SYNOPSISThe Paper describes recent research conducted at Cet article dkcrit des recherches r&e&es faites au the Road Research Laboratory upon subgrade moisLaboratoire de Recherches Routibres (Road Reture conditions, with the aim of extending to a search Laboratory) sur les conditions d'humidite des wider range of climates the research already carried sous-sols, dans le but d'etendre a une plus grande out on moisture conditions beneath British pavevariete de climats les recherches deja faites sur les ments. Measurements made under several road and conditions d'humidite sous les revetements britanairfield pavements in both tropical and semi-tropical niques. On y traite des mesures recueillies sous countries are considered. Where the water-table is plusieurs revetements de routes et de terrains d'aviation dans des pays tropicaux ainsi que dans close to the surface it is shown to be the main factor des pays semi-tropicaux. in determining the moisture condition of the subOn montre qu'oh la nappe aquifere est p&s de la grade irrespective of climate. Where the watersurface elle est le facteur primordial permettant de table is deeper, or non-existent, the relation between definir les conditions d'humidite du sous-sol quelque the subgrade moisture condition and the climatic soit la &mat. Lorsque la nappe aquifere est plus water balance is examined, and evidence is preprofonde, ou non existante, on examine la relation sented for a relation between the suction of soil entre les conditions d'humidite des sous-sols et moisture in the subgrade and the Thornthwaite l'equilibre d'eau climatique, et on offre les preuves d'une relation entre la suction de l'eau contenue dans Moisture Index. le sous-sol et l'indcx de teneur en eau Thornthwaite. INTRODUCTIONCertain methods of pavement design, that are available to the road engineer, suffer from the disadvantage that they apply only to the climatic environment for which they were developed. Rainfall and temperature control the soil moisture condition and influence the type and thickness of pavement required for roads and airfields. At the Road Research Laboratory, the applicability of the method already developed for estimating the ultimate moisture condition of subgrades under British conditions (Black, Croney, and Jacobs, 1959) 1 has been examined in more extreme climates.A tentative method of estimating the suction in terms of climatic data has also been developed. SOIL MOISTURE AND CLIMATEThe moisture condition of exposed soil depends principally on the precipitation or rainfall and on evapotranspiration.The change AM over a given time in the number of inches of water stored in an exposed soil profile is equal to R -E -D, where R is the precipitation in inches, E the actual evapotranspiration in inches, and D the drainage in inches, all occurring during that time. The latter term, which includes both surface run-off and sub-surface drainage, is not easy to measure except for certain complete catchment areas, and the moisture balance may alternativeIy be referred to the moisture h...

Synopsis The article describes investigations carried out in Trinidad to obtain information about moisture conditions under existing roads, and to see whether a method developed at the Road Research Laboratory for estimating the ultimate moisture content reached under impervious surfacings could be apphed to, or modified for use in, overseas territories. Borings were made under well-sealed roads in several widely spaced areas of the island of Trinidad. The moisture contents of the soil at various depths were compared with those found at the same depths in the road verges. Observations were made on the depth of the water-table (where found) and undisturbed samples were taken and dispatched to the Road Research Laboratory for testing. Comparison of the moisture contents showed that the variation in moisture content with depth was broadly similar under the roads and in the adjacent verges. The moisture content values, however, were too much affected by local variations of soil type to indicate whether the subgrades were significantly wetter or drier than the surrounding soil. At the two sites where the water-table was located the moisture contents measured under the pavements were in close agreement with those estimated from the suction properties of the soils using the method referred to above. For the sites where no water-table was found in the course of the boring, an estimate was made of the depth of the water-table from the suction and moisture content data. The conclusions were in general agreement with local knowledge. It appears therefore that for the climate of Trinidad (approximately uniform average temperature of 78°F over the year and annual rainfall 60 to 120 in.) the theoretical method can be used with satisfactory accuracy to determine the ultimate moisture content under the centre of well-sealed roads. In Trinidad, as in Great Britain, drying from the edges does not in general have a large effect on the moisture content of the subgrade as a whole. The suction and shrinkage curves were very similar to those found for British soils of comparable plasticity indices and particle-size distributions. L'article décrit les recherches faites à Trinidad pour obtenir des renseignements sur les conditions d'humidité sous des routes existantes et pour découvrir si une méthode développée au Laboratoire de Recherche Routiére pour estimer la teneur en eau définitive atteinte sous des revêtements étanches, pouvait être appliquée, ou modifiée pour être utilisée dans les territoires d'outre-mer. On fit des forages sous des routes bien étanchéifiées dans plusieurs régions de l'île de Trinidad très distantes les unes des autres. La teneur en eau du sol à des profondeurs variées fut comparée avec celle que l'on trouva aux mêmes profondeurs en bordures. de la route. On fit des observations sur la profondeur de la nappe aquifere (ou on put la trouver) et on préleva des échantillons intacts qui furent expédiés au Laboratoire de Recherche Routièe pour analyse. La comparaison des teneurs en eau montra que la variation de la teneur en eau selon la profondeur était en gros semblable sous les routes et leurs bordures. Les valeurs de la teneur en eau étaient pourtant trop affectées par les variations entre les types de sol pour montrer si les sous-sols étaient plus humides ou plus sets que le sol avoisinant, de manière significative. Aux deux chantiers où la nappe aquifère fut repérée les teneurs en eau mesurées sous les surfaces de routes étaient en relation étroite avec celles qui furent estimees d'après les propriétés d'absorption selon la méthode mentionée ci-dessus. Pour les chantiers où on ne trouva pas de nappe aquifère au tours des sondages, on fit une évaluation de la profondeur de la nappe aquifere d'après les données d'absorption et de teneur en eau. Dans l'ensemble, les conclusions concordaient avec les connaissances locales. Il semble done que, pour le climat de Trinidad (d'une température annuelle moyenne à peu près uniforme de 78° Fahrenheit et d'une chute des pluies de 60 à 120 pouces), la méthode théorique peut être employée avec une précision satisfaisante pour déterminer la teneur en eau définitive sous le milieu de routes bien étanches. A Trinidad, comme en Grande Bretagne, le dessèchement des bordures n'a pas, en général, un grand effet sur la teneur en eau de l'ensemble du sous-sol. Les courbes d'absorption et de contraction étaient très semblables à celles établies d'après des sols britanniques d'indices de plasticité et de répartitions de particules et dimensions comparables.

