Soil compression is a topic of increasing importance in the evaluation of foundation sites for the heavy, rigid structures being founded upon them. The first analytical approach to compressive behavior in soil was presented by Terzaghi in the 1920's. Since that time, his consolidation theory has formed the general basis for prediction of soil compressibility under load. Compressive behavior not explained by Terzaghi’s assertions is known to occur in soils. These aberrations may be broadly classified into three categories: (1.) Initial or Elastic Deformation, (2.) Secondary time effects, and (3.) Compression rate discontinuities not attributable to the exuding of water from the soil skeleton. This study attempts to explain such anomalistic behavior in terms of electrochemical characteristics of the clay-water system observed subsequent to acceptance of the consolidation theory.

The proposed mechanistic model of soil compression amends to Terzaghi’s considerations the internal energy consumed in the generation and degeneration of electrochemical bond. Such bond is the result of the electrochemical charges on clay mineral particles coupled with the strong polarity of water molecules. Under the influence of these electrochemical forces, each water molecule has a unique position and orientation commensurate with the condition of minimum potential energy. For relative movement to occur among clay particles or within the molecular water structure, electrochemical forces must be overcome at the expense of the clay-water system's internal energy, thereby creating an intergranular bond of structural water.

The bond process model considers soil compression to be an aggregate response of bond creep, bond rupture, and bond formation, which may or may not be joined by consolidation as a controlling factor. The model illustrates initial compression and compression rate discontinuities as bond creep/bond rupture manifestations and secondary compression as the outgrowth of bond formation. Implications are also made which attribute compression time-lag as much to the rheologic properties of the soil skeleton as to resistance to water flow as asserted by Terzaghi.

The findings of an experimental program are presented to substantiate the proposed model. Included in the findings are the results of three individual studies. The first study involves the visual inspection of compression curves from a representative group of undisturbed samples from throughout the United States. In keeping with the implications of the bond model, stress history appears to be a primary factor in control of soil compression and in the motivation of anomalous compressive behavior.

Secondly, the influence of temperature upon compression characteristics was studied in detail. The findings illustrate the effect of temperature action on the colloid system which in turn affects bonding energies. Temperature influence is considered to be representative of the effect of various parameters on the distribution of net electrochemical potential in the colloid system.

The final study entails determining the action of soil plasticity on soil time response. Comparison of compression curves from soils of similar characteristics, with the exception of plasticity, suggests that plasticity is coupled with permeability in controlling compression rate.