The concrete pipeline pressure influence on the cfa pile bearing capacity according to the soil base properties when installing the pile

Abstract

Today, CFA piles are one of the most common types of foundations for multi-storey buildings. They gained their popularity due to the relatively low cost, speed of installation and allowable load value according to the soil base properties. However, in the practice of construction there are often situations when the predicted value of the pile bearing capacity according to the soil base properties is significantly less than that one resulting from the static pressing load tests. As a rule, the reasons for such a significant difference depend on many factors, including the inaccuracy of the geological structure study, the equipment used for piling or observance of the minimum necessary technological piling parameters. In most cases, one of the main reasons for the significant reduction of the piles bearing capacity according to the soil properties is a parameter such as the pressure in the concrete pipeline during the piles installation. Quite often, 
the pile manufacturers are asked out that the concrete overconsumption should not exceed the standard value equal to 26 % of the geometric volume of the borehole under the pile. Thus, they want to save money on the piles installation. However, this approach to concrete saving results in much higher cost overruns, because at low pressure the value of the piles bearing capacity according to the soil base properties can be up to twice less. In this case, the number of piles must be increased by two times with the consequence that the 10… 15 % resulting concrete savings from installing the piles will lead to concrete overspending of 100… 200 %.
The paper presents the results of piles testing by static pressing load at the construction site, when the different pressure values in the concrete pipeline were used for pile groups. The values of piles bearing capacity reduction depending on the concrete pipeline pressure are shown.