With the dust beginning to settle, Christchurch is taking stock of the earthquake damage and what comes next. Chris Barton surveys the magnitude of the structural problems



Imagine Christchurch returned to swamplands - its two rivers fanning out in a delta of streams and tributaries meandering down to the sea among lush vegetation.

Dotted among this primeval garden teaming with birdlife are built-up islands - mounds in the marshes made from debris and sludge from the February 22 earthquake, compacted and engineered as solid, safe, unsinkable ground.

Connected by causeways, the islands are self contained, powered by sustainable energy and populated by high density mixed-use pavilion towers comprising apartments, offices, shops and other amenities.

Architects, the visionaries of our society, always have dreams. This is just one of the more extreme ideas swirling around architectural schools for the rebuilding of Christchurch.

Radical and challenging, it's an idea everyone knows will never see the light of day. But it encapsulates many of the issues the city now faces - how to defy liquefaction and how to live on unstable ground.

Another concept is to decentre the city by creating a long snaking settlement pattern - stretching from Blenheim in the north to Oamaru in the south - a sprawling megalopolis of satellite towns connected by bullet train.

The idea is not as silly as it sounds. Already thousands have fled the shaken city and taken up residence in towns along State Highway One - towns that until now might have seemed dead-end or dying.

Similarly, businesses, locked out of the central business district cordon, have decamped to the suburbs - to places like Addington, Hornby and Wigram. Landlords, seizing the main chance, have tied these businesses to long term leases, some up to 10 years, making it difficult to return.

But for Christchurch architects, talk about relocating the CBD or large parts of the city is not just impractical, it's barmy.

"Rebuilding elsewhere is not an economic reality," says architect Barry Dacombe pointing out that the consequence of the two earthquakes is a huge claim on insurance.

"There is going to be a $20 billion injection of capital into the country for Christchurch's rebuilding and we haven't had to sell one lamb chop or one pound of butter to get it."

Architect Richard Dalman speaks for many when he explains why Christchurch should be rebuilt where it is: "There are a lot of people who live here who have the choice of living anywhere in the world. Why? Because the climate is good, the landscape is great, and there are good schools.

It's a town of 400,000 and yet we have a rugby stadium, a symphony orchestra, art gallery and all the key things a big city would desire - plus we have a ski field an hour down the road and within half an hour you can get out to the countryside.

People who've lived overseas move back because they don't think there is any other better place in the world than Christchurch to bring up their kids. That will change for some people who are freaked out by the earthquake, but a lot will be happy to stay."

Similarly, Rehua marae kaumatua Mita Te Hae speaks for many in the city's eastern suburbs: "None of them want to move out of the area. They're reluctant to move out of their homes and relocate into suburbs where they probably wouldn't fit in. There are second and third generation families there."

Home is where the heart is. But while for many the will to stay remains rock steady, the upheaval of the earth on September 4 then again on February 22 has laid bare a terrible truth. Christchurch is built on unstable ground.

Evidence is everywhere - in once flat roads that undulate like rolling waves; in dark fissures in asphalt rent asunder; in fallen land slumped in drifts; in rocks and boulders beneath crumbling cliffs; in layers of silts boiled up from beneath; and in death among broken buildings, bricks and rubble strewn on streets. Rebuilding here will not be easy. And whatever is rebuilt has to withstand the possibility of the ground shaking again.

SUBURBIA

Raw sewage gushes into the Avon alongside New Brighton Road, the diesel pump in the middle of the road working overtime. The air is thick. But this will be a fact of life for residents in this low-lying flat land for months to come.

Roads and footpaths all around are buckled and bent, split and cracked; street gutters clogged and broken and stormwater drains blocked with silt.

While most in these eastern suburbs - places like Aranui, Dallington, Avondale, Wainoni and Bexley - now have water and power, for many the prospect of being able to flush toilets, shower, do the laundry or wash the dishes in the kitchen sink is a long way off. Beside the Avon on Avonside Drive, we see some of the reason why.

