2.1 Tools, Equipment and Materials for Control Survey

Control survey work demands a variety of specialized tools and materials, each chosen for its role in achieving precise measurements and establishing permanent reference points. Surveyors in Kenya must be adept at selecting and maintaining equipment suitable for conditions ranging from urban environments to rural and remote areas. The following sections examine each key item, detailing specifications, applications, and handling considerations.

2.1.1 Hammer

The hammer is a fundamental tool in control surveys, primarily used to drive markers such as iron pins into the ground, establishing permanent reference points. Selecting the right hammer and using it correctly ensures markers are securely embedded, maintaining the integrity of control points over time.

• The hammer must have sufficient weight to drive markers deeply without excessive effort, which is critical on hard or rocky soils common in parts of Kenya such as Rift Valley highlands.
• Handles made from fiberglass offer durability and reduce vibration impact, minimizing user fatigue during extended use.
• Regular inspection for head looseness or handle cracks prevents accidents and ensures consistent performance.
• When working near sensitive equipment like GNSS receivers, care should be taken to avoid impact damage.
• Proper storage in field kits protects the hammer from rust and damage, extending its service life.

2.1.2 Pegs

Pegs serve as temporary or semi-permanent markers in control surveys, used to outline survey stations or mark traverses in the field. Their visibility and durability directly affect the ease of relocating points during follow-up surveys.

• Hardwood pegs are preferred for their resistance to weathering and mechanical damage, especially in regions with heavy rains like coastal Kenya.
• Bright paint improves visibility against vegetation and soil, reducing the risk of losing markers in dense or rugged terrain.
• Pegs are often sharpened at one end for easy insertion into the ground and sometimes have reflective tape for night visibility.
• Pegs must be placed vertically and firmly to avoid displacement by wind or human activity.
• After completing surveys, pegs are either removed or left with field notes to prevent confusion in future land use.

2.1.3 Spade

A spade is essential for excavating soil to expose firm ground or create shallow holes for setting permanent control points. Its design allows for precise digging with minimal disturbance to surrounding areas.

• The steel blade must be sharp and rust-resistant to facilitate cutting through compacted soils common in Kenyan highlands.
• The spade’s handle length balances leverage and control, enabling efficient soil removal without excessive strain.
• Surveyors use spades to create level bases for placing iron pins or concrete monuments, ensuring stability.
• In urban areas such as Nairobi, care is taken to avoid underground utilities during excavation.
• After use, cleaning and drying the spade prevents corrosion and extends tool life.

2.1.4 Shovel

Shovels are used for moving larger volumes of soil, mixing materials like cement and sand, and backfilling holes after control point installation. The difference from spades lies in the blade shape and intended use.

• The shovel’s curved blade facilitates scooping and moving loose soil or mixed materials efficiently.
• Fiberglass handles reduce weight and increase durability, which is beneficial during prolonged field operations.
• Shovels are indispensable when mixing cement and sand on-site for setting permanent control markers.
• Proper technique avoids undue strain and enhances productivity, especially when working in compacted or rocky soils.
• Maintenance includes regular cleaning and storage in dry conditions to prevent rust.

2.1.5 Measuring Tape

Measuring tapes are fundamental for linear measurements in control surveys, providing direct distance readings between points. Accuracy and durability are critical, particularly when establishing baseline distances.

• Steel tapes offer excellent accuracy and resistance to stretching, suitable for precise baseline measurements in flat terrains such as agricultural lands.
• Fiberglass tapes are lighter and resistant to corrosion, preferred in wet or rough environments like riverine areas.
• Metric graduations ensure compliance with national standards and ease of data recording.
• Tapes must be kept taut and straight during measurement to avoid errors.
• Regular calibration against standard measures maintains measurement integrity.

2.1.6 Ranging Rods

Ranging rods assist in aligning survey lines and marking intermediate points between control stations. Their visibility and stability are vital in diverse terrains and vegetation cover.

• The alternating colour pattern enhances visibility from a distance, reducing alignment errors.
• Lightweight materials allow easy transport across rough or hilly terrain common in western Kenya.
• Ranging rods are often capped with reflective tape for use in low light conditions.
• Stability is ensured by driving the rod firmly into the ground or using weighted bases.
• Proper placement aids in directing total station or theodolite sighting during measurements.

