The integration of and landscape in a highway proximal environment through the smart use of earth berm sound barriers

Maria Kaskareli

Department of Architecture, Technical University of Delft, Delft, The Netherlands

14 January 2014

ABSTRACT

This paper is investigating the possibility of merging building and landscape in a highway proximal environment in the Netherlands. Green in urban areas is under constant pressure and adding green in cities is a contemporary challenge. This merging is approached by examining how to make smarter use of the earth berm sound barriers that are commonly used on the sides of highways by making them multifunctional. This approach can fit under the earth sheltering technique. Five aspects are identified and studied individually. First, the technique of earth sheltered construction is studied including considerations such as structural loading, the application of , moisture and humidity. Secondly, lighting conditions for earth covered or underground spaces are presented. Next, the acoustic performance of the earthen sound barriers is studied, including general principles, geometry, surface cover and the influence of vegetation. The fourth aspect studied is the greening part, which is comparable to intensive design, taking into consideration the slope. The final aspect studied is the thermal properties of , the potentials that are presented with its high and the thermal energy storage that is possible in it. Moreover, some references are presented as examples for the study. Finally, it is concluded that such integration, however complex, is a possible task that can have very positive effects of the dense urban environment of present cities.

Keywords: Earth sheltering; Earth berms; Sound barriers; Building - landscape integration; Underground building; Green roof; Thermal mass; Heat storage; Building with soil; Highway environment

1. Introduction around cities. “More trees are still being chopped down than planted, and more green areas are being It is a fact that world population is growing and that replaced by and paving than are being [1] urbanisation is increasing. As a result, cities are added.” It is a fact that almost 40% of the Dutch growing, in their need to accommodate more population lives in districts with insufficient green people. It is frequent that a city is surrounded by recreational facilities. The shortages are greatest in [2] major transportation infrastructure belts, which the Randstad urban conglomerate. This is while acting as connections in one direction, are especially true of the increasing urban density in great barriers on the other direction (perpendicular the Groene Hart zone of the Netherlands. The need to their axis of movement). Such transport for more buildings means that green is undervalued channels, whether highways or railways, are and construction is preferred over parks and green creating several problems to the areas they pass public areas, also because it brings higher profit. through. Mainly the sound pollution that they are a source of, has as a result that the proximal areas 1 Heat. More Urban Green Keeps the City Cooler 2 remain unused or are used but with low occupant “The monitor of the National Spatial Strategy and a study conducted by Alterra (2005) show that a great deal needs to be satisfaction. Architecture can take the role of done to bring Dutch towns and cities back to the level where reconnecting separated components of a city and they should be: almost two-thirds of the fifty largest Dutch physically absorbing infrastructure. municipalities offer less than 75 m2 of green within a radius of 500 metres of a given . Forecasts predict that the pressure on urban vegetation will increase further, since the population One other issue that appears with the growing cities is growing and policy dictates that the density of existing built- is the pressure that green areas are subject to in and up areas be increased.” - The social and economic importance of green and blue areas

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Adding green public space in a tight environment is more common in the United States than in Europe, a great contemporary challenge. A current where – as the name indicates – buildings are movement that is calling for more green in cities is covered by soil and thus can be made to blend in taking the form of green roofs and facades. with the natural landscape. However, even more important is the retention of existing green areas at ground level in order to have an essential impact on the urban living conditions.[3]

Green has been proven to have numerous benefits and is much desired and even necessary in urban areas. In recent years, more information is becoming available about the benefits of green in cities. The fact that vegetation enhances the quality of life is something that urban planners have been aware of since the start of the profession. “Most people prefer living in green districts. prices Fig.1.1 in green districts or along water or areas of vegetation are relatively higher than elsewhere. To draw citizens with higher levels of education, towns and cities need to be attractive and offer green and culture. Highly educated engineers, in particular, 2. Methodology prefer to remain close to green areas: both for where they live and for their holiday This earth sheltering technique is simple in its destinations.”[4] It is also a fact that vegetation principle and brings several benefits. One is the reduces stress levels and helps people to recover integration with the landscape. The building can be faster from illnesses. made to blend in with its surroundings and almost disappear. Another is the stabilization of internal Nature is being burdened and threatened constantly thermal environment due to the thermal mass of by the building sector. The solution is clearly not to soil. With around 40% of the total energy stop building, but ways must be found to continue consumed by the building sector being used for construction in agreement with nature. The term space conditioning, this aspect of earth sheltering is “nature” is used here in two ways, meaning first particularly important. As this paper will further nature as the natural landscape (green areas, explain, a building designed with this technique can vegetation, biodiversity etc.) and on the other hand present great energy savings from the respect of the natural resources (minimising energy space heating and cooling. It is interesting to see consumption, renewable resources, low emissions). that in the past, people used earth sheltering to It seems inevitable that we must learn how to better protect from the environment, while today, people overlap architecture and green space in smart ways. use it to protect the environment. In this specific case, a benefit of the technique is also its ability to be formed into a sound barrier and the sound In a dense urban centre, the increasing lack of insulation properties of soil. If not taken into space and the increasing land values often forfeit consideration, lighting in such semi-underground the luxury of typologies, and buildings can become a great disadvantage. quite often, disparate programs are forced to be Therefore this also needs to be given the combined. This paper will be dealing with the importance that it deserves. In order to study how specific case of an environment surrounding a busy the technique can be used as a solution to the highway in the Netherlands, with all the problems problem posed, it has been broken down to five it introduces, as above discussed. In order to aspects: achieve the merging of landscape and building in such an environment, the problem can be approached as making the typical earthen sound  constructing an earth barriers smart, by integrating functions in them and  light conditions & comfort in earth turning them into usable green areas, doing this in a sheltered buildings sustainable way and including energy  earth berm sound barriers & acoustic considerations [Fig.1.1]. The technical solution of properties of soil this approach can be fitted under the construction  green over earth sheltered buildings technique known as “earth sheltering”, a technique  thermal properties of soil & heat storage in the soil

