Numerical Modeling of the Effect of a Weak Zone on the Bearing Capacity of Strip Footings

This study presents the results of a comprehensive numerical modelling that was conducted to investigate the effect of different variables and parameters on the ultimate bearing capacity, qu, of strip footing on a sand layer underlying a clay deposit soil layer with a localized weak zone. The numerical model was developed using the finite difference FLAC2D software. The parameters investigated in this study are the thickness of the top sand layer, the undrained shear stress ratio of clay soil, and the location, depth, width, and height of the weak zone. The results clearly showed that the ultimate bearing capacity of strip footing, qu, decreases due to the presence of a weak zone, with the degree of reduction is a function of the soil properties and the weak zone parameters (depth, location and geometry), the value of qu increases with increasing the normalized thickness of the top sand layer, H/B, and with increasing the normalized vertical and horizontal distances of the weak zone (Yw/B, Xw/B). However, the qu value decreases significantly with increasing the normalized width and height of the weak zone (Bw/B, Hw/B) up to certain limits, where the reduction is negligible. However, the value of qu significantly increases with the increase in the shear strength of the clay layer, which indicates that higher shear strength of soil reduces the effect of the weak zone on qu, and therefore the weak zone has a different effect on different soil type and different soil strengths.