The Chernobyl Nuclear Power Plant

Report 04/2020CorbyMay 2020PrefaceThe purpose of a Rail Accident Investigation Branch (RAIB) investigation is to improve railway safety by preventing future railway accidents or by mitigating their consequences. It is not the purpose of such an investigation to establish blame or liability. Accordingly, it is inappropriate that RAIB reports should be used to assign fault or blame, or determine liability, since neither the investigation nor the reporting process has been undertaken for that purpose. the time of the investigation and are intended to explain what happened, and why, in a fair and unbiased manner. Where RAIB has described a factor as being linked to cause and the term is the presence of the factor and its direct relevance to the causation of the accident or existence of a factor, or its role in the causation of the accident or incident, RAIB will Where there is more than one potential explanation RAIB may describe one factor as to the causation of the accident or incident but are associated with the underlying management arrangements or organisational issues (such as working culture). means that, although there is some evidence that supports this factor, there remains a considered to be causal or underlying to the accident or incident being investigated, but does deserve scrutiny because of a perceived potential for safety learning. The above terms are intended to assist readers™ interpretation of the report, and to provide suitable explanations where uncertainty remains. The report should therefore be interpreted as the view of RAIB, expressed with the sole purpose of improving railway safety. sources. Considerations of personal privacy may mean that not all of the actual unexpected events can have both short- and long-term consequences for the physical and/or mental health of people who were involved, both directly and indirectly, in what happened.RAIB™s investigation (including its scope, methods, conclusions and recommendations) is independent of any inquest or fatal accident inquiry, and all other investigations, including those carried out by the safety authority, police or railway industry. Preface4Report 04/2020CorbyMay 20205Train collision with material washed out from a cutting slope at Corby, Northamptonshire 13 June 2019ContentsPreface 3Summary 7Introduction 9The incident 10Context 12The sequence of events 16Background information 20Analysis 25Summary of conclusions 52Immediate cause 52Causal factors 52Underlying factors 52Previous RAIB recommendations relevant to this investigation 54Actions reported as already taken or in progress relevant to this report 56Actions reported that address factors which otherwise would have resulted in a RAIB recommendation 56Other reported actions 56Recommendations and learning point 59Recommendations 596Appendices 62 Appendix B - Investigation details 637SummaryAt about 15:53 hrs on Thursday 13 June 2019, a northbound passenger train, adjacent cutting slope, around one mile (1.6 km) north of Corby station. After reporting the incident, the driver found the rear of the train had become trapped by further debris washed out from the cutting slope. All 191 passengers on the train were later to the north and south. Between 450 and 550 passengers (from both trains) were to continue their journey by rail. No one was reported as injured as a result of the collision or subsequent detrainments. However, conditions on the southbound train were very uncomfortable for passengers due to overcrowding. Temporary repairs were made to the cutting slope and track to allow the railway to reopen the following day with a speed restriction in place. The investigation found that the cutting slope had failed because it was not designed to cope with a large volume of water that had accumulated at its crest. Flood water with water from a nearby brook. A blockage beneath a bridge over the brook caused routinely pumped down for nearly four weeks. The bank of the pond closest to the and the crest of the cutting slope. Exceptionally heavy rainfall was not a factor in the incident.The investigation also found three underlying causes. One was a lack of engagement risk to the railway line, which is a principal transport route. Thirdly, although Network Rail was aware that the cutting slope was at risk of a washout failure when the nearby this risk in the short term. The investigation also considered why the rescue and for transferring passengers from one train to another was a factor. work with Northamptonshire County Council, Anglian Water, Homes England, Corby system at this location. The second calls for Network Rail to identify similar locations on how to better manage the short-term risks to earthworks while waiting for longer term planned work to take place. The fourth calls for Network Rail and the Rail management of stranded passenger train incidents, to jointly review their procedures for managing stranded trains to identify what emergency equipment is needed, and of work, taking steps with train operating companies to make this equipment available for use. Summarywhich are part of the United Kingdom™s national infrastructure, in their planning. Summary9Introduction1 Metric units are used in this report, except when it is normal railway practice to give speeds and locations in imperial units. Where appropriate the equivalent metric value is also given.2 evidence used in the investigation are listed in appendix B. 3 Introduction10© Crown Copyright. All rights reserved. Department for Transport 100039241. RAIB 2020 The incidentSummary of the incident4 At about 15:53 hrs on Thursday 13 June 2019, a northbound passenger train, travelling at 40 mph (64 km/h), collided with debris around one mile (1.6 km) north Figure 1: Extract from Ordnance Survey map showing location of the incident 5 After speaking to the signaller, the driver examined the train and found that its had washed out from the cutting slope in the time since the train had stopped southbound train by 23:14 hrs. One group of passengers was taken by road to Corby station and the remainder were taken to Kettering station, to continue their journey by rail. 6 No one was reported as injured during the collision or subsequent detrainments. However, conditions on the southbound train were very uncomfortable for passengers due to overcrowding. There was some minor damage to the sandy gravel and soil.The incident11Train 1D43 direction of travelspeed restrictionAqueductCutting Corby Tunnel southern portalDown Corby lineUp Corby lineFigure 2: Google Earth image showing overview of incident site The incident12Figure 3: The rear of the train after further sandy gravel washed-out around it (main image courtesy of Network Rail, other images courtesy of the driver of train 1C52). Context7 1 Junction, which is part of Network Rail™s East Midlands Route 2 within its Eastern Region.3 Here the railway passes through a cutting, on a left-hand curve (in the 1 A unit of length equal to 66 feet or 22 yards (around 20 metres). 2 3 & East.The incident13AWillow Brook North BBADown Corby lineUp Corby lineNcomprises the up Corby and down Corby lines. The permitted speed for trains on both lines is 60 mph (97 km/h). However, northbound trains were travelling slower than this as a temporary speed restriction of 40 mph (64 km/h) was in place on restriction was due to the condition of the track in Corby Tunnel. Just south of the Figure 4: The aqueduct over the railway9 counters4 and is controlled by a signaller in the East Midlands Control Centre 4 A system that detects the absence of a train by counting the individual axles of a train in at one end of a section of track and out at the other end.The incident14Willow Brook NorthNetwork Rail infrastructureBridge over the brook (Corby Borough Council)AqueductwashoutNto brook via spillway (Anglian Water) Housingto pond 1 (Homes England)Organisations involved10 Network Rail owns, operates and maintains the railway infrastructure where the incident occurred, including the track, cutting slope and aqueduct. It also 11 The two passenger trains involved were operated by East Midlands Trains, which time of the incident has since passed to East Midlands Railway. 