3 Pötz, p. 247 4 The social and economic importance of green and blue areas In order to research this broad topic, each of the five aspects, forming a distinct topic, has been 2 approached separately. To avoid presenting of Iceland being one of the most irrelevant research for the five separate topics and characteristic [Fig.3.1.1]. including excess information, the results for each topic have been limited to the information that could be directly relevant to the specific research, with all its limitations. Most of the research has been carried out by literature study. Books were usually a source of broader information, while focused articles on the specific topics provided the more detailed information. Moreover, some references were studied. Finally, professional experience has been taken into account by having direct contact with experts in each field within the academic environment. In order to make the results of this multifaceted research clearer, they have been translated into a diagrammatic form. In this Fig. 3.1.1 way (and as this paper is mainly directed at architects, and architects have a more visual Earth sheltered construction can be categorised in perception) the results can be easily read, three basic construction methods: appreciated and can inform a design in a more direct way than plain text would. Sometimes earth berming: where earth is packed against the underground buildings were used as reference walls of a building and over its roof and let to slope when the conditions studied were similar. down to the ground level, in-hill construction: where a building is set into a sloping hillside, and fully recessed construction: where a building is set below ground and is arranged around a central 3. Results .

For the purposes of this paper the first method is most relevant. However, most principles apply to The results of this research are more easily read as all three. a manual for designing with the technique of earth sheltering, in a manner as described before and with all the limitations and different aspects of the problem. The results are formulated in the categories that the research has been broken down to. The aim of this categorization is a clear and structured presentation of the vast information collected.

3.1 Constructing an earth shelter

Fig.3.1.2 Eart Berming

The idea of earth sheltering is not something new. Usually, a building site is extensively excavated It is being used as a principle maybe since humans before construction, beyond where the wall have been constructing their own shelter. It perimeter is planned. The most common structural presents several advantages and when done material used with earth sheltering is reinforced properly, the disadvantages are negligible. Some of concrete. The main reasons are its strength and the advantages are: making use of the earth’s durability, which relate to the extra load from the thermal mass, offering additional protection from earth and the different conditions that the earth the natural elements, providing high sound contact brings. Soil is a very heavy material. Loose insulation, providing high privacy and security, soil weighs approximately 1200kg per cubic meter, enabling efficient land use, having low rammed soil weighs approximately 1600kg per maintenance requirements and others. There are cubic meter, while wet for example can weigh numerous historical examples in different up to 1900kg per cubic meter. The load will not civilizations and climate regions, with the turf only be vertically on the roof; the lateral earth pressure must be carefully considered as well 3

[Fig.3.1.2]. Moreover, additional lateral thrusts very difficult to detect and repair leaks. Usually a may be exerted by the creep of the hill or berm layer of liquid asphalt, a heavy waterproof [Fig.3.1.3]. Last but not least in loading membrane and a final liquid water sealant are considerations, depending on the climatic region, combined for high quality waterproofing. Thermal snow setting over the structure must not be insulation may then be applied in a typical way, neglected [Fig.3.1.4]. but this unconventional technique with the added thermal mass that it introduces, means that what we normally know about thermal insulation does not perfectly apply. Depending on the thickness of the soil covering layer, the amount of thermal insulation required varies with depth for the vertical surfaces [Fig.3.1.7]. “Due to the longer path to the surface, the total resistance (R-value) is greater near the bottom of a fully insulated wall. Taking the path of least resistance, heat flux is therefore greater at the top of the wall.”[5] Therefore, the amount of insulation required increases with the height of a vertical wall.

A different way that thermal insulation can be In order to reduce this great added construction applied is what is referred to as “umbrella load exerted by the soil covering, it is possible to insulation” [Fig.3.1.8]. “The idea is very similar to replace typical soil for some lighter substrate the “Frost Protected Shallow Foundations” idea [Fig.3.1.5]. However, this reaches limitations when that has been widely used considered for large scale projects. One other in Scandinavian countries since the 1940′s.”[6] With solution to alleviate the load can be to use foam as this method, insulation is applied over the building an infill below the soil, but this would change the and over some of the soil keeping it dry. In this thermal mass advantages that will be presented way, all the amount of soil under the umbrella acts further in this paper [Fig.3.1.6]. Reducing the water as a thermal storage medium. “As a bonus, the dry content of the soil will generally reduce the lateral and almost airtight soil under the umbrella is also pressure on the structure. unattractive for most digging pests, tree roots, etc.”[7] Depending on the amount, this thermal storage can be adequate for even annual thermal storage, thus reducing heating and cooling demands, or even making them redundant. As the amount of thermal mass is proportional to the time of thermal storage, this relation must be carefully examined [Fig.3.1.9]. Typically, 5cm of concrete are sufficient to accommodate a daily thermal storage cycle. Detailed information about the construction of such an umbrella insulation can be found in the article Earth Sheltered Umbrella Basics. This umbrella insulation can be successfully paired with earth tubes for pre-treated ventilation. Two separate air supplies that can function both as inlets and outlets, one short connected directly to the outside and one long passing through the thermal storage. When heating

5 Earth Sheltered Umbrella Basics Waterproofing is very important in earth sheltered 6 ibid construction, as once the building is covered, it is 7 ibid 4 is required, the tube that passes through the thermal 3.2 Light conditions & comfort in earth sheltered store lets air in and the other lets air out. When buildings cooling is required, the system works the other way around. The tube coming in contact with the thermal storage must be planned to be long enough to allow for adequate thermal energy exchange. The lighting is treated here as a separate topic According to John Hait, 50-60 meters is a good because it is the most important physiological length. criterion when designing underground structures [Fig.3.2.1]. If lighting conditions in such a space are inadequate, the space is most likely to be unsuccessful and have low user satisfaction. This is due to the negative associations with death and burial that humans tend to have with the underground. Also, fear of structural collapse, fear of being trapped in a fire or fear of flooding bring feelings of claustrophobia. Nevertheless, it is possible to make underground spaces feel pleasant and disassociate them from the issues referred above. Therefore, some principles have been collected and generated to guide a designer to a good result.

