2480
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Fig.4 Types of foundation strengthening with jet grouted piles (technical decision)
by results of pile test at site and monitoring of post foundations
settlement (tables 2, 4). While analysis of the number of jet
grouted piles, the total load was taken to be transferred to those
piles, so the coefficient of subgrade reaction of the foundation
base under strengthening was taken to be equal 0.
When
piled foundations
strengthening with jet grouted piles,
analyses have been carried out for the total design load. Pile
stiffness was determined by data of pile vertical load test of the
driven- and jet grouted piles.
The authors of the paper made predictions of the foundation
settlement in axes 1’ 15’, P-S due to foundations load
increments, strengthened with the jet grouted piles after the
construction restart. The deformations are calculated with
regard for the different deformability of the post foundation
base and a pile. The coefficient of subgrade reaction in the post
foundation base (settlement marks M7 and M31 in fig.1) was
determined by results of settlements monitoring (table 2, fig.3a)
and stiffness coefficient of jet grouted piles – by tests data (table
4, fig. 3b). The design scheme is presented in fig.5. By results
of analysis of the base deformation of the most loaded post
foundations strengthened with the jet grouted piles, the
settlements after the construction restart with regard for the total
load were 13,8 and 12 mm, respectively. At present, when the
construction of the shopping center is completed, but the
building is not put into operation, the measured base
deformations of these foundations are 10,5 and 5 mm,
respectively. Such conformity of predicted and measured
deformations confirms the efficiency of the base strengthening
and high accuracy of the analysis methods based on in-place
tests.
Table 4
Test
number
(table
3)
Pile
(JGP)
length, m
Pile (JGP)
length in
soil, m
Pile
settlement
according
to test, mm
Stiffness ratio
of pile (JGP)
base, kN/m
1
10,6
10
13
50000
2
10,88
10,58
11
60000
3
11,50
11,10
10,35
60000
Fig.5. Design diagram of foundation strengthening
(strengthening types 1 and 4)
5 CONCLUSION
1. The complicated practical geotechnical problem of
strengthening of the skeleton building foundations under
construction, the necessity of which was provoked by change
of space-planning decision in the process of construction is
solved.
Within one 500x250 m building, four types of foundations have
been designed: post foundations on the bed without karst
protection; strip foundations on the bed designed for 7 m
diameter karst hole; piled foundations in kind of pile groups of
driven piles without karst protection and pile group foundations
combined with karst protected reinforced concrete strips on
piles.
2. Four types of foundations strengthening has been developed
with the use of jet grouted piles taking into attention loads
increase compared to design, acting (already imposed) loads
and foundations settlements at the moment of their
strengthening, structural concepts of foundations and the extent
of karst risk of the base.
3. Analysis of strengthening constructions and base
deformations was carried out according to data of jet grouted
piles vertical load test and settlements measurements of the
foundations under strengthening.
1 2
1 2
S S
N N К
4. The results of the strengthened foundations settlements
measurement after the building implementation showed the
good precision with analysis data. This proves the correctness of
the taken structural and design schemes.
