| 41. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety : Technical Problems of Aging Embankment Dams
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 281-322
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Tidskriftsartikel (refereegranskat)abstract
- Embankment dams undergo aging process due to the impact of different factors which can be attributed to geology of the site, design of the dam, materials selection and procedures followed in constructions. In the foundation the presence of faults or shearing planes, karst, compressible clayey material, soluble rock, and soft rock may establish conditions leading to high total settlement or differential settlements of the dam and its cracking. Deficient and deteriorating seepage control measures such as grout curtains or diaphragms enhance seepage flow leading to internal erosion and piping which endanger dams’ stability. Improper filling materials used such as dispersive clays and gap graded granular material show their bad influence after long time by creating conditions inducive to internal erosion and piping. Use of improperly designed and placed filter zones and drainage blankets can end in clogging of such filters and drainage blankets leading to the rise of the phreatic surface level and increasing uplift causing again conditions of internal erosion and piping and undermine stability. This work attempts to give an overview of these conditions and cite many case studies of rehabilitation works carried out in dams after long years of service. The conclusion reached is that rehabilitation works if done early when problems are discovered play well to elongate the service life of dams, but normally they require large investments. Sooner or later owners of such old dams will come to realize that more rehabilitation works, neither technically nor economically, are feasible and that more of such works are not possible. In which case they will come think seriously of decommission such expired dams.
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| 42. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety : Use of Seismic Monitoring Instrumentation in Dams
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:1, s. 203-247
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Tidskriftsartikel (refereegranskat)abstract
- Seismic instrumentation of dams and reservoirs sites is accepted today as a valuable tool to understand significant seismic hazards facing existing dams or future planed dams. With the advent of digital seismic accelerometers and recorders, it can now be used today as an integral part of dam safety monitoring systems. Outputs of these instruments help in understanding the dynamic response of dams during earthquake, assessing the damage caused by such events and determining required upgrading works necessary for existing dams and designing of safer dams in the future. Measuring and recording by strong motion seismographs covers the induced Peak Ground Acceleration (PGA), velocity and displacement recorded on time scale to indicate the intensity and frequency of ground vibration at the site during seismic events. Seismometers for such measurements and recordings have undergone considerable evolution and there exist today a variety of these instruments with high degree of refinement which can even provide for remote sensing. In this work, this development is outlined and examples of seismic instrumentation in strategic dams are described. Damages to actual concrete and embankment dams of various types are described indicating the associated PGAs experienced during the mentioned earthquakes. Damages in the form of cracking, increased seepage, additional settlements and displacements are described to show type and extent of possible consequences of such events on dams. The reached conclusion is that seismic instrumentation systems are desirable and highly recommendable for all types of dams; existing and future ones and their high cost is justified by the service they provide.
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| 43. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety : Monitoring of Tailings Dams and Safety Reviews
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:1, s. 249-289
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Tidskriftsartikel (refereegranskat)abstract
- The awareness to tailings dam safety monitoring and reviews has increased by the catastrophes resulting from failures of such dams worsened by increasing tailings waste and construction of larger dams. The losses born by the mining industry from high costs of compensations and environmental rehabilitation work have brought this matter into focus. In the present article the need for safety monitoring programs of tailings dam is highlighted and mode of failures and factors leading to them are described. Basic principles of such programs are investigated with all phenomena needing observation described and their impacts explained. As in conventional dams this work is carried out by visual inspections and use of similar methods and instruments. In similar manners in both types of dams’ observation and measurements are done for measuring seepage water quantity and quality, phreatic surface level and pore pressure and total earth pressure values in addition to deformation measurements; and all are done by similar devices and methods such as weirs, piezometers, inclinometers, settlement plates and geodetic surveying. Basic differences between safety monitoring systems of the two types of dam, however, are presented in a tabular form. The continuity of safety monitoring of tailings dams is emphasized not only during the long construction phase but also after that in the abandonment and closure phase which can last indefinitely in order to watch for possible adverse effects on the environment and ecosystem due to the winds eroding and carrying of poisonous tailings contents, in addition tocontaminated seepage water entering surface water streams and ground water. Justifications for using real time monitoring systems for recording and transmitting all data to the control center are presented with emphasis given on savings in both labor and time and need for the discovery of warning signs enabling raising earlier the alarm of possible failure or incident and the early taking of preventive measures. In this article it is argued that, in spite of the large investment of installing and running cost of comprehensive dam safety monitoring systems in tailings dams, such costs are justified as they form only a small percentage of the total investment in the tailings facilities projects, and may save huge costs if failure does happen. Such systems may be considered as an additional insurance against such events.
