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How safe are our structures? – Conceptual paper of the DGGT Working Group 2.15 "Reliability‐Based Methods in Geotechnical Engineering" The future Eurocode 7 will explicitly allow the use of reliability‐based methods in geotechnical planning and design. In Germany, there is hardly any experience in the practical application of such methods so far and thus the reservations towards these methods are plenty. The new DGGT Working Group (WG) 2.15 "Reliability‐Based Methods in Geotechnical Engineering" has set itself the goal of providing a practical access to those methods by means of practice‐oriented instructions and recommendations as well as accompanying training and further education courses. The aim is to clarify the possibilities and limitations and, above all, to exploit their potential. This article presents the general principles as well as the future fields of work of the WG 2.15. Starting with the introduction of relevant technical terms, the implementation of reliability‐based methods within the current codes of practice and regulations is shown. Using the life cycle of a geotechnical structure, the uncertainties in geotechnical designs and assessments are described. Subsequently it is outlined, in which situations and to what extend reliability‐based methods can aid engineers, clients and inspectors in verification and decision‐making processes. In the future, WG 2.15 will develop recommendations on individual topics and publish them successively. [ABSTRACT FROM AUTHOR]

Hydraulic heave in round excavation pits with relief boreholes – calculation approach The use of relief boreholes to reduce the effect of a vertical upward flow has proven to be a constructive measure to avoid the risk of hydraulic heave in excavation pits in groundwater. The applicable standards and regulations, however, only provide general information on the use of relief boreholes. A concept for the verification against hydraulic heave failure using relief boreholes is missing as well as defined information on the arrangement of the relief boreholes and the influence of the excavation geometry. Therefore, the aim of the research work at the Chair of Geotechnical Engineering of RWTH Aachen University was to develop a concept for the proof against hydraulic heave failure with the arrangement of relief boreholes. The result was a calculation approach that determines the decisive fracture body under consideration of the flow conditions due to the relief boreholes. This fracture body can then be used for the proof against hydraulic heave failure. Based on this, dimensioning diagrams were finally generated for typical excavation pit geometries in dimensionless representation. [ABSTRACT FROM AUTHOR]

Validation of the AVISA model Despite advanced design technologies, construction on cohesive soils is still a challenge. Especially when dealing with cyclic loading conditions combined with the time‐dependent behavior of cohesive soils, such as offshore structures or even dams, the tools to predict the long‐term deformations of fine‐grained soil are limited. Due to the complex influence of loading rate, preloading, and soil structure, it is necessary to understand the effects of these influences on cohesive materials through laboratory testing and describe them numerically through accurate and physically based constitutive equations. Researchers (continue to) develop many hundreds of material models each year. Most of them are used for PhDs and not investigated further. In this work, such a model, developed in the first author's PhD, is be validated. The performance of the AVISA model has been previously demonstrated on experiments of various fine‐grained soils. In this paper, a new experimental study on Malaysia Kaolin is used for the validation of the model. Furthermore, the reproducibility of the so‐called Krey and Tiedemann criteria, parameters φ′s , c′ und φ′ is investigated by simulations of simple shear tests. It should be noted that many constitutive models for fine‐grained soils fail in this task. [ABSTRACT FROM AUTHOR]

Steel tube struts in braced excavations – Simplified design for cross section class 4 Steel tubes are often used as excavation struts. When designing long struts without intermediate supports, tubes with large diameter and small wall thickness are particularly economical. This may lead to reaching the limit of cross section class 4 requiring a shell buckling analysis according to EN 1993‐1‐6. In this article a simplified design method using section‐related buckling stresses based on EN 1993‐1‐6 Annex D is described. Ready‐to‐use section‐related buckling stresses are given for commonly used steel tubes of cross section class 4. [ABSTRACT FROM AUTHOR]

Failure criteria for foam‐grouted gravel under multiaxial loading Foam grouting is an innovative method for improving the mechanical properties of cohesionless, coarse‐grained soils. Despite this, only a few experimental studies have been conducted to assess the failure of foam‐injected soils under multiaxial loading. This paper aims to fill this gap in knowledge. The stiffness and strength of the natural soil, which serve as reference values for the evaluation of the improvement effect due to the injection, are derived from drained triaxial tests. The mechanical behaviour of the foam‐injected soil is investigated using uniaxial, triaxial, and splitting tensile tests. The foam‐injected soil, exhibits significantly higher strength and stiffness but lower ductility than the untreated soil. The ductility of the foam‐injected soil increases with increasing lateral pressure. The splitting tensile strength is only a small fraction of the compressive strength. The adequacy of the failure criteria Mohr‐Coulomb, Hoek‐Brown and Lade for the description of the failure of foam‐injected coarse‐grained soils is verified. All three failure criteria are basically suitable to describe the state of failure in triaxial compression. For compressive and tensile loading, the Hoek‐Brown and Lade failure criteria seem to be more appropriate compared to Mohr‐Coulomb. [ABSTRACT FROM AUTHOR]

