Question

Two small commercial buildings have been constructed at a site underlain by a sandy silt (ML) that has D10 = 0.03 mm. The groundwater table is at a depth of 6 ft. Both buildings have concrete slab-on-grade floors. In Building A, the slab was placed directly onto the natural soils, while Building B has a 4-inch layer of poorly-graded coarse gravel between the slab and the natural soils. Both buildings have vinyl floor coverings similar to those typically used in residential kitchens. Both buildings are now three years old. Unfortunately, the tenant in Building A is having continual problems with the vinyl floors peeling up from the concrete slab. When the peeled sections are examined, moisture is always evident between the vinyl and the concrete. Curiously, the tenant in Building B has had no such problems, even though both buildings have the same floor covering. Could the problem in Building A be due to capillary action in the underlying soil? Explain why or why not. Also explain why Building B is not having any such problems.

Answer 1

Hi there,

Here is the explanation...

Yes, You are right, The problem in building A is due to capillary action of water in the underlying soil.

Capillary action depends mainly upon the soil particle's size. Finer size of soils (silt in our case) promote greater capillary action, allowing more than three meters of vertical capillary action whereas, the Loose coarse gravel size prevents capillary action and also this type of soil do not show any virtuall upward rise.

Vapour of water enters the pores of concrete floors, condensing into water once the vapour reaches adjacent space conditioned with air. This very condensation spoils the lamination of our building's finished floor surfaces and also causes staining and mildew.

The method in which this can be prevented is by sufficiently excavating below finished floor elevation and installing a capillary resistant soil bed which will provide drainage of water beneath floor slabs on grade. The assembly is soil composition and foundation draiange is neccesary to direct water away from building structures and is neccesary for wateeproofing, which is done is building B and is hence capillary resistant where as building A suffers capillarity.

Hope i am clear in my explanation. Please upvote if you like the explanation.