Adel Hanna

Evaluation of liquefaction potential of soil deposits using artificial neural networks

Purpose – In the literature, several empirical methods can be found to predict the occurrence of nonlinear soil liquefaction in soil layers. These methods are limited to the seismic conditions and the parameters used in developing the model. This paper seeks to present General Regression Neural Network (GRNN) model that addresses the collective knowledge built in simplified procedure.Design/methodology/approach – The GRNN model incorporates the soil and seismic parameters of the region. It was developed in four phases; identification, collection, implementation, and verification. The data used consisted of 3,895 case records, mostly from the cone penetration test (CPT) results produced from the two major earthquakes that took place in Turkey and Taiwan in 1999. The case records were divided randomly into training, testing and validation datasets. Soil liquefaction decision in terms of seismic demand and seismic capacity is determined by the stress‐based method and strain‐based method, and further tested w...

Mode of Failure of a Group of Stone Columns in Soft Soil

AbstractThe design of stone columns is currently based on theories developed for a single column, ignoring the group interaction and therefore the group efficiency. Whereas single stone columns mainly fail by bulging, a group of stone columns may fail by bulging or shear of the entire soil/columns mass. A numerical model was developed to simulate the case of a single stone column and a group of stone columns installed in soft clay. The model establishes the level of interaction between individual columns and therefore determines the mode of failure of a given geometry, soil, and loading condition. The model was validated with the available experimental data in the literature and used to generate data for a potential mode of failure. This parametric study is conducted to examine the effect of the parameters believed to govern the mode of failure and includes modulus of elasticity of the stone column material and the clay, column diameter, and the spacing and angle of shearing resistance of the column mater...

Effect of Compaction Duration on the Induced Stress Levels in a Laboratory Prepared Sand Bed

In foundation engineering, due to the complexity of the problems investigated, the need for laboratory testing of prototype models arises. The results of these tests are usually utilized to validate theories, or to develop empirical formulae for design purposes. The success in obtaining good predictions from these theories and empirical formulae lies heavily on the reliability of the experimental test results, and accordingly, on the test setup used and the procedure followed. In literature, a wide range of discrepancies can be found among various design theories for shallow and deep foundations in cohesionless soils. These discrepancies can be explained by the fact that the in situ stress levels in the prototype model have not been evaluated but rather ignored, in developing design theories. Accordingly, different theories may generate different results, depending on the techniques and procedures followed in developing the experimental results used to validate the theory. This paper presents the results of an experimental investigation on the effect of compaction duration in a prototype model on the mechanical properties, and the induced stress levels in the sand mass. The results of this investigation should develop some awareness of the validity of using the results of model testing as a guide in developing design theories. Furthermore, attempts should be made to measure and incorporate the in situ stress level as a governing parameter in design theories.

Identification of collapsible soil using the fall cone apparatus

Soils that go through a great loss of volume upon wetting with or without additional loads are identified as collapsible. In recent years, there has been an increasing awareness of this type of soil due to the expansion of urban developments to arid regions. Also man-made earth structures often exhibit collapsing behavior when compacted at water content less than the optimum moisture content. In the literature, methods can be found to predict this behavior based on field and laboratories test results. These methods, however, are time consuming and developed for the type of soils tested. This paper presents the results of an experimental investigation on collapsible soils using the fall cone and the oedometer apparatuses. The fall cone method, originally developed to determine liquid and plastic limits of soils, was adopted in this investigation to identify its collapse potential. A cone penetration limit (Plim) is introduced to identify collapsible soil and a correlation between the collapse potential, CP, and the cone penetration, P, was developed and validated with the present experimental results and those available in the literature. Furthermore, a simple procedure is introduced to determine the optimum Proctor Moisture Content for collapsible soils from the results of the cone test. The proposed procedure is simple and fast to evaluate soil collapsibility by a single reading of the cone penetration.

Bearing Capacity of a Group of Stone Columns in Soft Soil

Installation of stone column is a viable, cost effective, and environmentally friendly ground-improvement technique. Columns are made of compacted aggregate and are installed in weak soil as reinforcements to increase the shear resistance of the soil mass and, accordingly, its bearing capacity. While a single stone column mostly fails by bulging, a group of stone columns together with the surrounding soil may fail by general, local, or punching shear mechanism, depending on the soil/columns/geometry of the system. The mode of failure of the reinforced ground could be identified based on the ground geometry and strength parameters of both stone column and soft soil. This paper presents an analytical model to predict the bearing capacity of soft soil reinforced with stone columns under rigid raft foundation subject to general shear-failure mechanism. The model utilizes limit-equilibrium method and the concept of composite properties of reinforced soil. The proposed theory was validated for the case of bearing capacity of footings on homogenous soil and via the laboratory and numerical results available in the literature for this case. Design procedure and charts are presented for practicing purposes.

