Building Methods & Construction Technology

Site Clearance

Groundworks

Typical groundwork activities include:

• Site clearance.• Site preparation.• Excavation of foundation

trenches.• Groundwater control.

Site Clearance

It is normal practice for any above ground clearance requirements, such as removal of trees, bushes, walls, slabs, buildings etc to be shown on a site plan. This plan may show the position of services, both above and below ground, allowing these to be cleared if necessary or avoided for safety if to be left alone.

Site ClearanceConstruction sites vary a great deal, and clearance procedures will, of course, be different on each one.

A Greenfield site out of town may only require soil removal.

Site Clearance

Whereas a Brownfield site, having been previously developed, may need extensive demolition and clearance of concrete slabs etc before any excavation can commence.

Contaminated Ground

Due to the increase in use of brownfield sites, and regulations imposed by the government, many sites have to be decontaminated before structures can be built on them. This often involves the contaminated soil being totally removed from site and being replaced by clean soil when the site is landscaped.

Protection of TreesTrees may have a ‘preservation order’ placed on them by the local authority. This protects the tree from displacement or removal. The removal of other trees generally is subject to agreement with the planning authority before the work on site commences (usually at planning stage).

Removal of WasteWaste material can be removed by lorry or skip to a licensed landfill site, or if the waste is inert, such as brick rubble or subsoil, it can be used as ‘fill’ in certain earthworks. This will generally reduce the cost of removal of the waste to the contractor.

Burning of rubbish on building sites is not normally allowed.

Removal of WasteOn brownfield sites, where masonry and concrete demolition is required, it is often cost-effective for the material to be crushed and used for hardcore in the contract (if acceptable to the architect and building control).

Removal of Vegetable SoilThe Building Regulations Part C states that the ground to be built upon must be reasonably clear of vegetable soil and matter.

This photograph shows the organic vegetable or topsoil layer on top of the lighter coloured subsoil below.

Reduced Level ExcavationsGrading and levelling is carried out by the use of any of the following methods:

• Cut.• Cut and fill.• Fill.

‘Cut’ is the process of removal of high ground to produce a level work area. This method results in a solid and compact base.

‘Cut and fill’ techniques are used to provide a level base for construction on sloping sites This method requires compaction of filled areas of soil, in layers. The soil for filling may be ‘won’ from the cut areas. The cut area will be already sufficiently compact.

Cut Fill

Natural slope of the land.

Trench ExcavationFactors that influence the choice of methods for excavation include:

• Volume of subsoil to be excavated.• Nature of the site.• Type of soil (e.g. stone requires

mechanical excavation).• Time constraints (how much time

available for excavation).• Safety of operatives

Trench ExcavationManual or Use of Plant?

Or would this be better?

Sometimes this may be required.

All services below ground should be protected and identified by the

following methods:

Service providers should also have plans and information on where the location of pipes and cables

are before you start digging!

Groundwater ControlWater can be classified as either:

• Surface water. • Ground water. • Subsoil water.

Rain, snow etc on the surface

Water table

Upper levelof waterheld in thesubsoil

Surface water –run off from thesurface

Subsoil water –water held in theground belowthe water table

Ground water –water held in thesubsoil

Problems Caused by Subsoil Water

The contractor must, therefore, resist the ingress of water into excavations as much as possible. This is typically done by employing pumps.

A vacuum piston pump being used to reduce ground water from an excavation