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BORED PILES PRODUCED BY THE PULSED DISCHARGE TECHNOLOGY

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Modern Methods and Advances in Structural Engineering and Construction
Yuschube, S. V., Samarin, D. G. (eds.)
ISEC-6, Zürich, June 21–26, 2011
BORED PILES PRODUCED BY THE PULSED
DISCHARGE TECHNOLOGY
S.V. YUSCHUBE1 and D.G. SAMARIN2
1
Tomsk state university of architecture and civil engineering, Tomsk, Russia.
E-mail: [email protected]
2
Tomsk state university of architecture and civil engineering, Tomsk, Russia.
E-mail: [email protected]
Application of pulsed discharge technology at the device of bored piles substantially allows to
promote their bearing strength. It is connected with the forming of widening of barrel of bored
pile and with the compression of near pile soil. Such widening of pile barrel is created due to hydraulic surges produced with electric discharges in material of pile barrel (concrete mixture) at its
device. However, forming of widening of barrel of bored pile is a rather complex task. The
cause is in briefness of hydraulic surges activity. Influence of energy parameters of electric discharge (tension U, kv, capacity of condenser C, mcF) is experimentally set on duration of mechanical action of hydraulic surges.
Keywords: Bored pile, electric discharge technology, hydraulic surges.
1
Introduction
Over recent years in Russian foundation engineering practice, bored piles, arranged with
the use of pulsed discharge technology (pilesPDT) have become wide-spread (Evdokimov
et al. 1991, Buhov 1997, Baholdin et al. 1998,
Eremin et al. 2006). The researches, aimed at
development of the method of device of bored
piles with the use of pulsed discharge technology, are conducted at the Tomsk State University of Architecture and Civil Engineering.
Essence of this method consists in the following: formed electric discharges (further el.
discharges) in material of pile barrel provide
occurrence of hydraulic surges. Such surges
are able to accomplish mechanical work and
due to it widening of the pile body, compression of near pile soil and, consequently, increase of bearing strength of pile happen.
However, creation of electric discharges, able
to be transformed in hydraulic surges with the
identically effective mechanical operating on
different soils, is a rather complex task. One
of the determining factors is time of hydraulic
1
surges action (0,00002-0,00005 sec.), which
appears not enough for any meaningful widening of barrel of pile, e.g., in slightly wet
sandy or clay soils (Dzhantimirov C.А. et al.
2003, 2004). The object of this work was
revealing possibility of increase of action duration of hydraulic surges, produced in material of pile barrel. Analysis of the researches
results of hydraulic surges, produced with el.
discharges in liquids, shows that time of hydraulic surges activity is largely determined
by the energy parameters of el. charge such as
tension (U) and capacity condenser (С). Varying of their correlation can increase duration
of hydraulic surge’s action.
It is known, that depending on correlation
of tension and capacity of condenser it is
possible to form two types of el. discharge
(leader and thermal) in liquid.
2
Experimental researches
At the thermal type (Fig.1, a) of el. discharge,
its forming takes place in gas cover which
appears due to heating of liquid. In this case
Bored piles produced by the pulsed discharge technology
Yuschube, S. V., Samarin, D. G.
considerable part of energy of el. charge is
expended on formation of gas cover and only
its small part will be transformed in mechanical one. Severe losses of energy of el. charge
result in reduction of time of hydraulic surges
action.
a.
b.
Figure 1. a–The thermal type of el. discharge; b–
The leader type of el. discharge.
1 - electrodes; 2 –gas cover; 3 – electric discharge.
At the leader type (Fig. 1, b) of el. discharge, its forming takes place in liquid itself.
In this case considerable part of energy of el.
discharge will be transformed in mechanical
one. Transition from thermal type of el. discharge to leader one is possible due to level
raising of tension. However, safety norms of
piles- PDT production and durability of the
applied equipment place restrictions on using
very high tensions. By the carried out experimental researches (Samarin 2005) it is specified that minimum level of tension at which
the leader type of el. discharge is yet saved, is
within the limits of 30 kv. It provides possible
level of safety norms of piles-PDT production
2
and reliability of equipment. Reduce of voltage less than 30 kv generates thermal type of
el. discharge. The authors decided to analyze
influence of energy W change of el. charge on
time t of hydraulic surges activity at given
level of tension - U=30kv.
The researches were conducted on the experiment stand (Fig.2) that consists of working chamber (1 - 150150200 mm), filled by
concrete mixture, with built-in electrodes (2).
The carcass of chamber is fastened to the bed
(3). Appearance of el. discharges in the
chamber results in occurrence of hydraulic
surges. The pressure, created here, is passed
through a hard stamp (4) on a pressure monitor (5). The signal from a pressure monitor is
passed on the receiving-measuring system (9).
