Could rubber tyre foundations help protect buildings during earthquake?

Many homes in Lombok have been destroyed. Image: EPA/Adi Weda.

At the time of writing, 436 people have died following an earthquake in the Indonesian island of Lombok. A further 2,500 people have been hospitalised with serious injuries and over 270,000 people have been displaced.

Earthquakes are one of the deadliest natural disasters, accounting for just 7.5 per cent of such events between 1994 and 2013 but causing 37 per cent of deaths. And, as with all natural disasters, it isn’t the countries that suffer the most earthquakes that see the biggest losses. Instead, the number of people who die in an earthquake is related to how developed the country is.

In Lombok, as in Nepal in 2015, many deaths were caused by the widespread collapse of local rickety houses incapable of withstanding the numerous aftershocks. More generally, low quality buildings and inadequate town planning are the two main reasons why seismic events are more destructive in developing countries.

In response to this issue, my colleagues and I are working on a way to create cheap building foundations that are better at absorbing seismic energy and so can prevent structures from collapsing during an earthquake. And the key ingredient of these foundations is rubber from scrap tyres, which are otherwise very difficult to safely dispose of and are largely sent to landfill or burnt, releasing large amounts of carbon dioxide and toxic gases containing heavy metals.

Rubber-soil mixture

Previous attempts to protect buildings from earthquakes by altering their foundations have shown promising results. For example, a recently developed underground vibrating barrier can reduce between 40 per cent and 80 per cent of surface ground motion. But the vast majority of these sophisticated isolation methods are expensive and very hard to install under existing buildings.

Our alternative is to create foundations made from local soil mixed with some of the 15m tonnes of scrap tyre produced annually. This rubber-soil mixture can reduce the effect of seismic vibrations on the buildings on top of them. It could be easily retrofitted to existing buildings at low cost, making it particularly suitable for developing countries.


Several investigations have shown that introducing rubber particles into the soil can increase the amount of energy it dissipates. The earthquake causes the rubber to deform, absorbing the energy of the vibrations in a similar way to how the outside of a car crumples in a crash to protect the people inside it. The stiffness of the sand particles in the soil and the friction between them helps maintain the consistency of the mixture.

My colleagues and I have shown that introducing rubber-soil mixture can also change the natural frequency of the soil foundation and how it interacts with the structure above it. This could help avoid a well-known resonance phenomenon that occurs when the seismic force has a similar frequency to that of the natural vibration of the building. If the vibrations match they will accentuate each other, dramatically amplifying the shake of the earthquake and causing the structure to collapse, as happened in the famous case of the Tacoma Narrows bridge in 1940. Introducing a rubber-soil mixture can offset the vibrations so this doesn’t happen.

A promising future

The key to making this technology work is finding the optimum percentage of rubber to use. Our preliminary calculations echo other investigations, indicating that a layer of rubber-soil mixture between one and five metres thick beneath a building would reduce the maximum horizontal acceleration force of an earthquake by between 50 and 70 per cent. This is the most destructive element of an earthquake for residential buildings.

We are now studying how different shaped rubber-soil mixture foundations could make the system more efficient, and how it is affected by different types of earthquake. Part of the challenge with this research is testing the system. We build small-scale table models to try to understand how the system works and assess the accuracy of computer simulations. But testing it in the real world requires an actual earthquake, and it’s almost impossible to know exactly when and where one will strike.

The ConversationThere are ways of testing it through large scale experiments, which involve creating full-size model buildings and shaking them to simulate the force from recorded real earthquakes. But this needs funding from big institutions or companies. Then it is just a question of trying the solution on a real building by convincing the property owners that it’s worthwhile.

Juan Bernal-Sanchez, PhD Resarcher, Edinburgh Napier University.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

The Tory manifesto promises to both increase AND decrease the rate of housebuilding

Housing secretary Robert Jenrick. Image: Getty.

In his 2014 Mansion House speech, the then-chancellor George Osborne expressed with uncharacteristic honesty the motives at the heart of how the Conservatives see British housing politics: “The British people want our homes to go up in value, but also remain affordable; and we want more homes built, just not next to us.”

Five years later these contradictions remain unreconciled and present in their manifesto, which contains two different and contradictory – but clearly extensively targeted and focus-grouped – sets of policies.

