Ebook: Proceedings of the 5th International Young Geotechnical Engineers' Conference

The iYGEC conference series aims at bringing together young people who may be studying for a PhD or MSc or at the early stage of their career in engineering or academia. The idea is to enable delegates to communicate with others who are doing research or starting out in the geotechnical profession and to share their experience. Traditionally, the participants are selected by their respective member society. For this 5th edition of iYGEC, the participation is extended to all young geotechnical engineers.

The book presents the Proceedings of the 5th iYGEC held at Ecole des Ponts ParisTech, Marne-la-Vallée, France, on August 31–September 1 2013. This event was organised by the French Society of Soil Mechanics (CFMS) under the auspice of the International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE).

The papers published in these proceedings were peer-reviewed by experts in the field of geotechnical engineering. The topics covered are quite large, including laboratory testing, field testing, geology and groundwater, earthworks, soil behaviour, constitutive modelling, ground improvement, earthquake, retaining structures, foundations, slope stability, tunnels and observational method.

We would like to acknowledge the work done by the reviewers, for their fundamental contribution in ensuring the quality of the published papers. We also gratefully acknowledge the financial supports from the ISSMGE and the CFMS, which were absolutely essential for providing a good condition for our young geotechnical engineers, especially in terms of accommodations and registrations.

We do not forget of course to acknowledge the assistance of Ms. Séverine Beaunier (Pont Formation Conseil) without whom the Conference would not obtain such a success.

Yu-Jun Cui

Fabrice Emeriault

Fahd Cuira

Siavash Ghabezloo

Jean-Michel Pereira

Michael Reboul

Hugo Ravel

Anh Minh Tang

Strong wet seasons affect the stability of slopes as the pore pressure rises. One of the most effective methods used in the south of Chile, in fine soils, is horizontal drains. This method reduces the pore water pressure maintaining an adequate safety factor. A 3D seepage model is created to study the effects of horizontal drains on the pore pressure distribution under steady state conditions. Different physical approaches, that is, zero pore pressure and an input flow based on an energy balance, are studied to be able to represent the soil responds, decreasing the pore pressure due to the drains. This will allow considering adequately the influence of drains including aspects such as length, spacing, diameter and location of the openings of the drains.

Common geotechnical engineering practice deals with landslide modelling during the triggering and in some cases immediate post-failure phases. This is generally carried out using either Limit Equilibrium Method or Lagrangian formulation for Finite Element Method. The paper describes a method for assessing both the aforementioned phases and propagation of landslides, modelling the sliding mass by the methods of Eulerian formulation specific to Computational Fluid Dynamics. The equation of state parameters governing the fluid-soil equivalence, as well as the ones describing the velocity-shear strain behaviour are found both by numerical matching (the former) and a newly developed laboratory testing method (the latter). Similarities and differences with respect to the classical approach are pointed out as conclusions.

The research is conducted to model the stability of river banks subjected to tide variation, with particular reference to the Mekong delta. Dupuit assumption is supposed to find the variation of water level in the soil using a numerical solution by an explicit finite difference method which results are compared to field measurements. Under periodic tide variation, a stable ground water level is obtained far from the river bank and higher than the mean river water level. A limit equilibrium analysis (slice method) is developed to find the safety factor of the riverbank. Validation of the results is conducted by comparing to finite element calculations. The safety factors vary with the change of water level in the river. The critical instant (minimum safety factor) occurs during the low tide period. The soil permeability has an influence both on the critical moment and on the corresponding safety factor. Furthermore, the soil cohesion has an effect on the shape of the failure surface.

Reinforcing geosynthetics are used for lot of geotechnical works: embankments, bases stability on soft soils, secure a risk of potential sinkholes, retaining walls reinforcements, asphalt reinforcements, reinforcement of load transfer platforms on piles, optimization of road structures. Their utilization permits also to minimize the environmental footprint and construction costs (reduction of the quantity of soil material used). For these constructions, a long-term design is asked (50 to 100 years). To guarantee the functionality of the geosynthetic during all the life of a construction, safety factors are used in calculations, according to different standards including for instance Eurocode 7, NF P 94270, NFG 38064. Four main partial safety factors are: Creep reduction factor RF_CR, Chemical degradation reduction factor RF_CH, Installation damage reduction factor RF_ID, Global geosynthetic reduction factor RF_g.

