A Historical Perspective on Geotechnical Case Histories Courses

Ralph Peck introduced the concept of using a geotechnical case histories course to teach students problem solving and technical communications skills, beginning around 1956. This course was developed as a professional practice course at the graduate level, intended for civil engineers of diverse backgrounds as well as geoscientists. Students were required to prepare one-page summaries of each case history profiled in the course, a requirement that left an enormous impression on the students. A different approach was employed by the University of California, Berkeley, beginning around 1970. Berkeley offered two graduate courses in the mold of ABET “capstone courses,” graduate soil mechanics laboratory, and advanced foundation construction. These courses were intended to prepare students for geotechnical problem solving and professional practice using a single term project, which required student teams to prepare a comprehensive report, similar to those prepared by private sector consultants. The background on each of these courses, the individuals who taught them, and the techniques employed by those instructors are briefly profiled and their pros and cons are compared

Ralph Peck’s Circuitous Path to Professor of Foundation Engineering (1930-48)

When most geoengineers hear the name of Ralph B. Peck (1912-2008) they usually associate him with the father of soil mechanics, the legendary Karl Terzaghi (1883-1963), because of their long professional association, between 1939-63. But, Peck’s professional career in geotechnics was also influenced by other engineers and geologists, whose ingenuity he admired and tried to emulate. Some of these are names easily recognized, even 100 years later, while others are all but forgotten. This article seeks to introduce the reader to some of those luminaries that played a role in shaping Ralph Peck’s career as one of the founders of American foundation engineering and the father of the Observational Method, which he learned from others he worked with as well as some who preceded him. These accounts are based on a series of interviews with Dr. Peck carried out by the author, between 1991-2001

Quasi-Chemical and Structural Analysis of Polarizable Anion Hydration

Quasi-chemical theory is utilized to analyze the roles of solute polarization and size in determining the structure and thermodynamics of bulk anion hydration for the Hofmeister series Cl$^-$, Br$^-$, and I$^-$. Excellent agreement with experiment is obtained for whole salt hydration free energies using the polarizable AMOEBA force field. The quasi-chemical approach exactly partitions the solvation free energy into inner-shell, outer-shell packing, and outer-shell long-ranged contributions by means of a hard-sphere condition. Small conditioning radii, even well inside the first maximum of the ion-water(oxygen) radial distribution function, result in Gaussian behavior for the long-ranged contribution that dominates the ion hydration free energy. The spatial partitioning allows for a mean-field treatment of the long-ranged contribution, leading to a natural division into first-order electrostatic, induction, and van der Waals terms. The induction piece exhibits the strongest ion polarizability dependence, while the larger-magnitude first-order electrostatic piece yields an opposing but weaker polarizability dependence. In addition, a structural analysis is performed to examine the solvation anisotropy around the anions. As opposed to the hydration free energies, the solvation anisotropy depends more on ion polarizability than on ion size: increased polarizability leads to increased anisotropy. The water dipole moments near the ion are similar in magnitude to bulk water, while the ion dipole moments are found to be significantly larger than those observed in quantum mechanical studies. Possible impacts of the observed over-polarization of the ions on simulated anion surface segregation are discussed.Comment: slight revision, in press at J. Chem. Phy

Impact of Geographical Information Systems on Geotechnical Engineering

Over the last four decades Geographical Information Systems (GIS) have emerged as the predominant medium for graphic representation of geospatial data, including geotechnical, geologic and hydrologic information routinely used by geotechnical and geoenvironmental engineers. GIS allow unlimited forms of spatial data to be co-mingled, weighted and sorted with any number of physical or environmental factors. These data can also be combined with weighted political and aesthetic values to create hybrid graphic products capable of swaying public perceptions and decision making. The downside of some GIS products is that their apparent efficacy and crispness can also be deceptive, if data of unparalleled reliability is absorbed in the mix. Disparities in data age and quality are common when compiling geotechnical and geoenvironmental data. Despite these inherent shortcomings, GIS will continue to grow and evolve as the principal technical communication medium over the foreseeable future and engineers will be forced to prepare their work products in GIS formats which can be widely disseminated through the world wide web. This paper presents the historical evolution of GIS technologies as it relates to the impact in geotechnical engineering, concluding with four case histories on the application of this emerging technology

Seismic Site Classifications for the St. Louis Urban Area

Regional National Earthquake Hazards Reduction Program (NEHRP) soil class maps have become important input parameters for seismic site characterization and hazard studies. The broad range of shallow shear-wave velocity (VS30, the average shear-wave velocity in the upper 30 m) measurements in the St. Louis area results in significant uncertainties between the actual spot values and the averaged values used to assign NEHRP soil classes for regional seismic hazard studies. In the preparation of an NEHRP site classification map of the St. Louis urban area, we analyzed 92 shear-wave velocity (VS) measurements, supplemented by 1400+ standard penetration test (SPT) profiles in areas bereft of VS measurements. SPT blow counts correlated to VS values based on the published correlations. The data were then compiled for respective surficial geologic units and bedrock type. These data suggest that the reciprocal of VS30 exhibits a fairly linear relationship with depth to bedrock, likely because VS30 is a function of the thickness of surficial materials exhibiting relatively low VS values. The VS30 values were interpolated by summing the regressed VS30 on the depth to bedrock and kriged values of the regression residuals. The resulting NEHRP site classification maps predict that upland areas of the St. Louis area are spatially classified as soil site classes SB to SD, while the low-lying floodplains are consistently classified as SD to SF