First are presented some design principles and tricks about lighting. In general, natural light and views to the outside must be provided as much as possible. Ideally more than one natural light sources should be provided for each space [Fig.3.2.2]. Glass partitions between spaces can aid Another important consideration in earth to that end, letting light in one room from the one sheltered and underground building construction is next to it [Fig.3.2.3]. Large atrium spaces can be humidity. Humidity will accumulate during very good means in letting light in spaces summer in such spaces due to the fact that they are [Fig.3.2.4]. Beamed daylight systems such as light kept cooler. The warm humid outside air will tubes and optical fibre systems are a good condensate in the rooms and against the cooled by alternative solution to direct natural light the soil walls [Fig.3.1.10]. This issue can easily be [Fig.3.2.5]. When that is not possible, it is solved by providing good ventilation in the spaces. interesting to note that the spectral composition of artificial light plays an important role and is better if it replicates the composition of daylight. In this way, artificial light seems more natural [Fig.3.2.6]. As a design guide, narrow and dark corridors and especially stairways should be avoided, as they greatly enhance the negative feelings mentioned above [Fig.3.2.7]. In order to maximize the light from the outside that reaches the interior it is sometimes fit to have the surfaces on the exterior of the opening covered with a reflective material [Fig.3.2.8]. Mostly bright coloured surfaces, but also water act well in increasing the amount of light that bounces off [Fig.3.2.9]. Increased light From a construction point of view, these are the reflection within a space can also be achieved by most important and most common issues the use of curved surfaces and especially domed encountered when using this technique. As it is not ceilings, which can magnify reflection up to 3 very widely used and still considered times that of a flat ceiling8 [Fig.3.2.10]. unconventional, innovation and improvements are likely and anticipated.

8 Earth Sheltered : Myths and frequently asked questions 5

Several methods are available for predicting the Three simple rules of thumb can be followed in light levels in a space, both by specialised order to determine the limiting depth of a space - computer software and by hand calculations, by the that is the maximum depth that will be lit use of a dot diagram. While on a clear day the adequately for a given opening. These are outdoor iluminance levels are around 10000lux, explained better with some diagrams [Fig.3.2.11, with an overcast sky they are around 1000lux, 3.2.12, 3.2.13] where it is clearly shown that the typical requirements for residential spaces are limiting depth depends on the floor to window 150lux, while for office spaces, depending on the height, the reflectivity of the floor surface, the kind of work, they range from 250 to 500lux. angle the nearest obstacle on the outside makes Besides the light levels, there is another factor that with the opening, as well as the width of a space. needs to be considered when designing for lighting, Ideally, the smallest result of the three methods which is daylight uniformity. should be taken to determine a maximum depth.

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3.3 Earth berm sound barriers & Acoustic properties of soil

Two basic types of sound barriers are in common use along highways: sound walls and earth berms. They each have their advantages and disadvantages and one or the other is more appropriate for different road cases. This paper looks at earth berms only, as they fit in the research topic. Using earth for sound protection is a straightforward technique, where soil (that is usually available excess near the site) is piled in order to form a long hill that will act as a barrier for the sound waves.

A motorway with regular traffic of four lanes on each direction will typically produce around 80dB sound pollution. The maximum acceptable sound levels for an office space are 35dB, for a house living room 50dB and for a bedroom 30dB. It is clear that an effective sound barrier is required if the areas proximal to such a motorway are to be Regardless of the actual light levels in a space, usable. there is also the other aspect of windows that renders them essential: views. In general, there is a Some basic principles about sound attenuation need of the users of any space to connect with the must be established before examining more outside world and lack of an exterior view can be a detailed aspects of earth berm sound barriers. great reason for user dissatisfaction [Fig.3.2.14]. Firstly, the intensity of sound is reduced with Interestingly, studies have shown that people in distance; that is the distance sound must travel work environments are more likely to favour view between the source of the sound and the receiver of over direct sunlight, especially if no sunshading is the sound [Fig.3.3.1]. It is also reduced when it available, and the other way around for people in passes through a material and the greater the residential environments [Fig.3.2.15]. In the case density of that material, the greater the attenuation where it is not possible to provide views to the [Fig.3.3.2]. Buildings themselves can also act as outside, a good alternative is to plan for interior sound barriers and a building that is closer to a courtyards with dense vegetation which can act as a sound source is referred to as a more noise substitute view [Fig.3.2.16]. sensitive building, while the ones further are less noise sensitive [Fig.3.3.3]. Unlike light waves, sound waves have long wavelengths which cause them to be highly diffracted around objects [Fig.3.3.4]. Light does not bend around corners, it creates sharp shadows. The area protected from a sound is called an acoustic shadow zone, but acoustic shadows are much less sharp than light shadows [Fig.3.3.5]. This should be considered when looking at the section of a barrier, but also in plan. Sound barriers must extend well beyond the area that needs to be protected, typically 4 times the distance of receiver to barrier.[9] Discontinuous barriers will have very little effect. Besides the actual sound attenuation achieved by a sound barrier, there is also the perceived sound attenuation. This relates with psycho-acoustical effects and is explained by the fact that if a receiver (a person) cannot see the source of the sound, he/she is less bothered by it [Fig.3.3.6].

9 Noise Barrier Design Handbook: Acoustical Considerations 7

to consider are the reflected noise that could affect high areas on the other side of the road [Fig.3.3.9], and the difficulty of growing vegetation on very steep slopes. On the side of the receiver, the slope does not influence the performance of the berm. It is usually made to follow the local landscape, or decided according to space availability. Considerations such as planting or even agriculture (how steep a slope the machinery can cope with) can also be determining. The curvature of a berm plays an important role in its performance. The choice between smooth curves or sharp edges is straightforward. As mentioned before, sound waves have long wavelengths and are highly diffracted around objects. Soft, round edges encourage this diffraction, while sharp corners minimize it [Fig.3.3.10]. Sometimes a sharp small wall is added on top of a berm to improve its performance. Multiple edged barrier tops are also available that can increase even more the attenuation [Fig.3.3.11]. One more disadvantage of round edges is that they facilitate the propagation of surface waves that are created upon impact of the principle sound waves directly from the source with the surface of the berm [Fig.3.3.12].

