Energy dissipation in rocking bridge piers under free vibration tests

This research aims to investigate the dynamic characteristic of rocking bridge columns subjected to quick release loads. Precast columns anchored by unbonded steel bars at the centre of each column can rock on the foundation surface without inducing any residual deformation after earthquakes. The restoring force of columns relies on gravity load from the superstructure and tensile strength in anchor bars. Radiation damping is evaluated through each impact of column rocking. To validate the theoretical damping proposed by previous researchers, four columns were constructed. Research parameters included steel or plastic materials used as rocking interfaces, area of anchor bars, aspect ratio and size effect of columns. Test results revealed that stocky columns slid apparently in the first impact then rocked, but taller columns rocked with minor slips in the entire motion. And freestanding columns slid significantly in the first impact that led to a higher damping. Radiation damping due to impact in the entire motion for all tests was within 5%. Copyright © 2006 John Wiley & Sons, Ltd.     

One-phase-low-pH enzyme induced carbonate precipitation (EICP) method for soil improvement

Enzyme induced carbonate precipitation (EICP) is an emerging soil improvement method using free urease enzyme for urea hydrolysis. This method has advantages over the commonly used microbially induced carbonate precipitation (MICP) process as it does not involve issues related to bio-safety. However, in terms of efficiency of calcium carbonate production, EICP is considered lower than that of MICP. In this paper, a high efficiency EICP method is proposed. The key of this new method is to adopt a one-phase injection of low pH solution strategy. In this so-called one-phase-low-pH method, EICP solution consisting of a mixture of urease solution of pH?=?6.5, urea and calcium chloride is injected into soil. The test results have shown that the one-phase-low-pH method can improve significantly the calcium conversion efficiency and the uniformity of calcium carbonate distribution in the sand samples as compared with the conventional two-phase EICP method. Furthermore, the unconfined compressive strength of sand treated using the one-phase-low-pH method is much higher than that using the two-phase method and the one-phase-low-pH method is also simpler and more efficient as it involves less number of injections.

     

An integrated optimization algorithm for parameter structure identification in groundwater modeling

The inverse problem of parameter structure identification in a distributed parameter system remains challenging. Identifying a more complex parameter structure requires more data. There is also the problem of over-parameterization. In this study, we propose a modified Tabu search for parameter structure identification. We embed an adjoint state procedure in the search process to improve the efficiency of the Tabu search. We use Voronoi tessellation for automatic parameterization to reduce the dimension of the distributed parameter. Additionally, a coarse-fine grid technique is applied to further improve the effectiveness and efficiency of the proposed methodology. To avoid over-parameterization, at each level of parameter complexity we calculate the residual error for parameter fitting, the parameter uncertainty error and a modified Akaike Information Criterion. To demonstrate the proposed methodology, we conduct numerical experiments with synthetic data that simulate both discrete hydraulic conductivity zones and a continuous hydraulic conductivity distribution. Our results indicate that the Tabu search allied with the adjoint state method significantly improves computational efficiency and effectiveness in solving the inverse problem of parameter structure identification.     

Sediment transport trends and cross-sectional stability of a lagoonal tidal inlet on the Central Coast of Vietnam

Lagoonal tidal inlets are a typical morphology of the Central Coast of Vietnam. Recently, navigation channels in these inlets have become increasingly threatened by siltation. This study analyses the relations between sediment distribution and transport trends (using the technique of Sediment Trend Analysis-STA■) in the lagoonal system of the De Gi inlet and then proposes appropriate countermeasures against sand deposition in the navigation channel. The STA identified three types of transport trends in the De Gi inlet, namely dynamic equilibrium, net accretion, and net erosion. Processes associated with the tidal prism have resulted in trends of sediment transport and deposition across the flood and ebb tidal shoals, which maintain a present cross-sectional area of about 1000m^2. However, longshore sediment transport from north to south resulting from northeast waves cause additional sand deposition in the channel. In addition, the effects of refraction associated with a nearby headland and jetty also increase sedimentation. These processes provide the main reasons for sediment deposition in the De Gi inlet. Short term and regular dredging helps to maintain the navigation channel. A system comprised of three jetties (north, south, and weir) is necessary to ensure the longterm cross-sectional stability of the navigation channel.     

