Joints in unsaturated rocks:Thermo-hydro-mechanical formulation and constitutive behaviour

A formulation for the coupled analysis of thermo-hydro-mechanical （THM） problems in joints is first presented. The work involves the establishment of equilibrium and mass and energy balance equations. Balance equations were formulated taking into account two phases： water and air. The joint element developed was implemented in a general purpose finite element computer code for THM analysis of porous media （Code_Bright）. The program was then used to study a number of cases ranging from laboratory tests to large scale in situ tests. A numerical simulation of coupled hydraulic shear tests of rough granite joints is first presented. The tests as well as the model show the coupling between permeability and the deformation of thejoints. The experimental investigation was focused on the effects of suction on the mechanical behaviour of rock joints. Laboratory tests were performed in a direct shear cell equipped with suction control. Suction was imposed using a vapour forced convection circuit connected to the cell and controlled by an air pump. Artificial joints of Lilla claystone were prepared.Joint roughness of varying intensity was created by carving the surfaces in contact in such a manner that rock ridges of different tip angles were formed. These angles ranged from 0° （smooth joint） to 45° （very rough joint profile）. The geometric profiles of the two surfaces in contact were initially positioned in a ＂matching＂ situation. Several tests were performed for different values of suctions （200, 100, and 20 MPa） and for different values of vertical stresses （30, 60, and 150 kPa）. A constitutive model including the effects of suction and joint roughness is proposed to simulate the unsaturated behaviour of rock joints. The new constitutive law was incorporated in the code and experimental results were numerically simulated.

Effect of solid contents on the controlled shear stress rheological properties of different types of sludge

Controlled shear stress （CSS） test was used to study the effect of solid contents on the corresponding rheological parameters for sludge. Three types of sludge with or without conditioning, including activated sludge （AS）, anaerobic digested sludge （ADS）, and water treatment residuals （WTRs）, were collected for the CSS test. Results showed that the yield stress and the cohesion energy of the sludge networks were improved with increased total suspending solid （TSS） contents in most cases. For the conditioned AS/ADS and the raw WTRs, exponential law was observed in the relationships between cohesion energy of material networks or yield stress and the TSS contents, whereas for the conditioned WTRs, only exponential law dependence was found between the parameters of shear modulus or critical strain and the TSS contents.