EFFICIENCY OF PILE DRIVE TECHNOLOGY IN DIFFERENT SOIL CONDITIONS

Abstract

Based on the experience of SE NDIBV and TEHKOMP LLC in the development and application of pile and sheet piling technology in the construction of new and reconstruction of existing buildings, the article examines the effectiveness of pile piling technology in various soil conditions. The purpose of this article is to establish an effective field of application of the method of driving piles during installation or strengthening of building foundations.
In order to achieve the specified goal, the following were processed and summarized the results of pile driving works performed in the past years; the analytical dependencies (1) and (2) between the main parameters of the pile driving process, the violation of which makes pile driving impossible or impractical, were analyzed; on the basis of the statistical processing of the test results of the experimental depressed piles, the values of the coefficient of change in the bearing capacity of the soil around the depressed piles in Kgr time, the values of which vary in different soil conditions from 0.6 to 1.5, were specified and given.
It follows from dependence (2) that the greater the value of the coefficient of change in the load-bearing capacity of the soil around the pressed piles in the time Kgr, the less pressing force is required to ensure the same load-bearing capacity of the piles Fd. For example, to ensure the bearing capacity of a pile of 1000 kN, the following values of the compression force Nvd are required: at Kgr=1.5 Nvd=800 kN; at Kgr=1.0 Nvd=1200 kN; at Kgr=0.6 Nvd=2000 kN.
This means that in order to achieve the same effect when driving a pile in soil conditions where Kgr=0.6, the pressing force is 2.5 times more than in soil conditions where Kgr=1.5. Based on the above, all soil conditions, represented by several soils, are proposed to be classified (divided) into the following three groups according to the effectiveness of the pile driving technology application: Group I - "highly effective" - soil conditions that have Kgr≥1.1; II group - "effective" - soil conditions with 0.9≤Kgr≤1.1; III group - "not effective" - soil conditions with Kgr≤0.9.
The following conclusions are given in the article.
The field of application of the method of driving piles according to soil conditions is characterized by the presence of three groups of conditions: group I – highly effective conditions; group II – effective conditions; group III - not effective conditions.
Soil conditions of group I, in which the method of driving in piles is highly effective, are represented from above to the roof of the bearing layer by dusty clayey soils with a consistency index IL > 0.25 and have a value of the coefficient of change of the bearing capacity of the soil around the driven pile in Kgr time of at least 1, 10 (see items 1, 2, 3, 4 of table 1).
The soil conditions of group II, in which the pile driving method is effective enough, differ from the conditions of group I in that in dusty-clay soils with IL >0.25 cut by piles, there may be dense layers of sandy or dusty-clay soils and have the value of the coefficient of change in bearing capacity of soil around the driven pile 0.9 ≤ Kgr <1.1 (see items 5, 6, 7 of table 1). In such conditions, the piles are driven in, as a rule, through pilot wells, or using the effect of soil thixotropy by drilling wells without extracting the soil. Compared to soil conditions of the I group, this worsens such indicators as cost, productivity and terms of performance of works.
Soil conditions of the III group, represented by sands of medium density or dense with the value of the coefficient of change of the bearing capacity of the soil around the driven pile Kgr<0.9 must be excluded from the field of application of the technology of driving piles.