Semi-empirical Model for Estimating the Small-Strain Shear Modulus of Unsaturated Non-plastic Sandy Soils

The shear modulus at small-strain, G _max is a maximum value of shear modulus for a given stress state and void ratio, and is a key parameter to evaluate the dynamic response of geotechnical structures. However, the laboratory testing procedures for determining G _max are time-consuming, cumbersome and require elaborate equipment especially for unsaturated soil samples. A semi-empirical model is proposed in this paper that can be used to estimate the variation of G _max with respect to matric suction for non-plastic sandy soils (i.e. I _p  = 0 %). The proposed model uses the Soil–Water Characteristic Curve (SWCC) and the shear modulus at saturation condition along with two fitting parameters ζ and ξ. The proposed model permits estimation of the variation of G _max with respect to matric suction over different zones of the SWCC (i.e. boundary effect, transition, and residual zones) for various non-plastic sandy soils. The fitting parameters ζ and ξ required for the proposed semi-empirical model can be estimated from simple relationships derived from the grain size distribution curve.     

Characterization of alluvium soil using geophysical and sounding methods

The alluvial deposits are highly heterogeneous and thus special techniques for investigating the subsurface have been required to obtain high quality data. The objective of this study is to apply two geophysical methods to alluvial deposits: a seismic survey method and the electrical resistivity method. The one-dimensional sounding method known as the standard penetration test is also applied to investigate subsurface properties and to compare these results with those measured by the geophysical methods. In seismic survey method, the seismic impulse source system shotgun is used to strongly propagate the elastic wave through the soil. The nonpolarizable electrode is selected to obtain the most reliable result by reducing the contact resistance. The application test is performed at Nakdong River in the southern part of Korean Peninsula where the area consists of alluvial deposits. The four profiles are selected for conducting the geophysical methods and the ranges of profiles are 115 ～ 205 m with interval distance of 5 m. The six one-dimensional soundings are performed in the intersection of geophysical profiles. Even though the measured results based on the geophysical method and one-dimensional sounding show slight difference, every result is applied to estimate subsurface characterization as the complementary data.     

Effects of temperature and salinity on the asexual reproduction of <Emphasis Type="Italic">Nemopilema nomurai</Emphasis> (Scyphozoa: Rhizostomeae)

Asexual reproduction of polyps of Nemopilema nomurai, of which massive blooms have occurred in Korean waters every summer since 2003, were tested under 20 combinations of temperature (10, 15, 20, and 25°C) and salinity (12, 17, 22, 27, and 32 psu). Production of podocysts increased with increasing temperature (20 and 25°C), while strobilaton and ephyral liberation occurred at low temperatures (10 and 15°C). Temperature also affected the initiation of ephyral liberation (approximately 25 days at 15°C, and 50 days at 10 and 20°C, respectively). The number of podocysts was only significantly different between 27 and 32 psu, and salinity had no significant effect on the excystment of podocysts, ephyral liberlation, showing N. nomurai is euryhaline. These results demonstrated that temperature is an important factor on both the podocysts production and ephyrae liberation, possibly explaining early spring liberation of ephyrae and continuous introduction of medusae into Korean coastal waters through summer to fall.     

Geophysical Surveys in the Jebel Hamrat Fidan,Jordan

The Jebel (Jebel is mountain in Arabic) Hamrat Fidan marks the “gateway” to the Feinan district of southern Jordan—one of the largest sources of copper during the prehistoric and Early Bronze Ages in the eastern Mediterranean. Preliminary excavations and surveys at sites along the Wadi Fidan have revealed a long history of settled occupation extending from the Pre‐Pottery Neolithic (ca. 6,500 B.C.) to early medieval times. Because of this long history of occupation, and the fact that this area was a regional center for the production of copper, the study of this area is important for understanding early metallurgy, craft specialization, and social evolution. During the summer of 1997, geophysical investigations at a series of Neolithic and Bronze Age sites identified specific areas within Wadi Fidan for future intensive excavations. Three geophysical techniques (electromagnetic induction, ground‐penetrating radar, and magnetometry) were used to help locate buried architectural and industrial features remaining from early mining and metallurgical operations, including copper ore bodies or voids. Geophysics was not used at the actual mining sites because of scheduling constraints; however, geophysics did delineate buried stone walls at three distinct Wadi Fidan sites. Magnetometry and ground penetrating radar provided little useful information. Buried stone walls were apparently “masked” by numerous magnetic stones on the ground surface making magnetometry useless. Reflections from known strata demonstrated that radar penetrated the ground adequately; however, known shallowly buried walls were not recognizable. Electromagnetic induction produced maps of linear and rectilinear features that suggested spatial distribution of widespread buried stone walls suitable for future excavation. A significant and unexpected finding was that electromagnetic induction proved capable of delineating buried stone walls. © 2000 John Wiley & Sons, Inc.