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The significance of studying soil behaviour in a constant shear stress path to understand rain-induced slope failures and debris flows has long been recognized. Studies with constant shear tests have, however, been limited, and some past results from undisturbed soils appear to show stress path--dependent volume change behaviour. The present study systematically investigates the behaviour of recompacted residual soils in a constant shear stress path using a comprehensive experimental program. It is shown that the results of this test program and previously published data can be interpreted using the concepts of critic a I-state soil mechanics. Key words: constant shear, laboratory test, rain-induced failure, stress path, recompacted soil, pore pressure. Il est reconnu depuis longtemps que l'etude du comportement du sol suivant un cheminement des contraintes de cisaillement constant est importante lors de ruptures de pentes causees par la pluie ainsi que lors d'ecoulements de debris. Les etudes ayant utilise des essais de cisaillement constants sont limites, et certains resultats provenant d'essais anterieurs sur des sols non remanies semblent demontrer que les variations de volume sont dependantes du cheminement des contraintes. La presente etude evalue systematiquement le comportement de sols residuels recompactes suivant un cheminement des contraintes de cisaillement constant a l'aide d'un programme experimental complet. L'etude a demontre que les resultats du programme d'essais el les resultats deja publics peuvent etre interprets en utilisant les concepts de la mecanique des sols a l'etat critique. Mots-cles : cisaillement constant, essai en laboratoire. rupture causee par la pluie, cheminement des contraintes, sol recompacte, press ion interstitielle. [Traduit par la Redaction], Introduction Most slope failures are attributable to an increase in pore pressures following periods of intense rainfall. Rain-induced slope failures in steep natural terrains occur at shallow depths and frequently [...]

Soil nailing is commonly used for stabilizing cut slopes and retaining structures. The technique is, however, seldom used in stabilizing old loose fill slopes that were not constructed to the current standards. There is a concern that soil-nailed loose fill slopes may not render safety during heavy rainstorms. Little work has been carried out to investigate the behavior of soil-nailed loose fill slopes. This paper presents a comprehensive field test on a loose fill slope that was constructed by end tipping without any compaction--in the same way old fill slopes were formed. The slope was 4.75 m high, 9 m wide, and 33 deg to the horizontal. Two rows of five grouted nails were installed at a grid of 1.5 m X 1.5 m at an inclination of 20 deg from the horizontal. A surface grillage was used to connect the six nails in the middle of the grid. Performance of the nailed slope was monitored with various instruments for about six months until the slope was tested to fail by surcharging and wetting. The overall results show that soil nailing with a surface grillage is a potentially effective way to enhance the stability of old fill slopes. DOI: 10.1061/(ASCE)1090-0241(2008)134:3(277) CE Database subject headings: Field tests; Slope stability; Fills; Rainfall.

Abstract: Landslide 1 is located on the right bank of the downstream side of the dam for Hongjiadu Hydropower Station in Guizhou Province, China. In view of its close proximity [...]

Results of field monitoring of moisture content and matric suction at the crest and berm of a large cut slope in completely decomposed granite in Hong Kong are reported. Field moisture content and matric suction clearly show that the volumetric water content increases as a result of rainfall infiltration and decreases as a result of evaporation. Correspondingly, the matric suction decreases due to rainfall infiltration and increases due to evaporation. Soil--water characteristic curves at different depths at the crest and near the term of the cut slope are determined from the field data. Unlike soil--water characteristic curves determined in the laboratory by testing small specimens, the field measured soil--water characteristic curves show negligible hysteresis. Engineering implications of the field soil--water characteristic curves are discussed. DOI: 10.1061/(ASCE)1090-0241(2005)131:9(1176) CE Database subject headings: Monitoring; Field investigations: Soil water; Moisture content; Hysteresis.

The traditional approach for assessing the stability of slopes is using limit equilibrium methods. Recently, many efforts have been made to utilize limit analysis methods based on the upper bound and lower bound limit theorems in plasticity. In this paper, an upper bound limit analysis method using rigid finite elements is presented. Rigid finite elements are used to discretize the slope media. Kinematically admissible velocity discontinuities are permitted to occur at all interelement boundaries. The traditional definition of factor of safety is adopted in the present method so that the results from the limit analysis can be directly compared with those from methods of slices. The presence of water can be considered through work terms in the energy--work balance equation. To do this effectively, the pore water pressure is considered as an external force, similar to gravity and surface tractions. The proposed method formulates the slope stability problem as a nonlinear optimization problem with constraints based on the yield criterion, flow rule, boundary conditions, and the energy--work balance equation. The optimization problem is solved by a sequential quadratic algorithm. Two numerical examples are presented to illustrate the validation and potential applications of the present method. DOI: 10.1061/(ASCE)0733-9399(2004) 130:8(886) CE Database subject headings: Slope stability; Pore water pressure; Limit analysis; Nonlinear programming; Finite element method.

