Significant discrepancy exists among the available correlations that are commonly used for determining relative density using cone penetration test (CPT) data. These correlations recognize the difference in sand compressibility and its effect on CPT data. Experience has indicated that compressibility is not a well-defined parameter. Current knowledge on the subject of sand compressibility and its effect on CPT data is limited and qualitative. A new approach that aggregates some of the available correlations for the determination of relative density using CPT data is developed. The new approach uses a weighting scheme that relates the compressibility, measured by friction ratio and expressed as a fuzzy number, to the base correlations. Field CPT data are used to examine and demonstrate the new approach. Results of the limited cases studied show that relative density can be determined reliably from CPT data using the proposed model.

The purpose of this paper is to present methods available for engineered remediation of seismically deficient earth dams (not including tailings dams), to review their strengths and weaknesses, to present case histories of the application of these methods, and to draw conclusions about the state of practice. A survey of completed and active rehabilitation projects was made. This survey identified 30 dams with engineering fixes and 22 with operational fixes. Data was obtained and is presented in tabular form for 36 dams. Of these dams, 13 had seismically deficient foundations, 15 had deficient embankments, and 8 had deficiencies in both embankment and foundations. Synopses of case histories are presented for John Hart Dam, Sardis Dam, Mormon Island Auxiliary Dam, and Pleasant Valley Dam.

Cyclic constant-volume direct simple shear tests were performed on intact specimens of a sensitive clay reconsolidated to the in-situ stress state resulting in an overconsolidation ratio (OCR) of 2.2. The tests were conducted for different values of initial static undrained shear stress. The results confirmed that the high strain rate associated with cyclic loading has a significant effect on the cyclic resistance of soft clays. For up to 12 cycles, the strain-rate effect fully compensates the degradation of shear strength associated with cycling. The presence of an initial static shear stress decreases the cyclic resistance but increases the total undrained shear resistance, due to the partial or total disappearance of stress and strain reversal. The results indicate that for such a clay, the static undrained shear strength provides a conservative estimate in a pseudostatic analysis.

Isotropic triaxial compression tests were conducted on five different, fairly uniform sands, with mean grain sizes between 2.8 and 0.105 mm, to determine the effects of effective confining pressure, mean grain size, and relative density on unit membrane penetration. Volume changes due to membrane penetration were determined using sand specimens with identical void ratios and height to diameter ratios but with different sizes, surface areas, and volumes. A semiempirical exponential relationship with respect to effective mean stress was used to model unit membrane penetration, and the results were compared with some other models proposed in the literature. A posttesting correction procedure was formulated to calculate pore-pressure accumulation in monotonic and cyclic tests, taking into consideration coupling between membrane compliance and pore-pressure accumulation. The procedure developed is based on membrane flexibility and soil compressibility expressed as semiempirical exponential relationships with respect to effective mean stress. The applicability of the model is shown based on undrained monotonic and cyclic tests and with respect to some methods proposed in the literature.

Widespread liquefaction occurred in Kobe, Japan, during the 1995 Hyogoken-Nanbu earthquake. At the reclaimed Port Island in Kobe, the observed large-scale liquefaction was documented by acceleration records from a downhole seismic array. Four accelerometers recorded the soil stratum response, from the ground surface down to a depth of 83 m. These recorded accelerations are used here to obtain direct estimates of the corresponding seismic shear stress and strain histories within the soil layers, which shed light on (1) the site seismic response during liquefaction and associated loss of soil stiffness at shallow depths near the ground surface; and (2) the virtually linear site response at deeper elevations. Response of the liquefied upper layer is characterized by cycles of large shear strain and very small shear stress. Conversely, the lower strata exhibited no sign of stiffness degradation throughout the earthquake. A computational simulation of this case history is performed in order to assess the mechanisms of site amplification and excess pore-pressure buildup. The results of this study demonstrate that acceleration histories recorded by downhole arrays represent a valuable direct source of information on site response during seismic excitation.

This paper is concerned with a mathematical description of the undrained response of partially saturated soils having a continuous liquid phase (water) and a gas in the form of discrete bubbles. Two types of soil structures are considered. First is the case in which the gas inclusions, of size much smaller than the average particle size, are entrapped in the water phase. Second is the case in which the comparatively larger gas bubbles are embedded in the saturated soil skeleton. The fluid phases are assumed to be separated by boundaries across which discontinuities in pressure exist due to surface tension. The soil is treated as a three-phase composite medium and the mechanical properties are described in terms of average stress/strain measures in all constituents. The mathematical formulation incorporates the average pore/bubble size as an independent material parameter governing the mechanical response.

Chloride diffusion coefficients of 5.7 × 10 ⁻¹⁰ m ² /s, 9.0 × 10 ⁻¹⁰ m ² /s, and 9.8 × 10 ⁻¹⁰ m ² /s were obtained from diffusion tests conducted on a single isolated layer of clayey silt, silt, or sand, respectively. The advective-diffusive movement of chloride through a two-layer soil system consisting of a compacted clayey silt underlain by either a fine sand or silt was also examined. The agreement between the experimental results and model predictions suggests that existing solute-transport theory can adequately predict chloride migration through a compacted clay layer and underlying sand or silt layer at near-saturated conditions for Darcy velocities at least up to the maximum value examined (0.0183 m/yr or 500 L/ha/d). Chloride transport was dominated by diffusion in these tests.

The use of the cone-penetration-test (CPT) resistance data as a field index for evaluating the liquefaction potential of sands is receiving increased attention because of the popularity of this in situ test method for the site characterization. This paper examines the feasibility of using neural networks to assess liquefaction potential from actual CPT field data. A back-propagation neural-network algorithm was used to model actual field-liquefaction records. The study indicated that neural networks can successfully model the complex relationship between seismic parameters, soil parameters, and the liquefaction potential. The neural-network model is simpler than and as reliable as the conventional method of evaluating liquefaction potential. No calibration or normalization of the cone resistance q _c is required, unlike with the conventional method. As additional field case records become available, these data can be readily included in the neural-network training and testing data for further improvements of modeling of liquefaction potential.

In an earlier paper, the writer derived theoretical equations for void ratio as a function of grain-size distribution. Here, the equations are used to find the grain-size distributions that give the smallest possible void ratio for highly densified, cohesionless soils and similar materials that have different ratios, x₁₀₀ /x₀, for their largest and smallest grain sizes. Both numerical and analytical methods are used. Depending on the value of x₁₀₀ /x₀, materials that consist of two or three grain-size fractions with grading gaps between them have the smallest void ratios. Within the fine and coarse fractions, the grain sizes need to be as uniform as possible. The required grading of the medium fraction depends on the characteristics of the fine and coarse fractions.