EARTHQUAKE DAMAGE TO PIPELINES A CHRISTCHURCH PERSPECTIVE

Transcription

1 ABSTRACT EARTHQUAKE DAMAGE TO PIPELINES A CHRISTCHURCH PERSPECTIVE Author: J R Black, Technical Principal Pipeline Materials Opus International Consultants Ltd, Christchurch New Zealand. It can be said that there is no perfect pipe material for any purpose. Ground shaking and permanent ground deformation (PGD) during seismic events bring additional forces to bear on pipes and these forces can be destructive, particularly to any weak links. Some pipe materials and jointing systems have performed very poorly while others have suffered only minimal damage (or none) during the internationally significant Christchurch earthquakes between September 2010 and December This paper considers the effects of the Christchurch earthquakes on buried pipelines, gives examples of failure modes and presents some conclusions regarding earthquake resilience of water supply and drainage infrastructure as well as some final comments from a Pipe Whisperer of over 40 years experience. Key Words Pipe materials, earthquake, liquefaction, lateral spreading, pipe failure, earthquake resilience, asbestos cement, HDPE and PVC-U pipes. 1 Introduction Quote: Civilisation exists by geological consent, subject to change without notice (Attributed to Durant, [Nur and Burgess, 2008]). The Canterbury earthquake sequence has served as reinforcement of the relevance of this quote. Each of the main earthquake events has resulted in serious disruption to the essential horizontal services and parts of Christchurch are now no longer viable and may never be rebuilt. Christchurch, the second largest city in New Zealand with a population of 376,700 in 2010 was awakened by a magnitude 7.1 earthquake at 4:36am on Saturday September The quake epicentre was 40 kilometres west of the city, southeast of the town of Darfield near Greendale in the Selwyn District. The depth of the earthquake (about 10 kilometres below the surface) was relatively shallow and produced the strongest earthquake ground-shaking ever recorded in New Zealand up to that time, with the ground near the epicentre moving up 1.25 times the acceleration due to gravity. The fault rupture occurred along a previously unknown east-west fault-line which is buried deeply under the gravels that were deposited on the Canterbury plains at the end of the last glaciation period, estimated at about 16,000 years ago. ( The 4 September 2010 earthquake literally provided a wake-up call regarding the vulnerability of the buried pipelines and utility structures within the Selwyn and Waimakariri Districts, Christchurch City as well as the rest of New Zealand. The Canterbury area had not been perceived to be a particularly high-risk earthquake area but this event supported what the seismologists and geo-technical engineers had been saying since the original University of Canterbury Centre for Advanced Engineering s (CAE) Lifelines projects in Wellington (1991) and Christchurch (1997). Page 1 of 29

2 There was a sense of complacency because there was no loss of life and most buildings remained standing and were functional. There was a feeling that we had survived a significant earthquake and had escaped relatively unscathed. This complacency was shattered on February 22, 2011 when the 6 km deep, 6.3 magnitude earth quake struck at 12:51 pm. The vertical ground acceleration above the epicentre near the Port Hills was 2.2 times the acceleration due to gravity. 185 lives were lost and the cost of damage to property and buried infrastructure was immense. 2 Background It is this writer s general observation that ground shaking intensities of greater than 5 Modified Mercalli (MM) were needed to re-activate the liquefaction processes in the most susceptible areas. Many of the earthquakes and aftershocks between September 2010 and December 2011 exceeded this threshold and resulted in damaged sewers being re-choked with fine silty sand. The extent of liquefaction during the Christchurch earthquake sequence has been almost unprecedented and at the time of writing this paper (January 2013) the ground in many of the worst affected areas is still unstable with residents that remain in these areas urging motorists to reduce speeds to minimise the shaking. The Canterbury region (as with most parts of New Zealand) has a history of damaging earthquake events. Ground shaking intensities of 5 Modified Mercalli Intensity scale (MMI) have occurred on at least 16 occasions from 1848 to 1995 as shown In TABLE-1 (adapted from J. R. Pettinga et al 2002) and updated with the 2010 and 2011 Canterbury and Christchurch earthquakes. TABLE-1: List of Damaging Earthquakes Affecting Christchurch City Since Date & Year Known Name / Location Magnitude (Richter) Christchurch (MMI) Depth Oct Marlborough Shallow Jan Wairarapa km June Pegasus Bay Shallow Aug Lake Ellesmere 6 6, 7 Crustal Dec Castle Hill 6 6, 7 Crustal Aug Hope fault Nth Canterbury , 6, 7 12 km Nov Cheviot 6.9 6, 7 12 km Dec Motunau km Mar Arthurs Pass < 15 km June Buller, White Creek fault km June Lake Coleridge km May Waiau km 24 May 1968 Inangahua km May Marlborough km June Arthur s Pass km Nov Cass km Sept Darfield km Feb Lyttelton km June Redcliffs km 23 Dec 2011 South New Brighton km Over 500,000 tonnes of liquefaction ejecta was removed from Christchurch city during the Canterbury earthquake sequence (M. Villemure et al, 2012). This does not include the liquefaction removed from Kaiapoi, Pines Beach and Karaki Beach in the Waimakariri District that were also heavily affected by liquefaction in the September 2010 event. Page 2 of 29