Synopsis The Paper seeks to extend to a wider range of soil conditions the research already carried out upon the thermodynamics of soil moisture. The influence of the osmotic pressure of the salts dissolved in the soil water, the pressure in the pore air, and an applied general system of nine total stresses are briefly examined, in addition to the variables considered in earlier work. Use is made of the theory of dimensions to suggest that the invariants of both the stress and strain tensors could with advantage be employed in the study of soil moisture. The Paper concludes with a qualitative discussion of the probable performances of a wide range of soil types in the road subgrade, and subjected to diverse climatic conditions. Cet article cherche à étendre à une plus grande variété de conditions de sol, les recherches déjà faites sur les thermodynamiques de l'humidité des sols. En plus des variables traitées dans une étude précédente, on examine brièvement l'influence de la pression osmotique des sels dissouts dans l'eau du sol, la pression de l'air interstitiel et un système généale d'application de neuf tensions totales. On a utilisé la théorie des dimensions pour suggérer que les invariants des tenseurs de contrainte aussi bien que de déformation peuvent être utilisés avantageusement dans l'étude de l'humidite deś sols. L' article termine par une discussion qualitative des rendements probables d'une grande variété de sols types dans les sous-sols routiers, et soumis à diverses conditions climatiques.

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(Tropical Section, Road Research Laboratory) wrote that the Authors' description of large scale earth-moving operations in the wet tropical climate of Singapore provided much useful data on the standards of workmanship which could be attained under these adverse conditions. The extent of the adverse weather conditions could be seen in Fig. 7(a) which showed that rainfall was commonly of the order of 10 in. per month and occasionally this amount fell during a single week. That the standard of compaction in the embankments was high might be judged from Table 1 which showed that the maximum settlement recorded after 18 months was 0.86 in. for a 16-ft high fill overlying a particularly troublesome area of soft and wet soil. The figures shown were very similar to those obtained in Southern England2 and Kenya3 on closely controlled embankment construction.63. Work in East Africa on the compaction of soils on road construction schemes4 had shown that the most important single factor determining the level of compaction which could be achieved by normal techniques was the moisture content of the soil at the time of compaction. With moisture contents at or slightly in excess of the optimum moisture content in the B.S. Compaction Tests densities equal to the maximum dry density value in that test were readily attained; with moisture contents dry of the optimum moisture content in the B.S. Compaction Test, field densities averaged 93% of the laboratory maximum dry density values. In wet tropical climates the provision of moisture would not be a problem and the use of construction techniques which minimized the soaking of loose uncompacted layers by rainfall as outlined in &$30-31 ensured that the pavement builder exploited the climatic advantages of his environment to the full. 64.In 5 21 the Authors commented on the difficulties of achieving a target dry density of 112 Ib/cu. ft which was based on the values achieved in a trial embankment. In the writer's experience such a state of affairs was common and variations of the magnitude indicated in Fig. 4 and 8 10 were often found within quite localized areas of a visually uniform soiL4 It was therefore important that, when using dry density as a measure of compaction in the field, the values found were compared with a laboratory compaction test carried out on exactly the same soil. This could most easily be achieved by performing the laboratory compaction test on soil dug from the holes during the measuring of the dry density in the field.