ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The hysteretic relationship between hydraulic conductivity and suction is examined in the light of the domain concept. It is argued that the distribution functionGof the conductivity elements is strongly dependent on the suctionr8dat which the trend of suction reverses from increasing to decreasing irrespective of whether the relationship between pore water and suction conforms to the independent domain concept or not; it also depends strongly on the suctionr8wat which the trend of suction reverses from decreasing to increasing when the moisture characteristic shows dependent pore water properties. Thus the hysteretic curves describing the relationship between hydraulic conductivity and suction for a porous body with a moisture characteristic showing dependent properties cannot provide at present true values for theGfunction; in the case of a porous body with a moisture characteristic conforming to the independent domain concept they may still provide reliable values for theGfunction for a particular value of the reversal suctionr8dsince there is not a strong dependence ofGon the reversal suctionr8w.Experimental relationships between hydraulic conductivity and suction for three porous bodies confirm the above conclusions and show the effect of the dependence of the functionGon the reversal suctionsr8dandr8w.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Important contributions of the late Dr. E. C. Childs included early recognition of the nonlinear diffusion form of the nonhysteretic flow equation for unsaturated nonswelling soils, and of the importance of a predictive system based on the flow equation. The full equation is a nonlinear Fokker-Planck equation, and reduces to a diffusion equation when gravity may be neglected. Equations of the same form describe water movement and volume change in swelling soils. This paper reviews recent work on quasianalytical and analytical methods of solving these equations.Quasilinear solutions of the steady equation in two and three dimensions have received much attention. The extension to heterogeneous soils can be taken further to include sloping stratification. Theorems enable solutions for surface sources, and sources at arbitrary finite depth, to be deduced from mathematically simpler solutions in a region extending infinitely in all directions. A generalization to the case of sloping soil surface is given.In many real-world problems where similarity methods do not apply, integral methods offer the same possibility of effectively reducing the number of independent variables. Green and Ampt introduced a simple integral method; and more sophisticated methods have entered soil-water studies through the work of Parlange. Recent studies reveal the importance of preserving integral continuity in integral methods involving iteration.For diffusivityD= a(b - 0)−2, all problems of one-dimensional nonlinear diffusion subject to arbitrary initial conditions plus a flux boundary condition can be linearized. Exact solutions are therefore available for various problems, some of them in explicit form.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

A numerical solution technique was applied to the Richards equation for soil-water flow. Hysteresis in the water-content-pressure-head relation was incorporated into the solution procedure. Water content, pressure head, and flux time and depth distributions were calculated for a column of sand subjected to a periodic upper boundary condition. Two cases were examined: (1) an initially dry, deep (semiinfinite) sand column and (2) a sand column with a water table at a depth of 300 cm. In both cases the waveforms of water content, pressure head, and flux exhibited a progressive increase in phase lag and decrease of amplitude with depth. The highly nonlinear soil-water flow system introduced a high degree of harmonic distortion into the response of the system to a sinusoidal boundary condition.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Infiltration of water into soil from an application of constant water fluxris analyzed theoretically by treating the resulting soil-water profiles as step functions, as assumed in the approach of Green and Ampt (1911). Important features of the infiltration process then follow in fairly straightforward mathematical form. Asrdecreases toward the near-saturated soil hydraulic conductivityKb, the timetoof onset of surface-water excess is sufficiently increased so that the curves of infiltration fluxiversus cumulative timetare shifted toward larger times, progressively away from the curve ofiversustfor continuous ponding. Butiis not a simple function oft, primarily because the cumulative water infiltrationIis an implicit function oft. Two explicit-form equations are then proposed foriversust, both equations being integrable into explicit forms ofIversust. The one explicit equation is matched with the implicit function within ±11 percent, over the whole range fromr=Kbtor→ ∞ at continuous ponding. The other explicit equation is more suitable forrnearer toKb, the error of matching to the implicit function being within ±5 percent for 1 <r/Kb< 10. Thus, both explicit equations appear to have promise for expressing infiltration phenomena (flux and cumulative) as a function of time.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

A laboratory flume with transparent walls was used to observe simultaneously movement of the advancing front over the ground surface and depth of penetration of the wetting front. The experimental data were used to test Laplace transformations of the Lewis and Milne infiltration-advance equation involving:(1) a short-term infiltration equationy=S√t+At(Philip);and(2) a long-term steady-state infiltration equationy=y0+Kt.It is concluded thatto, defined asS√te=yoand which can be determined either independently or from the flume results, is a convenient soil parameter to determine the appropriate “advance-infiltration” equation.The transformation involving Eq. (2) was accurate to within 10 percent at all times greater than 1/2tefor three materials.The transformation involving Eq. (1) was accurate to within 5 percent only up to times less thante.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

This paper examines the process of self-weight filtration in saturated systems in terms of theory of water movement in swelling soils. Two aspects of the process are examined experimentally. It is shown that the Lagrangian mathematics of swelling soils is appropriate to liquid flow in consolidating saturated slurries. Also, the early stages of self-weight filtration of slurries correspond formally to conventional Eulerian mathematics of sorption in nonswelling soils. These are supported by experimental results obtained with Bentonite.Results obtained with Red Mud, produced during extraction of alumina from bauxite, are also consistent with these observations and, in addition, demonstrate that the final equilibrium profiles in slurries are predictable using the definition of the total potential of the water in a saturated swelling soil.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The concepts of the equivalent drain radius and entrance resistance of a nonideal drain are used to obtain drainage formulas to describe the relationships between the maximum water-table height and average flux through the water table for parallel drainage installations when there is infinite depth of soil below the drain and when the drain is laid on the impermeable floor. For small equivalent drain radii or large entrance resistances there is little difference in the two relationships. Experiments in a hydraulic model sand tank show that the proximity of an impermeable floor has little effect on the equivalent drain radius of a given drain, and that water-table heights are in fair agreement with the theoretical formulas.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Water-table heights in a drained soil under seasonally fluctuating irrigation intensities were investigated experimentally by means of a Hele-Shaw model and were compared with the theoretical harmonic predictions of E. C. Childs. Good agreement was found between theory and experiment in the values of mean water-table heights and their amplitudes of oscillation. The oscillation was found to deviate from the simple harmonic form predicted by the theory for short time periods. The deviation was attributed to limitations in the Hele-Shaw model.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID