Effects of installation sequence of concrete rigid inclusions by ground-displacement piling method on previously installed columns

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Ground improvement techniques using concrete injected column (CIC) or controlled modulus column (CMC) have been widely used since 1980s. However, impacts of ground displacement induced by the techniques have not been studied adequately. This project advances both experimental and numerical bases for assessing effects of installing CICs or CMCs on the surrounding soils and previously installed columns, with interests given to installation sequence and behaviour of concrete inclusion at early age. Three-dimensional numerical modelling was conducted to investigate how groups of columns installed in different sequences could affect previously installed columns. The assessment included coupled consolidation analyses in large strain mode, considering soil-column interaction. CMC installation was modelled numerically with the combined use of cylindrical and spherical cavity expansion theories. Where possible, the results were compared with analytical solutions and published field cases. The study revealed that the use of different installation sequences resulted in noticeable differences in the soil responses near existing CMCs as well as the difference in the bending moments generated in the previously installed columns. A soil-displacement piling rig and a fully instrumented soil tank were also designed and built in the laboratory to simulate column installations and to study the soil behaviour and the responses of previously built columns to nearby installations. A group of concrete columns were cast in-situ in soft soil using low strength concrete. The installation effects in terms of soil behaviours and structural responses of the columns were well captured by 3D laser scanning, soil miniature instrumentation, and a customised strain gauge system installed in CMCs. Test results revealed complex interactions between the soil and the columns, which are otherwise often difficult to observe in the field.
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