Slope failures happened at the Skudai campus in Johor, Malaysia. Two instrumented slopes were investigated for the effects of soil characteristics on the mechanism of rainfall infiltration in slope. One slope (Site-1) failed due to the rainfall while the other (Site-2) remained stable. Laboratory experiments were performed to examine one-dimensional rainfall infiltration behaviour for both sites soil. Analysis showed that for Site-1, the continuous rainfall has caused a significant increase in the soil's moisture, decrease in negative pore-water pressure (from 28 kPa to 0). On the other hand, the same rainfall induces a very small change in negative pore-water pressure. The results showed that the permeability of the soil mass plays an important role in slope instability. Comparison between predicted FOS based on SWCC curve and actual measurement showed that there are other factors that may influence the soil response to rainfall infiltration such as mineralogy of clay content and the dispersibility of the soil.

Upgrading railway embankments in Denmark is connected with high costs, using the partial factors for geotechnical design calibrated for general application. Reliability-based calibration of the partial factors to a reasonable safety level, taking into account the specific design situations and uncertainties relevant for railway embankments, is one way to reduce the costs. At “Nordvestbanen” in Northwestern Zealand, a reliability-based calibration of the partial factor has been performed, resulting in an optimal partial factor for the considered subsoil, cf. (Lodahl et. al. 2012).

In the present paper, two design cases where the updated partial factor was applied are examined. The evaluation of the actual design cases focuses especially on the validity of the chosen slip surface in the calibration. Examples of acceptable and unacceptable slip surfaces are presented and discussed.

Newmark sliding block method is a popular engineering method to evaluate permanent displacement of rock slope during seismic loading. In practice, a fixed threshold of horizontal seismic coefficient defined by the critical surface subject to factor of safety equal to 1.0 is used to examine the horizontal component of earthquake. The magnitude of displacement is obtained by integrating twice the difference of the applied acceleration and the critical acceleration with respect to time. However, this procedure does not rationally consider the variation of strength of rock mass during seismic loading and effect of vertical component of earthquake. The direction and quantity of displacement based on this approach is unclear. This study proposed modifications to improve the traditional Newmark sliding block method for consideration of the earthquake in horizontal and vertical directions and the variation of strength of Mohr-Coulomb material during earthquake. The proposed framework, compiled in the EXCEL program, is illustrated with an ideal model of sliding block. The yielding results are compared and discussed in this article. The modified analysis procedure is then applied to a real case of dip slope around reservoir in south of Taiwan for safety of reservoir. Satisfactory results are obtained in the demonstration example analyzed with the proposed framework. The effect of vertical earthquake is also discussed by this case.

Using terrestrial laser scanning technology for building point clouds with millions of points can be used to model an actual slope and allow high-resolution computer-based analysis of rock slopes, as a supplement or a substitute for conventional field data acquisition. In this research such methodology has been implemented on a pilot site in the City of Belgrade, Serbia. To provide a control reference, the site has been previously studied and analyzed with conventional reconnaissance methods. On the rock slope face, made of limestone, several families of ruptures have been mapped directly from the 3 cm resolution point cloud. Families of planar structures have been extracted and forwarded to the preliminary kinematic analysis for three displacements types: plane and wedge slide and toppling. As expected, the analysis corresponded well with the referent investigation of the pilot site, indicating that the most dominant failure type is a planar block slide. It has been shown that proposed technology gives reliable and concurrent results.

Drainage in the engineering practice is often used for stabilizing of instable areas. According to consumption of energy, the methods can be divided into two groups. Traditional methods of drainage without need of energy, i.e. using gravity, are usually limited by its maximal depth of 3–5 m (as gravel drains). Considerable length of subhorizontal wells can be another disadvantage. On that account, the innovative method of siphon drains represents a flexible alternative. In the paper, both the method of siphon drains and it's last applications in Slovakia are introduced. Conclusions and reflection of the drainage based on field observations and maintenance are included.

Rapid drawdown is a critical design condition for the upstream or riverside slope of earth dams and levees. A new total stress rapid drawdown method based on finite element analysis is used to analyze the rapid drawdown failure that occurred at Pilarcitos Dam in 1969. Effective consolidation stresses in the slope prior to drawdown are determined using linear elastic finite element analysis. Undrained strengths from isotropically consolidated undrained (ICU) triaxial compression tests are related directly to the calculated consolidation stresses and assigned to the elements in the model by interpolation. Strength reduction finite element analyses are used to evaluate stability of the dam. Back analysis suggests that undrained strengths from ICU tests must be reduced by 30% for use with this rapid drawdown method.

