Many factors influence the axial bearing capacity and performance of deep foundations embedded in sand deposits. Among these factors, the installation method is of great importance. The objective of this study was to investigate the construction effects on pile performance via physical modeling. The frustum confining vessel of Amirkabir University of Technology (FCV-AUT) was employed for this purpose. Six different installation methods were studied: jacking, drilling and grouting, driving, screwing, drilling and placing, and postgrouting. Up to 30 axial compressive and tensile load tests were carried out on different piles on Babolsar sand, from the northern coast of Iran, with relative densities of 45% to 50% within the FCV-AUT. Experimental results show that among different pile installation methods, jacked and precast-in-place piles had the greatest and lowest capacities, respectively. Moreover, the performance results of the different pile types in the FCV-AUT indicate that the axial bearing c...

Helical piles are structural deep foundation elements, which can be categorized as torque-driven piles without any limitations to implement in marine situations. Different methods are used to predict the axial capacity of helical piles, such as static analysis, but have some limitation for this type of piles on marine conditions. In situ testing methods as supplement of static analysis have been rarely used for helical piles. In geotechnical engineering practice, the most common in situ tests particularly applicable for coastal or offshore site investigation are cone penetration test (CPT) and piezocone penetration test (CPTu). The CPT is simple, repeatable, and prepares the continuous records of soil layers. In this paper, a data bank has been compiled by collecting the results of static pile load tests on thirty-seven helical piles in ten different sites including CPT or CPTu data. Axial capacities of thirty-seven helical piles in different sites were predicted by direct CPT methods and static analysis. Accuracy estimation of ten direct CPT methods to predict the axial capacity of helical piles was investigated in this study. Comparisons have been made among predicted values and measured capacity from the pile load tests. Results indicated that the recently developed methods such as NGI-05 (2005), ICP-05 (2005), and UWA-05 (2005) predicted axial capacity of helical piles more accurately than the other methods such as Meyerhof (1983), Schmertmann (1978), Dutch (1979), LCPC (1982), or Unicone (1997). However, more investigations are required to establish better correlation between CPT data and axial capacity of helical piles.

Piling procedure may disturb the surrounding soil, due to the installation particularly for cast-in-place piles. It causes a reduction in the soil strength parameters and, consequently, pile capacity. To overcome shortcomings and also for improving piles’ capacity, postgrouting as a compensation method is recognized and more developed in recent years. Helical piles, those are used widely in marine and land projects, although, are driven by torque implementation, but soil disturbance is noticed, where number of the helices become up to 3 and more. In this paper, an experimental study program is performed by frustum-confined vessel (FCV) to investigate bearing capacity of model helical piles and also postgrouted cases’ performance. FCV has been used because of its linear distribution of vertical and horizontal stresses from zero at top to maximum at bottom which simulates real field stress conditions. Through experimental study, small-scale helical model piles were made of 4-mm-thick steel plate and have been used with a length of 750 mm. The shaft and helix diameters of model piles have been 32 and 89 mm, respectively. So, the helix-to-shaft ratio (wing ratio) was about 2.8. The helical model piles installed in fine-grained sand as a surrounding soil and then axial loading tests before and after grouting were performed to achieve ultimate pile capacity. Results indicated postgrouting can improve both ratios of toe and frictional soil–pile interactions including upgrading β and N_t factors. In addition, the post grouting phenomena can change the pile geometry due to treated soil bond, resulting better functioning. Therefore, it is a proper method to improve helical piles performance and compensate installation effects in capacity mobilization.

Due to the variety of current Cone Penetration Test (CPT)-based methods of estimating the pile bearing capacity, for optimum design, it is necessary to evaluate the performance of such methods in various geotechnical conditions. Geotechnical databases including piling and in situ testing records have been recognised as useful tools for analysis, design and economical construction. In order to evaluate current CPT-based pile bearing capacity methods, AUT-CPT and Pile database has been compiled including 450 full scale pile load tests and CPT sounding records. This database consists of different pile types with a relatively wide range of geometries and various soil conditions. Forty-three records of piles driven in sand deposits were then employed to evaluate effects of ultimate capacity interpretation criteria from load displacement diagrams. The Brinch Hansen 80% criterion and the load at the displacement of 10% of the pile diameter were compared to estimated capacities from 10 CPT-based design methods currently used in practice. The Brinch Hansen 80% criterion and the load at the displacement of 10% of the pile diameter lead to reasonable results, the Brinch Hansen 80% criterion showed less scatter. For evaluating the accuracy and the precision of CPT-based methods, the results were compared to estimated capacities. Methods with the best performance are introduced. Generally, comparisons indicate that the CPT-based methods mainly predict the pile capacity with reasonable accuracy.