Journal of Geotechnical and Geoenvironmental Engineering

Field load tests of three drilled shafts socketed in Burlington limestone were conducted using the Osterberg load cell. The objective of the testing was to compare the load capacities obtained from the field load tests with load capacities predicted using empirical methods. Based on the results of this study, the following conclusions can be drawn. The observed values of unit side resistance exceeded predicted empirical values for two of the three shafts tested (2,343 and 2,278 kPa observed versus 1,550 and 1,252 kPa predicted). However, for one of the shafts, the observed value of unit side resistance was only about $\frac{3}{4}$ of the more conservative predicted empirical value (916 kPa observed versus 1,252 predicted). Bearing capacity failure did not occur for two of the three shafts. Bearing capacity failure may have occurred for one of the shafts. Using a factor of safety of 3 applied to the lowest observed value of end bearing pressure implies that the allowable bearing capacity for the Burlington limestone at this site (3 MPa, or ≅500 psi) exceeds the typical presumptive bearing capacity for sound limestone in mid-Missouri (1914 kPa or 277 psi).

The limit equilibrium method is commonly used for slope stability analysis. Limit equilibrium solutions, however, are not rigorous because neither static nor kinematic admissibility conditions are satisfied. Limit analysis takes advantage of the lower- and upper-bound theorems of plasticity theory to provide rigorous bounds on the true solution of a stability problem. In this study, finite-element models are used to construct both statically admissible stress fields for lower-bound analysis and kinematically admissible velocity fields for upper-bound analysis of soil slopes. While limit analysis of relatively simple slopes, typically homogeneous and of simple geometry, has been done previously, limit analysis of slopes with complex geometries, soil profiles, and groundwater patterns could not be effectively done in the past. In this paper, the theoretical basis and procedure for limit analysis of such slopes is presented. Various examples of slopes are selected from the literature and analyzed using both limit equilibrium and limit analysis. Factors of safety from limit equilibrium and limit analysis are compared. A comparison is also made, for each example, between the critical slip surfaces from limit equilibrium with the velocity field and plastic zone from the upper-bound solution and with the stress field from the lower-bound solution.

The effects of large sample spacing associated with evaluating the vertical strength variability of a clayey soil are discussed in this paper. The research concerns 0.2 m sample spaced cone penetration data profiles analyzed by means of statistical treatment. The aim is to verify the effects of this sample spacing, or that greater than 0.2 m, on trend definition and on parameters which describe the vertical strength variability of the soil. We consider the variance and the scale of fluctuation of the strength values compared to the trend. This investigation also involves the effects of large sample spacing on the location of geostatistical boundaries and the importance of the trend removal technique for obtaining a sound set of residuals. The results of this research provide both theoretical indications and engineering prescriptions for planning a site characterization program.

This paper evaluates the feasibility of using artificial neural network (ANN) models for estimating the overconsolidation ratio (OCR) of clays from piezocone penetration tests (PCPT). Three feed-forward, back-propagation ANN models are developed, and trained using actual PCPT records from test sites around the world. The soil deposits range from soft, normally consolidated intact clays to very stiff, heavily overconsolidated fissured clays. ANN model 1 is a general model applicable for both intact and fissured clays. ANN model 2 is suited for intact clays, and ANN model 3 is applicable to fissured clays only. The models are validated using new PCPT data (not used for training), and by comparing model predictions with reference OCR values obtained from oedometer tests. For intact clays, ANN model 2 gives better OCR estimates compared to ANN model 1. For fissured clays, ANN model 3 gives better estimates compared to ANN model 1. Some of the existing interpretation methods are reviewed. Compared to the existing methods, ANN models 2 and 3 give very good estimates of OCR.

This paper presents an assessment of existing and new probabilistic methods for liquefaction potential evaluation. Emphasis is placed on comparison of probabilities of liquefaction calculated with two different approaches, logistic regression and Bayesian mapping. Logistic regression is a well-established statistical procedure, whereas Bayesian mapping is a relatively new application of the Bayes’ theorem to the evaluation of soil liquefaction. In the present study, simplified procedures for soil liquefaction evaluation, including the Seed–Idriss, Robertson–Wride, and Andrus–Stokoe methods, based on the standard penetration test, cone penetration test, and shear wave velocity measurement, respectively, are used as the basis for developing Bayesian mapping functions. The present study shows that the Bayesian mapping approach is preferred over the logistic regression approach for estimating the site-specific probability of liquefaction, although both methods yield comparable probabilities. The paper also compares the three simplified methods in the context of probability of liquefaction, and argues for the use of probability-based procedures for evaluating liquefaction potential.

Transit-time design methods are presented in this paper for determining the design thickness for composite liners consisting of a geomembrane and a compacted soil liner or geosynthetic clay liner. The design methods are based on a closed-form analytical solution for transient solute diffusion of volatile organic compounds in a composite liner and results from a numerical model. An analytical solution for diffusion in a two-layer soil profile, which is useful for transit-time design of composite liners, is also presented. The analytical solutions are used to develop graphical solution charts that can be used to design composite liners for which the effluent concentration and contaminant flux are less than a specified value. Design examples are included for a composite liner having a compacted soil liner and a composite liner having a geosynthetic clay liner. The method is relatively simple to apply and can be used for preliminary design of composite liners, evaluating experimental results, and verifying more complex numerical models.

A method for predicting the complete time-domain vibration records of soil and structures prior to installation of foundations for impact machines is described in detail. A paper provides support for the validity of accepted assumptions about the use of impacts directly on the soil for estimating the impulse response functions, and the effect of load zone dimensions on soil vibrations. The procedures for experimental testing on a site and computing the predicted complete vibration records are developed. Resulting patterns of computed and measured vibrations are shown for block-type foundation and a foundation under a vibroisolated block for impact machine. Furthermore, the method enables us to consider the heterogeneity and variety of soil and structure properties. In particular, it is useful under nonuniform and complicated soil conditions for determination and verification of safe distances from machine foundations to objects sensitive to vibrations.

Based on a new type of kinematic hardening and the theory of critical state soil mechanics, a two-surface model is herein developed for predicting the undrained behavior of saturated cohesive soils under cyclic loads. The anisotropic hardening rule works in two steps: (1) introducing a new concept, memory center, to take into account the memory of particular loading history; and (2) regulating the movement of the bounding and loading surfaces according to the direction of loading paths in stress space. Conventional triaxial tests have been performed on reconstituted clay samples in the laboratory. The proposed model is verified with respect to the observed behavior of soil samples. It is shown that like a multisurface model, this model can realistically describe some important responses of clays subjected to both monotonic and cyclic loading, while incorporating the memory of particular loading events.