Ebook: Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering: 5-9 October 2009, Alexandria, Egypt (volume 5)

The International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE), the Egyptian Geotechnical Society, the Government of Egypt, and the city of Alexandria invited academics and practitioners in the field of geotechnical and ground engineering from around the world to attend the 17th International Conference on Soil Mechanics and Geotechnical Engineering (17th ICSMGE) on 5 to 9 October 2009. This quadrennial event ranks among the premier events in the field of geotechnical and ground engineering worldwide, and was held at the spectacular, international award-winning Bibliotheca Alexandrina on the coast of the Mediterranean Sea. A technical exhibition, a major component of the event, was held in parallel to the conference (5-8 October).

The geotechnical challenges the world faces are becoming increasingly more complex and interrelated. Geotechnical engineers have had to expand their thinking and develop new technologies to better integrate socio-economic and environmental issues into engineering solutions at the surface and below ground in our cities and towns, coastal areas and sea beds, and in a global context for the health of the earth. To prepare for the more challenging changes to come, closer collaboration among those who study, research, and practice geotechnical engineering is requisite. Thus, The Academia and Practice of Geotechnical Engineering was chosen as the main theme of the 17th ICSMGE.

The 17th ICSMGE provided a forum for academics and practitioners in the geotechnical engineering field to explore the future of the profession and what can be done to assure that society's needs and expectations are met. Interactive discussions, led by preeminent leaders in the field, addressed the research required to meet ever changing global issues. Participants also explored case studies that all could learn from, and identified the means and value in strengthening relationships among the engineering and construction communities, as well as the general public.

Egypt, the place where geotechnical engineering essentially began, was the ideal setting to determine the field's future directions.

P. Sêco e Pinto, ISSMGE President

M. Hamza, Chairman of XVII ICSMGE

In Albania are present many serious phenomena's as movement of terrains, landslides, slopes instability ect. All this problems are tied with the shear strength of soils. In this paper we would like to present a part of our study that determines the resisting characteristics of cohesive soils by different methods in laboratory. Also we would like to establish relations between resisting characteristics of soil determined by different methods and their correlation with physical and mechanical parameters of soil.

The monotonic shear response of natural low-plastic Fraser River silt was investigated using constant volume direct simple shear tests, employing specimens prepared from undisturbed field samples and by reconstitution of the same silt material at different initial confining stress levels. The specimens of undisturbed silt, despite having a looser density under identical consolidation stress conditions, exhibited extensively more dilative response and larger shear resistance in comparison to those displayed by counterpart reconstituted specimens. In addition to consolidation stress conditions and resulting void ratios, it appears that other naturally inherited parameters such as soil fabric and aging effects would critically influence the shear response of natural silt. It is possible that the shear response observed from reconstituted specimens may result in unduly conservative design parameters, in turn, demonstrating the value testing specimens from undisturbed samples to assess the expected field behaviour of natural silt.

GCLs used in landfill cover applications typically contain natural sodium bentonite. To examine the effect of ion exchange on the performance of GCLs, tests were performed in 60 cm diameter cells with 1 m of calcium rich soil below the GCL and a confining stress of 15 kN/m². The uptake of moisture and calcium from the underlying soil caused the moisture content of GCL to increase to 86% in the first 279 days of the test and then decrease to 68% after 625 days. The hydraulic conductivity of the GCL changed with cation exchange of Ca⁺⁺ for Na⁺ and varied from 1-3 × 10⁻¹¹ at the start of the test to 2 × 10⁻¹⁰ m/s after 625 days.

Bentonite, a smectite clay, is widely used in geotechnical engineering as drilling mud, liner material, and it has been proposed as buffer and backfill material for high-level nuclear waste disposal. An understanding of the microstructure formation of bentonite and its hydrophobic properties would enable the development of a methodology capable of predicting its behaviour when exposed to water. This study aims to gain an understanding of the microstructure formation of bentonite, specifically Kunigel-VI, by comparing its behaviour with that of a non-swelling clay, NSF Clay. Three different tests were performed to observe this behaviour: Constant Rate of Strain (CRS) consolidation testing, Mercury Intrusion Testing (MIT), and Scanning Electron Microscopy (SEM). Results indicated that aggregate formation occurred in both clays, but at water contents higher than 50 %, the aggregates in NSF Clay collapsed, while those of Kunigel-VI increased in number and size. An increase in applied pressure resulted in the dissipation of air, and a decrease in size of the intra and inter-aggregate spaces.

