Load testing of bored concrete micropile with enlarged base in dispersive soil conditions

Abstract

This article presents the results of field testing of a bored micropile with a base enlargement, installed within the foundation of a two-story civil building located in Lviv region. It is demonstrated that the use of a 350 mm diameter base enlargement of the pile significantly increases its bearing capacity. An engineering-geological survey of the site was conducted, identifying three engineering-geological elements encompassing weak water-saturated silty clay and sandy loam soils. Experimental data on the pile behavior under static compressive loading up to 72 kN were obtained, which is nearly twice the calculated design value of 38 kN. The testing methodology involved stepwise application of the load with simultaneous registration of vertical displacements using high-precision measuring instruments. Based on the test results, a load-settlement curve was constructed, exhibiting a typical behavior with stages of initial deformation, stabilized settlement, and elastic recovery. It is shown that the pile–soil system operates without signs of progressive deformation and demonstrates significant elastic rebound after unloading. The allowable load calculation, considering a reliability factor (γ=1.2), determined the actual bearing capacity of the pile at 60 kN, exceeding the design value by 57%. Hence, the pile design with a base enlargement proves effective for the given engineering-geological conditions and ensures foundation reliability with reduced pile quantity costs. The obtained results confirm the effectiveness of using bored micropiles with base enlargement in low-rise construction and indicate the need to improve current calculation methods by accounting for the influence of pile base geometry on its bearing capacity.