2646
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
concrete content in soil cement using method of estimation
of part of hydrated cement as for the time of research
conducting (
, %),
visual inspection of reinforcement cage mounting,
testing of concreting sampling.
Four average piles were selected from a pile field consisting of
256 piles, which data are specified in Figure 1 (1 – fill-up
ground, 5-6 – flow loamy soils, 7 – semisolid clays) and in
Table 1.
Figure 1 – Composite pile diagram: 1 – soil cement shell, 2 – cast-in-
place reinforced concrete pile, 3 – reinforcement cage.
Table 1. Test piles installation indices
№
,
mPa
D,
mm
, %
D
, mm
h, m
1
3.4
801
22
512
0.1
2
3.7
786
21.4
524
0.05
3
3.2
790
20
518
-
4
3.5
793
20.6
510
0.1
Findings of pilot works related to installation of composite
drilled piles in soil cement shells testifies the following:
soil cement elements buried in the clay-pans correspond to
the design size and properties. In 7 days after their
installation they can be lightly drilled and hold wellbore
walls in flow clay-bearing soils;
up to 10 cm of loose soil cement remains in drill holes and
can be compacted using earth rammer and impregnated
with fluid soil cement;
drill hole water flow makes ca. 20
l
per hour, what just
insignificantly influences the results of drill hole concreting;
reinforcement cage mounting and drill hole concreting can
be easily performed.
2 SOIL CEMENT PILES
Prism strength of soil cement manufactured by drilling mixing
method or jet method without using of reinforcing chemical
additives makes 1,5…4 mPa depending on water and cement
content (M. Zotsenko, Yu. Vynnykov, 2011). In many instances
such material strength seems insufficient for manufacturing of
underground supporting frames, so there is a necessity to
increase the soil cement strength.
This problem can be solved having applied reinforcing of
soil cement structures with steel reinforcement. Correspondence
of thermal-expansion coefficients of these materials apart from
rather high grip of reinforcement on soil cement as well as its
high waterproofing capacity is deemed to be the ground for
collaboration of soil cement and steel reinforcement.
Effect of reinforcement on soil concrete strength was studied
in vitro by testing of pile models of scale 1:4. Models
dimensions made up 100 х 100 х 400 mm (Fig. 2). 4 series each
per 6 samples were investigated. Samples of the first series were
not reinforced, while the samples of the following series were
reinforced 1,13%, 2,03% и 3,14% (P
f
,%) correspondingly. End
surfaces of reinforcement cages were equipped with supporting
plates with longitudinal reinforcement bars rigidly fastened
thereto. Reinforcement protective coating made 20 mm.
Figure 2. Axial compression testing of test samples
Soil cement was produced in vitro using the drilling mixing
method, i.e. no stabilization of loess soil-water-cement mixture
was carried out. M400 Portland cement content amounted to
20% by weight of soil skeleton. The soil-water-cement ratio
with consideration for soil natural humidity made up W/C
(Water/Cement) = 2.7. At that its slump of concrete cone flow-
ability amounted to 11 cm.
Properties of constructive materials used in the above
experiment are shown in Table 2.
Table 2. Materials mechanical properties
Reinforcement properties
Soil cement properties
E , mPa
s
R
sc
, mPa
E , mPa
s
R , mPa
b
210000
225
2000
1.12
All samples were subject to the axial compression test,
during which the average values of their bearing capacity were
determined, see Table 3.
Table 3. Values of bearing capacity of soil cement prisms
Series
No.
Section
reinforcement
percent
µ, %
Average values of
bearing capacity
N, kN
Coefficient of
variation, v
1
0.00
11.20
0.21
2
1.13
42.50
0.19
3
2.01
62.70
0.17
4
3.14
84.00
0.18
Definition of bearing capacity of steel soil cement prisms by
materials was performed using two methods to select the most
acceptable one for calculation of structural analysis of steel soil
cement structures.
The first method of testing the axially loaded elements’
strength with given dimensions, reinforcement quantity and
loads is equated as
