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Vibro-stone columns can improve the bearing capacity and reduce the settlement of foundations. Their performance depends on the strength of the column material, reinforcement method of column installation, type of in situ soil, area replacement ratio, and column length. This paper examines the behaviour of small laboratory specimens of soft clay (undrained shear strength ≈ 30 kPa) reinforced with sand columns when tested under known boundary stress conditions. Two series of tests were carried out on kaolin specimens (diameter 100 mm, height 200 mm) in a triaxial cell. In the first series, specimens were reinforced with a 32 mm diameter column of sand, 80, 120, 160, or 200 mm long. Columns were installed by (i) compacting moist sand into a prebored hole or (ii) freezing a column of moist sand before inserting it into a prebored hole. In the second series, columns were reinforced with geo-grids before installation. The specimens were subjected to (i) uniform loading in which the load was applied over the entire surface area of the specimen or (ii) foundation-type loading in which only a small area in the centre of the specimen was loaded. Under uniform loading, the specimens containing a full-depth column were significantly stronger than specimens without columns. Specimens with single, partially penetrating columns installed by wet compaction were weaker than specimens without columns. When frozen columns were installed, strengths increased progressively. Under foundation-type loading, bearing capacities increased with an increase in column length. Geo-grid reinforcement produced significant increases in load-carrying capacity.Key words: ground improvement, undrained shear strength, consolidation, stress path.

The vibrated stone column technique is an economical and environmentally friendly process that treats weak ground to enable it to withstand low to moderate loading conditions. The performance of the treated ground depends on various parameters such as the strengths of the in-situ and backfill materials, and the spacing, length and diameter of the columns. In practice, vibrated stone columns are frequently used for settlement control. Studies have shown that columns can fail by bulging, bending, punching or shearing. These failure mechanisms are examined in this paper. The study involved a series of laboratory model tests on a consolidated clay bed. The tests were carried out using two different materials: (a) transparent material with ‘clay like’ properties, and (b) speswhite kaolin. The tests on the transparent material have, probably for the first time, permitted visual examination of deforming granular columns during loading. They have shown that bulging was significant in long columns, whereas punching was prominent in shorter columns. The presence of the columns also greatly improved the load-carrying capacity of the soft clay bed. However, columns longer than about six times their diameter did not lead to further increases in the load-carrying capacity. This suggests that there is an optimum column length for a given arrangement of stone columns beneath a rigid footing.

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Coarse granular materials are widely used in construction. The required mechanical characteristics of the materials are determined by the specific civil engineering application. These coarse granular materials are often obtained by quarrying intact rocks. Growing environmental awareness, the need to ensure sustainability of the construction industry, and public concern to safeguard the countryside limit the use of quarrying sites and encourage the industry to look for alternative materials for engineering applications. The work described in this paper was undertaken to examine the characteristics of waste granular materials in regard to their potential for replacing quarried stone in vibro ground improvement processes. Three materials were considered: quarry waste, building debris and crushed concrete. These materials were examined under various testing conditions: dry, wet, and mixed with 10% and 20% clay slurry. Tests were carried out in a 305 mm × 305 mm direct shear box. The performance of these materials was compared with that of traditionally used crushed rock, in this case basalt. The results indicated that recycled material, for example building debris, showed significantly lower shear strength when compared with crushed rock. Building debris and crushed concrete exhibited a general tendency to reduce in volume during shearing at high pressures. This was due primarily to particle crushing. It was also apparent that there was a significant reduction in shear strength when the materials were smeared with clay slurry. Les matières constitutées de gros grains sont largement utilisées dans la construction le BTP. Les caractéristiques mécaniques qui leursont demandées requises sont déterminées par l'application spécifique en génie civil. Ces matiéres à gros grains sont souvent extraites de roches intactes. La conscience environnementale sensibilisation aux questions de l'environnement, le besoin d'assurer le renouvellement des ressources pour l'industrie du BTP de consruction et les inquiétudes du public quant à la préservation des paysages ruraux rendent les carrières moins acceptables limitent l'utilisation des carrières et poussent l'industrie à chercher d'autres matériaux pour les tâches travaux d'ingénierie. Les travaux décrits dans cet exposé ont pour but d'étudier les caractéristiques des matières granulaires récupérées, afin et de vor si celles-ci peuvent remplacer les pierres de carrière lors des processus d'amélioration au vibro. Nous avons étudié trois matériaux: les déchets de carrière, les débris de construction et du le beéton concasseé. Nous avons examinéces matériaux dans diverses conditions: à l'état sec et humide, ainsi que et mélangés à 10% et 20% de boue argileuse. Nous avons fait des essais dans une boîte de cisaillement diret de 30 mm × 305 mm. Nous avons comparé la performance de ces matières à celle des rouches broyàes untilisàes traditionllement, dans ce cas l'occurence de basalte. Les ràsultats ont indiquent indiquà que le matàriau recyclà, par exemple les débris dechantier, montrait une résistance au cisailleent considérablement plus basse que celle de la roche broyée. Les débrisde chantier, et le béton concassé ont généralement tendance à perdre du volume pendant le cisaillement sous hautes pressions. Ceci est dû principalement à l'écrasement des paricules. II est apparent apparu également que la résistance au cisaillement diminue de manière significative quand les matériaux sont enduits de boue argiluese.

High density polyethylene (HDPE) is predominately processed from the molten state. However, there is the potential to enhance the mechanical properties by forming below the melt temperature, in the semi-solid phase. To further investigate this enhancement, HDPE sheets were deformed under constant width, simultaneous equalbiaxial (EB), and sequential biaxial deformation. The samples were deformed at strain-rates, from 4 to 16 s 21 , up to nominal strains of 3.0 at temperatures below 1308C. The strain-rate and high-strain level applied were chosen so that the data was comparable to the thermoforming process. It was discovered that in order for the HDPE sheet to deform at the high-rate and high strains the processing temperature must be between 1268C and 1308C. This resulted in a processing window that was particularly small, 58C, and that within this window a temperature change of 18C had a significant impact on the stress-strain response. The samples were analyzed post deformation, where the elastic modulus was found to increase by a factor of 2.08 in the machine direction, when deformed via EB at 1298C. The results showed that HDPE can be deformed to strain levels comparable to the thermoforming process. POLYM. ENG. SCI., 00:000-000, 2017. FIG. 9. The effect of forming temperature (A) and strain-rate (B) on the Young's modulus of the sample post deformation at 1288C and strain-rate 4 s 21 , determined via tensile testing at room temperature.

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