BEARING CAPACITY OF DRILLED REINFORCED CONCRETE MICROPILES WITH DIFFERENT WIDENING DIAMETERS ACCORDING TO THE RESULTS OF THEIR FIELD TESTS

Abstract

In order to investigate actual operation of reinforced concrete micropiles with a widened heel under load, full-scale field tests were carried out at building sites in various soil conditions and their calculated and experimental load-bearing capacity was analyzed. In this case, the effect of changing the diameter of the widened heel on the bearing capacity of the experimental samples of micropiles was investigated.

As construction practice shows, field static tests directly on the site of the future building are always give more accurate results than their respective calculated values, since they take into account all the inaccuracies in the engineering and geological exploration, and better reflect the operation of the "pile-foundation" system. Field tests of natural piles are control and are carried out in order to check the load-bearing capacity of the piles with the design load's, which are included in the project, and to obtain data required to justify the choice of foundations, including: determination of pile type and size and their bearing capacity; checking the possibility of placing piles at the specified depth, as well as the relative assessment of the homogeneity of soils behind their resistance to pile immersion; determination of the dependence of the movement of piles into the soil on load and time. To study the operation of drilled reinforced concrete micropiles, it is necessary to conduct full-scale field tests of them and compare the obtained data with the theoretical data obtained as a result of the calculation according to the current standards (DBN and Eurocode №7) [1,2]. The effectiveness and load-bearing capacity of the bored micropile was tested using two experimental studies performed performed in similar soil conditions of one construction site. The testing of experimental samples of micropiles (MP-1 and MP-2) was carried out in order to experimentally check their bearing capacity and deformability of the foundation soils at the level of five piles. The experimental investigations were carried out according to the static indentation scheme. As a result of experimental and theoretical calculations, an underestimation of the bearing capacity of micropiles (30 and 38 %) and the ultimate load  (40 and 47 %) on them was established. The analysis of experimental and theoretically determined data showed that in both cases, the experimental values of the bearing capacity and ultimate load on the micropile exceed the calculated values. The data obtained as a result of experimental and theoretical research, presented in the article, make it possible to preliminarily estimate the real bearing capacity of drilled reinforced concrete micropiles.