Threshold Shear Strain for Cyclic Pore-Water Pressure in Cohesive Soils

Threshold shear strain for cyclic pore-water pressure, γt, is a fundamental property of fully saturated soils subjected to undrained cyclic loading. At cyclic shear strain amplitude, γc, larger than γt residual cyclic pore-water pressure changes rapidly with the number of cycles, N, while at γc<γt such changes are negligible even at large N. To augment limited experimental data base of γt in cohesive soils, five values of γt for two elastic silts and a clay were determined in five special cyclic Norwegian Geotechnical Institute (NGI)-type direct simple shear (NGI-DSS), constant volume equivalent undrained tests. Threshold γt was also tested on one sand, with the results comparing favorably to published data. The test results confirm that γt in cohesive soils is larger than in cohesionless soils and that it generally increases with the soil’s plasticity index (PI). For the silts and clay having PI=14–30, γt = 0.024–0.06% was obtained. Limited data suggest that γt in plastic silts and clays practically does not depend on the confining stress. The concept of evaluating pore water pressures from the NGI-DSS constant volume test and related state of stresses are discussed.     

Index Properties-Based Criteria for Liquefaction Susceptibility of Clayey Soils: A Critical Assessment

The Cooper marl in Charleston, S.C., a deep layer of clayey soils approximately 5–21?m below the ground surface, is generally recognized as nonliquefiable material. Data from field cone penetration tests and laboratory tests of samples taken from the Cooper marl are used to investigate the adequacy of index properties-based criteria for assessing liquefaction susceptibility of clayey soils. In particular, the criterion based on soil behavior type index (Ic) and that based on Atterberg limits are examined. The results show that the Atterberg limits-based criterion adequately reflected the characteristics of the marl, whereas the Ic-based criterion erroneously identified the marl as being liquefiable. A possible reason for the deficiency of Ic and a modification to overcome this deficiency are presented.     

Evaluation of a Predictive Constitutive Model for Sands

In this technical note, an evaluation of the robustness and predictive ability of a constitutive model for sands is performed. The model is shown to capture the main features of sand behavior under both drained and undrained monotonic loadings for a wide range of relative densities and stress paths. The main contribution of this technical note is to evaluate a robust, yet simple, constitutive framework based on a solid theoretical basis that fulfils the most fundamental requirement of any useful constitutive law: accurate predictions.     

Multiple-Porosity Model for the Transport of Reactive Contaminants in Fissured Soils with Nonequilibrium Partitioning

A multiple-porosity model for the transport of reactive contaminants in fissured media with multiple-source, nonequilibrium partitioning is proposed, widening the scope of existing models. The proposed model extends the bicontinuum, dual-porosity concepts by combining five contaminant compartments: (1) mobile water in the fissures; (2) immobile water in the fissures; (3) water diffusing into the soil matrix; (4) sorption in the fissures; and (5) sorption in the soil matrix. Both instantaneous and nonequilibrium sorption are represented in the fissures. Mobile/immobile compartments, fissured soils, and nonequilibrium sorption have been hitherto treated separately or in pairs. Exchange of contaminants occurs between all compartments. Equations for the model are formulated and transformed into the Laplace domain. Solutions for the one-dimensional problem of a leaking storage tank overlying a fissured soil are found. The effects of the inclusion of various contaminant compartments and exchange parameters are analyzed through numerical experiments.     

How Reliable is the Plasticity Index for Estimating the Liquefaction Potential of Clayey Sands?

This paper examines the validity of the plasticity index (PI) as a criterion for estimating the liquefaction potential of clayey soils under cyclic loading. The results of undrained cyclic stress-controlled ring-shear tests on artificial mixtures of sand with different clays saturated with water indicated that an increase in PI decreased the soil potential to liquefy, and soil with PI>15 seemed to be nonliquefiable, a finding that is in agreement with the results of other researchers. However, in this study some deviations from this relation were found when a bentonite–sand mixture was treated with solutions of different ions, thus bringing into question the effectiveness of PI as a measure of the liquefaction potential of clayey soil having a certain pore water chemistry.     

Application of Natural Clayey Soil as Adsorbent for the Removal of Copper from Wastewater

Use of clayey soil has been explored in the laboratory scale experiment as a low cost adsorbent for the removal of copper from wastewater. The influence of metal ion concentration, weight of adsorbent, stirring rates, influence of temperature, pH are also evaluated and the results are fitted using adsorption isotherm models. From the experimental results it is observed that almost 90–99% copper can be removed from the solution using clay at optimized pH 5.5. Langmuir adsorption isotherm, Freundlich isotherm and Tempkin isotherm model have been used to describe the distribution of copper between the liquid and solid phases in batch studies and it has been observed that Langmuir isotherm better represents the phenomenon. From the experimental results rate constant, activation energy, Gibbs free energy, enthalpy, and entropy of the reaction are calculated to determine the mechanism of the sorption process. Thomas, Adams-Bohart, and Yoon-Nelson models are applied to the experimental data to determine the characteristic parameters of the column for process design.     

