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“First we had SARS, then it was HIV, bird flu and dengue fever, followed by chikungunya virus, rabies and swine flu. There always seems to be another risk to our health but now we are faced with a really serious threat, an infestation of epic proportions that is taking hold in our midst. There is currently no protection, no treatment and no cure. I am referring, of course, to the Great Minimarket Pandemic or GMP.
People are scared, very scared. New cases are springing up all the time “like mushrooms in the night”. Communities are frightened to go to bed at night knowing that they might wake up in the morning with yet another minimarket next door. I ask you, just how many bags of crisps and bottles of pop can anyone drink in a day?
It's the spores you know. They are picked up and carried on muddy shoes, they can lie dormant in the ground for years and then, without warning, they suddenly spring up under cover of darkness. Before you know it there is a sea of flashing neon signs saying “Open 24 Hours”.
They are not easy to get rid of either. Only this morning I saw some council workers struggling to contain an infestation in Kerobokan, a particularly stubborn clutch of minimarkets down in Jalan Raya Semer.
Where the contamination has come from nobody knows though there are plenty of theories, some say it came from Australia in a bag of potato crisps while others blame a contaminated batch of syrup for a certain well known brand of fizzy pop. The latest, and probably more likely, theory is that it is a mutation of the virulent “Realestatus Officealis” virus or perhaps a strain of “Pertaminia Pompa Benzinibus” which have taken hold in recent years.
The authorities are working hard. Soil tests are being carried out to try to isolate the cause of the contamination and to determine how resistant minimarkets might be to attempts at their removal. It is an uphill battle with the virus mutating faster than science can keep up and new subspecies appearing every day.
Soil tests are also very useful to anyone wishing to build a building. You see the most important part of any building is, in fact, the part you cannot see, the bit under the ground, the foundations. The larger the building the more important this is.
The first thing required before designing any building is an investigation of the ground to determine what sort of foundations are required and indeed what sort of building can be built. The Leaning Tower of Pisa is a case in point. Giovanni Di Simone was only going to build a bit of a bandstand, they thought it would keep him out of trouble for a while, no one ever expected him to go up 8 floors (that was a highrise back in 1178!) checking the ground first might have been useful. It has only a 3 metre foundation in a weak unstable subsoil. Mind you nearly 900 years isn't too bad is it?
So what are soil tests and why are they carried out? A soil test is a scientific examination of a piece of ground to determine how stable it is and what sort of weight it can support. Samples are taken and tested to determine the weight, density, water content, shear strength, elasticity, the nature of the particles and of course, the load bearing capacity of the earth. Bores are sunk to extract cores so that the soil can be examined and tested at different depths and in different key locations on the site.
A comprehensive plan of the nature of the ground across a building site is compiled. From this information structural engineers can calculate the forces involved and design suitable foundations for the building that is to be built.
Soil tests are becoming more important as the nature of buildings change. Traditional Balinese houses tend to be relatively lightweight single storey structures. These days more and more people are building heavy multistorey buildings and even apartment blocks that are far more susceptible to damage or collapse from unstable land or earthquakes. (We must always keep earthquakes in the back of our minds when designing buildings in Bali – it is only a matter of time).
The nature of the ground anywhere varies enormously but let us consider five different types of ground that may be encountered in Bali.
Volcanic Rock
We live on volcanoes and the central core of the islands of Indonesia are volcanic. Volcanic rock varies from very light crumbly pumice to very hard basalts and granite. Basalt and granite are probably the strongest and most stable foundations you could find anywhere. Of course many volcanoes here are live and the best idea is to have the basalt under your house not on top of it. Perhaps volcanoes provide a new marketing angle for real estate salesmen - “Adventure Living”.
Sedimentary Rock
The southern hills of Bali (the Bukit) are made up of limestone which tends to be very stable and provides a good foundation. It is very soft and crumbly as limestones go and is in fact more of a chalk. True limestones tend to be hard (though nowhere near as hard as basalt). Limestone tends to be porous so, without a layer of topsoil it is usually very dry.
Sand
In the coastal areas such as Sanur, Nusa Benoa and Kuta you may find the ground near the beach is sand. Sand is good for building on and can be very stable, as long as it is contained. If it is not contained it can, of course, be easily washed away by heavy rains or high tides.
Alluvial Deposits
Look on a map and you will notice that the whole area from north of Denpasar southwards to Jimbaran is in fact a large flood plain. Note that flood plains do, from time to time, have a tendency to flood. Much of this area is not very high above sea level and it would be interesting to work out how much would be washed clean if a Tsunami the size of the one that hit Aceh were to hit Bali. This land varies considerably, some is fairly stable and is relatively straight forward to build on provided that foundations are properly designed. Other areas are clay which can be challenging.
Clay
Much of the land in Bali is, or was, rice fields. Rice fields, of course, are required to hold water and so are made of clay which is impermeable – it holds water. The clay is formed into rectangular basins which have a layer of mud in the bottom in which the rice is grown. Many, many buildings here are being built on the clay of former rice fields. Clay is a tricky material to build on because it changes it's nature between the wet season and the dry season. When it absorbs water it expands as the water content increases, when it is very wet it may be the consistency of toothpaste, a heavy building can squeeze it out. When it dries out it shrinks and large cracks can form in it. This is known as expansive clay.
This expanding and contracting of clay becomes a particular problem under the floor of a building. As the wet seasons starts the ground around the edge of the floor start to become saturated and expands while the ground under the centre of the floor is still dry and contracted. Gradually the water permeates into the area under the centre of the floor. Then as the dry seasons starts the effect is reversed with the ground around the edge starting to dry out and contract while the ground under the centre is wet and expanded.
This process puts enormous stresses on the structure of the floor slab and is why a common building foundation method used in Australia, a raft slab, is not suitable for the expansive clay of former rice fields found in Bali. A raft slab, as the name implies, is a concrete slab that “floats” as a self contained building platform on the surface of the ground.
With former rice fields it is particularly important to carry out soil tests to determine how far down stable ground can be found and the nature of the clay in between.
A final but important consideration is whether land has been filled. Most sites are not level and in the course of levelling some earth is cut out from one place and used to fill another. Unless the earth has been fully compacted or left to settle for years the filled areas will be softer and weaker than the cut areas. This is a very important consideration in designing foundations and the structure of the building.
I have just had a call from a military sounding gentleman with an American accent asking if the minimarket virus has been isolated yet. Very worrying. Can you imagine the devastating consequences of unleashing minimarkets on unsuspecting populations around the world. The mind boggles.
Phil Wilson
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