Mixed-in-place response of two carbonate sands

Abstract

At low confining stresses, calcareous sands exhibit many similar characteristics to silica sand deposits; however, at high stresses their shearing behaviour is quite different, exhibiting strong contraction due to grain crushing. Therefore, calcareous deposits can create significant challenges for driven pile foundations where the high installation energy causes particle damage, radial contraction and very low pile shaft friction. Drilled-and-grouted piles are often preferred in calcareous conditions. As an alternative to conventional foundation solutions, a novel pile has been developed based on the mixed-in-place technology. Two carbonate sands, the Dog's Bay foramol carbonate sand and the Ballyconneely sand, which is a calcitic carbonate algal sand, have been tested in the laboratory to investigate the geotechnical behaviour of these two sediments, which have different genesis and mechanical characteristics. The sands were mixed with concrete grout at cement-to-sand ratios of 15, 25 and 35%, and at a water-to-cement ratio of 0·4 to simulate the mixed-in-place pile installation technique. The results show similar geotechnical and structural performance for both sands.