12 and the organisations responsible for them. The watercourse, Willow Brook North, is designated as a main river. 5 This means the Environment Agency has permissive powers under the Flood and Water Management Act 2010 to maintain Rail is responsible for the aqueduct that carries Willow Brook North over the railway, and the trash screen at its entrance. Anglian Water is the owner of the is responsible for the structure and trash screens that connect it to Willow Brook now on referred to as pond 2) and is responsible for the culvert and trash screens that connect it to pond 1. Corby Borough Council is responsible for the bridge 13 All of the above organisations freely co-operated with the investigation. 5 Main rivers are usually larger rivers and streams on which the Environment Agency carries out maintenance, The incident15Train(s) involved 14 The train which struck the debris, reporting number 1D43,6 was the 14:34 hrs 15 The southbound train used for the train-to-train transfer of passengers, reporting coaches with a power car at each end. It too had been diverted due to the 16 The driver of train 1D43 had over 16 years™ experience of driving trains. He had The driver of train 1C52 had booked on for duty at Derby, where he took over this that the way the trains were driven contributed to the incident. 17 The signaller involved was working on the Kettering workstation7 at EMCC. RAIB found no evidence that the actions of the signaller contributed to the incident. room at EMCC, were responsible for managing the railway™s response to the evacuations,8External circumstances19 It was daylight at the time of the incident. The local weather conditions, based on rainfall radar data and closed circuit television (CCTV) footage, were cloudy with light rainfall. A local weather station, located 1.65 miles (2.65 km) away, reported the incident is discussed at paragraphs 20 and 96.6 infrastructure.7 A desk with the signalling in the area being controlled shown on a series of monitors, and a trackerball and keyboard provided to operate the signalling functions.8 The procedures followed by Network Rail and train operating companies for managing stranded trains use the another train or onto the track. In many cases, an evacuation from a stranded train will take place in a controlled manner without the passengers being in any immediate danger. The incident16The sequence of eventsEvents preceding the incident20 control room at EMCC directed a mobile operations manager, whose role is to its trash screen. He reported back at 09:47 hrs that he had removed debris from the aqueduct™s trash screen, and that the water level in Willow Brook North was that further visits should take place. 21 passed at 12:43 hrs on the up Corby line (the up line). CCTV footage from this train showed standing water between the rails of the down Corby line (the down line), over a length of around 40 metres. This started around 60 metres to the north of where the cutting slope was later washed out. There was no sign at that cutting slope. 22 the aqueduct was clear of debris. He also reported that the water in Willow Brook in its channels, issued an alarm to report that a 75% threshold level had been 23 At 14:33 hrs train 1C52 departed on time from Derby and at 14:37 hrs train afterwards, at 14:47 hrs, Network Rail received a call from the British Transport from the north and was held there. 24 train 1D43 to advise him that his train would be diverted and would no longer call at Kettering station. At 15:27 hrs, train 1D43 stopped at Kettering station to allow The sequence of events17LoughboroughTo Derby and Nottingham To Burton on Trent To Nuneaton To Peterborough LeicesterTrain 1C52 direction of travelTrain 1D43 direction of travelCorbyMarket HarboroughKetteringManton JunctionSyston JunctionCorby Tunnel Location of incidentTo London Figure 6: The planned diversionary route via Corby and Manton Junction25 After being advised of the diversion, the driver of 1C52 changed ends and train hrs, train 1D43 departed from Kettering towards Corby. Events during the incident26 while travelling at 43 mph (69 km/h), the driver of train 1D43 began applying the train™s brakes to slow it down for the start of the 40 mph (64 km/h) temporary speed restriction on the down line through Corby Tunnel. 27 while travelling at 40 mph (64 km/h), the driver made an emergency brake application. At about the same time, train 1D43 struck sandy gravel and soil that had been washed out from the cutting slope onto the track. Train 1D43 stopped at 15:50:40 hrs, after travelling for a further 193 metres.The sequence of eventsDebris on the down Corby line the cutting slopedown line.Events following the incidentOnce the train had stopped, the driver looked back from his cab to check that his train was not derailed. At 15:53 hrs, the driver called the signaller using the train™s derailed. After walking to the rear of his train, the driver found the rear coach and power car were still on the rails but could not be moved as more debris had washed underneath and around them. He reported back to the signaller that his train was stranded but the adjacent up line was still clear for the passage of trains. 29 (paragraph 23) had climbed down from the bridge parapet. Train 1C52 was now approaching Corby from the north. The signaller stopped train 1C52 at the signal before Corby Tunnel and explained to the driver that train 1D43 was stranded after striking a landslip. The signaller then authorised the driver of train 1C52 to Tunnel at 16:15 hrs. The sequence of events1930 After exiting the southern portal of Corby Tunnel, the driver of train 1C52 noticed the up line. Flood water was covering the sleepers but was still below the top of the front of train 1D43. At around 16:30 hrs, the driver of train 1C52 obtained permission from the signaller to leave his cab and went to speak to the driver of train 1D43. Both drivers spoke to the signaller who told them that three trains had room at EMCC were planning to evacuate the passengers from the stranded train 1D43 onto the third of these trains. The driver of train 1C52 was asked to proceed south at extreme caution.31 track, blocking it. At 16:45 hrs the driver of 1C52 reported this to the signaller, who control changed their plan, and decided to evacuate the passengers from train 1D43 onto train 1C52 instead. Train 1C52 would then return north via Manton 32 another. At 19:11 hrs the transfer of passengers from train 1D43 was complete. of the rails. The driver of train 1C52 spoke to the signaller and was instructed by the signaller to return south through the tunnel. Train 1C52 headed back south, arriving back at train 1D43 at 20:25 hrs. The driver of train 1C52 made this above the sleepers in many places throughout the tunnel. When asked to return the tunnel again.33 train 1C52 and onto the track. The evacuation started at 21:42 hrs after Network pathway from a railway access point near to the trains to the buses now waiting remaining buses took passengers to Kettering station. The last of the passengers station transferred onto additional trains provided by East Midlands Trains to take The sequence of events20Willow Brook North19501950 Water course now culverted Background information 34 carry Willow Brook North over the then new railway line it was constructing to shows the brook was an open watercourse, running through a rural area each Figure 8: Map dated 1885 showing the brook passing through a rural area and a map dated 1950 35 quarries appearing to the north east of the railway, but the brook was still an open watercourse. During the 1930s the industrialisation of this area accelerated alongside the construction and opening of the nearby steelworks in 1933. A map now culverted in two places to the east of the railway. A map dated 1950 shows 1950 there has been further extensive change in the area, with widespread Background information2136 asked Corby Urban District Council (which later became Corby Borough Council) whether it could install a trash screen at the entrance to the aqueduct. The council stated that it had no objections to this. 37 had only happened on the railway following exceptional rainfall. However, since four new outfall pipes from recent factory developments that were discharging surface drainage water into the brook. Additionally, pumps at the ironstone quarry workings were also pumping considerable amounts of water into the on occasions, but more often it overtopped the wing walls at the entrance to the water was also noted as eroding the aqueduct™s abutment. by water backing up on the eastern side of the railway at a syphon drainage pipe. This was because the aqueduct™s capacity to carry water was greater than the capacity of the syphon drainage pipe to take it away downstream. When the water backed up from the syphon drainage pipe, it overtopped the aqueduct. 