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Understanding the mechanism of excess pore water pressure generation in subgrades is essential for not only designing but also further maintenance purposes. The primary goal of this research was to investigate excess pore water pressure generation in fine granular materials under cyclic loading. A series of undrained cyclic triaxial tests were performed to study the excess pore water pressure generation in two selected fine granular materials: (1) railway sand and (2) tailings. The excess pore water pressure response of these materials was evaluated in terms of density conditions, number of cycles, and applied cyclic stress ratios (CSR). As a result, excess pore water pressure accumulated over time due to cyclic loading. However, its accumulation was significantly dependent on the governing factors, i.e., densities, CSR values, and material types. The excess pore water pressure exhibited a slight increase at low CSR values, but a sharp increase was observed at higher CSR values, which ultimately led to a failure state after a certain number of cycles. In addition, under the same loading conditions, the samples that had higher relative compaction showed better resistance to cyclic loads as compared to those with lower relative compaction. Finally, a relationship between excess pore water pressure and cyclic axial strain of the fine granular materials was discovered. Validerad;2023;Nivå 2;2023-03-27 (hanlid);Funder: Swedish joint research program for road and railway geotechnology Bransch-samverkan i grunden (BIG); Swedish Hydropower Centre (SVC)

To enable assess slope stability problems efficiently, various machine learning algorithms have been proposed recently. However, these developments are restricted to two-dimensional slope stability analyses (plane strain assumption), although the two-dimensional results can be very conservative. In this study, artificial neural networks are adopted and trained to predict three-dimensional slope stability and a program, SlopeLab has been developed with a graphical user interface. To reduce the number of variables, groups of dimensionless parameters to express stability of slopes in classic stability charts are adopted to construct the neural network architecture. The model has been trained with a dataset from slope stability charts for fully cohesive and cohesive-frictional soils. Furthermore, the impact of concave plan curvature on slope stability that is usually found by excavation in practice is investigated by introducing a dimensionless parameter, relative curvature radius. Slope stability analyses have been conducted with numerical calculations and the artificial neural networks are trained with dimensionless data. The performance of the trained artificial neural networks has been evaluated with the correlation coefficient (R) and root mean square error (RMSE). High accuracy has been found in all the trained models in which R > 0.999 and RMSE < 0.15. Most importantly, the proposed program can help engineers to estimate 3D effects of a slope quickly from the ratio of the factors of safety, FS3D/FS2D. When FS3D/FS2D is large (such as larger than 1.2), a 3D numerical modelling on slope stability analyses that can consider complex 3D geometry and boundary condition is advised. Validerad;2021;Nivå 2;2021-08-17 (johcin)

Field sampling for evaluation of mechanical behaviour in embankment dams is not easily performed, because the performance and the safety of the structure may be unfavourably affected. A non-destruc...

Fine-grained soils are often not suitable as subsoil for roads or railways or other large-scale constructions due to their sensitivity to settlements as well as their frost susceptibility. The engi ...

The rocking response of embedded foundations in sand is studied, combining centrifuge modelling and numerical analysis. In total, 51 centrifuge model tests are conducted at ETH Zurich, varying the embedment ratio D/B and the factor of safety against vertical loading (bearing capacity), Fs. The experimental results are used to validate three-dimensional finite-element models, which are subsequently employed for a parametric study. The initial two phases of non-linear response are studied, namely quasi-elastic and non-linear response, while the third phase (plastic response) will be examined in a forthcoming publication. Regarding small-strain rocking stiffness, Kr (first phase), an extended formula is proposed, accounting for soil inhomogeneity along the embedded sidewalls. Kr is shown to decrease with Fs, due to initial soil yielding from vertical loading. The formula is further extended to account for the role of Fs, offering improved estimation of small-strain rocking stiffness. With respect to the non-linear response (second phase), it is shown that the degradation curves of rocking stiffness with rotation can become approximately dimensionless, if the rotation θ is normalised to a characteristic rotation, θs. The increase of D/B leads to a reduction of the normalised rotation θ/θs at which the non-linear response is initiated, due to the increasing participation of sidewall friction.

