Ebook: Geotechnical Engineering: New Horizons
This book presents the proceedings of the 21st European Young Geotechnical Engineers’ Conference (EYGEC), held in the Netherlands in September 2011. Six sections cover the topics of underground construction, pile foundation and ground improvement, soil dynamics, dams, erosion and piping, deformation and soil properties, and geothermics. The papers present a new and refreshing perspective of young engineers exploring the field of geotechnics, aiming to contribute to sustainable living and to the creation of safe, economic and pleasant spaces to live, work and relax.
Rotterdam in 2011 is transforming its horizon. Old harbours are converted to city space, such as the RDM campus where this conference is hosted and new land is created. Underground space is becoming more and more part of the daily life for transport and storage. This requires top end geotechnical engineering, as harbours and infrastructure cannot be built economically, safe and efficient without properly addressing the challenges and opportunities the subsoil provides. Many well-educated and experienced engineers are needed for this kind of new horizons around the world.
Ask a geotechnical engineer what he or she is doing and you might get the answer: I am working on the 4D numerical modelling of the behaviour of saturated marine clay under cyclic loading conditions. Just a small number of people, probably the readers of this preface and just a handful of other geotechnical engineers, will understand the challenges and value of this specific topic. Had the engineer answered: I am predicting how we can build dikes that can withstand waves in a safe and economic way; a lot more people would have understood the importance of the work. This book shows an enormous variety of papers and topics, from the 4D numerical type to the more obvious societal issues, but all with the new and refreshing look of young engineers exploring the field of geotechnics.
I am proud to be a geotechnical engineer. I am even more proud of all the geotechnical engineers working worldwide contributing to sustainable living, to create safe, economic and pleasant spaces to live, work and relax. Some of these international experts provide key notes in this conference and have kindly agreed to interact with a new generation. It will give them the opportunity to exchange experiences and strengthen the field and network of geotechnical engineering.
The transformation continues. In 2004 and 2006 I attended the international YGEC conferences in Romania and Japan. Many of the participants from those conferences now play interesting and important roles in the international field of geotechnical engineering. It is my pleasure to organize the 21st EYGEC conference in the Netherlands together with an experienced scientific team and an enthusiastic organizing team. May the new horizons of Rotterdam and the views of the proud geotechnical engineers in this conference be an fertile inspiration.
EYGEC2011 Organising Committee
In the old central part of Zagreb, among a block of buildings, a business facility is being built. The underground structure consists of 5 belowground floors, with maximum excavation depth of around 19 m. For construction of belowground floors the so-called “top - down” method is used. This method is useful to avoid long-term work on the construction of geotechnical anchors and tampering of nearby parcels. Excavation support is ensured by a 24.5 m long reinforced concrete diaphragm wall held by floor slabs of the underground levels. The reinforced concrete diaphragm wall is designed as a permanent structure and presents a vertical cap wall of the underground part of the building. Floor slabs are retained with steel columns, which are founded on drilled shafts ∅120 cm, 12 and 15 m of length.
Trench is connected to very narrow and deep excavation filled with bentonite suspension. This paper presents estimation of its stability in cohesive soil. The stability is assessed by two calculation methods. The first involves the equilibrium of forces acting on the rigid wedge. The second one includes numerical calculations conducted in Plaxis 3D Foundations. A few examples having different dimensions (length and depth) are analyzed in uniform soil conditions. Graphs defining the dependence of length, depth and factor of safety are presented. It is found that for long trenches (L≥6m) the soil kinematics at failure coincides with the literature data. Short trenches are under a large influence of the arching effect and cohesive forces. The limit equilibrium method can be used under the condition of employing a factor, which reduces the value of the earth pressure.
