Armin W. Stuedlein

Geotechnical Characterization and Random Field Modeling of Desiccated Clay

AbstractAn extensive set of in situ and laboratory test data is presented for a footing load test site east of Houston, Texas, in desiccated Beaumont clay. The in situ test program included standard and cone penetration tests (CPTs), the latter of which was selected for statistical analysis to produce vertical and horizontal random field model parameters for corrected cone tip resistance. Given the relatively high sampling frequency of the cone tip resistance in the vertical direction, the vertical random field model parameters were determined using the modified Bartlett’s test statistic with fitted autocorrelation models subject to a strict fitting criterion. Horizontal random field model parameters were generated by collapsing the two-dimensional distribution of the CPTs to a one-dimensional representation and by using less stringent evaluation of the autocorrelation. The results of this study indicate that Beaumont clay exhibits greater inherent spatial variability than previously reported at other cla...

Reliability-Based Serviceability Limit State Design of Spread Footings on Aggregate Pier Reinforced Clay

Despite the availability of numerous methods to predict the load-displacement response of aggregate pier reinforced clay, accurately modeling the nonlinear displacement response remains challenging. Moreover, the uncertainty in the bearing pressure-displacement prediction has not been satisfactorily estimated, preventing the generation of reliability-based design (RBD) procedures. This study proposes a simple RBD procedure for assessing the allowable bearing pressure for aggregate pier reinforced clay in consideration of the desired serviceability limit state. A recently established bearing-capacity model for aggregate pier reinforced clay and its uncertainty is incorporated into a bivariate bearing pressure-displacement model appropriate for a wide range in displacement and calibrated using a high-quality full-scale load-test database. Several copulas were then evaluated for goodness of fit to the measured dependence structure between the coefficients of the selected two-parameter bearing pressure-displacement model. Following the generation of an appropriate performance function, a combined load and resistance factor is calibrated in consideration of the uncertainty in the bearing pressure-displacement model, bearing capacity, applied bearing pressure, allowable displacement, and footing width using Monte Carlo simulations of the respective source distributions. An example is provided to illustrate the application of the proposed procedure to estimate the bearing pressure for an allowable displacement at the desired serviceability limit probability.

Bearing Capacity of Spread Footings on Aggregate Pier Reinforced Clay

AbstractAggregate piers, also known as stone columns, are a commonly used ground improvement technique to stiffen existing soils for the support of structure foundations. This paper presents an evaluation of existing analytical expressions for the bearing capacity of spread footings supported on aggregate pier reinforced clay. The accuracy of these models was investigated using a database of high-quality footing load test data. The existing models were compared using the bias (i.e., the ratio of measured and calculated bearing capacity), and they produced a wide range in predicted bearing capacities. Selected analytical models were empirically modified using the load test database, and this resulted in improved accuracy and reduced variability. Back-calculated aggregate pier bearing capacity and cavity expansion factors are shown to be inversely proportional to undrained shear strength, and therefore to the ultimate confining pressure available at failure. This finding is attributed to the curved failure ...

Analysis of Footing Load Tests on Aggregate Pier Reinforced Clay

AbstractDespite the increased use of aggregate piers for soil reinforcement, the role of typical construction variables on footing performance remains uncertain. This paper describes a series of full-scale footing load tests conducted to evaluate the effect of aggregate gradation, pier length, and compaction method. Tests were conducted on small (0.76 m) and large (2.74 m) instrumented spread footings supported on single aggregate piers and groups of aggregate piers, respectively. The bearing pressure-displacement response of these tests is presented and the statistical significance of the construction variables is quantified for single piers using a 23 factorial analysis within an ANOVA framework. The statistical significance of the effect of pier length, gradation, and compaction was determined by controlling for the spatial variability in matrix soil strength and stiffness across the test site, which indicated that these variables were largely insignificant at the treatment levels evaluated. Additional...

Design and Performance of a 46-m-High MSE Wall

This paper focuses on the design and performance of a very tall mechanically stabilized earth (MSE) wall. Expansion of Seattle-Tacoma International Airport called for the construction of a third runway west of the two existing runways. A significant volume of compacted earth fill was required to raise the grade as much as 50 m to meet the level of the existing airfield. Nominal 2H:1V fill slopes were used where possible, but MSE retaining walls were used where fill slopes would have encroached into existing wetlands. Consequently a four-tier 46-m-tall MSE wall was constructed along a portion of the western edge of the embankment. Performance monitoring included strain gauge-instrumented reinforcing strips, inclinometer installations with sondex settlement rings, optical survey of the wall facing for vertical and lateral movements, and piezometers. This paper describes wall design issues, aspects associated with the instrumentation of the wall, and the observed performance. Monitoring indicates satisfactor...

