Ronald D. Andrus

Updated Liquefaction Resistance Correction Factors for Aged Sands

Data from over 30 sites in 5 countries are analyzed to develop updated factors for correcting liquefaction resistance for aged sand deposits. Results of cyclic laboratory tests on relatively undisturbed and reconstituted specimens suggest an increase in the correction factors of 0.12 per log cycle of time and an average reference age of 2 days for the reconstitute specimens. Laboratory and field test results combined with cyclic resistance ratio (CRR) charts suggest an increase in the correction factors of 0.13 per log cycle of time and an average reference age of 23 years. A reference age of 23 years seems appropriate for the commonly used CRR charts derived from field liquefaction and no liquefaction case history data. Because age of natural deposits is often difficult to accurately determine, a relationship between measured to estimated shear-wave velocity ratio (MEVR) and liquefaction resistance correction factor is also derived directly from the compiled data. This new MEVR-liquefaction resistance correction factor relationship is not as sensitive to MEVR as in the relationship derived indirectly in a previous paper.

Correcting Liquefaction Resistance for Aged Sands Using Measured to Estimated Velocity Ratio

Factors for correcting liquefaction resistance for aged sands using ratios of measured to estimated shear-wave velocity (MEVR) are derived in this paper. Estimated values of shear-wave velocity ( VS ) are computed for 91 penetration resistance- VS data pairs using previously published relationships. Linear regression is performed on values of MEVR and corresponding average age. Age of the sand layer is taken as the time between VS measurements and initial deposition or last critical disturbance. It is found that MEVR increases by a factor of about 0.08 per log cycle of time, and time equals about 6 years on average when MEVR equals 1 for the recommended penetration resistance- VS relationships. The resulting regression equation is combined with the strength gain equation reported by Hayati et al. 2008 in “Proc., Geotechnical Earthquake Engineering and Soil Dynamics IV,” to produce a MEVR versus deposit resistance correction relationship. This new corrective relationship is applied to create liquefaction r...

Liquefaction-induced ground failure: a study of the Chi-Chi earthquake cases

Abstract The 1999 Chi-Chi, Taiwan earthquake caused great destruction to buildings, bridges, and other facilities, and a death toll of more than 2400. Lessons should be learned from this event, which, albeit disastrous, represents a rare full-scale experimentation in geotechnical engineering and related fields. Of particular interest to geotechnical engineers is the phenomenon of soil liquefaction that caused significant damage to buildings, lifelines and harbor facilities. These liquefaction phenomena, in the forms of sand boils, lateral spreads, tilting and settlement of buildings, and ground settlement, were observed in the Chi-Chi event. Shortly after the earthquake, an extensive field investigation in the Yuanlin area, including in situ tests and laboratory tests, was conducted by Moh and Associates and other parties. These in situ and laboratory tests along with ground performance observations form the basis for the present study. In this paper, 24 cases of ground performance in the areas that suffered the most from liquefaction are studied. The ground performance in selected cases of the 24 cases is accounted for through a series of liquefaction analyses. The analysis of the potential of liquefaction and ground failure is performed using Cone Penetration Test (CPT) data. The results of the analyses show that the field observations of ground performance in the Yuanlin area in the Chi-Chi event can be accounted for satisfactorily using the evaluation procedure by Ishihara (Ishihara, K., 1985. Stability of natural deposits during earthquakes. Proc., 11th Int. Conf. on Soil Mechanics and Foundation Engineering, San Francisco, CA, vol. 1, pp. 321–376.).

Shear-Wave Velocity and Seismic Response of Near-Surface Sediments in Charleston, South Carolina

Six major geologic units in Charleston, South Carolina, are characterized in terms of shear-wave velocity ( V S ) in this article. The characterization is based on in situ V S measurements at 91 sites. The six units are man-made fills, Holocene and late Pleistocene deposits, the Wando Formation, the Ten Mile Hill beds, the Penholoway Formation and the Daniel Island beds, and Tertiary deposits. Median V S values for these units in the top 25 m are 145, 111, 189, 176, 285, and 399 m/ sec, respectively. For Tertiary deposits in the depth intervals of 25–55 m, 55–75 m, and 75–100 m, median V S values are 435, 533, and 663 m/sec, respectively. A seismic-response parametric study is conducted assuming several soil/rock models and two input rock outcrop motions with peak accelerations of 0.3 g and 0.1 g . It is found that Quaternary sections with V S of 190 m/sec (e.g., the Wando Formation) and thicknesses of about 7 m to 15 m exhibit predominant peaks in the acceleration- response spectra at periods of about 0.25 to 0.4 sec. These predominant peaks match fundamental periods of many existing buildings in the old city district of Charleston. The results suggest that local site conditions contributed to building damage in the 1886 Charleston earthquake.