Finite element modeling (FEM) is highly dependent on the reliability and the accuracy of the input data. The assigned Poisson's ratio is very dominant for the shear strength parameters in the case of the elastic and Mohr-Coulomb (MC) soil model. This value may vary between 0.25 and 0.45 (from gravel to clay). Using FEM analysis with MC soil model, the calculated deformations obtained from the model are not realistic, meanwhile it is perfectly suitable for stability calculations. More accurate displacement results can be obtained with the same software applying Hardening Soil (HS) model. In this case, additional factors are required for the model, such as unloading-reloading modulus of elasticity (Eur), and Over-Consolidated Ratio (OCR). The HS model is useable with dense and hard soils. The soil will behave 3–5 times “stiffer” in unloading-reloading, which defines the choice of the value of the Eur. The above-mentioned factors are important in determining the behavior of soils, especially at the reactions of retaining structures and deformations. The influence of factors is illustrated by a trusted, embedded retaining structure. This study draws attention to the importance of parameter analysis.
As a part of the new Spanish high speed railway line (AVE) connecting Madrid, Barcelona and the French border, currently a tunnel with a length of 5.6 km is built under the city centre of Barcelona. The tunnel line passes directly next to the famous church of Sagrada Familia and a building called “Casa Milà”. Both buildings belong to the World Heritage Properties of the UNESCO. To ensure the highest possible safety for these extraordinary historical buildings special requirements in control and construction had to be fulfilled during the tunnelling process. The tunnel is built with a tunnel-boring machine using an earth pressure balanced shield. The church of Sagrada Familia and Casa Milà have already been passed. The maximum measured settlements of Sagrada Familia and Casa Milà induced by the tunnel construction were in the range of the measurement accuracy. Some of the extensive data of the geotechnical and geodetic monitoring is presented focusing on possible influencing factors for the evolution respectively the prevention of surface settlements.
The paper presents the overall stability evaluation for a deep excavation in quick clay supported by flexible retaining structure (sheet pile wall) and ground improvement by lime-cement columns and vertical drains. The soil structure interaction analysis is performed using the finite element program Plaxis. The challenge of modelling the sloping layers with shear strength increasing linearly with depth is managed by using a special “vertical clusters” technique. Main conclusions from Plaxis analyses are as follows: Mohr-Coulomb model can be used to simulate pre-peak behavior of quick clay and the FE method can detect most critical failure mechanisms. The working sequences are monitored by lateral displacement (inclinometers), settlement and pore-water pressure measurements. Unfortunately, due to some site problems the quality of measurements is questionable. Despite some technical problems during the excavation work, the bottom of the excavation is now successfully closed by a concrete bottom slab and the structural work is in progress.
The use of fibreglass nails in tunnel construction for the reinforcement, as well as the placement of a steel tube umbrella, also known as forepole umbrella, for the protection of the excavation face, are two well known and extensively applied methods. They can be used solely or in combination, which is the most common case when adverse tunnelling conditions are expected. As the application criteria and design of these methods are still mainly based on experience and some simplified analytical methodologies, 3D finite element analyses provide a very useful optimization tool. The paper presents a series of analyses of circular lined tunnels in three dimensions, to show how such analyses can be used for tunnel face reinforcement and protection design. The analyses demonstrate the effectiveness of each method and the way it changes the stress and strain distribution around and in front of the tunnel. Fibreglass nails keep the advance core under compression and minimize extrusion, enhancing the stability of the tunnel face seriously, especially when placed in frictional soils. Forepole umbrella on the other hand does not minimize face extrusion significantly, but limits the extent of the plastic zone above the tunnel face. Finally, special attention is given to the interaction between these two methods. Taking the effects of this interaction into account can lead to a more rational and economic design, as these methods are not only quite expensive but also time consuming within the tunnelling process.
