Performing substructure works is a fundamental phase in building construction that directly influences the stability and longevity of a structure. Quantity surveyors in Kenya must have a thorough understanding of substructure activities such as site clearance and excavation, as these processes affect cost estimation, project scheduling, and risk management. Proper execution of these tasks ensures compliance with safety standards and environmental regulations, which is crucial in diverse Kenyan contexts ranging from urban commercial developments to rural housing projects. This chapter delves into site clearance and excavation methods, highlighting safety and technical considerations critical for quantity survey professionals.

2.1 Site Clearance

Site clearance involves preparing the land for construction by removing obstacles that may hinder the building process. For quantity surveyors, understanding the extent and methods of site clearance enables accurate cost planning and resource allocation. In Kenya, site clearance must also consider environmental regulations enforced by bodies such as NEMA to avoid penalties and project delays.

2.1.1 Methods of Site Clearance

Site clearance methods vary depending on the nature of the site and the type of obstacles present. Quantity surveyors must assess these methods to estimate costs and timelines effectively.

Manual Clearance

Manual clearance entails the use of hand tools to remove vegetation, debris, and small obstructions. This method is labour-intensive but suitable for sites with limited space or environmentally sensitive areas, such as near hospitals or schools where machinery use is restricted.

• Precision: Allows selective removal of unwanted materials without damaging the soil structure.
• Labour cost implications: Higher labour input increases direct costs, requiring careful budgeting.
• Environmental compliance: Minimizes disturbance to protected flora or fauna.
• Accessibility: Ideal for sites inaccessible to heavy machinery.
• Safety: Reduced risk of accidents compared to mechanical methods.

Mechanical Clearance

Mechanical clearance uses machinery such as bulldozers, excavators, and brush cutters to clear large areas quickly. This method is common in commercial or industrial projects, for example at county government office sites requiring rapid preparation.

• Efficiency: Speeds up clearance of dense vegetation and debris.
• Cost-effectiveness: Reduces labour costs but increases equipment hire and fuel expenses.
• Suitability: Best for flat or gently sloping terrain.
• Soil disturbance: May require additional remediation if soil compaction occurs.
• Environmental impact: Requires adherence to regulations to prevent excessive soil erosion.

Controlled Burning

Controlled burning is occasionally used to clear vegetation by fire under strict environmental guidelines. This method is generally discouraged in urban areas due to pollution concerns but may be used in remote agricultural sites.

• Speed: Rapid removal of dry vegetation.
• Cost: Low direct costs but potential environmental fines if mismanaged.
• Risk: Fire control measures essential to prevent spread.
• Soil health: Can improve soil nutrient content but may harm microbial life.
• Regulatory approval: Requires permits from local authorities.

Chemical Clearance

Chemical herbicides may be applied to kill unwanted vegetation prior to mechanical removal. Quantity surveyors must consider costs and environmental liabilities associated with chemical use.

• Effectiveness: Kills deep-rooted plants that are difficult to remove manually.
• Environmental concerns: Potential contamination of groundwater and soil.
• Safety: Requires trained personnel for application.
• Residual impact: May delay subsequent construction activities.
• Regulatory restrictions: Usage governed by environmental laws.

2.1.2 Safety Issues in Site Clearance

Safety during site clearance is paramount to protect workers and the public, and to avoid costly accidents or legal consequences. Quantity surveyors should incorporate safety provisions into project budgets and schedules.

Personal Protective Equipment (PPE)

Workers must use PPE such as helmets, gloves, boots, and eye protection to guard against physical injuries.

• Head protection: Prevents injuries from falling debris.
• Hand protection: Protects against cuts and chemical exposure.
• Footwear: Guards against punctures and slips.
• Eye protection: Shields from dust and flying particles.
• Training: Proper use of PPE reduces accident rates.

Hazard Identification and Risk Assessment

Before clearing, a thorough assessment identifies hazards such as underground utilities, unstable trees, or wildlife.

• Utility mapping: Prevents accidental damage to water, electricity, or gas lines.
• Tree stability: Avoids injuries from falling branches.
• Wildlife risks: Protects workers from harmful animals or insects.
• Terrain assessment: Identifies unstable ground or hidden pits.
• Documentation: Records risks for compliance and insurance.

Safe Use of Machinery

Operating clearance machinery requires skilled operators and adherence to safety protocols.

• Operator training: Reduces accidents caused by human error.
• Maintenance: Regular servicing prevents mechanical failures.
• Clear communication: Use of signals or radios avoids collisions.
• Exclusion zones: Keeps unauthorized personnel away from machinery.
• Emergency procedures: Readiness for accidents or breakdowns.

Environmental Safeguards

Protecting the surrounding environment is a safety and compliance issue.

• Dust control: Water spraying to minimize airborne particles.
• Erosion prevention: Use of barriers to control soil runoff.
• Waste management: Proper disposal of cleared materials.
• Noise control: Limits on machinery use during sensitive hours.
• Compliance checks: Ensures adherence to NEMA regulations.

Chapter Summary

This chapter covers the essential processes involved in performing substructure works, beginning with site clearance where various methods are employed to prepare the site safely. Excavation techniques are explored, including assessment methods, temporary supports to maintain excavation stability, and groundwater control measures. The chapter then explains levelling procedures through cut, fill, and combined cut and fill methods to achieve the desired ground profile. Profile boards are introduced with emphasis on their types, such as corner and single profile boards, and their practical use in guiding construction alignment. Different foundation types and the materials used in their construction are discussed to ensure structural stability. The role of hard core as a foundation base is detailed alongside its materials and characteristics, followed by blinding which serves to provide a clean, level surface with appropriate materials. Anti-termite treatment is highlighted for its importance in protecting structures, including the chemicals used and necessary safety precautions. Lastly, the chapter addresses damp proofing to prevent moisture ingress, describing suitable materials and their properties, and concludes with concrete bed construction, differentiating between mass plain concrete and reinforced concrete applications.