James Russell BSc (Eng) MIEI CEng
157 Shore Road
028 93 35 35 86
028 93 37 22 22
07715 32 42 54
07715 32 42 53
This sheet is an outline of general information for those considering piled foundations for dwelling houses and has been prepared in good faith. It should not be used as a replacement for expert analysis of individual situations.
As the availability of sites has become more limited and the cost of piled foundations has decreased, it is now commonplace to utilise piled foundations for dwellings in ground unsuitable for traditional foundations.
In making the decision whether to pile or trench fill, it is good practice to investigate the ground conditions by performing test holes by using an excavator (either on rubber tyres or tracks). Rubber tyre excavators can usually dig to 13 ft and tracked machines up to 20 ft. If either of these machines is at full depth and the strata has not improved then piling is almost certainly necessary. In these circumstances, early consultation with a civil or structural engineer experienced in soil mechanics is recommended.
Apart from the danger of deep dig, (health and safety regulations require excavations deeper than 1.2 metres to be propped), the breakeven point between piles and trench fill will depend on many other factors.
> Over-dig due to collapsing sides can result in a trench 3 to 4 times as wide as the bucket and a concrete cost to match
> The cost of spoil disposal and potential landfill tax
> The cost of shoring or risk of trench collapse, (particularly near other properties where piling is much safer than excavation below adjacent foundations)
> Ground water levels may make excavation even at shallow depths impossible*. (*Lowering the water table by pumping groundwater can cause serious damage to adjacent buildings. It is not uncommon to drive piles as short as 2 metres rather than dewater and risk damage to adjacent property.)
Typically, we have found that clients find piles to be more economical than 2 to 3 metres of under-building.
If you have any questions regarding the information found on the website, please feel free to get in touch via one of the methods shown on the left.