The experience on the collapsible soils of the south of Kazakhstan

Brovko I.S., Doctor of Engineering

(M. Auezov South Kazakhstan State University)

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.

The main sources of soaking and moisture of soil subsidence in the ground - buildings are water leaks from the communications (water, sewage, district heating) and technological devices (tanks, swimming pools, cleaning pads, etc.), precipitation, filtration of water from Channel-irrigators in irrigated areas, changes in aeration at building areas, raising the water table, etc. All these sources of soaking can occur at any time during the construction and operation of buildings.

Depending on the nature, intensity, soaking soil, source size soaking generated forms wetlands, increasing the degree of humidity and other factors in the design of the foundations on collapsible soils should consider the possibility of soaking and rising damp due to:

a) local soaking soil foundation on top, leading to subsidence in a limited area within the top or at least - the whole subsiding strata;

b) intensive soaking soil foundation on top for a long time, resulting in a soil wetting the entire thickness of the subsidence and subsidence as a full manifestation of its own weight of soil, and the loads from the foundation;

c) raising the water table, causing subsidence of the lower soil layers mainly from its own weight;

d) a slow increase in humidity foundation soil subsidence caused by the violation of the natural conditions of the evaporation of ground moisture due to construction and paving of the territory and the gradual accumulation of moisture in the soil infiltration of surface water.

Getting into the loess soil on top of the water spreads and moves in the interior as the top down, and away from sources of moisture to form a wetted zone of the soil. The nature of the formation and size of hydrated area affected by a number of factors, in particular: the shape and size of the source of soaking, the nature lithology column loess soils, their filtration properties, etc.