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The presence of underground voids within a failure zone usually results in a reduction in the bearing capacity of footings. This paper presents results for the ultimate bearing capacity ratio, qu/γB, of a strip footing on top of a sand layer overlying a clay layer with voids, with and without the placing of geotextile reinforcement at the interface between the sand and clay layers. Using the finite difference software FLAC 2D, the bearing capacity ratio of the strip footing was calculated for voids with different depths and horizontal distance for two configurations: parallel and symmetrical. The effect of parameters on the ultimate bearing capacity ratio was also investigated, including the undrained shear stress ratio of the soil, the thickness of the top layer and the size, location, height, width and spacing of the voids, with and without placing of geotextile layers at the interface between the sand and clay layers. It was found that the influence of a void on the ultimate bearing capacity ratio of the strip footing vanished when the void was located outside the failure zone beneath the footing and increased further with reinforcement until it reached a constant limit value.

In this paper, numerical computations using the FLAC code are carried out to investigate of the behavior the bearing capacity of strip footings embedded in sandy soil and under large eccentric vertical load conditions. The study focuses on an evaluation of the non-dimensional reduction factor (RF), which is the ratio between the average bearing capacity of an eccentric footing and its bearing capacity when subjected to a central load. The results indicate a significant decrease in RF when the eccentricity increases and the curve of the decrease is parabolic, even in large eccentricity cases. Based on the numerical results obtained, a new formula of the RF is proposed, and the reasons for the discrepancy between the RF proposed by several authors are identified. The values provided by the proposed formula are in close agreement with some experimental results available in the literature.

The present research work is concerned with the construction of road embankments on a Sabkha soil in Algeria. This soil is not only soft and very humid during the flooding seasons but also has frequent small areas of very soft soil which are called locally weak zones (LWZ) in the context of this study. LWZ are characterized by low strength and high compressibility. Two-dimensional axisymmetric analyses were carried out using PLAXIS 2D 2017. The study demonstrated that ordinary stone columns (OSC) are ineffective given the nature of these soils due to the excessive bulging caused by the lack of lateral pressure. On the other hand, the reinforced stone columns with external and internal reinforcements called as vertical encasement and horizontal strips (VESC+HRSC) are one of the best improvement methods of locally weak zones (LWZ), especially to increase the stability of embankment on the highway, namely, a much reduced bulging and a reasonable settlement, so that it is possible to build safe and very high embankments (indeed, numerical results showed for a (VESC+HRSC) combination, a vertical settlement of 0.74 m and a lateral deformation of 20.02 mm vs. 1.56 m and 221.16 mm for an OSC). Besides, an extensive parametric study was conducted to investigate the effect of the spacing of the horizontal reinforcing strips and of the column reinforced length. The influence of stone column diameter, depth of locally weak zone, and the effective stiffness of the geosynthetic, on the performance of the (RSC) - embankment composite were also investigated. The computational results are presented in the form of tables and graphs, and compared with previous published results available in the literature.