علي عبد الشهيد جاسم الجزائري

Allowable-bearing capacity is the competency of soil to safely carries the pressure from the superstructure without experiencing a shear failure with accompanying excessive settlements. Ensuring a safe bearing pressure with respect to failure does not tolerate settlement of the foundation will be within acceptable limits. Therefore, settlement analysis should always be performed since most structures are settlement sensitive. When visualising the movement of a soil wedge in the bearing capacity criterion, both vertically and horizontally, it becomes clear that by confining the soil surrounding the foundation, both the bearing capacity and settlement values improve. In this study, two sizes of spread foundation were considered; (2×4) m and (3×5) m. These represent two real problem case studies of an existing building. The foundations were analysed in terms of dimension as well as position with respect to a confining wall (i.e., sheet piles on both sides). Assuming B is the least foundation dimension, the study comprised the analyses of three distances; (0.1 B), (0.5 B), and (0.75 B) between the sheet piles and foundations alongside three depths of confinement (0.5 B), (1 B), and (1.5 B). Nonlinear three-dimensional finite element analysis (ANSYS) was adopted to perform an analytical investigation on the behaviour of the two foundations contained by the case study. Results showed that confinement of foundations reduced the overall stresses near the foundation by 65% and reduced the vertical displacement by 90%. Moreover, the most effective distance between the confinement wall and the foundation was found to be 0.5 B.

This paper sheds the light on the interaction between piles under lateral loadingconditions embedded in sandy soils and adjacent to cavities. The experimental study comprised a full laboratory testing programme carried out on small scale piles embedded in a soil mass with predetermined cavities. The experimental model has the capability to investigate the effect of different cavity locations on the ultimate pile resistances, bending moment along the pile length and pile rotation with the y-axis. Eighteen cavity locations were chosen in order to obtain a thorough investigation on how the ultimate load capacity of single piles is affected by their presence in sandy soil. It is concluded that reductions in pile capacities caused by cavity presence was ranged from 0% - 43.3% for the active side of pile while on the passive side was from 1.8% to 22%. No effect on pile capacities was registered for cavities located under the pile base. Pile settlement, bending moment and rotation values were also influenced by the presence of cavities in different ratios.

Presence of cavities in soil predictably induces ground deformation and changes in soil stress, which might influence adjacent existing pile foundations, though the effect of twin cavities on a nearby pile needs to be understood. This research is an at tempt to identify the behaviour of piles subjected to axial load and embedded in cavitied clayey soil. A series of finite element modelling were conducted to investigate the performance of piled foundation located in such soils. The validity of the numerical simulation was evaluated by comparing it with available field test and alternative analytical model. The study involved many parameters such as twin cavities size, depth, spacing between cavities, and eccentricity of cavities from the pile axis on the pile performance subjected to axial load. The study involved many cases; in each case, a critical value has been found in which cavities’ presence has shown minimum impact on the behaviour of pile. Load-displacement relationships of the affecting parameters on the pile behaviour were presented to provide helpful information for designing piled foundation situated near twin underground cavities. It was concluded that the presence of the cavities within the soil mass reduces the ultimate capacity of pile. This reduction differs according to the size and location of the cavity.

Presence of cavities in soils is an important area of interest within the field of geotechnical engineering. A better understanding of the behaviour of such soils, particularly in locations where the presence of gypsum deposits is apparent, will have a large impact on the stability of foundations and allows designers and engineers to have a convincing explanation of this phenomenon on the stability of foundations in general. The research offers an experimental investigation to study the performance of axially loaded piles embedded in sandy soils with cavities. The experimental study comprised a full laboratory testing programme carried out on small scale piles embedded in predetermined cavities within a soil mass. The experimental model has the capability to investigate the effect of different cavity locations on the ultimate pile resistances. Thirteen cavity locations were chosen to study their influence on the ultimate carrying load of single pile. It was concluded that the maximum ultimate carrying load of the pile is reduced by the presence of the cavity within the soil mass. This reduction varies according to the cavity location. The effect of cavity’s presence on the ultimate bearing capacity of pile ranged from 0% to 30.82% for side cavities, while the range of reduction factor for cavities under the pile tip is from 31.58% to 43.4%. The reduction in pile capacity increases when the cavity is closer to the pile. Also, pile settlement value without cavity is less than the settlement of the same pile with cavity.

Response of single pile subjected to lateral displacements of soil mass using 3D finite element software (PLAXIS) is studied. Embedded pile feature in which the pile composed of beam elements with special interface elements to represent pile-soil interaction is used. The Mohr–Coulomb elastic–plastic constitutive model was employed for the soil stress-strain behaviour. A good agreement between laboratory and predicted results is observed in the validation analysis. A parametric study was conducted to investigate the influence of soil Young's modulus and soil movement profile on the response of single "passive pile". The software results revealed that the distribution of bending moment along the pile length vary considerably and was in a very good agreement with the real pile behaviour when adopting a variation of soil elastic modulus with depth instead of choosing a constant value.