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The use of geophysical methods in dam sites investigations and safety monitory has proved their good value and versatility in many earthfill dam sites as early as the 1920s. In the following years great development has occurred in the methods, application procedures and tools used. They may be considered today as good ways for carrying out observation tasks on existing dams in non-intrusive and much faster and cheaper ways than the traditional geotechnical methods. It is possible using them to discover anomalies in the dam body or its foundation at an early stage and allowing quick intervention repair works. These methods seek to register and present variations in the basic geotechnical material properties in dams such as; bulk density, moisture content, elasticity, mechanical properties of rocks, electrical resistivity and mineralogy and magnetic properties and so forth. Such variations can indicate increasing seepage flow, progression in cracks’ sizes, formation of voids, caverns and other instability manifestations. Depending on how any investigation is carried out and the targeted anomaly, there is now selection of these methods such as: Electromagnetic Profiling (EM), Electrical Resistivity Tomography (ERT), Self- Potential (SP), Ground Penetration Radar (GPR), variety of Seismic Methods (SM) which can be applied using such equipment as in Seismic refraction, Seismic Reflection, Multi Analysis of Rayleigh surface waves (MASW) instruments, or using Refraction Micrometer (ReMi), macro-gravity method, and Cross-Hole Seismic Tomography. In addition, Temperature Measurements and other less used methods can be used like Microgravity measurement, Magnetic Profiling and Radio Magnetotelluric methods. An attempt is made here to cover the details of these methods, their advantages and limitations and to prove their usefulness in many dam sites all over the world. One observed issue is their adaptability to embankment dams more than to concrete dams and their popularity for checking seepage related problems and material changes within dam bodies and their foundations such as formation of voids and sinkholes. Validerad;2020;Nivå 1;2020-09-29 (johcin)

Water flow direction and velocity affect and controls erosion, transport and deposi- tion of sediment in rivers, reservoirs and different hydraulic structures. One of the main structures affected is pumping stations within the dams wherein the velocity distribution near the station intake is disturbed. The two-dimensional (2-D) HEC-RAS 5.01 model was utilized to study, analyse and evaluate the effects of pumping rates and flow depth on the flow velocity distribution, flow stream power and their effects in the Mosul Dam reservoir. The pumping station was considered as a case study. The station is suffering from sediment accumulation around, and in, its intake and suction pipes. The main inflow sources to the reservoir are the Tigris River and run-off from the valleys within its basin. The reservoir was divided into two parts for the present study, including the upper part near the pumping station (analysed as a two-dimen- sional zone), while the lower part was analysed as a one-dimensional flow to reduce the simulation period computation time (1986–2011). Different operation plans (i.e. pumping rate and water depth) were considered. The results of the depth-averaged velocity model indicated that when the pumping station was working at a range from the designed full capacity (100% to 25% of its full capacity), the maximum flow ve- locity increased from 75 to 4 times the normal velocity when there is no pumping dependent on pumping rate and flow depth. For the same operation plans, the flow stream power varied from around zero values to 400 times at full pumping capacity and low flow depth. For sediment routing along the reservoir, the considered statisti- cal criteria indicated the model performance in estimating the total sediment load deposition and invert bed level is much better than in the case of erosion and deposition areas for different considered bed sections of the reservoir. Validerad;2020;Nivå 1;2020-03-30 (alebob)

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...

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.

For discrete element methods (DEMs), integrating the equation of motion based on Newton's second law is an integral part of the computation. Accelerations and velocities are involved even for model ...

Sedimentation of reservoirs has its negative impacts on dams, first by reducing useful storage, altering the benefit/cost ratio originally calculated for the dam, and second by reducing the dams’ capacity for flood routing; increasing flooding hazards on the dam itself and for the downstream. More problems can be created by sediments and floating debris during floods on outlet structures by clogging them and thus creating dangerous situations, or damage trash screens leading to even more problems. If these debris and coarse sediments are allowed in, then they may damage dam structures such as gates, spillways intakes in addition to chutes, stilling basins and power penstocks by the mechanical abrasion impacts of such sediments on them. Frequent inspections, especially after floods must be made to ensure proper functioning of such structure and take actions for reducing the damage. In small reservoirs, dredging; although it adds to maintenance cost, may ease the problem, but in very large reservoirs, this may prove unpractical. Designers, therefore, have a duty to consider sedimentation problem seriously in the initial stages of design by: checking the anticipated accumulation of sediments, allowing enough storage free from siltation, foreseeing their negative impacts on intakes and outlet structures and taking design measures to reduce these impacts. At the same time, dam stability calculations shall have to provision for the anticipated new conditions of silting up at the face of the dam. Operators of dams, on the other hand, shall have to keep open eyes for all the negative issues created by sediments and floating debris, repairing damages caused by them and take measures to reduce their impacts in the future. Validerad;2020;Nivå 1;2020-09-29 (johcin)

