Dam safety & Safety Devices


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Dam safety & Safety Devices

  1. 1. DAM SAFETY AND SAFETY DEVICES VIVEK P. KAPADIA Sardar Sarovar Narmada Nigam Limited
  2. 2. Components of Dam Earthen Dam with Ungated Spillway
  3. 3. Components of Dam Dam with Power House
  4. 4. Components of Dam Gravity Dam
  5. 5. Components of Dam Earthen Dam with Gated Spillway
  6. 6. Components of Dam Buttress Dam
  7. 7. Criteria For Dam Safety <ul><li>Criteria for dams subjected to dam safety regulations </li></ul><ul><li>Structural safety of dams </li></ul><ul><li>Safety of dams against floods </li></ul><ul><li>Safety of dams against earthquakes </li></ul><ul><li>Monitoring and maintenance of dams. </li></ul>
  8. 8. Structure of Dam Surveillance System Level Responsibility Activities Reports 1 Owner (dam safety engineer, technical staff) Regular inspection of condition (by visual observations) and behaviour (by measurements). Tests of spillway and bottom outlet gates. Monitoring records and test protocols 2 Experienced engineer (civil engineer) Analysis of the measured data and observations. Annual inspection of the dam. Yearly report on condition and on measured behaviour. 3 Experts (civil engineer and geologist) Inspection and appraisal of the dam safety every five years. Report on condition and long-term behaviour. Analysis of special safety related questions. 4 Dam Safety Authority On-site inspection. Review of the annual reports and the expert’s appraisal. Verification of the implementation of the necessary measures. Interventions if measures have to be implemented.
  9. 9. Structural Safety <ul><li>Minimization of the risks calls for an appropriate design and construction of the dam </li></ul><ul><li>The design (design criteria and design concepts) should be periodically reviewed to ensure that the structural safety will be guaranteed according to the state-of-the-art </li></ul>
  10. 10. Structural Safety <ul><li>Sefid Rud Buttress Dam, Iran experienced much stronger earthquake actions than originally assumed in the design - Seismic design criteria and methods of dynamic analysis used for the design of the dam are considered obsolete today. </li></ul>
  11. 11. Dam Monitoring and Dam Maintenance <ul><li>Risks can be minimized but never totally eliminated even if a dam has been designed and constructed according to the latest state of knowledge </li></ul><ul><li>It is necessary to detect any signs of abnormal behaviour, damage, deficiencies in structural safety, and new types of threats and hazards etc. as quickly as possible, so that corrective measures can be taken in time </li></ul>
  12. 12. Dam Monitoring and Dam Maintenance <ul><li>Periodic inspections of the dam and periodic safety evaluations are needed </li></ul><ul><li>Purpose of the periodic inspections is to monitor the actual behaviour of the dam - periodic safety evaluations are used for control of the long-term behaviour as well as for verification of the structural safety </li></ul><ul><li>Dam surveillance system used in Switzerland is shown in Table 1. The responsibilities of the different parties involved in dam surveillance and dam safety monitoring are as follows: </li></ul>
  13. 13. Emergency Planning <ul><li>In case of an identified hazard to the dam the situation is managed according to the emergency planning concept </li></ul><ul><li>Measures to be taken are needed to be prepared in advance - should consist of a strategy and of emergency plans </li></ul><ul><li>The potentially flooded area in case of a dam break has to be determined, and the results should be presented in a flood wave inundation map. This map allows evacuation of the population in the flooded area to be planned </li></ul>
  14. 14. Emergency Planning <ul><li>Further emergency planning measures include the installation or at least the specification of the alarm devices, and the organizational provisions for ensuring the evacuation of the population </li></ul><ul><li>The emergency strategy defines danger levels </li></ul><ul><li>Specific technical and operational provisions as well as emergency actions are assigned to every danger level </li></ul>
  15. 15. Definition of danger levels of flood waves (h: water depth; v: flow velocity) Danger levels and intensity of flooding Dam safety regulations apply if danger levels are exceeded High danger h > 2 m or v·h > 2 m 2 /sec People inside massive buildings, in railway coaches, in passenger cars, or on camping sites are in danger. Medium danger 2 m ≥ h > 1 m or 2 m 2 /sec ≥ v·h > 1 m 2 /sec People inside buildings, in passenger cars or on camping sites are in danger. Moderate danger 1 m ≥ h > 0.5 m or 1 m 2 /sec ≥ v·h > 0.5 m 2 /sec People in passenger cars and on camping sites are in danger. Low danger h ≤ 0.5 m or v·h ≤ 0.5 m 2 /sec The regulations do not apply.
