Ammar Nechnech

Prediction of axial capacity of piles driven in non-cohesive soils based on neural networks approach

AbstractThis paper presents an application of two advanced approaches, Artificial Neural Networks (ANN) and Principal Component Analysis (PCA) in predicting the axial pile capacity. The combination of these two approaches allowed the development of an ANN model that provides more accurate axial capacity predictions. The model makes use of Back-Propagation Multi-Layer Perceptron (BPMLP) with Bayesian Regularization (BR), and it is established through the incorporation of approximately 415 data sets obtained from data published in the literature for a wide range of un-cemented soils and pile configurations. The compiled database includes, respectively 247 and 168 loading tests on large- and low-displacement driven piles. The contributions of the soil above and below pile toe to the pile base resistance are pre-evaluated using separate finite element (FE) analyses. The assessment of the predictive performance of the new method against a number of traditional SPT-based approaches indicates that the developed ...

Contribution to the Behavior Study and Collapse Risk of Underground Cavities in Highly Saline Geological Formations

The problem of saline soils reserved from occupation at Oran, North Algeria remained relatively unexplored or little known until recent years. Consequently, some studies were conducted, especially to characterize the real impact of an airport on these soils. The characterization of the real problems of saline soils, as well as the study of the behavior of their collapse under the coupled effect of thermal, mechanical and hydraulic, remains poorly known specially under an airport, where the instabilities and the risks of sudden collapses is an unknown problem for the authorities and citizens and the impact on the environment is not mastered. Under the action of water charged with carbon dioxide which dissolves the limestone, chalk or gypsum, many natural cavities are created. There are also pockets of dissolution filled with silt in the chalk, due to the irregularity of the contact chalk/silt. The flow of water can also enlarge the fractures at depth causing the silt that fills them and thus creating a surface subsidence due to infiltration. This phenomenon is found mainly in the dry valleys. To account for the effect of the hydro-thermomechanical coupling in predicting the collapse of saline soils, solutions were proposed for improvement of saline soil with a geosynthetic reinforcement, drainage, etc. These solutions are necessary for the proper design of airfield runways to avoid a disaster.

Development of Semi Empirical Method for Predicting Axial Pile Capacity

This study aims to estimate the axial pile capacity through the use of semi empirical analysis based on limit equilibrium theory and SPT data. An interesting alternative for improving the quality of bearing capacity prediction from the rational methods of plasticity is the definition of the required mechanical parameters, by correlation with those obtained from in-situ tests. In this context, Aback-calculation of mechanical parameters required by the numerical method has been carried out for calibrating the calculated limit vertical load to the interpreted load tests. It is established through the incorporation of approximately 60 data sets of pile loading tests on driven piles in sandy soils obtained from data published in the literature. Consequently, base and shaft resistances factors are estimated. The assessment of the predictive performance of the new method against a number of traditional SPT-based approaches indicates that the developed method can be used as an alternative for determining the bearing capacity of piles in geotechnical practice. For practical purposes, the end and shaft bearing resistances factors were proposed in relation with the N-SPT value.

Hydromechanical behaviour of an unsaturated Algiers clay

This article presents the results of the volumetric behaviour of an Algiers clayey soil. An experimental work was carried out both in situ (core drilling; pressuremeter testing) and in the laboratory (drying–wetting and oedometric tests). Drying–wetting paths of soil samples were obtained using vapour equilibrium method and osmotic technique. These suction-controlled methods have gained widespread acceptance as reliable methods for imposing suction on soil specimens. They allowed for tests to be performed in the range of suction comprised between 0 and 300 MPa. The ability to impose suction on soil specimens allows for drying and wetting stress paths to be imposed to evaluate resulting changes in void ratio, degree of saturation and water content. These paths were explored at different initial states of clay. Slurries of soil were used to characterise the reference behaviour, whereas undisturbed soil samples allow characterising the material under in situ conditions.

A Comparative Study of Hydromechanical Properties in Saturated and Partially Saturated Conditions of Two Soils from the Runway of Oran Airport

This study concerns the ground soils of the second runway of the Es-Sénia airport in Oran (Algeria). This airport was built on a very complex hydro geotechnical site when underground cavities, following the dissolution of gypsum soil, were found during the before-construction geologic studies. Several, techniques are used in laboratory (Permeability, triaxial compression tests at various confining pressure, and hydric tests in saturated and unsaturated conditions) and for in situ it’s used the results of SPT and pressure-meter tests. A comparison of parameters of two soils identified in saturated and partially saturated conditions by in situ and laboratory tests was performed in order to respond to questions of the similarity of hydro mechanical properties of two soils as well as their statistical representativeness of the in-situ reality. It is found that, in respect to the studied parameters, laboratory results are statistically significant and reconstituted soils is statistically representative of natural soil reconstitution.

Shear reinforcement effect of reinforced concrete tie-columns on the lateral resistance of confined masonry walls

Tie-columns improve significantly the lateral resistance of masonry bearing walls against persistent, transient and accidental loads. The research work described herein has been carried out to assess the lateral resistance of confined masonry walls, where contribution of the masonry panel is evaluated according to material mechanics and tie-columns effect is estimated by a proposed analytical formulation based on a model reported on previously. This approach takes into account the effect of dowel support on the reaction of its adjacent shear reinforcement: the conditions for the various contributions of transverse reinforcements are better defined following a clear evaluation of the participation ratio of these reinforcements. Lateral resistances of confined masonry walls measured in full-scale tests and gleaned from the literature are compared and checked with resistances calculated using the present approach.

Setback Distance Between Natural Slope and Building Along the RN8 in Algeria

The objective of this study is to determinate the required distances between the natural slopes and the buildings located nearly to these slopes. This approach permits to determining the distance between a building and the crest of a natural slope. The analysis of this case uses the geotechnical engineering and the results are applied during the design of the master plan by the town planners and the engineers of the transport and pavement administration. This study is limited to only the stability of natural slopes and the phenomenon of erosion is not taken into account.