Sewers Float and other aspects of Sewer Performance in Earthquakes

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1 Sewers Float and other aspects of Sewer Performance in Earthquakes Presented by Donald Ballantyne, PE Niigata Japan, 1964

2 Overview Introduction Earthquake Hazards Historic Damage Seattle 1965 Loma Prieta 1989 Northridge 1994 Kobe 1995 Nisqually 2001 Seismic Design and Retrofit

3 Donald Ballantyne, PE Senior Consultant, MMI Engineering Civil/Sanitary Engineer, 34 years experience Designer - wastewater treatment plants/pump stations in Bay Area Resident Engineer 80 miles sewer San Francisco Liquefaction Study following Loma Prieta Earthquake King County Wastewater WA, Seismic Vulnerability of Conveyance System American Lifelines Alliance - Wastewater Systems Utility Performance Assessment Earthquake Reconnaissance following 10 events including: Loma Prieta Northridge Kobe Nisqually

4 MMI Engineering Hazard risk management Earthquake engineering Structural engineering and structural mechanics Water/wastewater system assessments MMI Staff Clients SFPUC City of Hayward Santa Clara Valley WD Contra Costa WD Marin Municipal WD 50 professional staff located in: Oakland Huntington Beach Tacoma Houston United Kingdom Wholly owned subsidiary of Geosyntec Consultants

5 Performance Objectives Water Wastewater Life Safety Life Safety Fire Suppression Public Health Critical Services Environmental Impact Public Health Property Damage Property Damage Business Interruption? Business Interruption

6 Earthquake Impacts Sewers collapse and/or float causing backups and overflows requiring immediate response Sewers are damaged and/or float requiring increased maintenance, and infiltration Often cannot be detected from surface observations; requires TVing. Sewer leaks can result in sink holes, sometimes quite large Can go undetected until collapse occurs WWTP vulnerable to liquefaction, and shaking damage. Sea Cliff, San Francisco, 1995

7 Water versus Wastewater Water pipe is strong, designed to contain pressure and resist soil loading. Can be weakened by corrosion. When pipelines fail Leak or break System may drain System fails to function Leaks are located when repressurized Water Treatment Plants Often on competent soils where liquefaction is not an issue Sewer pipe is weak, designed only to resist soil loading. Can be weakened by corrosion in the crown of the pipe. When pipelines fail Collapse or offset can result in loss of function (only 1% of water pipe repairs). Sewage backs up or overflows Sewers damaged by shaking may continue to function in the short term; require replacement in the long term. Sewers in liquefiable soils can float, or otherwise fail, and may continue to function in the short term; require replacement in long term. Interceptors sewers are often located in lowlying liquefiable soils Treatment plants Tend to be located in low-lying liquefiable soils

8 Earthquake Hazards Wave Propagation Permanent Ground Deformation Fault rupture Landslide Liquefaction/settlement (structures) Liquefaction/lateral spread Liquefaction/flotation (pipe) Moss Landing, 1989

9 Wave Propagation Compression (P) Shear (S) Love (L) Rayleigh (R) Damage in compression/extension Function of shear wave velocity/soil stiffness Rock good; Soft soil bad

10 Landslide Leaking sewers can be the cause Avoid areas subject to landslide Locate pipe below the slide failure plain Geotechnical stabilization Support pipe on piles Continuous or restrained pipe design to span slide

11 Fault Crossings Determine expected fault offset direction and distance Align pipe crossing to be in extension when fault moves Select pipe material: Continuous, ductile HDPE, welded steel Segmented, restrained ductile iron Provide for extensive through pipe ductility or mechanical devices Alternatively design to allow quick repair

12 Liquefaction Occurs due to shaking Soil particles consolidate squeezing out water Water pore water pressure increases reducing friction between soil particles Soil becomes a viscous liquid Loosely packed sand grains Consolidated sand grains Costa Rica, 1991

13 Liquefaction Low density/blow count alluvial deposits Grain size distribution evenly graded sand Age of deposit (such as fill areas) Depth/overburden typically < 30 feet Geologic hazard mapping alluvial deposits, fills Groundwater table < 30 feet deep Shaking intensity ~ >15%g Shaking duration Peru, 2007