Frost heave is major problem for infrastructures build in cold regions. Frost heave occurs due to suction (negative pore water pressure) generated due to the freezing process close to the frost line, i.e., at the frozen fringe. To understand and predict these negative pore water pressures is a key factor to accurately calculate the segregation heave, i.e. heave related to the formation of ice lenses. Segregation heave is the major part of the total heave and also the most challenging to predict. Many attempts have been presented in literature where the generated suction during freezing is related to temperatures, temperature gradients, grain size of the freezing soil etc. Very few laboratory tests have been presented in which the actual suction is measured during the ice lens formation process and compared with theoretical estimations. One reason is that these measurements are challenging. This paper presents results from laboratory measurements of generated suction during freezing. Laboratory tests were conducted on a silty soil sample and suction was measured at the frozen fringe using small pore pressure transducers (PPT’s). The samples were subjected to one-dimensional freezing from top to bottom in an open water system at a constant temperature gradient. Temperatures were measured at various points along the height of the soil sample while suction was measured at middle of the sample. Test results have shown that PPTs do not show pressure change in long-term static pressure test under sub-freezing temperature. For suction measurement at the frozen fringe, pore pressure readings should be measured at various points along the sample height.

Groundwater flows from high to low hydraulic head regions. This flow is controlled by Darcy velocity equation. Darcy velocity represents the flow velocity within the cross-sectional area of the soil. Actually, however, groundwater flows at a higher velocity than that of Darcy’s, called seepage velocity. Seepage velocity considers the real area (pores area) that is available for groundwater flow in calculations. There are many applications which are affected by the seepage/Darcy velocity, e.g., underground thermal energy storage systems and contaminants transfer in soil. In spite of the importance of Darcy/seepage velocity in many applications, there is no specific method to depict these velocities on a large-scale map. This paper proposed a tool that can be used to depict the seepage velocity on a large scale. The considered tool is offered by ArcMap/GIS software. To explain how this tool works, Babylon (Iraq) was considered as a study area. ISBN för värdpublikation: 978-3-030-51209-5, 978-3-030-51212-5, 978-3-030-51210-1

When performing predictions of future behaviour and assessments of the safety for embankment dams, numerical modelling if often needed as support. For embankment dams a usual issue is to obtain values of the material parameters for the material in the dam. Sampling is not easily performed, and it could also negatively affect the performance and safety of the dam. One way to determine values of the material parameters is to create a digital copy of the dam by utilizing so called inverse analysis. The created numerical model is calibrated towards field measurements. To make the reality and the numerical model correspond to each other, the values of material parameters for constitutive models are calibrated. The calibration is done by an automatized process. Further, the calibrated model could be used in predictions of future dam behaviour. The methodology has been shown to work for field data containing errors of a usual magnitude.

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.

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.

Due to an increase in axle loads, the development of excess pore water pressure and settlement in a railway track foundation of fine-grained subgrade soil can be observed. A thorough understanding of the mechanism of development of excess pore water pressure is essential for understanding the development of settlements and the design of potential ground improvement. In this paper, a three dimensional numerical study is presented, which investigates the effects of an increase in axle loads of trains on both excess pore water pressure and settlement. Special attention is given to a soft soil layer beneath the embankment and the influence of ground improvement (deep soil mixing columns). As a result, an increase in axle loads leads to a considerable increase in both excess pore pressures and settlement in the subgrade layer. This increase is more significant in the case of heavy axle load (32.5 tons) than that of the light axle load (16 tons). In addition, cyclic loading can lead to a considerable increase in both vertical displacements and excess pore water pressure. The use of deep soil mixing columns reduces excess pore water pressures and settlements significantly.

