Centrifuge tests investigating inclined grout micro-piles as a method of liquefaction remediation for existing buildings

This paper presents a series of centrifuge tests carried out to investigate the performance of non-structural inclined micro-piles as a potential liquefaction remediation method for existing buildings. Both a single-degree-of-freedom frame structure and a two-storey, two-degree-of-freedom frame structure were used as model buildings in these tests. Centrifuge tests were carried out with and without micro-piles in the foundation soil for each structure. Results primarily from the tests with the SDOF structure are presented in this paper. It is found that the micro-piles have some beneficial effect by increasing shear strains in the soil in their vicinity and hence causing dilation in these zones. However, they also increase structural accelerations by transmitting accelerations from deep in the soil and the beneficial effects from increased dilation are outweighed by the detrimental migration of pore pressures.

Ground improvement methods for liquefaction remediation

Soil liquefaction continues to be a major source of damage to buildings and infrastructure after major earthquake events. Ground improvement methods are widely used at many sites worldwide as a way of mitigating liquefaction damage. The relative success of these ground improvement methods in preventing damage after a liquefaction event and the mechanisms by which they can mitigate liquefaction continue to be areas of active research. In this paper the emphasis is on the use of dynamic centrifuge modelling as a tool to investigate the effectiveness of ground improvement methods in mitigating liquefaction risk. Three different ground improvement methods will be considered. First, the effectiveness of in situ densification as a liquefaction resistance measure will be investigated. It will be shown that the mechanism by which soil densification offers mitigation of the liquefaction risk can be studied at a fundamental level using dynamic centrifuge modelling. Second, the use of drains to relieve excess pore pressures generated during an earthquake event will be considered. It will be shown that current design methods can be further improved by incorporating the understanding obtained from dynamic centrifuge tests. Finally, the use of soil grouting to mitigate liquefaction risk will be investigated. It will be shown that by grouting the foundation soil, the settlement of a building can be reduced following earthquake loading. However, the grouting depth must extend the whole depth of the liquefiable layer to achieve this reduction in settlements.

Centrifuge modelling of inclined micro-piles for liquefaction remediation of existing buildings

This paper describes four centrifuge tests investigating the performance of non-structural inclined micro-piles as a liquefaction remediation method for existing buildings. Two soil profiles with the same superstructure founded on each were tested under earthquakes of different magnitudes and durations. The first profile consisted of a deep, homogeneous layer of loose, liquefiable sand. The second comprised a shallow layer of loose sand overlying dense sand. Centrifuge tests were carried out with and without inclined micro-piles in each soil profile. The superstructure was modelled as an idealised single degree of freedom (SDOF) system. It is found that the micro-piles have no detrimental effect on the performance of the structure during and after earthquakes. It is also possible that their presence may decrease structural settlements in earthquakes which cause liquefaction to a depth less than that of the improved zone. However, no conclusive evidence is obtained to show that the micro-piles significantly restrain lateral soil movement due to monotonic shearing from the structure or impede the migration of excess pore pressures from the free field to the foundation zone. Both these processes have critical effects on structural settlement. The use of inclined micro-piles for liquefaction remediation should therefore be considered with caution.

Cementation liquefaction remediation for existing buildings

Many typical liquefaction remediation techniques are not appropriate for application under existing buildings and more novel techniques are required. This paper describes centrifuge tests investigating the performance of cementation as a liquefaction remediation method. Two soil profiles with the same superstructure were tested under earthquake shaking. The first profile consisted of a deep layer of loose, liquefiable sand. The second comprised a shallow layer of loose sand overlying dense sand. Centrifuge tests were carried out with a cemented zone underneath the structure, through the full depth of the liquefiable layers and also partial depth. The superstructure was modelled as a single-degree-offreedom system. It is found that a cemented zone through the full depth of a liquefiable layer results in considerable reduction of structural settlements. Increased magnitude and higher frequency accelerations are transmitted to the structure but, depending on the building characteristics, it is likely that improved overall seismic performance can be achieved. Improvements in structural settlements can also be obtained with partialdepth remediation, if the depth of the cemented zone is greater than the depth of liquefaction. This type of remediation seems to have little effect on the accelerations transmitted to the structure.

Role of RNA polymerase IV in plant small RNA metabolism.

In addition to the three RNA polymerases (RNAP I-III) shared by all eukaryotic organisms, plant genomes encode a fourth RNAP (RNAP IV) that appears to be specialized in the production of siRNAs. Available data support a model in which dsRNAs are generated by RNAP IV and RNA-dependent RNAP 2 (RDR2) and processed by DICER (DCL) enzymes into 21- to 24-nt siRNAs, which are associated with different ARGONAUTE (AGO) proteins for transcriptional or posttranscriptional gene silencing. However, it is not yet clear what fraction of genomic siRNA production is RNAP IV-dependent, and to what extent these siRNAs are preferentially processed by certain DCL(s) or associated with specific AGOs for distinct downstream functions. To address these questions on a genome-wide scale, we sequenced approximately 335,000 siRNAs from wild-type and RNAP IV mutant Arabidopsis plants by using 454 technology. The results show that RNAP IV is required for the production of >90% of all siRNAs, which are faithfully produced from a discrete set of genomic loci. Comparisons of these siRNAs with those accumulated in rdr2 and dcl2 dcl3 dcl4 and those associated with AGO1 and AGO4 provide important information regarding the processing, channeling, and functions of plant siRNAs. We also describe a class of RNAP IV-independent siRNAs produced from endogenous single-stranded hairpin RNA precursors.

