No abstract

Settlement of soil layers during and after earthquake shaking is a major cause of damage to buildings and geotechnical structures. The available empirical design methods to consider seismically induced settlement focus on sands in dry or water-saturated conditions, and there is currently a gap in the basic understanding of the mechanisms of seismically induced settlements of partially saturated sands. An effective stress-based empirical methodology is proposed to estimate the seismically induced settlement of a free-field layer of sand in partially saturated conditions. This approach estimates the settlement by separately considering the volumetric strains caused by compression of void space during strong shaking (seismic compression) and dissipation of excess pore water pressures generated during earthquake shaking (postcyclic reconsolidation). A parametric evaluation of the methodology indicates that the small strain shear modulus, the parameters of the modulus reduction curve, the approach to estimate the upper bound on volumetric strain during liquefaction, and the pore water pressure generation parameter can have significant impacts on the predicted settlement. The model predictions were validated using results from a newly developed centrifuge physical modeling system that involved the use of steady-state infiltration to maintain a uniform degree of saturation with depth in the sand layer. Both the model and experimental results show a nonlinear trend in surface settlement with degree of saturation, with a minimum value obtained for sand at a degree of saturation between 0.3 and 0.6.

The dynamic shear modulus of soils is needed to predict soil behavior in response to cyclic loading. Even though the effective stress has been shown to have a significant impact on the dynamic modulus of water-saturated and dry soils, its effect on the dynamic shear modulus of unsaturated soils has not been evaluated. Specifically, studies on the dynamic response of unsaturated soils have characterized variations in small-strain shear modulus (G max) as a function of the degree of saturation or matric suction alone. In contrast, this study evaluates the use of the suction stress characteristic curve to characterize the impact of mean effective stress (' m) on the dynamic shear modulus of unsaturated sand. A fixed-free resonant column test device was adapted with a hanging column setup so that the small-strain dynamic shear modulus could be measured for sand specimens under different confining pressures and matric suction values. Trends between the small strain shear modulus and effective stress for unsaturated sand were found to be different from those reported in the literature, where G max varied linearly with the square root of ' m .

AND Hox-Yru EatUnivusity of Colorado, B oulder, Colo. As a result of an examination of the behavior of soils s ubjected to rocket and jet exhaus t gases. it was concluded that th e gas pressure in the pores of the s oil played an important part in the process of s oil r e moval which occurred . Con s equently, a numerical s tudy of a."tially ,-mmetric isothermal nonlinear gas flow ill a porous medium wa undertaken. The paper ~resents the r esults and interpretations of the calculations for the particular boundary press ure conditions d eYelope d b~ a urveyo1· spacecraft vernier engine mounted 12 in . abO\-e a granular mate rial. lntroduction A PROPO 'ED experiment for the Sun·eyor :;;paceeraft ometime after a ucce-sful lunar landing is the firing of its vernier rocket. engines. 'ince Sun·eyors I and HI ha,·e demonstrated the existence of a granular medium at the moon's urface, the que...;;tion of the prediction and interpretation of the effect of the firing into a . oil under appropriate circumstance;: arise;;. In addition, the landing of lhe Apollo Lunar ::\1odule on the moon will require the conti.nuou" firing of the vehicle'· engine to a distance of a few feet abm·e the lunar wfaee. The con~uences of this must be reliably estimated in ad,·ance, ince the effect:> may require clo:::e consideration of the final stages of the L~I tra.jectory. A preliminary urveyor experiment will be of value in conducting L~I tudie;;.During the fii'l:lt lunar day of Sun·eyor l's life, consideration was given to a test employing the ,-ernier engine=-used in controlling the spacecraft's de ·cent, although there wa:; doubt both as to their actual operation and the thrl.1$t level they would achie,·e. :\ t the time. it wa., of course, already kno"·n that the lunar :;urface \Yas soil-like. so that the hazard to the spacecraft of filing the ,·erniers had to be a -essed. There were two danger-<. One con:;isted in the possibility that a thrust Je,·el might be reached which could overturn the . pa.cecraft. The econd danger, which concern-thi -paper, wa.s that a ucce-«ful fi1ing, which did not OYerturn the spacecraft, might howe,·er coYer it with soil expelled from the lunar surface below the engine nozzles. This material would impair the efficiency of the thermal control ;;mface and might also come in contact with the camera mirror and other .ensitin· surfaces.A number of i;;tudics were therefore initiated to clarif,· the que t ions relaliug to a te ' t firing of the vernier engi ne~. · One of these invoh·ed te~t firings of a SwTeyor \·eniier engine in a rocket engine Yacuum test chamber at the JPL-Xorthrop facility at Edwards .-\ir Force Base, Calif.. in June 1966 in order to simulate the un·eyor I temperature conditions at the lunar urface. The senior author sugge·ted that ,,ome of these firings be carried out on a soil simulating the obsen·ed lunar surface material as well as it could be judged, at the level of the lunar surface below the ~un·eyor I ,·ernier emrine nozzle, a distance of about 12 in. Xo attempt was made to Received Fe...

Synopsis The design and construction of a soil test box, capable of applying any combination of three principal stresses to a cubical soil specimen, is described. The principal stresses can be varied independently or by means of a stress control device which is a mechanical-hydraulic analog of an octahedral plane in the principal stress space. The three principal strains are measured, together with an independent measurement of the volume change of the soil sample. The behaviour of a medium dense Ottawa sand in an axial compression test at constant octahedral stress in the equipment is compared withthat of the same material in a conventional triaxial apparatus. On décrit la conception et la construction d'une boite d'essais de sol permettant d'appliquer n'importe quelle combinaison de trois contraintes principales à un échantillon de sol cubique. Les contraintes principales peuvent être variées indépendamment ou au moyen-d'un appareil de contrôle de contrainte qui est mécaniquement-hydrauliquement analogue à un plan octaédrique dans l'espace de contrainte principale. On a fait la mesure de trois déformations principales ainsi qu'une mesure indépendante de chargement volumétrique de l'echantillon de sol. On-compare le comportement d'un sable d'ottawa moyennement dense dans un essai de compression axial sous une contrainte octaédrique constante dans l'appareil avec celui du même matériel dans un appareil triaxial conventionnel.