This article was published on Arup Connect as "Ask Arup :. sandy loam Solutions "
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architect Juan Esteban Correa Elejalde him responsible for the design of a getaway off-the-grid to a rural site near Medellín, Colombia.. After completing the initial concept, Correa Elejalde commissioned a study of ground of the earth customer
Unfortunately, the results showed the site to be "roughly d a swimming pool, "he said, the high water table and thick soft ground layers provide little ability to withstand heavy objects above
After seeing. Arup Connect call for questions related to engineering of ArchDaily on, he reached out to see if we could offer any insight.
In Colombia, Correa Elejalde told us, the typical solution for this scenario would be to build a floating slab - a flat concrete layer resting on top of the floor, supported by vertical concrete piles under the outer edges. However, as both overcome the environmental objectives of the customer and exceed the budget available, he wanted to know if Arup could suggest alternatives to investigate.
The risk factors
Arash Erfani, a geotechnical consultant in our San Francisco office, advised him to get a better understanding of several critical risk factors before taking the design further.
first, because the initial geotechnical investigation found the ground to be made of silty sand, the project could be at risk for seismically-induced settlement due to liquefaction . In other words, the soil could essentially turn into jelly during an earthquake, causing the vertical settlement and lateral spreading.
In addition, as the clay the fat has been observed in some locations within the project site, he advised him to check if the expansive clay was a problem on the site. If water penetrates into the clay soil during the rainy season and causes swelling, unwanted movement could occur.
Based solely on the first results of the soil survey, Erfani said he could not recommend one solution over another. He warned, however, that if the liquefaction is an important issue on the site, the floating slab Correa Elejalde had considered would be undesirable.
alternatives
instead, he suggested working with a local geotechnical engineer to investigate two alternatives. The first, known as deep foundation, is to drive long piles into the ground to reach the most stable layers of the earth below.
The latter, known as soil improvement, mitigates the consequences of liquefaction and can take a variety of forms. One, the technique of vibro-replacement stone column, using a heavy vibrating weight to drill deep into the soil and create compacted stone columns supporting the land around them. Another, deep soil mixing, using heavy equipment to mechanically combine the weak soil with cement grout. Different types of grouting - compaction, permeation, deep mixing, chemical, or jet grouting - could also be options
Before choosing one of these solutions, however, said that Erfani it would be critical. to achieve a strong knowledge of the conditions of the subsoil and soil characteristics at the site.
cost, sustainability, feasibility
The two deep foundations and soil has potential drawbacks, however he warned. It may not be possible if the site is at high risk of liquefaction. The former would probably be very expensive, which may be impractical given the limited budget of the project
Framing these approaches in terms of another customer's main concern -. Durability - it should be more information about the specifics of the site, Erfani said.
structural considerations
Armin Masroor, a structural engineer also based in San Francisco, added that the first concepts design Correa Elejalde required further coordination with a local structure of expert such as vertical posts in the existing system would not be sufficient to transfer the lateral force from the floor above the ground.
Next steps
Since speaking with Arup, Correa Elejalde worked with a local engineer to move the design forward.
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