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.

Numerical investigation on the drag reduction properties of a suction controlled high-rise building

To reduce the wind-induced drag and improve the wind-resistance performance of a high-rise building, steady suction control is introduced into the building structure. Based on validation of the numerical methods by experiment with suction control over the flow separation of a 3D backward-facing step, the Reynolds stress equation model is used to investigate the drag reduction (DR) properties of a high-rise building whose side faces are controlled by all-height suction. Effects of the orifice geometrical parameters and suction flux parameters on the DR and the separation control are analyzed, and the detailed flow fields are shown to clarify the mechanism of suction control. The results indicate that suction control is very effective in reducing the wind loads on the high-rise building model, and only the dimensionless suction flux dominates. Lastly, the power consumed and the counterforce induced by suction are discussed, the suction models become the "zero-drag" model under certain suction angles.

Investigation of the hydro-mechanical behaviour of compacted expansive clay

The hydro-mechanical behaviour of compacted expansive Romainville clay was investigated.The soil was air-dried,crushed,and passed through a 2 mm sieve before being statically compacted to a dry density of 1.35 Mg/m3.The mechanical behaviour was investigated by tests in oedometer with controlled suction using the vapor equilibrium technique(suction s=0,9,39,and 110 MPa).The vertical stress was applied in the range of 0-800 kPa.The experimental results are shown as follows:1)wetting-induced swelling was higher at lower vertical stresses;2)the vertical stress under which no swelling occurred during water flooding was estimated at 60 kPa,which can be considered as the swelling pressure of the soil tested;3)the soil compressibility(changes of volume upon stress increases)was strongly influenced by the soil suction:the lower the suction,the higher the compressibility.The hydraulic behaviour was investigated using a large-scale infiltration chamber(800mm×1000 mm in section and 1000mm high).The large size of the soil column allowed bttrying the volumetric water content sensors(ThetaProbe)without significantly affecting the water transfer and the soil swelling during infiltration.The soil suction was monitored along the soil height(every 100 mm)using various relative humidity sensors and psychrometers.In the infiltration test,water was kept on the soil surface and changes in suction and volumetric water content were monitored for 338 d.The wetting front has reached the bottom of the soil column at the end of the test.The data from the simultaneous monitoring of suction and water content were used to determine the water retention curve and the unsaturated hydraulic conductivity using the instantaneous profile method.It has been observed that the soil water retention curve depends on the soil depth;that is to be related to the soil depthdependent swelling.The unsaturated hydraulic conductiv-ity was found to be quite low,comprised between 3×10-11m/s(at saturated state)and 10-14m/s(at about 100 MPa suction).