Damage survey Marlborough Region Earthquake Briefing No. 2

Transcription

1 Damage survey Marlborough Region Earthquake Briefing No. 2 Stuart Mead and Matthew Mason A survey of damage to buildings, property and infrastructure in the Marlborough region was carried out over two days by means of drive-through inspection of the greater region with more detailed inspection of areas/buildings deemed to be most significantly damaged. The South Island towns of Blenheim, Seddon and Ward were surveyed as well as the epicentral region of Lake Grassmere. A particular focus of our survey was on the earthquake impacts to the wine sector, the major industry in the region. Damage to buildings and Infrastructure Damage to buildings in Blenheim was generally light. No observations of major failures or external cracking were apparent from our drive-through survey. After speaking with several residents it was clear that this observation was by-and-large correct, but cases of internal cracking to walls mostly superficial as far as we could ascertain were reported and in a limited number of cases observed. There were several stories of objects falling off shelves, but again these did not seem to be too substantial. News reports did however indicate that supermarkets suffered loss of stock by this means. Some residents and business owners had made attempts to secure valuable items or shelving systems following the July event. The most significant damage to housing was observed in Seddon and Ward. News reports suggested that rapid assessment teams found damage to almost every home in these areas. A drive-through survey of homes in these areas, however, revealed that this damage may in many instances be limited to internal damage given we were unable to observe external damage from the road to a large proportion of buildings. This hypothesis was given more weight with the report that only 5 families required emergency accommodation (Marlborough Express) suggesting the majority of homes were deemed safe for occupation. There were of course some examples of major damage, with Figure 1 showing examples of observed failure types. The top image shows a timber frame, brick clad home that has lost much of its external cladding and chimney. The bottom image shows a type of façade cracking near the roof connection to walls that was observed. The predominant type of home construction in the area appeared to be timber frame/timber clad or reinforced concrete block, so the lack of major damage is perhaps unsurprising. Failures of brick chimneys were observed on several buildings, particularly on timber framed homes. Briefing Note 261 Page 1

2 Figure 1. Damage to timber frame brick clad home near Lake Grassmere (top) and example of cracking observed on home in Seddon (bottom). Briefing Note 261 Page 2

3 As in Christchurch, some of the buildings to suffer the greatest damage appeared to be churches. Figure 2 shows two examples, one in Ward and the other in Seddon, that sustained damage. The angled mortar cracking seen in the left image is reasonably standard for failure of brickwork facades/walls, and the loss of tiles seen in the top right image (same building) is common for steep pitched roofing and was seen extensively in Christchurch. Loss of tiles was not however observed on many other buildings during this event. Major damage was observed to the tower on Saint Peter Chanel s Church in Ward, with cracking of mortar and the arch clearly evident. It is unclear whether a spire originally sat on top of this tower. Figure 2. Damage to churches in Seddon (left and top right) and Ward (bottom right) A consistent observation along the main highway S1 (and side roads) between Blenheim and Seddon/Ward was the large number of landslips that occurred. Given the relatively steep terrain in the area and high levels of rainfall in the days following the main earthquake this is perhaps unsurprising. Many slips ran out onto roads and required road crews to temporarily close lanes or roads for removal. An example of a relatively large slip is shown in Figure 3, with Stuart Mead also pictured for scale and photogenicity. This particular slip was next to Lake Grassmere. Slumping of roads was also relatively common in the area, with temporary road closures again the result. Briefing Note 261 Page 3

4 An example of slumping on a Seddon road is also shown in Figure 3, with this type of ground failure evident near steep slopes or where roads ran near streams. Despite the road closures noted, no businesses we spoke with reported any major disruption because of this. Figure 3. Examples of landslip near Lake Grassmere (left) and destabilisation and slumping of roads in Seddon (right). Although power was cut following the initial earthquake, for most people and businesses it was restored within hours. This appears in part to be due to the good performance of power poles throughout the region, with no observations of failed poles -- we were told there was a limited number of these though. Speaking with a technician about the matter it appears that while most distribution stations were tripped during the earthquake, only a small number suffered any noticeable damage and the distribution network remained largely intact. This is an extremely good outcome for businesses, and limits their business interruption. Impacts on the wine industry The Marlborough wine industry is a significant employer within the region, employing up to 5000 people during peak times. Wineries in Marlborough produced 72% of New Zealand s 2012 vintage (Marlborough Wines). During our survey the Marlborough wine industry appeared to be the most significantly impacted industry because of the Lake Grassmere earthquake on the 16 th of August. Most of the damage observed and reported by the wineries was to the wine vats and barrels holding product. When full, the cost of the wine vats is small relative to the value of wine stored within them, and wineries were more concerned about loss of product rather than structural damage to the tanks themselves. The loss of product is a sensitive issue to most winemakers as it can affect product sales, so most were reluctant to give an estimate of the Briefing Note 261 Page 4

