Technology of strengthening of subgrade foundation with built-in-place piles, made in expanded wells, for construction of buildings and structures

19 january 2019, 09:45
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Novosibirsk university has developed a technology for the weak soil strengthening of constructions and buildings foundations without excavation. The technology feature fastening of subsiding soil with built-in-place piles when the ousting soil is compressed and provides the required strength. The University is looking for partners for joint further development and manufacturing agreement.
One of the trends of modern construction is lack of areas suitable for construction in the central parts of urban areas in almost all major cities. For this reason, the construction is implemented in the areas with complex geological structure that were previously seen unfavorable for construction. In such constructions the use of pile foundations of driven or bored piles is deliberately more expensive than the shallow foundations on reinforced ground base. The use of chemical methods of consolidation, mainly silication or cementation, considering large amounts of fastened soil, entails significant costs. Construction companies need a reliable and up to date method of solidifying of ground base foundations. Such as: - construction in cramped conditions in a dense urban environment; - reconstruction and refurbishing of buildings; - construction in suburban areas. The proposed method can be used in all those situations. The method consists in strengthening the ground base foundations with built-in-place piles made in rolled out wells. This method of fastening allows for the controlled amplification gain of the array with the liquidation of sagging soil properties. Plus the required strength and deformation characteristics can be achieved at lowest economic cost. In this method the well are formed by successive rolling of soil from its axis to the periphery by means of rolling working body – burnisher. It distinguishes them from punching holes where mainly bottomhole is compacted. Burnisher consists of conic rollers (of increasing diameter) that are eccentrically mounted on the drive shaft which, upon rotation of the drive shaft, rolling helically compact and form the wall of the soil hole. Turn of rollers of burnisher relative to the axis of the drive shaft and the rotation of the drive shaft to the right (view from drive side) provide direct self-promotion of a working body. A burnisher of a diameter of 0.25 m is primarily used for rolling out wells for tamped piles, which is working as a replacement body mounted on traditional and vertical drills. During rolling a zone of soil compaction is formed, the diameter of which is up to four diameters of the formed well. Radius of deformation zone is up to six diameters of rolled out well. Soil compaction when rolling out wells increases its strength and deformation characteristics, as well as provokes elimination of sagging properties. Wells cultivated by burnisher are filled with concrete or inert filler. The resulting piles, as reinforcing elements of ground base (not part of the foundations), significantly increase the deformation and strength characteristics of the array. Other technologies require forming of wells for built-in-place piles using pneumodrills, however in that case mainly bottom hole is compacted which is ineffective comparing with rolling out wells.

Innovative aspects

Благодаря использованию технологии на строительной площадке со сложным строением обеспечивается требуемая прочность грунта основания за счет формирования необходимого количества раскатанных скважин под набивные сваи. Кроме этого происходит объединение в единый технологических процесс способов закрепления грунтов цементацией, силикатизацией и изготовлением набивных свай в раскатанных скважинах. При химических способах закрепления обеспечение требуемой прочности грунтов основания сопровождаются более высокими экономическими и технологическими затратами.