Review of constitutive models for describing the time dependent behaviour of soft clays

Different classes of constitutive models have been proposed to capture the time-dependent behaviour of soft soil (creep, stress relaxation, rate dependency). This paper critically reviews many of the models developed based on understanding of the time dependent stress-strain-stress rate-strain rate behaviour of soils and viscoplasticity in terms of their strengths and weaknesses. Some discussion is also made on the numerical implementation aspects of these models. Typical findings from numerical analyses of geotechnical structures constructed on soft soils are also discussed. The general elastic viscoplastic (EVP) models can roughly be divided into two categories: models based on the concept of overstress and models based on non-stationary flow surface theory. Although general in structure, both categories have their own strengths and shortcomings. This review indicates that EVP analysis is yet to be vastly used by the geotechnical engineers, apparently due to the mathematical complication involved in the formulation of the constitutive models, unconvincing benefit in terms of the accuracy of performance prediction, requirement of additional soil parameter(s), difficulties in determining them, and the necessity of excessive computing resources and time. © 2013 Taylor & Francis.

Effect of geosynthetic reinforcement creep on the long term performance of an embankment

Geo-synthetic reinforcements are often used to enhance the stability of geotechnical structures such as embankments. These geosynthetic polymers often show significant creep deformational behaviour. In the short-term performance of a geotechnical structure, it may not play a significant role. However, while dealing with the long term behaviour, it is necessary to investigate its effect. In this paper two plane strain fully coupled finite element analysis have been conducted; one with and the other without taking into account of the creep behaviour of geosynthetics. A well documented field case of Leneghans embankment (Geogrid improved wide embankment constructed near Sydney, Australia in 1990s) have been used for this purpose. It is evident from the analyses that though the geosynthetic reinforcements may play a vital role in the performance/stability of an embankment in the early days (during and after construction), its contribution may become insignificant with time and the creep of geo-synthetic may not play a significant role in the long term stability. © 2012 American Society of Civil Engineers.

Sexual behaviour of young people in Northern Ireland: First sexual experience

Two National Surveys of Sexual Attitudes and Lifestyles in Britain (Natsal) were conducted, one in 1990 and one in 2000. Northern Ireland was excluded from both studies. Now, for the first time, comparable data about sexual attitudes and lifestyles of young people (14- to 25-year-olds) in Northern Ireland are available. Data were collected through self-administered questionnaires, one-to-one interviews and focus-group discussions. As in Natsal 1990 and 2000, young people were asked about their sexual attitudes towards sex, experiences of sex education, knowledge of sexually transmitted infections (STIs) and, if sexually active, about the circumstances in which sexual intercourse occurred. A total of 1013 young people in the target age group completed the self-administered questionnaire. Young people in Northern Ireland do not differ significantly from their counterparts in Britain in terms of sexual lifestyles and attitudes. Some 53.3% of all respondents reported that they had had sexual intercourse. Condom use at first sex was reported by 64% of sexually active respondents; 27.4% said they used no contraception; 26.7% of all respondents said they had sex before age 16. Respondents who first had sex when they were 15 or 16 years were more likely than other respondents to say that 'being drunk' was the main reason why intercourse occurred. Peer pressure to engage in sex was more prevalent among males than females. Young people in Northern Ireland regard friends as their most important source of sex education. School is the second most important source but most respondents wanted more sex education in school. It is important that it is needs focused and includes potentially sensitive and contentious information.