Hoyoung Seo

Assessment of the Axial Load Response of an H Pile Driven in Multilayered Soil

Most of the current design methods for driven piles were developed for closed-ended pipe piles driven in either pure clay or clean sand. These methods are sometimes used for H piles as well, even though the axial load response of H piles is different from that of pipe piles. Furthermore, in reality, soil profiles often consist of multiple layers of soils that may contain sand, clay, silt or a mixture of these three particle sizes. Therefore, accurate prediction of the ultimate bearing capacity of H piles driven in a mixed soil is very challenging. In addition, although results of well documented load tests on pipe piles are available, the literature contains limited information on the design of H piles. Most of the current design methods for driven piles do not provide specific recommendations for H piles. In order to evaluate the static load response of an H pile, fully instrumented axial load tests were performed on an H pile (HP 310 × 110) driven into a multilayered soil profile consisting of soils composed of various amounts of clay, silt and sand. The base of the H pile was embedded in a very dense nonplastic silt layer overlying a clay layer. This paper presents the results of the laboratory tests performed to characterize the soil profile and of the pile load tests. It also compares the measured pile resistances with those predicted with soil property- and in situ test-based methods.

Analytical solutions for a vertically loaded pile in multilayered soil

Explicit elastic solutions for a vertically loaded single pile embedded in multilayered soil are presented. Solutions are also provided for the case in which the pile base rests on a rigid material. Energy principles are used in the derivation of the governing differential equations. The solutions, which satisfy compatibility of displacement in the vertical and radial directions, were obtained by determining the unknown integration constants using the boundary conditions, Cramers rule, and a recurrence formula. The solutions provide the pile vertical displacement as a function of depth, the load-transfer curves, and the vertical soil displacement as a function of the radial distance from the pile axis at any depth. The use of the analysis is illustrated for a pile that was load-tested under well-documented conditions by obtaining load–transfer and load–settlement curves that are then compared with those obtained from the load test.

Instrumented Static Load Test on Rock-Socketed Micropile

AbstractRock-socketed piles are often used to transfer heavy loads from a superstructure to competent underlying rock layers. The loads are transferred by the pile to the surrounding rock mass through shaft and base resistance. Several researchers have investigated the behavior of rock-socketed drilled shafts and related the uniaxial compressive strength of intact rock to pile-shaft resistance. However, the load-transfer behavior and load-settlement response of micropiles are different from those of drilled shafts because of the large slenderness ratio (pile length/pile diameter) of micropiles. This study presents results from a fully instrumented field-scale load test on a 0.2-m-diameter micropile socketed 4.2 m into limestone layers (2.7 m into weathered limestone and 1.5 m into hard limestone). The results show that practically no base resistance is mobilized until the pile-head settlement reaches approximately 7% of the diameter of the test micropile. The measured limit shaft resistance values are com...

Improved Load Rating of Reinforced-Concrete Box Culverts Using Depth-Calibrated Live-Load Attenuation

AbstractThis paper describes depth-calibrated live-load attenuation for the load rating of reinforced-concrete box culverts using production-simplified models. In-plane depth calibration is accomplished using a production-simplified, two-dimensional, linear-elastic, finite-element, soil-structure interaction model with results compared with those from the recommended direct-stiffness, structural-frame model. Out-of-plane live-load attenuation considers each potential critical section depth rather than the cover soil depth only. The effectiveness of depth calibration is assessed by comparing predicted live-load moments obtained from the models versus measured live-load moments obtained from full-scale culvert load tests. A load rating case study illustrates the potential for improved alignment between load rating and observed performance. Findings show that depth calibration improves current load rating practice by increasing the accuracy and precision of live-load demand predictions, particularly in culve...

Hammer Efficiency and Correction Factors for the TxDOT Texas Cone Penetration Test

This study analyzes blowcount data from instrumented Texas Cone Penetration (TCP) tests. TCP hammer efficiency, rod length influence on the hammer efficiency, and overburden pressure correction factors for the TCP blowcounts (NTCP) are explored. Results are compared to published correction factors for the standard penetration test (SPT). The final dataset analyzed for this study consisted of 293 TCP tests from which 135 tests were instrumented. TCP hammer efficiency values for automatic trip hammers ranged from 74 to 101% with an average of 89%. Analyses showed a statistically-significant relationship between the TCP hammer efficiency and the rod length below ground surface. Statistical models were developed for undifferentiated soils, and corresponding rod length correction factors for the TCP test (CR-TCP) were obtained ranging from 0.90 to 1.00. In a second analysis, the relationship between the overburden pressure and NTCP was explored and a mathematical expression for the overburden correction factor for the TCP blowcount value (CN-TCP) was determined. This work represents the first study where corrections to NTCP are explored, and the outcome of this research benefits the geotechnical engineering community using the TCP test and its associated foundation design method.

