Journal of Geotechnical and Geoenvironmental Engineering

Following disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors H. B. Seed and I. M. Idriss developed and published a methodology termed the “simplified procedure” for evaluating liquefaction resistance of soils. This procedure has become a standard of practice throughout North America and much of the world. The methodology which is largely empirical, has evolved over years, primarily through summary papers by H. B. Seed and his colleagues. No general review or update of the procedure has occurred, however, since 1985, the time of the last major paper by Professor Seed and a report from a National Research Council workshop on liquefaction of soils. In 1996 a workshop sponsored by the National Center for Earthquake Engineering Research (NCEER) was convened by Professors T. L. Youd and I. M. Idriss with 20 experts to review developments over the previous 10 years. The purpose was to gain consensus on updates and augmentations to the simplified procedure. The following topics were reviewed and recommendations developed: (1) criteria based on standard penetration tests; (2) criteria based on cone penetration tests; (3) criteria based on shear-wave velocity measurements; (4) use of the Becker penetration test for gravelly soil; (4) magnitude scaling factors; (5) correction factors for overburden pressures and sloping ground; and (6) input values for earthquake magnitude and peak acceleration. Probabilistic and seismic energy analyses were reviewed but no recommendations were formulated. Publisher's Note. This paper is no longer the version of record, and is superceded by the version that appears in the October 2001 issue [Youd, T. L., et al. (2001). "Liquefaction resistance of soils: Summary report from the 1996 NCEER and 1998 NCEER/NSF workshops on evaluation of liquefaction resistance of soils." J. Geotech. Geoenviron. Eng., 127(10), 817–833, doi:10.1061/(ASCE)1090-0241(2001)127:10(817)]. All citations should be made to the October 2001 version of the paper.

The results from an experimental study on sands with high nonplastic silt content are presented. Drained and undrained triaxial compression tests, undrained cyclic triaxial tests, and drained/undrained instability tests were performed on specimens of loose Nevada sand with 40% silt content. The behavior was observed to be somewhat different from previously published tests with sands at lower silt content. The greater silt content appears to provide a more volumetrically contractive response throughout the entire stress-strain curve. However, some aspects of the response were similar to sands with lower silt content. Monotonic undrained tests indicated “reverse” behavior, i.e., static liquefaction occurred at low confining pressures and increasing dilatant volume-change tendency was observed with increasing confining pressure. Analyzing the results using the concepts of steady state resulted in a unique steady-state line only when undrained tests were sheared from the same isotropic compression line. When specimens of different initial densities were tested at the same initial confining pressures, the resulting steady-state points did not fall on the same steady-state line.

A risk indexing tool is proposed to assist in the prioritization of maintenance, repair, and evaluation tasks on embankment dams that are generally less than 33 m (100 ft) high and for which there is little or no instrumentation, limited or no information concerning as-built conditions, and little or no information on the performance history. Under such circumstances, there may not be enough information available to perform anything other than an “indexing” type of analysis to assist in prioritization. The risk indexing tool is based upon identifying potential deficiencies in the physical condition of the dam and rating the overall importance of these deficiencies to the safety of the structure. It is meant as an index of risk (indication) and not as a direct measure of risk. Checklists are presented for onsite inspections to determine current physical condition. Condition is defined in terms of a condition function that is based upon a condition indexing scale. Four potential failure modes are considered: (1) overtopping; (2) external erosion; (3) piping; and (4) mass movement (slope instability). Absolute probabilities are specifically not factored into the analysis. Conditional probabilities are estimated for each failure mode using a Bayesian updating procedure based on dam attributes. A simple failure criticality analysis is performed wherein specific changes in physical condition of the dam are considered to contribute to the probability of failure for each mode. From this failure criticality analysis and the conditional probabilities of failure, the relative importance of the various changes in physical condition is determined. The physical condition and the relative importance are then combined for each observable deficiency to form a risk index. These risk indices are used to prioritize expenditures for improvements on the premise that actions to address the most significant physical deficiencies are preferred.

