Seismic Response of Columnar Reinforced Ground

Ground improvement using stiff columnar reinforcement, such as stone, jet-grout and soil-mix columns, is commonly used for mitigation of seismic damage in weak ground. Seismic shear stress reduction in the reinforced soil mass is often counted on for reducing liquefaction potential. Current design methods assume composite behavior of the reinforced soil, where the shear stress reduction is based on the ratio of the columnar stiffness relative to the soil as well as the area replacement ratio. This implicitly assumes that the stiff columns will deform in pure shear along with the surrounding soft soil. Three dimensional dynamic finite element analyses were performed to better understand the column deformation and shear stress reduction behavior. The analyses focused on the deformation modes of the stiff column during shaking and the stress transfer mechanisms between the column and the surrounding soft ground. These analyses showed that the seismic behavior of columnar reinforced ground is more complicated than widely thought, and importantly, that current design methods may greatly over-estimate the shear stress reduction the columns provide. The study found that stiff columns do not behave as pure shear beams as implicitly assumed by current methods, but that their behavior is a combination of shear and flexural behavior. Further, the results indicate that the mode of deformation of the columns significantly influences their effectiveness in reducing shear stresses in the reinforced soil. For most common applications, the columns deform in combination of flexure and shear. The net effect is that stiff columns typically achieve only a small percentage of the shear stress reduction implied by area-replacement ratio methods that assume composite behavior for reinforced ground. In summary, columnar reinforcement provides little or no seismic shear stress reduction and current methods may be unconservative. The results of this analytical study are presented in this paper and the implications in terms of the current design practice are discussed

Seismic Performance of Soil-Mix Panel Reinforced Ground

Ground reinforcement methods such as stone columns, jet grouting, and soil mixing are commonly used to improve subsoil conditions for seismic mitigation. In most cases, the purpose of this improvement is for foundation support and/or liquefaction mitigation. Additional benefits of the improvement, such as possible reduction in seismic ground motions, are not explicitly considered in NEHRP/IBC code provisions for establishing site classification and seismic design motions. Such reductions, if present, can have significant payoff. Reduced seismic loads on the super structure result in lower seismic design levels and reduced construction costs. It is conceivable that the cost of ground improvement, typically about 5-15% of total construction costs, may be more than offset by lower overall costs resulting from reduced ground motions used in design. Ongoing research and analytical studies suggests that some soil improvement techniques using stiff reinforcing elements have the potential to reduce the intensity of earthquake shaking beneath structures. Of particular interest, our dynamic finite element modeling suggests that stiff ground reinforcements arranged in latticetype panels (i.e. soil-mix and jet-grout panels) has great potential. Such panels may significantly reduce ground motions and improve NEHRP/IBC site classification. This paper presents and summarizes results from preliminary dynamic three-dimensional (3-D) finite element analyses of soil-mix panel reinforced ground. Results are shown for a series of analyses where typical soil-mix panels are installed at replacement ratios of 24% and 36%. The improvement was found to cause reductions in spectral acceleration of up to 40% in comparison to unimproved ground conditions, especially for structural periods less than 1.0 second. A variety of geometrical configurations such as different replacement ratios, improvement depths as well as panel stiffnesses are currently being studied by the authors to provide further insight into the phenomenon

Numerical Modeling of Columnar Reinforced Ground 1999 Kocaeli Earthquake Case History

The Kocaeli Earthquake (M=7.4) struck Turkey on August 17, 1999 and caused significant damage along Izmit Bay. Following the earthquake, the authors investigated the field performance at improved soil sites. Of particular interest was the Carrefour Shopping Center that was under construction during the earthquake. The reclaimed site is underlain by strata of saturated soft clays, silts, and liquefiable loose sands. Small-diameter jet-grout columns had been installed at close spacings to reduce settlements and prevent liquefaction-related damage beneath footings and mats. Nonlinear dynamic three-dimensional finite element analyses were conducted to model the reinforced ground at Carrefour. The results show that the primary benefit of the columns was different than first suspected. That is, we initially thought the higher composite stiffness of the reinforced ground led to reduced seismic shear stresses and shear strains in the soil mass. However, the numerical results show that the reinforced ground did not behave as a composite mass during shaking due to strain incompatibility between the soil and stiff columns. The results indicate that the columns did not significantly reduce seismic shear stresses and strains (and thus pore pressures) in the soil mass. The effectiveness of the jet-grouting at Carrefour was more related to the vertical support the columns provided that prevented seismically-induced settlements. The implication is that commonly-used design methods and assumptions may lead to overestimates of the effectiveness of ground reinforcement for mitigating seismic damage

Privatization and regulation in Turkish telecommunications

Version of RecordThe importance of efficient workings of network industries and the markets in which they operate has long been recognized in the literature. In a parallel fashion, policy makers around the world initiated various restructuring efforts focusing on these sectors. However, the issues of privatization and much needed subsequent regulatory framework face considerable challenges in developing countries. Both political opposition and difficulties encountered in the process of privatization caused major delays in overall privatization and restructuring efforts of these countries. This paper focuses on the telecommunications sector and the Turk Telekom case, in particular, assessing the prospects for its much-debated divestiture, evaluating the company specifics and subsequent regulatory agenda. In doing that, it emphasizes the current "telecom meltdown" in international markets, and compares telecommunications privatizations of various nations. Additionally, the study reviews major regulatory methods and draws on some recommendations for policy makers in the light of the U.S experience in this sector.Aybar, C. B., Guney, S., & Suel, H. (2001, March). Privatization and regulation in Turkish telecommunications: A critical assessment (Working Paper). Manchester, NH: Southern New Hampshire University. Retrieved from http://academicarchive.snhu.ed