Recent Geotechnical Developments in Geospatial Information Systems Technology

Geotechnical engineering projects in current research and practice are increasingly undergoing geospatial analysis based on geologic and geotechnical data collected. The explosion of spatial data that is available for surface features, particularly from the raster based products, heavily used by commercial and available to the public, present only one dimension of site characterization. Geotechnical engineers are more interested in data with depth immediately below their project site retrieve from drilled and imaged subsurface surveys. The ability to optimize the use of new and existing subsurface data continues to be undermined by the lack of a common and agreed data format and structure. Over the past decade several initiatives have tried to develop some consensus, with limited success. The latest initiative for a common geotechnical data exchange standard is also described. Several projects based on the authors, experience are featured in this paper and serve as examples of the challenge of working with large and diverse subsurface geotechnical databases. Additionally, an update of a geotechnical data exchange format is also presented to point the direction for the future

Overview of the Seismic Threat in the Central United States

This paper summarizes geological, geophysical and seismological studies in two accepted and one candidate seismic zones in the central United States. The area was shaken by as many as 2,000 felt earthquakes in 1811-12, including four events greater than Magnitudes 7.0. These occurred before the area west of the Mississippi River was settled, so the intensity of shaking was not recorded over much of the affected region. Earthquakes in the central United States are felt over a much broader area than similar magnitude earthquakes in the western United States because of the low attenuation associated with undeformed Paleozoic age strata underlying the region. The New Madrid Seismic Zone (NMSZ) is believed to have been the source of the 1811-12 quakes and is the most studied source area in the central U.S. Some of the important structural features identified within this zone are summarized in this article, including the Reelfoot Fault scarp, Lake County Uplift, Crowley’s Ridge, Blytheville Arch, Bootheel Lineament and the Crittenden County Fault Zone. In just the last few years a GPS measurement array has been established around the Reelfoot Fault, and a debate has emerged about the accuracy and implications of these measurements. In the Wabash Valley Seismic Zone (WVSZ) limited historical and instrument arrays suggests that although the recorded seismic activity is much lower than a plate boundary region, it is, nevertheless, anomalously high activity for an intraplate region. Recent paleoliquefaction studies in the WVSZ suggest that it has likely spawned large-magnitude earthquakes, though not with as great a magnitude or frequency as the NMSZ. The anomalous historic seismicity recorded in South Central Illinois is believed to be the reactivation of old basement faults or background noise, but paleoliquefaction studies indicate that large magnitude earthquakes may also emanate from this region. It has not been accepted as a credible seismic source zone, but may be at some time in the future, as more data is collected and synthesized

Seismic-Hazard Map of Southeast Missouri and Likely Magnitude of the February 1812 New Madrid Earthquake

The New Madrid seismic zone lies beneath the upper Mississippi Embayment, straddling the border between southeastern Missouri and northwestern Tennessee. In late 1811 and early 1812, it produced five earthquakes of magnitudes \u3e6.5, violently shaking the central and eastern United States (CEUS). Its magnitude and recurrence are of concern to today\u27s central United States regions. By considering the effects of local geology, deterministic scenario maps (Mw 7.3 and 7.7) were produced for ground motions intended to simulate the 7 February 1812 event (NM3), which was the largest felt. These maps include spatial estimates of peak ground acceleration and of 0.2 s and 1.0 s spectral acceleration (SA). Compared with the isoseismic map of modified Mercalli intensities (MMIs) in southeast Missouri, the MMIs converted from 0.2 s SA suggest that Mw 7.7 is a plausible scenario for NM3. To better constrain its magnitude, other CEUS sites shaken during NM3 were also examined. Local site conditions were studied and evaluated before calculating the threshold magnitude for the reported MMIs. These results indicate that the magnitude of NM3 was at least Mw 7.6, which validates our estimated size of Mw 7.7 for southeastern Missouri

Earthquake Potential Along the Hayward Fault, California

The Loma Prieta event probably marks a renewed period of major seismic activity in the San Francisco Bay Area. Particularly ominous is the historic record of major events a few years apart on opposite sides of the Bay in 1836 (N. Hayward fault) and 1838 (N. Peninsula, San Andreas fault) and 1865 (Loma Prieta segment, San Andreas fault), and 1868 (S. Hayward fault) (Figure 1). Recent preliminary measurements of the Holocene geologic slip rate of the Hayward fault are as much as 9 mm/yr (Lienkaemper and others 1989) - about 80% greater than the first Holocene measurements determined as recently as 1987 (Borchardt and others 1987). Aseismic slip, as measured from monuments and offsets of cultural features, varies along the fault from 3 to 9 mm/yr and averages 5 mm/yr (Lienkaemper and others 1990). Although the earthquake potential calculated from such data are greatly affected by initial assumptions, the extremes are instructive: Method I assumes that the fault is freely slipping along the entire fault plane and that, until aseismic slip ceases, no major events are possible. Method II assumes that aseismic slip occurs throughout the 10-km deep seismogenic zone, but that strain continues to build at the deficit rate about 4 mm/yr and strain builds at slightly less than the geologic rate (9 mm/yr). Assuming that 1.1 to 1.2 m of displacement occurs at depth during M 6. 8 events (Slemmons and Chung, 1982), calculated recurrences range from 120 to 300 years. Thus, in view of the time elapsed since the two previous events (123 and 155 years), we have entered the earthquake window for the Hayward fault. The new geologic rate has increased the estimates of 30 year probabilities for major events from 20% to 28% on the north half of the fault and from 20% to 23% on the southern half (compare WGCEP of 1988 and 1990)