Recently Geoinvestigate were involved in an unusual subsidence investigation in the Vale of St Albans. Everything about the job was extreme to say the least. The clay soil at the property was weathered Reading Beds of the Lambeth Group with extremely high plasticity and very high shrinkage potential having a liquid limit of 99 and a plasticity index of 65.
The problem was that some 60 years before a house had been built on the land which was previously open pasture with a duck pond. The pond had been drained a year before the house was built and a year after that a Willow Tree was planted next to the house.
Consequently the conditions were perfect for extreme clay shrinkage and building subsidence to occur as a result of the growth of the Willow and because the clays moisture at the start had been elevated. In the years which followed moisture levels in the clay progressively reduced with moisture depletion reaching a maximum depth of 4m. The moisture depletion was severe and the worst that Geoinvestigate have experienced save for a subsidence investigation in Basingstoke 2 years ago which involved a Eucalyptus Tree and severe dessication.
Geoinvestigate’s boreholes next to the building recovered clay cores which were of hard strength and when opened exhibited a shattered or extremely close fissuring with polishing on many surfaces. Willow roots were recovered to a depth of 3.80m.
From our new Reading Office Geoinvestigate provides site investigation desk studies, contaminated land surveys, gas monitoring, borehole site investigation services and building subsidence site investigations in St Albans, Basingstoke, Oxford and Milton Keynes areas.