3 The consequences of liquefaction and lateral spreading on the buried infrastructure were not really understood or had been partly ignored by most infrastructure designers, even although the subject had been raised locally in the Report Risks and Realities (Christchurch Engineering Lifelines Group 1997) as well as in a paper about the 1901 Cheviot earthquake which caused liquefaction at Kaiapoi in the Waimakariri District, approximately 15 km north of Christchurch. ( Liquefaction at Kaiapoi in the 1901, Cheviot, New Zealand Earthquake [Berrill et al, 1994]). The dangers had also been highlighted in the Q Files Exposing Canterbury s Shaky Future (Environment Canterbury, circa 2001). FIG-1 shows the locations of earthquakes and after-shocks of greater than magnitude 3.0 that occurred between September 2010 and September 2012, including the four major events, Darfield, Sept 2010, Lyttelton, Feb 2011, Redcliffs, June 2011, and South New Brighton Dec FIG-1: Map Showing Earthquakes Magnitude 3.0 From September 2010 to September Source; Each of the main earthquake events resulted in serious disruption to the essential horizontal services, including power supply, in the worst affected areas. Many residents were without water supply for days or weeks at a time after the 4 September 2010, 22 February and 13 June 2011 events and raw sewage was still being pumped into the Avon and Heathcote rivers more than six months after the June 2011 event. Each new earthquake and significant after-shock re-activated the liquefaction and the damaged pipes allowed more silt and sand to enter and choke the sewers. CHART-1 shows the estimated daily volume of sewage overflowed to rivers and streams after the February 2011 earthquake. (Source, Christchurch City Council). Page 3 of 29

4 CHART-1: Chart Showing the Estimated Volume of Sewage Overflowed 3 Water Supply Network Damage after February 2011 Earthquakes find the weak-links in any system and can cause immediate breakage of many vulnerable pipes. There are also more subtle leaks that develop and these may take months or years to become large enough to be detectable or to show as wet spots on the ground surface. FIG-2 shows the location of repairs/faults on the watermains network following the 22 February 2011 earthquake superimposed on a background of the liquefaction map (Cubrinovski, 2012). FIG-2: Liquefaction Map of Christchurch & Locations of Water Network Mains Repairs After Feb 2011 From the concentration of repairs, there is a clear link between the damage to the pipe network and liquefaction severity. Cubrinovski, (2012) also found that polyethylene (PE) pipes and polyvinylchloride (PVC) pipes suffered significantly less damage (three to five times less on average) than asbestos cement (AC), steel (ST), galvanized iron (GI) and pipes of other materials. Page 4 of 29

5 It is worth noting here (based on this writer s personal experience with PVC pipes in Christchurch) that the City has had an on-going problem with PVC-U pipe failures over the years. Christchurch City Council adopted PVC pipes for water supply and sewage earlier than most other NZ cities and as a result, received some of the early production runs of quite poorly processed (brittle, low toughness) pipes. Many of these were already failing by longitudinal splitting before the earthquake sequence and some are continuing to fail. Poor quality pipes are more likely to split and fail catastrophically (by longitudinal splitting from end to end) than the high toughness PVC-U pipes produced from the late 1990 s onwards. 4 Increase in Background Water Supply Repair Rates Aside from the major pipe bursts that occurred immediately during the main earthquakes, more subtle damage also occurs and this damage may take weeks, months or years before it shows at the surface. This subtle damage includes leaks at deflected run-lead joints on cast iron (CI) and steel mains, joints on all pipe materials partially pulled out, breakage of CI gibault joints due to poor installation or overdeflection due to permanent ground deformation (PGD). Electro-fusion joints on PE pipes can start to leak and tapping saddles on all pipe materials can fracture or rotate and lose sealing. It is this writer s opinion that once a slow leak develops, a usually slow process begins. The escaping water damages the corrosion protection system on ferrous materials and allows corrosion to start. The leak develops slowly or it may increase in a number of discrete jumps if ground movement or water-hammer events occur. The increasing leak rate develops sufficient energy to activate sand particles in the pipe bedding and a wet sandblasting process gradually wears away the pipe wall to the point where the leak rate is detectable or shows at the ground surface. Plastics pipes are also frequently eroded to detectable leakage levels. (Kunkel, et al, 2008) has also reported that if these tiny leaks can be found early, they can be repaired before they lead to major pipeline ruptures. There has been a significant increase in the numbers of water supply leak repairs during 2012, particularly in Christchurch City. Many of these repairs are associated with run-lead joints that have been reported to be leaking and are believed to be the result of one or more of the main earthquake events. The data used to prepare CHART-2 was provided by Citycare (Christchurch City s maintenance contractor) (Blake-Manson, 2012). CHART-2: Chart of Water Supply Network Repair Numbers For Christchurch Number of Jobs Total Water Supply Network Repairs (Christchurch City Maintenance Contractor's Records) 12/13 11/12 10/11 09/10 08/09 07/ Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Page 5 of 29

6 The numbers of watermain repairs during the recovery phase after the September 2010 and February 2011 events do not show in CHART-1. The figures used to prepare CHART-1 include all water supply jobs, not just watermain repairs, that were carried out under the maintenance contract. Seasonal trends are obvious and there was already a clearly increasing trend over the three years prior to the September 2010 earthquake. It is expected that earthquake related damage repairs will continue for many years as slow leaks continue to grow to detectable size and ground conditions stabilise. Selwyn District, just south of Christchurch, had relatively few damaged horizontal services despite employing similar designs, pipe materials, construction methods and contractors. This was mainly due to the different ground conditions. The majority of Selwyn s 48 water and sewage schemes are located in stony soils with ground water levels well below the surface. Liquefaction was therefore limited and isolated to areas with recent marine sediments. The small township of Waimate, located approximately 100 km from the epicentre of the September 2010 earthquake experienced a significant increase in the number of water main bursts after the earthquake (McTigue, 2012). Waimate has a significant number of small diameter, 3 and 4 diameter (DN 80 and DN 100) cast iron water-mains that were installed in about These pipes are unusually thin in the wall, being only half the thickness of the lowest pressure class cast iron pipes covered by the earliest British or American standards, BS 78 and AWWA C-100. Waimate also has a number of old AC pipes (from the mid 1950 s) which have deteriorated to grade 5 i.e. very poor condition. (Black, 2012 A). The Waimate and Christchurch experiences serve to confirm that deteriorated pipes are more susceptible to failures caused by earthquake activity than pipes that are in better condition. 5 Pipe and System Vulnerability Observations of the earthquake response and on-going recovery phases has confirmed that piped networks can be divided into three categories of vulnerability, high, medium and low and within these categories, individual pipe materials can be roughly ranked in terms of relative vulnerability. The following lists represent the writer s opinion, based on years of experience and many direct observations over the period since the September 2010 earthquake. (Black, 2012). These lists are presented in the writers perceived order of damage susceptibility with the most vulnerable at the top. It should be noted that pipes and pipelines of any materials that have been poorly designed, are of poor quality, have deteriorated significantly, or have been poorly installed will be more vulnerable to damage than listed. (Black, 2011). 5.1 High Vulnerability Pipes & Joint Systems Ceramic pipes with rigid mortar joints. Unreinforced concrete pipes with rigid mortar joints Brick and stone barrels generally with lime mortar jointing. Old reinforced concrete pipes with rigid, mortar or run-lead joints. Ceramic pipes with rubber ring joints. Cast iron pipes with rigid, run-lead joints. Unreinforced concrete pipes with rubber ring joints. Low pressure class AC pipes of DN 150. High pressure class AC pipes of DN 150. Old, small diameter reinforced concrete (RC) pipes with rubber ring joints. Page 6 of 29

7 Screwed galvanised steel (GS) pipes (generally DN 50). Steel pipes with lead joints. CI pipes with rubber ring joints. AC pipes with rubber ring joints, DN Medium Vulnerability Pipes & Joint Systems Glass reinforced plastic (GRP) pipes with butt and strap joints. PVC-U pipes with solvent cement joints and poor quality PVC-U and modified PVC (PVC-M) pipes with rubber ring joints. Large diameter RC pipes with rubber ring joints. GRP filament wound pipes with rubber ring joints. Ductile Iron (DI) pipes with rubber ring joints. Steel pipes, generally concrete lined steel (CLS) with rubber ring joints. PE pipes with structured walls and rubber ring joints. PE pipes of the first generation (type 5 high density polyethylene [HDPE] resins) with end load bearing joints. High toughness PVC-U and PVC-M spigot and socket pipes with rubber ring joints. 5.3 Low Vulnerability Pipes & Joint Systems DI pipes with locking rings e.g. Tyton-Lok. PE 80B or PE 100 (Slow crack growth resistant HDPE) pipes with end-load bearing mechanical joints. Steel pipes with full strength welded joints. PE pipes with high quality butt fusion or full strength electro-fusion joints (Pipes of PE 80B & PE 100). 6 Response and Recovery Urgency In the aftermath of any major earthquake event, there is immense pressure on utilities and their operators to effect repairs and to get systems operating again, especially during the response phase. However, in the haste to make the essential repairs, some unique opportunities to investigate pipe condition and failure modes can be lost. Even in non-emergency times, broken and leaking pipes exhumed during repairs can often tell a story and teach valuable lessons. In the initial response phase after a major earthquake, pipe failure repairs are undertaken by multitudes of contractors which makes it difficult to keep track of the works in progress let alone carry out informed assessments and inspections to identify possible underlying causes. The damaged pipes are either loaded on trucks for immediate disposal or stockpiled in unidentifiable heaps for later disposal. By then it is too late to know where they came from and impossible to identify what is earthquake damage and what is damage caused by excavation and repair crews. A lesson that could be learned for future earthquake events is to appoint at least one independent and experienced pipe condition expert (a pipe-whisperer) to liaise with operations staff and contractors so that as many of the out-of-the-ordinary failures as possible are documented and investigated. This roving-brief could continue throughout the recovery phase as earthquake damaged pipes are likely to continue to be recovered for many years after the main event. Page 7 of 29

