Seismic Site Response for Near-Fault Forward Directivity Ground Motions

Forward directivity effects in the near-fault region produce pulse-type motions that differ significantly from ordinary ground motions that occur at greater distances from the causative fault. Current code site factors are based on empirical observations and analyses involving less intense nonpulse ordinary ground motions. Nonlinear site response analyses with bidirectional shaking are performed using representative site profiles to quantify seismic site response effects for intense near-fault motions resulting from forward directivity. Input rock motions are represented with simplified velocity pulses that characterize the amplitude and period of forward directivity motions. Results indicate that site response affects both the amplitude and period of forward directivity pulses, and hence, local site conditions should be considered when evaluating seismic designs in the near-fault region. Stiff soil sites tend to amplify the peak ground velocity and increase the period of pulse-type motions, particularly, when the period of the rock motion coincides with the degraded period of the site. Amplification is limited at soft soil sites by the dynamic strength of the weak soil, so attenuation occurs for intense input motions. This nonlinearity is not reflected in the site factors in current building codes. Guidance is provided for estimating the amplitude and pulse period for velocity pulses at soil sites.     

Small-Strain Behavior of Granular Soils. II: Seismic Response Analyses and Model Evaluation

Using the recorded response at two vertical array sites, the SimSoil model presented in the companion paper is evaluated. The SimSoil model, which describes the small strain nonlinear behavior of granular materials, is implemented as a material model in AMPLE2000, a nonlinear, one-dimensional site response analysis code. Shear wave velocity profiles and laboratory test data available for both the La Cienega site, which was instrumented over 250?m, and the Lotung site, which was instrumented over 47?m, were used to determine SimSoil model parameters. Predictions from AMPLE2000 are compared with the measured response at several elevations for earthquakes that resulted in both nonlinear and nearly linear soil behavior. Using the available laboratory data and known input motions, the predictions of the response at these sites matched the recorded response well for varied magnitudes of shaking with a single set of parameters for each site.     

车辆载荷作用下路基土的变形特性

通过路基土在重复荷载作用下的室内实验，研究了路基土回弹变形和累积变形随荷载轴次增长的发展规律以及各种因素对累积变形的影响。所有试验均在MTS试验系统上完成。相关研究及分析成果是发展路面力学设计方法所必备的依据之一。     

土壤的石油污染研究进展

当今土壤的石油污染是一种较为普遍的现象。土壤石油污染的治理是学术界研究的热点领域，从石油污染的微生物降解。在土壤中的吸附，解吸与迁移。对作物的影响及生物修复方面介绍了国内外的有关研究现状及其发展趋势。     

确定土壤刚度的机械阻抗方法

运用机械阻抗(Mechanical impedance)方法,结合不同土壤的机械模型(Mechanical model),给出了表示特定土壤一维刚度的数学表达式.     

Experimental Evaluation of Engineering Behavior of Soft Bangkok Clay under Elevated Temperature

This paper presents the results of a systematic well designed experimental investigation carried out to study the engineering properties of the soft Bangkok clay heated up to 90°C from room temperature (25°C). Details of modified oedometer and triaxial test apparatus that can handle temperatures up to 100°C are also presented. In the range of temperatures investigated, soft Bangkok clay exhibited temperature induced volume changes that depend mainly on the stress history, reduction in the conventional elastic zone, stiffening, and increased hydraulic permeability with increasing temperature as well as apparent overconsolidation state after subjecting the normally consolidated specimen to heating/cooling cycle. The results of this study provide additional data that can enhance the understanding of the thermohydromechanical behavior concepts of saturated clays.     

Time-dependent behavior of fine-grained model material in resonant column experiments

Cyclic shear experiments with saturated and dry fine-grained corundum powder, i.e. -Al₂O₃ particles, have been conducted in a resonant column device. After an increase of total pressure the shear stiffness showed a slight decrease and a subsequent increase with time. The equivalent viscous damping ratio followed an opposite trend. The increase of shear stiffness with time did not stop after the end of primary consolidation, which cannot be explained with the slight reduction of void ratio during secondary consolidation. Stiffening of grain contacts through different dissolution-precipitation mechanisms and creep at particle contacts can explain the increase of shear stiffness with time, which has also been observed in natural soils by other researchers. Smaller rates of stiffness increase of dry samples support the idea of dissolution-precipitation mechanisms in the pore water. Higher rates for samples with smaller particles show an effect of surface-to-volume ratio.The study described in this paper was sponsored by the German Research Council (DFG), Research Group FOR 371-2. The support is gratefully appreciated.We would like to thank Professor Gudehus for many interesting discussions and valuable advice.We thank the Institute of Mechanical Process Engineering and Mechanics and the Laboratory for Electron Microscopy, University of Karlsruhe, for providing the electron micrographs and the Institute for Ceramics in Mechanical Engineering for the grain size distribution.     

Nitrogen adsorption method for determining the mesopore slit-like size distribution of expansive soils

One of the most important structural parameters involved in the characterization of the void space of soils is the pore size distribution. In this work, a nitrogen adsorption method is presented as an alternative to determine the mesopore contribution of slit-shaped pores to the abovementioned parameter in montmorillonite-containing soils. The mesopore size structural parameter obtained via this sorption method is related to montmorillonite d₀₀₁ interlayer distances proceeding from either X-ray or electron diffraction analysis, if only by assuming during sorption analysis that mesopores resident inside clay grains adopt slit-shaped geometries. Mineralogical analysis and determination of some important geotechnical properties of these montmorillonite-containing soils complement the preceding sorption and structural studies.     

Inclusion of Some Aspects of Chemical Behavior of Unsaturated Soil in Thermo/Hydro/Chemical/Mechanical Models. II: Application and Transport of Soluble Salts in Compacted Bentonite

This paper presents an application of a coupled thermo/hydro/chemical/mechanical model via simulation of a laboratory experiment in order to investigate the transport behavior of ions in bentonite pore water. Chemical reactions considered include ion exchange reactions involving major cations (Na+, K+, Mg2+, and Ca2+) and precipitation-dissolution of trace minerals (calcite, dolomite, anhydrite, and halite). The following conclusions are drawn based on the numerical results. The development of both the temperature and moisture fields was captured by simulation, and a good correlation with the experimental water uptake results was observed. For all ions, the model showed a good qualitative and reasonable quantitative agreement with the experimental results.     

Postfailure Mechanics of Landslides: Laboratory Investigation of Flowslides in Pyroclastic Soils

Of all landslides, subaerial flowslides are the most dangerous. According to the literature, flowslides in saturated granular deposits are caused by static liquefaction induced by loss of stability. However, the catastrophic flowslides that occurred on steep slopes in Campania (southern Italy) in 1998, 1999, and 2005 were triggered by rainwater infiltration into shallow deposits of pyroclastic soils, which were initially unsaturated. Starting from the experience collected during the investigations of some of these landslides, the writers consider flowslide evolution as a result of a mechanical chain process characterized by saturation increase due to rainwater infiltration, mechanical degradation, volumetric collapse, and static liquefaction, culminating in complete fluidization of the soil. In the paper this chain process is investigated through wetting tests both in suction controlled triaxial apparatuses and in a well-equipped small scale slope model.