Analysing consolidation data to optimise elastic visco-plastic model parameters for soft clay

University of Technology Sydney. Faculty of Engineering and Information Technology.Analysing the behaviour of soft soils under embankments is a significant challenging task for geotechnical engineers. By having more insight into long term soil behaviour and understanding the key parameters influencing the results, there will be more chance to strategically plan and utilise the soft ground for construction purposes. The time–dependent behaviour of soft soils, especially the ground settlements under structural and non–structural loading, is considered as a significant issue, which has been studied for many decades. Prediction of creep settlement of soft soils is a challenging task, as a very long period of time counted in years is involved. Many theories have been proposed along with a large number of laboratory and field measurements in order to provide more precise knowledge of the time–dependent viscous behaviour of soft soils. However, there are still some disagreements between theoretical and practical studies, which may keep the accuracy of the predictions questionable. Among the great number of developed models for soft soils, the elastic visco–plastic model with the non–linear creep function is considered as an effective method to describe the long–term stress–strain behaviour of soft soils. However, the difficulties to determine the model parameters limit the application of the model in practice. Since the relationship between the effective stress and strain during the dissipation of the excess pore water pressure cannot be identified easily, in the current practice the creep strain limit ε_lm^vp and the creep coefficient ψo/V to form the creep function are determined based on the curve fitting of the experimental data after the end of the primary consolidation. As a result, the number of data points available for the curve fitting is limited, and the extremely long tests are required. Moreover, in the conventional procedure for the ease of the curve fitting, the time parameter to in the elastic visco–plastic, which is the time value of the reference time line in the space of ε-log(σ’z), has been assumed as the time at the end of primary consolidation process. Hence, based on this assumption of to, the reference time line would include viscous strain, which is contradict to the definition of a viscous free reference time line. Thus, the value of to influences not only the reference time line parameters, but also the parameters of the creep function. Additionally, the conventional determination approach for the model parameters is influenced by the thickness of the soil sample. Hence, the model parameters obtained by the conventional method may not be unique. As a result, the main objective of this research project is to propose a numerical solution to determine the model parameters for the elastic visco–plastic model adopting the trust–region reflective least square algorithm. The trust-region reflective least square algorithm is an advanced optimisation method for the non-linear equation system. A Crank–Nicolson finite difference scheme is applied to solve the coupled partial differential equations in order to simulate one-dimensional stress-strain behaviour of soft soil with different boundary conditions. The proposed method can adopt the experimental data during the dissipation of the excess pore water pressure to determine all the model parameters simultaneously. In this thesis, a series of laboratory experiments were conducted at the UTS soil laboratory using two sizes of hydraulic consolidation Rowe cell setups. A 29.5 mm thick soil sample of a kaolinite mixture was tested and adopted to determine the model parameters, while an experimental result of a thicker soil sample (i.e. 140.5 mm thick) was compared with the predictions using the optimised model parameters. The Rowe cell setups can measure the volume change, the vertical settlement and the excess pore water pressure continuously. Especially, the large Rowe cell setup to conduct the test on the 140.5 mm thick soil sample was modified to measure the excess pore water pressure at different depth and different distances to the centre line at the base. Moreover, other four validation exercises including two laboratory–based case studies and two field–based case studies were included to verify the ability of the proposed method to analyse the time-dependent behaviour of soft soils. The developed method can be considered as a simple, practical and accurate solution for the model parameter determination. The optimised model parameters allow the predictions of settlement to be in good agreement with the measurements, while the predictions of the excess pore water pressure are reasonably close to the measurement. Additionally, the variations of the creep strain limit, the creep coefficient and the creep strain rate during the dissipation of the excess pore water pressure can be observed. Moreover, the unusual increase of the excess pore water pressure in the early stages of loading can be also predicted. The numerical analysis applying the proposed method is able to illustrate the influence of the soil layer thickness on the time–dependent stress-strain behaviour of soft soil. The proposed approach can be adopted to back calculate the elastic visco-plastic model parameters for real case in the field utilising time-dependent settlement and excess pore water pressure measurements

Small-strain properties of soft clay treated with fibre and cement

To improve the dynamic properties of soft soil, the cement treatment technique combined with fibre reinforcement can be employed. In this study, the effects of two types of fibres (polypropylene and recycled carpet) on the hardening process and small-strain properties of cement-treated kaolinite and bentonite clays are investigated. Cement-treated clay specimens were prepared using cement contents of 5%, 10% and 15% by weight of dry soil for the kaolinite samples, and 30%, 40% and 50% for the bentonite samples. To investigate and understand the influence of different fibre types and contents, three different percentages of fibre content were adopted: 0.1%, 0.2% and 0.5% polypropylene fibres, and 0.5%, 0.75% and 1% carpet fibres. The results of bender element tests on 126 cylindrical samples of cement-treated clay with various cement and fibre contents were analysed to discern the relationships between fibre and cement content and the small-strain mechanical properties, including the shear wave velocity and maximum small-strain shear modulus of the treated soil. The influence of fibres and cement contents on the hardening time of treated soil has also been investigated. © 2013 Thomas Telford Ltd