  16. 16. Instrumentation - Parameters <ul><li>Horizontal and vertical movement </li></ul><ul><li>Alignment and tilt </li></ul><ul><li>Stresses and strains in soil and rock fill </li></ul><ul><li>Pore pressure </li></ul><ul><li>Uplift pressure </li></ul><ul><li>Phreatic surfaces </li></ul><ul><li>Seepage clarity and quantity </li></ul>
  17. 17. Common Maintenance Items
  18. 18. Piezometers <ul><li>The safety of a dam is affected by hydrostatic pressures that develop in the embankment, foundation, and abutments </li></ul><ul><li>Periodic piezometer observations furnish data on porewater pressures within the embankment, foundation, and abutments, which indicate the characteristics of seepage conditions, effectiveness of seepage cutoff, and the performance of the drainage system. </li></ul>
  19. 19. Piezometers
  20. 20. Piezometers
  21. 21. Piezometers <ul><li>Installation should consist of several groups of piezometers placed in vertical planes perpendicular to the axis of the dam so that porewater pressures and/or seepage pressures may be accurately determined for several cross sections. </li></ul><ul><li>At each cross section that piezometers are placed, some should extend into the foundation and abutments and be located at intervals between the upstream toe and the downstream toe, as well as being placed at selected depths in the embankment </li></ul>
  22. 22. Piezometers <ul><li>In addition to the groups of piezometers at selected cross sections, occasional piezometers at intermediate stations will provide a check on the uniformity of conditions between sections </li></ul><ul><li>Each piezometer should be placed with its tip in pervious material - if pervious material is not present in the natural deposit of foundation material, or if the tip is in an impervious zone of the embankment, a pocket of pervious material should be provided </li></ul>
  23. 23. Piezometers <ul><li>Two of the more important items in piezometer installation are the provision of a proper seal above the screen tip and the water tightness of the joints and connections of the riser pipe or leads </li></ul>
  24. 24. Surface Monuments <ul><li>Permanent surface monuments to measure both vertical and horizontal alignment should be placed in the crest of the dam and on the upstream and downstream slopes </li></ul><ul><li>Survey control should be maintained from offsite reference monuments located in stable material outside of the limits of influence from the construction and removed from the parameters being monitored. </li></ul>
  25. 25. Surface Monuments <ul><li>Monuments should be embedded in the embankment by means of a brass or steel rod encased in concrete to a depth regionally appropriate to avoid frost action </li></ul><ul><li>All monuments must be protected against disturbance by construction and maintenance equipment </li></ul>
  26. 26. Surface Monuments <ul><li>Guidance on spacing is as follows : 50-ft intervals for crest lengths up to 500 ft, l00-ft intervals for crest lengths to 1,000 ft, and 200 to 400 ft intervals for longer embankments </li></ul><ul><li>Monuments should be installed as early as possible during construction and readings obtained on a regular basis. </li></ul>
  27. 27. Inclinometer <ul><li>Inclinometers should be installed in one or more cross sections of high dams, dams on weak deformable foundations, and dams composed at least in part of relatively wet, fine-grained soils </li></ul><ul><li>Inclino meters should be installed particularly where dams are located in deep and narrow valleys where embankment movements are both parallel and perpendicular to the dam axis </li></ul>
  28. 28. Inclinometer
  29. 29. Inclinometer <ul><li>Inclinometers should span the suspected zone of concern </li></ul><ul><li>It is essential that these devices be installed and observed during construction as well as during the operational life of the project </li></ul>
  30. 30. Miscellaneous Movement Indicator <ul><li>Various types of instrumentation may be installed to measure horizontal spreading of the embankment (particularly when the foundation is compressible), movements adjacent to buried structures, foundation settlement, and internal strains. </li></ul>
  31. 31. Miscellaneous Movement Indicator <ul><li>Strain measurements are particularly significant adjacent to abutments and below the crest to detect cracking of the core </li></ul><ul><li>Where there is a possibility of axial extension, as near steep abutments, surface monuments should be placed on the crest at 50-ft intervals to permit measurement of deformations along the axis </li></ul>
  32. 32. Pressure Cells <ul><li>The need for reliable pressure cells for measuring earth pressures in embankments has long been recognized, and much research has been done toward their development </li></ul><ul><li>Many pressure cells now installed in earth dams have not proved to be entirely satisfactory - newer types are proving to be satisfactory and increased usage is recommended </li></ul><ul><li>Some types of pressure cells installed at the interface of concrete structures and earth fill have performed very well </li></ul>
  33. 33. Accelerographs <ul><li>Desirable to install strongmotion, self-triggering recording accelerographs to record the response of the dam to the earthquake motion </li></ul><ul><li>Digital accelerographs are recommended as replacements for existing analog film-type accelerographs - record and provide fundamental event information on a near real-time basis and should be incorporated into dam safety monitoring programs </li></ul><ul><li>Dam Safety engineers should establish and maintain close coordination with the appropriate organization for seismic monitoring. </li></ul>
  34. 34. Automated Data Acquisition System <ul><li>cost-effective real-time data collection from earth and rockfill dams </li></ul><ul><li>Preferred when </li></ul><ul><li>(1) The project is located in a remote area, or would be inaccessible during critical operating conditions </li></ul><ul><li>(2) Limited staffing is required to perform other duties when extreme loading conditions exist, such as flood fighting or emergency response, and is not available for monitoring requirements. </li></ul>
  35. 35. Automated Data Acquisition System <ul><li>(3) High frequency of data collection is necessary to help define complex or interrelated conditions </li></ul><ul><li>(4) Rapid or immediate dam performance assessments are required </li></ul>
  36. 36. Automated Data Acquisition System
  37. 37. Dam Failure - Earthquake <ul><li>Shih-Kang weir in Taiwan, destroyed by fault movement during the September 21, 1999 Chi-Chi earthquake </li></ul>
  38. 38. Dam Failure - Earthquake <ul><li>Embankment Failure – Bhuj Earthquake, 2001 </li></ul>
  39. 39. Dam Failure - Earthquake <ul><li>Embankment Failure – Bhuj Earthquake, 2001 </li></ul>
  40. 40. Dam Failure - Seepage <ul><li>Teton Dam - Initial Erosion in Left Bank </li></ul>
  41. 41. Dam Failure - Seepage <ul><li>Teton Dam – Seepage Widened </li></ul>
  42. 42. Dam Failure - Seepage <ul><li>Teton Dam – Beginning of Final Failure </li></ul>
  43. 43. Dam Failure - Seepage <ul><li>Teton Dam – Failure </li></ul>
  44. 44. THANKS TO ALL