39 storage reservoir. This led to the construction of pond 1 in 1976. In 1977, British the water when it reached too high a level on the aqueduct, by directing it into the track drainage. 40 Further letters between British Rail and Corby Urban District Council, from described problems with debris blocking various trash screens and silt building up in pond 1 which had reduced its capacity. This correspondence also noted that the downstream restriction at the syphon drainage pipe was still present. 41 slope next to the aqueduct. At the request of British Rail, Corby Urban District the same time, Anglian Water agreed to remove silt from pond 1, to restore its capacity to store water. Background information2242 and later Homes England) submitted plans to Corby Urban District Council for a new balancing pond (pond 2) alongside pond 1 to accommodate further developments that were taking place on the Earlstrees industrial estate to the constructed at some time between 1990 (when planning permission for pond 2 but Homes England does not hold any records that give an exact date. 43 which is next to the aqueduct. At the time, Railtrack, the then owner of the railway, questioned whether Anglian Water had reduced the water level in the ponds Railtrack claimed that Corby Urban District Council was not maintaining the trash screens and that Anglian Water had allowed the ponds to silt up. 44 In October 2006, Network Rail visited the site in response to further reports of the entrance to the aqueduct. 45 In October 2009, Network Rail completed work on the aqueduct to better manage the water at its entrance. This work extended the wing walls at the entrance, water down the bank, and into the drainage system running alongside the track. At the same time, Network Rail repaired the cutting slope following its failure work took place in 2011. 46 cause was debris in the trash screen which was diverting water onto the track. in the channel by the aqueduct™s entrance had allowed water to create a third 47 In October 2015, Network Rail held discussions with the Environment Agency 2016, Network Rail installed a second trash screen in the brook, upstream of the aqueduct™s entrance. However, this was soon removed at the request of the Environment Agency because it considered the installation had not been fully agreed and there were issues with its design. The trash screen had the potential to become blocked and cause water in the brook to back up, which then risked Background information23of the cutting slope and washing debris onto the track. In May 2017, when the cutting slope was examined as part of its routine examination regime, the examiner saw evidence of previous washouts, and so he noted the cutting slope as being at a high risk of washout.49 In February 2019, a senior asset engineer from the Route Asset Manager (RAM) 9 visited the site. This was to determine the scope of the repair work needed to the cutting slope following the previous washouts. The senior asset engineer reported that the washouts were due to water coming from Network Rail devised a scope of work to repair the cutting slope and planned to carry this work out within 16 weeks. The incident occurred before this work had taken place.Cutting slope examination regime50 10 on the East Midlands Route. The railway is divided into sections that are 5 chains (100.6 metres) long, and any section with an earthwork in it will count as one asset. The team manages the examination of each earthwork asset in accordance with and uses contracted examiners to do the routine examination work. The team which included the cutting slope that failed was being examined at the intervals next examination was due in 2020. Weather management processes 51 Network Rail has developed processes to take special measures when extreme weather is forecast. These include special inspections of earthworks other adverse weather conditions are forecast. Network Rail has a structured that considers both the likelihood of an earthwork failure and the potential consequence. Network Rail assesses the likelihood of failure by taking account of historic instability and indicators suggesting possible future instability. These indicators include earthwork category recorded during the examination process (paragraph 50). The assessment of likelihood also takes account of any water 9 working for the RAM is responsible for managing the safety of these earthworks by applying Network Rail™s processes for managing earthworks and delivering the associated work to achieve this. 10 boundary, that is equal to or greater than 3 metres high or, if less than 3 metres high, its failure could pose an unacceptable risk to the safe operation of trains or the performance of the railway infrastructure. Background information2452 The cutting slope where the incident happened was included on Network Rail™s an extreme amount of rain was forecast. However, Network Rail did not receive any forecasts of extreme rainfall on the day of the incident, nor in the seven days before it, so none of these processes to take special measures, including a special inspection of the cutting slope, applied. Background information25Analysis53 Train 1D43 did not stop before colliding with sandy gravel and soil that 54 rounded the left-hand curve approaching the washed out debris. The forward facing CCTV footage from train 1D43 showed a pile of debris on the down line at 55 the aqueduct and where the cutting slope had failed. It washed a large volume 56 The incident occurred due to a combination of the following causal factors:a. b. the cutting slope failed as it was not designed to cope with a large volume of c. Each of these factors is now considered in turn.57 Contractors called to the site by Network Rail after the incident found a large where the cutting slope had failed, and also at the northern side of the aqueduct 59 This causal factor arose due to a combination of the following:a. b. the eastern bank of pond 2 was the lowest point on the perimeter of the two ponds and was lower than the emergency spillway between pond 1 and the c. the pump to reduce the water level in the ponds was last operated on 17 May 2019 (paragraph 70).Each of these factors is now considered in turn.Analysis26ABAB Restriction under the bridge60 This caused water in the brook to back up to the spillways located about 25 in turn diverted more water over the service spillway and into the ponds. Analysis27ABspillway and into pond 1 and the connected pond 2.Cemergency spillway and back into the brook instead of into the ponds.To pond 1 spillwayCABWillow Brook NorthEmergency spillway X™ABCXFigure 10: The spillways connecting the brook and pond 1Analysis0.4 metres61 brook quickly rises, reducing this clearance and increasing the likelihood of debris becoming trapped at the water™s entrance to the bridge. Figure 11: Typical clearance between the underneath of the bridge and the brook when there has been no rainfall for several days62 amount of debris, mostly vegetation and large pieces of wood, trapped at the screen at the entrance to the aqueduct. 