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Columnar inclusion is one of the effective and widely used methods for improving engineering properties of soft clay ground. This article investigates the consolidation behavior of composite soft clay ground using physical model tests under an axial-symmetry condition and finite element simulations by PLAXIS 2D program. It is found out that the final settlement and the rate of consolidation of the composite ground depend on the stress state (of what ?). For an applied stress much lower than the failure stress, the final settlement of the ground is insignificant and the consolidation is fast. When the soil-cement column fails, the stress on column suddenly decreases (due to strain-softening) meanwhile the stress on soil increases to maintain the force equilibrium. Consequently, the excess pore pressure in the surrounding clay increases immediately. The cracked soil-cement column acts as a drain, accelerating the dissipation of the excess pore pressure. The consolidation of the composite ground is mainly in vertical direction and controlled by the area ratio, the ratio of diameter of soil-cement column to the diameter of composite ground, a . The stress on column is low for the composite ground with high value of a , resulting in less settlement and fast consolidation. ) obtained from the physical model test on the composite ground can be used to approximate the rate of consolidation. This approximation is validated via the finite element simulation. The proposed method is highly useful for geotechnical engineers because of its simplicity and reliable prediction.

Physical, hydraulic, and mechanical properties of clayey soil stabilized by Physical, hydraulic, and mechanical properties of clayey soil stabilized by lightweight alkali-activated slag geopolymer lightweight alkali-activated slag geopolymer Abstract Abstract Lightweight cement materials are extensively used in the infrastructure construction. Geopolymer is a low-carbon and environmentally friendly cementitious material. This paper presents an investigation on the physical, hydraulic, and mechanical characteristics of lightweight geopolymer stabilized soil (LGSS) and a comparison with lightweight cement stabilized soil (LCSS). Measurements of volumetric absorption (VA) of water, hydraulic conductivity (k), and unconfined compressive strength (qu), scanning electron microscope (SEM) observation, mercury intrusion porosimetry (MIP) test, and thermogravimetric analysis (TGA) are conducted. The results show that LGSS has higher VA than LCSS. The k of LGSS is one order of magnitude higher than that of LCSS. The qu of LGSS is 2-3.5 times of that of LCSS. Microstructurally, the VA and k of LGSS are found to be positively correlated with the volume of large air pores (>10 μm). Higher qu of LGSS than LCSS is attributed to more hydration products that fill up the voids of soil. It is concluded that LGSS gives better engineering performances than LCSS in terms of water absorption, permeability, and strength characteristics. Abstract: Lightweight cement materialsare extensively used in the infrastructure 5

Lightweight cemented clays have wide applications in the infrastructure rehabilitation and in the construction of new facilities. The strength and compression characteristics of lightweight cemented clays with non-to high swelling potential are investigated and presented in this article. The workable state, the optimum water content to produce the lightweight cemented clay, is about 1.9 times the liquid limit. The void/cement ratio, V/C, which is defined as the ratio of void volume of the clay to the cement volume, is proved to be the prime parameter governing the strength and compression characteristics of cemented clays. The fabric (arrangement of clay particles, clusters and pore spaces) reflected from both air foam content and water content is taken into consideration by the void volume while the inter-particle forces (levels of cementation bond) are governed by the input of cement (cement volume). A strength equation in terms of V/C at a particular curing time is introduced using Abram's law as a basis. From the critical analysis of test results, a mix design method to attain the target strength and unit weight is suggested. This method is useful from both engineering and economic viewpoints.

Cement stabilization is extensively used to improve engineering properties of soft 48 saline clay. The effect of salinity, which is altered with geological and climate changes, on the 49 strength development in cement admixed saline clay is investigated in this paper. For a 50 particular curing time and salt content, the strength development in cement admixed saline 51 clay is governed by the clay-water/cement ratio, w c /C. The strength increases with the 52 decrease in w c /C. The increase in salt content for a particular water content causes the increase 53 in generalized stress state, e/e L where e is the current void ratio and e L is the liquid limit void 54 ratio. The higher value of e/e L is associated with the lower effective stress and the inter-55 particle attraction. Hence, for the same clay-water/cement ratio, the strength of the cement 56 admixed clay with higher salt content is lower than that with lower salt content.

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