The article presents information about development of the composition of the mortars which are based on cement and sand-cement with the addition of a superplasticizing admixture for performing well crimping during drill-injection piles creation. The need to develop new compositions of the mortars was opened due to the discovery of some defects in the experimental drill-injection pile shafts which were created by using cement mortar with the addition of liquid glass, after their excavation and examination. These defects (massive soil penetration into the pile shaft near its wellhead and soil and mortar mixing along the perimeter of the piles) are takes place owing the insufficient mortar density, its high shrinkage and low strength. The developed compositions are free of these cons and have increased value of mortar key parameters (density, strength, shrinkage) which is too important during the drill-injection piles creations. After laboratory tests which were done to identify the optimal ratio of mortar components and determine their main parameters, control tests of these solutions were carried out on the investigation site to check the possibility of their use on existing technological equipment. Field tests of the developed mortars confirmed the possibility of their use for drill-injection piles creation. Using the developed compositions of mortars drill-injection piles were successfully performed for the foundation strengthening on some objects in Tyumen.

The paper presents the experience of building and structure strengthening in Tyumen soil conditions which are often presented by a soft water saturated clay and sand layer of the quaternary period. All buildings mentioned in the paper had uneven settlements due to complex engineering and geological conditions and the wrong choice of foundation type. Thin drilled injection piles with a diameter of 200 mm were used for foundation strengthening. All the piles were installed on the solid soil base during the drilling process regardless of the depth of its location. No rules have so far been approved to calculate the bearing capacity of thin drilled injection piles. That was the reason for defining the drilled injection pile bearing capacity at every facility. The paper describes the methods and test results obtained in the study. It was found out that all piles had unexpectedly high bearing capacity. The paper also contains the results of geotechnical monitoring before and after base building strengthening by drilled injection piles which show the current decrease of settlements and the efficiency of this base strengthening method.

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The article discusses modern methods of strengthening foundations on artificial bases that have received excessive precipitation and rolls. In the course of studies, it was found that the use of bored piles allows transferring the load to the underlying reliable foundation at any depth, and cementing the foundation soil contributes to improving the physical and mechanical characteristics of the backfill soil.

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