Numerical investigation of soil plugging effect inside sleeve of cast-in-place piles driven by vibratory hammers in clays.

During driving sleeve of cast-in-place piles by vibratory hammers, soils were squeezed into sleeve and then soil plugging was formed. The physic-mechanical properties of the soil plug have direct influence on the load transmission between the sleeve wall and soil plug. Nevertheless, the researches on this issue are insufficient. In this study, finite element and infinite element coupling model was introduced, through the commercial code ABAQUS, to simulate the full penetration process of the sleeve driven from the ground surface to the desired depth by applying vibratory hammers. The research results indicated that the cyclic shearing action decreases both in soil shear strength and in granular cementation force when the sleeve is driven by vibratory hammers, which leads to a partially plugged mode of the soil plug inside the sleeve. Accordingly, the penetration resistance of sleeve driven by vibratory hammers is the smallest compared to those by other installation methods. When driving the sleeve, the annular soil arches forming in the soil plug at sleeve end induce a significant rise in the internal shaft resistance. Moreover, the influence of vibration frequencies, sleeve diameters, and soil layer properties on the soil plug was investigated in detail, and at the same time improved formulas were brought forward to describe the soil plug resistance inside vibratory driven sleeve.

[Study on the prevalence and risk factors of "subhealth" status in college and university staff in Guangdong province].

OBJECTIVE: To understand the current status and risk factors of "subhealth" in college and university staff in Guangdong province. METHODS: Eight thousand four hundred and seventeen staff in 19 colleges and universities in Guangdong were investigated through a self-developed questionnaire, and statistically analyzed using chi(2) test, chi(2)(strand) test and odd ratio. Judgement was based on the criteria on "subhealth" through Delphi method. RESULTS: Overall incidence of "subhealth" was 69.18% in 8,417 staff members, and the highest was in the age group of 30 - 40 year olds (totally 79.17%). The prevalence of severe "subhealth" in females was significantly higher than that of males (chi(2) = 14.19, P < 0.01). The main risk factors of "subhealth" were occupational stress, psychological factors, bad habits and behaviors. 44.21% of the 8,417 staff were aware of the terminology "subhealth", and 36.84% thought themselves under "subhealthy" condition. CONCLUSION: The health condition of college and university staff in Guangdong was not satisfactory, thus it was essential to carry out active measures of prevention and intervention among this population.