Harmonization in Geotechnics – a statistical method to determine representative values for ground properties considering prior knowledge In the revised version of Eurocode 7 (prEN 1997‐1:2021‐11), the value for the geotechnical parameter to be applied in the design will in future be referred to as the representative value, which can be derived from the characteristic or nominal value. While the nominal value is determined using conventional estimation methods, the characteristic value is determined using statistical methods. For this purpose, an applicable statistical method is recommended in prEN1997‐1:2021‐11. In this article, a statistical method is explained that fulfils all requirements according to prEN 1997‐1:2021‐11 and also allows the possibility of taking into account prior information. Compared to the statistical method in prEN 1997‐1:2021‐11, the new method is to be considered more robust, as shown in application examples. [ABSTRACT FROM AUTHOR]

For the numerical calculation of the stability of structures in soil The use of the finite element method (FEM) for the design and recalculation of geotechnical structures is steadily increasing. For both slopes and retaining walls, the advantages of the FEM are already used for accurate determination of the deformations and stresses of structures in the serviceability limit state (SLS). The application in the ultimate limit state (ULS) is currently still a research topic for structures with soil‐structure interaction, such as retaining walls. An extended strength reduction, where component strength is reduced in addition to the shear parameters of the soil, is intended to account for the influence of the structure in ULS‐simulations. In addition to the component strength, other parameters, such as the external load‐bearing capacity of anchors or the contact friction between soil and component, play a role for determination of the governing failure mechanism. Using a Python script, the strength reduction approach implemented in PLAXIS 2D is re‐implemented and verified exemplarily on a braced excavation pit and a tie‐back quay wall. By extending the own strength reduction implementation with additional parameters, which are relevant for the stability of geotechnical structures, their influence on the stability calculation and the resulting failure mechanisms is investigated. [ABSTRACT FROM AUTHOR]

On the application of earth resistance models of p‐y curves and DIN 4085 for the design of laterally loaded piles in layered soils The design of laterally loaded piles in Germany is based on a simplified subgrade reaction modulus or the method by Blum. With these methods the lateral pile deflection cannot be calculated very accurately. Internationally the so‐called p‐y approach is widely used, which is based on nonlinear spring stiffnesses to define the subgrade reaction modulus. In this paper the p‐y approach is described in detail and the application of each calculation model is discussed. For the consideration of the effect from multi‐layered soils the approach by Georgiadis is used. The earth resistance determined by this procedure is then compared with the spatial earth resistance from DIN 4085. Because DIN 4085 just offers equations for homogenous soils, the relevant equations are extended for layered soils. In a parameter study on typical soil conditions the decisive differences of the individual approaches are shown and discussed. [ABSTRACT FROM AUTHOR]

Compression behavior of sand‐silt mixtures The choice of an appropriate material model for mixed‐grained soils is crucial for the design of a challenging geotechnical structe. For the development of an accurate material model, the experimental investigation of the soil is indispensable. Hereby, the compression behavior of sand‐clay mixtures is investigated on the basis of oedometer tests of mixtures with different fines contents. It can be observed that with increasing fines content, the compressibility of the material increases significantly. Nevertheless, an exponential relationship between equivalent void ratio e* and vertical strain has been established independently of the fines content. On this course, the deformation model of Ohde (1939) was generalized to mixtures by considering e*. The simulations with hypoplasticity for granular soils and with the AVISA‐model for fine‐grained soils show a need for the coupling of the preconsolidation pressure as well as the normal consolidation line at a 1:1 ratio of sand to silt depending on the fines content. [ABSTRACT FROM AUTHOR]

Rock stress determination by means of the overcoring method. Part 1: Triaxial strain cells – Recommendation No. 14 (revised) of the Commission on Rock Testing of the DGGT The Commission on Rock Testing of the Deutsche Gesellschaft für Geotechnik e. V. (German Geotechnical Society) is compiling instructions for rock mechanical laboratory and field tests as well as for monitoring in rocks and geotechnical structures on‐site. The presented revision of recommendation No. 14 covers the determination of rock stresses by means of overcoring tests and considers the development of this method since the publication of recommendation No. 14 in 1990 [1]. Further, requirements for the measuring instruments and the procedures regarding the execution and evaluation of these tests are specified. Reference is made to the ISRM Suggested Method, in which overcoring tests are dealt with [2, 3]. Recommendation No. 14 is divided into two parts. This first part deals with overcoring tests using triaxial strain cells. The second part covers overcoring tests using borehole deformation gauges. [ABSTRACT FROM AUTHOR]