It is difficult to define a simple mathematical equation for the best geometry of earth berms, as their performance depends on many different factors. Their slope, height, width, curvature and distance from source are only some of the geometric factors that influence their performance. Some rules about the geometric composition are hereby presented. For any sound barrier, it is more effective the closer it is to the sound source. For earth berms of trapezoidal section, this stands for their top part. Clearly, this top part can never be as close to the source as a completely vertical wall could. In this respect, the slope facing the source (the road) is more effective when steeper. As shown in the diagrams, the closer the barrier to the source and the steeper the slope, more sound waves are blocked and the greater the shadow zone [Fig.3.3.7 & 3.3.8]. It is needless to say that the higher the berm the greater the sound protection. This is true also for the berm’s width, as it necessarily makes the distance between the source and the receiver greater. The steepness of the two slopes of a berm can be different. On the side of the source, as already mentioned, steeper slopes bring the barrier closer to the source. Some other things

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Having explained these geometrical concerns, it should be clear that deciding on the shape of a berm is not a simple task, but some things are preferred. In order to determine the sound attenuation achieved by a barrier, two paths can be followed: mathematical calculations and software simulations. The path difference method is a simple way to quickly make such calculations. The path difference is derived from the difference between the total distance that sound has to travel from source to receiver and the direct line from source to receiver [Fig.3.3.13]. The path difference can then There is a lot of research on the effect of give the Fresnel Number, which in its turn gives vegetation on sound attenuation. Counter to the Insertion Loss, meaning the magnitude of sound popular belief, vegetation does not form a good attenuation [see Appendix B]. A sound barrier will sound barrier, unless it is very dense and thick. not perform well, regardless of its geometry, if its Vegetation can reduce sound in 3 ways: material is not thick enough to stop sound from passing through. For an earth berm of the typical dimensions this goes without saying. However, it is  scattering. Sound can be reflected and necessary to prove it scientifically and not rely on scattered by plant elements (trunks, what is considered common knowledge. In branches, leaves) Note: this can also lead Appendix C it is shown that a very thin layer of to downward scattering, only close to the solid soil (4.5cm) would already achieve adequate vegetation and below tree crowns sound attenuation.  absorption. The mechanical vibrations of the plant elements caused by the sound waves convert sound energy into heat.

 destructive interference of sound waves. Vegetation creates a very acoustically soft soil by the presence of dead matter and the roots, which can lead to constructive interference between the direct sound coming from the source ad a ground reflected contribution.

Some further considerations should be mentioned The effect of vegetation on sound reduction about the design of earth berms. The surface depends principally on the height, width and material is of great importance. If the surface cover density of the belt of trees [Fig.3.3.16]. This can be is acoustically hard, then the insertion loss can be quantified as follows: 5dB reduction per 30m deep simply measured solely according to the geometry. forest for at least 5m tall densely planted trees. This If the surface cover however is acoustically soft, it can reach up to 10dB with a taller and wider belt of means that sound is also being absorbed by the trees. While the actual effect might not be so surfaces, and therefore some excess noise significant, trees can have the effect of the attenuation is present (also called “ground effect”). perceived noise reduction mentioned earlier: by A sound absorptive surface will prevent reflections removing traffic from view, many of the traffic and eliminate surface waves. The acoustic induced negative effects are reduced. If not absorption of the berm can further increase sound carefully planned, vegetation can have a negative attenuation by up to approximately 4-5dB effect. Where vegetation overtops a barrier, it will [10] compared to grassland [Fig.3.3.14]. Research scatter the sound back down behind the barrier, has shown that the best performing surface cover is reducing its overall effectiveness. Therefore, what is called “forest floor”. Forest floor is the planting on a berm side is acceptable, but surface that develops under a forest, where dead vegetation must not grow to higher than the top of leaves and branches are decomposing on the soil the berm [Fig.3.3.17]. A different effect that trees making up a highly sound absorptive, porous layer. can have has to do with the wind. Wind can Grass cover does not perform as well as forest floor transport sound waves down into the shadow zone but better than plain soil. In this respect, the width and thus greatly reduce the barrier’s effect of the berm, and especially of its flat top, gains [Fig.3.3.18]. Because of their more aerodynamic greater importance. The greater the width of a shape, noise berms are quite resistant to these sound absorptive berm, the greater the sound negative downwind effects and with decreasing absorption [Fig.3.3.15]. internal slope angle, wind refraction effects nearly disappear. Moreover, a row of trees behind a noise 10 On the choice between walls and berms for road traffic noise barrier can act as a windbreak, reducing this shielding including wind effects, p. 204 negative effect [Fig.3.3.19]. 9

water can flow through. The composition of a green roof, with its layers and various substrates will not be further explained here, as it can vary with every case and is information easily found.[11]

3.4 Green over earth sheltered buildings

One big advantage of the earth sheltering technique is that a building can be made to blend into the Planting on a slope is different than planting on surrounding landscape. Earth sheltered buildings horizontal ground. One big difference is how the consist of two layers: the building layer and the water flows and settles within a berm. It is very landscape layer over it. This allows for more likely that puddling will occur around a berm when efficient land use, where the roof of the building water runs down the slope. In order to avoid this, can be used as a garden, for food production, for good drainage should be planned at the base of the recreation, for producing energy or for almost any berms [Fig.3.4.4]. The water falling on the berms is use a green area could have [Fig.3.4.1]. also not absorbed uniformly by the soil. The soil at the top of the berm is in risk of being dry and the Earth sheltering is not the same as a typical green soil at the bottom too moist. Since water will tend roof. It could be compared to an intensive green to drain off the top of the berm more quickly, roof, or a “super-intensive” green roof, because the plants that are more tolerant of drier conditions way it works is not by merely adding a substitute should be planted towards the top of the berm. medium where vegetation could grow, but really Slopes that are steeper than 1:3 may not retain recreating the top layer of the earth’s surface and water adequately for plant growth [Fig.3.4.5]. the natural conditions that plants prefer. Again, different vegetation has different Nevertheless, it is still not exactly the same as requirements. A slope of 1:3 may be the maximum natural ground, since it is always over a building. for low plants and shrubs, but for trees it is [12] The kind of vegetation that is intended for an earth suggested not to exceed 1:5 - 1:7 [Fig.3.4.6]. If sheltered roof will determine the depth of the soil steeper slopes than that are preferred, there are cover required. Typically, grass and flowers grow some solutions that allow successful planting. One their roots 6-20cm deep. Shrubs and medium height would be to turn the slope into a stepped slope vegetation need about 30-40cm and in order to [Fig.3.4.7]. In this solution, the bigger the steps, the grow trees, at least 1m of soil is required greater the water retention. Moreover, there are [Fig.3.4.2]. In order to make sure that the roots of several retention techniques available in the the vegetation do not reach deeper than planned, market, with retention modules or boxes that damaging the construction, a root protection layer compose a whole slope by smaller parts [Fig.3.4.8]. should be placed between the growing medium and 11 the construction [Fig.3.4.3]. This is usually a The International Green Roof Association is a good source for this kind of information. [http://www.igra-world.com] densely woven fabric that roots cannot puncture but 12 Building Soil Berms 10

