Two aspects of seismically-induced liquefaction are discussed which are of vital engineering significance: the triggering condition and the consequences of liquefaction. The triggering condition is examined with respect to liquefaction analysis, note being taken of the onset condition which is governed by cyclic strength. Consequences of liquefaction are discussed with respect to post-seismic stability analysis, in which the residual strength plays a major role. Procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced, and the applicability of this method for estimating associated ground settlements is discussed. The evaluation of residual strength requires a better understanding of undrained sand behaviour. Results of extensive laboratory rests on Japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better. The results of laboratory tests on silty sands are examined in the same way. AH the results are...

Liquefaction and flow failure during earthquakes.

A simplified procedure using shear-wave velocity measurements for evaluating the liquefaction resistance of soils is presented. The procedure was developed in cooperation with industry, researchers, and practitioners and evolved from workshops in 1996 and 1998. It follows the general format of the Seed-Idriss simplified procedure based on standard penetration test blow count and was developed using case history data from 26 earthquakes and >70 measurement sites in soils ranging from fine sand to sandy gravel with cobbles to profiles including silty clay layers. Liquefaction resistance curves were established by applying a modified relationship between the shear-wave velocity and cyclic stress ratio for the constant average cyclic shear strain suggested by R. Dobry. These curves correctly predicted moderate to high liquefaction potential for >95% of the liquefaction case histories and are shown to be consistent with the standard penetration test based curves in sandy soils. A case study is provided to illustrate application of the procedure. Additional data are needed, particularly from denser soil deposits shaken by stronger ground motions, to further validate the simplified procedure.

Liquefaction resistance of soils from shear-wave velocity

Predictive equations for estimating normalized shear modulus and material damping ratio of Quaternary, Tertiary and older, and residual/saprolite soils are presented in this paper. The equations are based on a modified hyperbolic model and a statistical analysis of existing Resonant Column and Torsional Shear test results for 122 specimens obtained from South Carolina, North Carolina, and Alabama. Variables used in the equations for normalized shear modulus are: shear-strain amplitude, confining stress, and plasticity index (PI). The equations for damping ratio are expressed in terms of a polynomial function of normalized shear modulus plus a minimum damping ratio. It is found that the Quaternary soils exhibit more linearity than soils of the other two groups. Also, it is found that the effect of PI on dynamic soil behavior is not as significant as previously thought. Data from all three groups exhibit significant variations with confining stress, similar to the variations determined by Stokoe et al. The uncertainties associated with the equations for PI of 0 and mean effective confining stress of 100 kPa are quantified using the point estimate method. A case study from Charleston, S.C. is provided to illustrate an application of the equations to seismic response analysis and the importance of considering confining stress and geologic age.

Normalized shear modulus and material damping ratio relationships

This paper presents a complete methodology for both probabilistic and deterministic assessment of seismic soil liquefaction triggering potential based on the cone penetration test (CPT). A comprehensive worldwide set of CPT-based liquefaction field case histories were compiled and back analyzed, and the data then used to develop probabilistic triggering correlations. Issues investigated in this study include improved normalization of CPT resistance measurements for the influence of effective overburden stress, and adjustment to CPT tip resistance for the potential influence of "thin" liquefiable layers. The effects of soil type and soil character (i.e., "fines" adjustment) for the new correlations are based on a combination of CPT tip and sleeve resistance. To quantify probability for performance-based engineering applications, Bayesian "regression" methods were used, and the uncertainties of all variables comprising both the seismic demand and the liquefaction resistance were estimated and included in the analysis. The resulting correlations were developed using a Bayesian framework and are presented in both probabilistic and deterministic formats. The results are compared to previous probabilistic and deterministic correlations.