Liquefaction Potential Assessment of Pleistocene Beach Sands near Charleston, South Carolina

Abstract:Liquefaction potential of four Pleistocene beach sand deposits in the Greater Charleston area, South Carolina, is assessed. The assessment is based on a review of 51 sites of conspicuous craterlets and horizontal ground displacement that occurred in beach sand deposits during the 1886 Charleston earthquake and an analysis of 82 seismic cone penetration tests with pore-pressure measurements. Of the 51 ground failure sites, 23 are associated with the Ten Mile Hill beds; 13 with the Wando Formation; 13 with the Silver Bluff terrace and younger deposits that lie adjacent to the harbor, rivers, and creeks; and two with the Ladson Formation. Liquefaction potential is analyzed using the seismic cone data with and without correction for age-related processes (diagenesis) and then expressed in terms of the liquefaction potential index (LPI). Probability curves are developed from the LPI calculations for different earthquake ground-shaking parameters. The probability curves for the Wando Formation overpred...

Characterizing the Liquefaction Resistance of Aged Soils

The occurrence of liquefaction in soils is often evaluated using the simplified procedure originally proposed by Seed and Idriss based on in situ indices. Although numerous studies have been conducted to improve and extend this procedure, the effect of age on liquefaction resistance is still poorly understood and correction factors have not been generally accepted. Nine published studies on the effect of age are reviewed in this paper. A regression line representing the average variation in liquefaction strength grain with time was developed from cases where strength was expressed based on recommended liquefaction resistance curves. This regression line is considered an update of the previously proposed relationship by Arango et al. The results indicate that commonly used liquefaction evaluation procedures can be overly conservative in many natural soil deposits.

Seismic Site Factors and Design Response Spectra Based on Conditions in Charleston, South Carolina

Seismic site factors based on conditions typical of Charleston, South Carolina, are derived from the results of more than 13,000 one-dimensional equivalent linear and nonlinear dynamic response simulations. The site factors are plotted versus average shear wave velocity in the top 30 m (VS30) of soil and grouped by spectral acceleration and period. Median relationships for the site factors are expressed by a linear model for lower values of VS30 and a linear or exponential model for higher values. The computed factors are found to be somewhat different from the factors recommended in design codes. It is also found that amplifications greater than predicted by the common (or three-point) acceleration design response spectrum method can occur at periods greater than 1.0 s, particularly when VS30 < 200 m/s. Thus, when VS30 < 200 m/s, it is recommended that a multipoint response spectrum be constructed and compared with the three-point spectrum.

Dynamic Periods and Building Damage at Charleston, South Carolina During the 1886 Earthquake

Fundamental dynamic periods of Quaternary deposits beneath the peninsula of Charleston, South Carolina, are characterized spatially using an updated isopach map of Quaternary thickness, characteristic small-strain shear wave velocity information, a 1:24,000 geologic map, and a simple approximating equation. The updated isopach map is developed from subsurface information from 266 investigation sites. Estimates of fundamental periods for the Quaternary sediments primarily range between 0.3 and 0.7 s. These periods are lower end estimates of actual ground periods, based on a comparison with modeled response-spectra ratios. Estimates of fundamental periods range from 0.1 to 0.4 s for over 95% of the buildings present in 1886. Thus, the overlap between the range of building periods and the range in periods corresponding to high spectral ratios is not great. This finding agrees with the observation of Marciano and Elton that damage was independent (or only slightly dependent) of building height.

Liquefaction Susceptibility of Fine-Grained Soils in Charleston, South Carolina Based on CPT

The liquefaction susceptibility of four fine-grained soils in Charleston, South Carolina was examined primarily using cone penetration test (CPT) measurements. Ages of these four soils range from <6,000 years to about 30 million years. The liquefaction susceptibility criteria by Robertson and Wride appear to be adequate for the three younger soils, which are estuarine deposits. However, as noted previously by Li et al., the criteria incorrectly predict liquefaction susceptibility for the oldest soil, called the Cooper Marl. The Cooper Marl is a deep marine deposit that consists of 60-80% calcium carbonate and often classifies as MH to CH, based on the Unified Soil Classification System. The results illustrate the usefulness of also measuring pore water pressure during cone testing in fine-grained soils, for classification and liquefaction evaluation. A new CPT-based liquefaction susceptibility chart for screening out non-susceptible fine-grained soils is proposed.

Ground Freezing and Sampling of Pleistocene Sand near Charleston, South Carolina

AbstractThe procedures used to freeze and sample a Pleistocene sand deposit near Charleston, South Carolina to preserve and study the effects of diagenesis are presented in this paper. Based on the results of geotechnical tests and a feasibility ground freezing study, a freezing system with a central freeze pipe was installed to target a column of clean sand 1 m in radius and 2.3 m in length. Liquid nitrogen was continuously supplied to the freeze pipe fabricated to freeze the sand between depths of 1.8 and 3.8 m below the ground surface for 270 h. Frozen sand cores taken from five locations 0.65 to 0.7 m away from the central freeze pipe indicate the ground was frozen between depths of 1.8 and 3.8 m at all but one location. Ground temperature measurements, growth of the frozen zone, and the amount of liquid nitrogen consumed are presented and compared with predicted values. Recorded temperatures indicate that the freezing was influenced by the direction of groundwater flow, the flow rate of liquid nitrog...