Relationship between the Undrained Shear Strength, Water Content, and Mineralogical Properties of Fine-Grained Soils

The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soils; these relationships, however, have not yet been investigated. The findings described in this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals, their quantity in soil composition, and the interlayer water quantity in the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.     

Probabilistic Model for the Assessment of Cyclically Induced Reconsolidation (Volumetric) Settlements

A maximum likelihood framework for the probabilistic assessment of cyclically induced reconsolidation settlements of saturated cohesionless soil sites is described. For this purpose, over 200 case history sites were carefully studied. After screening for data quality and completeness, the resulting database is composed of 49 high-quality, cyclically induced ground settlement case histories from seven different earthquakes. For these case history sites, settlement predictions by currently available methods of Tokimatsu and Seed (1984), Ishihara and Yoshimine (1992), Shamoto et al. (1998), and Wu and Seed (2004) are presented comparatively, along with the predictions of the proposed probabilistic model. As an integral part of the proposed model, the volumetric strain correlation presented in the companion paper is used. The accuracy of the mean predictions as well as their uncertainty is assessed by both linear regression and maximum likelihood methodologies. The analyses results revealed that (1) the predictions of Shamoto et al. and Tokimatsu and Seed are smaller than the actual settlements and need to be calibrated by a factor of 1.93 and 1.45, respectively; and (2) Ishihara and Yoshimine, and Wu and Seed predictions are higher than the actual settlements and need to be calibrated by a factor of 0.90 and 0.98, respectively. The Wu and Seed procedure produced the most unbiased estimates of mean settlements [i.e., their calibration coefficient (0.98) is the closest to unity], but the uncertainty (scatter) of their predictions remains high as revealed by the second to last smaller R2 value, or relatively higher standard deviation (σε) of the model error. In addition to superior model predictions, the main advantage of the proposed methodology is the probabilistic nature of the calibration scheme, which enables incorporation of the model uncertainty into mean settlement predictions. To illustrate the potential use of the proposed model, the probability of cyclically induced reconsolidation settlement of a site after a scenario earthquake to be less than a threshold settlement level is assessed.     

Centrifuge Permeameter for Unsaturated Soils. II: Measurement of the Hydraulic Characteristics of an Unsaturated Clay

This paper presents the hydraulic characteristics of an unsaturated, compacted clay, including its soil-water retention curve (SWRC) and hydraulic conductivity function (K function), determined using a new centrifuge permeameter developed at the University of Texas at Austin. A companion paper describes the apparatus, its instrumentation layout, and data reduction procedures. Three approaches are evaluated in this study to define the SWRC and K function of the compacted clay under both drying and wetting paths, by varying the inflow rate, the g level, or both. For imposed inflow rates ranging from 20 to 0.1 mL/h and g levels ranging from 10 to 100 g, the measured matric suction ranged from 5 to 70 kPa, the average volumetric water content ranged from 23 to 33%, and the hydraulic conductivity ranged from 2×10?7 to 8×10?11?m/s. The SWRCs and K functions obtained using the three different testing approaches were very consistent, and yielded suitable information for direct determination of the hydraulic characteristics. The approaches differed in the time required to complete a testing stage and in the range of measured hydraulic conductivity values. The g level had a negligible effect on the measured hydraulic characteristics of the compacted clay. The SWRCs and K functions defined using the centrifuge permeameter are consistent with those obtained using pressure chamber and column infiltration tests. The K functions defined using the centrifuge permeameter follow the same shape as those obtained from predictive relationships, although the measured and predicted K functions differ by two orders of magnitude at the lower end of the volumetric water content range.     

Contractor Performance Prediction Model for the United Kingdom Construction Contractor: Study of Logistic Regression Approach

An accurate prediction of contractor potential is of vital importance during contractor selection and evaluation process. Such prediction enables identification and classification of contractor performance to ease the selection process. This paper outlines the use of clients' tender evaluation preferences for predicting a contractor performance via a logistic regression (LR) approach. A total of 31 clients’ tender evaluation criteria were selected to develop a LR model for predicting contractor performance. The proposed model was developed based on 48 of United Kingdom public and private construction projects and validated in 20 independent cases. It was found that 75% of the cases correctly and the model statistically accurate for contractor performance prediction, where the input variables consist of nominal and interval data. The paper summarized techniques and advantages of LR analysis and discussed literature findings of contractor selection and evaluation methodologies undertaken by construction researchers and commentators from the United Kingdom and Northern America.     

Effective Void Ratio for Assessing the Mechanical Properties of Cement-Clay Admixtures at High Water Content

Portland cement is widely used for the improvement of soft clay in many applications and construction methods. Because of the high initial water content of in situ soft clay, the additional water in the cement slurry to be mixed, and the added air in some applications, the mixtures have a high water content and void ratio in either almost-saturated or unsaturated conditions. The mechanical properties of cement-clay admixtures—including cement-treated clay and air-cement-treated clay—are affected by several parameters, e.g., mixing proportions, curing time, and the initial state of the mixture. To facilitate engineering decisions regarding mixing design and the development of a constitutive model, a single parameter that can characterize the mechanical properties of such mixed materials is advantageous. This paper recommends a parameter defined as the effective void ratio that could appropriately quantify the dependency of the mechanical properties of cement-clay admixtures on the influencing parameters on the basis of the results of unconfined compression, oedometer, and triaxial tests. The proposed parameter tends to capture the mechanical characteristics of cement-clay admixtures under different test conditions.     

