Abstract
There are a lot of the parameters which affect pile group behavior in soil. One of these factors is the distance of piles from each other. The impact of distance on pile groups in sand has been investigated through some researches, whereas most of them have not represented an exact estimation according to the continuous change of the distance in sand. Moreover, most of previous investigations have considered two piles as a perfect group. Since two-pile group has the least interaction effect among piles, it cannot suitably demonstrate the influence of spacing. In this lecture, several 4-pile groups modeled with different spacing were subjected to axial loading in laboratory. The pile groups were free-head with length to diameter ratio of 13.5. The piles are designed in a way which the shaft resistance of piles can be completely mobilized through the test. Then, the bearing capacities of pile groups are measured and compared with the single pile's resistance in order to calculate the efficiency coefficient of the groups. It is revealed that the distance is noticeably effective in efficiency factor and this effectiveness, non-linearly decreases by increase of spacing. The results show that the efficiency coefficient is changing between almost 1 and 1.4.
Highlights
Since the computational formulas are too conservative, designers take the advantages of practical experiment, satisfied with concepts such as the efficiency coefficient and the ratio of the pile group settlement
The influence of distance on group piles' behaviour has been investigated through some researches and it is clear that the increase of piles' spacing declines the effect of piles on each other in most aspects [1, 2], but most of them have not represented an exact estimation according to the continuous change of distance in sand
The results show that in the spacing of 6 times the diameter, the efficiency coefficient reaches less than 1, but considering the error factors, it can be stated that the efficiency coefficient in the spacing of 6 times the diameter is approximately 1
Summary
Since the computational formulas are too conservative, designers take the advantages of practical experiment, satisfied with concepts such as the efficiency coefficient and the ratio of the pile group settlement These two factors are properly able to represent the performance of the group. The interaction factors for the bivalent pile groups in two modes of friction (floatation) and end bearing These factors, which are used to estimate settlements, display how piles influence each other. The interaction factor decreases with the increase of distance-diameter ratio As a result, their influence declines [4]. Ismael (2001) conducted some experiments on sand in real size He concluded that pile group with distance-diameter ratio of 2 and 3 has the efficiency coefficient of 1.22 and 1.93, respectively [6]. The efficiency coefficient exhibits a decrease with an increasing pile spacing ratio when considering shaft friction [8]
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