One of the greatest advantages when building with soil is that is brings low cost thermal inertia to the design. Soil has a high thermal mass, meaning that it retains its temperature for longer. Daily and seasonal temperature fluctuation varies with depth and deep enough temperature becomes constant. At 30cm below ground, the daily fluctuation is reduced to a maximum of 5oC. At 1m below ground, the average monthly temperature may be considered as constant, and at 10m below ground, the yearly average temperature is constant. In the Netherlands this is around 10-11oC[14] [Fig3.5.2].

Fig.3.5.2

In this way, the soil can provide passive radiative cooling or heating depending on the season, even in small depths and thickness [Fig.3.5.3]. As a result, the yearly temperature fluctuation of the interior of an earth sheltered building is lower than that of the outside air, meaning that it will never reach the 3.5 Thermal properties of soil & Heat storage in maximum and minimum extremes that the the soil. environment around it will and that it remains to a much more constant temperature all year around [Fig.3.5.4].

Soil is a poor insulator compared to modern insulating materials such as expanded polystyrene, but it has some R-value, which with increased thickness becomes non negligible. The U-value of one meter depth of soil can range between 0.6 – 4 W/m2K for saturated soil, and between 0.15 – 2 W/m2K for soil containing organic matter. Therefore, a layer of soil around a building reduces the thermal energy exchange between building and its surroundings [Fig.3.5.1]. “The R value of soil is proportional to many things, including the distance the energy must travel through the soil, the moisture content, density, soil type, etc.”[13] According to these figures, in order to achieve passive house standards only by soil insulation, the thickness of the layer required would range between 1m (for the best conductivity (k value) of soil containing organic matter) to 13m (for the worst k value of soil containing organic matter).

13 Earth Sheltered Umbrella Basics 14 Kristinsson, J. 11

As most earth sheltered buildings will not be buried The thermal energy storage principle that can be under 10 meters of soil, the temperature in them is applied in a building scale as just explained, can not completely constant, and does change with the also be applied at a larger scale underground, in seasons. However, the retardation of the interior order to achieve inter-seasonal thermal storage temperature is a phenomenon that is experienced [Fig.3.5.8]. Heat available naturally during summer [Fig.3.5.5]. For example, when the maximum time is stored in the ground for use in the winter, temperature of 32oC in the Netherlands occurs in while cold available naturally during winter time is mid-July, inside an earth sheltered building the stored for use in the summer. The “heat” and maximum temperature, which will be much lower “cold” are stored in the form of hot or cold water than 32oC, might be experienced in August. The which is usually stored in an . An aquifer, temperature retardation time depends on the simply explained, is a layer of water permeable thickness of the soil layer. This effect can be material in the ground (such as sand) in between exploited to work in a beneficial way. In a case two layers of material with low water permeability where the soil layer thickness has been calculated (such as ) called aquatards [Fig.3.5.9]. as such to retard the minimum temperature for two are widely available in the ground of the months, if the minimum outside temperatures occur Netherlands and make a good thermal storage in February then the minimum inside temperature medium because water has very high specific heat will occur in April, when the outside temperature is capacity (thermal mass). The warm and cold already getting higher. Even more, the minimum created for inter-seasonal thermal storage in an can be shifted to occur in summer time. This is a aquifer are located between 100-500m below earth result of the thermal energy storage that occurs surface. Such thermal energy storage systems within the soil mass. Solar design is usually paired usually function together with a solar thermal with earth shelters, to exploit the thermal mass of system for the hot/cold water collection and are the soil. The soil can act as a thermal battery. usually combined with low temperature heating and Charged in the summer by the solar energy, the cooling systems, such as under-floor systems. heat is stored for passive use in the winter. It is Moreover, they are combined with a ground source imperative to optimize the thermal mass, space heat pump system (GSHP). The temperature of the volume and glazing ratio, in order to make such a water in the wells does not stay the same over the design successful [Fig.3.5.6]. The are a months that it is stored and cannot be used directly good example that uses exactly those principles to for space heating. The GSHP changes that stored create buildings that do not require any active temperature to a usable level, using electric power. thermal conditioning [Fig.3.5.7] [15]. Another type The reason why this is desirable and a good of thermal energy storage is with phase changing sustainable measure is that the GSHP consumes materials. A lot of advancement in this field is much less electricity to raise the temperature of currently happening, but it will not be further water to 40oC from 25oC than from 5oC (which explained here, as it is out of the scope of this would be the outside water temperature in winter) paper. and the same goes for summer cooling. As the GSHP works with electricity, it is common to pair it with sustainable electricity producing technology, commonly Photovoltaic cells.