5 amount of wine lost. This said, public reports suggest the loss of wine was insignificant on a regional/national level, but through our discussions with a number of industry representatives and wine makers it appears that this loss was not uniformly distributed across all wineries, and the losses at some may have a notable impact. Wine vats vary in size from to litres and are made of thin stainless steel. For the large scale producers tanks are usually stored together in tank farms, the largest being hundreds of metres in size. Depending on the size and design of these tanks, they were either bolted to the floor on concrete plinths or free standing on legs (Figure 4). After the July Cook Strait earthquake, some wineries began to strengthen legs of the wine vats by welding struts between the legs (Figure 5). Other companies with bottling plants in Auckland began shipping wine out earlier than normal to reduce the amount of wine stored in the region Figure 4. A winery tank farm near Blenheim (left) and the different types of tank footings for wine vats (right). Vats are usually either secured to the floor using seismic bolts (1) or free standing on legs (2). Figure 5. An example of the strengthening struts welded to legs of wine vats since the July 2013 Cook Strait earthquake. Damage to the wine vats was variable, however most damage was reported to be sustained in wineries closer to the epicentre of the earthquake. In a number of cases seismic bolts that Briefing Note 261 Page 5

6 kept vats secured to the floor failed due to the tensile stresses and either broke or suffered significant plastic deformation (Figure 6). Freestanding vats appeared to be damaged the most, with their legs buckling under the weight and movement of the vats. Figure 6. A failed seismic bolt used to secure vats to the floor (top), damaged vats caused by buckling of the legs (middle and bottom). Briefing Note 261 Page 6

7 Less damage was reported for barrel stored wine, with the wineries we spoke to reporting losing no more than 12 barrels. The loss of barrels was strongly correlated with the storage method, two wineries using earthquake proof barrel racks reported they lost no barrels of wine during the earthquake. The older, traditional style of barrel storage was not as secure as more modern storage methods, with many barrels lost when stored using this method (Figure 7). Figure 7. Traditional style wine barrel racks (left) and an example of modern, more secure wine racking system (right). After the earthquake, power was lost to most wineries for at least 2 hours. This complicated recovery efforts to pump wine from damaged vats into undamaged empty vats. Access to the vats via gantries running along the top of and between them was also an issue given that during the earthquake several gantries were damaged or warped. A large concern for grower groups and certain wineries were the occupational health and safety issues during aftershocks while product was still being moved between vats. Some wineries shut down operations immediately after the first earthquake on Friday and only returned to assess the damage on the Saturday, while others returned as soon as possible to recover wine from damaged vats. From a risk management perspective, approaches to risk reduction varied between wineries. Some were confident in their procedures and had made no changes following the July Cook Strait event. Most wineries visited made some attempts at risk reduction, common examples were to strengthen vat footings, anchor wine racks to walls or ship wine out earlier for bottling in other locations. Winery managers, industry experts and leaders tended to agree that the damage could have been much more significant had it occurred at different stages of the winemaking cycle. During harvest, resulting loss of power would lead to an almost total loss of product, and the effect of sloshing in half full vats could have caused more widespread and significant vat damage. In August, vats are generally full or empty, which would have reduced the effect of sloshing within the vats. From a long term impact point of view, industry representatives were concerned about the damage to housing within Seddon and Ward, which is used to house temporary labour needed during peak seasons. The other concern was the requirement for a large number of vats to be inspected for structural damage before the grapes are harvested next. Briefing Note 261 Page 7