Paul W. Mayne

Lithology and Shear-Wave Velocity in Memphis, Tennessee

We have derived a new three-dimensional model of the lithologic struc- ture beneath the city of Memphis, Tennessee, and examined its correlation with measured shear-wave velocity profiles. The correlation is sufficiently high that the better-constrained lithologic model may be used as a proxy for shear-wave velocities, which are required to calculate site-amplification for new seismic hazard maps for Memphis. The lithologic model and its uncertainties are derived from over 1200 newly compiled well and boring logs, some sampling to 500 m depth, and a moving- least-squares algorithm. Seventy-six new shear-wave velocity profiles have been measured and used for this study, most sampling to 30 m depth or less. All log and velocity observations are publicly available via new web sites.

Geotechnical site characterization in the greater Memphis area using cone penetration tests

Abstract The determination of seismic ground hazards in Memphis and Shelby County, Tennessee is facilitated by the use of electronic cone penetration tests that can provide up to four independent readings with depth from a single sounding. One series of soundings is being performed for site-specific mapping to determine the presence and extent of potentially-liquefiable sediments, in-situ soil resistance to liquefaction, and initial soil stiffness for ground motion amplification studies. Another series of soundings is being conducted in conjunction with field paleoliquefaction mapping in the New Madrid seismic zone to better define the intensity, magnitude, and geographic extent of ground failures caused by large past earthquake events, as well as information about the source sands. In this paper, an overview is given on the types of multi-channeled penetrometer data that are being collected, including vertical profiles of cone tip stress (qt), sleeve friction (fs), penetration porewater pressure (u1 or u2), downhole shear wave velocity (Vs), and/or electrical conductivity (ke). Representative soundings are presented from select sites to illustrate repeatability, data post-processing methods, and that derived downhole Vs profiles are generally in good agreement with non-invasive surface techniques at two Memphis test sites. Cyclic stress based procedures for liquefaction are discussed with relation to data from a paleoliquefaction site in Germantown, Tennessee, and estimates of the minimum magnitude of the historic event are discussed. While estimates of the earthquake magnitude are preliminary pending additional study on attenuation relationships and site response in the deep soils of the Mississippi Embayment, it is inferred from evaluation of in-situ test data using cyclic stress based techniques that the December 1811 New Madrid earthquake was likely larger than a Mw=7.5 event.

Seismic Flat Dilatometer Tests in Connecticut Valley Varved Clay

Downhole shear wave velocity measurements have been incorporated within a “Marchetti” flat dilatometer by placing a velocity transducer in a connecting rod just above the blade. The hybrid of combining downhole seismic with flat dilatometer, termed the seismic dilatometer test (SDMT), has the superior advantages of determining both the routine estimates of soil properties and stratigraphic information, while also measuring the small-strain stiffness within a single sounding. The SDMT is rapid, simple, and cost effective, requiring essentially no more time than a conventional dilatometer sounding. Results of seismic dilatometer testing in clays at the National Geotechnical Experimental Test Site (NGES) in Amherst, Massachusetts are presented and compare favorably with results from companion series of seismic cone penetrometer tests.

PROFILING OCR IN STIFF CLAYS BY CPT AND SPT

Standard penetration tests (SPT) and cone penetration tests (CPT) have conventionally been used to index profiles of undrained shear strength s sub u in clay deposits. Since s sub u is related to stress history, an alternative use of penetration resistances is the profiling of in-situ overconsolidation ratio (OCR). An empirical methodology is developed based on compiled data bases from 50 sites investigated by SPTs and 40 sites tested by CPTs. The study indicates general trends occur between the in-situ OCR and penetration resistances normalized to effective overburden stress in clays. Site specific calibration with laboratory consolidation tests is required, however, for profiling. Electric CPTs are preferable over SPTs and mechanical CPTs for profiling stress history because they are more repeatable and less subject to operator influence.

Cone Penetration Test Based Direct Methods for Evaluating Static Axial Capacity of Single Piles

The direct cone penetration test (CPT) based pile design methods use the measured penetrometer readings by scaling relationships or algorithms in a single-step process to enable the assessment of pile capacity components of shaft and base resistance (fp and qb, respectively) for evaluation of full-size pilings. This paper presents a state-of-the-art review of published works that focus on direct CPT evaluation of static axial pile capacity. The review is presented in a chronological order to explicate the evolution over the past six decades of an in situ test based solution for this soil-structure interaction problem. The objective of this study is an attempt to assemble maximum published methods proposed as a result of past investigations in one resource to afford researchers and practitioners with convenient access to the respective design equations and charts. In addition to an all-inclusive summary table and the design charts, a compilation of significant findings and discussions thereof are presented. Furthermore, potential future research directions are indicated, with special emphasis on the optimal use of the modern multi-channel hybrid geophysical-geotechnical seismic CPT to evaluate the complete axial pile load–displacement response.