Due to the lack of environmental awareness and proper monitoring of wastes resulting from industrial facilities in Egypt; it is considered a common practice to dispose inorganic wastes in possibly unsuitable nearby land. This practice results in contaminating large areas of soil which, in turn, affects the construction activities in these regions among other hazardous environmental impacts. Generally, contamination of soil changes its mechanical behavior, specifically, its shear strength. This paper investigates the change in shear strength of soil due to the exposure of sand and sand mixed with fines to inorganic contaminant. Soil samples are prepared with 0%, 20% and 40% of fines. Samples are prepared at different compaction ratios and are mixed with 0%, 2%, 6%, and 10% of contaminant. The contaminant used in this research is an acid produced as waste from industrial detergents plants. Research results showed definite negative impact on the shear strength of the contaminated soil.

A number of elastoplastic models have been proposed for unsaturated soils over the past three decades. These models have generally taken the form of simple extensions of elastoplastic models previously proposed for saturated soils. Laboratory testing programs have given rise to several unanswered questions regarding the acceptability of these models for unsaturated soils. There are questions related to: 1.) the variation of the yield stress with soil suction, 2.) the modeling of soils prepared from slurry conditions, and 3.) the existence of a smooth transition between saturated and unsaturated soil conditions. The model proposed in this paper addresses each of these questions by re-formulating the elastoplastic model for unsaturated soils through use of independent stress state variables. The re-formulation provides a smooth transition between the elastoplastic model for saturated and unsaturated soil conditions.

It is recognized that the loads attracted to buried structures cannot be accurately estimated by simply considering the self-weight forces generated by the prism of soil supported by the structure. Incompatibility between the stiffness of a buried structure and the surrounding soil leads to the development of local soil arching around the structure, the degree of which is dependent on the relative stiffness between the structure and the surrounding soil. This arching can induce structural damage or collapse, or indeed can be utilized to optimize the efficiency of the structure. The paper presents numerical finite element analysis of the results of a series of scaled physical model tests conducted on a large fixed beam centrifuge designed to investigate the contribution of the deflection of structural elements (top slab and side wall) of a buried structure and local soil stiffness, to the overall loads attracted to the structure. The results of the test program have been interpreted to establish the contributions to the total load attracted to a buried structure from deflection of the top slab and the side-walls respectively. Results of comparative analyses using the finite element software Plaxis are presented.

This work presents results of the geotechnical characterization of an unsaturated residual mature soil of granite involved in a landslide which occurred in the city of Camaragibe situated in Pernambuco, Brazil. The geotechnical characterization of this material was performed including physical characterization, soil-water characteristic curve and shear strength (saturated and unsaturated condition). The soil-water characteristic curve was obtained through filter paper method, Haines Funnel and Richards pressure Chamber. The shear strength parameters were determined using direct shear tests (saturated condition) and direct shear tests with controlled suction, with suction varying from 0 - 500kPa (unsaturated condition). The results were discussed and compared with literature presenting satisfactory values.

The determination of geotechnical charactertiscs of waste rock is essential for addressing issues of in situ hydrology and the stability of steep and high-standing dumps. Based on laboratory investigations and numerical modeling, this paper gives the geotechnical properties of a selected waste rock under saturated and unsaturated conditions. Results indicated that the engineering behavior of the investigated waste rock is similar to granular soils and governed by the “well-graded” and “very angular” nature of the materials. The samples exhibited low air entry values (0.2 and 0.8 kPa) and low water storage (0.44) along with a high saturated hydraulic conductivity (1 × 10⁻⁵ m/s). The hydraulic conductivity dropped sharpely beyond the air entry value by up to eight orders of magnitude at 200 kPa. The shear strength was identical to loose coarse materials and was primarily derived from the angle of internal friction that measured 37° to 39°, similar to the angle of repose. Additional strength can be availabe in the form of effective cohesion due to clays and cementation and apparent cohesion due to matric suction.

