Components of Pore Water Pressure and Their Engineering Significance

J. K. Mitchell1
University of California, Berkeley
1 Assistant Professor of Civil Engineering and Assistant Research Engineer, Institute of Transportation and Traffic Engineering, University of California, Berkeley.

Abstract: Pore fluid pressures that develop within soil masses as a result of both mechanical and physico-chemical effects influence the magnitude of the intergranular or effective stresses. The intergranular stresses control, in many cases, soil behavior in shear and compression. The physical significance of pore water pressure in a cohesive soil is examined in terms of several components which combine to give the total pressure. An analysis of fluid pressures at various points within a soil mass based on a condition of no flow at equilibrium shows that changes in any one component of the total pressure from point to point are offset by changes in other components.

The analysis shows that a pore pressure measurement reflects interparticle repulsive pressures and water adsorptive forces as well as purely hydrostatic pressures arising trom mechanical effects. The individual components of total pore pressure are not directly measurable except in special systems. Data are presented which indicate that a significant portion of the swell of a compacted soil is attributable to water pressure deficiencies caused by mechanical and capillary components which act in addition to osmotic pressure components.

Component water pressures are related to stresses between particles. It is shown that intergranular pressures are dependent on osmotic and adsorptive components of the total water pressure.

Clays and Clay Minerals; 1960 v. 9; no. 1; p. 162-184; DOI: 10.1346/CCMN.1960.0090109
© 1960, The Clay Minerals Society
Clay Minerals Society (www.clays.org)