Ten embankment dams managed by the Massachusetts Department of Environmental Management Office of Dam Safety have been prioritized according to their physical deficiencies. Based upon visual inspection reports by several independent engineers engaged by the Department of Environmental Management and using a computer program that automates the risk indexing procedure, the 10 dams have been assigned a risk index (or priority ranking) number that identifies potential deficiencies in the physical condition of each structure and provides an evaluation of the overall importance of these deficiencies. Comparisons of the computed total risk indices for all dams in an inventory provides a basis for prioritizing future maintenance and repair actions for that inventory. Examination of the risk indices for each physical condition at a single dam can also give an indication as to which deficiencies may be the most significant. This paper will assist dam safety engineers in evaluating the potential benefits of the application of risk indexing to dams within their inventory. A companion paper presents the theoretical basis for prioritizations presented herein.

This paper describes the results of a centrifuge modeling study of the response of piles embedded in calcareous sand under monotonic lateral loading. A number of features have been explored, including method of installation, rate of loading, and pile head restraint. The study has led to recommendations for load-transfer curves with the magnitude of lateral resistance linked to the soil strength through the cone resistance. Modification factors have been developed to allow for different methods of installation and for different rates of loading. The proposed load-transfer curves and resulting pile response are shown to provide an excellent match with the experimental data, and are compared with results derived using existing guidelines for terrigenous sands. Significant differences are demonstrated, confirming the need to treat calcareous sediments separately from other soil types with respect to lateral pile response.

Excess foundry sands from gray-iron casting are a mixture of sand, bentonite, and additives that can have properties desirable for structural fills and hydraulic barriers, depending on their bentonite content. To facilitate beneficial reuse of foundry sands, typical strength parameters need to be available so that designers can make comparisons with designs employing virgin earthen materials. To provide typical design parameters, a testing program was conducted to characterize the strength of foundry sands and their interaction with geosynthetics. Small-scale direct shear tests, large-scale multistage interface shear tests, and pullout tests were conducted using foundry sands with bentonite contents representing the range normally found in the casting industry and three geosynthetics (geotextile, geogrid, and geomembrane). The results indicate that foundry sands can be used effectively in geotechnical construction. Friction angles of the as-compacted foundry sands generally ranged between 39° and 43°, and the as-compacted cohesions ranged between 17 and 28 kPa. Drained friction angles were similar to as-compacted friction angles except at high bentonite content. Typical interface friction angles ranged between 25° and 35°, with efficiencies ranging between 0.5 and 0.9. Interaction coefficients from the pullout tests ranged between 0.2 and 1.7.

This study quantified the effects of four quaternary ammonium cations (TMA, DTMA, HDTMA, and BTEA) on the mechanical properties of a modified Wyoming bentonite. TMA, DTMA, and HDTMA are organic cations with alkyl chains of lengths 1, 10, and 16 carbons, while BTEA has a benzyl ring attached. Substitution of the organic cations onto the bentonite surfaces altered the soil's behavior by: (1) reducing the soil's specific gravity, with the specific gravity decreasing linearly as the size of the exchanged organic cation was increased; (2) dramatically reducing the soil's liquid limit (from 458% for the unmodified bentonite to 52–65% for the organoclays); (3) reducing the compressibility of the clays (from a compression index of 5.5 for the unmodified bentonite to compression indices of 0.47–0.59 for the organoclays); (4) reducing the swell potential (C_s = ∼1.5 for bentonite compared with 0.035–0.083 for the organoclays); and (5) increasing the direct shear friction angle (7° for unmodified bentonite compared with 34–37° for the organoclays).

Lunar soil consists of dry silty sand. Observations and measurements conducted during Surveyor, Apollo, and Luna missions indicated that the lunar soil is unusually cohesive. This is attributable to the fact that thick layers of adsorbed gases, which coat and lubricate soil particles on Earth, are absent in the ultrahigh vacuum on the Moon. “Surface cleanliness” is introduced as a new parameter for describing soils in different planetary environments. It is defined as the dimensionless inverse of adsorbate thickness on solid surfaces. By this definition, the ultrahigh vacuum on the Moon is associated with high surface cleanliness, while Earth's atmosphere is associated with low surface cleanliness. A model is developed to calculate surface cleanliness and its effect on shear strength in any planetary environment. Results obtained from the model compare well with data from previous ultrahigh vacuum and variable temperature laboratory experiments on Earth soils. It is shown that surface cleanliness is an important parameter with respect to lunar soil shear strength.