Small-strain foundation response has mostly been studied analytically, with limited experimental verification against 1g physical model tests. This paper revisits the problem of small-strain foundation response, conducting a series of centrifuge model tests, aiming to eliminate the limitations of 1g testing. A centrifuge modelling technique is developed, combining static pushover and dynamic impulse testing for similar systems. To allow for derivation of meaningful insights, a novel procedure for in-flight measurement of the distribution of shear modulus with depth is also developed. The latter combines spectral analysis of surface waves (SASW) measurement of the shear modulus G0 at the surface, and estimation of the distribution of the shear modulus G with depth using acceleration measurements in shaking tests. A novel centrifuge tube–actuator is developed and employed to discharge spherical projectiles against single-degree-of-freedom models lying on shallow foundations on sand. This allows generating dynamic impulse excitation, which is used to measure the small-strain dynamic rocking stiffness. The developed actuator is versatile, and was also used for in-flight SASW testing. The centrifuge model tests are shown to confirm the widely used and well-known formulas. This good agreement can also be seen as a confirmation of the validity of the developed experimental techniques.

Managing tailings deposition in cold climate requires specific measures not to create permafrost. The risk of generating permafrost due to tailings deposition exists even in regions where permafrost would naturally not occur. Material being frozen during winter might not fully thaw in the following summer due to added height of the tailings on the surface. Such embedded layers of permafrost should be avoided especially close to tailing dams. Main reasons are to prevent impermeable layers in tailings facilities, and to reduce the risk of having implications if such layers thaw during warmer summers causing increase in pore water pressure, reduced effective stress, and increased water content. This paper presents a numerical study on the effects of tailings deposition in cold regions in relation to the potential formation of permafrost. Various deposition rates, schedules and tailings properties were evaluated. One-dimensional heat conduction analyses were performed with a temperature scenario representing a mine district in northern Sweden. Results show, that the thickness of permafrost layers increase with increased deposition rate and with increased water content. It was also shown that wet and loose tailings must be deposited in short periods during summer to avoid permafrost generation. In the case of dry and dense tailings more time is available for deposition in order not to cause aggradation of permafrost in the deposit. These findings can help mining operation to set up deposition schedules for tailings facilities in cold climate. For known tailings properties, results can be used to identify periods of the year when, and how much, tailings can be deposited in critical areas of a deposit in order to avoid permafrost formation.

A freezing test apparatus was supplemented with a digital camera to allow for recording and monitoring one-dimensional freezing tests to analyze the development of ice lenses via particle image velocimetry (PIV) in the laboratory. Two tests on disturbed, partially saturated samples of silt loam were conducted. Image recording and correlation analyses provided detailed information about frost front penetration and ice lens formation(s) under varying temperature boundary conditions. Thawing has also been regarded in further studies. Results of the image analyses were compared to readings from conventional displacement measurements during the same test. Significant agreement between the results of image analyses and displacement measurements has been found. Advantages and disadvantages of utilizing image analysis methods were discussed. Potential remedies for overcoming the drawbacks of using image analysis are suggested. Image analysis is shown to be a viable method in further understanding of frost heave mechanisms.

Mosul Dam is an earth fill dam, with a storage capacity of 11.11 km3 constructed on highly karstified gypsum beds alternating with marl and limestone. After impounding in 1986, seepage locations were recognized. The dam situation now indicates that it is in a state of extreme relative risk. If it fails, then 6 million people will be affected and 7202 km2 area will be flooded. Grouting operations will elongate the life of the dam but will not solve the problem. Building a protection dam downstream will be the best measures to secure the safety of the downstream area and its’ population.