Development of a Python script for strength reduction with numerical methods The application of numerical methods in geotechnics until now is mostly limited to the prediction of the deformation behaviour of structures regarding the serviceability limit state. The ultimate limit state has so far been handled rudimentarily (e.g. for homogeneous slopes and piled raft foundations), using numerical methods, such as the finite element method. In the present paper, therefore, the basis for the application of a unified method for parallel strength reduction on structural elements and a reduction of the shear parameters of the soil is discussed. In a first parametric study, a script based on the Python programming language for reducing the shear parameters of the soil is verified by comparison with approved methods for calculating the overall stability of slopes. Subsequently, the application boundaries of the Python script are extended to reduce the strength parameters of structural elements within a slope at risk of stability in the framework of a second parametric study. Based on this, an assessment of probable first failure mechanism (soil or structural failure) is made. Finally, the results of the two parametric studies are put into a causal context, considering a numerical verification with discussion of future research approaches. [ABSTRACT FROM AUTHOR]

Consideration of rigid inclusions at the proof of overall‐stability Rigid inclusions are hydraulically bound, unreinforced pile‐like elements, which are used to reduce settlements and to improve the overall‐stability. Due to the non‐existing reinforcement and the small diameters, rigid inclusions are not adapted for bearing lateral stresses. The present article explains the lateral load‐bearing behaviour of rigid inclusions. In a short overview existing approaches for consideration of rigid inclusions at the proof of overall‐stability are shown and worked out, that the contribution of rigid inclusions is often overestimated. A numeric model for investigation of the lateral load‐bearing behaviour of unreinforced, pile‐like elements is presented. As a result of systematic studies on the numeric model, the activation of the ulitmate transverse force is being explained in a simple mechanical model and outlined, which failure mechanisms will be relevant for consideration. Based on the findings from the mechanical model, fundamental guidelines for design of structures on rigid inclusions are being given. Two approaches for consideration of rigid inclusions at the proof of overall‐stability in Bishop's slip‐circle method are introduced. The applicability of the approaches is been demonstrated on a published damage case. [ABSTRACT FROM AUTHOR]

Level of development and attribution of the specialized model subsoil – Recommendations No. 2 of the working group 2.14 (DGGT) "Digitalization in geotechnical engineering" The second recommendation of the working group 2.14 "Digitalization in geotechnical engineering" defines the level of development with respect to the life cycle of the specialized model subsoil. Furthermore, the minimum requirements regarding the implementation of geometrical and semantical data (attribution) into the model are discussed. For consequent use of the specialized model subsoil in context with BIM it is necessary to standardize the data with respect to the model level as well as the object level by means of properties which have to be defined. These recommendations describe the essential requirements for standardized geotechnical properties which still have to be developed. Therefore, data‐related requirements for creation as well as the attribution of the specialized model subsoil are discussed. [ABSTRACT FROM AUTHOR]

Harmonization in geotechnics – a consistent design method The different used design approaches of EN 1997 are based on different traditions and philosophies in the European countries regarding to the type and time of factoring actions and resistances. The resulting variety of formats for the design approaches will also be retained in the future standards generation. Therefore, the goal of a harmonized design approach with a uniform level of safety is not achieved. In this article, the so called MRFA design approach is presented which is based on the basic equations of EN 1990 providing an own partial safety factor for each parameter (actions, effect of actions, ground resistances and geotechnical parameters). To determine these partial safety factors, reliability calculations were carried out for common geotechnical structures with different boundary conditions and for different limit states in such a way that a certain probability of failure is not exceeded. The method is explained in an application example. [ABSTRACT FROM AUTHOR]

Slope stability with regard of the stress‐strain behaviour during shearing The state of equilibrium of a slope is often evaluated with help of limit equilibrium methods. Here, it is neglected that a deformation in the shear zone has to take place before the maximum shear resistance is reached. The shear stress development depends amongst others on soil density and hydraulic conditions. Consequently, the mobilization of the shear resistance in the shear zone is not homogeneous, which can lead to an overestimation of the slope stability. This report shows a calculation method which couples the development of the slope stability with shear strain in the shear zone. For illustration purposes, two simple examples of a slope with a planar slip surface are shown. [ABSTRACT FROM AUTHOR]

