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Soft soil in Hanoi, Vietnam, is mainly originated from lacustrine and shallow-sea sediment. This is the youngest formation with
around 3000 years of age. To serve the research purpose, clayey soil samples at ten areas in Hanoi and some places in the RRD
are prepared. Mineral composition of soils determined by X-ray diffraction analysis shows that clay minerals are predominated
by Illite, Kaolinite, Chlorite, and Montmorillonite respectively. Many previous researches indicated that in saline-saturated
condition, types of cation in saline water and types of clay mineral in soil layers, as well as their predomination decide the
changing process of geotechnical properties in other manner. In this paper, the initial relationship between geotechnical
properties and clay mineral composition of Hanoi soft soils in saline-saturated media is established

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The Stone-column is a useful method for increasing the bearing capacity and reducing settlement of foundation soil. The prediction of accurate ultimate bearing capacity of stone columns is very important in soil improvement techniques. Bulging failure mechanism usually controls the failure mechanism. In this paper, an imaginary retaining wall is used such that it stretches vertically from the stone column edge. A simple analytical method is introduced for estimation of the ultimate bearing capacity of the stone column using Coulomb lateral earth pressure theory. Presented method needs conventional Mohr-coloumb shear strength parameters of the stone column material and the native soil for estimation the ultimate bearing capacity of stone column. The validity of the developed method has been verified using finite element method and test data. Parametric studies have been carried out and effects of contributing parameters such as stone column diameter, column spacing, and the internal friction angle of the stone column material on the ultimate bearing capacity have been investigated.

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In soft soil areas, equal-length piles are often adopted in the retaining system. A decrease in the bending moment value borne by the retaining structure along the pile depth (below the excavation bottom), leads to an inadequate use of the pile bending capacity near the pile bottom. This paper presents retaining systems with long and short pile combinations, in which the long piles ensure integral stability of the excavation while the short piles give full play to bearing the bending moment. For further analysis on pile and bottom heaves deformations and inner-force characteristics, three-dimensional models were built in order to simulate the stage construction of the excavation. The ratio between long and short pile numbers, and the effects on short pile length pile horizontal deformation, pile bending moment and bottom heave are investigated in detail. In the end, a feasible long-short pile combination is established. Obtained results from the simulation data and the field data prove that the long-short pile retaining system is feasible.