The purpose of this experimental investigation is to obtain strain measurements via optical fibre sensors in the drum geotechnical centrifuge of ETH Zurich. It is part of a test series with main goal to study the behaviour of reinforced slopes subjected to self weight loading and subsequently to an impact from a rockfall event. In total 13 scaled reinforced slope models were built with a height of 180 mm and a slope inclination of 2V:1H, optimising the materials used and the different ways of model making. The maximum g-levels were 50 and 100 g and the impact loading was applied at 50 g. The optical fibre sensors were placed on various layers of the reinforcement and at different positions. Strain measurements that were recorded during different tests are logical and expected, demonstrating that optical fibre sensors can successfully be used for measuring linear strain on reinforcement layers that are tested under enhanced gravity in the geotechnical centrifuge. The experimental set up as well as the opportunities and challenges of these measurements are presented and discussed. Finally, correspondent prototype numerical models were created and analysed and the results of this analysis are compared to the corresponding experimental ones.

The Tohoku earthquake in 2011 caused several damages to the pipeline network in the Tokyo Bay area. Predominantly, the main damages were noticed in the artificial islands, where liquefaction destroyed and deformed numerous embedded pipelines. During a seismic event, lifeline systems are subjected to buoyancy forces in the liquefied soil, causing permanent deformations to pipelines and interrupting their serviceability. The current mitigation methods (backfill improvement) are not suitable for regions prone to future earthquakes because pipe excavation and improvement is time-consuming and costly. Therefore, the aim of this study is to present a new effective mitigation method: the so-called horn-type structure. This innovative mitigation method was analysed with different analytical, experimental and numerical methods.

In this paper, a new approach abbreviated as SOCP-SFEM is developed for analysing geomechanical problems in elastoplasticity. The SOCP-SFEM combines a strain smoothing technique with the finite element method (FEM) in second-order cone programming (SOCP) and thereby inherits the advantages of both the smoothed finite element method (SFEM) and the SOCP-FEM. Specifically, the low-order mixed element can be used in the SOCP-SFEM without volumetric locking issues and the singularity associated with some typical constitutive models (e.g. the Mohr-Coulomb model and the Drucker-Prager model) is no longer a problem. In addition, the frictional and the cohesive-frictional interfaces can be implemented straightforward in the developed SOCP-SFEM owing to the adopted mixed variational principle and the smoothing technique. Furthermore, the multiple contact constraints, such as a cohesive interface with tension cut-off which is commonly used for analysing the bearing capacity of a pipeline buried in clays, can be simulated with little extra effort. To verify the correctness and robustness of the developed formulation for SOCP-SFEM, a series of benchmarks are considered where the simulation results are in good agreements with the analytical solutions and the reported numerical results.

Nonlinear analysis for reinforced concrete members (R.C.) with two types of bars also with unsaturated and saturated soils was used to represent the models. To control the corrosion in the steel bar that used in R.C. member and decrease the cost, the geogrid with steel bar reinforcement are taken in this study to determine the effect of load-deflection and stress-strain relationships. The finite element method is used to model the R.C. member, bars and soil. A three-dimensional finite element model by ABAQUS version 6.9 software program is used to predict the load versus deflection and stress versus strain response with soil. The results for the model in this study are compared with the experimental results from other research, and the results are very good. Therefore, it was concluded that the models developed in this study can accurately capture the behavior and predict the load-carrying capacity of such R.C. members with soil and the maximum stresses with strains. The results show plastic strain values in the R.C. member with saturated soil are larger than their values in unsaturated soil about (54%, 58%, and 55% and 52%) when the geogrid ratios are (without geogrid, 60%, 40% and 20%) respectively, with the same values of stresses. Validerad;2019;Nivå 2;2019-11-06 (johcin)

Excessive richness of nutrients in water bodies such as rivers, lakes and ponds lead into deterioration of aquatic life as a results of dense growth of algae. Phosphate is one of the main nutrients that should be controlled to prevent this serious issue. Utilizing low cost material as a phosphate sorbent is offering a treatment method characterized as a sustainable solution. In this study the efficiency of biomass bottom ash BBA as phosphate sorbent material from aqueous solution is investigated. Batch experiments were undertaken, in which a particular mass of BBA was brought into contact with the phosphate solution. The experiments studied the influence of pH (different phosphate solutions were prepared with pH range 4 to 8), temperature (adsorption capacity measured at the temperature range of 10 to 30 °C), and contact time. In addition, the adsorption isotherm models were also applied to better understand the mechanism of phosphate sorption by BBA. The results revealed that the bonding between the cations (BBA surface) and anions (phosphate solution) is significantly affected by the pH of the solution. BBA presents an excellent phosphate sorption, especially, at low pH value and temperature around 20 oC. The method of this research can be adopted as a followed strategy for examination the capability of selected material for phosphorus removal from wastewater. Validerad;2019;Nivå 2;2019-11-06 (johcin)