Technical‐biological bank protection measures – Design concept for the engineering practice To improve the ecological condition of inland waterways, extensive bank redesigns are planned over the next few years. More natural bank protection measures using plants are to replace the existing rip rap where possible to create more habitats for plants and animals and more structural diversity. So far, relatively little experience has been gained with technical‐biological bank protection measures on waterways with the current shipping impacts. On the basis of various research results and experience from a large‐scale nature experiment on the river Rhine near Worms, a first design concept for the engineering practice of the waterway and shipping administration was developed, taking into account the experience on small rivers without shipping. The concept was also integrated into a software. This means that bank protection with plants can now be dimensioned in addition to riprap revetments. The special features of living building materials, the hydraulic effects, the geotechnical failure mechanisms to be investigated and the individual design steps are presented below. [ABSTRACT FROM AUTHOR]

With a new concept for the critical void ratio, barodesy yields promising simulations of element tests. Some shortcomings of this theory hitherto when simulating the behaviour of sand can be overcome by generalizing the widespread assumption that the critical void ratio is a function of the mean stress. Barodesy deviates from established lines of thought in soil mechanics. The interested reader can judge from this article whether this paradigm shift is worthwhile. [ABSTRACT FROM AUTHOR]

Impacts on rigid barriers by flow‐like gravitational mass movements The climate‐change‐induced influences on the environment represent an increasing importance and challenge for the evaluation of flow‐like rock avalanches. Extreme conditions for settlement areas in the alpine region result in the necessity to erect protective structures. Rock avalanches increasingly threaten people and infrastructure in settlement and economic areas in Alpine regions. The design impact based on empirical models, areas of influence, deposition sites and flow depth can be roughly estimated. Very different (mostly unknown) input parameters are required for the different numerical programs based on continuum mechanics. For a more precise definition of the relevant parameters, model tests are often carried out to validate the different design models. The basis of the present model experiment is the experimental setup and the investigations at the University of British Columbia which were replicated and extended at the University of Innsbruck. [ABSTRACT FROM AUTHOR]

Approach to determine ultimate stress mobilization in the Interface of rigid inclusion head and load transfer platform One field of application for rigid inclusions is the soil improvement for large‐area structures such as (fibre‐) reinforced slabs of logistics centers and other complexes. To optimise the slab (thickness and reinforcement), a load transfer platform (LTP) is usually installed above the columns. The aim of the LTP is to decouple the rigid inclusions from the structure and to enable a shallow foundation design of the slab. The interaction between columns, LTP and slab must be taken into account, which can cause additional stresses in the LTP and in the slab. In this paper, the approach proposed by french ASIRI recommendation for a granular LTP over rigid inclusions is presented, considering the conventional failure mechanism according to German standard DIN 4017. In a parameter study, influencing variables on the limit state of the LTP be evaluated. In addition, the results of FE calculations on an axisymmetric unit cell with a stiffness reduction of the surrounding soil are used. The FE calculations show that the allowable limit stress increase with a reduction of the LTP thickness, but up to the critical height additional bending moments in the slab must be taken into account. The bending moment increases with a reduction of the LTP thickness. [ABSTRACT FROM AUTHOR]

A newly developed design concept for plane earthwork structures on pile foundations is presented. This design concept is based on a complex mathematical background that has been derived using fundamental mechanical principles. The mechanical system comprises the arching effect in a plane earthwork structure on punctual supports. It incorporates the effect of an elastic membrane that is formed by orthogonal ribs of geogrids, the modulus of subgrade reaction between the piles and the elastic settling of the piles. Some practical design examples are shown. The important aspects of the analysis and the design are pointed out. The complete mathematical background and a comprehensive design tool for free use have been prepared and are provided through a download link: https://gft‐pes.blogspot.com. [ABSTRACT FROM AUTHOR]

Challenges in foundations for high‐rise buildings in glacially preloaded soils The economical and safe design of foundations for high‐rise buildings in Berlin requires a realistic assessment of the expected settlements for both the building itself as well as for existing neighboring structures. In this context taking account of glacial preloading and the corresponding increase of soil stiffness has a significant impact on the quality of the settlement prediction. In this paper different approaches to derive soil stiffness parameters are compared with regard to settlement measurements at various buildings in Berlin. It can be shown that stiffness values based on the correlations of EC 7‐2 significantly underestimate the in‐situ stiffness of the soil types encountered in Berlin. A more realistic reproduction of soil stiffness is possible with the stiffness values of TEV Gesteinseigenschaften and a stiffness approach developed by the authors. In these approaches soil density respectively soil consistency as well as the geological history of the soil layers with regard to glacial preloading are taken into account. [ABSTRACT FROM AUTHOR]

