Civil and Building Engineering.

On small projects, it may not be economically possible to perform laboratory tests. Consequently, geotechnical design computations are carried out using estimated values for soil properties. On other projects, the cost of the structure is such that a few laboratory tests can be performed but the soils under the
structure are so highly variable that no reasonable number of consolidation tests would provide the needed information. In such cases, it would be desirable if the slope of the consolidation curve could be correlated with some soil property that is simpler to measure (and less expensive). These correlations
tions may be made by an individual firm for soil deposits encountered in their locale, or correlations may be developed that apply to soils with a common geologic origin. Several examples will be cited. Peck and Reed (1954) reported that
Moran et al. (1958) showed that
where w0 is the field water content in percent. Terzaghi and Peck (1967), based on a paper by Skempton (1944), showed that
where LL is the liquid limit. None of these correlations are exact, but when used with the soils for which
the correlation was developed, they are often accurate within 30%. Considering that soil properties sometimes change by more than 30% within a few feet or meters or less, such correlations may be sufficiently accurate and may yield far more accurate estimates than would be obtained by investing the
same money in a few consolidation tests.

A major source of uncertainty in using such correlations is the issue of whether or not the soil is normally consolidated in the field. Since the reloading index is usually four to six times less than the compression index, it is important to know whether to use the reloading index or the compression index. If no laboratory consolidation test results are available, the best estimate of whether a soil is normally consolidated or overconsolidated is obtained by comparing the strength of the soil in the field with the strength expected for a normally consolidated soil.