Performance of different constitutive soil models: from element tests to the simulation of vibratory pile driving tests

The present study deals with the investigation of the applicability (by means of parameter calibration), robustness and prediction quality of advanced constitutive soil models for the numerical investigation of complex geotechnical problems. The range of available constitutive soil models extends from simple linear to time-dependent and hydromechanically coupled nonlinear modelling approaches. It is the user's task to select a constitutive model suitable for the problem at hand. This requires in-depth knowledge of the soil behaviour as well as the strengths and weaknesses of the available constitutive models, most of which have only been validated using element test simulations. The procedure from parameter calibration using laboratory tests under well-defined boundary conditions (element tests) to the simulation of boundary value problems is complex in many respects and is often not followed with advanced constitutive models due to the large number of parameters required and the necessary laboratory tests. In this paper, the prediction quality of three models, namely Hypoplasticity with Intergranular Strain, Sanisand and Hypoplasticity with Intergranular Strain Anisotropy is inspected. The investigation is carried out based on back-calculations of laboratory tests and a well-documented model test to evaluate their suitability in representing complex soil mechanical aspects, such as the material behaviour under cyclic loading, particularly pore pressure accumulation. The parameter calibration is performed both "manually" as well as with a specially developed automatic calibration software. Subsequently, model tests of vibratory pile driving in water-saturated sand are simulated using the previously calibrated parameters

Back-calculations of centrifuge tests on pile groups subjected to high-cyclic loading

The majority of heavy or strongly loaded structures, for instance high-rise buildings, large span bridges or gas storage tanks are founded on pile groups. However, current design codes and guidelines do not provide a standard procedure for their design under lateral dynamic and high-cyclic loading arising from e.g. wind, temperature or earthquake loads. To establish appropriate design strategies, a better understanding of the pile-soil, pile-pile and pile-cap interaction is required. This paper is focused on finite element backcalculations of centrifuge tests on single piles and pile groups subjected to up to 500 lateral load cycles. For the finite element simulations, a special calculation procedure is applied, combining two kinds of constitutive models, a conventional (Hypoplasticity with Intergranular Strain extension) and a special highcycle accumulation (HCA) model. The parameters of the constitutive models are calibrated based on static and cyclic laboratory tests on the sand used in the centrifuge tests. The performance of the applied numerical procedure is evaluated based on a detailed comparison of the simulation results with the measured data from the centrifuge tests. Overall the applicability of the used numerical strategy for simulating the behavior of pile groups subjected to high-cyclic loading is shown

Investigation of three sophisticated constitutive soil models: From numerical formulations to element tests and the analysis of vibratory pile driving tests

The performance of three advanced constitutive models has been evaluated based on element tests and on a comparative study on the simulation of vibratory pile driving tests in saturated sand. The inspected constitutive models are the Sanisand model and Hypoplasticity with Intergranular Strain (Hypo+IGS) as well as with Intergranular Strain Anisotropy (Hypo+ISA) extension. The performance of the constitutive models is first evaluated by the simulation of element tests used for the parameter calibration of the sand used in the model tests. The constitutive models are then applied for the simulation of a vibratory pile driving test. The pile penetration, the driving force, the pore water pressure development and the incremental displacement in the vicinity of the pile tip are compared to the measurements in the model tests. The strengths and weaknesses of the different constitutive models are assessed. Generally, the model predictions showed good agreement with the experimental results. Despite different constitutive formulations (hypoplastic vs. elasto-plastic), all three models were able to reproduce the main mechanisms of the driving process properly. It may be concluded that all three models allow a proper prediction of vibratory pile driving as long as a proper calibration of the material parameters is secured

A Review of Medium-to Large-Scale Laboratory Testing Facilities for Soil-Pile Interaction

A recently started European Union (EU) project, GEOLAB brings together 11 unique facilities for studying soil-structure interaction (SSI). The ultimate aim is to integrate key European national research infrastructures into an excellent one-stop-shop for performing groundbreaking research and innovation with respect to SSI in order to address the challenges faced by the critical infrastructures (CI) of Europe. Among these installations is the Geotechnical Test Pit of the Technical University of Darmstadt (TUDa), Germany. With a plan dimension of 19.5 m x 5 m, the facility allows for medium- to large-scale pile model testing, thereby closing the gap between small-scale testing, on one hand, and very rare and expensive in-situ testing, on the other hand. In this paper, the TUDa test pit is presented and a review of other globally existing pile testing facilities of similar scale is given, with focus on parameters as model preparation, pile installation, and instrumentation, among others. The aim is to present the state-of-the art in medium- to large-scale physical modelling of soil-pile interaction, and identify the gaps for further development, particularly where they are relevant for enhancing CI resilience. Potential scope for future collaborations is also highlighted

On the automatic parameter calibration of a hypoplastic soil model

This paper presents an approach for the automatic parameter calibration (AC) of a hypoplastic constitutive soil model. The calibration software developed in this work simplifies the parameter calibration, reduces the subjective “human” factor on the calibration result and lowers the entry hurdle for the use of the hypoplastic constitutive model. The performance of the software was demonstrated by comparing automatically calibrated parameter sets for two sands and their related simulations of the underlying experimental data with simulations using two reference parameter sets. The first reference parameter set was calibrated the classical way, "by hand", and the second was calibrated using the AC tool ExCalibre. Two different optimization methods were used, namely the Differential Evolution (DE) and the Particle Swarm Optimization (PSO). The simulations performed with the parameters obtained from the AC agree well with the experimental data and show improvements over the reference parameter sets. With respect to the optimization method, the performance of the DE proved superior to that of the PSO. Various measures of comparison were examined to quantify the discrepancy between experiment and simulation. By repeating 500 calibration runs, the dispersion of parameters was determined and correlations between different parameters of the hypoplastic model were found