Mosul Dam is multipurpose earth fill dam 3.4km long, 113m in height and its storage capacity reaches 11.11 km3 of which 2.95 km3 dead storage. The dam is located on the River Tigris in the northern part of Iraq about 60km north west Mosul city. The dam was built on highly karstified alternating beds of gypsum, marl and limestone. The dam was operating in 1986 and since then, seepage problems started due to the solubility of the gypsum beds, presence of karstification and the effect of the local groundwater aquifer. To stop the seepage insensitive grouting program was put to ensure the stability of the dam. Despite the injection of large quantities of grouting material, it did not stop the seepage. The situation became worse in 2014 when ISIS occupied the dam area and grouting operations were halted. Recent evaluation of the conditions indicates that the dam is in its worst conditions. The failure models of the dam indicate that 6 million people will be affected, and 7202km2 of land will be inundated. It is believed that to stop this catastrophe, grouting operations should be continued intensively to elongate the span life of the dam. As a permanent solution, another dam should be built downstream Mosul Dam so that it can take the wave of Mosul Dam in case of its failure. Validerad; 2017; Nivå 1; 2017-04-03 (andbra)

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.

Badush Dam is a partially completed dam and a unique case of flood reten- tion dams. Its intended main function is to perform flood protection once in its lifetime; that is if Mosul Dam would collapse. In such a case, the Badush dam would temporarily store the whole flood wave and route it safely to the downstream. For this end, the bulk of the reservoir is left dry, while the re- maining volume at the lower part which is intended for power eneration does not give an economic justification for building the full height of the dam. The short duration of the intended use as a protection dam has led to relaxing many design assumptions which have raised concerns over the dam integrity. The current controversy rages now over whether to continue the construction of the dam as it was first designed or to change all that in view of the similar site geology of Mosul Dam. Mosul dam foundations suffer at the moment from the severe continuous dissolution of the soluble materials in its foundation leading to continued maintenance grouting of that foundation. This paper gives an overview of the history of Badush dam, its current design and what new equirements which are needed if it is to replace Mosul Damitself. Validerad;2020;Nivå 1;2019-12-19 (johcin)

Dams with core of broadly graded glacial moraines (tills) exhibit signs of internal erosion by suffusion to a larger extent than dams constructed with other types of materials, as reported by Sherard (1979). Garner and Fannin (2010) indicated that internal erosion initiates when an unfavorable combination of soil material, stress conditions and hydraulic load occur. A laboratory program, carried out at Lulea University of Technology (LTU), aims to study the effects of void ratio and hydraulic gradient on the initiation of suffusion of glacial till. It consists of suffusion tests conducted in permeameters with an inner diameter 101.6 mm and a height of 115 mm. Results show, as expected, that the hydraulic conductivity is lower with lower void ratio. Nevertheless, as the hydraulic gradient increases, the hydraulic conductivity reaches steady values. Changes in the hydraulic conductivity suggest variation in the initial void ratio due to detachment of the finer particles from the soil matrix. These fine particles start clogging the lower layers, therefore the rate of water flow decreases and so does the hydraulic conductivity. The hydraulic gradient for which the hydraulic conductivity reaches steady values is considered as the upper limit without suffusion evolved.

Tailings is a waste stream produced by mining industry. It is often stored on the surface in a retaining structure, called tailing impoundment surrounded by tailing dams. Strength property of taili ...

Geophysical Journal International, 178 (3), ISSN:0956-540X, ISSN:1365-246X

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.

This contribution shows how the unsaturated properties of a uniform sandy material are used to create stable vertical surfaces when building dyke models for testing in a geotechnical drum centrifug ...

Raw data processing from a ShapeAccelArray field (SAAF) inclinometer were made using proprietary software from Measurand, the manufacturer of the SAAF inclinometer. When the inclinometer data obtained from the same borehole were reprocessed with an updated software version, the results were found to differ significantly from the values derived using the previous version of software. Neither the absolute displacements, nor the curve representing displacements with depth, agreed with the previous values, despite best attempts to compare data with alternative sparse field measurements of surface displacements. There was a change in inclination of the segments above the shear zone, and the strain rates in the shear zone were reduced significantly during the winter months. In contrast, there was no change in the depth of the shear zone. Therefore, the ground model presented in the original study is still considered to be the optimal ground model of the Furggwanghorn rock glacier. Finally, a simple trigonometrical approach was conducted to investigate the validity of both software versions. The simplified recalculations could confirm mostly the results of the updated software version., Vadose Zone Journal, 15 (4), ISSN:1539-1663

Deformation of the sub-soil is one of the major risk scenarios being confronted in the event of earthquakes. One of the mechanisms involved in causing large deformations under cyclic loading is liq ...