|Research projects_21||[email protected]||Wear-resistant materials in hydraulic Engineering|
Hydroabrasion includes all types of wear on wetted surfaces caused by water and sediments contained therein. It presents an ubiquitous and not yet satisfactorily solved problem which causes in hydraulic Engineering worldwide high maintenance costs. Particularly affected by hydroabrasion are hydraulic strucutres, which are exposed to high flow velocities and increased sediment transport. Next to dams, weir systems and construction diversions, also sediment diversion tunnels are affected. They contribute to a sustainable management of storage power plants by allowing sediment rich inflows to bypass the dam and in this way avoid or slow down the progressing silting-up of the reservoir. In order to be able to economically operate plants affected by hydroabrasion, not only the operation modus, but also the choice of materials for the internal lining plays an important role. However, there are still no generally accepted recommendations or guidelines. In many cases different linings are installed, refurbished and again substituted according to the “trial and error” principle, while a satisfactory solution in this context has not yet been found. To close this knowledge gap, the laboratory of hydraulics at the ETH Zürich (VAW) initiated a corresponding research project. The aim is to determine and optimize wear-resistant materials on the basis of field tests in the sediment diversion tunnel Solis as well as in the diversion tunnel Pfaffensprung, and to determine the situational most economical lining solution in consideration of the whole lifecycle costs.
The research is performed within the framework of a PhD program at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) at the Swiss Federal Institute of Technology in Zurich (ETHZ).
|Research projects_27||[email protected]||Innovative measuring method for chloride transport in concrete|
Early deterioration in civil infrastructure is mainly caused by chloride-induced corrosion of steel in reinforced concrete. The prediction of chloride transport in concrete is very often based on oversimplified material models, many of which were developed a few decades ago. Most of the required input parameters are either difficult to measure, or are established by empirical equations.
This limitation to the application of reliable chloride transport models in practice is specifically addressed by a research project launched at the Institute for Building Materials of the ETH Zürich.
Within the framework of a PhD project, which is financially supported by the Foundation Lombardi Engineering, an innovative method to measure the transport coefficient of chlorides in existing reinforced concrete structures will be developed. This measurement method should work on a micron to millimeter scale, being applied on concrete cores taken from real structures. The obtained information shall help to explain how the diffusion coefficient is affected by material variations on the micro-, milli- and centimeter scales, by age as well as by the binding capacity of chlorides. It is aimed to develop in this way not only a relatively fast method, but to get also a more representative idea of the actual processes in concrete structures in order to better understand the “natural” chloride transport in this medium. Involving analytical chemistry techniques and thermodynamic modeling, it is tried to spatially resolve transport information on multiple length scales of interest and in a way to avoid artifacts induced by artificial acceleration.
This new analytical procedure refers to quantitative high spatial resolution chemical imaging, which is based on micro analytical techniques using micro- X-Ray Fluorescence.
If successful, this innovative method would be much faster than existing procedures and would additionally provide the actual spatial resolution of transport coefficients, which can then be used as reliable input for predictive models on a case to case basis.
|Research projects_30||[email protected]||Hydraulic performance of stepped spillway aerators and related downstream flow features|
In order to prevent cavitation damages on spillways, bottom chute aerators can be installed. They have been extensively studied on smooth spillways. However, in the past decades stepped spillways have become widespread and research has shown that for high specific discharges they might be affected actually more by the cavitation process than smooth spillways. As consequence, and besides issues of energy dissipation, the specific discharge of stepped spillways is usually limited to lower values than smooth spillways. Until today there is no guideline for the design of such aerators.
Therefore, the hydraulic performance of stepped spillway aerators and related downstream flow features is now addressed by a PhD work performed at the Laboratory of Hydraulic Construction, LCH at the École polytechnique fédérale de Lausanne. The main objective of this research is to reduce this knowledge gap by in-depth studies of an aerator and its effects on the flow by means of a physical model. The model involves a 0.5 m wide channel, up to 8 m long, which can be supplied with a discharge of 240 l/s. Altogether six parameters, that is spillway slope, step height, approach flow depth, approach flow Froude number, deflector slope, and deflector height are varied in order to study their influence on the global air entrainment and the local air concentrations in the flow downstream of the aerator. With the results of this research, it is expected to establish general design recommendations for stepped spillway aerators.
|Research projects_33||[email protected]||High-Performance Concrete in Tunnels - The spalling sensitivity in case of fire|
Despite the rather good knowledge about the mechanical behaviour of High-Performance Concrete (HPC) at high temperatures, further studies related to spalling (to which HPC is very sensitive) are still required. Spalling presents a complex process, which is especially for tunnels of particular concern. It is a result of a combination of mechanical concrete decay with temperature, pore-pressure build-up due to water vaporization, and stress induced by both thermal gradients and external loads. How these different aspects influence each other is not yet completely understood.
In collaboration with the CTG-Italcementi Group, the Politecnico Milan launched therefore a research project with the purpose to investigate the interaction between pore-pressure and stress triggering explosive spalling. This is done by subjecting concrete slabs (800x800x100 mm) to a standard fire on one side. At the same time a membrane compressive stress of 10 MPa is applied and kept constant by means 8 hydraulic jacks as shown in the figure above. The membrane load helps to limit the onset of tensile stress, which might lead to cracking and to the consequent release of vapour. A steel frame restrains the hydraulic jacks, while the whole loading system is located on a small horizontal furnace. During the test, the development of pressures and temperatures is continuously monitored at 6 different depths, and transversal displacements are measured via LVDTs.
