Abstract
This paper presents the results from a full-scale field study on the 3 different types of cast-in-place piles: rotary drilling piles (RDPs), manual digging piles (MDPs), and impact drilling piles (IDPs), for a bridge construction project of Wuqi–Dingbian Expressway, in Shaanxi. The results indicate that under the similar conditions, MDP exhibits the largest bearing capacity (11000 kN) in the loess area, followed by RDP (9000 kN) and IDP (8000 kN). And all tested values exceed the estimated value (7797.9 KN), indicating that the calculation formula of bearing capacity recommended by the Chinese standard is safe and conservative. During the load transfer process, the axial force attenuation rate of the pile body increases with pile side resistance. The average attenuation rate of MDP is the largest (24.2%), followed by RDP (19.72%) and IDP (16.69%). The bearing characteristics of these test piles are mainly pile side resistance, but the manual digging method created the least amount of disturbance to the soil around the pile, and due to its hole wall being rough, this enhances the pile-soil interactions. Hole-forming methods mainly affect the exertion of pile side resistance compared with pile end resistance. In view of pile side resistance and pile end resistance not taking effect at the same time, degree of exertion of these 2 resistances should be considered when designing cast-in-place piles in loess areas, and different partial coefficients should be used.
Highlights
Pile foundations have been developed for thousands of years since the discovery of early pile foundation sites in the Republic of Chile
Loess is widely distributed in Asia (74°N-32°N, based on data from Baidu Encyclopedia), especially in the central and western regions of China, where there is continuous development of China’s economy and infrastructures in the promotion of the Belt and Road program; a large number of transportation networks are being built in the loess area, and cast-in-place piles will be widely used in this process
Loess has strong structural characteristics. e construction of cast-in-place piles in the loess strata will inevitably destroy the structure of loess, which will affect the mechanical properties of loess and pile-soil relationship [18,19,20,21]. ere are many research studies on the holeforming methods and loess in the cast-in-place pile foundation engineering, but the influences of hole-forming methods on the bearing capacity of pile foundation are not universal [22,23,24,25,26,27]
Summary
Ere are many research studies on the holeforming methods and loess in the cast-in-place pile foundation engineering, but the influences of hole-forming methods on the bearing capacity of pile foundation are not universal [22,23,24,25,26,27]. Erefore, the influences of hole-forming methods on bearing characteristics of cast-in-place piles in the loess are uncertain and need further research [28,29,30]. E influence of the hole-forming methods on the bearing characteristics of the cast-in-place piles is analyzed from the following aspects: (1) pile body settlement; (2) transfer law of axial force for the pile body; (3) distribution of the pile side resistance; and (4) exertion degree of pile end resistance Based on this, combined with the actual situation of Wuqi–Dingbian Expressway test area, static load tests of RDP, MDP, and IDP have been carried out. e influence of the hole-forming methods on the bearing characteristics of the cast-in-place piles is analyzed from the following aspects: (1) pile body settlement; (2) transfer law of axial force for the pile body; (3) distribution of the pile side resistance; and (4) exertion degree of pile end resistance
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