63 into the brook instead. This was evidenced by the water level in the ponds falling so that water no longer covered the path adjacent to the eastern bank of pond 2 to the level of the service spillway, which was the approximate water level in the ponds noted later by RAIB when on site at 21:00 hrs. Analysis29Debris removed from under the bridgeBeforeAfter from the watercourse. blockages were cleared and right image (looking in opposite direction) shows the path after the 64 After the incident, Network Rail commissioned a level survey which recorded the height of various points in the area relative to each other and the ordnance survey datum (mean sea level). RAIB also carried out its own survey of the area using aerial images taken by its drone which were processed using photogrammetry software to produce a 3D model of the area and a contour map.Analysis30104.50 metres AOD contour 104.50 metres AOD contour104.40 metres AOD 104.11 metres AOD104.63 metres AOD104.45 metres AOD 104.43 metres AOD Area prone to water over-tops pond 2N65 Along a 40 metre long section of this bank, the lowest level was recorded as 104.40 metres above ordnance datum (AOD), with typical levels over this section Figure 14: The levels as recorded by the surveys for the spillways and ground showing the low point on the eastern bank of pond 266 The level survey, supported by RAIB™s measurements of the spillways and drawings provided by Anglian Water, recorded a level of 104.11 metres AOD as brook into the ponds. 67 level in the ponds by allowing water back into the brook, was recorded by the level survey, measurements and drawings as having a level of 104.63 metres AOD. This is 0.14 to 0.23 metres higher than the 40 metre-long section of the brook via the emergency spillway. RAIB obtained copies of the planning application submitted to Corby Borough included a plan which showed the maximum water level for pond 2 was expected spillway. Analysis31in the red boxes are the levels shown indistinctly on the plan.104.42104.72104.44104.62Figure 15: The plan from the planning application for pond 269 The plan also showed levels of 104.42 and 104.44 metres AOD recorded for the eastern bank of pond 2, indicating this bank was designed to be lower than the controlling the maximum water level in the ponds. Instead, the maximum water level in the ponds was controlled by water over-topping the eastern bank and with over 15 years™ experience of this location reported to RAIB that they had never seen the water level in the ponds reach the point where water had passed over the emergency spillway. Operation of the pond discharge pump70 by gravity to reduce their level. The water level in the ponds needs to be reduced so that the ponds have capacity to store water when the next rainfall event occurs. An electric pump is used to pump water from the ponds back into Willow Brook North once the water level in the brook has fallen. Analysis32Outfall for pumpFloat switch for pump control location for pump controlsFloat switch for pump controlControls for operating the pumpOutfall for pumpWillow Brook NorthN71 The pump is installed next to the trash screen by the entrance to pond 1, with Anglian Water is responsible for the pump and its operation. When pond 1 was constructed a pump system was installed and its operation was automated, with sensors that measured the water levels in the brook and pond 1 to determine when the pump should run. However, the system was frequently vandalised and so Anglian Water moved the controls for the pump to its nearby sewage controlled. RAIB has not been able to establish the exact date of this change. in 2006, refers to the pump being manually controlled. Figure 16: The pumping system at the spillwaysAnalysis3372 Anglian Water has reported to RAIB that it does not have any formal arrangements in place for the manual operation of the pump, such as when it should be used or what the water level in the ponds should be reduced to. employed by Anglian Water who uses his experience to decide when to run the pump.73 run the pump if the water level in the ponds is high enough and the water level technician does run the pump, he will return before the end of his shift, at about pump at night due to complaints from neighbours about the noise the water makes at the outfall as it discharges into Willow Brook North.74 to about 0.3 metres below the end of the spillway apron at the entrance to pond 1 at the trash screen. The recorded level at the end of the spillway apron is 103.76 metres AOD so this equates to reducing the water level in the ponds to a level of about 103.46 metres AOD. This is 0.65 metres below the top of the service metres. When the ponds were full, the technician reported that he would expect to run the pump during the daytime for four days to reduce the water level by the required amount. 75 another technician to attend but there is no formal process in place to guarantee technician who works nearby. He has attended at this location often enough to know what to do and is able to judge whether to run the pump. 76 technician maintains his own notes of when he attends the site, including when of the operation of the pump can be seen in the data recorded by the telemetry maintenance technician™s notes. Consequently, no water had been pumped out of the ponds for about one month before the incident. During this intervening The telemetry data showed each of these rainfall events raised the level in Willow the ponds. This meant the ponds had reduced capacity to store water from the persistent rainfall in the four days prior to the incident, and made it likely that the Analysis3477 and 12 June. He explained that these visits were in response to rainfall or forecasts of rainfall, but each time he had visited he had deemed the water level in the brook to be too high for him to switch the pump on. If the water level in the brook is higher than the service spillway, operating the pump only circulates the water (as the outfall is upstream of the service spillway, water that is pumped into the brook simply passes back over the service spillway and back into the ponds). The pump™s outfall is positioned upstream of the service spillway so that the control of the water level provided by the service spillway cannot be bypassed by operating the pump. Cutting slope designThe cutting slope failed as it was not designed to cope with a large volume 79 The repair to the cutting slope that was undertaken in 2009 (paragraph 45) was not designed to cope with large volumes of water accumulating at the crest of the cutting slope. Instead the 2009 repair was designed alongside some other changes aimed at minimising the accumulation of water at the cutting crest by The geology of the cutting slope comprises a sandstone rock base with layers water in 1999 (paragraph 43). At the time, the earthwork engineer who attended track, but the earthwork itself was stable. This allowed the railway to reopen within Rail in 2004, during an earthwork examination, show material from the cutting can be found to indicate that any work took place on the cutting slope after the landslip in 1999, until it was repaired in 2009 (paragraph 45). Existing palisade fenceClayBackscarp of landslipFigure 17: The geology of the failed cutting slope Analysis35 that the material was from the landslip in 1999. The visit report noted that a track renewal was planned which included digging out the material in the cess. It failures would occur. Therefore, the cutting slope needed to be repaired before the track renewal work proceeded. The 2006 site visit report formed the basis for the subsequent work to repair the included the installation of a barrier material at the crest of the cutting slope to provide some protection from small amounts of water draining through the accumulating at the crest of the cutting slope, as occurred immediately prior to this incident. washout failure as coming from the entrance to the aqueduct when it became Network Rail scoped, designed, obtained