15 Biotecture 12

Before deciding on the active heating and cooling strategies for a building, one must first optimize the passive strategies, which will reduce the demand of active measures. When it comes to passive heating the principle actor is the sun. Of the total solar radiation that leaves the sun, 20% of it is absorbed by the atmosphere, 31% is reflected back to space from the earth’s surface, and the rest, 49%, is absorbed by the earth’s surface [Fig.3.5.11]. This last percentage is not absorbed uniformly from all surfaces that cover the earth. Absorption will depend on the material, solar exposure, water contact and other factors. When it comes to soil, several factors should be considered. Grass covering the soil will shade the surface below it, causing less solar heating [Fig.3.5.12]. It will also entrap a thin insulating layer of air that keeps its temperature more steady [Fig.3.5.13]. Moreover, the moisture released by the vegetation will eliminate solar gains even more [Fig.3.5.14]. More greenery will increase the evaporation rate, but as this evaporation rate happens away from the ground, it has no direct effect to the energy balance at the surface [Fig.3.5.15]. Another type of cover, snow, will also change the temperature of the soil beneath it, by providing an additional insulating layer in winter time [Fig.3.5.16]. Soil can also lose or gain heat when it comes in contact with water of different temperature. If warmer or colder rain drops on the soil it will respectively raise or lower its temperature [Fig.3.5.17]. However, this only affects the first few centimetres up to a meter of soil depth. One more way that soil changes temperature by coming in contact with water is during phase changes. Water will absorb or release heat when it evaporates or freezes, transporting this temperature to the soil [Fig.3.5.18]. These two effects can be used to influence the heat flux in the soil, by using programmed irrigation [Fig.3.5.19]. In midday summer, irrigation can cool the top layers of soil through evaporation and warm the lower ones by the warmed water infiltrating. Inversely, on a summer early morning or night, irrigation will cool the lower layers of soil. One more way in which water influences heat flux in soil is by changing its properties. Higher water content will increase its thermal conductivity but also its heat capacity [Fig.3.5.20].

13

One of the numerous designs Malcolm Wells has realised is his own architectural office. The earth sheltered design is responsible for energy savings and constant interior temperatures, but also of acoustic insulation. With a road with truck traffic only 6 meters away, the house is surprisingly quiet. The open courtyard is also quiet, while in the innermost rooms there is absolute silence.

Fig.3.6.2 The courtyard seen between the fully vegetated roof.

Villa Vals

3.6 Case studies

Architects such as Malcolm Wells and William Morgan are pioneers in earth sheltered design and have put on the map many such buildings.

Malcolm Wells’ Office Fig.3.6.3 Limited presence in the landscape.

This modern villa in Switzerland by SeARCH & CMA, was not perceived as a typical structure but rather as an example of pragmatic unobtrusive development in a sensitive location. The villa is fully embedded in the landscape, being conceived as a circular cut made in the mountain slope. The presence of the villa in the landscape is thus limited to minimum. Fig.3.6.1 The section of the office shows the amount of earth on top of the building.

14

Terraset Elementary School Erdhaussiedlung Lättenstrasse

Fig.3.6.4 The earth shelter during final construction stages. Fig.3.6.6 The housing complex disguised under the green layer.

Built in Switzerland, this complex of nine earth covered houses is grouped around a closed oval The Terraset School, meaning "set in the Earth," centre pond. The architect’s attitude is that “what was built in 1977 in Northern Virginia during an you take from nature you must give back”, so they era dominated by an energy crisis. The whole work with the principle that no land leaves the site school was set on a hill. The top of the hill was – it goes on top again. There, sitting areas, shaved, the school was built and the soil was placed playground areas even vegetable gardens are back over it. The earth cover provides natural created. Inside the houses, the living areas are insulation and the high thermal mass achieved located to the South and sleeping areas to the together with the school's depressed floor slab was North. In the middle are the bathrooms and stairs to expected to eliminate the effect of outside the . In this way, natural light is provided temperatures. “The design of the school has where it is most needed. The bathrooms are provided insulation that saved thousands of barrels connected to the outside through skylights. The of oil” [16]. The planted roof resembles a complete construction is earth covered sprayed concrete. The meadow, with trees and skylight structures. water barrier layer is applied directly on the concrete layer, with the insulation over it. The final layer is the excavated material, functioning as a protective layer where grass and flowers can grow. The thermal mass of the earth layer is responsible for great energy savings. According to the architect, in wintertime the houses use only 1/3 of the energy a comparable conventional house would, while in summertime no space conditioning is required, as the houses are kept cool naturally.

Fig.3.6.5 The roof fully grown is indistinguishable from a meadow.