Large concrete chambers - pumping stations - have lifted out the ground. Diesel pumps provide a temporary replacement, chugging incessantly feeding fat hoses snaking along the road.

Christchurch City Council water and waste manager Mark Christison says two waste water pumping stations by the Avon were badly damaged in the September earthquake. Another was taken out of service on February 22. "With the latest damage we have got quite a few overflows back into the river." Health warning signs are posted by the riverside.

Two thirds of the city's sewage is now getting to the treatment ponds near Bromley, a situation that's improving as more trunk sewers are repaired. "But we still have about a third getting into the rivers," says Christison. Because trunk sewers are still broken he says there is still no flow path out of much of the eastern suburbs catchment area.

That results in sewage backing up in pipes which are also compromised by silt. "It means people can't use their sanitary services because it's got nowhere to go. If they try and use them it will end up in their backyard." Hence the emergency pumps at these low points and pumping into the river in an effort to drain down to the network.

To deal with the crisis, the first phase was port-a-loos deployed somewhat haphazardly around the affected areas. That's been followed by thousands of chemical toilets provided to households with tanks in the streets where they can be emptied.

The next phase says Christison is to "jet out the network" to get a better picture of the damage and hopefully enable some to use the "greywater" systems in their houses. "The final phase is replacement and repair of the infrastructure in the ground - that's going to take years."

Jetting out the network involves putting high pressure lances into the pipes to cut out all the sand which is then sucked out and trucked away.

It's a slow process. Some pipes are so damaged - floated up by liquefaction or dropped down by sunken ground - that the high pressure lances can't be used because they undermine the road. In situations where pipelines have to be replaced, the aim is to put tanks into front yards and connect "laterals" from houses to the tanks which have to be periodically sucked out.

The combination of land damage caused by liquefaction and the prospect of sub standard sanitary conditions has led to suggestions that some of these suburbs may have to be abandoned. In some areas like Bexley rumours abound that the land has dropped so much that it now lies below the flood plain.

There are concerns, too, that the Avon, now shallower and narrower because of silt and lateral drift, is more prone to flooding and repair work is ongoing to lift the level of the river's stopbanks.

Speaking at Rehua marae in the centre of Christchurch a few blocks away from the cordoned off CBD, Regan Potangaroa, an engineer who has worked in disaster zones all over the world, says the earthquake exposes more than an infrastructure problem.

"We find it hard to fess up that there are inequalities in our system," he says. "The reality is that prior to the earthquake these areas were ignored and after the earthquake they're also being ignored."

Kaumatua Mita Te Hae, who is also Canterbury District Health Board's health promotion and cultural advisor, agrees: "There seems a public bias out there to certain parts of Christchurch with respect to water and particularly port-a-loos."

The marae has served as a command centre for an army of field workers since the earthquake who have gone out daily to the community - door knocking to assess and help the elderly and others in need. Te Hae says it was astonishing to find, for example, that a supermarket with 10 port-a-loos in its carpark locked them at 6pm when it closed its doors.

"Obviously the powers that be are looking at the CBD as a priority area," he says. "They're trying to get the city back on its feet and that's understandable, but cities require people. If you have all the services but no one is going to purchase those services then it's pointless."

Potangaroa who is an associate professor at Unitec's School of Architecture and a member of RedR (Registered Engineers for Disaster Relief) says the assumption is areas like the eastern suburbs don't actually contribute to the city.

"They actually do. Our research shows the poorer parts of town are actually the engines of cities - that's the part that councils or authorities need to really foster because that's where all the people who work in all sorts of lower paid jobs all across the city come from."

He says the focus on the CBD, rather than the suburbs, assumes that by getting businesses up and running there will be a trickle-down effect. "But we don't actually see that happen in disasters." A lot of the smaller businesses are in lower cost premises, in cheaper buildings spread out across Christchurch, and they are the ones he says that are going to be worst affected.