The Conservatives have two housing targets. The first is to make significant progress to hitting “our target of 300,000 houses built a year by the mid-2020s”. The second is their aim to build “at least a million new homes” during the next parliament, which implies a target of 200,000 homes a year. This is not only 100,000 lower than their initial target but also lower than the current rate of housebuilding: 213,660 new homes a year. They have therefore implied at separate points in the same manifesto that they intend to simultaneously increase and decrease the rate of housebuilding.  

There are similar conflicts in their approach to planning. They intend to make the “planning system simpler” while simultaneously aiming to introduce community-led design standards for development and planning obligations to provide infrastructure for the local community.

None of this is unsurprising, The Tories don’t seem to know if they want to build more houses or not – so of course they don’t know whether they wish to make it easier or harder to do so.  

Politicians like obfuscation on housing policy to placate NIMBY voters. Take for example prospective Conservative MP and ‘environmentalist’ Zac Goldsmith’s crusade to save treasured local car parks. The manifesto can equally be accused of pandering to NIMBY instincts, protecting their shire voters from all housing, including ones they might actually need or want, by promising to protect the greenbelt.  

Instead, Conservatives intend to foist development on Labour-leaning inner-city communities and prioritising brownfield development and “urban regeneration”. This requires massive, infeasible increases in proposed density on brownfield sites – and research by Shelter has shown there are simply not enough brownfield sites in cities like London. Consequently, it is not clear how such a policy can co-exist with giving these inner-city communities rights on local design. Perhaps they intend to square that circle through wholesale adoption of YIMBY proposals to let residents on each street opt to pick a design code and the right to turn their two-storey semi-detached suburban houses into a more walkable, prettier street of five-storey terraces or mansion blocks. If so, they have not spelt that out. 

Many complain of NIMBYism at a local level and its toxic effects on housing affordability. But NIMBYism at the national level – central government desire to restrict housebuilding to make house prices rise – is the unspoken elephant in the room. After all, 63 per cent of UK voters are homeowners and price rises caused by a housing shortage are hardly unpopular with them. 


There is anecdotal evidence that protecting or inflating the value of homeowners’ assets is central to Conservative strategy. When George Osborne was criticised for the inflation his help to buy policy caused within the housing market, he allegedly told the Cabinet: “Hopefully we will get a little housing boom, and everyone will be happy as property values go up”. More recently Luke Barratt of Inside Housing noted that most Conservatives he spoke to at the 2018 party conference were scared “they’d be punished by their traditional voters if the values of their homes were to fall”. He was told by a Conservative activist at the conference that, “If you build too many houses, you get a Labour government”.

But the senior figures in the Conservative Party are painfully aware that the continuing housing shortage presents major long-term problems for the Party. As the manifesto itself acknowledges: “For the UK to unleash its potential, young people need the security of knowing that homeownership is within their reach.” Perpetual increases in house prices are incompatible with this goal. The problem has greatly contributed to the Conservatives’ severe unpopularity with a younger generation priced out of decent accommodation. 

Equally, there is increasing evidence that ‘gains’ from rising house prices are disproportionately concentrated in the south of England.  The differences in housing costs between regions greatly reduce labour mobility, suppressing wage growth in the north and midlands, which in turn leads to greater regional inequality. The policy of coddling southern homeowners at the expense of the economic well-being of other regions is a major long-term stumbling block to Conservative desires to make inroads into the ‘red wall’ of Leave-voting labour seats outside the south.

Before dealing with the issue of where housing should go, you must decide whether you want to build enough housing to reduce the housing crisis. On this issue, the Conservative response is, “Perhaps”. In contrast, even though they may not know where to put the necessary housing, the Labour Party at least has a desire in the abstract to deal with the crisis, even if the will to fix it, in reality, remains to be seen. 

Ultimately the Conservative Party seems to want to pay lip service to the housing crisis without stopping the ever-upward march of prices, underpinned by a needless shortage. Osborne’s dilemma – that the will of much of his party’s voter base clashes with the need to provide adequate housing – remains at the heart of Conservative housing policy. The Conservatives continue to hesitate, which is of little comfort to those who suffer because of a needless and immoral housing shortage.

Sam Watling is the director of Brighton Yimby, a group which aims to solve Brighton’s housing crisis while maintaining the character of the Sussex countryside.