Analyzing consolidation data to obtain elastic viscoplastic parameters of clay

© 2015 Techno-Press, Ltd. A nonlinear creep function incorporated into the elastic visco-plastic model may describe the long-term soil deformation more accurately. However, by applying the conventional procedure, there are challenges to determine the model parameters due to limitation of suitable data points. This paper presents a numerical solution to obtain several parameters simultaneously for a nonlinear elastic visco-plastic (EVP) model using the available consolidation data. The finite difference scheme using the Crank-Nicolson procedure is applied to solve a set of coupled partial differential equations of the time dependent strain and pore water pressure dissipation. The model parameters are determined by applying the algorithm of trust-region reflective optimisation in conjunction with the finite difference solution. The proposed method utilises all available consolidation data during dissipation of the excess pore water pressure to determine the required model parameters. Moreover, the reference time in the elastic visco-plastic model can readily be adopted as a unit of time; denoting creep is included in the numerical predictions explicitly from the very first time steps. In this paper, the settlement predictions of thick soft clay layers are presented and discussed to evaluate and compare the accuracy and reliability of the proposed method against the graphical procedure to obtain the model parameters. In addition, comparison of the available experimental results to the numerical predictions confirms the accuracy of the numerical procedure

Predicting consolidation coefficient of soft clay by time-displacement-velocity methods

The coefficient of consolidation is a parameter, governing the rate at which saturated clay undergoes consolidation when subjected to an increase in pressure. The rate and amount of compression in clay varies with the rate that excess pore water pressure is dissipated; and hence depends on clay permeability. Over many years, various methods have been proposed to determine the coefficient of consolidation, c , which is an indication of the rate of foundation settlement on soft ground. However, defining this parameter is often problematic and greatly relies on graphical techniques, which are subject to some uncertainties. This paper initially presents an overview of many well-established methods to determine the vertical coefficient of consolidation from the incremental loading consolidation tests. An array of consolidation tests was conducted on fully-saturated and undisturbed clay samples retrieved by an oil-operated sampler, collected at various depths from a site in Nakdong river delta, Busan, South Korea. The test results on these soft sensitive clay samples were employed to predict the settlement rate of Busan clay. To establish the relationship of time-displacement-velocity, a total of 3 method groups from 10 common procedures were classified and compared together. Detailed discussion on the results of this study is also provided.

Utilization of services provided by village based ethnic minority midwives in mountainous villages of Vietnam

Introduction: Since 2011, the Vietnam’s Ministry of Health implemented the ethnic minority midwives (EMMs) scheme in order to increase the utilization of maternal health services by women from ethnic minorities and those living in hard-to-reach mountainous areas. This paper analyzes the utilization of antenatal, delivery, and postpartum care provided by EMMs and reports the key determinants of utilization of EMM services as perceived by service users. Methods: A structured questionnaire was administered in 2015 to all mothers (n=320) who gave birth to a live-born during a 1-year period in 31 villages which had EMM in two provinces, Dien Bien and Kon Tum. A multivariate logistic regression model was used to examine the association between all potential factors and the use of services provided by EMMs. Results: We found that EMMs provided more antenatal care and postnatal care as compared with delivery services, which corresponded to their job descriptions. The results also showed that utilization of antenatal care provided by EMMs was lower than that of postnatal care. The proportion of those who never heard about EMM was high (24%). Among the mothers who knew about EMM services, 33.4% had antenatal checkups, 20.1% were attended during home deliveries, and 57.3% had postnatal visits by an EMM. Key factors that determined the use of EMM services included knowledge of the location of EMM’s house, being aware about EMMs by health workers, trust in services provided by EMMs, and perception that many others mothers in a village also knew about EMM services. Conclusion: EMM seems to be an important mechanism to ensure assistance during home births and postnatal care for ethnic minority groups, who are often resistant to attend health facilities. Building trust and engaging with communities are the key facilitators to increase the utilization of services provided by EMMs. Communication campaigns to raise awareness about EMMs and to promote their services in the village, particularly by other health workers, represent an important strategy to further improve effectiveness of EMM scheme

Effectiveness of tapentadol prolonged release (PR) compared with oxycodone/naloxone PR for the management of severe chronic low back pain with a neuropathic component: a randomized, controlled, open‐label, phase 3b/4sStudy

