Effects of Soil-Structure Interaction on Stress Distribution within a Pile Group under Multi-Dimensional Loading

To investigate inertial and kinematic effects on stress distributions within a pile group, physical model tests were conducted at EDefense, one of the largest shaking table facilities in the world. A 3x3 steel pile group supporting a foundation with a superstructure was set in a dry sand deposit prepared in a cylindrical laminar box with a height of 6.5 m and a diameter of 8.0 m. Natural periods of superstructures were variable in the tests. The tests were conducted under one-, two- or three-dimensional shaking. The test results have shown that pile stresses were mainly controlled by the inertial force when the natural period of superstructure was shorter than or close to that of the ground. In this case, the pile group effects were remarkable, in which pile stresses were the largest in the leading pile and the smallest in the following pile. In contrast, the pile stresses were mainly controlled by the ground displacement when the natural period of superstructure was longer than that of the ground. In this case, the pile group effects were insignificant in such a way that the pile stresses were almost the same within the pile group

Estimation of Local Site Conditions in Kushiro City Based on Array Observation of Microtremors

Possible use of short-period microtremors is explored for estimating the effects of subsurface soil conditions on the ground motion characteristics. For this purpose, microtremor measurements are conducted using arrays of sensors at two strong motion stations (Kushiro Japan Meteorological Agency and Kushiro Harbor, Hokkaido, Japan), which are located nearby but on different soils. Based on the F-k spectrum analysis of microtremors, dispersion curves of Rayleigh waves for the sites are determined. The inverse analysis of these dispersion curves results in shear wave velocity profiles down to a depth of 300 m. With these profiles, the spectrum ratio of ground surface motions between the two sites is computed, and compared with that of the observed records. The computed and observed spectrum ratios show a fairly good agreement, indicating that the array observation of microtremors is an economical and yet reliable means of estimating local site conditions

Site Effects Estimated From Microtremor Measurements at Selected Strong Motion Stations in Taiwan

Microtremor measurements are conducted using arrays of sensors at six strong motion stations in Taiwan where the peak ground accelerations over 400 cm/s2 were recorded during the 1999 Chi-Chi earthquake. Shallow shear wave velocity profiles of these stations are estimated based on an inverse analysis of microtremor dispersion characteristics and H/V spectra. At Wufeng (TCU065) where building damage was the most extensive among others, a thick soft surface layer with a shear wave velocity less than or equal to about 200 m/s overlies a stiff layer with Vs greater than 400 m/s at a depth of about 30 m. At other stations, stiff layers with Vs greater than 300-400 m/s occur from the ground surface or at a depth less than 20 m. Linear and equivalent linear analyses are conducted using the estimated Vs profiles. The natural site periods computed from an equivalent linear analysis are generally consistent with the peak periods of the response acceleration spectra of the recorded strong motions, but they are considerably longer than those estimated from a linear analysis, regardless of the value of the shallow shear wave velocity. This suggests that local soil conditions including nonlinear soil behavior might have had significant effects on the ground surface motion and performance of buildings during the earthquake

Field Correlation of Soil Liquefaction with SPT and Grain Size

Two earthquakes of magnitudes 6.7 and 7.4 that occurred in 1978 off the Pacific coast of Miyagi Prefecture, Japan, provided field liquefaction data for a fairly wide range of peak ground surface acceleration from 100 to 290 gal. The range of SPT N-values was also fairly wide because special efforts were made to collect non-liquefaction data in addition to liquefaction data. Dynamic shear stress ratios adjusted for earthquake magnitudes and effective overburden pressures are plotted against N-values adjusted for effective overburden pressures. The field data are compared with two methods proposed recently, one by Seed and the other by Iwasaki et al, after a critical review of the methods and the SPT\u27s in the U.S. and Japan. The method by Seed tended to underestimate the resistance to liquefaction for small N-values, particularly for silty sands; whereas the method by Iwasaki et al tended to underestimate the resistance to liquefaction for large N-values

Measuring Weak Sustainability for the future: Calculating Genuine Saving with population change by an integrated assessment model

This paper presents a future figure of Genuine Saving with population growth (GSn). This was enabled by using an integrated assessment model, similar to the RICE model by Nordhaus. The model consists of sub-models that evaluate various kinds of mineral resources and environmental impacts. Results indicates that GSn is positive i) in OECD during the 21st century, ii) in World and the former Soviet Union and East Europe after 2030, and iii) in Asia and the Middle East and Africa after 2050. GSn is negative in Latin America during the 21st century.Genuine Saving, population change, sustainability, integrated assessment model, impact assessment model, growth model

