УДК 624.159.5

The modern experience of building on the collapsible soils of the south of Kazakhstan

Brovko I.S., Doctor of Engineering; Baibolov K.S., Candidate of Technical Sciences; Ibragimov K.I., Candidate of Technical Sciences;

Atambayev I., Post graduate student

(M. Auezov South Kazakhstan State University)

Soil conditions of south of Kazakhstan are complex and very diverse. This is primarily due to the prevalence of collapsible loess soils of type I and II according to subsidence, which make up the range from weakly collapsible ones to soils with vividly expressed collapsible properties.

From the point of view of economy the foreign investors find the investment of finances into the construction in the south of Kazakhstan to be attractive. But at the same time, the selected construction sites are often on the most complex in geological aspect areas of urban development.

In this context very typical is the recent example, when the Western construction company "Metro Cash & Carry" was building a multi-functional shopping center in Shymkent. The construction and commissioning of this object must provide the city with food products, to create new jobs and to enrich the market with new imported goods and to promote further qualitative development of trade sphere. In this case the central street of recently built microdistrict "Nursat" has been chosen as the location of the construction site. The largest part of this district is located at 15-20 metres thickness of collapsible loess soils of type II according to the subsidence. The main method of preparing the beds of five-storeyed, more rarely of nine-storeyed buildings of local development is deep seated moistening of the whole subsidence thickness through drainage wells with further compaction of the top 4.5-5 m layer by heavy earth rammers. The degree of dampening in this case was controlled by selection of samples along the depth of the bed, and the reached soil density of the top layer -through the selection of samples by method of the "cutting ring". The greatest difficulty in this method of bed preparation was to create optimum moisture in the soil of backfilling at creating the top layer of compacted soil. In the dry, hot climate it is practically very difficult to create qualitatively a uniformly distributed moisture of the soil in its large massives on the construction site.

The difficulty of achieving optimum moisture in the soil ,compacted by the builders, is compensated by increasing the number of earth rammer strikes on one track i. e. this leads to increased labor intensity and building time. The building time is also influenced by a sufficiently long cycle of moistening, that is why the work only for bed preparation in these soil conditions makes 3-6 months.

At the construction of "Metro" shopping centre the worked methods of funding were immediately rejected because of their long time of implementation. The customers indispensable condition was the building of this object in

3,5 months. As a result, the following version was approved: the foundations of bored piles of great length (25 m) with cutting of the whole subsidence thickness and deepening of low ends into pebble gravel soil for 1,5 -2m. To prevent the development of negative friction forces at possible emergency moistening the field of piles was supplemented by waterproof shield, located in the upper part top of the bed. The work in foundations construction was carried out in the following sequence:

- a waterproof shield with thickness of 1 m was installed on the surface;

- through it a well was bored to produce a bored pile with the length of 25m and

1m in diameter (the size of diameter was specified on the basis of seismicity of the region);

- after the installation of the reinforcing cage, filling the well with concrete and the formation of grills, one more layer of waterproof shield with thickness of 1m was installed. Thus the upper part of the pile bore and grills were covered by the waterproof shield with total thickness of 2 m. The waterproof shield was also necessary, because significant loads on floors (up to 3 t/m2) from the stored wholesale goods are stipulated in the shopping centre building.

Figures 1,2 present photographs of wells boring, and view of the well with compacted soil in upper part of the bed

Fig 1.Work to construct wells for bored piles

Fig 2. View of the well with diameter (1m) and depth (25m) with compacted soil in the upper part of the bed

At the moment of writing the article, the shopping centre ‘Metro’ successfully is maintained for more than one year.