Refining the origin of thermal water using stable isotope,hydrochemistry and GIS approaches in Jiaoxi,Taiwan

Comprehending the recharge of thermal springs is crucial for preserving the water quality of such springs. However, limited groundwater well data in mountainous areas presents a challenge to determining thermal-spring recharge areas. This study analyzes the isotopes (δ²H and δ¹⁸O) and major ions in rainwater, streamwater, mountain groundwater and thermal spring water in Jiaoxi, located near Taiwan's largest city, Taipei. The results of the isotope-elevation relationship and GIS recharge analysis indicate that the thermal spring water originated from a remote mountain at elevations of approximately 1170–1480 m, rather than the upstream watershed. The thermal spring water was divided into two groups based on the carbonate saturation index (SI) and isotope composition: the foothill group, which had a positive SI and lower δ value, and the downstream group, which had a negative SI and higher δ value. This study improved the conceptual model of the thermal flow path by demonstrating that the recharge of thermal water is a transboundary regional flow and that the foothill thermal water does not mix with the meteoric water. The revised model also highlights the role of structural lineament trends (faults, fractures and folds) in the movement of regional flow in fractured mountain blocks.     

Stochastic competitive analysis of hydropower and water supplies within an energy–water nexus

Energy and water are scarce resources and understanding the complicated energy–water nexus is an important issue for effective resource management. The purpose of this research was to analyze the competitive and cooperative relationships involving energy and water production and use. Specifically, tradeoff and integrated management of hydropower generation and water supplies are analyzed for energy–water systems. A Nash–Cournot model was established to analyze strategic behaviors among participants in energy–water systems. In the model, tradeoff analysis and integrated management of hydropower and water supplies were simulated for a reservoir system. In addition, hydropower and thermal power generation in competitive energy markets was examined. A case study of Dajia River reservoirs in the Tai-Chung and Chang-Hwa energy–water systems is presented. Dajia River is the second longest river in central Taiwan; the reservoirs system of Dajia River generates hydropower with installed capacity of 1150 MW. Strategic competitive and cooperative behaviors regarding energy–water linkage were quantified in the results. The results show that integrated management of hydropower and water supplies can increase renewable energy production, lower electricity equilibrium price, and decrease carbon dioxide emission.     

Peak and trough distributions of nonlinear waves

The exact and approximate probability density functions of wave peaks and troughs are derived for nonlinear, narrow-band waves. A comparison of these quantities with those of linear waves is given. It is shown that nonlinearity has significant effect on these quantities.     

Tectonic implications of Mesozoic magmatism to initiation of Cenozoic basin development within the passive South China Sea margin

International Journal of Earth Sciences - The South China Sea (SCS) is one of the classical example of a non-volcanic passive margin situated within three tectonic plates of the Eurasian,...     

Glacially derived material in an Inner Mongolian desert lake during Marine Isotope Stage 2

Establishing the precise timing of continental glacial dynamics and abrupt high‐latitude climate events is crucial to understanding the causes of global climate change. Here we present multi‐proxy records in a lake sediment core from arid Inner Mongolia (Wuliangsuhai Lake) that show two distinct glacially derived sedimentation events at ～26.2–21.8 and ～17.3–11.5k cal a BP. Fine sediments from the Last Glacial Maximum separate these glacially derived coarse sediments. Within these intervals, the occurrence of granite clasts at ～24–23.5, 17.3–17 and 15.6–14.1k cal a BP implies either sediment discharge by meltwater as well as strong current flow in the Yellow River and/or sediment influx through hill‐slope mass wasting and landsliding from the nearby Yin Mountains. Surface microfeatures of quartz grains and spot elemental analysis of black specks in these intervals, however, indicate that physical weathering is dominant and that the provenance of the rocks is probably from a glacial source. To the best of our knowledge, this is the first time glacier‐derived materials have been detected in any desert lake in the Yellow River basin. The occurrence of granite clasts roughly correlates with Heinrich events in the North Atlantic, suggesting synchronous ice sheet dynamics in high‐ and mid‐latitude regions during the Last Glacial period. Although our data provide unprecedented evidence for the influence of glacier‐related processes in arid Inner Mongolia, further well‐dated records are clearly needed to re‐evaluate the correlative inference drawn between granite clast layers in Wuliangsuhai Lake and Heinrich events in the North Atlantic. Copyright © 2012 John Wiley & Sons, Ltd.