The Effect of Climatic Factors on Subgrade Moisture Conditions

Abstract

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...

Study of the Influence of Groundwater Table in Mechanical Behavior of a Full-Scale Pavement Structure Modeled in a Test-Pit

“…They concluded that moisture directly influences the stress and strain in pavement layer systems. The authors also concluded that the matric suction measured in situ shows a good correlation with the Thornthwaite index and with soil type, a very similar result obtained previously by Russam and Coleman [4].…”

Estimation of soil cracking and the effect on surface runoff in a Texas Blackland Prairie watershed

“…The two parameters, which must be defined in a study of swelling of soils, are the depth of the active zone and the seasonal change of soil moisture with depth. Plots of soil suction with depth based on field and laboratory derived suction measurements are often used to assess the depth at which the equilibrium suction (active depth) is reached according to the Russam Coleman curves (Bryant, 1999;Russam and Coleman, 1961). The depth of changes in soil moisture and suction in Bryant's study extended to 6 m. Most of the reported variation occurred in the top 4 m. Wise and Hudson (1971) indicate that the common depth of active swelling in Texas is slightly less than 2 m. At the study site in Riesel, soil suction was computed (ASTM D5298-93) during the fall of 1999.…”

Desiccation of a Clay by Grass, Bushes and Trees

“…It has also been recognized for many years that both the processes of desiccation and swelling can cause damage to shallow foundations and road pavements on clay. Early examples are Collins' (1957) observations of the patterns of movement (long term heave with superimposed seasonal heave and shrinkage) of buildings on desiccated clays in South Africa, Aitchison and Holmes' (1962) observations of suction profiles beneath and adjacent to road pavements in Australia and Russam and Coleman's (1961) work on the effect of climatic factors on subgrade conditions beneath roads in the UK.…”