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| 44. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety : Use of Instrumentation in Dams
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:1, s. 145-202
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Tidskriftsartikel (refereegranskat)abstract
- Dam safety concerns do not stop at site selection, or the design and construction stages of a dam, but continue throughout its whole life. Seeing to safety issues of any dam is done by following up its behavior through visual observation supplemented and enriched by data collection from all the devices installed on or implanted in a dam to follow its reactions to the forces and conditions in action. Analysis of the accumulated data will show the safety level and the need or, otherwise, of any remedial works. Using measuring devices to quantifying seepage conditions at any dam and correlating this with water levels’ fluctuations is the first main issue that concerns dam safety. Added to this, measurement of pore water and total earth pressure in earthfill dams, temperature measurements in concrete dams, uplift and displacement measurements, and measurements of stresses and strains can all give good pictures of what is happening inside the dam and/or its foundation in both types of dams. In the following work, a summary of typical instrumentations and monitoring used in evaluating causes of common problems is given. Moreover, requirements for good instrumentation program are explained and the methods of data collection, whether manual, or use of stand-alone loggers and real-time monitoring networks are touched upon. The various devices in current use are described in more details. Actual examples of monitoring systems in existing dams are presented to show the value and importance of these systems to the safety of these dams.
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| 45. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety : Hazards Created by Human Failings and Actions
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:1, s. 65-107
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Tidskriftsartikel (refereegranskat)abstract
- Dam Safety and dam incidents are treated here looked at from the "Human Factors" perspective. An attempt is made to explore these factors as an important drive in impairing dams’ safety and increases their risks. Distinction is drawn between the "Normal Human Caused Incidents" and the "Extraordinary Human Caused Incidents" together with the description of their root origins and subsequent consequences. The first type includes unintentional mistakes, errors and flaws committed by the operators of dams inadvertently, in addition to negligence, lack of experience or overconfidence. Such failings can happen in manual operation of dams, or through the use of their Supervision, Control and Data Acquisition (SCADA) systems as in industrial control system (ICS). They can occur also due to flaws in software or even in the application of information and communication technology (ICT) in remote control operations. As for the second group; the extraordinary human factors, they are defined here as those committed by man with the full understanding of their possible damage. They are done purposely for destabilizing dams after thoughtful and carefully meditated decision making process and they are manifested in acts of war, sabotage and terrorists actions. In this modern age, these acts are characteristics of hackers’ attacks on dam(s) operating systems. This is done through the use of cyberspace by the widespread interconnected digital technology with the accompanying advances in the communication technologies. As such, these technologies have made remote control of such systems possible. Not limited to this, dams remain now, as they were always in the past, the obvious targets in wars and conflicts to inflict losses on the enemy and to use them as weapons, and for terrorism actions for challenging governments. Examples of the aforementioned threats are described with examples given from real cases to elucidate the dangers involved. Lessons to be learned from these incidents are derived and recommendations are presented to be followed to avoid risky situations.
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| 46. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety : Sediments and Debris Problems
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:1, s. 27-63
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 47. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety and Dams Hazards
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 23-40
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Tidskriftsartikel (refereegranskat)abstract
- Dam safety hazards towards human communities have increased tremendously during the last decades. They have resulted from dam safety problems leading to failure and being exasperated by the large losses at downstream areas due to increasing populations and land use. In this work, an attempt is being made to review the procedures being followed to reduces these hazards by improving dams safety standards. Classification of dams by their potential hazards are explained as used today for prioritize remedial actions in various countries of the world. The guiding principles of these classification are indicated and they are based on height of such dams and their storage and linked to the potential damage and harm they can create. Normally such classification and follow up actions are supported by various legislations and regulations issued by the respective governments. Moreover, conventions signed by riparian countries promote cooperation on mitigating safety problems of dams on transboundary rivers. Examples of such legislations and conventions are mentioned. Looking for having safer dams is an objective continually which is being pursued as more dams are needed in the future while existing dams continue to serve their objectives. Therefore, using lessons learned from previous failures is recommended taking the question of loss of life as a main doctrine.