8 7 Pipe Failures 7.1 General Comments There is no perfect pipe material. All pipe materials have their advantages and disadvantages and the lifetimes of pipelines and their vulnerability can be affected by any one of the following: (Black, 2012 A) Pipe manufacturing faults (pipe quality), Poor workmanship during construction, Poor detailing and lack of flexibility at connections to structures and anchors (design issues), Misapplication of the pipe material through lack of understanding of pipe material limitations or the mitigation measures needed (design issues). In the course of pipe condition assessments and cause of failure investigations over 40 years, this writer has found combinations of any (or sometimes all) of these have contributed to pipe failures. Pipe failures usually occur at the weakest link in the pipeline at any time, but particularly so during an earthquake event or other event that imposes stress on the pipe. Brittle pipe materials with rigid joints usually are relatively short, have a greater number of weak links and usually suffer the greatest amount of damage and numbers of failures. As a general rule, the larger the pipes and the deeper their burial, the less susceptible they are to earthquake damage. Larger diameter pipes (even of brittle materials) have significantly greater beam strength than smaller pipes of the same materials and are therefore less susceptible to bending and circumferential cracking (broken-back) failures. Pipe materials such as AC, CI, DI and steel all suffer from a range of corrosion mechanisms which reduce their strength and make them progressively more vulnerable to failure as they deteriorate. Modern corrosion protection systems will certainly delay the onset of corrosion but to be effective, they must be applied correctly and remain undamaged throughout the design life of the pipe, usually at least 100 years. The plastics pipes, PVC and PE, do not suffer from corrosion but there are other mechanisms at play that affect the vulnerability of these pipes. Chemical break-down of the polymer structure can occur (Burn, et al, 2005). Poor quality plastics pipes can have a compromised lifetime (failures within 10 years are not unheard of) especially if the pipes are subjected to additional stresses caused by poor bedding, pressure over-load or cyclic fatigue, etc. In pipes extruded from the older PE resins (particularly type 5 HDPE in New Zealand) break-down of the stabilisers leads to longitudinal splitting, particularly associated with point load stresses caused by impingement of large angular bedding particles. Very few pipelines were installed in the Darfield fault shear zone (horizontal movement 3 m [10 ]) but those that were (mainly small bore PE and PVC pipes) stretched, buckled and ruptured. In the areas worst affected by liquefaction, the maximum ground settlement was over 1 metre (3-3 ) and lateral spreading caused up to 2 metres (6-6 ) of horizontal movement adjacent to stream and river channels. PGD of this magnitude is sufficient to damage pipes and pipelines of any materials. 7.2 Brick Barrels Brick barrels were constructed in Christchurch in the late 1870 s. Many have an egg shaped profile and have a concrete base which forms the lower part of the egg shape. The upper, semi-circular crown section was formed using special tapered, fired clay bricks. FIG-3 shows a typical brick barrel sewer in Christchurch. Page 8 of 29

9 FIG-3 : Egg-profile brick barrel 1878 (Photo 2007) The construction of these sewers pre-dated the production of Portland cement in New Zealand by nearly 10 years. It is therefore likely that the concrete and the mortar between the bricks is a hydraulic lime product, although Portland cement could have been imported from the UK. (Black, 2007). Photo, J Black. These brick barrels had been in operation for over 130 years with few problems (apart from significant levels of infiltration) before the 2010/2011 earthquakes struck. It is not known how much damage they had suffered from the 11 earthquake events between 1881 and 2010 that were capable of initiating liquefaction (>MMI 5 see Table-1). However, is highly likely that some damage could have happened as subsidence of streets above the brick barrels has occurred over the years. This subsidence was caused by cracking of the brick crown and concrete base which allowed the groundwater to carry silt and sand into the barrel, leaving voids that gradually collapsed. These brick barrel sewers are generally laid at least 1 metre (3-3 ) below the water table level. The earthquake sequence increased the number of fractures in these barrels and required repeated cleaning by high pressure water-jet to remove the sand and silt and to restore the flow capacity, before remedial work involving cure-in-place liners began. FIG s-4 and 5 show CCTV views of cracking in the concrete base and silty water flowing in weeks after the June 2011 earthquake. FIG-4 & FIG-5: Near vertical cracks in the concrete base & silt ingress into the brick barrels Page 9 of 29

