Genetic appraisal of the culex sitiens subgroup in Australasia : major arbovirus vectors

University of Technology, Sydney. Faculty of Science.Culex annulirostris Skuse, Culex palpalis Taylor and Culex sitiens Wiedemann are members of the Culex sitiens subgroup that exist in Australasia. They are widely distributed and regularly comprise over the half of mosquitoes collected from arbovirus surveys and field collections in Australia and PNG. From these mosquitoes, Cx. annulirostris is the major vector of endemic arboviruses in Australia and is also responsible for the establishment of the Japanese encephalitis virus (JEV) in southern Papua New Guinea (PNG) as well as JEV incursions into northern Australia. Papua New Guinea and mainland Australia are separated by a small stretch of water, the Torres Strait, and its islands. While there has been regular JEV activity on these islands, JEV has not established on mainland Australia despite an abundance of its vector Cx. annulirostris and porcine amplifying hosts. Despite the public health significance of this mosquito and the fact that its adults show overlapping morphology with close relative Cx. palpalis, its evolution and genetic structure remain undetermined. I address a hypothesis that there is significant genetic diversity in Cx. annulirostris and that the identification of this diversity will shed light on the paradox that JEV can cycle on an island 70 km from mainland Australia while not establishing in Australia itself. My study assessed the biodiversity within Cx. annulirostris and Cx. palpalis using a extensive collection of mosquitoes and analysing both mitochondrial (COl) and a nuclear (ace-2) markers using phylogenetic reconstruction and hypothesis testing. I provide evidence of subdivision of these two species into several geographically delimited lineages, which indicates the presence of highly divergent populations or cryptic species. However I found lack of congruence between nuclear and mitochondrial markers. While I found eight divergent lineages geographically restricted within Cx. annulirostris and Cx. palpalis at the mitochondrial level, only four lineages appeared at the nuclear level. Two lineages appeared consistent using both markers: Cx. palpalis S-AUS and CX.annulirostris PNG1. Notably, the southern limit of the Cx. annulirostris PNG1 lineage coincides exactly with the current southern limit of JEV activity in Australasia suggesting that biological variation in this lineage may be the key to why JEV has not yet established yet on mainland Australia. I assessed the discrimination power of COl barcoding for Culex mosquitoes and conclude that DNA barcoding using COl may actually overestimate the diversity of Culex mosquitoes in Australasia and should be applied cautiously with support from nuclear DNA, such as the polymorphic ace-2 gene. Finally I designed and developed a PCR-based diagnostic tool to discriminate Cx. annulirostris PNG1 from its morphologically identical relative. This tool will greatly assist identification and surveillance of Cx. annulirostris PNG1 into Australia mainland in the future as it may move south into Australia as a consequence of climate change or population expansion

Finite Element Analysis of Floatation of Rectangular Tunnels Following Earthquake Induced Liquefaction

Underground structures such as tunnels, pipelines, car parks etc. can suffer severe damage during strong earthquake events. As many of these structures are buoyant, soil liquefaction due to earthquake loading can result in their floatation. In this paper, the floatation of rectangular tunnels, normally constructed by the cut-and-cover method, is investigated using dynamic finite element analyses. Sinusoidal and more realistic earthquake input motions are considered. The acceleration response of the tunnel and the soil surface following soil liquefaction is investigated. The generation of excess pore pressures in the soil around the tunnel and the consequent floatation of the tunnel are observed for both types of input motions. It will be shown that the amount of tunnel uplift depends on the type of input motion with the sinusoidal motion leading to a significantly larger uplift compared with the more realistic Kobe motion. Further, the effect of soil permeability on the floatation of the rectangular tunnel is investigated. It will be shown that tunnels can suffer floatation in finer soils with low permeabilities, whilst coarser soils with high permeability can lead to tunnel settlements owing to the rapid re-consolidation of the liquefied soils. The average axial strains in the soil above the tunnel will be shown to decrease with decreasing permeability.This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s40098-014-0133-

Centrifuge simulation of heave behaviour of deep basement slabs in over-consolidated clay

High demand on land in major cities is driving construction of basement structures to create additional space. Long-term heave of base slabs is a pertinent problem in deep basement construction in over-consolidated clay strata, such as the London clay. Sub-structures must be designed to withstand soil pressures and displacements that evolve gradually for many years after construction is complete. This paper discusses an ongoing research project using centrifuge modelling to quantify the development of long-term heave by shortening the time-scale through dimensional similarity. The excavation process is simulated by draining of a heavy fluid (sodium polytungstate) and a model basement structure is instrumented to record the evolution of heave movements with time. This paper presents the preliminary results of a centrifuge test, which captured the magnitude of short-term differential and total heave deformation, the changes in support loads in horizontal props, and the evolution of pore pressures around the basement structure. Challenges encountered in this experimental technique and plans for further experimental work are discussed.This research project is supported by the EPSRC Centre for Doctoral Training in Future Infrastructure and Built Environment in the University of Cambridge