planning permission and made changes to the inlet of the aqueduct, installation of a new trash screen with a platform installed an emergency drain pipe, with its inlet at the boundary fence line of the aqueduct. Network Rail completed these changes to the aqueduct™s entrance in 2009, at the same time that the earthwork was repaired. It believed that these changes would The as-built drawings for the repair to the cutting slope show that a series of steps, called benched excavations, were cut into the cutting slope. The void Analysis36to track drainageEmergency drain pipe outfall into New trash screen with platformTrash screen as installed in 2009 Revised inlet, wider with wing wallsTrash screenEmergency drain pipeNFigure 18: The changes made at the aqueduct™s entrance, 2007-2009 (images courtesy of Network Rail)Analysis37Figure 19: The repaired cutting slope in 2009 (image courtesy of Network Rail)Once the sandy gravel was washed out from the cutting slope during this incident, revealed the benched excavations made when the 2009 repair was carried out Benched excavationsFigure 20: The void left in the cutting slope showing the benched excavations from the 2009 repair, viewed from the top of the cutting slope looking towards the railwayAnalysisThe sandy gravel chosen for the repair in 2009 was suitable for the volume of water that Network Rail expected the cutting slope would be exposed to. The expectation was that the water would be limited to surface water from rain falling large volume of water seeping through the cutting slope from water ponding at its crest. while travelling at 40 mph (64 km/h). From this speed, the distance the train took to stop after application of the emergency brake was 193 metres.11 This was greater than the available sighting distance for the debris, which the CCTV footage from train 1D43 suggests was around 100 metres. There was therefore nothing the driver could have done to stop the train before running through the debris on the track. Engagement and communication between parties90 91 Copies of correspondence between British Rail (and later Railtrack), Corby Urban District Council (later Corby Borough Council) and the steelworks™ owners, dating from the 1960s through to the early 2000s, indicate that previous engagement between the involved parties was often adversarial, seeking to apportion blame and recover costs. 92 However, more recent correspondence indicates signs of cooperation between Network Rail and Corby Borough Council. For example, in 2009 Corby Borough Council gave planning permission to extend the walls at the aqueduct™s entrance over who would be responsible for clearing the trash screen which would now be located on land owned by the council. Additionally, Network Rail held meetings (paragraph 47). However, these meetings did not result in any actions to address 11 RAIB™s investigation into a near miss at Didcot North Junction on 22 August 2007 ( ) found Analysis3993 At the time of the incident, there were no clear lines of communication between Consequently, each of the asset owners was focused on their own assets in isolation:a) Network Rail was primarily concerned with keeping the trash screen at the aqueduct clear of debris, monitoring the water levels over the aqueduct, managing the water at the entrance to the aqueduct, examining its cutting b) Anglian Water managed the water level in the ponds by maintaining and operating the pump and kept the spillway apron and trash screen at the entrance to pond 1 clear of debris.c) at this location, but as Willow Brook North was designated a main river, it Willow Brook North, which in this instance consisted of localised vegetation management.d) Homes England was solely focused on inspecting and maintaining pond 2.e) 94 another party, there were no clear lines of communication to pass on this information. There was also a reluctance within the various organisations to these organisations to work together rather than in isolation. As a result, the was not addressed in a holistic way. Flood management system95 in place, given the presence of nearby national infrastructure in the form of 96 (paragraphs 36 to 49). Rainfall radar data for the Willow Brook North surface indicated the rainfall was not exceptional. It was less than a 1 in 1 year12 rainfall also shows that the size of the water catchment area is not large, covering about system at this location could not cope with the volume of surface water that was discharged into the brook during that period. This was primarily due to three factors:a) the system lacks capacity to cope with the increased surface water drainage from the housing and commercial developments that have taken place within the brook™s catchment area over the years 12 A 1 in 1 year event has a 100% probability of occurring in any given year. Analysis40Willow Brook NorthincidentCorby stationN2.0 miles (3.2km)1.0 miles (1.6km)b) and susceptibility to blockages due to debris in the brookc) vandalism and anti-social behaviour leading to damage to the original into the channels of Willow Brook North. courtesy of the Environment Agency, see https://environment.data.gov.uk/catchment-planning/ WaterBody/GB105032045590 )97 location. In accordance with the Flood and Water Management Act 2010, Northamptonshire County Council assessed the railway to be critical national assets (physical or electronic) that are vital to the continued delivery and integrity of essential national services, the loss or compromise of which would lead to infrastructure. Northamptonshire County Council has drafted a section 19 report provided a publicly available web-based toolkit to understand the risk of 13 to be the greatest risk believed that management of this risk rested with the Environment Agency. 13 land. Analysis41Willow Brook Northincident greater than 1 in 30 between 1 in 1000 and 1 in 10099 The Environment Agency has a duty, under the Flood and Water Management Act In 2004 Willow Brook North (from Rockingham Road, Corby, through to where it joins the River Nene near Elton) was designated as a main river under sections 193 and 194 of the Water Resources Act (WRA) 1991. This designation did not place any additional duties on the Environment Agency but gave it permissive powers to carry out maintenance and improvement works. The Environment Agency does not own any of the land the brook passes through or the structures it passes under or over, so the basic common law obligations and statutory responsibilities for the brook remain with its landowners. Under its permissive powers, the Environment Agency does carry out some basic routine maintenance on the brook, such as clearing vegetation from it twice a year, and monthly inspections from October to March, which include removing debris from the brook™s channels. The Environment Agency has not used its permissive powers to carry out any improvements on the brook. Traditionally, any action taken by Analysis42100 The need for housing development in the Corby area, driven by government plans in 2003 to address housing shortfalls across the south of England, resulted in Corby Borough Council commissioning studies between 2003 and 2006 which looked at its water infrastructure. A strategy document issued in 2006 detailed the water infrastructure that was required to facilitate this growth in Corby, and in Corby. 