10 CCTV images from C. Manse, Stronger Christchurch Infrastructure Recovery Team (SCIRT) 7.3 Ceramic (Earthenware) Pipes Ceramic pipes have been used extensively for gravity sewers in Christchurch since the first sewers were laid in the 1870 s. Under normal circumstances, the principal forces acting on gravity sewers are due to the soil column above the pipe plus any surcharge loads. In earthquake and liquefaction events, the pipes are subjected to shaking, bending and joint rotation, as well as sometimes fluctuating compression and tension forces. Ceramic pipes are brittle, the sockets and pipe ends shatter and pipes break. The damage to ceramic sewer mains and laterals was widespread and allowed massive ingress of liquefied silt and sand, completely blocking the network. Each successive aftershock > MMI 5 reactivated the liquefaction process and required repeated high pressure water-jet cleaning as well as Page 10 of 29

11 wide-spread repairs to damaged pipes. The water-jet cleaning also created problems and frequently made the damage worse. Pipes with deteriorated cement mortar joints have been highly susceptible to damage but even the more modern elastomeric ring jointed ceramic pipes suffered severe damage (see FIG s-6 and 7). Customer lateral connections, mainly DN 100 (4 ) with rigid (mortar) joints, were particularly susceptible to damage. In many cases, laterals were completely ripped from the main see(fig-8. FIG-6 to FIG-8: Broken ceramic pipes and broken lateral junction G. Boot, Waimakariri DC 7.4 Asbestos Cement (AC) Pipes The response of AC pipes to the earthquakes has been quite variable. In areas not subjected to PGD, e.g. Rangiora in the Waimakariri District, only 8.5 km (5.2 miles) from the closest damaging events and most of the Selwyn District including Darfield, also only 8.5 km, from the September 2010 event, there were remarkably few AC pipe failures, even in the relatively fragile DN 50 (2 ), DN 80 (3 ) and DN 100 (4 ) sizes. In the areas subjected to lateral spreading, AC watermains and gravity sewers suffered badly with failures ranging from broken collars and fractured spigots to circumferential cracking (broken-back), blow-outs and longitudinal splits. AC pipes of greater than DN 150 (6 ) have significant beam strength (even in a deteriorated state) and this strength combined with the flexible elastomeric ring jointing system and their relatively short length (4.0 m [13-1½ ]) allow movement before pipes break. Most of the failures in AC pipes of DN 200 (8 ) and larger occurred near to points where the pipe was securely anchored e.g. thrust blocks on bends, tees, valves or connections to structures. During the response to the earthquakes, AC watermains and pressure sewers were re-commissioned progressively and broken pipes were repaired as they were found. If there were more than 2-3 failures on any pipeline, the entire AC pipeline was abandoned and replaced with a new butt fusion jointed PE 100 (HDPE) pipeline. In one DN 300 (12 ) Class B ( 85 psi) AC sewage pressure main, 2 breaks (in close proximity to concrete thrust blocks at bends) were located and repaired immediately after the 22 February 2011 earthquake. These two repairs were sufficient to have this main put on the list for urgent replacement even although this pipeline continued to operate through the June earthquake and thousands of aftershocks until it was replaced with a new DN 355 (12 ) PE 100 pipeline in July There were a number of similar instances where pipelines were replaced unnecessarily due to the need to make decisions quickly. For future reference a more measured approach to determining whether repair or replacement is the best option would be desirable. Such an approach should take into account the nature and location of the damage (relative to thrust blocks, etc.) and the amount of damage to street paving etc. (this gives an indication of the potential for damage to the buried pipes) as well as the condition and estimated remaining life of the pipe. These sorts of decisions take time and require experience and expertise in Page 11 of 29

12 pipe design and condition assessment. Other issues, e.g. the responsibilities to customers and the number of customers affected will also affect the decision making process. Unfortunately, it may not be possible to take the time to evaluate the options. In the Christchurch case, contractors from around New Zealand were waiting for works to be allocated. Delays would have been frustrating and could have led to some contractors moving their work-forces out of the area. FIG s-9 to 12 show a few of the broken AC sewer and watermain pipes that were removed during repair works or to allow new pipes to be installed. It is impossible to tell from piles of broken pipes what actually failed and what the main cause was. FIG-9 to FIG-12: Broken AC sewer and water main pipes removed during renewal works Photos J Black 7.5 PVC Pipes Photos, F O Callaghan, IPLEX PIPELINES NZ In general, well processed PVC pipe varieties (PVC-U, PVC-M) have proved to be satisfactory for use in all but a few areas where significant liquefaction and associated PGD is identified as a risk. There was little PVC-O (bi-axially molecularly oriented PVC) installed in the Christchurch piped networks but we would expect PVC-O to perform as well as (or potentially better than) the other PVC pipe varieties. The CCTV surveys of hundreds of kilometres of PVC gravity sewers viewed to date indicate that there have been remarkably few failures. Of those failures, partial joint pull-out is reasonably common. Over-insertion in sewers has not been reported, largely as it is likely to be difficult to recognise in the relatively thin walled (non-pressure generally SDR 36) pipes and CCTV pipe inspection operators may not recognise this type of problem. Over-insertion (sometimes known as super-socketing) of PVC pipe joints both in gravity sewers and pressure pipes is rare but certainly happened. Over-insertion at joints in gravity sewers is unlikely to require remedial work, even in the long term, because well processed PVC is unlikely to split or crack and the forces in the pipe wall gradually relax with time. The restriction in the pipe bore is small and is unlikely to compromise flow capacity or cause blockage. In two areas of Christchurch, Parklands and Brookhaven, the PVC-U gravity sewer pipes survived the earthquakes but the pipelines were no longer functional due to major grade disruption. It is unlikely that a gravity flow system could be designed to survive the PGD that occurred. The number of examples presented below reflects more the need to illustrate and document the types of failures that occurred, rather than the total number of failures that occurred. Fig-14 shows an over-inserted DN 100 (4 ), PN 6, (87 psi) PVC-U watermain pipe that had not split. There were a number of these found in the Pines/Karaki Beach after the September 2010 earthquake. FIG-15 shows an over inserted DN 100 (4 ) PN 12 (174 psi) pressure pipe joint that was found. This joint required a force of 34.6 kn (7,800 lbs.) to start to move. It should also be noted that the sockets had not split. FIG-14: Over-inserted PN 6 (87 psi) PVC Pipe FIG-15: DN 100 (4 )PN 12 Pipe Over-inserted Page 12 of 29

