THE ROLE OF STRUCTURAL COHESION IN CLAY SOILS IN THE EVALUATION OF SOIL BASES BEARING CAPACITY

Abstract

The article examines the causes of bearing-capacity failures in foundations of buildings and structures situated on sloping areas in Republic of Moldova, focusing on the response of Sarmatian clay foundation soils, which exhibit time-dependent strength reduction and variations of shear resistance when subjected to prolonged loading. The experiments included tests on undisturbed monolithic samples using a direct shear apparatus at various levels of normal stress, as well as an evaluation of residual and long-term strength in accordance with the principles of the physico-technical theory of creep. The obtained data indicate that the investigated clays are characterized by a significant structural cohesion (average value of approximately 60kPa) and a relatively low internal friction angle of 7-12° (average around 9°). It was established that the application of long-term loads leads to a pronounced reduction in shear strength parameters: the long-term strength reaches approximately 40kPa, while the residual strength is on the order of 20kPa. Calculations of ultimate bearing capacity showed that, depending on the applied stress level, the permissible bearing capacity of the foundation may decrease by 2.5-3 times compared to the initially determined values. These findings highlight the need to account for time-dependent strength degradation when designing foundations on Sarmatian clays and emphasize the importance of accurately determining soil strength parameters, particularly the structural cohesion.