101 Willow Brook North catchment area. They reported the combined water storage noted that while pond 1 had an estimated capacity of 15,500 cubic metres, at cubic metres for a 1 in 10 year14 rainfall event. While the construction of pond 2 provided some additional capacity, it was still not adequate for a 1 in 10 year rainfall event. The strategy document noted that Willow Brook North had a low standard of protection upstream of the aqueduct over the railway line, with the aqueduct spilling at a 1 in 10 year standard of protection (in its simplistic form, repair, were heavily silted and full of debris, and so spilled at between a 1 in 2 year and 1 in 5 year rainfall event. It also noted that the trash screen at the 102 assessment document, which it had updated in response to legislative changes. Meanwhile, there had been further commercial and housing developments in the catchment area during this time. Although the rate at which surface water can run into the brook.14 A 1 in 10 year event has a 10% probability of occurring in any given year, a 1 in 5 year event has a 20% probability of occurring in any given year, and a 1 in 2 year event has a 50% probability of occurring in any given year. Analysis43103 2004 when Willow Brook North was designated as a main river, the Environment capacity. No evidence has been found that any further work has taken place since that time to remove silt from either pond. Anglian Water reported that both ponds to remove the silt. 104 antisocial behaviour. The automated pumping system stopped working due rubbish and items being thrown into the channels of Willow Brook North, causing to form blockages at restrictions, such as under bridges or at trash screens, Network Rail mobile operations manager found and removed debris from the aqueduct™s trash screen in the morning. It was still clear when checked again in the early afternoon (paragraphs 20 and 22) but after the incident, Network Rail™s Figure 23: Debris in the aqueduct™s trash screen after Analysis44105 Network Rail had not implemented any short-term mitigations while longer term actions to repair the cutting slope were being planned, even though it was aware that the cutting slope was at risk of washout due to water 106 After the 2009 cutting slope repair and changes to the aqueduct™s entrance by Network Rail as coming from Willow Brook North due to blockages in the brook™s channel. 107 earthwork examiner attended a reported landslip. They found a washout had well as from the entrance to the aqueduct. They also noted that the emergency places along the cutting slope and recorded the cutting slope as being at high team in February 2019.109 team prepared a remit for work to be carried out on the cutting slope. The remit noted that as well as debris in the brook™s channels and at the aqueduct™s trash water then seeping through the crest and washing away sections of the cutting slope. Consequently, the remit called for work to prevent water passing through an impermeable layer on the boundary side of the crest, keyed about one metre below the natural ground level to prevent water passing through it. The remit was time of 16 weeks in which to complete the work. This work had not started prior to Analysis45110 implementing any short-term mitigations to manage this risk. Network Rail its twelve supporting modules, outline the controls that Network Rail can use to a) reduce the impact of an earthwork failure should one occur (for example, a temporary speed restriction or a line closure)b) (for example, early slope movements detected by equipment such as inclinometers or surface-mounted tiltmeters)c) linked response to control normal operations (for example, using a link to the signalling system)d) slope and the railway line to protect the line from material falling onto the track 111 and their implementation. All the mitigations described in these modules are solely focused on using geotechnical instrumentation to monitor slopes. Implementing geotechnical instrumentation in accordance with the modules of the instrumentation to provide a monitoring or alarm/alert system. However, the repair work on the cutting slope was planned to take place within 16 weeks, so due to washout in the time before this work took place. 112 The cutting slope™s risk of failure due to washout could have been mitigated in the short term by monitoring the water level in the adjacent ponds. In practical terms, within other functions in Network Rail (such as its drainage and operations functions), Anglian Water for any work related to pond 1, and Homes England with other asset owners as a possible outcome of an evaluation. However, there is no reference to liaison with others in either module 5 or 6 when choosing a mitigation. 113 (paragraph 20). The date and time of the last visit was recorded on a status board in the control room.Analysis46114 morning (paragraph 20) and early afternoon (paragraph 22). Both visits reported 115 The RAM Drainage team had installed remote monitoring telemetry at the aqueduct to measure the water levels (paragraph 46). The RAM Drainage team had provided the EMCC with access to the data output by the telemetry via a website, along with instructions on what actions to take when extreme rainfall was forecast. Actions to take included monitoring the live data from the site and working in control at the time were not aware of these instructions. 116 capacity of the aqueduct. Consequently, the telemetry issued an alarm at 12:45 hrs when the water level exceeded the 50% threshold, and at 14:15 hrs when it exceeded the 75% threshold (paragraph 22). The telemetry measured the water level at the aqueduct, so it would not have detected the upstream blockage in Willow Brook North (paragraph 60). It is likely that the water level exceeded the 75% threshold when water which had overtopped pond 2 found its way back into the cutting slope. 117 At the time of the incident, no one in the control room at EMCC was set up to receive these text message alarms so no action was taken in response to them. day (paragraphs 20 and 22), it is likely that a third visit, in response to the 75% and on the railway. However, it is uncertain whether this would have resulted in recognition that the cutting slope was at risk of failing, for which immediate mitigation was required. 119 was stranded, they began planning an evacuation of the passengers onto another train. However, these plans ran into various problems resulting in the need to second evacuation, from the rescue train which also became stranded, to the track and onward road transport.Analysis47Up Corby line120 (paragraph 23) and planned to use the last of these to collect passengers from train, train 1C52, arrived at the incident site, its driver found that the up line passengers.Figure 24: Flood water and sandy gravel blocking the up line (image courtesy of Network Rail)121 that train 1C52 was loaded with between 250 to 350 passengers, and it needed to accommodate a further 191 passengers from train 1D43. This meant there were 60 to 160 more passengers than seats available on train 1C52. AnalysisTransfer of passengers from train 1D43 to train 1C52 122 evacuation onto the track shall be used as a last resort due to the inherent risks associated passengers from train 1D43 by a side-to-side transfer onto train 1C52, rather than 123 However, side-to-side transfer between trains 1D43 and 1C52, both of which were of the track, which prevented passenger doors being fully opened because they were fouled by the adjacent train. This meant a side-to-side transfer between the the drivers lined up the sliding doors on the front power cars of both trains for a side-to-side transfer. 124 To facilitate a side-to-side transfer from one train to another, a train evacuation bridge is needed. This bridge provides a platform between two adjacent trains, the bridge from one train to another without the need to set foot on the track. However, neither train 1D43 nor 1C52 carried this item as it was not included in onto the track. 125 Evacuation™, states the mandatory requirements for the emergency and safety equipment that must be carried on trains. In part d), which lists the equipment which must be made available to both traincrew and passengers, it lists 'one ladder or step ladder made from non-conducting material'. There is no 126 The drivers attempted to overcome this issue by constructing a temporary bridge cover for the emergency equipment cubicle, which they secured using rope. The drivers tested its robustness and deemed it suitable for passengers to use for the its use on the grounds of safety and so instead Network Rail arranged with British Corby station. This caused further delay. 