13 Over insertion 70 mm Normal socket depth Over insertion 50 mm Normal socket depth Photos J Black. Joint pull-out also occurred in some areas subject to significant PGD. One joint leak occurred on a DN 300 (12 ), PN 9 (130 psi), PVC-U sewage rising main, 1,100 m long (3,610 ) that was laid in an area that suffered severe liquefaction. However, a number of other joints that have partially pulled out (but are still sealing) were found by CCTV survey. FIG-16 shows the joint that had pulled apart sufficiently to allow loss of seal. FIG-17 shows a partially pulled-out joint on this same DN 300 (12 ) sewage rising main that was identified by CCTV, recovered and cut open. The photo shows that there is a significant angular deflection at the joint and that 25 mm of additional pull-out would be needed to cause leakage. FIG-16 DN 300 (12 ) pipe joint with pull-out and leakage. FIG-17: Another joint with partial pull-out G. Boot, Waimakariri DC In the Pines Beach area of the Waimakariri District (one of the areas most severely affected by liquefaction and lateral spreading), complete joint pull-out and re-insertion (a little offset) occurred at a few joints (only 3 are known). FIG s-18 to 21 show examples of watermain pipe joints (viewed from the inside and the outside) that have suffered pull-out and re-insertion a little offset (enough to cause splitting of the socket or spigot end of the pipe). FIG-18 & FIG-19: Example of joint pull-out & re-insertion, offset viewed from pipe exterior & interior Page 13 of 29

14 Photos J Black FIG-20 & FIG-21: Example of joint pull-out & re-insertion, offset - viewed from pipe exterior & interior Photos J Black. The most extreme amount of re-insertion found is shown in FIG-22. In this case, the pipe has completely pulled-out to clear the socket and then more than fully re-inserted but offset enough to cause the pipe spigot end to split. The jointing witness mark is clearly inside the mouth of the socket and pull-out of > 100 mm (4 ) with re-insertion of 115 mm (4½ ) must have occurred to cause this damage. FIG-22: Example of joint pull-out & re-insertion to full depth with sufficient off-set to split the spigot Joint witness mark Photo J Black Many other PVC-U and PVC-M pressure mains (water supply and sewage) of all diameters up to DN 500 (20 ), some installed in areas within 1 km of areas of severe PGD, survived all of the earthquakes and after-shocks without developing leaks although some older (pre 2000) low-toughness PVC-U pipes have split longitudinally. Page 14 of 29

15 FIG-23 shows an example of a vertically deflected DN 300 (12 ) PVC-U sewer pipe showing what was reported by the CCTV camera technician as deformed plastic pipe, medium. The superimposed red circle shows that the actual vertical deflection is approximately 14%. The extensive CCTV surveys carried out in the region have shown excessive vertical deflection on very few pipes in the hundreds of kilometres of PVC gravity sewers surveyed. FIG-23: Vertically deflected PVC-U sewer pipe CCTV Survey image Christchurch CC. 14% deflection is almost double the maximum allowed long-term deflection given in AS/NZS :2002 (Buried Flexible Pipes - Construction) and would suggest that the pipe could be in danger of collapse. It is difficult to know how much influence the earthquake had because deflection testing and CCTV inspections were not undertaken until the 1990 s, long after this particular sewer main was installed. It is possible that poor installation and lack of attention to embedment compaction could have caused some (if not most) of the observed deflection, long before the earthquake. 7.6 Steel Pipes Steel pipes are ductile and will generally buckle and bend when earthquakes occur. Compression and tension forces due to shaking lateral spreading have been sufficient to cause unrestrained rubber ring spigot and socket joints to pull-out and cast iron gibault joints to break or pull-out. Joint pull-out has occurred on a number of concrete lined steel (CLS) water mains that have been jointed using CI gibault type joints and in areas where liquefaction and PGD have been severe. As with the PVC pipe examples, some joints have pulled out and then re-inserted a little off-set. FIG-24 shows a DN 300 (12 ) CLS watermain pipe that was subjected to compressive forces, sufficient to break the cast iron gibault joint and split the steel longitudinally. FIG-25 shows a DN 300 (12 ) CLS pipe joint at a bridge abutment. Compressive forces have also broken the cast iron gibault joint and caused shearing of the pipe end. Page 15 of 29