Geotechnical and tunneling aspects during the construction of the U5 in Frankfurt am Main The new district Europaviertel in Frankfurt is developed, and will be connected to the public transport system. Therefore, two tunnel tubes of 7.1 m in diameter and approximately 840 m in length will be excavated with an EPB‐TBM. The ARGE U5 Europaviertel, PORR and Stump, were selected by the client, the Stadtbahn Europaviertel Projektbaugesellschaft (SBEV), to build the tunnels. The start for the tunnel drive of the south tube was in August 2019. The project has challenging subsoil conditions. Especially the Frankfurt Clay with chalk and sandstone layers is important but also the western part, directly after the start of each tunnel drive, is challenging due to the heterogeneous subsoil conditions, too. [ABSTRACT FROM AUTHOR]

Evaluation of software for the creation of soil models In the "Road Map for Digital Design and Construction" of the Federal Ministry of Transport and Digital Infrastructure (BMVI), public infrastructure projects are required to use the Building Information Modeling (BIM) method. As a result, the Federal Department of Foundation Engineering of the Federation of the German Construction Industry (Hauptverband der Deutschen Bauindustrie e. V.) demands a discipline‐specific model for foundation soil from the client in its technical position paper. The discipline‐specific model should consist of the earth's surface in the form of a digital terrain model (DTM), the soil layer model and also the subsoil data on which it is based (drillings, survey data, etc.), as well as layer information and soil characteristics of the subsoil on the basis of the geotechnical report. The location of the layer boundaries between the outcrops is to be derived by using interpolation methods and adjusted by manual post‐processing. In order to manage these challenges, different software is evaluated. [ABSTRACT FROM AUTHOR]

Advanced application of barodesy in finite element calculations Advanced application possibilities of barodesy in FE‐calculations are presented in this article. On the one hand, the application of the intergranular strain concept to consider the stiffness increase in the small strain range is presented, together with the corresponding FE implementation. By using the so‐called asymptotic State Boundary Surface of barodesy, the effects of exceeding admissible states associated with the intergranular strain concept can be reduced, allowing a more realistic deformation prediction. On the other hand, an improved approach to stability analysis by means of parameter reduction for barodesy is presented. Using simple FE applications, the presented extensions are verified and their influence on the calculation result is investigated. [ABSTRACT FROM AUTHOR]

Project FOUR: Top‐Down‐Method with a combined diaphragm wall‐pile‐raft‐foundation At present the revitalization project FOUR of the former Deutsche Bank area in the center of the city of Frankfurt is under construction. The project contains of four high‐rise buildings. These four high‐rise buildings are sharing a reinforced concrete slab at ground level and four basement levels. The deep excavation has an area of approx. 15,000 m2 and a depth of 20 m and is surrounded by other skyscrapers. A total number of 370 bored piles were required. For the basement excavations the top‐down method was considered as an appropriate method in the conceptual design stage. It is the first time that a diaphragm wall is being constructed in the city center. Hence, it was essential for the realization of the project with the large‐scale top‐down method and construction embedded permanent diaphragm wall, that appropriate verification strategies were successfully developed. [ABSTRACT FROM AUTHOR]

Execution of a building pit under Amsterdam Central Station using ground‐freezing technology Construction of a building pit underneath one of the busiest railway stations in the Netherlands, with as a little disturbance to the public as possible, calls for innovative engineering solutions. This paper focuses on the design and execution methods for the project "Cuyperstrap", a staircase connecting the entrance hall of the Amsterdam Centraal Station and the subjacent metro distribution level. Due to the challenging boundary conditions, e.g. limited workspace, high groundwater level and fragile adjacent structures, common methods for constructing building pits were not applicable. Using a retaining wall consisting of artificially frozen ground Max Bögl BV was able to execute the project successfully. Artificial ground freezing is a technique commonly known in tunnelling and mining projects, but as is shown here can also be applied to other fields of structural engineering. Freezing the pore water in the ground increases the bearing strength and makes the frozen area impermeable. The iteratively refined design included structural and thermal calculations, taking into account the on‐site conditions. Starting with drilling of the freeze pipes and installation of the site equipment the construction period commenced at the beginning of 2019. The freezing period started in April and ended in November, after completion of the outer concrete structure. The Cuyperstrap was be opened to the public in July 2020. [ABSTRACT FROM AUTHOR]

