Properties of an artificially cemented clay

Abstract

A high clay strength and apparent preconsolidation may be a result of chemical processes such as cementation at the contact points of the clay particles. In order to study some of the mechanical properties of a cemented clay two artificially cemented simple shear samples were produced and tested. Their engineering properties were compared to those of non-cemented clay samples with a real preloading. The cementing agent that was introduced into the sample was CaCO3. This was achieved by a sequence of treatments of CaCl2, Na2CO3, and original pore water. The different solutions were transported into the samples by diffusion. The cementation process took 90 days. The average amount of CaCO3 introduced into the two samples was 3.3 and 4.2%, respectively. By electron microscope techniques it was revealed that calcium carbonate was precipitated in spots of 5–10 μm diameter. One of the samples was run with undrained static loading. The other sample was first subjected to undrained cyclic loading and then to undrained static loading. Cementation increased the horizontal shear stress at failure by 35–40%. This corresponds to an apparent overconsolidation ratio of about 1.75. Both for static and cyclic loading the engineering properties were essentially independent of whether their high strength was achieved by cementation or by a real preloading.