Assessment of Axially-Loaded Pile Dynmaic Design Methods and Review of INDOT Axially-Loaded Design Procedure

Abstract

IntroductionThe main goal of the present study is to make a comprehensive assessment of the existing methods for the dynamic analysis of pile driving, identify the shortcomings and propose improvements. A review of existing shaft and base soil reaction models used in dynamic pile analyses is done to evaluate their effectiveness and identify points that require improvement. Subsequently, we develop improved shaft and base reaction models for use in 1-D dynamic pile analysis. The proposed models are validated using experimental data recorded during driving of field piles and model piles. The procedures currently used by INDOT for the design of axially loaded piles are also examined. For this purpose, interviews were conducted with INDOT engineers and private geotechnical consultants involved in INDOT projects. FindingsThe interviews with INDOT engineers and consultants focused on the methods and procedures presently followed in deep foundation design projects. The methods and the computer software used by private consultants involved in INDOT projects for the design of axially loaded piles are consistent with those used by INDOT's geotechnical engineers. These methods and software follow FHWA guidelines and are in accordance with the standard practice in the U.S. Pile design is mostly based on Standard Penetration test (SPT) data and undrained shear strength measured in unconfined compression tests. Cone penetration tests are rarely performed, although both INDOT and private soil exploration companies have the necessary equipment. Pile drivability calculations and back-calculation of the pile capacity from dynamic test data are done using software that employs Smith-type soil reaction models. Pile driving monitoring and restrike tests are usually performed only in projects whose cost exceeds a certain limit. Static load tests are reserved mostly for research projects.The methods for estimating the unit shaft and base resistances currently used by geotechnical engineers (INDOT or private consultants) have been developed over twenty years ago and have a large empirical content. There has been significant progress regarding methods for the calculation of unit base and shaft resistances. Numerous improved methods that are grounded on the physics and mechanics governing the development of pile resistance have been developed by combining experimental data with analysis. In the case of clayey soils, the differences between the state-of-the-practice methods and the updated methods are not large. In contrast, the formulation of the new methods for piles in sands has important fundamental differences with respect to traditional methods. The new methods for the base resistance in sands use as input either the relative density or the cone resistance directly. The recently developed methods recognize the fact that the limit base resistance is almost equal to the cone penetration resistance and that the ultimate unit base resistance in sands is smaller than the limit unit base resistance. Notably, the equations for β adopted by...

Use of Dynamic Cone Penetration and Clegg Hammer Tests for Quality Control of Roadway Compaction and Construction

“…Recently, Loukidis et al (2008) The source of material damping is the nonlinear behavior of soil and its hysteresis, which is reflected in the nonlinear spring function, a mathematically advanced form of the extended Masing-type function introduced by Kramer (1996). According to the dynamic model presented by Loukidis et al (2008), the spring constant of this function is a hyperbolic-type load displacement relationship that can be expressed as:…”

“…The dynamic model selected, originally presented by Loukidis et al (2008), accounts for the unloading-reloading response of soil due to dynamic loads. As shown in Figure 5.6, the base reaction due to dynamic loading reaches R bf asymptotically, with an increase in the dynamic displacement.…”

“…The path of the unloading-reloading curves takes the same shape as that of the backbone curve. The selected model captures hysteretic damping by using variables such as LOI, R b,rev and the signum function (Loukidis et al 2008).…”

“…The selected model also accounts for viscous damping. According to Loukidis et al (2008), the dynamic limit bearing capacity R bf is set as a function of the base velocity and is expressed as:…”

“…Using the rheological model combined the spring constant suggested by Loukidis et al (2008) and the dashpot constant suggested by Lysmer (1965), the equation of motion can be applied to obtain the dynamic response of the Clegg hammer test.…”