Numerical studies for the support of excavation pits and slopes with panels In this contribution the results of numerical studies of the investigation of the internal and overall bearing behaviour of vertical panels and shell type support systems for excavation pits and slopes are presented. Such types of support systems are used, when the installation of nails and/or ground anchors is not possible e.g. because of legal restrictions concerning the respective interest of neighbours. Support panels and shell type support systems can be constructed for instance by means of contignuous bored pile walls, jet grouting columns or mixed in place columns. The verification procedure for the external bearing capacity of such panels is in general performed by simplified analytical methods, called „Palisadentheorie". The verification procedure for the internal bearing capacity of such structures is in most cases not possible employing analytical methods. The numerical studies presented in this contribution highlight the significant potential for optimization of such structures designed by the above mentioned analytical „Palisadentheorie". Furthermore, the internal bearing capacity of such structures is discussed, applying advanced constitutive models for soil as well as structural elements. Based on the results of the presented numerical investigations it can be concluded that there is a significant optimization potential for the design of such structures using 3D‐numerical methods with advanced constitutive models. [ABSTRACT FROM AUTHOR]

Forecast model for soil movements caused by dewatering – Development and previous application in the Rhenish lignite mining area A model based on soil mechanics principles was developed to map current soil movements and to forecast further soil movements caused by dewatering. To date, the model has been applied at more than 30 points in the Rhenish lignite mining area, both within the framework of the evidence required under mining law by RWE Power AG and within the framework of environmentally relevant investigations by the Landesamt für Natur, Umwelt und Verbraucherschutz NRW. The soil movement behaviour observed and measured since the 1950s can be mapped qualitatively and quantitatively very well and future soil movements can be forecasted based on this. Uncertainties that still exist with regard to the uplift behaviour of cohesive soils can be further reduced by continuous measurements and recalibration, thus continuously improving the forecast. Furthermore, the model can be easily adapted to new boundary conditions, e.g. as a result of the coal phase‐out decided by the Federal Government, and can also in principle be transferred to other lignite mining areas or adapted for other applications. [ABSTRACT FROM AUTHOR]

The coefficient of earth pressure at rest K0 of frictional soils – material law and determination from results of a standard triaxial test The conventional formula of Jáky and a newer calculation approach for the coefficient of earth pressure at rest (K0) are reviewed and evaluated. Considering a straightforward material law for proportional strain and stress paths observed with highly accurate rectilinear extension tests on sand, an equation for the K0 value as a function of the angle of internal friction and the ratio of dilatancy under triaxial compression is deduced. The included constants can be determined with an ordinary drained triaxial compression test. The K0 values resulting from the presented material law are significantly higher than the values from the existing methods. The differences increase with increasing angle of internal friction and ratio of dilatancy. [ABSTRACT FROM AUTHOR]

Effects of groundwater flow on local hydraulic safety – examples with FEM In practice, hydraulic safety is usually calculated for predefined failure mechanisms and without consideration of a soil history. The mathematical analysis of changes in effective stresses induced by groundwater flow can be related to local hydraulic safety in the considered area. For this purpose, pore water pressure distributions and effective stresses are evaluated with the FE method. In FE software, which enables calculations with pore water pressures, adjustments in post‐processing are sufficient to determine local hydraulic safety level. [ABSTRACT FROM AUTHOR]

Settlement performance of vibratory compacted granular soil. Vibratory compaction is widely used to reduce settlement in granular soils. The cone penetrometer CPT and the Dilatometer DMT are particularly suited for the planning and execution of compaction projects, as the soil stiffness as well as the increase in horizontal stress can be measured. The stress path during vibratory compaction is described, which explains the permanent increase of horizontal stresses and the resulting preloading effect. The settlement behaviour of normally consolidated soils is discussed. The application of the tangent modulus method for settlement analysis before and after compaction is presented. The modulus number as well as the overconsolidation ratio can be derived, from field tests (CPT and DMT). Compaction criteria for settlement reduction can be chosen based on CPT and DMT investigations. The practical application of the proposed method of settlement analysis is described by a case history, where a silty sand was compacted using the VibroWing method, followed by surface treatment using a vibratory plate. [ABSTRACT FROM AUTHOR]

