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Recent theories indicate that capillary pressure is perhaps not only a function of saturation but may also depend on the time rate of change of saturation. This is known as the dynamic or non-equilibrium effect. There is compelling experimental evidence reported in the literature that the non-equilibrium effect is observable, quantifiable, and significant. However, almost all reported experiments relate to unsaturated systems. In this work, we report on a recent series of experiments involving water and PCE. Quasi-static as well as dynamic capillary pressure curves for primary drainage, main drainage, and main imbibition, are measured. The data are used to estimate the non-equilibrium capillary pressure coefficient. Finally, a continuum-scale two-phase flow model has been employed to simulate the experiments. Variations of average pressures and average water saturation with time are calculated and compared with measured curves. It is found that the displacement process takes place much faster in simulations than in experiments. This is believed to be due to presence of dynamic effects not captured with the numerical model.

In this study the behavior of an unsaturated sand is examined. The sand used is Hostun sand from France. The Soil-Water-Characteristic Curves (SWCCs) of loose and dense specimen were determined by using the suction mode and pressure mode axis translation technique under various vertical net stresses. One dimensional compression and rebound behavior was studied for specimens at different initial matric suction values. During these tests the matric suction was maintained constant during loading and unloading processes. To study the wetting induced collapse of the sand, specimens with a known matric suction and water content were prepared and then saturated at several vertical net stresses during loading. The study showed that the SWCC is not significantly influenced by vertical net stress. However there is a influence of initial suction on the compression behavior of the material which is manifested on the stillness moduli, compression index and collapse potential of the sand used in this study. In comparison to these results, results from one dimensional compression and rebound tests, where water content was kept constant, for Quartz sand Weferlingen were added. Results from collapse potential test for Quartz sand Weferlingen are given, too.

This paper presents the experimental results from several conventional oedometer tests conducted on compacted and unsaturated soils. Soil samples of medium plasticity, but with different grain size distribution and degree of saturation were tested. Some of these tests were interrupted before consolidation was achieved, and the water content of the soil was measured both before and after each test. The results point out that the recorded time-settlement curves consist of two distinct stages that are characterized by a different settlement rate. The early stage should essentially be ascribed to the faster dissipation of air pressure, while the final stage should be caused by the gradual expulsion of water from the soil. The results are also analysed using Terzaghi’s theory [1] in order to ascertain whether this theory is suited to simulating the time-histories of settlement recorded during the tests.

The paper presents an experimental investigation into the permeability of compacted kaolin. Tests were performed in a suction-controlled oedometer using the air overpressure technique: ambient air pressure (raised above the atmospheric pressure) was kept constant and pore water pressure was modified. Permeability was measured by monitoring water inflow in response to a suction decrease and interpolating experimental data using a simplified solution of Richards’ equation (unsteady-state method). Corrections were made to account for the impedance of the high air-entry ceramic disc, the water lost by evaporation into the air pressure line and the air diffusing through the ceramic. The experimental results have shown that axis-translation technique may be problematic at high degrees of saturation and that permeability can be significantly underestimated.

Moisture content and moisture movement are key factors in controlling the progress and rate of biodegradation within a landfill as it is the aqueous environment that facilitates the transport of nutrients and microbes. The modelling of infiltration and water movement requires information on the moisture retention and hydraulic conductivity properties, usually in the form of empirical functions such as those proposed by van Genuchten (1980). In waste however, the particle and pore size distribution, heterogeneity of waste composition and leachate chemistry complicate the determination of moisture retention and hydraulic conductivity. In this paper we describe the modification and use of a standard pressure plate apparatus to establish moisture retention properties of samples of 250 mm in diameter and the difficulties of using this method. Some initial results are presented.

