Application of the impact-free piling technique during construction of exhibition pavilion «Expocenter» in narrow urban environment in Moscow
The evaluation of the ultimate load capacity and settlements of the piles, made by the impact-free technique in the narrow urban places is of vital importance. These kinds of piles involve first of all precast piles, driven down by static force (DDSF), bored piles and micropiles.
DDSF piles are recognized to have apparent advantages as compared to other piles:
- no problems with impacts, vibrations, noise;
- possibility to control the load capacity of the pile during it’s indentation ;
- absence of the additional technological settlements of near-by structures during the piling.
Contrary to the vast experience and publications on bearing capacity of bored piles and micropiles the data on DDSF piles is limited.
This paper presents the approach to predicting the necessary driving down (indentation) force and the ultimate load capacity of the DDSF piles in the case of one of the Moscow projects.
The construction of a new exhibition pavilion №8 was carried out on the territory of the operating exhibition complex «Expocenter» in Krasnopresnenskaya embankment in Moscow, as an addition between existing pavilions №№6,7 immediately adjacent to them. The metal frameworks of the existing pavilions №№6,7 were erected in 1970-1980s, rest on the pile foundations, driven by impact.
The new pavilion width is 36 m, lenghth-246 m, vertical loads on the columns-2,4-2,80 MN. Additional settlements of the existing pavilions, caused by new construction were not to exceed 10mm.
Geological stratum under the most part of the new pavilion (150 m) is non-homogeneous and includes the hard cracked limestone, underlying layer of the saturated filled weak soil 3,5-9m deep. Under the rest part of the pavilion (80 m) lime stone was not found ,and here weak saturated fill soils and layers of sandy clays occur at the depth of 13-15 m, overlying the coarse sand.
According to geological strata, under the most part (150 m) of the new pavilion 812 bored end-bearing piles 6,б-10,5 m long 0,32 m in diameter with expected 750 kN of ultimate load capacity each were designed. Under the rest length (80 m) of the pavilion 400 common precast,30x30 cm in cross-section,12 m long, friction piles (DDSF) were designed. The expected ultimate load capacity of each pile was 370 kN. Driving of the precast piles was performed by static indentation with the special pile-driving machine capable to reach the indentation force of 640-720 kN.
Bored end-bearing piles were done according to common practice and field test results show close agreement with expected values.
The indenting driving down force of DDSF piles reached 560-640 kN and according to field pile-test results and in-situ piezo-cone penetration tests (CPTU) the ultimate load capacity of DDSF piles ran into 600-720 kN.
The increase of the load capacity by 1,5-2 times, as compared to the calculated one, can be explained by the development of an additional component of the base resistance of the indented DDSF piles, caused by elastoplastic axisymmetric expanding of the surrounding soil with due account of hardening.
The design of the DDSF piles according to the suggested method and performed field pile tests showed the ultimate load capacity up to 600-720 kN, which made it possible to reduce the number of piles to 186 as compared to 400 originally designed.
Suggested method of prediction of driving down (indentation) force and ultimate load capacity of DDSF piles is expedient to apply to other projects.