2.1 Site clearance works

Site clearance works are all the activities carried out to prepare a plot for construction by removing everything that would obstruct or endanger the new works, including vegetation, trees and stumps, rubbish, old structures, unwanted services and the topsoil over the building area. Proper clearance gives a safe, open and level site for setting out, excavation and storage, prevents organic material and debris from weakening foundations, and reduces hazards such as hidden pits, snakes and fire. In practice, the site is first surveyed and demarcated, permits are obtained, services are located and disconnected, and clearance then proceeds manually or with machines, followed by safe disposal of the cleared material. Example: before construction of a new dormitory at a secondary school in Kitui, the contractor fenced the site, removed bush and three dead trees, demolished an old pit latrine after filling it with lime and soil, stripped 200 mm of topsoil and stockpiled it for later landscaping of the school compound.

Tools and Equipment for Site Clearance Works

Activities Involved in Site Clearance Works

• Demarcation and fencing: Marking the site boundaries and erecting a hoarding or fence to keep out the public and livestock.
• Clearing vegetation: Cutting grass, bush and shrubs from the building area and access routes.
• Felling trees and removing stumps: Cutting down trees that cannot be kept and grubbing out roots and stumps that would rot under the building.
• Demolition of existing structures: Pulling down old buildings, walls, foundations, latrines and slabs that are not part of the new design.
• Disconnection and diversion of services: Arranging for water, electricity, sewer and telecommunication lines to be disconnected or rerouted by their owners.
• Removal of rubbish and debris: Collecting and carting away waste, scrap metal, old building materials and dumped rubbish.
• Treatment of termite mounds: Excavating termite mounds and their queens and treating the soil before construction.
• Filling old pits and wells: Filling abandoned pit latrines, wells, septic tanks and soak pits with suitable compacted material, after treatment where necessary.
• Topsoil stripping: Removing the top layer of organic soil from the building area and stockpiling it for landscaping.
• Temporary drainage: Forming cut-off drains to divert surface water away from the cleared area.

Methods of Site Clearance

Legal and Approval Requirements

• Environmental approval: Projects that require an Environmental Impact Assessment must obtain a licence from NEMA before clearance begins, and comply with its conditions.
• Building and demolition approvals: County governments approve building plans and may require a demolition permit before existing structures are pulled down.
• Tree felling permission: Felling of protected or indigenous trees may require permission from the county government or the Kenya Forest Service.
• Utility disconnections: Only the owners of services, such as the power company and water service provider, may disconnect or divert their lines.
• Waste disposal: Debris must be taken to approved disposal sites, and waste transporters may need county licences.
• Occupational safety: Work must comply with the Occupational Safety and Health Act, including safe use of machines and provision of PPE.

Steps to Carry Out Site Clearance Works

1. Study the drawings and site: Review the site plan, boundaries and features to be retained, and walk the site to identify obstacles, services and hazards.
2. Obtain approvals: Confirm that environmental, building, demolition and tree felling approvals are in place before work starts.
3. Demarcate and fence the site: Locate boundary beacons, mark the clearance limits and erect a fence or hoarding with warning signs.
4. Locate and isolate services: Use service drawings and locators to find cables and pipes, and arrange for the owners to disconnect or divert them.
5. Mark features to be retained: Fence and tag trees, structures and survey beacons that must be protected during clearance.
6. Clear vegetation: Cut grass, bush and small trees, starting from one side of the site and working systematically.
7. Fell trees and remove stumps: Fell trees in a controlled direction away from people and property, then grub out stumps and large roots.
8. Demolish unwanted structures: Demolish old buildings and slabs from the top down, salvaging reusable materials and removing foundations within the building area.
9. Treat and fill pits and mounds: Treat and fill old pits, wells and termite mounds with compacted material.
10. Strip topsoil: Remove topsoil from the building area and stockpile it separately from other excavated material.
11. Remove and dispose of debris: Load and cart away waste to approved disposal sites, and keep records of disposal.
12. Inspect and hand over: Inspect the cleared site with the supervisor, confirm all obstructions have been removed, and hand over for setting out.