Hydraulic heave safety in many cases is a relevant factor for designing the embedded length of excavation walls of deep excavation pits. To reduce the embedded depth, a surcharge filter can be placed on the bottom of the pit. Numerical based analyses show that the conventional design of excavation pit with installed surcharge filter according to Terzaghi/Peck and Baumgart/Davidenkoff is not valid. A theoretical approach, which considers the vertical flow forces below the base of the excavation wall was developed by the Federal Waterways Engineering and Research Institute. To verify this theoretical approach, the Institute for Soil Mechanics and Geotechnical Engineering of the Bundeswehr University carried out numerous laboratory tests in a specific box to simulate hydraulic heaves. During the series of experiments, the embedded depth of the wall and the thickness of the filter layers were varied. Moreover, the elevations on the excavation side of the wall were detected by displacement transducer, the water pressure around the end of the wall was detected by water pressure sensors and the figure of failure was mapped by Picture Image Velocimetry (PIV) Method and video camera. The Paper shows the results of the laboratory experiments and the consequences for the design of the filter layers on the excavation side of the wall by under-flown and small-embedded depth.
The project discussed in this paper is a tower located in Bucharest with a height of 137 m. To find the optimal layout of the foundation elements with respect to minimising vertical displacements, conventional calculations are in general not sufficient and advanced numerical modelling of the soil-structure interaction is essential. The paper shows results from numerical analyses with the objective to assess the settlement behaviour of the tower. Due to the geometric layout 2D analyses proved to be too conservative and therefore a number of 3D analyses have been performed. Different arrangements of diaphragm wall panels have been investigated to find an economical and technical feasible solution for the layout of the foundation elements. For the executed deep foundation concept a parametric study based on soil data recently published in the literature is presented. Finally results from 3D finite element simulations of an in situ load test, performed to obtain additional information of the settlement behaviour of the deep foundation, are presented. The test was conducted on a diaphragm wall element (barrette) using the “Osterberg Method”.
There is a very significant boom of the tunneling industry in the Czech Republic and generally worldwide in recent years. The main reason is the lack of space on surface in major cities together with requirements for faster traffic connections. Therefore a very significant number of tunnels are either under construction or in the design stage. The recent rapid increase in the capability of computers and user-friendly software has led to a proliferation in the use of numerical analyses in design of underground structures. One important fact is often overlooked. No matter how sophisticated a numerical model is, it is only an approximation of the real situation. The presented paper deals with the optimization of numerical modeling for underground structures. The results of research, which we are working on, should be recommendations for designers of underground constructions using numerical modeling with regard to the application of software and input data. Due to the scope the paper is divided into several parts. The first part is devoted to introduction into current problems. The second part discusses influence of non-linear material model on precision of analyses of tunnels in clays. The last part is devoted to the experience with numerical modeling of underground structures in Prague.
Baku Flame Towers Project, consisting of three high-rise towers, a shopping mall and an underground car park is being constructed in Baku, Azerbaijan. The project site is located on the city center neighboring two major boulevards, and some important buildings such as National Assembly of Azerbaijan, General Staff Building and Central Clinic Hospital. The soil profile at the site generally consists of a fill layer and slope debris with varying thicknesses from the ground surface, and very stiff – hard clayey silt underlying the fill layer. Below the silt layer, a poorly cemented sedimentary rock layer with a poor rock quality is encountered. Due to the inclined topography of the project site, excavation slopes with depths varying between 2.0m and 29.0m have been foreseen in accordance with the architectural design. In order to carry out the foundation excavation safely an earth retaining structure consisting of bored piles tied-back by temporary ground anchors has been designed and constructed successfully. The retaining system constructed within Baku Flame Towers Project has the distinction to support the deepest foundation excavation ever made in Baku, Azerbaijan. Due to high structural loads, tower buildings have been designed to rest on raft foundations with large diameter piles. Bored piles with a diameter of D=1.20m and length of L=36.0m have been designed in accordance with the required load capacities, and anticipated pile capacities have been proved successfully with pile loading tests performed by using Osterberg Cells.
