Influence of Osmotic Suction on the Soil-Water Characteristic Curves of Compacted Expansive Clay

Unsaturated clays are subject to osmotic suction gradients in geoenvironmental engineering applications and it therefore becomes important to understand the effect of these chemical concentration gradients on soil-water characteristic curves (SWCCs). This paper brings out the influence of induced osmotic suction gradient on the wetting SWCCs of compacted clay specimens inundated with sodium chloride solutions/distilled water at vertical stress of 6.25 kPa in oedometer cells. The experimental results illustrate that variations in initial osmotic suction difference induce different magnitudes of osmotic induced consolidation and osmotic consolidation strains thereby impacting the wetting SWCCs and equilibrium water contents of identically compacted clay specimens. Osmotic suction induced by chemical concentration gradients between reservoir salt solution and soil-water can be treated as an equivalent net stress component, (pπ) that decreases the swelling strains of unsaturated specimens from reduction in microstructural and macrostructural swelling components. The direction of osmotic flow affects the matric SWCCs. Unsaturated specimens experiencing osmotic induced consolidation and osmotic consolidation develop lower equilibrium water content than specimens experiencing osmotic swelling during the wetting path. The findings of the study illustrate the need to incorporate the influence of osmotic suction in determination of the matric SWCCs.     

Shear Strength and Shear-Induced Volume Change Behavior of Unsaturated Soils from a Triaxial Test Program

A series of unsaturated soil triaxial tests were performed on four soils including sand, silt, and a low plasticity clay. Attempts were made to correlate unsaturated soil properties from these tests and data from the literature with soil-water characteristics curve (SWCC), soil gradation, and saturated soil properties. The feasibility of estimating unsaturated soil property functions from saturated soil properties, SWCCs and gradation data, is demonstrated. A hyperbolic model for estimation of the unsaturated soil parameter, ?b, versus matric suction is presented. Shear induced volume change behavior was also studied, and results are included in this paper. Although not correlated with soil index properties, these shear-induced volume change data are important to complete stress-deformation analyses, and represent a significant addition to the existing data base of unsaturated soil properties.     

Influence of Shear Rate on Undrained Vane Shear Strength of Organic Harbor Mud

Dredging operations in European harbors for maintenance of navigable water depth produce vast amounts of harbor mud. Between 2005 and 2007, the second largest harbor construction project in Germany was designed as a pilot study to use dredged harbor mud as backfill material to avoid expensive disposal or ex situ treatment. During this project, a partial collapse of the backfill highlighted the need for an improved assessment of undrained shear strength of naturally occurring liquid harbor mud. Using vane shear testing, this study evaluates the effect of shear rate on the undrained shear strength of harbor mud. It is shown that measured values for both peak and residual shear strength are significantly influenced by shear rate effects. Furthermore, the influence of shear rate on the peak shear strength is found to be independent of water content while the influence of the shear rate on the residual shear strength strongly depends on water content. New shear rate dependent correction factors μ are proposed using the test results and the observed time to failure in the harbor basin. The proposed correction leads to significant lower design undrained shear strengths than the classical Bjerrum correction and would have predicted the failure during the construction.     

Effects of Bromide Ion and Natural Organic Matter Fractions on the Formation and Speciation of Chlorination By-Products

The impacts of bromide concentration and natural organic matter (NOM) characteristics on the formation and speciation of disinfection by-products (DBPs) in chlorinated NOM fractions were investigated. A total of 20 bulk water NOM fractions with a wide range of specific ultraviolet (UV) absorbance (SUVA254) values were obtained from a source water employing XAD-8 or XAD-4 resin adsorption in completely mixed batch reactors. SUVA was not a good predictor of DBP [trihalomethanes (THMs), haloacetic acids (HAAs), and adsorbable organic halogens (AOX)] formation and speciation. The destruction in the UV254 absorbance from chlorination did not correlate with DBP formation at any bromide level. NOM moieties which do not absorb UV light at 254?nm significantly contributed to DBP formation. Mass balance calculations on halogens using THMs, HAAs, and AOX data indicated that significant amounts of DBPs (>54% of AOX) other than THMs and HAAs were formed in NOM fractions with 60–110?μg/L bromide concentration. The relative occurrence of such other halogenated by-products decreased with increasing bromide concentrations up to 500?μg/L level. NOM in the studied water was more susceptible to the formation of brominated THM species as opposed to brominated HAAs. At constant dissolved organic carbon concentration, chlorine dose and pH, increasing bromide concentrations in NOM fractions increased the total concentrations of DBPs and resulted in a shift toward the formation of brominated species. Further, increasing bromide concentrations increased the spectrum of detected species (i.e., occurrence of all nine HAAs) and provided a competitive advantage to THM and HAA precursors in NOM over precursors of other DBPs.     

