Abstract
Estimation of ultimate bearing capacity (UBC) of pre-stressed high-strength concrete (PHC) pipe pile is critical for optimizing pile design and construction. In this study, a standard penetration test (SPT), static cone penetration test (CPT) and static load test (SLT) were carried out to assess, determine and compare the UBC of the PHC pipe pile embedded in saturated sandy layers at different depths. The UBC was calculated with three methods including the JGJ94-2008 method, Meyerhof method and Schmertmann method based on in-situ blow count (N) of SPT (SPT-N) which was higher than the values recommended in survey report regardless of pile length. The average UBC values calculated with cone-tip resistance and sleeve friction from CPTs was also higher than the value recommended in the survey report. Moreover, the actual UBC values directly obtained by load-displacement curves from SLTs were in line with the calculated values based on in-situ SPTs and CPTs, but approximately twice as high as the values recommended in the survey report regardless of pile length. For the SPT method, the application of bentonite mud in saturated sand layers is critical for the assessment of pile capacity in the survey phase, CPTs can provide reliable results regardless of soil characteristics and groundwater if the soil layer can be penetrated, and SLTs are necessary to accurately determine the UBC in complex stratum.
Highlights
Pile foundations as structural elements are widely applied to back up superstructures, such as high-rise buildings, large highway bridges, harbors, wind power plants and oil extraction facilities, by safely transferring the load from the shallow soft surface layers onto the deep firmer layer underground for the superstructure’s stability [1,2,3,4]
The blow counts (N) were adopted to calculate the ultimate bearing capacity (UBC) of a single pile in this study based on the JGJ94-2008 method [50], Meyerhof method [51] and Schmertmann method [52], respectively
In survey report are in the range of 2191~3055 kN, while the UBC values calculated with the JGJ94-2008 method, Meyerhof method, and Schmertmann method were in range of 3570~4560 kN, 3437~5268 kN, 3316~5283 kN, respectively
Summary
Pile foundations as structural elements are widely applied to back up superstructures, such as high-rise buildings, large highway bridges, harbors, wind power plants and oil extraction facilities, by safely transferring the load from the shallow soft surface layers onto the deep firmer layer underground for the superstructure’s stability [1,2,3,4]. Determination of the ultimate bearing capacity (UBC) of designed piles is necessary and significant because that governs the safe geotechnical engineering design of pile foundations. It is always a complex problem to create pile foundations under loading and precisely predict a pile’s load-bearing capacity for geotechnical design engineers [5]. Numerous methods including experimental methods, numerical methods, and analytical methods, have been proposed to estimate pile behavior and pile load-bearing. Sci. 2020, 10, 6269 capacity [5,6,7,8,9,10]. It is well established that the level of accuracy and consistency of the estimated bearing capacity is of prime importance for those methods; for example, the difference of estimated bearing capacity between the Meyerhof method and semi-empirical method [11]
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