"In humanitarian work it's called picking the low hanging fruit - doing the easier recovery work first. But it is the remaining 15-20 per cent - the houses that still don't have power, the parts of the city that can't use their toilets, that's the hard work that needs to be addressed."

In his experience, relocation should be seen as a last choice option. What's needed now is alternative ideas and assistance to deal with recovery.

The disaster has already got many architects thinking about how to design low cost earthquake resilient homes - dwellings that not only have foundations to survive on liquefaction prone ground, but also a degree of self-sufficiency in terms of water power and wastewater. (See: A Resilient Urban House).

What also needs to be addressed is domestic building codes for houses on liquefaction ground. Although it's long been known that vast areas of flat land in Christchurch are liquefaction prone, the building code allows un-reinforced concrete slabs.

As architects and engineers point out, slabs with mesh are not considered reinforced and what's needed on liquefaction ground is a raft foundation. That's a steel reinforced slab about 350mm thick that will literally float on watery ground during an earthquake and, while it may tilt if the ground falls away, wont break - thereby keeping the house intact. If such slabs do tilt, they can be re-levelled by pumping grout into subsided ground.

Architects and engineers have always known about what needs to be done on such soils, but such knowledge has largely bypassed most Christchurch residents. Map Architects director Kerry Mason designed a house 15 years ago by the river in Fendalton.

Following geotech reports on the soil and engineering advice to deal with liquefaction it was decided to "go through the jelly" with concrete piles. "It cost $40,000 to pile it to a depth of 12-15 metres," says Mason. After the two earthquakes the house has stayed exactly where it was, but the ground has fallen - 300mm the first time and another 400mm the next time - so the ground has slid into the river but the house has done exactly what it was designed to do."

THE HILLS

The hill suburbs and Lyttelton also suffered building and services damage in the latest quake with. Here, the danger came from landslides and crumbling cliffs in suburbs like Sumner and Redcliffs where large rocks crushed houses below leaving those on the cliff tops teetering precariously.

The lesson is obvious. "We shouldn't be building on those faces or below them. You would never consider building there now," says Mason who lives high on Scarborough Hill in Sumner. There are obvious lessons about building materials too: "A lot of the damage is in tile roofs and I think there will be a change away from those because of how they juggle around and bash each other to bits." Bricks, especially when used structurally, have also frequently failed.

Mason's house, well engineered on piles into the rock, came through the earthquake undamaged. It's given him new respect for engineers. "We have always grizzled about the engineering component of a house and how much money that takes out a project. I'll never complain about an engineer again. I don't think you can have too much structure."

Sumner was without water for 10 days and without power for a week. The Mason household coped surprisingly well. The swimming pool provided the bathroom, and plenty of fresh water in mains and storrnwater storage tanks below the house could be bucketed where needed.

Cooking was fine too thanks to a barbecue and an outdoor Warmington oven/fireplace. Mason says the experience has given him a new focus on providing features in house designs that make life easier when the power goes out - sometimes as simple as making sure bottle gas fed appliances can function without electricity. "A lot of our practice is housing and it's made us think about self sufficiency differently - water storage, solar heating and solar gain and other services that can be made to work without mains power."

THE CBD

Life around the fenced-off CBD, guarded 24 hours a day by bored army personnel, is increasingly frustrating. Visiting dignitaries are taken on escorted tours but the Herald was refused access for this story.

Building owners keen to retrieve items and assets are met with autocratic emergency powers and bizarre decisions. Throughout the off-limits zone, demolition crews bring down more and more buildings - although in the daily media briefings this is now called "deconstruction" rather than demolition.

"The cordon seems unnecessarily heavy handed," says Mason whose architectural office is in the CBD. His wife also has premises in the area. "We are all businesses and pay significant taxes. I would have thought the most critical thing is to get people back so they become productive again," he says.