As a source of charges, the generator of impulsive currents was used (10). Creation of el.
charges with set tension of U=30 kv took
place at the different values of capacity of
condenser C = 4, 6 and 10 mcF. The carried
out researches showed that at the leader type
of el. charges, the growth of energy results in
intensive increase action of hydraulic surges
time. So, at the capacity of condenser C = 4
mcF (energy of el. charge W = 1,8 kJ) time of
hydraulic surge activity is 0,002 sec (Fig. 3,
a). The increase of capacity of condenser to
10mcF (energy of charge W =4,5 kJ) brings to
the increase of duration of hydraulic surges to
0,006 sec. (Fig. 3, b).
The experiments of Dzhantimirov and
others (2003, 2004) on the device of bored
piles with the use of explosives showed that
meaningful widening of barrel of bored pile
was attained at the time of action of pressure, t
≥0,001 sec.
The analysis of our researches shows that
the required time of action of hydraulic surge
can be attained by the selection of energy parameters of el. discharge.
Further experiments were aimed at analyzing the influence of fitted energy parameters of el. discharge on forming of widening of
bored piles, carried out with the help pulsed
discharge technology.
Modern Methods and Advances in Structural Engineering and Construction
Cheung, S. O., Yazdani, S., Ghafoori, N., and Singh, A. (eds.)
ISEC-6, Zürich, June 21–26, 2011
The researches were carried out in the experimental module (Fig. 4). The methodology
of realization: working chamber (1) with diameter of 800 mm, height of 900 mm, filled
with slightly wet sandy soil. After installing
the basic elements of the experimental module
on soil, pressure q = 100 kPa has been passed.
Then the barrel of bored pile (11) has been
formed.
bore which was entered into soil through the
central hole (5) in the hard stamp (2); setting
in the mining hole of discharger (6), linked to
the generator of impulsive currents ; replacement into the mining hole of concrete mixture
and its treatment by el. charges (12).
Figure. 3. The oscillograms of pressure p at energy
of discharge W: a - at W = 1,8 kJ; b - at W = 4,5 kJ
Figure. 2. The chart of the experiment stand:
1 - working chamber; 2 - electrodes; 3 - bed;
4 - hard stamp; 5 - pressure monitor; 6 - plates;
7 - metallic rods; 8 - rubber diaphragm;
9 - receiving-measuring system; 10 - generator of
impulsive currents.
The process of this pile forming: mining
hole boring with diameter of 110 mm by a
3
During process of the pile producing the
gel-forming substance was added into the
concrete mixture for limitation of desiccation.
Slightly wet sands were used in researches of
the following characteristics: density γ = 16.5
– 16.8 kN/ m3; density of soil mineral particles
γ s = 26.5 – 26.6 kN/ m3; coefficient of porosity e = 0,76 - 0,79; natural humidity w = 9 -
Bored piles produced by the pulsed discharge technology
Yuschube, S. V., Samarin, D. G.
11%; coefficient of water saturation Sr = 0,3 0,35; internal friction angle of soil  = 23 25°; specific cohesion C = 1-2 kPa; module of
deformation of E = 15 - 18 MPa.
parameters - U = 30 kv, C = 10 mcf, result in
substantial widening of barrel of bored pile.
The diameter of the extended part of pile barrel exceeds her primary one practically twice.
The primary diameter of the pile (D = 110
mm) arised to 200 mm after the series of hydraulic surges. It is known, that discharge
energy for a pile expansion by hydraulic
surges in a concrete mixture is equal 100 kJ.
The experiment shows that revealing possibility of increasing duration of hydraulic
surges allows to improve effectives of the
pulsed discharge technology using by producing the bored piles in different soils. In this
case discharge energy for the pile expansion is
decreasing considerably.
References
Figure. 4. The chart of the experimental module:
1 - working chamber; 2 - hard stamp; 3 - bed; 4 –
ribs; 5 - central opening; 6 - discharger; 7 - rubber plate; 8 - pressure, transferred from a compressor; 9 – rubber chamber; 10 - manometer; 11
- barrel of bored pile; 12 - el. discharge; 13 formed widening of pile.
Figure. 5. Dependence of diameter of pile D on the
amount N of hydraulic surges : U = 30 kv, C = 10
mcf (W = 4,5 kJ); U is tension; C is a capacity of
condenser; W is energy of discharge.
3 Conclusions
The results of our researches are presented on
Fig. 5. It is defined, that hydraulic surges, at
energy of el. charge W = 4,5 kJ and energy
4
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