A recently developed two-component model for the relationship between saturation and pore water suction (pF-curve) is used, whose frame consists of simple, physically meaningful values. The main purpose in this paper is to describe the amount of pore water in soils at high suction. Relative air humidity may be regulated by salt solutions of defined concentration or by sulfuric acid of varying concentrations, which leads to a steady-state water content in soil specimen. In the range of high suction values, data achieved in this way are fitted by the twocomponent model with high accuracy. The comprehension of many phenomena such as drying and cracking, apparent overconsolidation near the surface or strength loss of cuttings in overconsolidated soils by weathering depends on the understanding of water binding behavior in soils, which is improved by this quantitative model.

Clays are geomaterials which are used in various applications in ur society. The mor common geotechnical applicatio s are: waterproof cores of dams, barriers to contain waste, slurry walls etc. But even if clays are not used as construction materials the geotechnical engineer encounters them frequently during construction of e.g. foundations and tunnels. Within the group of clay minerals we find individual clay species that possess geotechnical properties that vary enermously. These differences in geotechnical pr perties can b related directly to the differences in microstructure of the clay minerals. In this contribution it is shown how the knowledge of clay microstructure from X ray diffraction analysis, thus knowledge of the clay mineralogy, can be used to assess the geotechnical behavior of the clay. When mineralogy alteration processes of the clay are know from appropriate geological analogues, the geotechnical characteristics of the engineered clay structure can be estimated on the basis of these processes (e.g. containment of hazardous waste, infiltration of permeates in dams etc.). This implies however that the clay used as construction material is well characterised. A method to prepare such a clay atlas and how to use it is presented in this contribution.

The paper aims at investigating suction induced by static compaction in clay specimens. To this end, kaolin powders prepared at target water contents were statically compacted in a shear box apparatus. Trento (TNT) high-suction tensiometers (0-1800 kPa) were in stalled through the loading pad to monitor suction changes during the loading-unloading paths. Specimens were compacted at water contents ranging from 0.22 to 0.30 and at vertical stresses of 300,600, and 1200 kPa. This made it possible to explore abroad spectrum of compaction conditions. Experimental results are presented and discussed in the paper. The most striking aspect of the results is that suction of unloaded specimens increased as degree of saturation increased. This can be explained by the dependency of the main wetting curve upon void ratio.

One-dimensional consolidation tests are often performed without accurate control of the initial degree of saturation, since most commercially used testing apparatuses do not permit back-pressuring. As a result, the initial degree of saturation is often less than unity and, thus, the measured ‘Apparent’ Compression Index can be very different than the value corresponding to a fully saturated sample. Similar differences are caused by most oedometer tests being performed up to a maximum stress lower than the maximum pre-consolidation pressure. Oedometer tests on undisturbed samples, on initially unsaturated samples of reconstituted soil, and a data-base of commercial oedometer tests are presented in order to exhibit the effect of high maximum preconsolidation pressure, cementation and initial unsaturation. Finally, expressions for the volumetric deformation of unsaturated soils proposed by Alonso et al. (1990) are used to explain different trends exhibited by the ‘Apparent’ Compression Index for low- and high-plasticity soils.

Loess is a loose, open-structured metastable soil of aeolian origin, predominantly composed of 20–60 µm quartz particles bonded together by clay particles and, in some cases, carbonate compounds. When dry it can withstand high overburden stresses, whilst upon saturation it collapses creating potentially enormous engineering problems. The mechanisms controlling this metastable behaviour involve the disintegration of inter-particle clay and chemical bonding and variations in the pore water pressures (i.e. suctions) during saturation.

The paper describes methods of creation of artificial loess samples using an airfall approach to allow the variation of bonding constituents, arrangements and formation processes. The amount of powdered clay added to primary quartz particles (ground silica) was varied and three methods for activation of clay bonding were employed, i.e. water spray, capillary wetting and steaming. The reproducibility of the synthetic loess created was determined through oedometer testing of the resulting samples, the results of which are reported together with those for undisturbed samples of mid-European loess. Similarities and differences are discussed in the context of the likely bonding mechanisms. It is concluded that creation of reproducible synthetic loess samples, while controlling its constituents, makes possible the individual examination of the different parameters that control bonding in loess.