A numerical study has been performed of the air/fuel preparation process in a cold-starting port-injected spark-ignition engine. The latest models were implemented for spray impingement and multicomponent vaporization of the droplet and wall film accounting for finite diffusion in the liquid. The infinite diffusion model was found insufficient for predicting vaporization in this engine, and the single-component fuel representation yields results significantly different from those from the multicomponent one. The operating parameters studied included injection timing, swirl, speed, target path, enrichment, and fuel accumulation. In-cylinder measurements were compared and good agreement was achieved. Detailed quantitative analysis of the air/fuel preparation of the engine was reported. [DOI: 10.1115/1.1760524]

Slope failures in fill slopes formed by loosely compacted, completely decomposed granite in Hong Kong occur commonly during intense tropical rainstorms. The stress path greatly influences the shear strength of the soil mass, and is therefore crucial to the identification of slope-failure mechanisms. The soil mass in this case is largely unsaturated. In situ hydrologic response to rainstorms indicates that soil suction is reduced by rainfall infiltration, which often becomes the triggering factor in initiating slope instability. The constant dead-load tests on unsaturated, loosely compacted, completely decomposed granite appropriately simulate the field stress path of rainfall-induced fill-slope failure by reducing suction. The tests indicate that matric suction contributes to the dilative or contractive behavior of the unsaturated soils. The anisotropically consolidated undrained triaxial tests demonstrate the consistently contractive behavior of the specimens. On this basis, we delineate the in situ stress conditions leading to the initiation of rainfall-induced fill-slope failure, and the stress paths of the transformation from local failures to flowage. Based on a systematic study of fill-slope case records in Hong Kong, implications of such mechanisms on fill-slope stability are given. CE Database subject headings: Slopes; Failures; Rainfall; Soil suction; Dead loads; Unsaturated soils.

Using Schwarz's alternating method and Muskhelishvili's complex variable function techniques, this paper presents an iterative algorithm method for the effective and accurate calculation of the stresses in an elastic solid of infinite extent containing multiple elliptic holes and subject to external loading at the infinity. The elliptic holes can have different dimensions and locate at any points while their axis orientations must be orthogonal. The proposed iterative algorithm method is based on the approximation of the resultant force vector on each elliptic hole boundary as a series of complex variable. As a result, exact closed-form analytical stress solutions can then be obtained for the solid with a single elliptic hole whose boundary is subject to the reverse resultant force vector in the forms of complex series. The numerical results presented in the paper show that the iterative solution converges quickly and stably. The proposed convergent criterion ensures the satisfaction of the required accuracy of the stress results. The stress concentration at elliptic holes can then be evaluated with high accuracy. CE Database subject headings: Elasticity; Holes; Stress analysis; Stress concentration; Computation.

In this paper, the Lagrangian finite element method is formulated along with the Bingham model for simulating natural transient slurry flows. The numerical model thus developed is validated with available experimental results. As well, a back-analysis of the dynamic behavior of the 1997 Lai Ping Road landslide in Hong Kong is conducted. Correlating well with field observations, the modeling results are satisfactory in terms of predicting the hazard areas of the debris trail during runout and the debris distribution on deposition fan. The present method is also able to demonstrate the multidirectional sliding features of natural slurry flows. It is noteworthy that the availability of high quality data on site topography is crucial for modeling such a gravity-driven flow. A knowledge of dynamic runout information is useful in estimating landslide mobility, potential hazard areas, and debris impact loads, and in evaluating the effectiveness of counter measures in the debris released area, in relation to downslope property development. CE Database keywords: Slurries; Finite element method; Waste sites; Debris; Hazardous materials.

