Saturation swelling pressure

The general model was built up from the following sub-models, [2] 1. The load pressure in saturated porous media is the sum of the matric pressure p and the swelling pressure II ... 

The swelling pressure II is, under saturated conditions, a function of the void ratio e according to... 

At saturation with resin 1 fully swollen, the relative humidity P /Pq) is equal to unity whilst the reference resin at the same specific water content cannot be at saturation and exhibits a lower partial pressure or relative humidity. Hence the swelling pressure is found from the relationship ... 

The transport of caibon dioxide in polymers has historically been analyzed in the same manner as other simple gases (1). Recent studies have shown, however, that the effects of CX>2 on polymers include scrnie features commonly associated with organic solvents, including swelling (2-5). and depression of glass transition temperatures, i.e., plasticization (6-8). Moreover, CO2 can be handled as a liquid at room temperature under ratho moderate pressures its critical temperature is 31 0 and its saturated vapor pressure at 25" C is 64.6 atm (950 psi). For these reasons it seems appropriate to consider near-critical CX>2 as a highly volatile solvent, rather than as a gas, in its interactions with polymers. 

Swelling pressure tests were performed using conventional oedometers on samples saturated with distilled water. A regression curve was developed as a function of dry density for the swelling pressure... 

During the re-saturation process of buffer, swelling pressure under unsaturated conditions is important, though the above equation is limited to saturated conditions. 

The infiltration of water into clay-like materials causes changes in the pore structure of the material. Water molecules place in the solid matrix and become immobile. In consequence the effective porosity and the intrinsic permeability decrease. If the volume expansion of the material is restrained, swelling pressure is observed which increases linearly with the degree of water saturation, Studer et al. (1984), and BSrgesson (1984). The correlation between swelling pressure p, and void ratio e can be expressed best with the following empirical relationship, Bdrgesson et al. (1995) ... 

This test has been modeled with RockFlow/ RockMech in ID to check the chosen hydraulic parameters for the modeling of the FEBEX in situ experiment. The capillary pressure curve has been set as shown in Figure 3. Relative permeability for gas has been developed from the experimental results shown in Figure 4. Relative permeability for water has been assembled from the dependency on saturation and swelling pressure and an additional factor c. 

Bbrgesson, L. 1984. Water flow and swelling pressure in non-saturated bentonite-based clay barriers. In Clay Barriers for Isolation of Toxic Waste Proc. Intern. Symp., Stockholm, Sweden, 28-30 May 1984. 

In a HLW repository, the coupled thermo -hydro -mechanical and chemical (T-H-M-C) processes will occur, involving the interactive processes among radioactive decay heat of the vitrified waste (thermal processes), infiltration of groundwater (hydrological processes), swelling pressure of buffer material due to saturation (mechanical processes) and chemical evolution of buffer material and porewater (chemical processes). 

Evaluation of maximum swelling pressure in saturated media... 

During the resaturation process of the buffer material, the swelling pressure in unsaturated condition is important, though the model explained in the previous section is limited to the saturated condition. In this section, a new equation is proposed to treat swelling pressure in the unsaturated condition. 

Figure I. Swelling pressure with degree of saturation...

Figure 2. Swelling pressure against degree oj saturation...

Assuming that the swelling pressure is a function of the degree of saturation, good agreement between the simulation and the experiment was obtained. This indicates a one-to-one correspondence between the swelling pressure and the degree of saturation. 

Swelling pressure is likely to occur in the earlier stages of the resaturation process, and the value is strongly related to the initial degree of saturation. 

Since the model involves the Komine s theoretical model for evaluating swelling pressure in saturation, it has the potential to include the effects of chemical change in bentonite and pore water. Using this model, fully coupled thermal, hydraulic, mechanical and chemical analysis can be conducted in the future. 

Instead of applying the loads in discrete increments, as in the standard test, stresses, strains or pore pressures maybe varied continuously Additional tests are carried out to determine the swelling pressure and the swelling or settlement on saturation... 

Failure of consolidated and poorly cemented rocks occurs during saturation when the swelling pressure or internal saturation swelling stress, Os developed by capillary suction pressures exceeds their tensile strength. An estimate of as can be obtained from the modulus of deformation, ... 

For the determination of sorption data, gravimetric methods are usually used the most difficult task is to take into account the buoyancy effect. This effect is negligible at low pressures, but becomes important at SCF densities. Accurate equations of state for pure fluids are used to calculate gas densities, and swelling data are needed to calculate the volume of the polymeric phase. Generally, the amount of dissolved gas increases with increasing pressure until a saturation value is reached. 

Saturated Hydraulic Conductivity, 393 Diffuse double layer, 367-369 Na-Ioad, 379, 410-416 ESP 379, 410-416 SAR, 197, 412 Dispersion, 414 Swelling, 103-115 Osmotic pressure, 377 Secondary Contaminants, 478, 479 Copper, 479, 488 Iron, 479, 488 Zinc, 479, 488 Foaming Agents, 488 Chloride, 488 Color, 489 Corrosivity, 489 Hardness, 489 Manganese, 489 Odor, 490 pH, 490 Sodium, 490 Sulfate, 490 Taste, 490... 

Although the kinetics of liquid uptake to attain gel-saturation is history-dependent, the composition at the true end-state (i.e. thermodynamic equilibrium in excess liquid) is not therefore the observed end-state is usually reproducible [19]. Gel-saturation is attained when the restraining force (per unit area) of the polymeric crosslinked network becomes equal and opposite to the osmotic pressure that causes the system to swell [20], In other words saturation is achieved when the chemical potential of swelling liquid, p1 in the swollen network is equal to the chemical potential of the excess pure liquid, p , outside the network. It was logical to anticipate that the volume of liquid sorbed per gram of polymer, at this state of thermodynamic equilibrium with excess liquid, would correlate with the molecular structure of the liquid. In fact two parameters already exist which relate the sorption affinity to the molecular structure, namely the solubility parameter, 8, first proposed by Hildebrand [21], and the interaction parameter, %, introduced by Flory [22] and Huggins [23-26],... 

Figure 5 describes the evolution of the Tobermorite interlayer distance upon rehydration at room temperature and water vapour pressure equal to the saturating pressure value (j.e. relative humidity RH=100%, P/Po=l). No swelling phenomenon was observed after 48 hours hydration the interlamellar distance remains unchanged at 11.5 A. The dehydration process (14 A-11 A) is thus irreversible with these rehydration conditions. 

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