Evaluating the Competitiveness of the Methods of Bored Cast-in-Place Piles Underreaming when Constructing the Foundations of Multistorey Buildings

Introduction. The bored сast-in-place piles are the type of piles most adjusted to specifics of the multistorey building construction. The article studies the existing methods of underreaming such piles as the main tool to minimise their diameter, length, and quantity, thus optimise and reduce the cost of foundation design and its subsequent construction. It is acknowledged that despite the diversity of these methods, the information about them is scattered, confusing, and sometimes contradictory, making it difficult to choose the optimal design solutions. To facilitate the choice, an application-oriented classification of the methods under study has been proposed aiming to specify the areas of rational implementation thereof. Materials and Methods. The study took into account the data of the guidebooks on norms of production and estimate norms, the reference, normative and standard design documentation, as well as national practices and solutions proposed by the professional subcontracting organisations. Upon analysis of the above materials, the information on the advantages, disadvantages and implementation area parameters of the existing methods of bored cast-in-place piles underreaming was systematised based on the internal and external factor criteria used for selecting the appropriate solutions in the competitive conditions of multistorey building construction. The competitiveness of three most advanced of such methods was investigated by a comprehensive (multi-criteria) evaluation method. Results. It was found that under general conditions that were studied, the most competitive among the selected methods was mainly the pulse-discharging treatment of a pile shaft and (or) pile base. The respective results were presented graphically in the form of the bar charts of unit labour costs and costs of underreaming by the studied method, as well as the radial bar charts showing the cumulative effect of these and other taken into account parameters on solving the set task of optimisation. Discussion and Conclusion. The reflections upon the efficiency of implementing the obtained results in the present-day designing have been further evolved, and the ways and circumstances of changing thereof depending on the project specification and local conditions of construction have been presented. On the whole, that allowed for specifying the areas of rational implementation of the studied methods and providing the recommendations on updating the relevant regulatory framework.