Reinforcement of drill-injection piles

Abstract

Introduction. The paper presents the possibility of reducing the reinforcement length of flexible drill-injection piles with diameters up to 0.3 m without compromising their material bearing capacity, based on an analysis of bending moment distribution along the pile length. The relevance of the study stems from the need to find technical solutions that simplify and reduce the cost of foundation reinforcement while maintaining reliability and durability. The main objective is to provide a computational justification for the minimum required reinforcement length of drill-injection piles, considering their actual behavior in soil mass.

Materials and methods. To achieve this goal, the distribution of bending moments was analyzed for piles with diameters of 0.2, 0.25, and 0.3 m in two types of soil conditions. The assessment was performed using known analytical solutions and numerical modelling in Midas FEA NX software. The sufficiency of reinforcement was evaluated based on the ratio between actual loads and the ultimate tensile strength of concrete, allowing determination of necessary reinforcement zones along the pile length.

Results. The analysis of bending moment distribution in flexible piles showed that maximum stresses occur only in the upper section (up to 3–4 m depth), with rapid attenuation of bending moments below this level. For silty-clay soils, the sufficient reinforcement depth for flexible piles up to 0.3 m diameter was established as 15–16 pile diameters.

Conclusions. The study demonstrates the fundamental possibility of reducing reinforcement cage length in flexible drill-injection piles (up to 0.3 m diameter) without compromising bearing capacity. Practical recommendations for reinforcement depth depending on pile diameter and soil characteristics were developed. The results facilitate the installation of small-diameter drill-injection piles, particularly in confined working conditions.