Centrifuge testing to evaluate the liquefaction response of air-injected partially saturated soils beneath shallow foundations

Earthquake-induced liquefaction of saturated soils continues to cause severe damage to structures with shallow foundations. In recent years, artificially reducing the degree of saturation and forming partially saturated zones within saturated soils has been proposed as a liquefaction mitigation technique. This study experimentally investigates the liquefaction response of air-injected partially saturated soils beneath shallow foundations. A series of centrifuge tests were conducted on the shallow foundations with different bearing pressures. The results of the tests show that the generation of excess pore pressures and consequent liquefaction-induced settlements of shallow foundations were a strong function of the degree of saturation. Forming spatially distributed partially saturated zones in the liquefiable soils limited the development of high excess pore pressures and liquefaction susceptibility of soils, particularly at the higher confining stresses. The reduction in the degree of saturation of soils decreased the depth of liquefied soil layer, and increased the resistance of soil to the bearing capacity failure. On the other hand, the decrease in the degree of saturation of liquefiable soils led the larger accelerations to be transmitted to the foundations through unliquefied soil zones. It is therefore concluded that use of air-injection as a liquefaction mitigation measure does reduce structural settlements, but will have the consequence of larger structural accelerations.Ministry of National Education (M.E.B.) of TurkeyThis is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s10518-016-9968-

Liquefaction induced displacement and rotation of structures with wide basements

Earthquake induced liquefaction can cause structures with shallow foundations to experience large settlement and rotation, and can cause subsurface structures to uplift. The performance of structures with basements, which intuitively combine these two problems, is not understood. In this paper, data from three dynamic centrifuge tests on structures with wide basements are examined. The ratio of upward to downward vertical forces was varied, and a symmetric and asymmetric superstructure was tested. Digital image correlation was used to capture the soil displacements, providing novel insight into the co-seismic soil-structure interaction. The inclusion of wide basements was shown to reduce the overall settlement of structures by providing an increased uplift force during the liquefi ed period. For symmetric structures, symmetric soil displacements occurred around the basement during consecutive half-cycles of sinusoidal shaking, resulting in negligible accumulation of rotation. In contrast, significant rotation was accumulated for an asymmetric structure as a result of the P -delta effect due to the eccentric mass.The first author would like to thank the Engineering and Physical Science Research Council (EPSRC), United Kingdom, for their financial support through a Doctoral Training Account (DTA) studentship

Soil liquefaction-induced uplift of underground structures: Physical and numerical modeling

Underground structures located in liquefiable soil deposits are susceptible to floatation following a major earthquake event. Such failure phenomenon generally occurs when the soil liquefies and loses its shear resistance against the uplift force from the buoyancy of the underground structure. Numerical modeling accompanied with centrifuge experiments with shallow circular structures has been carried out to investigate the floatation failure at different buried depths of the structure. The influence of the magnitude of input sinusoidal earthquake shaking was also studied. Both numerical and experimental results showed matching uplift response of the structures and acceleration and pore-pressure measurements in the liquefied soil deposit. A higher uplift displacement of the structure was observed for shallower buried depth, thereby indicating the influence of overlying soil weight against floatation. Results also showed that the structures commenced floatation in the presence of high excess pore pressure, but they ceased when the earthquake shaking stopped. The higher rate of uplift in stronger earthquake shaking further substantiates the dependency of the uplift to the shaking amplitude. A constant rate of uplift of the structure was attained after the soil liquefied, hence postulating a possible limit to shear modulus degradation of the surrounding soil caused by soil-structure interaction. This is inferred by the lower excess pore-pressure generation near the structure. The displacement of liquefied soil around the displaced structure was also confirmed to resemble a global circular flow mechanism from the crown of the structure to its invert as observed in displacement vector plots obtained from numerical analysis and particle image velocimetry (PIV) in centrifuge tests. Further numerical analysis on the performance of buried sewer pipelines in Urayasu City, Chiba Prefecture following the 2011 Great East Japan Earthquake indicated high damage susceptibility of rigid pipelines in the liquefiable soil deposit. These consistencies with field observations clearly demonstrate and pave the prospects of applying numerical and/or experimental analyses for geotechnical problems associated with the floatation of underground structures in liquefiable soils.The authors are grateful for the financial support from the Cambridge Trust at the University of Cambridge and the Japan Ministry of Education, Culture, Sports, Science and Technology via the International Urban Earthquake Engineering Center for Mitigating Seismic Mega Risk program at Tokyo Institute of TechnologyThis is the final published version. It first appeared at http://ascelibrary.org/doi/abs/10.1061/(ASCE)GT.1943-5606.0001159