"A week after the quake USAR went down Victoria Street and any locked door they found they broke it down with sledge hammers inflicting thousands of dollars of damage on businesses. Couldn't they have taken a locksmith or tried to get hold of building owners?"

Another disturbing feature is the number of multi-storey buildings in the area that have developed an unsettling lean. Other than the already troubled Hotel Grand Chancellor, a glass curtain wall office building at 90 Armagh Street is thought to be leaning about 400mm and the taller Victoria Square Apartments next door also appears to be off kilter. There are concerns too about the Copthorne Hotel, the Crowne Plaza and Pacific Brands House.

Speculation is rife about what has caused the tilting, but many note several of the buildings are near the river and subsidence due to liquefaction may be the culprit. How many of these relatively unscathed modern buildings will now have to be demolished is yet to be decided.

The damage to modern buildings in the CBD has led many to question whether the current earthquake codes are sufficient. (See: Codes) "Many were so shaken about that the joints were broken and the buildings are buggered," says Dacombe. "In a lot of cases they would have to come down."

Architects are also shocked by how hard the city's heritage buildings have been hit. "It is really depressing - generations of great building craft and art work lost," says Warren and Mahoney architect Bill Gregory. "You are alternately shocked at how badly buildings have failed and thankful that more people were not injured or killed. I guess we could have expected it, but nothing prepares you for seeing it."

Jasper van der Lingen of Sheppard and Rout points out that after the September quake many said the heritage buildings which had been strengthened to 33 per cent of the earthquake code seemed to stand up reasonably well. "People said it was OK and it was an over reaction to go to the 66 per cent strengthening. I don't think you hear those voices anymore."

Most list the Christchurch Cathedral, The Cathedral of the Blessed Sacrament, the Provincial Council Buildings, and the Arts Centre as the damaged heritage buildings that must be rebuilt. Most damaged is the 1864 Provincial Stone Chamber with its magnificent high gothic interior designed by Benjamin Mountfort which is now mostly a pile of stone rubble "There are some places that you just have to accept you do a rebuild of what was there before," says van der Lingen.

"If you do a total reconstruct, maybe you do some clever little twist or hint in the building design indicating that this is a post quake reconstruction done with love and care and passion."

Others are not convinced. "I wouldn't rebuild that [the stone chamber] the way it was - why not keep the timber portions if it is still intact and build something new?" says Dalman. "For the cathedral maybe we should repair what we can and build a contemporary spire." He argues that stage when heritage buildings are beyond repair is when a contemporary style rather than trying to replicate is more appropriate.

"Otherwise we just become main street Disneyland where everything is olde-world and it's false. The cost of rebuilding something like the stone chamber in the original style and materials would be tens of millions of dollars. Who is going to provide the money to rebuild it?"

There is however a general consensus that whatever is rebuilt in the CBD should be lowrise - four to six stories at the most - mainly because of the psychological trauma. "A lot of people are over it," says Dacombe.

"Many people who were even four stories up are saying "I'm not going to go back into that building. They cannot contemplate being in a situation again as they were on the 22nd." Gregory agrees: "It is going to be hard to justify building high rise in this city, where there already was lot of uncertainty about finding tenants for single major structures anyway." Dalman believes the market rather than any height code will determine the CBD's skyline. "I doubt if anyone will put up a building more than six stories high in Christchurch at the moment because no one will want to go into it."

Most architects favoured mixed use buildings combining apartments, rental and office space. There were concerns that the insurance money would be insufficient to build a high tech, good quality, sustainable central city.

"Many building owners will want to put up something relatively cheap because they won't want to spend any more money than their insurance cover," says Dalman. "There is the potential to get a whole lot of cheap crappy buildings in the central city."

Enter central government, says Dacombe. "At a certain point there needs to be some kind of nationalisation of land because we have to recognise what's happened in Christchurch is going to devalue the land."

He says there needs to be a way to show the land does have value by advocating for higher density development over city blocks. "You cannot allow people to debate this thing forever - someone has got to make a decision and they have got to make it soon."

