed without extensive relocation of underground services.

4.1.2 Deep Foundations for Building Shores

Deep foundations transfer loads from building shores to deeper, more stable soil strata or rock layers when surface soils are weak or compressible. These foundations are critical in areas with poor topsoil or where heavy loads are imposed, such as multi-storey building sites in Nairobi’s CBD.

Types and Applications of Deep Foundations

• Pile Foundations: Vertical elements driven or bored into the ground to support shores where shallow foundations are inadequate. Common types include timber piles, concrete piles, and steel piles.
• Caissons: Large-diameter drilled shafts filled with concrete, used where very heavy loads must be supported and access is limited.
• Load Transfer Mechanism: Deep foundations bypass weak surface soils, transferring loads to firmer layers, ensuring stability for temporary works.
• Suitability: Ideal for shores supporting heavy formwork or scaffolding in soft clay soils found near Lake Victoria basin.
• Cost and Time: More expensive and time-consuming than shallow foundations, requiring specialized equipment and skilled labor, factors quantity surveyors must incorporate in budgeting.

4.1.3 Proprietary and Adjustable Foundation Systems for Shores

Modern construction projects in Kenya increasingly adopt proprietary foundation systems designed for temporary works, offering adjustability and ease of installation. These systems enhance efficiency and safety, particularly in urban settings with limited space.

Features and Benefits of Proprietary Systems

• Adjustability: Systems such as screw jacks and adjustable base plates allow precise leveling and load distribution, accommodating uneven ground conditions common in informal settlements.
• Modularity: Components are prefabricated and standardized, facilitating rapid assembly and dismantling, reducing labor costs on projects like university expansions.
• Load Capacity: Designed to support specific load ranges, ensuring shores remain stable under variable construction loads.
• Compatibility: Can be combined with shallow or deep foundations, providing flexibility in foundation design.
• Safety Enhancements: Incorporate features to prevent slipping or movement, critical for shores supporting fragile structures at Nairobi County government offices.

Quantity surveyors must evaluate these systems’ upfront costs against time savings and safety benefits when preparing project estimates.

4.1.4 Considerations for Foundation Selection in Kenyan Construction Sites

Selecting the appropriate foundation type for building shores depends on multiple factors that must be weighed carefully by quantity surveyors during project planning and cost estimation.

Key Factors Influencing Foundation Choice

• Soil Investigation Results: Comprehensive geotechnical surveys determine soil bearing capacity, moisture content, and depth of firm strata, guiding foundation type selection.
• Load Characteristics: The magnitude and duration of loads from shores and supported structures affect foundation design, with heavier loads requiring more robust foundations.
• Site Accessibility: Remote or congested sites may limit the use of deep foundations or heavy equipment, favoring shallow or proprietary systems.
• Environmental Conditions: Presence of groundwater, seasonal rainfall, and risk of erosion influence foundation stability and construction methods.
• Budget and Schedule Constraints: Quantity surveyors balance foundation costs with project timelines, opting for solutions that meet safety requirements without inflating budgets unnecessarily.

Chapter Summary

This chapter covered the essential aspects of erecting and dismantling building shores, starting with the various types of foundations that provide the base support for temporary works. It then explored the different types of shores assignments, highlighting their specific roles in supporting structures during construction. The chapter detailed common shoring materials used in the industry, emphasizing their properties and suitability for different tasks. Methods for connecting shores were examined to ensure stability and safety during use. Legal requirements were addressed through construction laws that govern safe practices in temporary works. Local authority guidelines were discussed to align shoring activities with regulatory standards. Practical procedures for shoring construction and erection were outlined, focusing on correct installation techniques. Finally, the chapter explained the safe dismantling of shores to prevent accidents and maintain site safety.