An allelic series reveals essential roles for FY in plant development in addition to flowering-time control

The autonomous pathway functions to promote flowering in Arabidopsis by limiting the accumulation of the floral repressor FLOWERING LOCUS C (FLC). Within this pathway FCA is a plant-specific, nuclear RNA-binding protein, which interacts with FY, a highly conserved eukaryotic polyadenylation factor. FCA and FY function to control polyadenylation site choice during processing of the FCA transcript. Null mutations in the yeast FY homologue Pfs2p are lethal. This raises the question as to whether these essential RNA processing functions are conserved in plants. Characterisation of an allelic series of fy mutations reveals that null alleles are embryo lethal. Furthermore, silencing of FY, but not FCA, is deleterious to growth in Nicotiana. The late-flowering fy alleles are hypomorphic and indicate a requirement for both intact FY WD repeats and the C-terminal domain in repression of FLC. The FY C-terminal domain binds FCA and in vitro assays demonstrate a requirement for both C-terminal FY-PPLPP repeats during this interaction. The expression domain of FY supports its roles in essential and flowering-time functions. Hence, FY may mediate both regulated and constitutive RNA 3'-end processing.

Modelling of liquefaction-induced instability in pile

Centrifuge testing has been undertaken to investigate instability failure of pile groups during seismic liquefaction, with specific reference to the 'top-down' propagation of liquefaction during the earthquake and to account for initial imperfections in pile geometry. The results of these tests were used to validate numerical models within the finite element program ABAQUS, based on the popular p-y analysis method. Pseudostatic classical and post-buckling analyses were conducted to examine the collapse behaviour of the pile groups and were found to give reasonable predictions of collapse load and conservative predictions of the associated deflection conditions. This numerical model was compared to currently published methods which were found to over-predict collapse loads. The resulting insights into the collapse of axially loaded pile groups revealed that the failure load is strongly dependent on both the depth of liquefaction propagation and initial imperfections, which reduce the collapse load.

Optimisation of fuel usage and steam availability in the power and steam plant of a paper mill

This paper presents the results of a project aimed at minimising fuel usage while maximising steam availability in the power and steam plant of a large newsprint mill. The approach taken was to utilise the better regulation and plant wide optimisation capabilities of Advanced Process Control, especially Model Predictive Control (MPC) techniques. These have recently made their appearance in the pulp and paper industry but are better known in the oil and petrochemical industry where they have been used for nearly 30 years. The issue in the power and steam plant is to ensure that sufficient steam is available when the paper machines require it and yet not to have to waste too much steam when one or more of the machines suffers an outage. This is a problem for which MPC is well suited. It allows variables to be kept within declared constraint ranges, a feature which has been used, effectively, to increase the steam storage capacity of the existing plant. This has resulted in less steam being condensed when it is not required and in significant reductions in the need for supplementary firing. The incidence of steam being dump-condensed while also supplementary firing the Combined Heat & Power (CHP) plant has been reduced by 95% and the overall use of supplementary firing is less than 30% of what it was. In addition the plant runs more smoothly and requires less operator time. The yearly benefit provided by the control system is greater than £200,000, measured in terms of 2005 gas prices.

Effect of superstructure stiffness on liquefaction-induced failure Mechanisms

Soil liquefaction following strong earthquakes causes extensive damage to civil engineering structures. Foundations of buildings, bridges etc can suffer excessive rotation/settlement due to liquefaction. Many of the recent earthquakes bear testimony for such damage. In this article a hypothesis that "Superstructure stiffness can determine the type of liquefaction-induced failure mechanism suffered by the foundations" is proposed. As a rider to this hypothesis, it will be argued that liquefaction will cause failure of a foundation system in a mode of failure that offers least resistance. Evidence will be offered in terms of field observations during the 921 Ji-Ji earthquake in 1999 in Taiwan and Bhuj earthquake of 2001 in India. Dynamic centrifuge test data and finite element analyses results are presented to illustrate the traditional failure mechanisms. Copyright © 2010, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited.

Control of meiotic recombination frequency in plant genomes.

Sexual eukaryotes reproduce via the meiotic cell division, where ploidy is halved and homologous chromosomes undergo reciprocal genetic exchange, termed crossover (CO). CO frequency has a profound effect on patterns of genetic variation and species evolution. Relative CO rates vary extensively both within and between plant genomes. Plant genome size varies by over 1000-fold, largely due to differential expansion of repetitive sequences, and increased genome size is associated with reduced CO frequency. Gene versus repeat sequences associate with distinct chromatin modifications, and evidence from plant genomes indicates that this epigenetic information influences CO patterns. This is consistent with data from diverse eukaryotes that demonstrate the importance of chromatin structure for control of meiotic recombination. In this review I will discuss CO frequency patterns in plant genomes and recent advances in understanding recombination distributions.