Essam Badrawi Attia

Soft clay layers beneath embankments could cause slope instability and excessive settlement under embankment loads. Previous studies have not investigated the use of Pu-Foam piles as a partial vertical replacement within soft clay layers to reduce the consolidation of the embankment body. The main purpose of the present study is to conduct a more comprehensive slope stability evaluation using 3D numerical modeling by Abaqus software, investigating the effect of soil shear strength parameters and limiting values of slope settlement. The effectiveness of polyurethane (Pu) foam piles is investigated as a ground improvement technique. The study offers practical insights into optimizing Pu pile configurations for safer, more reliable embankment design. Furthermore, a set of practical design charts is developed based on the comprehensive analysis of all modeled cases. These charts are designed to aid engineers in evaluating the safety factors of improved slope systems under similar conditions. It was found that Pu-Foam piles should extend till the firm soil. The optimum values of improved area ratio ranged from 40% to 50% and the Pu-Foam piles stress sharing ratio could be up to 90%.

Geosynthetics are man-made materials used to increase the tension, compression, and shear characteristics of soil. Geogrid-reinforced material is regarded as one of the most widely used soil reinforcements. The Abaqus software (Ver. 2017) is used to simulate a 3-D fine sand model. The load-carrying capacity is investigated for both unreinforced and geogrid-reinforced fine sand supporting a 2.0m x 2.0m square footing. The relative density (Dr) of un-reinforced fine sand is 40%, the geogrid axial stiffness (J) used in the analysis varies at 250 kN/m, 500 kN/m and 1000 kN/m. The bearing capacity ratio (BCR) of geogrid-reinforced fine sand is influenced by the use of geogrid-layers with different axial stiffnesses (J). The influence of geogrid axial stiffness is evaluated using four investigated parameters: geogrid-layers number (N), vertical spacing (h/B), geogrid width/length (b/B), and first geogrid-layer depth (u/B). The results show that the numerical model validation agrees with the experimental results of Hotti and Gupta with an agreement ratio of 98% and 93%, respectively. The geogrid-reinforced fine sand with appropriate dimensions and proper geogrid-layers number has significantly increased the square footing bearing capacity. The load-bearing capacity of geogrid-reinforced fine sand increases with geogrid axial stiffness. The bearing capacity ratio is 1.45 and 2.13 when the geogrid axial stiffness increases from 250 kN/m to 500 kN/m and from 250 kN/m to 1000 kN/m, respectively. The most efficient and economical values of (u/B), (b/B), (h/B) and (N) are 0.30, 3.0, 0.15 and 3.0 for all values of geogrid axial stiffness, respectively.

Fine-sand soils cannot support the design loads due to their low load-bearing capacity. Soil reinforcement with geogrid-layers is a common technique to increase the low bearing capacity of fine-sand. Using the commercial finite element analysis package Abaqus (Ver. 2017), a three-dimensional numerical model is used to determine the effect of geogrid-aperture size on the square footing bearing capacity of geogrid-reinforced fine-sand. In the numerical analysis, the geogrid-aperture size ratio ranged from 1.0 to 4.0. These variations in the geogrid-aperture size ratio were used to estimate the effect of first geogrid-layer depth (u/B), geogrid-layer width (b/B), vertical spacing between geogrid-layers (h/B), and geogrid-layers number (N) on bearing capacity ratio (BCR) and horizontal stresses that were transferred to the fine-sand through geogrid-layers. The bearing capacity of a square footing on geogrid-reinforced fine-sand increases with inclusion of a geogrid-layer, provided it has the appropriate dimensions and numbers. The horizontal stresses transferred to the fine-sand through the geogrid-layers also increased. The results indicate that the interlocking between fine-sand and the geogrid-layers increases due to the reduced movement of fine-sand particles. For the variation of geogrid-aperture size ratio from 1.0 to 4.0, the maximum decrease rates of the (BCR), HSR-(Cross), and HSR-(Machine) values are 12.06%, 15.25%, and 18.22%, respectively. The optimal values of (u/B), (b/B), (h/B) and (N) are 0.3, 3.0, 0.15, and 3.0 for all values of geogrid-aperture size ratio. For the maximum (BCR) values of the square footing on fine-sand, using a biaxial geogrid-layer is considered more efficient than using a uniaxial geogrid-layer.

One of the most popular methods for improving weak soil properties is soil reinforcement with geogrid-layers. The geogrid-layer increases the low shear resistance of fine sand, thereby reducing the cost of soil improvement methods. The Abaqus 3-D model is utilized to simulate large-scale direct shear apparatus. Numerical models are conducted on geogrid-reinforced fine sand to estimate how geogrid-axial stiffness affects the shear strength behavior. Shear parameters, shear strength ratio, internal shear coefficient, and mobilized geogrid tensile strength are studied in both longitudinal and transverse directions. The steel box for large-scale direct shear consists of two separate parts with dimensions of 200 mm x 200 mm x 100 mm. A geogrid-layer with different axial stiffness between 200 kN/m and 1000 kN/m with an increment of 100 kN/m is fixed between the two separate parts to estimate the shear resistance increase of geogrid-reinforced fine sand. The shear strength of geogrid-reinforced fine sand increases with geogrid-axial stiffness; for the fine-sand elastic modulus of 10 MPa, the shear strength ratio (SSR) increases from 1.80 to 3.10 when the geogrid-axial stiffness increases from 200 kN/m to 1000 kN/m. However, the (SSR) values decreased with increasing fine-sand elastic modulus, the (SSR) values were 1.0 and 1.60 for the variation of geogrid-axial stiffness from 200 kN/m to 1000 kN/m when the fine-sand elastic modulus increased to 40 MPa. The most economical and optimal values of geogrid-axial stiffness are 500 kN/m and 300 kN/m for fine-sand elastic moduli of 10 MPa and 40 MPa, respectively.