|M.Sc Student||Shehadeh Sharbel|
|Subject||Determination of Mechanical Parameters of an Anisotropic|
Chalk as a Function of Degree of Saturation
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Mark Lloyd Talesnick|
This experimental investigation was carried out on an Eocene chalk of the Marasha Formation, from the Beit Guvrin National Park. The rock is characterized by a low dry unit weight which varies between 11.3 and 12.5 kN/m3, specific gravity Gs=2.6, resulting in a porosity of 58%.
The experimental program included four laboratory test procedures: (a) Uniaxial compression tests of solid cylinders, (b) Outer radial compression tests of hollow cylinders, (c) Hydrostatic (Isotropic) compression tests of solid cylinders, (d) Outer hydrostatic compression tests of hollow cylinders.
The test results illustrate the non-linear and anisotropic nature of the stress–strain response of the chalk. In the four different testing configurations, no linear zone was detected. The material stiffness declines at a maximum rate upon initial loading. The material clearly displays transverse isotropy, with horizontal bedding planes corresponding to the plane of material symmetry. The modulus of deformation within the plane of material symmetry is significantly higher than that perpendicular to bedding planes.
The effect of water content on the strength of the chalk has been addressed. The effect of water content on material stiffness is very pronounced. Drastic reductions in the modulus of deformation are noted due to very mild changes in water content at initially dry conditions. Furthermore increases in water content significantly reduce the compressive strength of the material.
The effect of the water content on pore collapse and the development of elasto-visco-plastic strains are examined during loading in the hydrostatic compression tests. Drastic increase in the component of elasto-visco-plastic strain, especially the viscous response is noted due to very mild changes in water content at initially dry conditions.