A multicomponent droplet vaporization model including both gas and liquid phase transport processes was developed for multidimensional spray computations. This paper focuses on two effects altering vaporization in a high-pressure and high-temperature environment. One effect is on droplet surface regression caused by a higher vaporization rate. This effect is well characterized by the Lewis number and the Peclet number with the regression velocity. Formulas based on the two numbers were included to improve model accuracy. The other effect is on the nonideal behavior and was covered in the model by using the Peng-Robinson equation of state to determine phase equilibrium at the droplet surface. The model was validated by the results from an accurate simplified vortex model and experimental measurements, and excellent agreements were demonstrated. Further comparisons against the model without the two effects and an infinite diffusion model show that significant improvement was achieved by the model for single-droplet and spray computations.

Byline: Y.-L. Lai (1), C. F. Lee (1) Keywords: Key words: Airway reactivity--Leukotrienes--Lipid peroxidation--Oxygen radicals--Substance P. Abstract: Leukotrienes (LTs), tachykinins (TKs), and oxygen radicals have been suggested to be important modulating factors for the hyperpnea-induced bronchoconstriction (HIB) of guinea pigs. In this study, we tested the hypothesis that LTs and oxygen radicals modulate HIB by triggering TK release. Eighty-five Hartley guinea pigs were divided into four groups: control, dimethylthiourea (DMTU), FPL 55712, and A63162. DMTU is the scavenger for hydroxyl radical. FPL 55712 is an antagonist of LT receptor, whereas A63162 is an inhibitor of lipoxygenase. Each group was further divided into three subgroups: baseline, hyperpnea, and recovery. Each animal was anesthetized, cannulated, paralyzed, and artificially ventilated. We measured dynamic respiratory compliance (Crs), maximal expiratory flow at 50% total lung capacity (V.sub.max50), and forced expiratory volume in 0.1 s (FEV.sub.0.1) during the baseline and recovery periods. Hyperpnea caused significant decreases in Crs, V.sub.max50, and FEV.sub.0.1, indicating HIB in the control group. Pretreatment with DMTU, FPL 5712, or A63162 attenuated HIB. Plasma substance P (SP) levels increased progressively during the experiment in all groups. However, both FPL 55712 and A63162, but not DMTU, significantly decreased SP levels. Similarly, lung malondialdehyde (MDA) contents increased progressively during the experiment in the control group. Neither FPL 55712 nor A63162 significantly affected the increase. On the contrary, DMTU significantly attenuated the increase in MDA during the recovery period. These results suggest that inhibition of LTs leads to suppression at SP levels and HIB, whereas DMTU attenuates HIB by means of other mechanisms. Author Affiliation: (1) Department of Physiology, National Taiwan University College of Medicine, No. 1, Sec. 1, Jen-Ai Road, Taipei, Taiwan, TW Article note: Accepted for publication: 25 April 2000

The linear or loglinear ex post return generation model is widely used to test Capital Asset Pricing Model (CAPM) and its many other applications. A study is conducted to examine the viability of the estimation of a generalized nonlinear functional form for the ex post return process as an alternative. An international sample of 425 stocks is used to examine an empirical stock return model in terms of three specification issues: functional form (linear, loglinear or nonlinear), factor structure (with or without a global index, equally- or value-weighted) and price adjustment pattern (static vs. dynamic). The study provides support for the use of the generalized functional form.

Hydroelectric power resources constitute a renewable and economic means of providing electricity to serve the energy needs of our modern society. As dams get older, there is a need to ensure that their conditions of safety and integrity are also consistent with today's acceptable standards and criteria. This paper outlines the scope and major engineering tasks in the Dam Safety Assessment Program undertaken by Ontario Hydro in Toronto, Canada. Methodologies used to determine the probable maximum flood for a high-hazard dam are presented together with a flood routing model. The 2012 MW R. H. Saunders/Robert Moses Generating Station on the St. Lawrence River is used as an example to illustrate such methodologies adopted for dam safety assessment. It is demonstrated that under probable maximum flood conditions together with extreme wind effects, the main dam of this power station would still have a comfortable freeboard allowance, primarily because of the vast storage capacity of Lake Ontario. The spill capacity is also found to be adequate. The dam meets the requirements and pertinent standards of dam safety assessment.

A methodology developed to handle dispersive materials in the time domain is extended to model the dispersive characteristics of the impedance boundary condition used for a thin layer coating over perfect conductors. The impedance boundary condition is first approximated as a rational function of frequency. This rational function is then transformed to a time domain equation, resulting in a partial differential equation in space and time. Discretization of the time domain model to efficiently handle the thin layer coating is presented in the context of the finite-difference time-domain (FD-TD) technique. The methodology is verified by solving a one-dimensional problem using the FD-TD technique and comparing with the analytical results.