The Numerical Modelling of Shallow Foundation of Expansive Soil under Wet and Dry Cycles

Numerical Modelling of Expansive Soil

Abstract

The research paper investigates the behavior of shallow foundations on expansive shale soil under varying hydrological conditions, such as rainfall and drought. Expansive soil experiences volumetric changes due to fluctuating water conditions, resulting in differential movements of foundations. Settlement and swelling computations were simulated using Plaxis 2D FEM software under different soil saturation, loading, and rainfall conditions. The user defined swelling rock model was used to assess the variation of swelling with time numerically under different loading, dry and wet cycles. The first part of the study was to determine the swelling characteristics of expansive soil of study area of Jamshoro and model parameters such as cohesion, angle of internal friction, swelling pressure, swelling potential and modulus of elasticity. Laboratory testing and calibration was also performed to determine the model parameters. After this numerical modelling was performed with swelling rock model to observe the heaving of shallow foundation due to swelling of expansive soil in wet conditions.  Modelling in Plaxis 2D conducted model studies with a 100 kPa foundation pressure on shale soil, followed by unloading and saturation. Short-term heaving remained within tolerable limits. However, over 100 days, extensive vertical movement exceeding the tolerable limit was observed due to continuous shale swelling. Rapid water table increase caused significant vertical movement, but gradual rise reduced it. The depth of the shale layer, underlain by stiff limestone, significantly influenced foundation movement, even at 1 meter depth causing intolerable movements.