16 FIG-24: DN 300 (12 ) CLS Pipe Split FIG-25: DN 300 CLS Pipe at bridge abutment Photo by P. Free Photo by J Walter, SCIRT There were numerous examples of old, screwed GS sub-main pipes generally DN 50 (2 ) that had fractured at threaded joints. Threading GS pipes cuts up to 50% of the pipe wall away and corrosion weakens the remaining wall making these pipes highly vulnerable to damage. FIG s-26 and 27 show other examples of lateral spreading damage to steel pipes. The DN 80 (3 ) galvanized steel water pipe (FIG-26) has deflected upwards due to lateral spread of 0.8 m. The adjacent DN 100 welded steel sewer lateral was strong enough to crush the connected ceramic pipes. FIG-26 shows an old DN 25 (1 ) galvanized steel pipe that was forced to the surface. FIG-26 & FIG-27: Bent steel pipes Photos J Black. A number of 1920 s spiral riveted steel water main pipes of various diameters up to DN 250 (10 ) are still in service in parts of Christchurch. The steel shell is as little as 2.0 mm ( 0.08 ) thick in some DN 100 (4 ) pipes. These pipes have been in service for 90 years and have performed remarkably well. They were protected from corrosion by a hot-dip in a vat of bitumen and then wrapped with hessian. With such a thin wall, it is no surprise that the corroded DN 100 (4 ) steel pipe shown in FIG s-27 to 29 has ruptured. FIG-28: DN 100 (4 ) spiral riveted pipe. FIG-29 & FIG-30: DN 100 (4 ) spiral riveted pipe end Photos J Black Page 16 of 29

17 7.7 PE Pipes The 1980 s and 1990 s Type 5 HDPE pipes used mainly for water supply sub-mains and consumer connections in sizes of DN 50 (2 ) are jointed using compression couplers. Many of these joints pulled apart under the tension loads imposed by lateral spreading. Type 5 HDPE resin pipes are also highly susceptible to longitudinal splitting. There were few of the second and third generation PE pipes (PE 80B) or PE 100) water supply or sewage pumping mains in service prior to September A number of PE 100 water supply pipelines and sewage rising mains were installed in the response phase after the September 2010 and February 2011 earthquakes and aftershocks. As expected, these PE pipes (manufactured to AS/NZS 4130:2009 Polyethylene [PE] Pipes for Pressure Applications) using PE 100 have survived the June and December 2011 events without incident. Long coils of DN 63 (2 ) PN 12.5 (180 psi) PE 80B pipe laid out over the ground allowed the water supply to be quickly re-established to areas that had suffered extensive damage to the existing (mostly DN 100 (4 ) and DN 150(6 ) AC) water mains. In some cases these temporary pipelines were still in place more than 18 months after the September 2010 event. FIG-31 shows one such temporary DN 63 (2 ) PN 12.5 (180 psi) PE 80B pipe laid along a grass verge and connected to individual customer supply pipes. FIG-31: View of temporary water supply main Photo G. Boot, Waimakariri DC PE pipes have become more widely used over the last years and improvements in resins and extrusions techniques have made it possible to produce ever larger pipes. The Achilles heel of these pipes is the jointing process. Butt fusion joints have an extremely high rate of success. Electro-fusion (EF) joints on the other hand, have a greater risk of failure and leaking joints are found from time to time most (if not all) have been leaking since installation and are usually the result of faulty technique and poor workmanship. EF joints are frequently used to make joints between strings of butt-fused pipes in the trench. There is often limited space in the trench, the conditions are dirty and wet and the pipe strings may not be well aligned. These constraints work against the chances of long-term success of the joint. Earthquake stresses can cause partial or full pull-out of poorly fused EF joints. When leakage starts, the escaping water jet can erode the pipe wall by a wet sandblasting process, to the point of failure. FIG-32 shows one leaking EF coupler (of four installed at the same time in a short length of pipeline) that had been leaking for six years when it was repaired (not earthquake damage). FIG-33 shows one EF coupler (of five failures on this pipeline to date) that had been leaking for 3 years. The erosion is up to 30% of the wall thickness and is approaching the burst point. Page 17 of 29