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| 48. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety and Earthquakes
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 79-132
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Tidskriftsartikel (refereegranskat)abstract
- Earthquakes may cause failure or profound damage for dams. Factors contributing to this are, magnitude on the Richter scale, peak horizontal and vertical accelerations, time duration, in addition to the epicentral distance, nature of foundation rock, criteria of the design, and finally, if appropriate type of dam and materials has been used. Extensive lists of dam failures and damaged once are presented with many case histories. Most failed dams were tailing dams or hydraulic fill dams or small earth fill dams, which reflect the weight of the design and construction factors. Embankment dams, normally, are less tolerant to ground shacking than concrete dams. While rockfill and RCC dams have shown good performance. The developments of design methods and criteria are traced here, from the early use of the pseudoptotic method to the more rational dynamic analysis, which is used nowadays making construction of very large safe dams in seismic regions possible. The method adopts peak ground accelerations from anticipated earthquakes as inputs to the analysis which produce a full spectrum of the factor of safety during any considered event. This has led to increased use of seismic instrumentation to produce seismographs of actual events in the free field, and on dams hit by earthquakes for comparison with outputs of this analysis and for future use for similar dams in similar circumstances, and to decide on rehabilitation measures. The safety levels to which any dam is to be designed are defined in terms of the Maximum Credible Earthquake, Safety Evaluation Earthquake, Maximum Design Earthquake and other similar terms. Dam repairs after sustaining earthquake damages are described in real cases and upgrading of older dams to withstand higher expected seismic events are also treated here and supported by case histories.
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| 49. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety and Οvertopping
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 41-78
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Tidskriftsartikel (refereegranskat)abstract
- Overtopping is one of the most serious modes of failures for all dams causing great numbers of human fatalities and material damages. Statistics show that overtopping failures are the highest, especially for embankment dams. The main reason for this is the erroneous prediction of the inflow design discharge, which has resulted from lack of realistic flow data and imperfect hydrological procedures. Failure in most cases occurs when the inflow exceeds the spillway design capacity, but to a lesser extent from the buildup of very high wave setup and runs up. This has led to active efforts in upgrading dams for such occurrences, by either upgrading spillways, adding auxiliary spillways, increasing freeboard by either heightening the dams or the parapet walls on the crest. Advancement in predicting the safe inflow discharges are also made by adopting such procedures as the calculation of the Probable maximum flood based on predicting the Maximum Probable Precipitation or using statistical methods by treating long records of available flow data. Recently, another challenge has come up facing dam owners and builders who are represented by the climate change impacts on the hydrological cycle; this has put a new responsibility to the governments to issue new regulations and plans to mitigate these impacts reducing failure possibilities and improve dam safety against overtopping.
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| 50. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety Problems Related to Seepage
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 191-239
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Tidskriftsartikel (refereegranskat)abstract
- Dangerous occurrences affecting dams take multiple forms, but seepage caused cases are the most numerous. Some of the cases are related to the geology of the foundation and the magnitude and type of discontinuities in the rock mass of the dam. Other are mainly due to of construction material in earth fill dams. Seepage occurs in all earth fill dams regardless of its materials, and seepage water can daylight at the downstream face causing erosion, piping and sloughing and instability; unless certain measures are taken. Instability can be controlled mainly by adding, filter material zones at the contacts with the clay core, chimney filter drain at the downstream part of the dam, filter zone or bench at the toe together with the drainage blanket under the downstream part of the dam. Seepage within the dam is enhanced by cracks which may result from uneven settlement of the dam due to different elastic behavior of the foundation materials, hydraulic fracturing, and differential settlement of parts of the dam or due to ground shaking in earthquakes. Preferential seepage paths can develop in such cracks, especially if the fill material is dispersive or suffusive. Similarly, such paths may develop along the contact surfaces of conduits installed under dams as outlet structures due to the low degree of compaction as a result of narrow trench dimensions. Using properly designed filter and drainages can reduce seepage quantities and the erosive force which causes internal erosion. In dam’s foundation grout curtains or other type of cutoffs can reduce the hydraulic head and hence uplift under the dam and hinder seepage. Drainage, however, remains as the most efficient method in controlling this uplift in artesian conditions under dams, especially under concrete gravity dams. Generally, such drainage may take the form of drainage blanket and use of filters material.
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