Monopiles are an often-used foundation concept for offshore wind turbine converters. These piles are highly subjected to lateral loads and overturning bending moments due to wind and wave forces. To ensure enough stiffness of the foundation and an acceptable pile-head deflection, monopiles with diameters of 4 to 6 m are typically employed. In current practice these piles are traditionally designed by means of the p-y curve method although the method is developed and verified for slender piles in sand with diameters up to approximately 2 m. One of the limitations of the p-y curves used in current design (e.g.  and ) is the effects of diameter on the initial part of the p-y curves. This part is especially important in connection with the serviceability limit state and fatigue. The effects of diameter on the p-y curves can be investigated by means of either numerical analyses or physical modelling (large- or small-scale). This paper investigates the effects of diameter on the initial part of the p-y curves by small-scale testing. A new and innovative test setup is presented. In order to minimize scale effects the tests are successfully carried out in a pressure tank enabling the possibility of increasing the effective stresses. The test setup is thoroughly described in the paper. Two non-slender aluminium pipe piles subjected to lateral loads have been tested in the laboratory. The piles are heavily instrumented with strain gauges in order to obtain p-y curves, displacement and bending moment distributions along the pile.
The results of experimental research on the strength and deformation characteristics of soil-concrete as a function of jet-grouting parameters are described in this article. Some experimental works of jet-grout column construction in sandy ground are carried out. At the end of these works soil-concrete samples are taken and laboratory research is carried out. Relationships between the deformation modulus (E), compressive strength and tensile strength and the cement consumption per 1 m3 are obtained.
The vibro stone columns technique is one of the most used techniques for ground improvement processes all over the world. In recent years this technique is also used in Albania. For the first time in our country this method is used for ground improvement at Ferry Terminal of Durres, which is the biggest harbour of Albania. In this case the technique is used to reinforce silty clay and silty sand soils. There are two methods of construction in the vibro replacement technique named: the wet method and the dry method. In Durres Ferry Terminal building and yard infrastructure the dry method is used. The paper outlines the technique, the ways of application in different types of soil, and settlement and bearing capacity calculations for this case.
The paper presents the results of plate load tests on a driven stone column. The results were used to calibrate a proposed numerical model. The calibration is based on semi-reverse analysis. The calibrated model was used for analysis of model sensitivity to the assumed shape of the column as well as the analysis of the adequacies of existing settlement analytical methods.
In this article in-situ and laboratory tests of “Atlant” anchor piles are described and the results are compared with other types of ancho piles.
The paper presents results of a laboratory study on the compacted mixture of clayey silt with 1–8% of CaO. Adding of CaO increased the maximum dry density and decreased the optimum water content. In the case of 4–8 % of added CaO the size of the pores kept decreasing until 360 of curing days, while with 2% of CaO the decrease stopped at 120 days and no further pore size changes were detected with 1% of added CaO after 28 curing days. The hydraulic conductivity of the treated soil increased from ca 10−9 ms−1 to 10−7 ms−1 on adding CaO, but then decreased back to the order of 10−9 ms−1 during several days of carrying out the permeability tests. At pH higher than 11.7 the pozzolanic reaction occurred and the soil voids changed due to the new mineral phases, hydrated calcium aluminates especially.
The calculation of the axial bearing capacity for pile foundations vary widely from one country to another, depending on the methods that each country use or on the building codes that has adapted in the legislation. In Albania, a legislation nor a building code exist for this purpose, but during years a design practice for pile foundations is consolidated. In this paper the calculation of the axial bearing capacity of a pile using Albanian Design Practice is shown in comparison with 3 other methods, which are: analytical method based on SPT data; analytical method based on CPTu data; method based on Japanese Design Practice. In order to have a satisfactory comparison between the results of the used methods, the calculations are carried out for both driven and cast-in-place piles, considering for each case several values for pile length and diameter. Analysis of the complete results enables to compare the method described in Albanian Design Practice with other proposed methods. The calculated bearing capacities show that the differences between the methods are apparent.