127 Once the platform-train access ramp was in place, along with rope handrails between the two trains, the side-to-side train transfer began. All 191 passengers from train 1D43 had to make their way to the front of the train, cross over the to complete (paragraph 32). Analysis49After being given permission by the signaller, at 19:32 hrs, train 1C52 began moving very slowly north in an authorised wrong direction movement along the up line. This was about three and a half hours after train 1D43 had stopped, and by drainage and along the track, to an outfall just to the north of Corby Tunnel. The water above the height of the rails on the line ahead of him. 129 room decided to send train 1C52 back to the incident site to pick up Network Rail 130 Train 1C52 travelled back to the incident site, through Corby Tunnel, at a very along the tracks through the tunnel and its level was still rising. After arriving back at the incident site (paragraph 32), the drivers told the Network Rail operations Train 1C52 was now also trapped at the incident site. Evacuation from train 1C52 onto road transport131 transport to take the passengers to either Corby or Kettering stations. There was an access point at the incident site which was suitable for the passengers to use, but it did require the passengers to walk about 400 metres along a path to the along with its contractors that were on site, needed time to clear it to make sure it was safe. Network Rail also needed to set up lighting along the path as it would become dark during the evacuation. 132 While Network Rail was making these arrangements, the drivers, traincrew and passengers on the train were not given any information about what was happening. During this time conditions on the train were uncomfortable and deteriorating. East Midlands Trains control noted that the train™s lights and toilet systems were still functioning, but the air conditioning was struggling to cool the coaches and it was becoming very hot on board. The catering car had also service and ambulance service to attend. The ambulance service treated one Analysis50133 Train 1C52 was moved so that the sliding door on its front power car was assisting able-bodied passengers down onto the track from a second door towards the rear of the train. These passengers needed to be able-bodied as they were required to walk a short distance along the track to the access point. Just over seven hours after train 1D43 had stopped, the transfer of about 450 to 550 being reported. Previous occurrences of a similar character134 In June 2012, a passenger train scheduled to operate between Belfast and Antrim branch line in Northern Ireland (RAIB report 14/2013). The investigation found there had been heavy rainfall in the area during the previous evening, and a system of culverts at and downstream of the washout could not cope with to the washout. In a similar way to the incident at Corby, the investigation found that there was no engagement between the infrastructure operator and the the location. Analysis51135 In June 2016, three passenger trains passed over a section of the single line at Baildon, West Yorkshire ( RAIB report 03/2017), where part of the supporting unsupported. Of relevance to the incident at Corby, that investigation found that the drainage system running under the track could not cope with the quantity of water following a short period of intense rainfall, and a repair made to the would then respond to these alerts to inspect or monitor the site. The system because the system was still in its trial stage. Analysis52Summary of conclusionsImmediate cause 136 had washed onto the track from the adjacent cutting slope (paragraph 53).Causal factors137 The causal factors were:a) This causal factor arose due to a combination of the following:i. Recommendation 1)ii. The eastern bank of pond 2 was the lowest point on the perimeter of the two ponds and was lower than the emergency spillway between pond 1 and the brook (paragraph 64, Recommendation 1)iii. The pump to reduce the water level in the ponds was last operated on 17 May 2019 (paragraph 70, Recommendation 1)b) The cutting slope failed as it was not designed to cope with a large volume of Recommendation 2)c) Underlying factorsThe underlying factors were:a) (paragraph 90, )b) in place, given the presence of nearby national infrastructure in the form of the railway line which is a principal transport route (paragraph 95, )c) Network Rail had not implemented any short-term mitigations while longer term actions to repair the cutting slope were being planned, even though it was aware that the cutting slope was at risk of washout due to water overtopping pond 2 (paragraph 105, Recommendation 3).Summary of conclusions53139 Recommendations 4 and 5).Summary of conclusions54Previous RAIB recommendations relevant to this investigation2012 and February 2013, , Recommendation 1140 In response to six landslips which occurred on Network Rail infrastructure between June 2012 and February 2013, RAIB carried out a class investigation into earthwork issues related to land neighbouring the railway and to risk management during adverse weather. The landslips were caused by factors or not undertaken, on neighbouring land. In several instances, trains were being encountering a landslip. The following recommendation made by RAIB in that class investigation has some relevance to this investigation.Recommendation 1Network Rail should review and improve its processes for managing earthworks related risk arising from neighbouring land, including associated drainage issues. This should provide a documented process which takes account of the extent to which it is practical and proportionate for Network Rail to review and/or rely on land management activities undertaken by neighbours.The new process should, where reasonably practicable: obtain relevant information from other sources where it cannot be collected by earthwork examiners (eg where examiners are unable to view areas due to access constraints, fences, etc); areas at risk from ground movement and areas where ground movements are occurring; provide a robust process for identifying, and responding appropriately, to increase risk to the railway between routine earthwork examinations; and issue alerts identifying heavy rainfall when this has not been forecast.141 reported that after reviewing the information provided to it by Network Rail, it concluded that Network Rail had taken the recommendation into consideration, and had taken action to implement it. Previous RAIB recommendations relevant to this investigation55142 In implementing this recommendation, Network Rail developed a nationwide to understand the relative consequence of a natural slope failure at a particular location on the railway network. This work then formed the basis for a process to assess the hazards arising from natural slopes and the consequences of natural of the earthwork, which in turn can lead to a site-based review, and ultimately a landslide hazard assessment as documented in module 3. The assessment process in module 3 is primarily focused on outside party natural slopes. in streams, and the presence of water concentration features above the slope. Previous RAIB recommendations relevant to this investigation56Actions reported as already taken or in progress relevant to this reportActions reported that address factors which otherwise would have resulted in a RAIB recommendation 143 Network Rail has procured a number of train evacuation bridges for use by East Midlands Trains (now East Midlands Railway) for side-to-side transfers between trains. These bridges are placed at stations along the routes it operates between evacuation bridge. It also states that a train evacuation bridge will be taken to site by either the chosen rescue train or by a Network Rail employee in a road vehicle. The provision of this equipment allows Network Rail and train operating companies to carry out side-to-side transfers between trains in line with Network Rail™s national operating procedures. 