Nonlinear Soil Properties Estimated from Strong Motion Accelerograms

A rational procedure is developed for estimating dynamic soil properties from strong motion accelerograms obtained only at the ground surface. The method consisting of spectrum analysis and multi-reflection analysis could permit evaluation of time histories of shear modulus versus shear strain in the soil during an earthquake. The method is applied to four sites where the soil profile is relatively simple and where several strong motion records are available. The analytical results show that (1) the first predominant period of surface soil increases with an increase in shear strain developed in the soil, (2) the strain-dependent shear moduli evaluated from strong motion records are in fairly good agreement with laboratory test results in a strain range from 10-5 to 10-3, and (3) the shear modulus ratio is better correlated with peak particle velocity at the ground surface than with peak acceleration

Liquefaction Potential Evaluation Based on Rayleigh Wave Investigation and Its Comparison with Field Behavior

A simplified method is presented for evaluating liquefaction potential of sand deposits using shear wave velocity. Effectiveness of the proposed method is evaluated through field tests at 17 sites in Niigata city where field performance during the 1964 Niigata earthquake is known. A modified version of steady state Rayleigh wave method is used in which the amplitude ratio between vertical and horizontal ground surface motions can be measured in addition to the phase velocity. Based on the measured phase velocity vs. wavelength relationship, shear wave velocity profile is determined using an inverse analysis. The liquefaction potential of each site is then evaluated using the shear wave velocity. The estimated results are reasonably consistent with the actual field behavior during the earthquake, indicating that the proposed method is effective

Soil liquefaction-induced uplift of underground structures: Physical and numerical modeling

Underground structures located in liquefiable soil deposits are susceptible to floatation following a major earthquake event. Such failure phenomenon generally occurs when the soil liquefies and loses its shear resistance against the uplift force from the buoyancy of the underground structure. Numerical modeling accompanied with centrifuge experiments with shallow circular structures has been carried out to investigate the floatation failure at different buried depths of the structure. The influence of the magnitude of input sinusoidal earthquake shaking was also studied. Both numerical and experimental results showed matching uplift response of the structures and acceleration and pore-pressure measurements in the liquefied soil deposit. A higher uplift displacement of the structure was observed for shallower buried depth, thereby indicating the influence of overlying soil weight against floatation. Results also showed that the structures commenced floatation in the presence of high excess pore pressure, but they ceased when the earthquake shaking stopped. The higher rate of uplift in stronger earthquake shaking further substantiates the dependency of the uplift to the shaking amplitude. A constant rate of uplift of the structure was attained after the soil liquefied, hence postulating a possible limit to shear modulus degradation of the surrounding soil caused by soil-structure interaction. This is inferred by the lower excess pore-pressure generation near the structure. The displacement of liquefied soil around the displaced structure was also confirmed to resemble a global circular flow mechanism from the crown of the structure to its invert as observed in displacement vector plots obtained from numerical analysis and particle image velocimetry (PIV) in centrifuge tests. Further numerical analysis on the performance of buried sewer pipelines in Urayasu City, Chiba Prefecture following the 2011 Great East Japan Earthquake indicated high damage susceptibility of rigid pipelines in the liquefiable soil deposit. These consistencies with field observations clearly demonstrate and pave the prospects of applying numerical and/or experimental analyses for geotechnical problems associated with the floatation of underground structures in liquefiable soils.The authors are grateful for the financial support from the Cambridge Trust at the University of Cambridge and the Japan Ministry of Education, Culture, Sports, Science and Technology via the International Urban Earthquake Engineering Center for Mitigating Seismic Mega Risk program at Tokyo Institute of TechnologyThis is the final published version. It first appeared at http://ascelibrary.org/doi/abs/10.1061/(ASCE)GT.1943-5606.0001159

Back-Calculated p-y Relation of Liquefied Soils from Large Shaking Table Tests

Time histories of the p-y behavior during soil liquefaction, defined as the relation between subgrade reaction and relative displacement between pile and soil, are back-calculated based on shaking table tests using a large-scale laminar box. The results show that, if the pile pushes the soil, the subgrade reaction is correlated with the relative displacement between pile and soil. In contrast, if the soil liquefies and pushes the pile, the subgrade reaction becomes correlated with the relative velocity between pile and soil. The p-y curve of loose sand shows stress-softening behavior after liquefaction, while the p-y curve of medium dense to dense sand shows stress hardening behavior. The stress-hardening behavior tends to diminish with cyclic loading after liquefaction if the sand is not sufficiently dense or the input acceleration is high. The coefficient of subgrade reaction is affected by such factors as the pore pressure ratio, relative displacement, and soil density

<Preliminary>A Role of Oxalic Acid in Acid Hydrolysis of Non-Phenolic β-O-4 Type Lignin Carbohydrate Complexes (LCC) Model Compounds

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