Relationship between the Undrained Shear Strength, Water Content, and Mineralogical Properties of Fine-Grained Soils

The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soils; these relationships, however, have not yet been investigated. The findings described in this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals, their quantity in soil composition, and the interlayer water quantity in the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.     

Influence of Clod-Size and Structure on Wetting-Induced Volume Change of Compacted Soil

Volume changes due to wetting may occur in naturally deposited soils as well as earthen construction (e.g., compacted fills or embankments). Depending on the stress level, some soils exhibit increase in volume upon wetting (swell) while others may exhibit decrease in volume upon wetting (collapse). The work described in this paper focused on wetting-induced volume changes in compacted soils. Motivation for this work stemmed from observations of earthen structures that exhibit problematic behavior under wetting conditions, even though soils were compacted to engineering specifications (i.e., at or above minimum density and within moisture content ranges). Not only is this problematic behavior a concern but also the laboratory tests used to predict settlement of constructed facilities may not properly model the actual behavior of soil compacted under field conditions. For example, settlements experienced by compacted fills may be different from settlement predictions based on one-dimensional oedometer tests. These differences are partly related to the variations in the soil structure in tested specimens that arise because soil clods compacted in the laboratory are smaller than soil clods compacted in the field. The term “soil structure” includes the combined effects of soil fabric and interparticle forces. “Fabric” generally refers to the geometric arrangement of particles, whereas interparticle forces include physical and physicochemical interactions between particles. The soil structure in this case is associated with specimen preparation methods and is influenced by several factors including soil composition (including pore water chemistry), compaction method, clod sizes, initial moisture condition of clods, dry density or void ratio, and compaction moisture content. A laboratory research study was conducted to investigate the influence of variations in clod-size and structure on one-dimensional volume change, with emphasis on wetting-induced volume change, for nine different fine-grained soils. The results of the study suggest that the influence of structure in one-dimensional oedometer tests depends on soil type and nature of the clods in the compacted soil. Clayey soils appear to be influenced more by differences in structure, whereas silts or clayey sands of low plasticity (PI<10) do not appear to suffer as much from structure effects in one-dimensional oedometer tests. This is attributed to more extensive clod development in clayey soils. Furthermore, the moisture condition of clods appears to have an important influence on volume change behavior.     

Crushed Glass-Dredged Material (CG-DM) Blends: Role of Organic Matter Content and DM Variability on Field Compaction

Trial embankments comprised of crushed glass-dredged material (CG-DM) blends and a 100% DM embankment were constructed to provide the necessary data sets to determine if a moisture content (MC) correction was required for the nuclear density (ND) gauge, as DM may contain a high organic matter content (OC). The MCs of thin-walled tube samples of CG-DM blends collected immediately below the ND gauge were compared to the corresponding ND gauge readings. A direct correlation between the MC data pairings from the tube samples and ND gauge readings showed that the ND gauge was greater than 97% accurate for MCs up to 55% and OCs up to 10% for the CG-DM blends evaluated in this study. However, the MC determined by the ND gauge was underpredicted (not overpredicted) by approximately 2.5%, contrary to theoretical expectations. A comparison of the average MC results per embankment indicated that the ND gauge was generally within 1% of the tube sample values, again on the low side. Interestingly, the rutting of the individual embankment lifts, often used as an informal metric for compaction compliance also was found to be contrary to expectations. The (re)constructed CG-DM embankments of this study were again shown to satisfy local Department of Transportation embankment construction criteria in most cases.     

Effects of TMCP Schedule on Precipitation,Microstructure and Properties of Ti-microalloyed High Strength Steel

Using the similar compositions of the Ti-microalloyed high-strength steels produced by the thin-slab casting process of compact strip production(CSP),four thermo-mechanical control processes(TMCP)after the simulated thickslab casting,i.e.the two hot rolling routes and the two cooling processes,were designed,aiming at achieving the same mechanical properties as the thin strip products.The final microstructures after the four TMCP processes were examined by optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM).The tensile properties and Charpy impact energy were measured correspondingly.Strain-induced TiC precipitation was found in the two-stage rolling route with the finish rolling temperature at low levels,leading to grain refinement due to the pinning effect during austenite recrystallization.Precipitation hardening in ferrite was observed when a period of isothermal holding was applied after hot rolling.It could be concluded that both finish rolling temperature and the subsequent isothermal holding temperature were crucial for the achieved strength level due to the combined effect of grain refinement and precipitation hardening.At the same time,it was found that the isothermal holding led to poor impact toughness because of remarkable precipitation hardening.Therefore,it was suggested that the precipitation kinetics of titanium carbides in both austenite and ferrite should be investigated in future.