Numerical Modeling of Piles in Collapsible Soil Subjected to Inundation

Collapsible soil exhibits considerable strength when it is dry, but when it is inundated, it loses its strength and experiences significant volume reduction. Foundations on collapsible soils subjected to inundation may experience sudden settlement without any increase in the in situ stress level. Pile foundations are often used to penetrate layers of collapsible soil to transfer the load to a lower, stronger soil layer. Nevertheless, because of indentation, these piles may experience negative skin friction, which may lead to significant reduction in the pile capacity, or perhaps separation of the pile from its cap. In the literature, although several theories can be found dealing with the design of pile foundations and the prediction of negative skin friction on these piles, little to none was found to estimate the negative skin friction because of the sudden collapse of the surrounding soils. This is mainly because of the difficulties associated in modeling collapsible soil experimentally or numerically. This paper presents a numerical model, which is capable of incorporating the effects of inundation of collapsible soil, and the negative skin friction on axially loaded vertical piles. The model uses the theories of the unsaturated soil and soil-water characteristic curve to estimate the effect of soil suction because of progressive inundation. The procedure takes place by estimating the change in the soil properties and the irrecoverable soil-volume change during inundation. The paper also presents the results of laboratory tests conducted on a single pile driven in collapsible soil subjected to inundation. The measured values of the negative skin friction compared well with the predicted values from the numerical model presented. The pile design guideline is also presented to assist designers in predicting negative skin friction because of inundation. Furthermore, the theory developed can be used to evaluate the condition of an existing pile foundation driven in collapsible soil and to establish the remedies needed to avoid catastrophic failure.

3D Numerical Model for Piled Raft Foundation

AbstractLoad sharing of piled raft foundations is known as an economical design for deep foundations. Nevertheless, research in this area has been lagging because of the complexity of the problem and lack of field data. Numerical modeling can be used to provide valuable data with a high level of success. A three-dimensional finite-element model of a piled raft foundation was developed to simulate the case of a piled raft foundation. The model accounts for pile-to-pile, raft-to-pile, pile-to-soil, and raft-to-soil interactions. The model was used to examine the effect of the key parameters governing the performance of this foundation during loading and, accordingly, the load shared by the piles and the raft. After validating the numerical model with available data in the literature, the model was used to develop data for a wide range of parameters and to examine the role of the foundation geometry, including pile spacing in the group, pile length, pile shape, pile diameter, and raft thickness. Furthermore,...

Prediction of collapse behaviour in soil

ABSTRACT The drastic decrease in volume of a natural, unsaturated soil deposit or compacted fill that occurs upon wetting at virtually constant total stresses is termed “collapse”. Several methods can be found in the literature that predict collapse behavior based on easily obtained soil parameters. Nevertheless, discrepancies were reported among the results of these methods. This paper presents the results of an experimental investigation on carefully conducted laboratory prepared collapsible soils in the oedometer apparatus. These results were used to develop an empirical model for predicting soil collapse in terms of the initial dry unit weight, initial water content and the soil gradation. The values predicted by the proposed model agreed well with the experimental results of the present investigation and those available in the literature.

Experimental Investigation of Foundations on Sensitive Clay Subjected to Cyclic Loading

AbstractSensitive clay subjected to cyclic loading may experience gradual loss of its shear strength, which may lead to a significant reduction in its bearing capacity, excessive settlement, and perhaps catastrophic failure. This may be caused by the cyclic loading, which acts as a disturbing agent and a major cause for increasing pore-water pressure, leading to leaching of salt content and the failure of the card house structure of the sensitive clay. This paper presents the results of an experimental investigation on sensitive clays subjected to cyclic loadings under undrained and drained conditions. Tests were conducted to examine the effects of cyclic loading, deviator stress, load frequency, preconsolidation pressure, overconsolidation ratio, confining pressure, sensitivity, liquidity index, and degree of saturation on the shear strength of sensitive clay. Depending on the combined effect of governing parameters, the shear strength of the clay may significantly be reduced, and the clay may reach a li...

Performance of Reinforced Collapsible Soil

Geotechnical engineers face serious problems when construction sites contain collapsible soils, which are known by their strength when dry and experience sudden and excessive settlement when inundated. The amount of soil collapse depends on the extent of the wetting zone and the degree of saturation reached when the surface water is the source of inundation. On the other hand, full saturation of the collapsible soil and accordingly, the maximum collapse are expected when the source of inundation is the rise of groundwater table. In this thesis, experimental investigation was carried out on prototype set-up to simulate the case of a surface rigid strip footing resting on collapsible soils. The objective of this research has been to evaluate the collapse settlement of the footing when the collapsible soils are subjected to full inundation due to the rise of ground water table. The case of footings on homogeneous collapsible soils having various collapse potentials, heights and applied stresses were first examined. Then, the case of footing resting on partially replaced collapsible soils by compacted sand was tested to establish the optimum thickness of the soil replaced on the collapse settlement of these footings. In addition, tests were carried out on these footings where geosynthetic layers were placed at the interface between the replaced and the collapsible soil layers and within the replaced soil layer. Analytical and empirical models were developed to predict the collapse settlement of these footings for a given soil / replacement layer / geotextile layer conditions. Design procedures and charts were provided for practicing use.