ÓÄÊ 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.