At-Rest Earth Pressure Coefficient K0: Formulations, Physical Assumptions, and Engineering Implications

The coefficient of earth pressure at rest, K0, is central to defining initial stress states in soils, yet its estimation remains uncertain because formulations differ in calibration basis, governing variables, and physical meaning. This review examines and compares more than 40 analytical, empirical, experimental, and constitutive-model-based approaches for estimating K0. The formulations are classified by soil type, stress history, determination method, and limitations, covering friction-angle- and OCR-based correlations, laboratory testing, in situ inference, and field-oriented developments. The comparison shows that values reported under the common notation K0 are not necessarily equivalent, because they may represent different loading paths, material states, or interpretations of zero lateral strain. For the selected friction-angle-based formulations, extreme predictions define a relatively broad envelope, whereas most expressions cluster within a narrower band. However, this variability does not translate uniformly into engineering response. Its significance depends on soil type, stress history, and whether the initial stress state persists or is modified by construction-induced deformation and stress redistribution. The unresolved issue is therefore not the absence of estimation methods but their limited transferability across geotechnical contexts. K0 should consequently be selected as a modelling parameter with explicit consideration of its physical basis, applicability, and expected influence on the problem under analysis.