SHANSEP-Based Approach to Account for Consolidation Induced Strength Gain in Capacity Assessment of Shallow Foundations

Abstract

Abstract It is well recognised that soil strength increases with time due to consolidation under sustained foundation load. This is typically termed ‘consolidation strength gain’. Quantification of such beneficial effect on the foundation capacity, however, is not straightforward for design. In this paper a practical approach is described to account for this effect in the design of shallow foundations on seabed dominated by fine-grained sediments. This approach is based on the relationship of Stress History and Normalised Soil Engineering Properties (SHANSEP), and featured by a consistent procedure throughout the processes from soil characterisation to foundation capacity assessments. The SHANSEP relationship can be parameterised during the site characterisation stage and is used in the numerical modelling to estimate strength increase due to consolidation effects, which in turn is used in the capacity calculations of a mudmat foundation. Data from a deepwater project is used to demonstrate the entire process. The beneficial effect of consolidation on the foundation capacity is illustrated through the expansion of the failure envelopes in the horizontal-vertical-moment load space. The magnitude of such effect is expected to vary between soils and interface conditions and be affected by the consolidation load and consolidation period. However, in general the horizontal and torsional capacities are expected to increase more significantly than the vertical and moment capacities.