Hydrology of Swelling Soils

The methods of thermodynamics are employed to develop a nonlinear integral equation for the equilibrium moisture profile in a swelling soil which is assumed to be uniform in the distribution of dissolved substances. The equation is shown to be identical with an expression suggested (but not derived) by Philip in response to criticism of his discussion of the hydrostatics of swelling porous media. Philip [1969a, b] has given a discussion, in fluid mechanical terms, of the condition for moisture equilibrium in the profile of a swelling soil which is assumed to maintain a uniform distribution of dissolved substances. The general expression that he presented is

Section: (B = Xlt --Z* Q-•-• E ( O ) --[--3' Dz' = --mentioning

confidence: 94%

Section: (B = Xlt --Z* Q-•-• E ( O ) --[--3' Dz' = --mentioning

confidence: 99%

A thermodynamic integral equation for the equilibrium moisture profile in swelling soil

Sposito¹

1975

“…The overburden pressure was assumed to have a negligible effect on the volume change, and such assumptions cre- below shallow water tables [Youngs and Towner, 1970]. Although the load factor was corrected to include the effect of overburden pressure on the volume change as given by (1) [Philip, 1970;Groenevelt and Bolt, 1972], the equilibrium moisture distribution in swelling soils has not been corrected accordingly.…”

Section: Introductionmentioning

confidence: 99%

“…Final settlements of civil engineering structures could be predicted using the relationship e(O, P), if the equilibrium moisture profile is evaluated using the shrinkage cu•es obtained for a sufficient range of overburden pressures. overburden pressure are considered to be valid and applicable for swelling soils which exhibit one-dimensional and reversible volume changes [Tempany, 1917;Haines, 1923;Lauritzen and Stewart, 1941;Holmes, 1955;Warkentin and Bozozuk, 1961;Fox, 1964;Philip and Smiles, 1969;Philip, 1969aPhilip, , 1971Philip, , 1972Groenevelt and Bolt, 1972;Sposito, 1973;Talsma, 1977;Giraldez and Sposito, 1983]. Volume change of a swelling soil under an overburden pressure takes place in three shrinkage phases from saturation to oven dry at a moisture ratio equal to !9 o.…”

Section: Introductionmentioning

confidence: 99%

Gravitational Equilibrium Moisture Profiles in Swelling Soils

Ekanayake¹,

Painter²

1995

Abstract. Extension of the work of Philip (1969aPhilip ( , 1972 has shown that the effect of overburden pressure on volume change of swelling soils produces equilibrium moisture profiles entirely different from those predicted without considering the overburden pressure effects. Volume change of swelling soils accompanied by moisture changes also affects the overburden pressure. The total volume change under an overburden pressure occurs in three different shrinkage phases from saturation to oven dry. These volume change characteristics are usually described on the shrinkage surface, a surface drawn as void ratio e (volume of voids/volume of solids) versus moisture ratio O (volume of water/ volume of solids) for different overburden pressures. A relationship for the moisture gradient is developed by assuming that the overburden potential, a component of the total potential of soil water, is a function of moisture ratio only across a small soil element of a long swelling soil column which consists of large numbers of finite soil elements. The moisture gradient has complex behavior based on the properties of the three shrinkage phases on the shrinkage surface. Distribution of equilibrium moisture paths is then explained by evaluating the moisture gradients at points on an idealized shrinkage surface. It is shown that the soil at great depths could either be saturated or unsaturated at equilibrium. (These depths could be over 250 m for some sodium montmorillonite clays).

“…In the absence of possible, and consequently, point C' may not correspond to adequate supporting experimental data many workers have point C. It should be noted that the state is still reversible, at not been convinced of its validity, although such doubts have least in the mechanical sense, so that unloading by the reduconly been expressed in private discussion. Philip [1970Philip [ , 1971, tion of the mechanical load P and/or the relaxation of the pore 1972, 1973], Groenevelt and Bolt [1972], and Sposito [1973] water pressure u will eventually restore the state to A in Figure returned to a reanalysis of the problem and derived a revised 1 and the whole cycle can be repeated. Whether such hysteresis expression, but they all again appealed to an application of does occur in practice can only be ascertained by experiment.…”

mentioning

confidence: 99%

The application of the overburden potential theory to swelling soils

Towner¹

1976

From a consideration of alternative loading paths in the shrinkage diagram of swelling soils it is shown that hysteresis in the relationship between the voids ratio and the moisture ratio may occur even though no actual reversals of loading have been allowed nor any irreversible structural changes have taken place. It is therefore argued that the application of the overburden potential theory to the analysis of situations such as water profiles above water tables in vertical soil columns is questionable. The need for experimental studies is stressed.The analysis of static soil-water profiles in swelling soils is complicated by the fact that the water content at any point is determined not only by the negative pore water pressure at that point, arising for instance because of the presence of a water table, but also by the overburden pressure due to the mass of wet soil above that point and also to any surface loading. Coleman and Croney (unpublished laboratory note, 1952) and Croney et al. [1958] applied reversible thermodynamics without any qualification to the derivation of the equation for the water content of a soil sample under the combined influence of a pressure in the pore water and a mechanical load applied to the soil mass. Schofield [1960] questioned such an which the pore water pressure has been increased from zero to ut, a constant load P' (P' < P) applied at u = 0, to bring the state to point B', where the load is then increased to P so as to bring the state to point C' while maintaining the pore water pressure constant at ut. Points C and C' should coincide. It should be noted that no actual reversals of the loading, either in the externally applied load P or in the pore water pressure u, have taken place along either path. (It is assumed that no irreversible structural changes occur.) If the slope of the path B'C' is sufficiently greater than unity, i.e., (•e/•0)u >>> 1, the actual degree of saturation will increase although the moisture ratio decreases. In other words, if (•e/•0)u >>> 1, hysteresis is application of reversible thermodynamics. In the absence of possible, and consequently, point C' may not correspond to adequate supporting experimental data many workers have point C. It should be noted that the state is still reversible, at not been convinced of its validity, although such doubts have least in the mechanical sense, so that unloading by the reduconly been expressed in private discussion. Philip [1970, 1971, tion of the mechanical load P and/or the relaxation of the pore 1972, 1973], Groenevelt and Bolt [1972], and Sposito [1973] water pressure u will eventually restore the state to A in Figure returned to a reanalysis of the problem and derived a revised 1 and the whole cycle can be repeated. Whether such hysteresis expression, but they all again appealed to an application of does occur in practice can only be ascertained by experiment. reversible thermodynamics without experimental verification. They assumed that hysteretic effects were avoided or nonexistent. It seems desirable t...