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University of Colorado at Boulder (2000)

Collapse of cemented carbonate sand

Al Kandari, Fawzi Abdullah M

Titre : Collapse of cemented carbonate sand

Auteur : Al Kandari, Fawzi Abdullah M

Université de soutenance : University of Colorado at Boulder

Grade : Doctor of Philosophy (PhD) 2000

Calcareous sands exist in many parts of the world where arid and semiarid conditions prevail. They are characterized by the presence of carbonates deposited at the point of contacts between the particles. Carbonate minerals are unique in the sense that they act as cementing agents when the soil is dry or near dry conditions. When wetted, these soils exhibit strong tendency for collapse as the cementing action of the carbonate minerals would be destroyed or greatly reduced, leading to diverse consequences that affect the serviceability and stability of the structures supported by these soils. In order to further the understanding of collapse in carbonate sands, over 20 conventional and modified single oedometer collapse tests were conducted on artificially lightly cemented reference sand. Artificial cementation with CaCO3 by precipitation was used to have better control over the various factors that affect the collapse behavior, as naturally cemented soils exist with various degrees of cementation and composition. The research program was conducted in two phases. In phase I, 15 conventional oedometer collapse tests were conducted on a reference sand cemented with different percentages of CaCO3 in order to study the effect of CaCO3 on the collapse behavior. The results indicate that both the collapse potential and the collapse time increases with the amount of CaCO3 . In phase II, the collapse behavior of the reference sand when uncemented and when cemented with 3% CaCO3 was studied within a theoretical context consistent with the concepts of unsaturated soil mechanics. Six modified oedometer collapse tests with matric suction measurements using flexible tube tensiometers were conducted in order to obtain data that relate the initial matric suction of the specimens to their volume decrease during inundation. The laboratory test results indicate that the water action in weakening and/or destroying the bonds between the particles as a result of the presence of the clay materials in the uncemented soil or CaCO 3 in the cemented soil is the main reason of the collapse. In other words, the change in the degree of saturation during inundation is the main factor that causes the collapse. The increase in the degree of saturation is followed by a reduction in the matric suction, but the matric suction by itself as a source of an intergranular bonding has little effect on the collapse

Mots clés : Soil, Collapse, Cemented, Sand, Civil engineering, Applied sciences

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