A simple method is proposed to estimate suction values in unsaturated soils ranging from 1,200 to 60,000 kPa in this paper using the conventional tensiometer results and the Kondner (1963) hyperbolic model. The proposed method uses the initial tangent value of suction versus time response in the suction range of 0 to 50 kPa for estimating the equilibration suction value. The model was tested on the published results of suction versus time response of high capacity tensiometers from the literature and an experimental program undertaken on compacted glacial till specimens with reasonably good results.

This paper presents an innovative procedure to model collapsible soil before-during-after inundation using the finite element method. The proposed numerical model can easily be implemented to analyze the case of shallow or deep foundations on/in collapsible soils. The model developed takes into account soil suction reduction resulted from progressive inundation, from two different aspects: soil stress state and its properties, and irrecoverable volume change of the soil. The theories of Unsaturated Soil Mechanics, including Soil Water Characteristic Curve (SWCC), are employed to take into account the effects of inundation on collapsible soil properties. For illustration purpose, numerical modeling of a single pile in collapsible soil before-during-after inundation is presented.

The paper describes a series of laboratory tests that were carried out to quantify the saturated-unsaturated hydraulic properties of woven and nonwoven geotextiles in virgin condition and contaminated with kaolin fines. The test program included 1-D column tests of a single geotextile layer in sand subjected to surface water infiltration loading. The column tests showed detectable changes in rate of wetting front advancement in the vicinity of the geotextile layer consistent with a capillary break mechanism. Transient ponding of water above the geotextile was observed to vary with the initial unsaturated hydraulic conductivity of the geotextile. A numerical code was developed to simulate the 1-D column tests and numerical results are shown to be in good agreement with physical test results. The work reported here leads to the recommendation that the ratio of geotextile to sand saturated hydraulic conductivity may have to be greater than one to prevent lateral flow of water above a geotextile in sand fills used in wall, embankment and road applications.

A system capable of measuring both gravimetric and volumetric water content of unsaturated soils, at different soil depths, is presented. This system, based on the Time Domain Reflectometry (TDR), uses a new probe with helical electrodes assembled to a cylindrical core. The new probe was designed to work in conjunction with CPTU equipment. Tests performed in the field have demonstrated that the use of the proposed technique is perfectly feasible and could be of great usefulness in geotechnical applications.

The residual shear strengths of saturated sandy and silty soils are often estimated from the relationships between insitu penetration resistances and residual shear strength obtained from the back analysis of post failure geometries of embankments that suffered varying degrees of distress resulting from static rapid (undrained) loading. The procedures for back analysis employed so far do not account for viscous drag and strain energy. A simple procedure has been proposed herein approximately accounting for viscosity and strain energy. The results from back analysis of ten flow failure case histories using the proposed energy approach were used to develop a correlation between residual shear strength and Standard Penetration Test (SPT) blow counts.

Effective stress shear strength parameters for cohesive soils are important parameters in geotechnical analysis and design. These parameters can be determined by carrying out consolidated undrained tests with porewater pressure measurements. Those parameters can be also determined based on interpretation of piezocone penetration tests. The current state of the art status had not reached to a level where reliable estimate of effective stress shear strength parameters can be made from the CPTU data. The aim of this paper is to provide additional data on both effective stress shear strength data measued from isotropically consolidated undrained triaxial tests and CPTU data for normally consolidated to slightly overconsolidated clay from the Nile delta deposits based on geotechnical investigations in nine major sites in Egypt. It is beleived that the addition of this data to the literature provides a better ground for improving the current state of the art of estimating effective stress shear strength parameters from the CPTU data. With such beleif, the data are used to evaluate and modify the available method(s). Such an exercise empirically contributed to judgment of angle of plastification and modification of bearing capacity factor, N_q, in the Senneset-Janbu method.

Floating Production Storage Offloading (FPSO) Vessels are widely used in offshore oil and gas industry. In offshore Atlantic Canada, mooring piles driven in the seabed, in water depths ranging from 80 to 200 m, are used to moor these FPSOs. These mooring piles are subjected to oblique pull forces. In this paper, a 3D finite element method has been used to study the behaviour of steel pipe piles in saturated sand under mooring forces. The main objective of the present study is to check the validity of the available theoretical models in the literature. It has been found that most of the previous theoretical models should be modified to consider the prototype behaviour.