连铸板坯二冷配水换型研究

根据板坯连铸机的特点,建立了不锈钢板坯凝固传热数学模型;分析了工艺参数对结晶器和二冷区铸坯凝固的影响;确立了不锈钢二冷区最佳冷却冶金准则。经过大量计算,总结出二冷水量的计算公式和操作工艺参数图。由本模型计算的二冷各段水量与奥钢联提供的水表值基本接近。     

Mass Conservative Transport Scheme for the Application of the ELCIRC Model to Water Quality Computation

An attempt was made to couple the water quality model of Danshuei River to the three-dimensional unstructured-grid hydrodynamic model [Eulerian–Lagrangian circulation model (ELCIRC)]. The Eulerian–Lagrangian scheme for the solution of the transport equations of salt in ELCIRC was demonstrated to be not mass conservative. The scheme was replaced with a finite-volume/finite-difference upwind scheme to ensure mass conservation both locally and globally. The same scheme was also used for the scalar transport equation in the water quality model. The representation of mass flux in the scalar transport equation is carefully formulated to be consistent with that of volume flux used in the continuity equations of ELCIRC. It was demonstrated that the newly revised scheme (1) conserved mass locally and globally; (2) conserved mass for both conservative and nonconservative substances subjected to biogeochemical transformation; and (3) preserved the integrity of the wetting-and-drying scheme. Further, the baroclinic simulation using the newly revised scheme showed a better result in terms of salt intrusion and salinity distribution in the Danshuei River estuary.     

Model for the Simulation of Water Flows in Irrigation Districts. I: Description

Significant improvements in the profitability and sustainability of irrigated areas can be obtained by the application of new technologies. In this work, a model for the simulation of water flows in irrigation districts is presented. The model is based on the combination of a number of modules specialized on surface irrigation, open channel distribution networks, crop growth modeling, irrigation decision making, and hydrosaline balances. These modules are executed in parallel, and are connected by a series of variables. The surface irrigation module is based on a numerical hydrodynamic routine solving the Saint Venant equations, including the heterogeneity of soil physical properties. The simulation of water conveyance is performed on the basis of the capacity of the elements of the conveyance network. Crop growth is simulated using a scheme derived from the well-known model CropWat. The irrigation decision making module satisfies water orders considering water stress, yield sensitivity to stress, multiple water sources, and the network capacity. Finally, the hydrosaline module is based on a steady state approach, and provides estimations of the volume and salinity of the irrigation return flows for the whole irrigation season. The application of the model to district irrigation management and modernization studies may be limited by the volume of data required. In a companion paper, the model is calibrated, validated, and applied to a real irrigation district.     

Model for the Simulation of Water Flows in Irrigation Districts. II: Application

In a companion paper a model for the simulation of water flows in irrigation districts was formulated. The model combines a series of modules specialized in surface irrigation, open channel distribution networks, crop growth modeling, irrigation decision making, and hydrosaline balance. The objective of this paper is to calibrate, validate, and apply the model, using the Irrigation District Five of Bardenas (Spain) as a study area. Two years of study were used for the analysis, which could be classified as normal (2000) and dry (2001) from the point of view of crop water requirements. Model calibration was performed in one of the 11 hydrological sectors in which the district is divided. The control variable was the monthly water demand, while the calibration variables were related to irrigation operation and scheduling. The seasonal differences in observed and simulated water demand amounted to 0.9 and 1.9% for 2000 and 2001, respectively. Model validation was performed in the rest of the sectors, and the regression line of observed versus simulated monthly water demand could not be distinguished from a 1:1 line in both years. Model application explored scenarios based on management improvement (controlling the irrigation time) and structural improvement (increasing drainage water reuse for irrigation). These scenarios permitted one to sharply reduce water demand, halve the irrigation return flows, and reduce the daily irrigation period from 24?to?16?h.     

基于分段线性化模型的冷连轧机PID解耦控制

针对冷连轧机采用基于工作点的线性化模型进行动态规格变换控制时系统误差和张力波动较大的问题,提出了一种基于递推分段线性化模型的PID解耦控制方案。通过对五机架冷连轧机进行动态规格变换仿真表明,该方案可保证系统的控制精度,满足动态规格变换的控制要求。     

Genetic Algorithm Solution of a Gray Nonlinear Water Environment Management Model Developed for the Liming River in Daqing, China

This paper presents the genetic algorithm (GA) solution of a gray nonlinear water environment management model we developed for the Liming River basin in Daqing, China to improve the water environment management. The model has been developed by both optimizing the operation of wastewater treatment plants and making full use of assimilative capacity of the river so that the optimum integration of these two measures can keep the water quality in the Liming River basin up to a satisfactory standard at a reasonable cost. It can be used as an example to illustrate the potential application of a GA-based gray nonlinear programming in the field of water environment management.