Highlights from the article: Die vorliegenden Empfehlungen befassen sich mit dem Nachweis und der Quantifizierung der Standsicherheit von geotechnischen Bauwerken, bei denen die Berechnungen mithilfe der FEM durch die Reduzierung der Festigkeitsparameter des Bodens durchgeführt werden. Wenn für das Tragverhalten eines Systems die Berücksichtigung großer Verformungen relevant wird und dies durch entsprechende geometrisch nichtlineare Berechnungsansätze berücksichtigt wird, muss beachtet werden, dass in dem durch die Reduzierung der Festigkeitsparameter hervorgerufenen rechnerischen Grenzzustand die errechneten Verformungen keine physikalische Grundlage haben. Die in Tabelle dokumentierten Berechnungsergebnisse zeigen, dass die Baugrundschichtung mit den unterschiedlichen Scherparametern den maßgeblichen Einfluss auf die berechneten Sicherheiten besitzt. Der Versagensmechanismus, der mit der KEM ermittelt wurde (Bild), unterliegt ebenso wie die in Bild und dargestellten Bruchfiguren, die mit klassischen Verfahren ermittelt wurden, der irrealen Annahme, dass die Stützwand nicht rotieren kann.

Numerical determination of the slopes stability under earthquakes – an example of an earth dam in a centrifuge experiment. The stability of slopes can be severely affected by seismic events. Although the slope behaviour under earthquakes is complex, most calculation methods in practice assume a pseudo‐static situation in which the dynamic earthquake effect is replaced by an additional static force. In this work, a recalculation of a centrifuge test is used to check to what extent the pseudo‐static analysis can describe the failure by reaching the states out of the limit equilibrium. Subsequently, a dynamic FEM‐recalculation of the centrifuge is been performed in order to test the potential of an advanced analysis with hypoplasticity. The results of the FEM calculation are used for the back analysis of the pseudo‐static results in order to illustrate the deficits of the latter method. A possible combination of dynamic FEM‐calculations and the pseudo‐static analysis is discussed with respect to a more realistic procedure. For this purpose, additional dynamic FEM‐calculations are carried out with an elastoplastic constitutive model. [ABSTRACT FROM AUTHOR]

Comparison of different material models by simulation of an excavation. The choice of a suitable material model, which is able to represent the soil behaviour in FE‐simulations realistically, has a significant influence on the calculation results obtained. With the help of comparative calculations using several material models, the similarities and differences in the results will be clarified. For this purpose, an excavation is simulated and both the occurring deformations and the stability determined by parameter reduction are considered. Besides the more known models Hardening Soil and Hypoplasticity, Barodesy is presented as model for FE‐calculations. While all models show comparable deformations, the calculated stability shows clear differences. [ABSTRACT FROM AUTHOR]

Contribution to solution of bearing capacity problems by kinematical elements with dilatancy. After a repetition of the upper and lower bounds of plasticity theory and a short introduction to the Kinematical Element Method, a simple example of earth pressure is presented. The graphical output shows the different results due to dilatancy and without, which hopefully will be accepted as an objective view to an often controversely discussed matter in soil mechanics. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of the spread of the temperature plume of small borehole heat exchanger systems. Small shallow borehole heat exchanger (BHE) systems with a heat capacity smaller than 30 kW can be found mostly in the private housing sector. The heat extraction of the BHEs causes temperature changes in the ground. The form of the temperature changes depends on the project relevant parameters such as geothermal ground conditions, operation of the BHEs and groundwater movement. During the approval processes the approval authority claims for global and non‐project related border distances of the BHEs. The compliance can be difficult due to smaller property sizes. The use of an analytical method for the determination of the length of the temperature plume is needed in order to allow the determination of border distances fitting to the project while taking into account the groundwater velocity, the operation mode as well as the number of BHEs of small shallow geothermal systems. [ABSTRACT FROM AUTHOR]

Abstract: Geotechnical rich due to loss of stability. In this paper the geotechnical risk as expected value of sizes of geotechnical events within an operation region and time is specified. Causative losses of stability are related with domino‐like chain reactions and losses of control which as yet cannot be calculated. Their physical extent is given by the released energy. The bigger this is and the more something or someone is exposed to a chain reaction, the higher is the damage. Due the “wild” randomness the number of chain reactions depends on the energy which is released at least by a power‐law. The exponent of it is nearly –1 as the reaction of geo‐matter is nearly rate‐independent. The power‐law has physically justified lower and upper cut‐offs. Thus the geotechnical risk is the product the lower damage cut‐off and the logarithm of the ratio of upper and lower cut‐offs. Expected values of cut‐offs have to be determined for scenarios by means of ground data, technical and other actions. Thus the risk can be calculated objectively, insurance fees can be estimated and total expenses from feasibility study to use can be reduced. [ABSTRACT FROM AUTHOR]