The design of industrial and logistic building's slab-on-grades is a complex exercise. The design needs to consider the different loading types and configurations (uniform or alternated loading, racks, live loadings…) together with the relative positions from the hinged constructions joints to the loads, whose position and intensity can vary during the life of the structure. The non-uniform stress reaction distribution in the soil reinforced with rigid inclusions creates an additional stress in the slab with a different pattern than the ones of the loads and of the joints. The optimization of the design of the slab becomes a complex problem with three different intertwined patterns (loading, joints, and rigid inclusions) that can move relative to one another with usually no typical symmetry conditions. Existing code of practice dedicated to slab-on-grades are only able to consider uniform soil conditions and the typical size of those structures forbid the modelling of the full extent of the slab. Through the decomposition of this complex problem into the sum of three unit variable-separated problems, this paper presents a simple and comprehensive method to take into account all the parameters of the equation. This method is a powerful solution which is easy to use while allowing for the precise optimization of the design of slab-on-grades. The approach has been validated and calibrated with an extensive number of finite element calculations and has been integrated in the French ASIRI national research program in France.
Building and designing on semi-rocky soils is problematic for many countries in the world. In particular, in Russia the problems of building on semi-rocky soils are not given clearly enough in national construction norms and standards. There is a necessity to analyse strength and deformation properties of semi-rocky soils, to work out the theory of interaction between a deep base and semi-rocky soils, and to develop a mathematical model of “deep base – semi-rocky ground” interaction. In that paper some results of static load soil test are presented. The possibility of the use of lower Permian soils as the end-bearing pile base within the bounds of a particular case was confirmed.
Within the framework of the regional express network around Brussels, an existing railway line will be extended from 2 to 4 tracks. The extension needs to be realized as much as possible within the existing properties and possess a green character. The chosen solution consists of a stepped embankment at a 45° angle, departing close to the existing embankment toe and with a flat terrace every 1.8 m. For the design of these green terraces, the concept of reinforced earth was adopted. A classic small cantilever wall will be adapted by anchoring a geogrid in the base slab. The cantilever wall acts as a facing element for the reinforced earth fill. In places where the geogrid cannot be sufficiently anchored, the geogrids will be attached to soil nails. Due to the specific geometry, the required high stiffness and the high pH resulting from the concrete curing, a geogrid based on PVA with a high strength of 800kN/m will be used. This system of reinforced earth leads to a lower concentration of loads on the foundation, so a foundation made up from stone columns will be sufficient. The complete system and the interaction between the different structural elements were extensively studied through numerical analysis in FLAC. The embankments are currently under construction. Preliminary testing on the stone columns, soil nails and geogrid anchorage has been carried out.
Railway traffic induced vibrations in dwellings often cause irritation or disturb the inhabitants. Mitigation has been performed, and measurements prove their effectiveness. The effect of vibration countermeasures on the quality of living however has not been studied earlier. The objective of the study was to evaluate the effects of vibration mitigation compared to the increase of inhabitant satisfaction, would the halving of vibration levels lead to a doubling of satisfaction? The investigation was done by means of a literature study, vibration measurements and written surveys with the financial aid of the Finnish Rail Administration. The testing was carried out in Raunistula, a suburb of Turku, in Southwestern Finland. Passing along the side of the residential area, the Toijala-Turku railway line causes vibrations in the surrounding areas affecting the quality of residents' life. To attenuate the vibration, two different structures were constructed, a sheetpile wall and a matrix of lime-cement columns. Typical to the Southwestern region of Finland, the soil in Raunistula consists of a thick layer of clay with low shear strength. This soil type allows large displacements in railway sub-structures, especially if ground supported. Additionally, the low natural frequency and damping coefficient of clay lead to minimal attenuation and widespread effects in the surrounding area. The level of vibrations and residents' satisfaction was evaluated prior to construction. After the installation of the aforementioned barriers, a new round of measurements and surveys was performed in order to find out how the mitigation succeeded. Results were satisfactory, the greatest amount of mitigation was achieved nearest to the track and comments of a rise in the quality of living were achieved. The mitigation however was limited to a certain distance from the track. Farther away, partly due to other sources of vibrations and noise, the mitigating effect of the structures was negligible. The results of both the surveys and measurements show an improvement of 30 to 50 %, confirming the hypothesis that inhabitants' satisfaction increases as much as the intensity of vibration decreases.