Abstract
This study investigated the compressive behaviour of super-long pile foundations with large diameters. Three 52 m, 73 m, and 83 m long piles with a diameter of 1500 mm, 1500 mm, and 1800 mm were cast and tested, respectively. Given that large loading was required, an improved compressive static load test was introduced, and the load transfer mechanism, shaft resistance development, and distribution were analysed. This study found that the transferred load decreased along the pile during each applied load, but the gradients were different. For most layers, when increasing the load, the shaft resistance developed in the upper layers first, while the shaft resistance from the lower part did not always fully develop. Moreover, the “mutual compensation” phenomenon was discovered, which was when the shaft softening occurred from one soil layer, the shaft hardening of the other soil would occur simultaneously. Under consideration of the soil layer differences around these piles, it was recommended that shaft and base grouting should be applied on 52 m and 73 m piles, while only shaft grouting should be applied on the 83 m pile. For this longest pile design, whose toe resistance was discovered to be very small, increasing the pile length was not appropriate; thus, it was preferable to increase the pile diameter to increase the ultimate bearing capacity.
Highlights
A compressive loaded pile is a slender element that transfers the loading from the upper structure to the soil layers
Comparing to P66, as demonstrated in Figure 6, the stable settlement of the P66 was found as 22.92 mm when loads of 28,000 kN was applied, and the total head settlement was small (55.49 mm) when maximum loads of 40,000 kN was applied. is represents that the capacity of P66 is greater than P12. This phenomenon illustrated that increasing the pile length, especially when reaching a harder bearing stratum, can effectively increase the ultimate bearing capacity of the single pile
When loads of 40,000 kN was applied, the vertical settlement of P105 was determined as 27.33 mm, which was less than the settlement of P66 (55.49 mm). is is primarily due to the increment of the pile diameter and the pile length that improves the total capacity of a single pile
Summary
A compressive loaded pile is a slender element that transfers the loading from the upper structure to the soil layers. Advances in Civil Engineering using reaction beams, the beams are prone to fail because the bending movement is too great Under such conditions, other test methods are preferred, such as dynamic load tests and O-cell tests. Is paper presents a case study referring to super-long and large-diameter piles and introduces an improved static load test (SLT) method. Three drilled shaft pile foundations with various lengths and diameters were tested in a construction project. In order to determine the shaft resistance, four strain gauges were symmetrically installed in each soil layer. The reinforcement ratio from the upper part is twice the lower part. e diameter of the auxiliary steel bar and the main longitudinal steel is 28 mm, and the diameter of the stirrup is 25 mm (upper part spacing is 100 mm and the other part is 150 mm). ough the total reinforcement ratio of these three tested piles is different, the reinforcement effect is ignored in this research. is is because this paper is researching the capacity under compressive loads, all these applied loads are resisted by concrete material, and the compressive contribution by the steels is very small
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