18 FIG-32: View of leaking DN 180 (6 ) PE EF coupler FIG-33: PN 16 (232 psi) DN 180 PE Coupler Photos J Black 7.8 RC Pipes RC pipes in small diameters DN 450 have generally suffered spigot and socket damage caused by bending, joint rotation and fluctuating tension and compression forces. The larger diameter RC pipes (including pressure pipes used for rising mains) have generally suffered less damage than the smaller pipes. However, the full extent of damage is still unclear as many of the main sewer pipelines are still running nearly full because of infiltration and loss of capacity due to sediment from liquefaction. It has been difficult to conduct detailed CCTV inspections of some of these sewer mains. FIGs -34 and 35 show part of a DN 1200 (4 ft) RC rubber ring jointed (RCRRJ) pipeline laid in 1975 that jack-knifed during the September 2010 earthquake even although the pipes were full at the time. The pipes were undamaged and were re-installed on line and grade before 22 February No further damage has occurred during any of the subsequent earthquakes. FIG-34: Displaced RCRRJ pipes FIG-35: Displaced RCRRJ pipes Photos John Walter, SCIRT FIG s-36 and 37 show a DN 525 (21 ) RC stormwater outlet to a tidal estuary that had been encased in concrete. The concrete broke and pulled away from the retaining wall when the estuary level settled by more than 500 mm (20 ). Page 18 of 29

19 FIG-36 and FIG-37: Fractured concrete encasement on DN 525 stormwater outfall Photos J Black 7.9 Glass Reinforces Plastic (GRP) pipes There are only a few GRP pipelines installed in Christchurch. No failures have occurred and this is as expected for flexible, segmented pipe systems with flexible joints. At a major sewage pumping station where the differential movement exceeded the flexibility provided by the length of rocker pipes, the GRP pipes and fabricated bends, reducers, etc. were undamaged. 8 Detailed Examination of Failed Pipes & Fittings A few earthquake damaged pipes and fittings failures have been examined and investigated in reasonable detail by the writer. This has enabled identification of likely contributing factors that resulted in failure, aside from the earthquake. The principal contributors to failure identified include: The pipes or fittings were of poor quality and probably should never have escaped the manufacturer s quality assurance checking, The design has not had sufficient flexibility and allowance for differential movement, The pipes have been poorly installed, They have deteriorated to become the weak-link. Examples of poor quality pipes and fittings that failed during the earthquakes (the weak links) are presented below. Other pipes failed because of insufficient flexibility and provision for differential movement, or survived because of the inherent flexibility of the pipe material in spite of design and installation issues. It should be noted that without a close inspection many of these issues may not have been recognised or recorded. 8.1 CI Pipes FIG s-38 to 41 show an example of a 1930, DN 150 (6 ) Class B (design pressure rating 60 metres head [87 psi]) CI sewage pressure main with rigid, run-lead joints. The pipe OD was 178 mm (7 ), average wall thickness 11.0 mm (0.43 ), minimum thickness, 8.3 mm (0.33 ). The contemporary manufacturing standard was BS 78:1917. The measured dimensions of the pipe show that the minimum wall thickness was < 85% of the allowed minimum of the standard. The standard required all pipes to be tested to 400 ft head (120 m, 173 psi) without showing any signs of leakage, sweating or other defect before being coated with an approved (bituminous) composition. Page 19 of 29

20 FIG-38 to FIG-41: Fractured DN 150 (6 ) CI pipe (as recovered and after cleaning) Photos J Black The photos show what appears to be just a rusty old CI pipe. However, the real weakness is only revealed by a much closer examination, in this case by sandblasting the pipe surface to white metal (Sa3) as shown in FIG s-42 to 45. The extreme levels of porosity in the metal are clearly obvious. This pipe would have had minimal resistance to bending forces and the original factory test pressure is likely to have been close to causing failure, if it was carried out. These casting faults, combined with a thinner wall than allowed by the standard have resulted in a pipe that is at greater risk of failure under earthquake imposed stresses than other higher quality pipes. It is a little surprising that a pipe in this condition passed the factory proving tests. The hot-dip bitumen compound coating process would have covered up any traces of the porosity (the weak link) and without the earthquake generated bending forces on the pipe it may have lasted for many more years as the operating pressure was less than 200 kpa (30 psi), i.e. of its nominal design rating. While this pipeline was in service for nearly 80 years and had probably reached the original design expectations, had the pipe been full strength, the likelihood of failure would have been reduced. In this case, two similar failures dictated replacement of the entire pipeline (approximate length 1,100 m [3,600 ]). FIG-42 to FIG-45: Views of sandblasted pipe showing close-ups of the porosity Photos J Black FIG s-46 and 47 show a fairly typical run lead joint on a 1914 DN 100 (4 ) cast iron watermain that had been deflected almost 3º by earthquake induced movement and was repaired in January Some streets with lead jointed watermains (steel and cast iron) have shown a marked upsurge in the number of leaking joint repairs recently (more than a year after the last significant earthquake). FIG-46 and FIG-47: Views of a deflected, leaking lead joint as recovered and after cleaning Photos J Black Page 20 of 29