Load-displacement uncertainty of vertically loaded shallow footings on sands and effects on probabilistic settlement estimation

This article focuses on the statistical characterisation and stochastic modelling of the load-displacement behaviour of shallow footings on cohesionless soils and on the probabilistic estimation of settlement for serviceability limit state design (LSD). The study relies on a field database of 30 full-scale footings subjected to vertical loading with cone penetration testing data available for each site. The performance of three load-displacement models in replicating field data is assessed comparatively through statistical analysis. Load-displacement uncertainty is subsequently modelled probabilistically to perform Monte Carlo Simulation (MCS)-based estimation of footing settlement using the best-performing power law model. The dependence among load-displacement model parameters is investigated and replicated using copula theory. Samples are generated to account for parametric uncertainties in model inputs. The simulation output samples of settlement are examined statistically in order to assess the relevance of parametric and load-displacement uncertainties in settlement estimation, as well as the importance of accounting for correlation between power law model parameters. A simple analytical model for the estimation of settlement at any target reliability level is obtained on the basis of the outputs of MCS. The model can be practically implemented in geotechnical LSD at serviceability limit states.

Serviceability limit state CPT-based design for vertically loaded shallow footings on sand

In this study, reliability-based design of vertically-loaded shallow foundations on cohesionless soil at the serviceability limit state is addressed and related to cone penetration resistance. A special database of 30 large footings on 12 different sands is investigated in a statistical and probabilistic perspective to quantify the load-displacement-capacity response and derive a direct design method based on cone penetrometer testing (CPT). A reference load-displacement model is identified through a comparative assessment of fitting of model types to load test data. The uncertainties in the load-displacement model and in the model inputs are modeled probabilistically. The probability of exceedance of a target probability of occurrence of a pre-established allowable settlement is computed in the form of a reliability index through Monte Carlo simulation. A partial load factor is defined and calibrated based on simulation outputs. Analytical expressions for the load factor as a function of the ratio of allowable settlement to footing dimensions are derived using least squares regression. The final design format allows simple and practical utilization on the part of the engineer while ensuring the minimization of excess conservatism.

Evaluating the In Situ Lateral Stress Coefficient (K0) of Soils via Paired Shear Wave Velocity Modes

AbstractThe utilization of shear wave velocities toward the evaluation of the in situ geostatic horizontal stress state in soils is validated, specifically the lateral stress coefficient K0. Field shear wave velocities from paired sets of different directional and polarization modes are compiled from 16 well-documented test sites involving a variety of geomaterials. Focus is particularly placed on shear wave velocities measured by downhole tests (VsVH), crosshole tests (VsHV), and special rotary-type crosshole tests (VsHH). At these sites, field K0 stress states have been quantified using one or more direct assessment techniques, including self-boring pressuremeter, total stress cells, and hydrofracture in field testing, as well as suction measurements, special consolidometers, and/or triaxial arrangements on undisturbed samples in the laboratory. Although the specific delineation of stress-induced versus inherent or fabric anisotropy may be difficult, it is shown that the ratio of horizontally polarized ...

CPT site characterization for seismic hazards in the New Madrid seismic zone

A series of cone penetration tests (CPTs) were conducted in the vicinity of the New Madrid seismic zone in central USA for quantifying seismic hazards, obtaining geotechnical soil properties, and conducting studies at liquefaction sites related to the 1811– 1812 and prehistoric New Madrid earthquakes. The seismic piezocone provides four independent measurements for delineating the stratigraphy, liquefaction potential, and site amplification parameters. At the same location, two independent assessments of soil liquefaction susceptibility can be made using both the normalized tip resistance ðqc1NÞ and shear wave velocity ðVs1Þ: In lieu of traditional deterministic approaches, the CPT data can be processed using probability curves to assess the level and likelihood of future liquefaction occurrence. q 2002 Elsevier Science Ltd. All rights reserved.

Determining Preconsolidation Stress and Penetration Pore Pressures from DMT Contact Pressures

Over recent years, several geotechnical explorations in clay deposits have shown the flat dilatometer test (DMT) to provide reasonable estimates of in-situ overconsolidation ratio with depth. Why should the horizontal strass index (K sub D = initial contact pressure minus hydrostatic pressure normalized to the effective overburden stress) show an empirical trend with over consolidation ratio (OCR)? It is postulated that, since the closing pressure and contact pressures are nearly equal, the initial contact pressure in clay is an approximate measure of the total pore pressure induced during penetration of the dilatometer blade. Published data from a clay site tested by a special DMT having a pore-pressure sensor, as well as piezocone/dilatometer data from 7 other sites, support this hypothesis. Since the pore-pressure response of clay is influenced by the in-situ OCR, the initial effective DMT contact pressure can be used to profile the stress history.