Calculating Topsoil Stripping and Disposal

Example: a site for a SACCO office in Nyeri measures 40 m by 25 m. Topsoil 150 mm deep is to be stripped, it bulks by 25% when excavated, and surplus topsoil will be carted away in 10 m³ trucks at Ksh 4,500 per load.

Area to strip = Length × Width

Area = 40 m × 25 m

Area = 1,000 m²

Volume of topsoil = Area × Depth

Volume = 1,000 m² × 0.15 m

Volume = 150 m³

Bulked volume = Volume × 1.25

Bulked volume = 150 m³ × 1.25

Bulked volume = 187.5 m³

Number of truck loads = Bulked volume ÷ Truck capacity (rounded up)

Number of truck loads = 187.5 m³ ÷ 10 m³

Number of truck loads = 18.75, rounded up to 19 loads

Cost of carting away = Number of loads × Cost per load

Cost = 19 × Ksh 4,500

Cost = Ksh 85,500

Disposal of Cleared Materials

• Reuse of topsoil: Stockpile good topsoil for landscaping, gardens and grassing after construction.
• Salvage of building materials: Recover reusable stones, blocks, roofing sheets, doors and steel from demolished structures.
• Mulching vegetation: Chip or shred cut vegetation and use it as mulch or compost instead of burning it.
• Use of timber: Cut felled trees into firewood, poles or timber where suitable, with any required permits.
• Disposal at approved sites: Take rubbish and unusable debris to county-approved dumpsites, never to rivers, roadsides or neighbouring plots.
• Special handling of hazardous waste: Handle asbestos sheets, chemicals and contaminated soil according to NEMA waste regulations, using licensed handlers. Example: during clearance for a farm processing shed in Nakuru, old asbestos roofing sheets from a demolished store were wetted, wrapped in polythene and removed by a licensed waste handler.

Safety Precautions During Site Clearance

• Wear PPE: Use helmets, gloves, safety boots and goggles, with ear defenders and chainsaw protective clothing where required.
• Control tree felling: Only trained persons fell trees, and the area within twice the tree height is kept clear of people.
• Isolate services: Never dig or demolish near live services until they have been confirmed disconnected.
• Separate workers from machines: Keep workers out of the operating radius of bulldozers and excavators, and use banksmen.
• Beware of hidden hazards: Watch for old pits, wells, snakes, wasps' nests, broken glass and sharp metal in bush and rubbish.
• Avoid uncontrolled burning: Do not burn vegetation or waste without permission, as fires spread easily and cause air pollution.
• Provide first aid: Keep a first aid kit and trained first aider on site during clearance work.

Environmental Considerations

• Retain valuable trees: Keep healthy trees where possible to provide shade, reduce erosion and improve the finished site.
• Prevent soil erosion: Clear only the area needed, and install cut-off drains and silt fences to stop soil washing into drains and streams.
• Control dust and noise: Water haul routes in dry weather and limit noisy work to permitted hours.
• Protect watercourses: Keep debris, fuel and chemicals away from rivers, wetlands and boreholes.
• Minimise waste: Reuse and recycle cleared materials to reduce the amount taken to dumpsites. Example: a hotel developer in Nanyuki saved several mature acacia trees during clearance by adjusting the position of the car park, and they now provide natural shade for guests.

Chapter Summary

This chapter covered essential aspects of performing earthworks, beginning with the interpretation and use of earthwork working drawings to guide site operations accurately. It examined the processes involved in site clearance works, ensuring the area is prepared for subsequent earthmoving activities. The role of cross sections in measuring and planning earthworks was explained to facilitate precise volume calculations. The removal of topsoil was addressed as a critical step to preserve fertile material and prepare the site for construction. Excavation to the required formation or reduced level was detailed, focusing on achieving the specified depth and accuracy. The formation of embankments according to design drawings was discussed to ensure structural stability. Compaction techniques at the formation level were emphasized to enhance soil strength and prevent future settlement. Finally, the chapter highlighted the proper disposal of excess earthwork material to maintain environmental compliance and site safety.