A new macro-element model encapsulating the dynamic moment–rotation behaviour of raft foundations

The interaction of shallow foundations with the underlying soil during dynamic loading can have both positive and negative effects on the behaviour of the superstructure. Although the negative impacts are generally considered within design codes, seldom is design performed in such a way as to maximise the potential beneficial characteristics. This is, in part, due to the complexity of modelling the soil–structure interaction. Using the data from dynamic centrifuge testing of raft foundations on dry sand, a simple moment–rotation macro-element model has been developed, which has been calibrated and validated against the experimental data. For the prototype tested, the model is capable of accurately predicting the underlying moment–rotation backbone shape and energy dissipation during cyclic loading. Utilising this model within a finite-element model of the structure could potentially allow a coupled analysis of the full soil–foundation–structure system's seismic response in a simplified manner compared to other methods proposed in literature. This permits the beneficial soil–structure interaction characteristics, such as the dissipation of seismic energy, to be reliably included in the design process, resulting in more efficient, cost-effective and safe designs. In this paper the derivation of the model is presented, including details of the calibration process. In addition, an appraisal of the likely resultant error of the model prediction is presented and visual examples of how well the model mimics the experimental data are provided. The authors would like acknowledge the collaborative and financial support received through the European Community’s Seventh Framework programme (FP7/2007-2013) under grant agreement number 227887 (SERIES – Seismic Engineering Research Infrastructures for European Synergies).This is the accepted manuscript. The final published version is available at http://www.icevirtuallibrary.com/content/article/10.1680/geot.SIP.15.P.020

Centrifuge investigation comparing the rocking response of two soil-structure systems

Seismic protection of structures by means of rocking isolation is becoming increasingly popular, because allowing uplift is an inexpensive way to reduce structural demand. However, understanding the role of soil–structure interaction in the response of rocking systems is important to define what type of rocking system might be most effective. To address this challenge, a campaign based on centrifuge modelling and testing is currently ongoing. The primary objective is to assess the force demand that rocking systems experience during their motion. Flexible structures that rock while stepping on discrete footings (structural rocking) and flexible structures with discrete footings rocking on soil (foundation rocking) are both considered. Following this distinction, two building models were designed with the only difference being the connectivity of the columns to the footings. For structural rocking, columns were designed to detach and step on their footings, while for foundation rocking the footing-column connection was designed to be rigid. The two building models were tested side-by-side in a centrifuge. A second test was also conducted, where thin steel “fuses” were installed in the interface of structural rocking, to further study the allocation of energy dissipation between structural elements and fuses, and soil medium. The building models were placed on the surface of dense sand and then tested using sinusoidal ground motions which caused a combination of sliding and rocking. The global response of the models in terms of overturning moment and storey shear was investigated and back validated by obtaining directly the internal loads, which were found capped regardless of the extent of rotation. More-over, the base isolation effect was evident during large amplitude resonant excitations, whereas during a low frequency low amplitude excitation there was no clear benefit of rocking. Finally, no significant effect was observed in limiting the base shear demand by using the steel fuses

Designing urban deep basements in South East England for future ground movement: Progress and opportunities for experimental simulation of long-term heave

In recent years, there has been a boom in urban infrastructure projects in and around London that require deep basements to be excavated, such as underground railway stations and shopping malls. The permanent removal of topsoil due to basement construction inevitably causes upward movement of the remaining soil. In London clay and other over-consolidated clay strata, this upward movement continues over many years after the basement structure’s completion, a process known as long-term heave. Urbanisation causes more and more of such deep basements to be constructed to greater depths and sizes than before. This has renewed interest in research on the long-term behaviour of base slabs in over-consolidated clay, because the basement structure must be designed to accommodate these long-term heave movements. The drive towards green construction techniques in next-generation infrastructure will require the methods of design need to be updated to allow more efficient use of material. This paper reviews a range of current techniques used in the design of deep basement slabs where significant long-term heave deformations are expected. While current design guidance is sufficient in ensuring the safety of construction and operation of underground urban spaces, there is a strong feeling within the construction industry that the design criteria are inefficient and need to be improved with the help of experimental data. Geotechnical centrifuge simulation is the main technique for physical modelling of long-term heave behaviour, as artificial gravity allows a year of real-life movements of soil to be replicated in a small-scale model in an hour of laboratory time. This paper reviews recent research in geotechnical centrifuge simulations on heave behaviour of deep excavations in over-consolidated clay, identifying key findings and pointing out areas that will require further research. These experimental simulations will allow the effect of long-term heave to be quantified more accurately in future design guidance, thereby addressing the need to conserve construction material as the requirement for urban underground space increases