16 History of Terraset 15

4. Conclusion & Discussion would be to take some time to fully understand to a good level at least the basics of all the separate aspects of the case they are approaching, whether these fall into the five categories identified in this paper or they go even further. Only in this way will As a conclusion from this research it is clear that a it be possible to achieve a successful integration merging of landscape and building in an and reach a working multifunctional result. I environment surrounding a busy highway is possible by making smart design of earthen sound myself am also currently exploring the topic from a barriers. However, this is a design process that design point of view and this paper is my guide for a complete result. requires a lot of information on different topics to be taken into account. The aim of this paper was to investigate the In terms of the construction process the basics are potential merging of building and landscape in a established. Reinforced concrete construction is the highway proximal environment, by making smart use of earthen noise barriers and with the technique most suited and the way insulation will be applied of earth sheltering. Having examined the different depends on the amount of thermal mass that will be aspects that such a question includes, it is fair to included in the design. From the point of view of say that – although not an easy task – such lighting, the principles are not much different from conventional building, but it should be given integration would be possible and could have very special attention in order to make the building feel positive effects of the dense urban environment of present cities. pleasant and not bring the negative aspects usually associated with underground space. Visual connection with the outside world and natural light sources are crucial points. The function of sound barriers has several aspects to it. The shape, surface References cover and surrounding vegetation all play a role in the performance of the earth berms and the sound Principle references reduction that is achieved. It is possible to achieve the desired sound reduction in a highway [1] Anselm, A. J.; Passive annual heat storage environment with the use of earthen sound barriers. principles in earth sheltered housing, a They are a good solution when the visual impact is supplementary energy saving system in residential important and they have some additional benefits housing; Huazhong University of Science and Technology; China; 2007 over sound walls, mainly the fact that they are not [2] Barker, M. B.; Using the Earth to Save Energy: Four mono-functional. The matter of planting and Underground Buildings; Tunnelling and greening the surface over earth sheltered buildings Underground Space Technology, Vol. 1, No. 1, pp. can be viewed as super-intensive green roofs. Some 59-65, Great Britain, 1986 [3] Bartz, J.; Post-Occupancy Evaluation of Residents of aspects of green roofs apply, but in general, it is Single- and Multi-Family Earth-Sheltered Housing; possible to achieve full scale vegetation, keeping in Tunnelling and Underground Space Technology, mind the differences from a regular garden: the Vol. 1, No. 1, pp. 71-88, Great Britain, 1986 slope and depth of soil. Finally, concerning the [4] Bosch, J. W.; An Underground Bus Terminal for Amsterdam: Construction Issues; Tunnelling and thermal properties of building with soil, several Underground Space Technology, Vol. 8, No. 1, pp. aspects of the material can be exploited to work 19-24, Great Britain, 1993 towards a more sustainable, less energy consuming [5] Carmody, J. C., Sterling, R. L.; Design strategies to building. Passive measures, using the high thermal alleviate negative psychological and physiological effects in underground space; Tunnelling and mass of soil, can help reduce the energy demand of Underground Space Technology, Vol. 2, No. 1, pp. such a construction, and active measures can aid to 59-67, Great Britain, 1987 make the active conditioning of space more [6] Design for Environmental Barriers; Design Manual efficient. for Roads and Bridges; Vol. 10; Section 5; Part 1; 2001 [7] Dinçer, I.; Rosen, M. A., Thermal Energy Storage, The references studied show different aspects of Wiley, United Kingdom, 2002 the problem, and different solutions to the topics. [8] Eckert, E. R. G., Bligh, T. P., Pfender, E.; Energy exchange between earth-sheltered structures and the Some other things that are also demonstrated surrounding ground; University of Minnesota; through the references are, among others, the likely Minneapolis; 1978 visual appearance, scale, amount of coverage, [9] Edelenbos, J., Monnikhof, R., Haasnoot, J., Hoeven, different organisational options and kind of van der, F., Horvat, E., Krogt, van der, R.; Strategic Study on the Utilization of Underground Space in the vegetation. Netherlands; Tunnelling and Underground Space Technology, Vol. 13, No. 2, pp. 159-165, Great After having researched deep in the topic of this Britain, 1998 [10] Environmental Barriers: Technical Requirements; paper, some personal advice I can offer to any Design Manual for Roads and Bridges; Vol. 10; designer who might be dealing with a similar topic Section 5; Part 2; 2001