Assessment of Reinforcement Strains in Very Tall Mechanically Stabilized Earth Walls

The grade raising associated with the Third Runway Project at Seattle-Tacoma International Airport included construction of tall mechanically stabilized earth (MSE) walls, including the near-vertical, two-tier, 26-m North MSE wall and the near-vertical, four-tier, 46-m tall west MSE wall. Twenty reinforcement strips at critical wall cross sections were instrumented with over 500 strain gauges to monitor strains during and following construction. The reinforcement loads inferred from observed strains are of interest because of their great height and global reinforcement stiffness, which place these walls outside the range in height and stiffness used to calibrate commonly used design methods. This paper presents the development and distribution of reinforcement strains measured during and following the construction of these walls. The reinforcement stresses calculated using the original reinforcement load design methods and design friction angle agreed with those inferred from the measured strains. The accuracy of two standard-of-practice and two alternate design methods is evaluated by compar- ing the reinforcement loads inferred from measured strains to those calculated using the actual friction angle of the reinforced fill material. Advantages and limitations in these design methods are identified, and recommendations for the improvement of some of these methods are provided. DOI: 10.1061/(ASCE)GT.1943-5606.0000586.

Reliability of Spread Footing Performance in Desiccated Clay

AbstractTo advance the use of reliability-based design procedures, it is necessary to evaluate the sources of the design parameter uncertainty including inherent variability, measurement error, and transformation uncertainty. The results of a probabilistic evaluation of undrained footing bearing performance are discussed in the context of an extensive test site characterization described in a companion paper. Kriged cone tip resistance values are transformed into design parameters using a second-moment probabilistic approach and compared with the parameters obtained from the laboratory test analyses on specimens retrieved from the test site. The spatial, measurement, and transformation uncertainty are incorporated into probabilistic finite-element and bearing capacity analyses in which the results are compared against a full-scale load test performed at the test site. The results indicate that the reliable assessment of the spread footing response depends to a large degree on the assumed strength anisotro...

Displacement of Spread Footings on Aggregate Pier Reinforced Clay

AbstractAggregate piers, also known as stone columns, are commonly used to improve ground for the support of structure foundations. Despite the number of existing analytical and semiempirical methods available to predict the displacement of shallow foundations resting on aggregate pier reinforced clay, the accuracy of these models remains uncertain. After a brief review of existing load-displacement estimation methods, the accuracy of those models valid for isolated spread footings was investigated using a database of high-quality footing load test data. The methods were compared using the bias (i.e., the ratio of measured bearing capacity to that calculated) and were shown to exhibit a high degree of variability in the prediction of load and displacement. Then, the database was used to develop a multiple linear regression model for the prediction of footing displacements for aggregate pier reinforced clay under a wide range of pier configurations and soil conditions. The proposed statistical model is sho...

Stress-Strain Response and Dilatancy of Sandy Gravel in Triaxial Compression and Plane Strain

AbstractThe strength and stress-dilatancy of uniform sands has been studied extensively in geotechnical investigations, and practitioners can draw on a wealth of previously reported data for the estimation of their volumetric response. However, the suitability of accepted stress-dilatancy theory and empiricism has not been evaluated for well-graded gravelly soils. Axisymmetric, isotropically consolidated drained compression, and pure shear, plane strain quasi-K0 consolidated drained tests were performed on well-graded Kanaskat gravel using confining pressures ranging over three orders of magnitude to determine its stiffness, strength, and stress-dilatancy response. The plane strain stiffness, strength, and stress-dilatancy of Kanaskat gravel is observed from tests performed using a large cubical true-triaxial device with flexible bladders. The observed response is interpreted with a view of experimental boundary conditions and their impact on the volumetric response. The observed plane strain shear modulu...

Factors Affecting the Reliability of Augered Cast-In-Place Piles in Granular Soils at the Serviceability Limit State (DFI 2013 Young Professor Paper Competition Winner)

Abstract Owing to an increasing demand to manage risk and maximize cost-effectiveness, preference for reliability-based design (RBD) over traditional deterministic design procedures has increased for deep foundation elements. In this study, factors affecting the reliability of augered cast-in-place (ACIP) piles under axial compression at the serviceability limit state (SLS) are addressed using a simple probabilistic hyperbolic model and a database of static loading tests conducted on ACIP piles in cohesionless soils. The aleatory and model uncertainty in a selected two-parameter load-displacement model is statistically characterized for use in reliability simulations. Reliability simulations incorporating the correlated bivariate model parameter distribution were generated using a statistical translational model and various parametric and non-parametric correlation coefficients to assess the effect of correlation coefficient type on the reliability simulations. The first-order reliability method (FORM) was used to determine the effect of sample size on the stability and uncertainty of the serviceability limit state reliability index. Sample sizes greater than about 40 provided relatively consistent estimates of the reliability index; however, its uncertainty continued to decrease with increasing sample sizes. A parametric study was conducted in order to determine the variables (i.e. allowable displacement, predicted pile capacity, slenderness ratio) which govern reliability. In general, the uncertainty in the model used to predict pile capacity had a more significant impact on foundation reliability compared to the uncertainty in allowable displacement; this finding illustrates one advantage of having an accurate capacity prediction model. The slenderness ratio had the largest effect on foundation reliability at the SLS, and illustrates the importance for accounting for the pile geometry in reliability assessments.