Disposal of excavated material

The primary factors in disposal of excavated material arc as follows:

• What type and condition is the material?
• Is it suitable for back filling?
• Is it suitable for general filling?
• Has it to be disposed of in a particular way, in spoil heaps for later use, or to a coup? 
• Does the contractor have a choice?

Other factors arc the distance to spoil heaps or the proximity of a tip external to the site, the value of any surplus material, and whether or not the client wishes to retain a proprietary interest in it up to the point of disposal. For example, hand excavation followed by disposal into spoil heaps on site carried out using wheelbarrows might be reasonable if the wheeling distance was not too far. the ground was suitable, or barrow runs could be economically provided. A maximum distance might be in. the region of 150 m. Beyond this distance mechanical barrows or small dump trucks might be more suitable, bearing in mind that mechanical devices run on four wheels and need wider roadways, and that they bog down in poor soil conditions.

Wheeled or tracked plant engaged in bulk excavations such as reduced level or basement work could 'wheel' each bucket load to a disposal point. but this is only economic if the bucket is of reasonable capacity, the wheeling distance is less than 50 m and the machine can get out of the excavation to deposit the load, For distances beyond this it is considered more economical to utilize dump trucks or light tramway and hutches for on-site disposal and tipping lorries for off-site disposal,

When considering disposal_ the estimator must be aware that excavated material is measured in the bill as the volume of the void to be created. Le. the volume of compacted spoil removed. As soon as it is removed it will increase in volume, This phenomenon is called bulking and is ignored by the quantity surveyor when measuring disposal. However_ the estimator must allow in his rates for the fact that whenever he disposes of one meter cube of spoil as measured. the mm on site will he handling one and a bit meters cube of spoil.

The corollary of course is that the cubic meter handled on site is not as heavy as when it was in the ground, This is important when loading lorries which have axle weight restrictions when on the public roads. For example. loading a 6-tonne payload lorry with soil having a weight of 1..5 drill and a bulking rate of 15 per cent means that the lorry might carry (6/1.5) + 15 per cent = 4.6 m3.. However. the soil must not be beyond the bulk capacity of the lorry body, causing it to overflow onto the roads:, the authorities do not allow that either.

Matching the output of the men and/or machines digging to the means of disposal is of great importance if maximum efficiency is to be achieved, Whether disposal is by barrow or lorry_ it is costly to have the excavation lagging behind the disposal or vice versa, They must match., as explained in Chapter 3 on mechanical plant.

In October 1996 HM Government introduced a `Landfill Tax'. The aim is to encourage the recycling of building materials. a reduction in the amount of material. dumped in landfill sites and encouragement of more responsible disposal of hazardous waste. The tax is administered by HM Customs and. Excise, an agency with the broadest and strictest powers of all government agencies within the United Kingdom.. The level of taxation was introduced on a sliding scale, increasing each year to a ceiling of £13.00 per tonne by April 2004. There are two levels of taxi the lower one for 'inert' waste and the higher one for 'active waste'. As with all legislation the whole thing is bound, by 'ifs' and i'buts'. Greater detail can be obtained by visiting the web site at http://www.hmce.gov.uk and searching there for Landfill Tax. Payment of the tax on a construction contract can be tackled in two ways.. The estimator can include the amount in each bill item priced or a sum/per cent can be included in the Preliminary Works Bill. In very, rare cases, the Building Employer will undertake to pay the tax but a sum would he included in the Bill of Quantities (probably as a Provisional Sum) so that the cost was included in any budgeting. The tax is NOT taken into account for the examples in this chapter as at the time of writing there is some doubt about the classification of the waste as inert or active and without quantities it is not entirely possible to ascertain the correct amount of tax without being able to calculate mass. Table 5.8 summarizes the factors for consideration in excavation and disposal.