Clayey soils, among other features, are characterized by their strong tendency to undergo significant creep deformations. It is also a well-accepted fact that the primary consolidation phase involves creep deformation. However, there are still contradicting opinions on the effect of creep during primary consolidation phase of clays. As a result two distinct schools of thoughts, referred to as creep hypotheses A and B, have been used as a basis of discussion to assess the effect of creep during the primary consolidation phase. In this work the implication of the two creep hypotheses are illustrated and then evaluated based on relevant and high quality laboratory tests. The test tests are seen to be in excellent agreement with creep hypothesis B and can numerically be described using elaso-viscoplastic formulation.

As the soft plastic is an abundant material in the Municipal Solid Waste (MSW) mass, and considering that it acts as a reinforcement element, its influence on MSW shear strength has been a target of constant study. The variables involved in this study are the amount of plastic, its inclination to normal and shear stresses, its tensile strength, the issues related to the mobilization of strength stresses by the plastic, etc. The present paper aims to study the variables involved into the contribution of soft plastic on MSW shear strength, through the execution of direct shear tests to samples of sand combined with plastic bag strips. Some of these strips were previously immersed into leachate at different periods of time, in order to provide information about the influence of this substance on the specimens shear strength. It is expected through this study to help the understanding of the soft plastics influence on the MSW behavior, contributing to improve the design, construction and storage capacity of sanitary landfills.

A large part of research in the field of unsaturated soil mechanics is focused on cohesive soils due to their distinct capillarity. High suction is controlled and measured in laboratory tests with different techniques, e.g. the axis translation technique or the osmotic technique in combination with pore fluid pressure transducers. In the case of non cohesive soils, such as sands, a lower range of suction is relevant and the chosen methods of suction control should be accurate at very low matric suction. In this contribution a method is presented in which a computer controlled vacuum regulator is applied to impose negative water pressures on a sand specimen. This method allows to control low negative water pressures as occurring in nature for the determination of the soil water characteristic curve (SWCC) or for laboratory tests with controlled suction.

One of the most important soil parameters is deformation modulus. In Ukraine during recent years increasingly using oedometer tests when assessment the soil compressibility. However, the reference value of soil deformation modulus is its determination by plate loading tests with plate area not less than 0.5 m². The deformation modules E_oed significantly lower than E_PLT.

Methods analysis and features of oedometer soil test specimens showed that more than 20 factors may affect the results but two types of factors have the crucial influence to the determination of E_oed: sample crumbling on contact with oedometer stamps, the influence of loading history and test time.

So the real values of E_oed can be obtained directly by measuring of soil samples deformation in the area that does not effected by plastic deformation (crumbling) and with correct selection of deformation stabilization criteria, which will depend on the depth of soil sampling.

The containment of high ionic strength leachates by bentonite-polyacrylate composites is presented. Sodium bentonite (Na-bentonite) was modified to control flow and contaminant migration in containment applications where natural Na-bentonite barriers, such as geosynthetic clay liners (GCLs), will not adequately control flow and contaminant migration. Polyacrylate was combined with Na-bentonite by in situ polymerization of acrylic acid within bentonite slurry to create a bentonite-polymer nanocomposite (BPN). BPN swells more than two times more than Na-bentonite from a GCL (73 vs. 30.5 mL/2 g), but in high strength CaCl₂ solutions, has a swell similar to calcium bentonite (< 10 mL/2 g). Thin layers of BPN and Na-bentonite simulating GCLs were directly permeated with 50, 200, and 500 mM CaCl₂. BPN maintained low hydraulic conductivity (<8×10⁻¹¹ m/s) to hydraulic and chemical equilibrium termination criteria, while Na-bentonite had hydraulic conductivities at least three orders-of-magnitude higher. The mechanisms underlying these behaviors are also discussed.

The growing concern regarding the production of wastes in general with regard to its disposal in increasingly confined urban spaces, and the exhaustion of natural resources and their close relationship with the cost of extraction and transport of materials from dumps even farther from the cities, causes concern in evaluating in more detail the question of waste produced in large urban centres. The purpose of this paper is to check the performance of Construction and Demolition Waste (CDW) when applied to improving soils using compaction piles to replace natural aggregate. With this in mind, it was done an experimental compaction mesh consisting of CDW and conventional piles on site, where it was possible to drill boreholes and perform 15 plate bearing tests. The borehole and plate bearing tests made on the experimental compaction mesh helped confirm good performance of CDW piles compared to conventional piles.