14 Liquefaction/Lateral Spread Costa Rica, 1991 Philippines, 1990 Loss of bearing

15 Liquefaction Lateral Spread Movement is perpendicular to pipe (A) Pipe can accommodate some bending Segmented pipe will separate at joints, shear and bend Movement parallel to pipe (B) Segmented pipe will pull apart at one end, and crush at the other B A

16 Liquefaction/Lateral Spread Permanent Ground Deformation (PGD) used as a proxy to estimate pipeline damage. Soil strain not evenly distributed along ground. PGD is proportional to shaking duration, so the CAP LAYER Lateral Spread larger the magnitude, the greater the PGD Typically use Multiple Linear Regression analysis to estimate LIQUEFIABLE LAYER PGD, based on empirical data (Bartlet Float (Buoyancy) & Youd). Pipe may be in nonliquefiable cap layer or Loss of Bearing within liquefiable layer. Subsidence Viscous Drag (Flow Failure)

17 Bartlett-Youd - Lateral Spread Log D H = M Log R* R Log W LogT Log(100-F 15 ) Log (D mm) D H Horizontal distance lateral spread M earthquake magnitude R Logarithmic distance from fault W = Height/distance to free face T 15 Thickness liquefiable layer F 15 Fines content of liquefiable layer D50 15 Average soil particle diameter mm - millimeters Horizontal Distance Height Liquefiable Layer

18 Liquefaction - Flotation Sewers and manholes are vulnerable to liquefaction induced flotation Change in grade will impact gravity sewer operation and maintenance Sewer must be within liquefiable layer (below groundwater) Nearly complete liquefaction must occur Flotation is dependent on buoyancy Larger pipe more buoyant than small diameter Heavier pipe (concrete) is less buoyant than lighter pipe (PVC)

19 Bay Area Liquefaction Susceptibility

20 Seattle 1965 Pipeline floated in 1965 Seattle Earthquake

21 Loma Prieta 1989 San Francisco Municipal Water Supply System Liquefaction Area San Francisco - Liquefaction

22 Marina District 100mm settlement 60mm 20mm

23 San Francisco Liquefaction Study - Sewer Damage Algorithms Percent Replacement New VCP New Concrete Old VCP and Concrete Permanent Ground Deformation (inches)

24 Palo Alto Wastewater Treatment Plant

25 Wastewater Treatment Sloshing damage to clarifier San Mateo WWTP

26 Wastewater Treatment Sloshing damage to clarifier (Hayward) EBMUD - damage to digester floating cover EBMUD lost secondary treatment process Chemical spill high ph Loss of power

27 Santa Cruz Pipelines Water Pipe Failures 13% of the sewers required replacement primarily in liquefiable soils along the San Lorenzo River due to flotation. Replacing 25% of the sewers would have eased future maintenance problems.

28 Philippines 1990

29 Sewer Damage 10 collapsed sewers in San Fernando Valley required pump-arounds; minimal liquefaction Compares to water line failures Sewer line inspection using TVing equipment and replacement negotiated with FEMA based on building and water pipe damage, and surface cracking

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31 Northridge Sewer Damage After the event: TV d high risk areas 16% required emergency repairs 49% repairs 35% OK 2 years later - $200M Limited liquefaction; ground cracking Glendale, Saugus, Valencia reclamation plants were damaged but remained on line.

32 Kobe - Higashinada WWTP

33 Higashinada WWTP 2 meters lateral and 1 meter vertical movement

34 Higashinada WWTP Liquefaction Pile failure under end of aeration basin

35 Higashinada WWTP Liquefaction

36 Higashinada WWTP Liquefaction Piping on collapsed bridge Sedimentation tank sludge scrapers dislodged

37 Higashinada Wastewater Treatment Plant, Kobe, Japan 1995 Higashinada WWTP Liquefaction

38 Floating Sewers Kobe, Japan 1995

39 Kobe Wastewater Collection Longitudinal cracks in concrete lining of shield tunnel #2 in Naruo-Mikage trunk line

40 Kobe Wastewater Collection Flotation and longitudinal cracks in 2,000 mm concrete pipe in Ohama Trunk Line in Nishinomiya

