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2014SprShotcreteEMag

Briardale Gardens By John Anderson Wcontinues to grow. The most recent already-dense neighborhood, they knew construc-When homeowners in Hampstead wanted toconstruct a new home with a basement in theith a population of over 8.17 millionpeople, the city of London, England, census, released in 2012, reported a population tion would be a challenge. The proposed basement increase of 12% over the past 10 years.1 This filled the footprint of the restricted site entirely, makes London the fastest-growing city in England. sandwiched between two existing luxury homes Hampstead, part of the Borough of Camden and immediately adjacent to the narrow road. The in Inner London, is known for some of the most local geology, consisting of clays with sandy expensive housing in the city. The village of gravel lenses, gave rise to a very unpredictable Hampstead has more millionaires within its hydrogeology (the distribution and movement of boundaries than any other area of the United groundwater in the soil). This, coupled with the Kingdom. As Hampstead village is located near site being located on a hill, created a unique and many transit hubs, it is known as one of London’s complicated hydrological circumstance. One “Urban Villages.” This, along with the tight thing was certain: the below-grade structure urban growth boundaries in such a desirable would need a permanent waterproofing solution neighborhood, has resulted in clusters of high- for the concrete, which could withstand high density development. hydrostatic pressure. The requirement to achieve the largest possible Tight Spaces internal space, without affecting adjoining homes, With no room to grow outwards, many people considerably limited the techniques that could be outgrowing their current homes have chosen to used both to construct and waterproof the structure. expand downward, creating subterranean extensions The final design also called for an exposed archi- which can sometimes triple the size of the street- tectural concrete finish to the internal face of the level home. perimeter walls. Waterproofing Choices In accordance with the British Structural Waterproofing Association code of practice for protection of below-grade structures against water from the ground (BS 8102),2 when exposed concrete finishes are specified, only Type A or B systems are possible as concrete waterproofing options. Type A is defined as “Tanking Protection” and uses an external barrier system, otherwise known as “Sheet Membranes.” Water resistance is achieved by waterproofing products applied either externally, internally, or sandwiched between two elements of the structure. Type B systems, or “Structurally Integral Protection,” rely entirely on the concrete structure to prevent water ingress. An additive is added to the concrete mixture at the time of batching or on site, and waterproofs the concrete from within. Integral concrete water- proofing systems can be densifiers, water repellents, After a unique piling system was developed and implemented for this or crystalline admixtures. project, shotcrete containing KIM crystalline waterproofing admixture One major drawback to the Type A system in was applied to the slab and walls of the basement (Photo courtesy of Abbey this instance was that these types of systems Pynford—Basement Engineering Specialists) require significant space around the perimeter for 12 Shotcrete • Spring 2014


2014SprShotcreteEMag
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