Field Evidence and Laboratory Testing of the Cyclic Vulnerability of Fine-Grained Soils During the 1999 Kocaeli Earthquake

Significant earthquake-induced settlements occurred in saturated fine-grained soils at the Carrefour Shopping Center in Turkey during the 1999 Kocaeli Earthquake (M=7.4). Most of the settlement was due to the undrained cyclic failure of silt/clay (ML/CL) and highplasticity clay (CH) strata within the subsoil profile. Each suffered about 1% vertical strain. Extensive laboratory testing on undisturbed samples from these silty and clayey strata has been performed to investigate this behavior. The laboratory testing included monotonic and cyclic simple shear tests, triaxial tests and conventional 1-D consolidation tests. Considerable pore pressure increases have been measured during cyclic simple shear test which was later followed by significant reconsolidation settlement. It was found that significant pore pressures begin developing in these soils at cyclic stresses at about 50% of their monotonic shear strength. This transition in behavior with high pore pressure development and subsequent post-cyclic volume changes corresponds to about 0.5% cyclic shear strains. The study demonstrates the limitations of generalized liquefaction screening methods, and dispels the common misconception that high plasticity soils cannot generate high pore pressures and fail under cyclic loading. Test results indicate that the soils at the site can generate significant pore pressures when shaken at levels expected to have occurred during the Kocaeli Earthquake. The findings from this study are inline with the limited number of studies on this topic. Fine-grained soils, if shaken hard enough, can suffer strength loss and reconsolidation settlements. The challenge remains to better understand such phenomenon and incorporate this into engineering practice. This paper presents the observed ground failure at the site, site characterization studies and following laboratory testing program

Internal Structure and Breakage Behavior of Biogenic Carbonate Sand Grains

This Study Investigates the Mechanical Behavior of Biogenic Carbonate Sands from Puerto Rico at Grain-Scale Level. Micro-Computed Tomography Has Also Been Used to Get Insights on the Internal Structure of These Particles Before and after Loading. the Crushing Strength of These Particles Are Smaller Comparing to the Values Reported for Silica Sands. It Has Also Been Shown that These Particles Have Complex Internal Structure Including a Network of Pores Connected with Channels. This Study Also Demonstrates the Effect of Intragrain Structure of Biogenic Carbonate Sands and Shows How Internal Grain Structure Plays a Role on Particle Fracture

Liquefaction Potential of Railway Embankments

This paper presents an overview of the nature of train-induced vibrations and discusses the liquefaction potential of railway embankments under such low-level vibrations. The paper also presents the results of static and dynamic finite difference numerical analyses performed for a simple railway embankment geometry. The liquefaction potential for the railway embankment foundation was estimated using the results corn FLAC numerical analyses, as well as a cyclic shear stress liquefaction resistance approach using a modified cyclic resistance ratio curve. Liquefaction of railway embankment foundations was found to be possible. However, based on the majority of reported failures the liquefaction potential remains low unless the train-induced vibrations are coupled with factors such as loose foundation, and sudden rise of pore water pressures due to poor drainage, flooding, or heavy rainfall

Transfusion-transmitted virus prevalence in subjects at high risk of sexually transmitted infection in Turkey

ObjectiveTo assess the possible sexual transmission of virus and to identify the prevalence of TTV viremia in Turkey and its association with other hepatotropic viruses.MethodsSerum samples were collected from 81 subjects (74 prostitutes and seven homosexual men) at high risk of sexually transmitted infection and from 81 healthy controls (74 females and seven males). Sera of patients and controls were tested for TTV, hepatitis A virus, hepatitis B virus, hepatitis C virus, and human immunodeficiency virus. Also, serum alanine and aspartate aminotransferases were measured.ResultsThe prevalence rates of TTV viremia in the risk group and control group were 86.4% and 82.7%, respectively. There was a statistical difference in mean age between TTV-infected and uninfected subjects (38.6 ± 9.9 versus 32.2 ± 6.1 years, respectively, P < 0.001). Prevalence rates of TTV infection in subjects with positive anti-HAV and positive anti-HBc were high when compared with subjects who were negative for these.ConclusionWe suggest that TTV infection has a diverse route of transmission, and its prevalence increases with age; also, the prevalence rate of TTV is high in certain risk groups. The prevalence rates of TTV in the group at risk for sexual transmission (86.4%) and in the control group (82.7%) were among the highest ever reported in the world. Also, we suggest that TTV generally does not cause clinical disease, in spite of this high prevalence

miR-34a-FOXP1 Loop in Ovarian Cancer

Ovarian cancer (OC) is the main cause of gynecological cancer mortality in most developed countries. microRNA (miR) expression dysregulation has been highlighted in human cancers, and miR-34a is found to be downregulated and associated with inhibition of tumor growth and invasion in several malignancies, including OC. The winged helix transcription factor forkhead box P1 (FOXP1) is reported as either an oncogene or tumor suppressor in various cancers. This study aimed to elucidate potential clinical and biological associations of miR-34a and transcription factor FOXP1 in OC. We investigated nine OC patients’ blood samples and two OC cell lines (SKOV-3 and OVCAR-3) using quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR) to determine both miR-34a and FOXP1 expressions. We have found that miR-34a and FOXP1 are reversely correlated in both in vitro and in vivo. Inhibition of miR-34a transiently led to upregulation of FOXP1 mRNA expression and increased cellular invasion in vitro. Our data indicate that miR-34a could be a potential biomarker for improving the diagnostic efficiency of OC, and miR-34a overexpression may reduce OC pathogenesis by targeting FOXP1