No abstract

The behaviour of stone columns has yet to be captured fully by analytical and numerical techniques, and predicting column behaviour in soft cohesive soils brings specific challenges. This paper provides a comprehensive review and assessment of some aspects of field performance of stone columns in soft clays and silts, from both published and unpublished data and for loading over both wide areas (i.e. embankments) and small areas (i.e. footings). In particular, a new database of settlement improvement factors is developed, which gives an indication of the reliability of a traditional analytical approach, as well as distinguishing clearly between the performance of the preferred dry bottom feed system and other column construction systems. The paper gives evidence highlighting the key construction issues central to the successful performance of treated ground. Some data are also presented on pore pressure and total stress changes as a result of column installation and loading, and interpretation of these data benefits from a direct comparison with driven piles.

Extensive damage to dwellings in the east of Ireland, arising from the expansive pyritic fill material used beneath the floor slabs, prompted the laboratory study presented in this paper to quantify the expansion and study its influencing factors. A novel experimental arrangement, in which sample height and water supply were varied, was used to test a large quantity of active pyritic infill taken from an affected house in the greater Dublin area.The expansion of ten separate fill specimens was measured over a 175 day period from December 2010 to May 2011. Remarkably consistent results were obtained when the expansions were normalised by the sample height, with expansion rates of approximately 2-3 mm/year/metre height of fill for specimens standing in water, where the rates were largely insensitive to the amount of water supplied. More rapid expansion was noted for one specimen to which no additional water was supplied during the test. A steady reduction in pH of the water, although relatively small, was consistent with pyrite oxidation reactions occurring in the samples during the test, and also implies the occurrence of leaching of ions from the pores in the mudstone and also that oxidation reactions may have been occurring in the saturated mudstone. Changes in expansion were found also to correlate strongly with changes in the ambient temperature in all specimens.