This theoretical study focuses on the influence of geometrical imperfections of rigid soil reinforcement columns. Discrepancies compared to projected values are investigated for different parameters like the column position, the column diameter or the column length. The effects of an unintentional curvature, inclination, and load eccentricity are examined. The consequences of the different geometrical imperfection types are classified in terms of loss of structural capacity (brittle failure), loss of bearing capacity (extreme column displacements), or loss of stability (buckling), establishing the most decisive imperfection types. Threshold levels leading to particular sensitivity of the system will be defined, in order to increase the quality of such systems by a more careful execution of the determining parameters.

The acceleration of global warming is not only inducing rising sea levels and abnormal climate problems, but also geotechnical hazards such as farmland and coastal erosion, yellow dust, and desertification. Recently, 30% of Earth's dry land has been affected by desertification, and approximately 850 million people are suffering due to famine, poverty, and hygiene problems induced by desertification. Moreover, UNEP warns that tens of millions of people could be driven from their homes by encroaching deserts, particularly in sub-Saharan Africa and central Asia, in the next 10 years. Global warming and unsustainable land development are known to be major triggers promoting desertification. New forestry practices, such as encouraging forests in dry land areas, are simple measures that can remove more carbon from the atmosphere and prevent the spread of deserts. Numerous global agencies and companies are thus contributing to anti-desertification movements. However, tree planting alone is not an ideal solution given that it takes approximately 2~3 years for stabilization. It is thus imperative to develop innovative technology that can promote vegetation growth and improve soil erosion resistance. In this study, a unique soil treatment and anti-desertification method is developed using environmentally friendly biogenic biopolymers. Biopolymers can effectively strengthen soil and improve durability. In particular, anionic-hydrophilic biopolymers delay water evaporation, thereby retaining a higher soil moisture condition compared to non-treated soil. For technical verification, series of laboratory investigations (i.e. water erosion test, seed germination and growth,) were performed by applying target biopolymers to soil specimens. The results indicate that environmentally-friendly biopolymer treatment is highly effective in improving both vegetation growth (3 times faster) and soil erosion resistance (less than 2%), compared to a non-treated condition.

During the last decades, the precast concrete and bored pile foundation system installed to significant toe bearing in dense soils are typically used for high-rise buildings in the Quang Nam province, Vietnam. Because of the anticipated significant costs of this solution, a more economical alternative foundation system was essential, and the alternative of the foundation rested on floating soil-cement columns was proposed for a 5-story hospital building. The soil profile consists of medium dense silty clay into 28 m depth deposited on dense to compact silty sand. Two single columns and one group of 5 columns with open spaces between columns from 30 through 100 mm, 800 mm in diameter, were constructed using the wet deep mixing method into 14 m depth to serve for test and design of building foundation. The head-down tests were performed and the maximum test loads on the single columns and column group were about 400 and 2,000 KN, respectively. The measured maximum movements ranged from about 3.4 through 6.5 mm. The proposed solution saved about 30 % of cost of original designed foundation supported by 300 mm square precast concrete piles driving into 30 m depth. Effectiveness of solution is illustrated and discussed and modeling of soil-cement columns is analyzed by means of the Unified Design Method to response long- term settlements of building.

As development continues, buildings and highways must be constructed over collapsible soils. Based on experience with behavior of loess in its natural state and after wetting, loess is classified as a difficult foundation soil, therefore improvement is typically recommended. Settlements associated with collapsible soils can lead to expensive repairs if not treated in some way prior to construction. Dynamic Compaction is a semi empirical technique for improving the mechanical properties of soil, developed by Louis Menard in 1970's. This technique was used recently in Romania for the treatment of 240,000m² of loess. This paper presents the criteria and tests used to certify the improvement of the physical and mechanical parameters of loess including its porosity, humidity, density, plasticity, additional settlement index, and structural resistance and deformation modulus.

A major aspect in geosynthetics creep analysis is the load level applied to the specimen, usually referred as a percentage of the geosynthetic ultimate tensile strength (UTS). Since both tensile and creep standard tests are performed with in-isolation specimens, they may not reproduce the possibly significant effect of soil-geosynthetic interaction. A new creep testing machine was recently developed and successfully addressed this concern. However, further developments allowed tensile tests to be performed in the same conditions used in nonconventional creep ones. This paper presents the results of nonconventional tensile tests performed with a woven biaxial polyester geogrid. They were used to define its UTS in the same conditions employed in creep tests performed with the new equipment. Despite changes in tensile curves shapes were found, the UTS from confined, accelerated and confined-accelerated tensile tests were quite similar to those obtained with standard tensile test procedure.