41 Kobe Wastewater Collection Longitudinal cracks in 2,000 mm concrete pipe in Ohama trunk line in Nishinomiya

42 Asymmetric Loading Pipe section designed to accommodate soil loading Movement of seawall resulted in asymmetrical loading on the pipe cm

43 Fill/Liquefaction Impacts on on Lifelines Bridges 4 th Ave. Harbor Island Swing Bridge Holgate Overpass Water Main Breaks Gas Main Leak Spokane Starbucks St.- Restrainers 1 st Ave. Boeing Field South Park

44 Seismic Resistant Design of New Sewers in Competent Soils Bell & spigot pipe with flexibility at joints and MHs Allow for differential settlement at connections to structures

45 Joint Movement Capacity Design joint to allow extension and compression to relieve ground strain Design bell depth to minimize joint pull out

46 Seismic Resistant Design of New Sewers in Liquefiable Soils Avoid areas with liquefiable soils Directionally drill below the liquefiable layer (pressure lines and siphons) Geotechnical mitigation Stone columns Compaction grouting Pile support provide flexibility at connections

47 Seismic Resistant Design of New Sewers in Liquefiable Soils - continued Bed or backfill with concrete to make neutrally buoyant. Install anchors to keep from floating Used in gas industry Anchors must get below liquefiable layer Install fins on pipe to take advantage of backfill weight Design bedding and backfill to relieve pore water pressure

48 Pipe Selection Competent soils B&S joint PVC - deep bell, moderately ductile, wedge effect Concrete, vitrified clay - shallow bell, brittle Liquefiable soils Continuous or restrained joint Design to maintain grade when liquefaction occurs

49 American Lifelines Alliance System Assessment Methodology Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Define Project Objectives and Select Required Level of Assessment Select Performance Metrics Define Performance Objectives Define the Wastewater System to be Assessed Define Relevant Natural Hazards Assess Vulnerability of System Components to Natural Hazards Step 7 Assess System Performance under Conditions of Natural Hazards and Human Threats YES YES YES Step 8 Performance Objective Met? NO Modify System Response? NO Modify Component? NO Modify Performance Objective? YES NO NO NO FINISH Accept Performance Level Step 9 Define and Assess Vulnerability to Human Threats

50 Asset Management Sewer seismic vulnerability should be addressed Probability of occurrence during the expected life of the sewer Take into account Earthquake risk (probability, intensity) Liquefaction probability Pipe type Location within the liquefiable layer CAP LAYER LIQUEFIABLE LAYER Float (Buoyancy) Lateral Spread Viscous Drag Loss of Bearing Subsidence

51 Retrofit of Existing Sewers Sewers in competent soils Slip line polyethylene, Insituform Sewers in liquefiable soil Slip line? Resulting reliability questionable as the sewer can still float. Geotechnical mitigation? Must maintain the grade of the sewer. Emergency response

52 Emergency Response Provide for improved emergency response Keep pumps and hoses on hand Restoration capability Maintain access to equipment through ownership or through agreements with contractors Stockpile repair materials that are difficult to obtain

53 Summary Many sewers have floated in past earthquakes Hazards: Liquefaction, Shaking Performance Objectives: Life Safety, Public Health, Environmental Impact, Property Damage, and Business Interruption Failure Impacts Collapse (1%): cause backups/ overflows requiring immediate response; Flotation, other damage results in increased maintenance requiring longer term repair; WWTPs and Interceptors: vulnerable to liquefaction because they are typically located in low-lying areas.

54 Summary - continued Design in competent soil Bell & spigot pipe with flexibility at joints and MHs Design in liquefiable Avoid, install below liquefiable layer Geotechnical stone columns, compaction grouting Pile support Emerging designs for liquefiable soils Weight to make neutrally buoyant Anchor to prevent floating Fins to hold in place Design bedding/backfill to relive pore water pressure

55 Evaluation and mitigation of risk posed by major hazards and threats through the application of innovative and high quality science and engineering Engineering a Safer World dballantyne@mmiengineering.com