This paper discusses pore pressure response of clay-lumps and slurry mix when subjected to freezing and thawing cycle. This study was undertaken to access the adequacy of the thawed sample in flexible wall permeameter tests. Speswhite kaolin clay was used in all the tests. A 100 mm diameter cylindrical block of known volume of clay lumps and clay slurry was prepared in a split mould. The sample was then allowed to gradually freeze in a chamber maintained at -10 and -18 ⁰C. The sample was then allowed to thaw in two different test conditions. In the first case, the samples were allowed to contract and volume permitted during de-freezing. In the second case, volume of the sample was maintained constant during de-freezing. In all the cases, the tests were conducted using a flexible wall permeameter. The permeameter was modified to take independent measurements of pore pressures within the lumps and within the slurry using miniature pore pressure transducers (PPTs). The effect of temperature and confining pressure on the pore pressure was observed. It was observed that freezing caused transient increase in the pore pressure. The pore pressure increase was noticeably higher in the clay slurry than in the clay lumps. Beyond the transient peak, the pore pressures reduced to negative because the ice lens generated suction in slurry and lumps. The magnitude of pore pressure decrease was more in the lumps than the clay slurry. It was also observed that the samples which were frozen at a faster rate, exhibited less loss in water content wen thawed compared to the samples which were frozen at a slower rate. This will have significant effect on the shear strength and softening of permafrost soils which are now thawed because of climate change.

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Pond ash, being a form of coal ash, consists mainly of glassy particles with a significant percentage containing internal occluded voids. By analysing the evolution of particle size distribution before and after triaxial testing at normal stress range using a Laser Particle Size Analyser, specific gravity and SEM photography, it was found that these hollow particles may breakup as a result of shearing. This type of particle disintegration is different from localised grain crushing or shearing off of asperities at high contact stress points. The stress-strain responses measured in an extensive programme of triaxial testing were synthesised. It was established that a unique and consistent critical state line was achieved, irrespective of initial state, drainage conditions and stress histories. Furthermore, the overall pattern of stress-strain responses was related to the location of initial state relative to the critical state line. This supports the use of critical state soil mechanics framework in synthesising and modelling the stress-strain behaviour of pond ash.

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In order to apply the mixtures of dredged soils with slag to geotechnical field, the compressive strength characteristics should be identified. In this study, unconfined compressive strength tests for two local dredged soils mixed with three different types of slags were performed. In this study, factors affecting the compressive strength of soil-slag mixture including the types of dredged soil, types of slag, mixing ratio of soil/slag and mixing water content were investigated. Higher slag portion in the soil-slag mixture induces greater strength improvement. The increase of compressive strength in soil-slag mixture was more significant in the case of mixing with steelmaking slag than GFNS and AFNS. The sufficient fine content of dredged soil and CaO of slag was found to have a significant influence on the solidification effect. In addition, the initial mixing water content was higher, strength improvement might be limited.

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A series of unconfined compression tests and triaxial compression tests was conducted for the mixture of dredged soil and steel slag with various sand contents. Furthermore, internal structure and microfabric of the specimens were observed by X-ray CT, scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP). The compressive strength increased with increase in sand content, and the failure process observed by X-ray CT varied according to sand content; however, a clear difference was not seen in the microfabric of the dredged soil - steel slag mixture by SEM and MIP even if the sand content changes.

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The vacuum and siphon dewatering tests were performed to investigate the dewatering behavior of the high moisture content ultra-soft clay, respectively. All the tests are conducted in the small-scale tanks with plastic drainage board installed horizontally at the bottom. The influence of the magnitude of the negative dewatering pressures on the dewatering behavior of the dredged slurry was investigated. The test results show that the initial dewatering efficiency shows no significant difference when the slurry exists in the slurry-like state. Thereafter the dewatering efficiency increases with the magnitude of the applied dewatering pressure. The test results also show that the corresponding compression indexes in the pressure ranges from 0 to 30 kPa and 30 to 80 kPa are 0.33, 0.3, respectively.

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This paper aims to present a study of a shrinkage potential of cement and/or fly ash treated soft clay. The soft clay specimens used in this study were prepared from reconstituted Bangkok clay. The soil-cement mix specimens were prepared with cement/clay-water ratio (C/wc) of 0.2, 0.3 and 0.4 and the liquidity index (LI) of 1.0, 1.3 and 1.6. The fly ashes as wastes from the electricity generating industries were used in this study. The replacement ratios of fly ash to cement were varied from 15 to 60% by weight. The experiments were performed to determine the strength, stiffness and shrinkage potential. The strength and stiffness were determined by the unconfined compressive strength (UCS) and the secant Young’s modulus at 50% of strength (E50). The shrinkage potential was loosely defined based on an image processing technique. Finally, the results of the study could be used to draw a conclusion of optimised fly ash and cement contents for the soft soil improvement.

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This paper aims at investigating a rapid and environmentally friendly soil stabilization method to significantly increase the strength of carbonated reactive magnesia (MgO)-treated soil by exposing it to substantial quantities of CO₂. Soil specimens treated with 10, 15 and 20% reactive MgO were subjected to accelerated carbonation tests for 1.5, 3, 4.5, 6, and 12 hr. Later, tests of specimen weight, permeability, unconfined compressive strength and pH value were performed on soil specimens after carbonation. The results can be summarized as follows: the weight of carbonated soils increases with dosage and carbonation time (especially 3 hr); the permeability coefficient increases with the increase of porosity and the decrease of dosage of reactive MgO and it decreases first and then increases with the carbonation time; the strength of carbonated soils increases with dosage, and increases quickly with carbonation time in first 3 hours, then keeps stable. The strength reaches or exceeds the strength of cement-stabilized soils for 28 days with the same dosage; the pH value first increases and then decreases generally with reactive MgO content increasing, and a critical carbonation time (about 3 hr) exists in terms of the varying trend.

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