Compression of Foundations Soils as a Way of Decreasing of Their Sinking and Expenses on Foundations and Substructure Works

The slab and pile foundations are mostly spread in modern building practice. Slab-pile foundations, where a slight part of the load is given to a slab, start to have some place, but actually they remain pile foundations.

Preliminary compression of foundations soils by any loadings, which are comparable to foundation loads, could significantly expand the sphere of application of both non-pile and pileslab foundations. Nevertheless, they extremely seldom use compression of soils while constructing foundations. As a rule, as a preparation of a base they use manual scraping of the bottom of the foundation pit and roadmetal and concrete preparation. Under the circumstances they keep the top decompressed or loosened layer of soil, which cause primary technological sinking.

Different ways of surface compression of soils of the foundation by a calender or heavy rammers are widely known. Compression of soils by calenders is actively used in road building, but extremely seldom in construction of foundations. The usage of calenders is useful for compression of the top loosened layer of soil, but because of the slight pressure which they make on the soil their application is not efficient for the common decrease of sinking of buildings. Heavy rammers are used mainly at the newly built territories to compress sinking soils.

Within the last 10 years modern pile squeezable devices which can produce squeezable power of 70–320 tf and more have become widely used. If we use an impermeable slab of 2–5 sq. m instead of a pile, we can get a significant impermeable load on the soil at the level of the foundation pit which is comparable to the load from the constructed building or exceeds it. While having big loads they apply impermeable static loading stepwise in order not to cause fractures in the soil. In calculations of sinking we need to take into consideration the fact that because of big sizes the depth of compressible thickness under an impermeable slab at the equal pressure will be less than under a foundation slab or a separate foundation of bigger sizes.

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Text: Iosif Ladyzhenskiy, Ph.D. in Engineering Science;
Alexey Sergienko, Chief Engineer of Research,
Planning & Survey and Design Technological
Institute of Foundations and Underground Structures (NIIOSP) n.a. N.M. Gersevanov