2.1.7 Total Station

The total station is a modern electronic instrument combining the functions of a theodolite and electronic distance measurement (EDM). It is central to control surveys for its precision and efficiency.

• Total stations simplify data collection by electronically measuring angles and distances, reducing human error.
• Their data storage capabilities facilitate immediate digital processing and integration with GIS systems.
• Bluetooth connectivity allows real-time data transfer to field computers, streamlining workflows.
• Calibration and regular maintenance are critical to preserve accuracy, especially in dusty or humid Kenyan environments.
• Surveyors use total stations to establish precise control points in urban development projects such as county government offices.

2.1.8 GNSS Receivers

Global Navigation Satellite System (GNSS) receivers provide high-accuracy positioning using satellite signals. They have revolutionized control surveys by enabling rapid data acquisition over large areas.

• GNSS receivers are indispensable for establishing geodetic control networks in Kenya’s varied landscapes, including remote arid areas.
• Multi-constellation support ensures consistent satellite coverage and positioning reliability.
• RTK technology enables real-time corrections, achieving centimetre-level accuracy essential for cadastral surveys.
• Surveyors must ensure clear sky visibility and proper antenna placement to minimize signal obstruction.
• Regular firmware updates and battery management are necessary for optimal performance during extended field operations.

2.1.9 Theodolite

The theodolite is a precision instrument used to measure horizontal and vertical angles, fundamental in triangulation and traversing control surveys.

• Optical theodolites require careful reading and recording of angles, while digital models improve speed and reduce reading errors.
• Theodolites remain crucial in areas where electronic distance measurement is not feasible.
• Accurate leveling and centering of the instrument over the station mark are essential for reliable measurements.
• Regular calibration against known angles ensures continued precision.
• Theodolites are widely used in university surveying departments for training and in field surveys around municipal boundaries.

2.1.10 Sand

Sand is a key material in forming stable foundations and bedding for control markers, preventing movement caused by soil settlement or erosion.

• The absence of organic material in sand prevents decomposition and subsequent ground settling.
• Coarse sand provides drainage, reducing water accumulation that could destabilize control points.
• Sand is mixed with cement to form concrete for permanent markers.
• Proper compaction of sand layers ensures firm support for embedded pins or concrete monuments.
• In coastal Kenya, local sand is often sourced to reduce costs and maintain ecological balance.

2.1.11 Cement

Cement is used to create concrete foundations that protect control points from displacement and environmental damage.

• KEBS certification guarantees quality and performance under Kenyan climatic conditions.
• The correct cement-to-sand ratio is critical for strength and durability.
• Concrete bases prevent marker corrosion and physical damage during farming or construction activities.
• Cement storage must be dry to avoid premature hardening.
• Mixing is usually done on-site with shovels and spades to ensure fresh and workable concrete.

2.1.12 Iron Pins

Iron pins serve as permanent markers for control points-driven into the ground to establish fixed reference locations.

• Galvanization or protective paint extends the lifespan of iron pins in Kenya’s humid highlands.
• The diameter ensures resistance to bending or breaking under soil pressure or agricultural activities.
• Pins are driven into firm soil or concrete bases for stability.
• Location coordinates of iron pins are recorded for future reference and verification.
• Iron pins facilitate re-establishment of control networks during land subdivision or infrastructure projects.

Chapter Summary

This chapter covered the essential tools, equipment, and materials used in control surveying, including basic hand tools like hammers and pegs, measurement devices such as measuring tapes and ranging rods, and advanced instruments like total stations, GNSS receivers, and theodolites. It also highlighted construction materials like sand, cement, and iron pins that are necessary for establishing permanent survey markers. Various methods for collecting control survey data were examined, focusing on traverse surveys, the use of GNSS technology for precise positioning, and traditional taping techniques. The chapter then discussed the practical aspects of conducting control survey data collection in the field, emphasizing accurate measurement and recording. Finally, it addressed the computation of control survey data, explaining how raw measurements are processed into usable coordinates and survey information necessary for further engineering and mapping tasks. Through this comprehensive overview, students gain a solid foundation in both the equipment and methodologies critical for effective control surveying.