With this research project, which is co-financed by the foundation Lombardi Engineering, it is expected to obtain a better insight into the actual spalling process and its causes.
|Research projects_37||[email protected]||Hydro-Power Control Valve - Numerical study to develop an energy recovery control valve|
In hydraulic engineering, control valves are used to control various parameters, such as the pressure and flow rate in a pipeline system through the dissipation of flow energy. Within the framework of a research project launched at the Department of Civil and Environmental Engineering (D.I.C.A.) at the Politecnico di Milano, the performance of the so-called Green Valve, a control valve designed to use energy from the flow control process, is numerically evaluated.
The Green Valve concept is based on the idea that it is possible to recover part of the dissipated energy and to re-use it. But it is not only this positive environmental aspect in general that makes the Green Valve an interesting device, but also the possibility to produce off-grid energy that may be useful for many applications, such as for feeding monitoring and measuring tools or the valve actuator.
By means of a computational fluid dynamic approach this research allows to extend the fields of applications and to improve the performances of the device. It is aimed to fully understand the potential uses of the Green Valve involving CFD methods and to evaluate the environmental impact of this valve in terms of control performances and energy production.
|Research projects_41||[email protected]||Air demand of bottom outlets – Prototype measurements|
Bottom outlets are a key safety feature of large dams. Their primary roles are (i) control of the water level, e.g. during the first impounding, (ii) rapid water level drawdown in emergency situations, e.g. war and terrorist threats, iii) discharge of excess floods and (iv) the flushing of sediments. Future demands on bottom outlet operation will likely increase due to dam heightening as promoted by the Swiss energy strategy 2050 and more frequent sediment flushing following increased reservoir sedimentation.
The high-speed free surface flow downstream of the gates results in considerable air entrainment and air transport and consequently negative pressures along the bottom outlet. Therefore, the gate chamber is equipped with an aeration conduit that guarantees sufficient air supply into the bottom outlet. Problems regarding cavitation damage and gate vibrations may consequently be prevented. Up to date, the existing design criteria for the required air demand do not allow for a coherent hydraulic design of bottom outlets.
In an ongoing PhD thesis at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of the Swiss Federal Institute of Technology Zurich (ETH Zurich) the air demand and two-phase flow features of bottom outlets are investigated in a large-scale hydraulic model. Prototype measurements are crucial for a proper upscaling and validation of the model results. However, prototype data is scarce, especially for static heads H0 > 80°m w.c. Therefore, the Lombardi Engineering Foundation financially supports prototype measurements in the bottom outlets of Luzzone and Malvaglia arch dams.
|Research projects_42||[email protected]||Large-scale implementation of soil bio-improvement for a series of engineering applications|
In ecology, sustainability stands for a system’s capacity to endure changes and sustain its productivity and, ultimately, its existence. In engineering and construction, sustainability has been associated with the goal to provide long-term safety to man-made infrastructures, reduce their energy needs and minimize their impact on the natural environment. This is the only way for engineering works to meet the needs of both current and future generations. The introduction and development of novel, “smart” materials, has unleashed a vast potential in increasing the sustainability and environmental performance of constructions. This is the case of the Microbially Induced Calcite Mineralization (MICP) for soils which aims at introducing a new paradigm for improving soils and redefining, at the same time, the role of earth as a building material. The technique is inspired by the natural process of the bio-mineralization of calcium carbonate crystals and has at its core the metabolic activity of the soil bacterium Sporosarcina Pasteurii.
The project «Large-scale implementation of soil bio-improvement for a series of engineering applications», funded by the Lombardi foundation, puts the focus on the “bio-improved geo-material”, which is currently engineered at the Laboratory of Soil Mechanics (LMS) of the Swiss Federal Institute of Technology in Lausanne (EPFL). So-far, the soil bio-cementation technique has been studied and controlled at the LMS in multiple scales, ranging from the scale of a few micrometres to that of real engineering applications. The project allows investigating the technique at the large experimental scale, where the soil bio-cementation will be studied under various scenarios, for its potential to offer solutions in a series of engineering problems including: the stabilisation of soils and slopes and the restauration of week foundations, the enhancement of soil-structure thermal interactions for an efficient energy performance of buildings and the protection of soils against erosion.
|Research projects_43||[email protected]||Stress state identification in tunnels via continuous deformation monitoring under coring|
The design of new tunnels and the safety assessment of existing ones are made difficult by many uncertainties such as initial stress state and mechanical properties of soil and stress state in the tunnel lining. As regards this latter point, a possible solution is to evaluate the stress state experimentally through different slightly destructive techniques, such as over-coring and under-coring methods. The basic idea is to measure the deformation at the external surface of a R/C member afterwards an hole is drilled orthogonal to the surface. These established techniques provide useful and reliable information for plane stress state, in which the dependency on the investigated depth is negligible. On the contrary, in concrete tunnel linings, the stress state is generally expected to vary along the element thickness due to bending effects. Hence, taking inspiration from the abovementioned techniques, a new method is under development at Politecnico di Milano in order to take into account the variability of the stress state with the depth. In the project at issue, the idea is to monitor the displacement field during coring, in order to investigate an increasing depth of the concrete member along with the progress of hole boring. This analysis is made complex by the non-negligible boundary effect at the bottom of the hole, this making the inverse analysis more complex and the implementation of numerical models mandatory.