Civil engineering projects begin with thorough preparations on site, known as preliminary works. These initial activities set the foundation for successful construction by ensuring that the site conditions are well understood and that all necessary data is collected. In Kenya, where diverse terrains and variable soil conditions are common, carrying out comprehensive site preliminary works is essential for safe, cost-effective, and durable civil engineering structures. This chapter explores the critical components of site preliminary works, focusing on site survey methods that provide essential information for project planning and execution.

1.1 Site Survey

Site surveys are fundamental in civil engineering as they provide precise data about the physical characteristics of the project location. This information guides design decisions, construction methods, and risk management. In Kenyan projects such as county road expansions or urban housing developments, accurate site surveys prevent costly mistakes and delays by revealing topographical features, boundaries, and subsurface conditions.

1.1.1 Use of Surveying Equipment

Surveying equipment is the backbone of any site survey, enabling engineers to measure distances, angles, and elevations with precision. The choice of equipment depends on the survey type, site conditions, and required accuracy.

• Total Stations integrate angle and distance measurement, making them versatile for most site surveys. Their digital output facilitates rapid data processing.
• Theodolites are preferred for high-precision angular measurements, especially in boundary surveys and control networks.
• GPS Receivers are invaluable in remote or large-scale projects like dam sites or road corridors, providing coordinate data without the need for line-of-sight.
• Leveling Instruments establish elevation benchmarks critical for drainage design and earthworks planning.
• Measuring tapes remain essential for quick checks and small-scale measurements where electronic instruments are impractical.

Maintenance of surveying equipment involves regular calibration, cleaning of optical components, battery checks, and safe storage to prevent damage and ensure accuracy.

1.1.2 Topographical Survey

Topographical surveys map the natural and man-made features of a site, including contours, vegetation, buildings, and water bodies. This survey forms the basis for design layouts and earthworks calculations.

Topographical surveys in Kenya must contend with varied landscapes from the Rift Valley escarpments to coastal plains, requiring adaptable methods to capture terrain detail.

Purpose of Topographical Survey

• Establishes ground elevations and contour lines necessary for drainage and grading design.
• Identifies existing structures and features to be preserved or demolished.
• Provides spatial data for planning access roads and construction zones.
• Detects potential obstacles such as rock outcrops or wetlands affecting design.
• Supplies data for environmental impact assessments and regulatory compliance.

Methods Used in Topographical Survey

• Ground-based total station surveys for detailed, high-accuracy mapping in developed areas.
• GPS surveys for rapid data collection over large or inaccessible terrain.
• Photogrammetry using drones to produce digital elevation models and orthophotos.
• Leveling for precise elevation measurements at critical points.
• Manual sketching supported by measurements for small or preliminary surveys.

Data Processing and Presentation

• Raw survey data is processed using CAD and GIS software to produce contour maps, profiles, and 3D terrain models.
• Contour intervals are selected based on project scale, typically 0.5m to 2m for civil works.
• Surveyors annotate maps with features such as trees, fences, and utilities for design reference.
• Digital models enable volume calculations for cut and fill estimations.
• Final survey reports include accuracy statements and metadata for quality assurance.

1.1.3 Geotechnical Investigation

Geotechnical investigations examine the subsurface soil and rock conditions to assess their suitability for supporting structures. This investigation is critical in Kenya, where soil types range from expansive clays to loose sandy deposits, affecting foundation design and construction methods.

Objectives of Geotechnical Investigation

• Determine soil bearing capacity to guide foundation type selection.
• Identify soil stratification and groundwater conditions affecting stability.
• Assess soil properties such as cohesion, density, and permeability.
• Detect potential geohazards like fault lines, sinkholes, or high water tables.
• Provide data for earthworks design, including excavation and compaction requirements.

Methods of Geotechnical Investigation

• Borehole drilling to extract soil samples at various depths for laboratory testing.
• Standard Penetration Test (SPT) to estimate soil density and strength in situ.
• Cone Penetration Test (CPT) for continuous profiling of soil resistance.
• Laboratory tests including Atterberg limits, grain size analysis, and triaxial shear tests.
• Geophysical methods like seismic refraction to map subsurface layers without excavation.

Interpretation and Reporting

• Engineers analyze test results to classify soils according to Kenyan and international standards.
• Recommendations include foundation types (e.g., shallow footings, piles), bearing capacities, and necessary ground improvement.
• Reports highlight risks such as expansive soils or seasonal water table fluctuations.
• Data informs cost estimates and construction scheduling.
• Geotechnical reports are essential for obtaining regulatory approvals and ensuring structural safety.

Chapter Summary

This chapter covers the essential preliminary works required before commencing civil engineering construction on a site. It begins with the site survey process, detailing the use of various surveying equipment, the execution of topographical surveys, and the importance of geotechnical investigations to assess soil properties. The identification and demarcation of site boundaries are explained, including surveying techniques and the marking and fencing necessary to secure the site. Site clearance procedures are discussed comprehensively, highlighting the removal of vegetation, debris, and obstacles, as well as proper management of soil and topsoil. The chapter also emphasizes the importance of accurate site layout, the use of surveying tools for marking reference points, and the setting out of structures and features in accordance with construction standards. Preparation of the site preliminary report is outlined, summarizing survey findings, geotechnical assessments, environmental impact analyses, utility evaluations, and the status of site clearance. Finally, the chapter reviews the provision of essential site utilities, covering temporary washrooms, water sources, storage facilities, and site offices to support construction activities.