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[11] Garre, S., Meeus, S., Gulinck, H.; The dual role of [http://www.gsd.harvard.edu/research/gsdsquare/Pub roads in the visual landscape: A case-study in the lications/DiffuseDaylightingDesignSequenceTutorial area around Mechelen (Belgium); Katholieke .pdf] Univesiteit Leuven, Belgium, 2009 [12] Givoni, B., Katz, L.; Earth Temperatures and Underground Buildings; Energy and Buildings, 8; Online Sources 1985; (p15-25) [13] Grindley, P. C., Hutchinson, M.; The thermal [1] Architect of the invisible, behaviours of an Earthship; Cranfield University, [www.subsurfacebuildings.com/ArchitectoftheInvisi United Kigdom, 1996 ble] Accessed on: 12.01.14 [14] Hasegawa, F., Yoshino, H., Matsumoto, S.; Optimum [2] The Underground Terraset School In Reston, Justin Use of Solar Energy Techniques in a Semi- Thomas, [www.treehugger.com/sustainable-product- Underground House: First-Year Measurement and design/the-underground-terraset-school-in-reston] Computer Analysis; Tunnelling and Underground Accessed on: 12.0.14 Space Technology, Vol. 2, No. 4, pp. 429-435, Great [3] Heat. More Urban Green Keeps the City Cooler Britain, 1987 [www.urbangreenbluegrids.com/social] Accessed on: [15] Hughes, P. C.; The use of simulated natural light in 15.12.13 the design of the earth sheltered environment; [4] Vetsch Architektur; Tunnelling and Underground Space Technology, [www.erdhaus.ch/main.php?fla=y&lang=de&cont=e Vol. 2, No. 1, pp. 73-81, Great Britain, 1987 arthhouse] Accessed on: 12.01.14 [16] Ip, K., Miller, A.; Thermal behaviour of an earth- [5] The social and economic importance of green and sheltered autonomous building – The Brighton blue areas [www.urbangreenbluegrids.com/social] Earthship; University of Brighton; United Kingdom; Accessed on: 15.12.13 2009 [6] Malcolm Wells [www.malcolmwells.com] Accessed [17] Kind-Barkauskas, F.; Creative Aspects of and Uses on: 12.01.14 for Underground Structures – Examples from [7] History of Terraset Germany; Tunnelling and Underground Space [www.fcps.edu/TerrasetES/about/history] Accessed Technology, Vol. 8, No. 1, pp. 25-30, Great Britain, on: 12.01.14 1993 [8] Earth Sheltered Umbrella Basics [18] Kotzen, B; Environmental noise barriers; Taylor and [www.homeintheearth.com/tech_notes/basics-of- Francis; United Kingdom, 2009 earthsheltering/umbrella-basics] Accessed on: [19] Kristinsson, J. (2012), Integrated Sustainable 18.12.13 Design, Delftdigitalpress, Delft [9] Earthship Biotecture [earthship.com] Accessed on: [20] Kumar, R., Sachdeva, S., Kaushik, S. C., Dynamic 11.01.14 earth-contact building: A sustainable low-energy [10] Wikipedia: Earth Sheltering technology; India; 2006 [http://en.wikipedia.org/wiki/Earth_sheltering] [21] Lee, S.W., Shon, J. Y.; The Thermal Environment in Accessed on: 18.11.13 an Earth-Sheltered Home in Korea; Tunnelling and [11] EarthSheltered Homes Underground Space Technology, Vol. 3, No. 4, pp. [http://www.inspirationgreen.com/earth-sheltered- 409-416, Great Britain, 1988 homes.html] Accessed on: 25.11.13 [22] Monnikhof, R. A. H., Edelenbos, J., Hoeven, van [12] Earth Sheltered Homes der, F., Krogt, van der, R. A. A.; The New [http://www.earthshelteredhome.com/] Underground Planning Map of the Netherlands: a [13] Noise Barrier Design Handbook: Noise Barrier Feasibility Study of the Possibilities of the Use of Types; US Department of Transportation; Federal Underground Space; Tunnelling and Underground Highway Administration Space Technology, Vol. 14, No. 3, pp. 341-347, [http://www.fhwa.dot.gov/environment/noise/noise_ Great Britain, 1999 barriers/design_construction/dsign/design04.cfm#sec [23] Moreland, F. L.; The Use of Earth Covered Buildings 4.1.1] Accessed on: 7.11.13 (Alternatives in ); University [14] Noise Barrier Design Handbook: Acoustical Press of the Pacific; 2000 Considerations; US Department of Transportation; [24] Oehler, M.; The 50$ & Up Underground House Federal Highway Administration Book; Mole Publishing Company; New York; 1978 [http://www.fhwa.dot.gov/environment/noise/noise_ [25] Pötz, H; Urban green-blue grids for sustainable and barriers/design_construction/dsign/design04.cfm#sec dynamic cities; Coop for Life; 2012 4.1.1] Accessed on: 7.11.13 [26] Renterghem, van, T., Botteldooren, D., Verheyen, [15] Outdoor Noise Barriers: Design and Applications K.; Road traffic noise shielding by vegetation belts of [http://www.enoisecontrol.com/related_articles/outdo limited depth; Ghent University; Belgium; 2011 or_noise_barrier_wall.pdf] Accessed on: 14.11.13 [27] Renterghem, van, T., Botteldooren, D.; On the choice [16] Introducing Acoustifence between walls and berms for road traffic noise [http://www.acoustiblok.com/acoustical_fence.php] shielding including wind effects; Ghent University; Accessed on: 2.12.13 Belgium; 2011 [17] Noise Barriers in Wind [28] Report on Underground Solutions for Urban [http://users.ugent.be/~tvrenter/GeluidsschermenEN. Problems; ITA Working Group, ITA Report No11; htm] Accessed on:6.12.13 April 2012 [18] Home in the Earth [29] Sobotka, P., Yoshino, H., Matsumoto, S. I.; Thermal [http://www.homeintheearth.com/] Accessed on: Comfort in Passive Solar Earth Integrated Rooms; 26.10.13 Building and Environment, Vol. 31, No. 2, pp. 155- [19] http://terrasierra.weebly.com/index.html Accessed 166, Great Britain, 1996 on: 22.11.13 [30] Wade, H. Building Underground – The Design and [20] Building Soil Berms Construction Handbook for Earth-Sheltered Houses, [http://www.sustland.umn.edu/implement/soil_berms Radale Press, Emmaus, Pa., 1983 .html] Accessed on: 7.12.13 [31] Wade, H.; Cook, J.; Labs, K.; Selkowitz, S.; Passive [21] Effiient Earth Sheltered Homes Solar: Subdivisions, Windows, Underground; [http://energy.gov/energysaver/articles/efficient- American Solar Energy Society, USA, 1983 earth-sheltered-homes] [32] Otis, T., Reinhart, C.; Daylighting Rules of Thumb; Harvard Graduate School of Design; 2009

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Appendix A – Sound Berm Geometry

The following table is a documentation of an investigation of different earth berm sizes and the resultant insertion loss, as performed through the use of the computer software SoundPlan Essential 3.0. The results are derived considering only the geometrical barrier to sound and for a linear source of 80dB. Each case has four results which represent the resultant sound levels at four receiver heights: 2m, 4m, 6m and 10m. The receiver was taken 10m from the fixed side (source side of the barrier). The variables considered were the height of the berm and the slope of the berm.

The results of the four receiver heights are inserted in the table as shown:

2m 4m 6m 10m

Berm

Slope

1:0.5 1:1 1:2 1:3

Berm

Height (m) 2 70.3 71.2 70.3 71.2 70.3 71.2 70.4 71.2 72 73.4 72 73.4 72 73.4 72 73.4 6 62.2 65.2 66.7 69.8 66.8 70 66.9 70.1 70.2 73.4 70.2 73.4 70.2 73.4 70.2 73.4 10 56.6 58.3 55.9 57.9 56.5 58.8 55.2 57.9 62.2 72.1 62.3 72.7 64.5 73.4 65.2 72.7 14 53.1 54.3 53 54.4 52.5 54.1 50.9 52.9 56.7 64.9 57.3 67.7 58 72 57.7 73.4

The table clearly demonstrates the relation between barrier height and sound attenuation. The steeper slopes in general show better results than the less steep. It can be observed that the higher receiver (10m) is influenced very little by the presence of the barrier and only with the steeper slopes.

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Appendix B – Path Difference Calculation Method.

The path difference is given by:

The Fresnel number is given by:

( )

where

No: Fresnel Number f: sound frequency [550Hz typically for fast motorised traffic] δο: path difference c: speed of sound [343.2 m/s]

When the Fresnel Number has been determined, the following graph can be used to determine the insertion loss.

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Appendix C - Theoretical mass law for oblique incidence

The theoretical mass law is a way to determine the insertion loss achieved when sound passes through a specific medium.

Theoretical mass law for oblique incidence

( )

Where

R: insertion loss f: sound frequency [550Hz typically for fast motorised traffic]

ρ: density of medium considered [1000-1600kg/m3 typically for soil] d: thickness of medium considered cosθ: angle of incidence of sound wave

Solving for a desired insertion loss can give the required medium thickness. Doing so for soil, with an assumed sound source of 80dB, required sound level of 35dB and an angle of incidence of 90o gives:

( )

( )

( )

For the lowest typical soil density, a mere 4.5 centimetres would be enough to reduce sound by 45 decibels.

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