144 The route control manager based in the control room at EMCC now receives the text message alarms issued by the telemetry that measures the water levels at instruction that when the route control manager receives a 50% or a 75% level train passing the site. This instruction to caution trains will remain in place until over the aqueduct, cleared the trash screen if required, and checked the water level in the nearby ponds. Other reported actions145 In July 2019 Network Rail completed repairs to the cutting slope. The repair crest of the cutting slope, from the aqueduct through to the bridge to the north of 146 between the aqueduct and the bridge was protected by the piling. However, the system resulted in the problem being moved to another location. This showed that solutions to problems involving drainage issues.Actions reported as already taken or in progress relevant to this report57Existing palisade fenceBackscarp of landslip with granular materialClayAqueductField adjacent to pond 2Track south of the aqueduct Figure 26: Drawing of Network Rail™s repair to the cutting slope Figure 27: The repaired cutting slopeActions reported as already taken or in progress relevant to this report147 Anglian Water was planning to modify the outfall for the pump that takes water noise that the operation of the pump makes so that Anglian Water can leave the pump running overnight. This will reduce the time it takes Anglian Water to restore the ponds™ capacity to store water after a rainfall event. Anglian Water is also considering options to reinstate an automated system to run the pump, removing operation of the pump, Anglian Water is assessing options for how it can monitor the water level in pond 1 and provide remote access to this data. In March 2020 Anglian Water removed silt and vegetation that had built up on parts of the concrete structure that connects the brook to pond 1 via the service 149 Corby Borough Council now visits the site when requested by Network Rail or Anglian Water to take away any rubbish that has been removed from the trash able to remove rubbish from the site so it is sometimes left on the banks and, in the past, it was often found thrown back into the brook. 150 Homes England has appointed a consultant to look at what improvements it can make to the management of pond 2. Network Rail had approached Homes England about raising the level of the eastern bank of pond 2 to prevent it from over-topping. However, both Homes England and the Environment Agency would not agree to this work until its consequences were understood and, if necessary, The Environment Agency has provided Network Rail with its river model for Willow Brook North so that Network Rail can get it updated and then use it to better 151 In response to requirements set by the ORR, Network Rail is leading an ongoing procedures and reporting requirements for stranded passenger trains. To date the work has completed a survey of all industry stakeholders to validate its scope of work and identify the next steps to take. Work on drafting guidance has also commenced. 152 One of the intended outcomes for this work is for stranded train incidents to be managed in a consistent way across the industry by embedding good practice and knowledge sharing. Another intended outcome is to improve the rail industry™s response to stranded trains through improvements to requirements and guidance notes. To achieve these outcomes, one of the future priorities for this work is to share knowledge of good practice, procedures and equipment. Another priority is to understand the existing evacuation practices and the key equipment that is used. These future work priorities, both of which are related to equipment needs, have the potential to address the issues encountered during this incident when transferring the passengers from the stranded train to the rescue train. Actions reported as already taken or in progress relevant to this report59Recommendations and learning pointRecommendations153 The following recommendations are made:151 The intent of this recommendation is that the owners of the surface railway in that area, both in the short and long term. The Environment Agency should, in conjunction with Northamptonshire County Council, Anglian Water, Homes England, Corby Borough Council and Network Rail, lead the production of a timebound plan to implement actions to address the system™s susceptibility to blockages and the limitations of the ponds to store water (paragraphs 137a(i), 137a(ii), 2 The intent of this recommendation is to manage the risk of washouts which falls below the threshold of Network Rail™s adverse/extreme weather plans. Network Rail should: a) compile a list of locations on or around its infrastructure where it is safety occurs during normal levels of rainfall (that is, during rainfall as adverse/extreme weather)b) at the locations listed in (a)c) identify the organisations responsible for each of the assets that form related risk to the railway at the locations listed in (a)15 legislation, and need to take these recommendations into account in ensuring the safety of their employees and others. Additionally, for the purposes of regulation 12(1) of the Railways (Accident Investigation and Reporting) Regulations of Rail and Road, to enable them to carry out their duties under regulation 12(2) to: (b) report back to RAIB details of any implementation measures, or the reasons why no implementation measures are being taken.Copies of both the regulations and the accompanying guidance notes (paragraphs 200 to 203) can be found on RAIB™s website www.gov.uk/rai b.Recommendations and learning point60d) take steps to establish lines of communication with the organisations (paragraph 137b).3 management of the short-term risk to earthworks while waiting for planned work to take place in the longer term, when mitigations using geotechnical instrumentation are not viable options. Network Rail should review, and amend as necessary, its processes earthworks are trained and have clear guidance on when and how to trigger appropriate monitoring and/or other short-term mitigations. This is particularly relevant when mitigations using geotechnical instrumentation are not viable options and actions that involve other functions within Network Rail or external organisations are needed instead 4 The intent of this recommendation is to better enable the safe and needs to be available for train evacuations. As part of the ongoing industry-wide programme of work to improve the management of stranded passenger train incidents, Network Rail procedures and codes of practice for managing stranded trains and carrying out train evacuations, to identify what equipment is needed to deliver the requirements in these procedures for each method of train evacuation. They should then provide this information about what equipment is needed to those responsible for the implementation of recommendation 5 (paragraph 139). 5 The intent of this recommendation is to better enable the safe and train evacuations. Upon completion of recommendation 4, as part of the ongoing stranded passenger train incidents, Network Rail should:a) take steps, in cooperation with the train operating companies, so that and train evacuations is available for use when needed (such as route)b) stranded trains and train detrainments on how to get the equipment made available in (a) to the site of a stranded train and how to use it correctly once it is thereRecommendations and learning point61c) work with each train operating company to prepare rolling stock trains and train detrainments on what to expect when this equipment is to be used to evacuate passengers from its trains (paragraph 139). 154 161 accordance with the Flood and Water Management Act 2010 (in England the rail network as part of the United Kingdom™s national infrastructure) a) The Environment Agency (in England) and National Resources the Department for Infrastructureb) c) d) e) Internal Drainage Boardsf) Highways Authorities g) Water and sewerage companies h) Riparian owners.respons