18-07-2012, 10:58 AM
UNDER GROUND STRUCTUR
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UNDERGROUND STRUCTURE
Abstract: -
More and more people, worldwide, have already or plan to build an Eco-Friendly earth-sheltered or earth-bermed home. In this article, an effort has been made to study Eco-Friendliness of earth sheltered structure. Earth-sheltered homes usually have their tops and sides completely covered with earth, while earth-bermed homes usually have an exposed side and roof. The governmental as well as non-governmental agencies across the world, researching on planning and construction of eco-friendly housing have supported the idea of earth sheltered structure.
The DOE (U.S. Dept. of Energy) says, “An earth-sheltered home is less susceptible to the impact of extreme outdoor air temperatures, so you won’t feel the effects of adverse weather as much as in a conventional house”. Temperatures inside the house are more stable than in conventional homes, and with less temperature variability, interior rooms seem more comfortable. The non-governmental groups working on this research add that buried houses not only afford protection from natural disasters but also from man made as explosion, nuclear accidents etc.
To plan and built any structure factors that affect are amount of land available and overall need of consumer. One of advantage of underground structure is the environment is stable beneath earth surface. Another advantage is that open space above the structure can be utilized for plantation, thus maintaining eco-balance. In the Netherlands, a heavily-populated country fast running out of space, underground construction is taking place with increased frequency.
These structures generally suffer from humidity, capillary action and problems of drainage facilities, which can be controlled. Moreover, natural sunlight, temperature and ventilation can be provided in these structures. It is not that underground structure is modern aspect in construction industry.
What is underground building?
Underground building, itself is self explanatory word, i.e., building located under or below ground .Yet, problem crop to many people, how much a building should be under the ground to be called as “UNDERGROUND BUILDING”.
Finally, and perhaps easiest to resolve, is the case of a building located at or above the surface level of its entrance, but enclosed in the earth.
Earth sheltered homes: -
Earth sheltered homes are those having their roof as well as their exterior wall covered with earth as shown in fig. A.
Besides reduced maintenance costs and increased safety from fire and tornadoes, earth sheltered homes are much more energy efficient. According to a study, the temperature in summer at surface of earth is much higher than at higher depths. Earth sheltered homes have one more advantage that the below grade walls and floor are 2-4 feet away from earth surface. Therefore, a building constructed with 100% R..C.C. structure with high quality reinforcement would help more to save net energy due to moderate earth temperature.
Earth bermed structures: -
One aspect of the problem is illustrated by the Silvestre S. Herrera Elementary School in Phoenix, Arizona (fig.1 (b)). Like many earth-sheltered buildings, this one-story structure raises approximately one-half story above ground level. Most of the wall surfaces are bermed (i.e., an embankment of earth is sloped up to cover all or part of each wall). The roof is not covered with earth, but with concrete. As students run up the gently sloped, landscaped ground from a play yard to the rooftop basketball courts, they are oblivious to the school building beneath their feet.
On the other hand, people approaching the front door of the school see a typical, although low-profile, facade and enter it in a normal way after walking down only a few steps from the parking lot. This building seems more deserving of being labeled underground than one that is built 1 foot below grade and has soil bermed only 3 feet up the exterior walls. But where is the dividing line in terms of a definition of underground building? These types of structures are called as Earth-Bermed structure. The images can be seen in fig. 1(a) & 1(b).
The confusion still remains if Underground building is defined as a building having its roof covered with earth, because some houses are crowned with “living roof” of vegetation. A truck factory currently under construction at the Ford Rouge Center in Dearborn, Michigan, is one example. The 600,000-square-foot building, which rises from ground level, will be topped with a field of ivy, and vines will be encouraged to cover its exterior walls. That will not transform the structure into an underground building.
The hostel at St. John's University in Collegeville, Minnesota, consists of five buildings consists of four 2-story apartments. At the front of the building, the upper story is at ground level, and the ground slopes down to daylight the lower level. The grass-covered roof slopes down toward the back of the building, where it seamlessly joins the surrounding lawn. An impression of whether these are underground buildings.
ECO-FRIENDLY NATURE OF UNDER-GROUND STRUCTURE:
It is now clear from the above definition that the underground structure is located below earth surface and covered with earth on all sides. On account of this, these underground structures can be said as eco friendly due to following points:
1) The temperature below the earth surface is stable ie the temperature fluctuation does not affect the temperature within the structure.
2) As the structure is covered by earth it is well protected from pollution i.e. air pollution, water pollution etc.
3) as the structure is below earth surface the free space at earth ground level can be utilized for plantation
4) as its entire structure has earth covering, earth being good sound insulator, structure is sound proof.
5) These structures are less susceptible to extreme outdoor condition and natural calamities like high wind, tornado, and cyclones.
6) If properly ventilated there is no way, either from inside or outside of structure, to break fire and cause damage.
7) During war times, these under-ground structures are not affected by any disaster activity caused during war like nuclear explosion and missile attack etc.
But, it also becomes necessary to properly plan and designs this construction to make it eco friendly in two ways—friendly to nature and friendly in economy. This type of construction requires high technology, which also increases the cost of construction. So, to properly plan and develop an underground structure, down listed points should be looked into carefully.
Types of Planning:
There are three general planning methods for under ground building are categorized as under.
An atrium design offers an open feeling because it has four walls that give exposure to daylight. This design uses a sub grade open area as the entry and focal point of the house. It is built completely below ground on a flat site, and the major living spaces surround a central outdoor courtyard. The windows and glass doors that are on the exposed walls facing the atrium provide light, solar heat, outside views, and access via a stairway from the ground level. Atrium/courtyard homes are usually covered with less than 3 feet (0.9 meters) of earth primarily because there is no benefit in energy efficiency from greater depths. This style also offers the potential for natural ventilation.
Atrium (or courtyard) plan: -
In an underground structure where an atrium serves as the focus of the house and the entry into the dwelling
The atrium design is hardly visible from ground level and barely interrupts the landscape. It also provides good protection from winter winds and offers a private outdoor space. This design is ideal for an area without scenic exterior views, in dense developments, and on sites in noisy areas. Passive solar gain—heat obtained through windows—might be more limited, due to the window position in an atrium plan. Courtyard drainage and snow removal are important items to consider in design.
Elevational plan:
- In elevational plan, bermed structure has a south-facing entry.
Elevational plans expose one whole face of the house and cover the other sides—and perhaps the roof—with earth. The covered sides protect and insulate the house. The exposed front of the house, usually facing south, allows the sun to light and heat the interior. The floor plan is arranged so common areas and bedrooms share light and heat from the southern exposure. This type of house may be placed at varying depths below ground level and is usually set into the side of a hill. The view provided will be one of landscape, rather than open sky, as in the atrium design. A structure designed in this way can be the least expensive and simplest to build of all earth-sheltered structures. However the elevational design may have limited internal air circulation and reduced daylight in the northern portions of the house, although there are ways to alleviate these problems by using skylights. The wide design of the house can be offset by close attention to architectural details, landscaping, and exterior materials.
Penetrational plan:
- Penetrational plan is built above or partially above grade and is bermed to shelter the exterior walls that are not facing south.
In the penetrational plan, earth covers the entire house, except where it is retained for windows and doors. The house is usually built at ground level, and earth is built up (or bermed) around and on top of it. This design allows cross-ventilation opportunities and access to natural light from more than one side of the house.