[Abstract] OBJECTIVE: To evaluate the effectiveness of tapentadol prolonged release (PR) vs. oxycodone/naloxone PR in non-opioid-pretreated patients with severe chronic low back pain with a neuropathic pain component. METHODS: Eligible patients (average pain intensity [numerical rating scale-3 (NRS-3)] ≥6; painDETECT positive/unclear) were randomized to twice-daily tapentadol PR 50 mg or oxycodone/naloxone PR 10 mg/5 mg. After a 21-day titration (maximum twice-daily doses: tapentadol PR 250 mg, or oxycodone/naloxone PR 40 mg/20 mg plus oxycodone PR 10 mg), target doses were continued for 9 weeks. The primary effectiveness endpoint was the change in NRS-3 from baseline to final evaluation; the exact repeated confidence interval (RCI) for tapentadol PR minus oxycodone/naloxone PR was used to establish noninferiority (upper limit <1.3) and superiority (confirmatory analyses). RESULTS: For the primary effectiveness endpoint, tapentadol PR was noninferior to oxycodone/naloxone PR (97.5% RCI: [-1.820, -0.184]; P < 0.001). This exact RCI also yielded evidence of superiority for tapentadol PR vs. oxycodone/naloxone PR (significantly greater reduction in pain intensity; P = 0.003). Improvements (baseline to final evaluation) in painDETECT and Neuropathic Pain Symptom Inventory scores were significantly greater with tapentadol PR vs. oxycodone/naloxone PR (all P ≤ 0.005). CONCLUSIONS: The study was formally shown to be positive and demonstrated, in the primary effectiveness endpoint, the noninferiority for tapentadol PR vs. oxycodone/naloxone PR. The effectiveness of tapentadol PR was superior to that of oxycodone/naloxone PR by means of clinical relevance and statistical significance (confirmatory evidence of superiority). Tapentadol PR was associated with significantly greater improvements in neuropathic pain-related symptoms and global health status than oxycodone/naloxone PR and with a significantly better gastrointestinal tolerability profile. Tapentadol PR may be considered a first-line option for managing severe chronic low back pain with a neuropathic pain component

Design and fabrication of effective gradient temperature sensor array based on bilayer SnO2/Pt for gas classification

Classification of different gases is important, and it is possible to use different gas sensors for this purpose. Electronic noses, for example, combine separated gas sensors into an array for detecting different gases. However, the use of separated sensors in an array suffers from being bulky, high-energy consumption and complex fabrication processes. Generally, gas sensing properties, including gas selectivity, of semiconductor gas sensors are strongly dependent on their working temperature. It is therefore feasible to use a single device composed of identical sensors arranged in a temperature gradient for classification of multiple gases. Herein, we introduce a design for simple fabrication of gas sensor array based on bilayer Pt/SnO2 for real-time monitoring and classification of multiple gases. The study includes design simulation of the sensor array to find an effective gradient temperature, fabrication of the sensors and test of their performance. The array, composed of five sensors, was fabricated on a glass substrate without the need of backside etching to reduce heat loss. A SnO2 thin film sensitized with Pt on top deposited by sputtering was used as sensing material. The sensor array was tested against different gases including ethanol, methanol, isopropanol, acetone, ammonia, and hydrogen. Radar plots and principal component analysis were used to visualize the distinction of the tested gases and to enable effective classification

Predicting Distribution of Aedes Aegypti and Culex Pipiens Complex, Potential Vectors of Rift Valley Fever Virus in Relation to Disease Epidemics in East Africa.

The East African region has experienced several Rift Valley fever (RVF) outbreaks since the 1930s. The objective of this study was to identify distributions of potential disease vectors in relation to disease epidemics. Understanding disease vector potential distributions is a major concern for disease transmission dynamics. DIVERSE ECOLOGICAL NICHE MODELLING TECHNIQUES HAVE BEEN DEVELOPED FOR THIS PURPOSE: we present a maximum entropy (Maxent) approach for estimating distributions of potential RVF vectors in un-sampled areas in East Africa. We modelled the distribution of two species of mosquitoes (Aedes aegypti and Culex pipiens complex) responsible for potential maintenance and amplification of the virus, respectively. Predicted distributions of environmentally suitable areas in East Africa were based on the presence-only occurrence data derived from our entomological study in Ngorongoro District in northern Tanzania. Our model predicted potential suitable areas with high success rates of 90.9% for A. aegypti and 91.6% for C. pipiens complex. Model performance was statistically significantly better than random for both species. Most suitable sites for the two vectors were predicted in central and northwestern Tanzania with previous disease epidemics. Other important risk areas include western Lake Victoria, northern parts of Lake Malawi, and the Rift Valley region of Kenya. Findings from this study show distributions of vectors had biological and epidemiological significance in relation to disease outbreak hotspots, and hence provide guidance for the selection of sampling areas for RVF vectors during inter-epidemic periods

One-step isolation and biochemical characterization of a highlyactive plant PSII monomeric core

We describe a one-step detergent solubilization protocol for isolating a highly active form of Photosystem II (PSII) from Pisum sativum L. Detailed characterization of the preparation showed that the complex was a monomer having no light harvesting proteins attached. This core reaction centre complex had, however, a range of low molecular mass intrinsic proteins as well as the chlorophyll binding proteins CP43 and CP47 and the reaction centre proteins D1 and D2. Of particular note was the presence of a stoichiometric level of PsbW, a low molecular weight protein not present in PSII of cyanobacteria. Despite the high oxygen evolution rate, the core complex did not retain the PsbQ extrinsic protein although there was close to a full complement of PsbO and PsbR and partial level of PsbP. However, reconstitution of PsbP and PsbPQ was possible. The presence of PsbP in absence of LHCII and other chlorophyll a/b binding proteins confirms that LHCII proteins are not a strict requirement for the assembly of this extrinsic polypeptide to the PSII core in contrast with the conclusion of Caffarri et al. (2009)