Abstract: Pile driving of open‐ended steel piles in offshore wind industry – comparison of prognosis and measurements. Today popular foundation methods of offshore wind turbines (Jackets, Tripods or Monopiles) are mainly realised with steel pipe piles. Against the background of cost effectiveness, the selection of a driving system as well as design fatigue calculations it is of importance to run driveability analysis prior to the installation process. Results and criteria for that are amongst others (e.g. propagation of underwater sound, not discussed here) blow count and duration of a driving process as well as the soil resistance at the moment of driving (with or without driving stops) being the so‐called static resistance to driving (SRD) and compressive and tensile stresses within the pile. At real pile driving usually dynamic pile tests are performed in order to record real blow counts und stresses in the pile and furthermore, to verify pile capacity. In the present paper theoretical driveability analyses and thus SRD models will be compared with results of dynamic pile tests in certain offshore wind farms in the North and Baltic Seas in order to check their applicability based on sand or chalk dominated soils. [ABSTRACT FROM AUTHOR]

Vibratory driving is a common method for installing or extracting piles and sheet piles as well as for deep vibratory compaction. The most important parameters are vibration frequency, vibration amplitude and eccentric moment. These parameters govern vibratory driving and, in particular, the soil resistance at the toe and along the shaft of a pile. Pile driving causes oscillating horizontal ground vibrations in coarse-grained soils. It can be shown that these horizontal vibrations reduce the shaft resistance during driving. The process results in a permanent increase in the horizontal effective stress, which causes arching around the vibrated pile. The increase in horizontal effective stress is also important for deep vibratory compaction. The resonance frequency of the vibrator-pile-soil system significantly affects pile penetration and the emission of ground vibrations. At resonance, the vertical vibration velocity in the soil reaches a maximum and pile penetration becomes very slow, whereas beyond resonance, the vibration velocity decreases and the pile penetration speed is high. Field monitoring of the vibratory driving process can be used to optimize vibratory pile driving, as examples have shown. A new concept is proposed in which the driveability can be determined from a correlation between penetration resistance measurements (blows/depth) and penetration speed. The validity of the concept is demonstrated by a case history and project references. [ABSTRACT FROM AUTHOR]

Calculation of the earth pressure at rest - analytical approaches for arbitrary inclinations of ground surface and wall. The earth pressure at rest is defined as a statically indeterminate stress strain problem. The formulas to estimate the coefficients of earth pressure at rest for normally consolidated as well as for over consolidated soils commonly assumed and proposed in DIN 4085 are explained on the basis of more general material behaviour observed in element tests. Equations to calculate the earth pressure at rest in case of horizontal ground surface and inclined wall are deduced from the rules of stress transformation. For the case of a uniformly inclined ground surface the equations of the stress field are formulated using a characteristic coordinate system with axes parallel and orthogonal to the surface. Thus, the equilibrium equations are reduced from a pair of partial to two ordinary differential equations which simply can be solved, and the coefficient of earth pressure at rest depending on the angle of surface inclination β can be introduced. This coefficient is estimated by interpolation between the values for β = 0 and the limit case β = φ (angle of internal friction). The interpolation formula is the unique assumption in the calculation. On the basis of these equations the earth pressure at rest on a wall with given inclination is determined analogously to the case with horizontal ground surface by stress transformation. Examples are presented. A simplified calculation method used commonly in practice is elucidated and discussed; for its application to inclined walls under inclined ground surface a correction factor is deduced from the strict method. [ABSTRACT FROM AUTHOR]

About the influence of one-way loading on the bearing be haviour of precast concrete piles for onshore wind energy plants. Due to the energy transition several wind energy plants are built. Precast impact driven concrete piles represent one option to realise foundation piles onshore. In Germany, the bearing capacity of these piles can be estimated using empirical values taken from current standards or using in-house specifications of plant producers. Cyclic loading of such foundations exceeding 20 % of the static characteristic pile bearing capacity have to be considered when estimating the pile bearing capacity. However, the consequences of cyclic loading for the bearing behaviour of precast impact driven concrete piles are not fully understood yet. Therefore, field tests in cohesive and non-cohesive soils considering static and cyclic loading with different load amplitudes have been conducted and are presented within this paper. Using prevalent methods stated in current standards to estimate the bearing capacity of piles under static and cyclic loading are applied to recalculate the results of the field tests. Thereby, the suitability of these methods for estimation of the bearing behaviour of precast impact driven concrete piles under static and cyclic loading is reviewed. [ABSTRACT FROM AUTHOR]