Mason sees a similar problem. "Christchurch probably won't do it wrong, but the risk is we will spend years arguing about it." He advocates buying in the best advice in urban planning to set the framework for the city, plus bringing in top "starchitects" to design some of the new buildings.

"There is more than enough work for the local architects. For the sake of another million dollars of consultant's fees you could get a Renzo Piano and create something that was such a high standard the city could thrive off it for years to come."

CODES

Compusoft Engineering director Barry Davidson is succinct: "Nobody needed to die." It's not something one with thirty years of engineering experience says lightly or with the benefit of hindsight. Davidson who is highly respected in the field of seismic design has been on the record with his concerns for some time. In 2007 as a member of the Department of Building and Housing's Structural Advisory Panel he promoted the concept that all multi-storey buildings of a certain height in Wellington should be seismically isolated.

"My point that no one needed to die is because the piles of rubble you saw in the streets of Christchurch and especially the CBD has been seen before - in Turkey, Mexico, Haiti or anywhere else in the world over the last 20-50 years of earthquakes in cities which have old brick, and unreinforced masonry buildings," says Davidson.

"What has fallen on the ground is these old buildings that haven't been fixed up, or have been poorly or inadequately fixed up. You can fix these things, but it does cost."

What has happened is distressing because New Zealand has led the way in seismic design since the 1976 change to its seismic loading standard. "The 1976 code was a watershed," says Davidson. "The concept of it was that it would prevent collapse of buildings in an earthquake and ensure occupants may egress safely."

The code was based on capacity design - the idea that if something in the building has to give in an earthquake, then the engineer ensures it's the part of the building that's designed to give, usually the beam in a frame structure and not the column.

"If the building loses a column it loses its ability to carry gravity so we design the building so it yields and deforms but doesn't collapse. It will not hit the ground, it may be damaged, but people will be able to evacuate."

For many of the post-1976 buildings in the CBD, indications are the code did its job, allowing safe exit. But there were also failures, like the Forsyth Barr building suffering from stairwell collapse. "That's a failure in seismic engineering," says Davidson.

Just as it was known that unreinforced masonry, brick and stone buildings would collapse or suffer severe damage in an earthquake, it was also know that pre-1976 buildings also had design flaws.

"The buildings built in the 1950-1960 have under reinforced concrete. It's not surprising that a building built in that era that hasn't been fixed up in any way would behave poorly in an earthquake." Typically, buildings of that era have beams that are too strong for their columns so the column is more likely to give way than the beams. They also have design flaws in the beam-column joint zone.

Knowledge of such fundamental design flaws will no doubt play a significant part in the Royal Commission of Inquiry into the catastrophic failure of the Pyne Gould and Canterbury Television buildings in the Christchurch quake.

"Building design in the 60s is know by all structural engineers to have critical structural weaknesses." Davidson says while the problems have been known for some time the political will to deal with them has been sorely lacking. "No one wants to say: 'You own this building. It's old and has design faults. Either knock it down or fix it."

In many cases fixing could involve base isolation. It's a technique whereby buildings rest on isolator bearings - typically made of layers of high density rubber and steel plates around an inner core of lead - designed to move in any horizontal direction so that when the ground shakes, they move and building doesn't.

Christchurch Women's Hospital and Te Papa in Wellington are base isolated buildings. Davidson says the technique works best on buildings up to six or seven stories and can be retrofitted to historic buildings as seen in the old Parliament buildings which have also been seismically isolated.

"Our codes are still very good, but the philosophy is somewhat based in the 70s and 80s. The new philosophy that has been developing in the last 10-15 years is to have buildings designed in such a way, that not only do they not collapse in the earthquake, but suffer very little damage."

Davidson has also long advocated for a much more rigorous checking of engineers' designs - calling for truly independent consultants to review engineering drawings and calculations. At present designs can be simply signed off by any other chartered engineer.