Use of Micropiles for Foundations of Transportation Structures Final Report

In pile design, piles must be able to sustain axial loads from the superstructure without bearing capacity failure or structural damage. In addition, piles must not settle or deflect excessively in order for the serviceability of the superstructures to be maintained. In general, settlement controls the design of piles in most cases because, by the time a pile has failed in terms of bearing capacity, it is very likely that serviceability will have already been compromised. Therefore, realistic estimation of settlement for a given load is very important in design of axially loaded piles. This notwithstanding, pile design has relied on calculations of ultimate resistances reduced by factors of safety that would indirectly prevent settlement-based limit states. This is in part due to the lack of accessible realistic analysis tools for estimation of settlement, especially for piles installed in layered soil. Micropiles have been increasingly used, not only as underpinning foundation elements but also as foundations of new structures. Prevalent design methods for micropiles are adaptations of methods originally developed for drilled shafts. However, the installation of micropiles differs considerably from that of drilled shafts, and micropiles have higher pile length to diameter ratios than those of drilled shafts. Improved understanding of the load-transfer characteristics of micropiles and the development of pile settlement estimation tools consistent with the load-transfer response of these foundation elements are the main goals of the proposed research. A rigorous analysis tool for assessment of the load-settlement response of an axially loaded pile was developed in this study. The authors obtained explicit analytical solutions for an axially loaded pile in a multilayered soil or rock. The soil was assumed to behave as a linear elastic material. The governing differential equations were derived based on energy principles and calculus of variations. In addition, solutions for a pile embedded in a multilayered soil with the base resting on a rigid material were obtained by changing the boundary conditions of the problem. The authors also obtained solutions for a pile embedded in a multilayered soil subjected to tensile loading. They then compared the solutions with the results from FEA and also with other solutions available in the literature. Finally, they compared the results of a pile load test from the literature with the results obtained using the solutions proposed in this study. Using the obtained elastic solutions, extensive parametric studies on the load-transfer and load-settlement response of rock-socketed piles were also performed. The effects of geometry of rock socket, rock mass deformation modulus, and in situ rock mass quality were investigated. To facilitate the use of the analysis, a user-friendly spreadsheet program ALPAXL was developed. This program is based on the elastic solution obtained in this study and uses built-in functions of Microsoft Excel. ALPAXL provides the results of the analysis, the deformed configuration of the pile-soil system and the load-settlement curve in seconds. It can be downloaded at http://cobweb.ecn.purdue.edu/~mprezzi. In the context of an INDOT project, a fully instrumented load test was performed on a rock-socketed micropile. The results of this micropile load test, on a pile with high slenderness ratio and high stiffness of surrounding rock, confirmed that most of the applied load was carried by the pile shaft. The shaft capacity of hard limestone obtained from the load test at the final loading step was 1.4 times larger than the shaft capacity that is obtained using the highest value of limit unit shaft resistance suggested by FHWA. Using pile and soil properties, predictions were also made using ALPAXL. The results from ALPAXL were in good agreement with the measured data at the design load level.

The Effect of Concrete Deformation on Displacement of an Axially Loaded Drilled Shaft

This article presents the settlement of drilled shafts resulting from their structural deformations. Although drilled shafts are widely used as foundations for settlement-sensitive structures such as bridges and high-rise buildings, the structural deformations of drilled shafts are not typically taken into account in the design process. However, if unexpected structural deformations of drilled shafts cause additional settlement to the foundation, the serviceability of the superstructure can be jeopardized. Unfortunately, very few research efforts have been made to quantify the structural deformation of drilled shafts; this needs to be addressed to accurately predict the settlement of drilled shafts. In this study, we investigate the effect of structural deformation on displacement of axially loaded drilled shafts. Finite element analyses were performed to quantify the structural deformation of drilled shafts. The analysis results indicated that the structural deformation of drilled shafts could be quite significant for long drilled shafts. The main factors that affected the structural deformation of drilled shafts were found to be pile length, the material properties of drilled shafts, and the relative humidity of surrounding soil. An approximate equation is proposed to estimate the long-term deformation of drilled shafts.

Elastic Analysis of Rock-Socketed Piles

Rock-socketed piles are used to transfer through shaft and base resistances the loads from a superstructure to competent rock layers. In many situations, rock-socketed piles are expected to behave linear elastically under working loads. In this paper, the authors present an elastic analysis that applies to piles with circular cross sections installed in rock layers. The analysis follows from the solution of the differential equations governing the displacements of the pile-rock system obtained using variational principles. The input parameters needed for the analysis are the pile geometry and the elastic constants of the rock and pile. A parametric study is used to illustrate the most important factors that need to be considered in the design of rock-socketed piles.