Constructing embankments on soft ground to adhere to the requirements of modern codes of practice is challenging without ground improvement. An overview is presented on the types of columnar inclusions and embankment base reinforcement in terms of load–settlement behaviour, together with calculation procedures using partial safety factors. These are based on the Swiss Code 267, Switzerland's national annex to Eurocode 7; they are relevant in the project phase and in understanding the general behaviour of the whole system. Three-dimensional inclusions have been incorporated in a two-dimensional slip circle analysis. Simple assumptions are validated against a physical model for the serviceability limit state, with good agreement. First design approximations may therefore be calculated in this way.

A series of prototype dynamic centrifuge experiments is carried out to investigate the influence of soil properties and structural parameters on the Soil Structure Interaction (SSI) effect. Established analytical models are herein experimentally verified, and are proven accurate in estimating the system's natural frequency characteristics. It is observed that period elongation is strongly correlated to the relative superstructure-foundation stiffness. Although the present study deals exclusively with the small-strain near-linear range, the experimental response indicates occurrence of nonlinearity. The identified damping results remarkably larger than its analytical estimate and proves highly strain-dependent, raising questions on the reliability of existing analytical methods in capturing the actual dissipation mechanisms. An extended experimental dataset is formed under realistic stress and strain soil conditions, and is implemented, for the first time, for verification of existing analytical models offering valuable insight into the theory and serving as a benchmark for engineering practice. ISSN:0267-7261 ISSN:1879-341X

Physical modelling of debris flows has been carried out in the geotechnical drum centrifuge at ETH Zürich. A new apparatus to model debris flows in the centrifuge is described. The apparatus permits the final reach of a typical debris flow to be modelled within the centrifuge, with unconsolidated material flowing down a slope to deposit as a fan around the drum. Experiments are described for both fixed base conditions and erodible bases. Tests to examine the verification (modelling) of models show that debris flow behaviour is governed mainly by friction and consolidation processes, although some resolution is required between flow behaviour downslope and flow arrest during runout. The results are compared with bulk parameters determined for field-scale debris flows. It is found that some important flow mechanisms, such as contact-dominated behaviour and high pore pressures, are developed that are closer to those developed at field-scale than tests conducted at 1g. Velocity profiles for erodible beds are compared with a semi-empirical expression derived for experimental debris flows at 1g. Normalized velocity profiles are found to be in agreement; however, absolute velocities differ from those predicted. Scaling, the limitations of the apparatus, and potential for future work are discussed.

Two instrumented embankments built on a double-porosity landfill of clayey lumps were monitored in situ and modelled in a geotechnical drum centrifuge. Field measurements of hydrostatic levelling, depth reference points and pore pressure gauges showed high and variable compressibility of the landfills. Introductory modelling in a mini-centrifuge, combined with oedometer testing, demonstrated the key mechanisms in the double-porosity fills: irreversible deformation at low stress ranges as a result of rearrangement of the lumps, and reversible deformation (swelling) at higher stresses, similar to the behaviour of reconstituted material. Placing fill under water resulted in high initial void ratios followed by large deformations while loading. Dry filling followed by saturation may be recommended for further development of the landfills in future. Data from the geotechnical centrifuge models confirmed that permeability was controlled by the complex structure of the clay fills. Similarly to the field measurements, there were significant initial settlements on loading as a result of compression of open macro-voids. The double-porosity structure in the fresh fill allowed excess pore pressures to dissipate quickly, which accelerated the consolidation process initially. Thereafter, dissipation was controlled by the permeability of the intragranular pores in the clay, once the intergranular pores had closed.

