Jie-Ru Chen

Updating Uncertainties in Friction Angles of Clean Sands

It is essential to characterize the uncertainties of soil shear strengths, including friction angles of sands, for geotechnical reliability-based design. In particular, it is of practical interest to update the uncertainties in friction angles on the basis of all available information by correlation, given the considerable cost of a typical site investigation. Although it is relatively simple to update uncertainties by correlation when the information is one dimensional (1D) or univariate, it is quite challenging to update uncertainties by using multivariate information through multiple correlations. This study proposes a systematic way of constructing multivariate correlations on friction angles of reconstituted clean sands. A set of simplified equations are obtained through Bayesian analysis for the purpose of updating uncertainties. The inputs to the equations are the results of field and laboratory tests, and the outputs are the updated mean values and standard deviations of the friction angles. Test ...

Robustness of Constant Load and Resistance Factor Design Factors for Drilled Shafts in Multiple Strata

AbstractThis study addresses the issue of adopting constant resistance factors for the LRFD approach to the axial compression of drilled shafts in multiple strata of clay, sand, gravel, and rock. The focus is on how to achieve a uniform reliability level for a wide range of stratum scenarios with constant or nonconstant LRFD factors. The main finding is that a uniform reliability level cannot be achieved if the LRFD factors are constant and are independent of the thicknesses or relative contributions of the strata. This conclusion is confirmed in three separate ways from examination exercises: (1) by using LRFD factors recommended in a recent Federal Highway Administration manual, (2) by using tailor-made LRFD factors derived from optimization, and (3) by using LRFD factors calibrated from the first-order reliability method. A possible strategy of calibrating nonconstant LRFD factors without resulting in a proliferation of factors is proposed in this study. The use of this approach is demonstrated by a de...

Discussion of ‘Interpretation of augered cast in place pile capacity using static loading tests’ by A. W. Stuedlein*, S. C. Reddy and T. M. Evans, The Journal of the Deep Foundation Institute, 8(1), 2014

The authors have presented an interesting study on interpreting the results of static load tests on augered cast-in-place (ACIP) piles, including numerical evaluations of several load test interpretation criteria. Both warrant query and comment. The discussers have conducted some similar prior studies that can be used for comparison. This discussion first will compare the authors and discussers databases and then will focus on the initial response of the load-displacement curve, interpreted failure load, extrapolation of load test data, and recommendations on selection of methods. The focus will be on comparing the Davisson, slope tangent in compression, and L1–L2 methods.

Evaluation of Relative Density from In Situ Test Correlations for Cohesionless Gravelly Soils

The SPT N vs. relative density (D r ) correlations for cohesionless soils were examined in detail using available laboratory and field data. For these correlations, corrections are applied to N, giving the recommended normalized value of (N 1 ) 60 . The D r is linked to (N 1 ) 60 as a function of soil characteristics that include the particle size, aging, and overconsolidation. Three correction factors for sandy soils were found to be appropriate for a wider range of soils, up to gravelly soils with D 50 at least on the order of 5-10 mm. Use of the large penetration test (LPT) could extend these correlations to larger sizes.