Infilling of underground voids using a cement mixture is an effective measure to prevent the collapse of old mines, or to restore the ground reaction against overlying foundations. Normally a slurry mixture with high workability is placed into a void under gravity allowing a wide areas to be filled effectively from a single pouring point. However a different type of mixture, a plastic grout, is needed when only limited area is to be filled or where mixtures spillage would lead to problems. The aim of this study is to better understand the behavior of plastic infilling material in the quest for greater reliability in actual work. Two full-scale model tests using plastic grout are described with the spreading pattern and infilling pressure experimentally and numerically assessed. The first test involved filling a 5 m by 7 m void of 500 mm height with plastic grout in a single filling step. In the second test, 2.6 m by 3.0 m void of 200 mm height, was filled in two steps. Both the tests were numerically simulated, with results that quantitatively recreated the experimental infilling pressures.

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Growing infrastructure development gives rise to new advancements in construction industry. Nanotechnology contributes to the construction industry development by improvements made in the engineering properties of construction materials from the micro to the macro level as nano-composites. Cement plays a vital role in geotechnical applications as a chief material for wide range of ground modification techniques. Grouting is one of the techniques extensively applied to enhance advantageously the properties of different soil profiles and grain size with good reports of improved performance. This paper discusses the performance study made on a neat cementitious grout incorporated with nanosilica (nSiO₂). This study has been performed on the grout with a w/c ratio 1.20 at 0%, 0.10%, 0.50%, 1.0%, 1.50% of nanosilica dosage to cement content. Various rheological properties of the grout were studied along with permeation grouting onto a coarse sand column. It has been found that the nano silica enriched cementitious grout results in higher groutability, flowability with controlled bleedability with higher efficiency, reduced permeability and remarkable changes in the compressive strength.

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Soil cement mixing by deep mixing technique is used as a soft soil improvement method. Deep mixing columns are widely used to support embankment constructed on a soft ground area. In order to applying this improvement method, the failure pattern of group column type improvement should be analyzed. Researches on the failure pattern of columns are done by some authors when the columns individually fail. Due to individual failure of col-umns under loading, a layer of shallow mixing is proposed to reinforce individual columns working as a group in order to increase the stability as well as loading capacity of columned improved area. This research focuses on the failure pattern of group of columns which are fixed by the shallow mixing layer under embankment loading layer. By comparing to failure mechanism of individual columns, the effect of shallow mixing on failure pattern of deep mixing columns is also discussed. Finite element method is used for this analysis with Plaxis code under plain strain condition. The effect of shallow mixing layer thickness on reducing horizontal displacement of embankment is various with different values of strength and stiffness of cement mixing area which is discussed in this research.

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The wet and dry types of deep mixing methods have been developed and widely been applied for on-land and marine constructions. The quality assurance (QA) of the methods has been usually carried out by unconfined compression test on field stabilized soil sampled by core boring in Japan. In some countries, stabilized soil excavated by the wet grab sampling is subjected to unconfined compression test. There are several merits and demerits in each method, but few studies compare the strength of these two specimens to discuss its applicability to practical construction. In this study, the wet grab sampling was carried out at two road embankment construction sites where the wet and dry types of deep mixing method were applied. The cement stabilized soil was excavated by a wet grab sampler soon after the DM column construction. The test result is compared with the previous studies to discuss the applicability of the web grab sampling method.

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A simplified method for evaluating the liquefaction of sandy soil confined by a lattice-type deep mixing wall is proposed in this paper. The method calculates the cumulative excess pore water pressure from the initial shear strain using an equivalent shear-stiffness model created using a homogenization method. The proposed method uses parameters whose physical meaning is clearly defined, and can evaluate not only the effect of variations in the external forces but also the physical properties of the ground. This paper first explains the proposed idea and then presents the calculation procedure using an actual site plan.

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