Stone columns are primarily used for the purpose of ground improvement in fine grained soils in order to reduce settlements and the risk of bearing failure. They are also designed to improve the drainage conditions in the ground and to accelerate the consolidation processes within the clay. However, smear and disturbing effects caused during the construction of stone columns result in degradation of consolidation performance in comparison with the theoretically ideal conditions. Model stone columns are constructed in-flight under 50 times gravity in centrifuge tests and the soil micro-structure in the vicinity of these columns is investigated by applying different methods, including environmental scanning electron microscopy and mercury intrusion porosimetry. The results of these tests confirm that smear and disturbance occur owing to stone column installation and the region influenced can be divided into three sections: a penetration zone (1) where the sand particles are squeezed through the clay; a smear zone (2) where the soil particles have experienced a significant reorientation; and a densification zone (3) where the structure of the clay does not appear to change, but compaction of the clay is measurable. The extremes of the disturbed zone around model stone columns are determined to extend to about 2·5 times the column radius.

Concrete protection galleries are generally used in mountainous regions to protect the local infrastructure and lifelines against potential impacts from rock boulders. These can be protected further by carefully designed cushion systems, most of which rely on granular geomaterials. Rockfall impact energies can reach magnitudes of the order of millions of Joules, requiring understanding of the combined energy absorption mechanisms at high energy levels for improved design of the gallery and cushion. These prototype high-energy ranges can be achieved at the laboratory scale with the help of a geotechnical centrifuge. The model is rotated under high g levels, thereby increasing the unit weight of the material. Prototype energy levels can be represented in a small scale model with consideration of appropriate scaling laws, and although free fall events in a centrifuge experience components of the Coriolis acceleration, projectiles (boulders) will move out of the centripetal gravity field when losing contact with the rotational field. A guiding tube is used in this case to keep the boulder in the acceleration field (ng) in order to achieve sufficient input energy levels to represent existing design criteria. The change in the g-level during the fall of the boulder in the centrifuge, due to the change in the radius, has to be taken into account for determination of the impact energy. In this case, direct application of traditional scaling laws for centrifuge modelling is invalid. This paper focuses on the determination of the change in the g field with time during the fall of the boulder to estimate the g level at the time of impact and this value is used in the calculation of the prototype energy levels. A summary of the performance of various cushion materials is given.

A new 2.2 m diameter drum centrifuge with a maximum acceleration level of 440 g has been installed at the Institute of Geotechnical Engineering of the Swiss Federal Institute of Technology in Zurich (Eidgenossiche Technische Hochschule: ETHZ). Twin concentric shafts allow separate control of a central tool table and a drum channel. Together with multipurpose actuator units, which can be fitted to the tool table, radial, circumferential and vertical control of construction processes or test activities may be achieved. Control and data acquisition systems are provided in modular form, allowing a flexible choice of sampling and recording modes. The development of the facility, the additional accessories required and the first geotechnical centrifuge test are described.

The seismic design of slopes, dams, or embankments is usually based on limit-equilibrium calculations, which include the seismic action by means of an equivalent static force acting on the failure mechanism. This approach is limited, especially in situations in which existing over-inclined structures or steep natural slopes have to be analyzed. An alternative approach which overcomes the limitations of the classical limit-equilibrium calculations is available with displacement-based methods. The displacement-based analysis offers the possibility of evaluating the seismic behavior in terms of displacements, in contrast to the limit-equilibrium calculations, which only provide information about the ratio between the stabilizing and destabilizing forces acting on the structure. The displacement-based approach allows the analysis of the seismic behavior and, based on the resulting deformations, the corresponding risk evaluation. In addition to that, the optimized seismic design of new geotechnical structures is possible by ensuring the compliance of the seismic behavior with given requirements. This paper presents a displacement-based procedure to be incorporated in the Swiss design codes for the seismic analysis of slopes, dams, and embankments.

When performing centrifuge tests, it is necessary to carry out in-flight tests such as the cone penetration test (CPT). Recently, miniature CPTs have formed one collaboration entitled 'European Pro ...