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CPT-based probabilistic and deterministic assessment of in situ seismic soil liquefaction potential

A literature review of next-generation smart sensing technology in structural health monitoring

Two of the most important parameters in any dynamic analysis involving soils are the shear modulus and the damping ratio. Because both shear modulus and damping are strain dependent, curves must be developed to define their variation with shear strain. Fifteen studies (including this one) now provide results from tests on a wide variety of gravels. This paper combines the results of available investigations to develop best-fit relationships between (1) shear wave velocity and equivalent N60 from Becker penetration tests; (2) normalized shear modulus and shear strain; and (3) damping ratio and shear strain. The mean curve for the normalized shear modulus reported for gravelly soil in this study falls near the mean curve reported for sands by Seed and Idriss (1970). The normalized shear modulus curve is dependent on confining pressure, but essentially independent of sample disturbance, relative density, and gradation. The mean damping ratio curve falls toward the lower range of the data reported by Seed and...

Shear modulus and damping relationships for gravels

A static lateral load test was performed on a full-scale pile group to determine the resulting pile-soil-pile interaction effects. The 3 × 3 pile group at three-diameter spacing was driven into a profile consisting of soft to medium-stiff clays and silts underlain by sand. The piles were instrumented with inclinometers and strain gages. The load carried by each pile was measured. A single pile test was conducted for comparison. The pile group deflected over two times more than the single pile under the same average load. Group effects significantly reduced load capacity for all rows relative to single pile behavior. Trailing rows carried less than the leading row, and middle row piles carried the lowest loads. Maximum moments in the group piles were 50–100% higher than in the single pile. P-multipliers were 0.6, 0.38, and 0.43 for the front, middle, and back row piles, respectively. Good agreement between the measured and computed pile group responses was obtained using the p-multiplier approach. Design c...

Lateral Load Behavior of Full-Scale Pile Group in Clay

Current seismic design of bridges is based on a displacement performance philosophy using nonlinear static pushover analysis. This type of bridge design necessitates that the geotechnical engineer predict the resistance of the abutment backfill soils, which is inherently nonlinear with respect to the displacement between soil backfill and the bridge structure. This paper employs limit-equilibrium methods using mobilized logarithmic-spiral failure surfaces coupled with a modified hyperbolic soil stress-strain behavior (LSH model) to estimate abutment nonlinear force-displacement capacity as a function of wall displacement and soil backfill properties. The calculated force-displacement capacity is validated against the results from eight field experiments conducted on various typical structure backfills. Using LSH and experimental data, a simple hyperbolic force-displacement (HFD) equation is developed that can provide the same results using only the backfill soil stiffness and ultimate soil capacity. HFD is compatible with current CALTRANS practice in regard to the seismic design of bridge abutments. The LSH and HFD models are powerful and effective tools for practicing engineers to produce realistic bridge response for performance-based bridge design.

Nonlinear Soil-Abutment-Bridge Structure Interaction for Seismic Performance-Based Design

Closure of "Measured and Computed Lateral Response of a Pile Group in Sand"

Lateral load test was performed on a full-scale pile group following blast-induced liquefaction to evaluate pile–soil–pile interaction effects. The 3×3 pile group at 3.3 pile diameter spacing was driven into loose to medium dense sand. A single pile test was conducted for comparison. In contrast to preliquefaction tests, group interaction effects were insignificant after liquefaction. The lateral resistance of each pile in the group was similar and about the same as that for the single pile test. p–y curves were developed based on the bending moment versus depth data for Ru values of 95%. While the slope of p–y curves for nonliquefied sand typically decreases with continued deflection, the slope of the backcalculated p–y curves for liquefied sand increases with deflection. This phenomenon appears to be connected with load-induced dilation and a decrease in excess pore pressure locally around the pile. The p–y curves stiffened with depth and as the excess pore pressure ratio decreased. Equations were devel...

Kyle M. Rollins

Papers

Shear modulus and damping relationships for gravels

Lateral Load Behavior of Full-Scale Pile Group in Clay

Nonlinear Soil-Abutment-Bridge Structure Interaction for Seismic Performance-Based Design

Closure of "Measured and Computed Lateral Response of a Pile Group in Sand"

Lateral Resistance of a Full-Scale Pile Group in Liquefied Sand