Test on Mechanical Properties of Cemented Soils Using Secondary Development Data Acquisition Test System
A secondary development of computer aided data acquisition test system is performed in order to improve the disadvantages of original system. In this way, the qualified influences of cement content and curing time on yield strength and stiffness of soil can be automatic acquisition in consolidated undrained triaxial tests. The data collected from the system show that the deviatoric stress of soil increases with increasing axial strain initially followed by a relatively smooth decline after yield point. Yield strength increases with increasing cement content and curing time at the same strain. A well-defined linear relationship between yield strength and cement content are observed and also the relationship between yield strength and curing time. Finally, a linear function is defined to express the linear relationship between yield strength and those two factors and corresponding linear coefficients are obtained through a multiple regression analysis of test data. Stiffness of specimens shows an initial sharp degradation followed by smooth attenuation with increasing axial strain. The addition of cement and long curing time can effectively improve the stiffness of specimens especially at low strain areas.
Circular footings on a cemented layer above weak foundation soil
This work proposes a method for predicting the behavior of shallow footings bearing on an upper layer of processed cemented soil that overlies a lower layer of weakly bonded residual soil with a high void ratio. The paper describes the results of a series of field plate tests and numerical simulations. The results lead to a semi-empirical method for designing shallow foundations on a double-layer system. The method has been validated by comparison of predicted values with results from a separate series of plate-loading tests. For engineering practice, the proposed method provides acceptable predictions of bearing capacities and loadsettlement curves.Key words: footings, cemented layer, layered system, weakly bonded, high void ratio.
Long term response stability of a well-type ionization chamber used in calibration of high dose rate brachytherapy sources
Well-type ionization chamber is often used to measure strength of brachytherapy sources. This study aims to check long term response stability of High Dose Rate (HDR)-1000 Plus well-type ionization chamber in terms of reference air kerma rate (RAKR) of a reference 137Cs brachytherapy source and recommend an optimum frequency of recalibration. An HDR-1000 Plus well-type ionization chamber, a reference 137Cs brachytherapy source (CDCSJ5), and a MAX-4000 electrometer were used in this study. The HDR-1000 Plus well-type chamber was calibrated in terms of reference air kerma rate by the Standards Laboratory of the International Atomic Energy Agency (IAEA), Vienna. The response of the chamber was verified at regular intervals over a period of eight years using the reference 137Cs source. All required correction factors were applied in the calculation of the RAKR of the 137Cs source. This study reveals that the response of the HDR-1000 Plus well-type chamber was well within ±0.5% for about three years after calibration/recalibration. However, it shows deviations larger than ±0.5% after three years of calibration/recalibration and the maximum variation in response of the chamber during an eight year period was 1.71%. The optimum frequency of recalibration of a high dose rate well-type chamber should be three years.