Water - a pressing problem
Water that reaches the ground in the form of precipitation always finds its own way. Ideally, it will seep away quickly and immediately without building up pressure against a building structure. If, however, it seeps away only slowly it will exert pres-sure on a building as long as precipitation endures. A similar situation applies whene-ver water that has seeped into the ground encounters and easily permeable soil layer through which it pushes towards a building. These two variants occur fairly fre-quently. Things get tough, however, when precipitation water encounters imperme-able ground through which it cannot seep away. In such a case, a building will be per-manently exposed to water pressure.
These three degrees of water exposure cru-cially determine the planning of waterproo-fing, drainage, and protection measures. Therefore, any building project should be based on a careful investigation and evalu-ation of the local ground structure and any other relevant factors such as, for example, the terrain configuration. Depending on local constraints, very dif-ferent volumes of water may be involved. If, for example, a building does not stand on level ground but is built against a slope water may normally be expected to accu-mulate against the building wall at a rate of up to 0.3 l/s · m, as DIN 4095 suggests. This is the minimum volume which the drai-nage layer must be designed to handle if the building is to be safely protected from damage by moisture.
Effective protection from seepage water is essential not only because water will worm its way in, as building experts are aware. When waterproof concrete is made, its quality and thus its impermeability crucially depend on complying exactly with the water-cement ratio specified. Whenever this ratio is changed by intruding water, the concrete will become water-permeable or worse: a water vein may penetrate the enti-re wall, forming a local leak. However, hydrostatic pressure also stresses the waterproofing of a building, threa-tening its functional reliability. Besides, a water column several meter in height exerts great structural strain on a building. This strain becomes particularly critical whenever water pressure is confined to certain circumscribed areas, generating asymmetrical loads. In many cases, effecti-ve drainage may help in this context as it facilitates markedly simplifying the const-ruction of the waterproofing, thus reducing its susceptibility to defects. For these reasons, seepage water should always be drained away across entire sur-faces. In such cases, dimpled and drainage sheets made of plastic have been tried and trusted as compression-resistant seepage layers for many years, one reason why the are so frequently used being that they are easy and inexpensive to install.
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