Horizontal Compression Test: A Proposed Method for Indirect Determination of Tensile Strength of Stiff Soils and Soft Rocks

Tensile strength is an important parameter in many engineering applications. In loess slopes, for instance, it governs the development and propagation of tension cracks that usually ultimately lead to crack–sliding and toppling failures, which are among the most common modes of slope failure in the Loess Plateau of China. Reliable measurement of tensile strength of geomaterial is therefore a necessity. Commonly used methods for tensile strength measurement have important limitations and shortcomings, which become magnified when dealing with soil and soft rock. This study developed a new indirect tensile test, the Horizontal Compression test, for use with these materials. The proposed method not only involves simple sample preparation and test operation, it also addresses the eccentric force and stress concentration problems that are common in conventional tensile tests. To evaluate the method’s validity, its performance was compared with the ISRM-suggested direct tensile test and the closely related Brazilian test. The tensile strength values from the horizontal compression test strongly correlate with those from the direct tension test, and are more stable than those obtained with either of the two conventional tests. Thus, the proposed method can be used and deemed more suitable for tensile strength determination than these conventional test methods

Effect of soil moisture content on the bearing capacity of small bored piles in the unsaturated soil of Maringá, Paraná, Brazil

In this study, the influence of soil moisture on the bearing capacity of piles founded in an unsaturated clay soil was investigated. The soil studied, composing the upper soil layer in Maringá, Brazil, is lateritic, has degree of saturation between 37% and 70% and has collapsible behaviour when wet. The bearing capacity was determined by full-scale load tests following the Brazilian Standard for Static Load Test. Two pile lengths, 4 m and 8 m, were considered. To analyse the influence of soil moisture, two tests were performed for each pile length: one in soil in its natural moisture content and another in pre-moistened soil. Results show that for both pile lengths, an increase in water content caused a significant reduction in bearing capacity, which is attributed to the decrease in the matric suction of the soil. This is confirmed by the results of the initial evaluation made on the variation of matric suction and its contribution to the bearing capacity with changes in water content. In summary, this study confirms that the pile bearing capacity in unsaturated soil is dependent on soil water content, highlighting the fact that the approach of assuming full saturation condition in the evaluation of the pile bearing capacity in such soil may give erroneous results. Moreover, this study demonstrate that the empirical methods most commonly used in Brazil for pile bearing capacity determination, the Décourt & Quaresma and Aoki & Velloso methods, are overly conservative when applied to the Maringá soil

Climate Change Adaptation of Geo-Structures in Europe: Emerging Issues and Future Steps

Climate change is already being felt in Europe, unequivocally affecting the regions’ geo-structures. Concern over this is rising, as reflected in the increasing number of studies on the subject. However, the majority of these studies focused only on slopes and on a limited geographical scope. In this paper, we attempted to provide a broader picture of potential climate change impacts on the geo-structures in Europe by gathering the collective view of geo-engineers and geo-scientists in several countries, and by considering different geo-structure types. We also investigated how geo-structural concerns are being addressed in national adaptation plans. We found that specific provisions for geo-structural adaptation are generally lacking and mainly come in the form of strategies for specific problems. In this regard, two common strategies are hazard/risk assessment and monitoring, which are mainly implemented in relation to slope stability. We recommend that in future steps, other geo-structures are likewise given attention, particularly those assessed as also potentially significantly affected by climate change. Countries considered in this study are mainly the member countries of the European Large Geotechnical Institutes Platform (ELGIP)

Climate Change Adaptation of Geo-Structures in Europe: Emerging Issues and Future Steps

Climate change is already being felt in Europe, unequivocally affecting the regions’ geo-structures. Concern over this is rising, as reflected in the increasing number of studies on the subject. However, the majority of these studies focused only on slopes and on a limited geographical scope. In this paper, we attempted to provide a broader picture of potential climate change impacts on the geo-structures in Europe by gathering the collective view of geo-engineers and geo-scientists in several countries, and by considering different geo-structure types. We also investigated how geo-structural concerns are being addressed in national adaptation plans. We found that specific provisions for geo-structural adaptation are generally lacking and mainly come in the form of strategies for specific problems. In this regard, two common strategies are hazard/risk assessment and monitoring, which are mainly implemented in relation to slope stability. We recommend that in future steps, other geo-structures are likewise given attention, particularly those assessed as also potentially significantly affected by climate change. Countries considered in this study are mainly the member countries of the European Large Geotechnical Institutes Platform (ELGIP)

Beiträge zum 29. Darmstädter Geotechnik-Kolloquium am 7. März 2024

Themenschwerpunkte: 1. Klimawandelfolgen und Nachhaltigkeit 2. Digitalisierung und künstliche Intelligenz 3. Planung und Bemessung von Infrastrukturprojekten 4. Großprojekt