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Chalk breaks easily when subjected to human action such as mechanical handling, earthworks operations or pile installation. These actions break the cemented structure of chalk, which turns into a degraded material known as putty, with lower strength and stiffness than the intact chalk. The addition of Portland cement can improve the behaviour of chalk putties. Yet, there are no studies determining the tensile strength of chalk putty-cement blends, the initial stiffness evolution during the curing time and other design parameters such as friction angle and cohesion of this material. This paper addresses this knowledge gap and provides an interpretation of new experimental results based on the dimensionless index expressed as the ratio between porosity and volumetric content of cement (g/C iv ) or its exponential modification (g/ C iv a ). This index aids the selection of the amount of cement and density for key design parameters of compacted chalk putty-cement blends required in geotechnical engineering projects such as road foundations and pavements, embankments, and also bored concrete pile foundations.
Despite the vital importance to the contemporary economy, some drawbacks are mainly associated with the waste derived from mining activity. Essentially, this waste consists of tailings that end up being hydraulically disposed of in large impoundments, the tailings dams. Thence, as the dams are enlarged to accommodate higher amounts of materials, the stress states at which the deposited tailings are submitted change. This may be a concern for the stability of such structures once the geotechnical behavior of this sort of material may be complex and difficult to predict considering the existing approaches. Thus, the present study concerns the mechanical response of bauxite tailings under a wide span of stresses, ranging from 25 kPa to 4,000 kPa. One-dimensional compression tests, CIU, and CID triaxial tests were carried out on undisturbed and remolded samples of the bauxite tailings. The after-shearing grain size distribution was, as well, characterized. The results have shown a stress-dependency of the critical state friction angle for the intact material which may be related to fabric alterations derived from structure deterioration and particle breakage.
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