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Lower bounds for the strength of the lunar surface have been derived from the properties necessary to provide stability of the slopes observed in Ranger 7, 8, and 9 imagery. Additional information was obtained from Luna 9 data, from hydrostatic considerations, and from laboratory tests. Utilized in some of the calculations were density data derived from radar and thermal emission measurements. Densities obtained are 0.6 to 0.7 g/cm 3 for the few cm, g/cm 3 or more at 10 −1 meter, and 2 to 3 g/cm 3 at 10 0 to 10 1 meter. Safe lower bounds for mass-bearing capacity on 0.1-meter bearing widths are 10 1 and 10 2 g/cm 2 , respectively, with no sinkage, 3 × 10 1 and 10 3 g/cm 3 with sinkage equal to bearing width. Probably realistic lower bounds for these widths are 10 3 and 10 4 g/cm 3 , respectively; there is a little evidence to suggest representative values are only slightly higher. A model of the surface layer is outlined.

Synopsis The origins and general characteristics of a very soft, sensitive, normally consolidated marine clay are described. The clay was formed in a sheltered location from restricted types of source material and could be expected to be more uniform than most shallow marine deposits, yet its properties show fairly large variations about a mean trend. Standard sampling methods provided satisfactory samples for compressibility tests but not for strength test. In situ vane tests and laboratory tests on samples obtained with a Swedish foil sampler gave equivalent undrained shear strength results. The clay has a small finite surface strength and strength incrcascs linearly with depth. The overall ratio of undrained shear strength to effective over-burden pressure is rather smaller than would be expected from the Atterberg limits. Une description est faite dcs origincs et des caractéristiques d'une argile marine normalement consolidée, très molle et sensible. L'argile a été formée dans un emplacement abrité à partir de types limités d'un matériau de base et l'on pouvait s'attendre à la trouver plus uniforme que la plupart des dépôts marins à peu de profondeur. mais ses propriétés présentent cependant des variations assez importantes par rapport à un type moyen. Les méthodes d'échantillonnage standard ont fourni des échantillons satisfaisants pour des épreuves de compressibilité mais pas pour des épreuves de résistance. Des essais sur place avec palettes et des essais de laboratoire sur des échantillons obtenus à l'aide d'un échantillonneur enfeuilles suédois ont donné des résultats équivalents de résistance au cisaillement à teneur en eau constante. L'argile possède une petite résistance superficielle finie et sa résistance augmente linéairement avec la profondeur. Le rapport total de la résistance au cisaillement à teneur en eau constante à la pression de surcharge effective est plutôt plus petit que l'on pourrait s'y attendre d'après les limites d'Atterberg.

Polishing of sapphire surfaces with energetic Ar+ ion beams is shown to result in a substantial increase in laser damage threshold over that for conventionally polished surfaces. Data for both entrance and exit damage are presented. The results are interpreted in terms of an increase in surface strength with ion beam polishing.

Lunar Orbiter II photographed a 13-meter boulder which has rolled down the inner slope of a 3-kilometer crater leaving a track 6 meters wide. A static-bearing . strength of 4 x 10(6) dynes per square centimeter at 75-centimeter depth is estimated from these data if certain assumptions are made.

All manufactured products require a surface finish of some sort, whether it is the natural finish of the part or a subsequently applied finish. Natural finishes may be employed for reasons of economy, for decorative purposes, or for imparting durable surface strength. Some of these finishes are itemised in the first part of Table 1, but apart from the mechanical finishes classed in engineering parlance as natural finishes, and ground finishes employed on running surfaces, a subsequently applied finish is frequently required.

The ability of the lunar surface to support statically the Luna 9 copsule indicates that the surface can bear at least 5 x 10(3) dyne per square centimeter (10(-1) lb/in.(2)). Analysis of the landing dynamics, using available data, gives a lower bound of about 1 to 2 x 10(5) dyne/cm(2), but this estimate may not be conservative because of uncertainties regarding the shock-absorbing system used and the direction of the velocity vector at impact.