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Design Calculation of Drill-Injection Piles with
Controlled Broadening and Silty-Clayed Soil
Foundation Basic Interaction Parameters
Mikhail Samokhvalov1, Juriy Zazulya 1, Roman Melnikov1,* and Victor Mironov 1
1Industrial University of Tyumen, 625001 Volodarskogo str. 38, Tyumen, Russia
Abstract. The paper describes a new method of drill-injection pile
installation formed by the sleeve technology with solution injection using
the "fracturing" mode and the controlled broadening at the pile end. This
method is aimed at high-quality and effective compaction of the soil under
the strip foundation of the reconstructed building. Analyzed are the results
of the in-situ tests intended to interaction of drill-injection piles
manufactured by the sleeve technology and single and repeated solution
injections using the “fracturing” mode and the controlled broadening at the
pile end. The radius of the neighboring compacted soil massif zone was
determined. The geometric parameters of the pile shaft broadening, and
fractures were identified. The algorithm for calculating the basic
parameters of the proposed piles was developed in order to forecast their
interaction with a silty-clayed soil foundation under static loading. A
comparison with classical analytical solutions after soil mechanics, theory
of elasticity and plasticity was made.
1 Introduction
There are a large number of buildings and structures worldwide (including cultural
heritage) which are in need of renovation, restoration and modernization in accordance with
modern requirements which regulate the development of underground space of the
buildings in order the objects of social and engineering infrastructure to be housed there [1 -
4]. As a rule, they are located in the constrained urban areas of city centers, in difficult
engineering-geological and hydrogeological conditions [5-8]. In this regard, it is necessary
to develop an efficient and reliable means for strengthening strip foundations by soil
foundation compaction [1, 9-11].
The analysis of different ways of strengthening revealed that the embedded reinforcing
elements of different shapes were of high-priority: piles with the controlled broadening at
their ends, drill-injection (injection) piles with broadening in the diameter of the pile shaft
and the sleeve technology with solution injection using the "fracturing" mode [2, 10, 12,
13]. At the same time, these ways incorporate the main drawback in a varying degree, i.e.
unpredictable and uncontrolled expansion of the solution in silty-clayed soil massif, and as
a consequence, possible irregular compressibility of the base in plan and other unfavorable
effects [10, 14]. As a result, to further improve the workability and effectiveness of the
* Corresponding author: tgasu.melnikov.roman@mail.ru
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© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative
Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).
proposed strengthening methods, the authors suggest the new combined universal method
of drill-injection pile installation manufactured by the sleeve technology with solution
injection using the "fracturing" mode and the controlled broadening at the pile end. (Fig. 1).
Fig. 1. Schematic illustration of drill-injection pile installation with the controlled broadening: 1-
borehole, 2-injector tube, 3-clamp, 4- membrane cup, 5-rubber sleeves, 6 - hose, 7-packer, 8-concrete
plug, 9-compressed zone of soil massif. [15]
2 Subject and methods of research
The injector tube with three zones of perforation is used for pile installation. The first zone
is located at the end of the membrane cup, the second – beyond the end zone, and the third -
in the zone of foundation strengthening. In doing the injection of the first zone the
membrane cup is stretched and forms a broadening in the soil massif; the sizes can be
controlled with the grout injection pump gauge by the volume flow and solution injection
pressure. Then the packer is moved to the second and third zones to form pile shafts;
solution injections are done for the foundation members being strengthened using
"fracturing" and “healing of cracks” modes. The rubber shell of the membrane fits close the
lower end of the injector as a "cup" [15].
3 Design calculation of the proposed pile basic parameters.
3.1 Calculation parameters in controlled broadening development.
Evaluated is the radial movement of the membrane cup wall u1 under injection pressure
depending on the required depth of the broadening in the soil massif (pile length), injection
pressure and the volume of solution, as well as the stress-strain state of soil under the
foundation based on the analytical solutions after O. Hoffman, et al. [16-17]:
=
(
+) ⇒
=
−
(1)
in elastic stage with ≤
:
=( −
)( +
)
(2)
in elastic-plastic stage with >
:
=
+
()
−
(3)
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where – initial radius (depends on the screw diameter), rс=0.04 m;
E – deformation modulus in the broadening zone, kPa;
– solution injection pressure on the membrane cup walls, kPa;
=
,= 1; =()
; (4)
=
+,=
+;=( +
(5)
=
+
(1−)( +); =(+
); (6)
– horizontal side deadweight contact soil pressure, kPa;
=()
=
(7)
– gravity weight of the soil massif, kN/m2; z –depth, m;
– Poisson ratio; – angle of internal friction;
– critical pressure kPa of the membrane on the soil massif during solution injection
when its elastic strains become plastic ones:
=()
(()) (8)
=
−
(9)
=1, =−2, =−, =(1−) (10)
– multimodulus factor (ratio of compressive deformation modulus E to tensile
deformation modulus Et) allows the elastic-plastic characteristics of silty-clayed soil to be
considered; it ranges from 1.0 to 5.0 depending on the type of clay and soil moisture. Fig. 2
Fig.2. Dependency diagram u from acting solution injection pressure in elastic and plastic zones of
the soil massif: 1, 2 – on the 1st site V = 10 and 20 l correspondingly; 3, 4 – on the 2d site V= 30 and
40 l correspondingly.
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Evaluated is the radius of the compacted zone depending on :
=(
+),
=
(11)
Evaluated are the residual stresses
depending on and :
=
−
∗ (12)
11
11
() 1,
()
nn
in c com
rnnn
com c
pru R
Rru r
∗=− ()
()
+1 (13)
where n – factor to be determined from the power law of deformation under shear,
=
, n – varies in the range of 0<n<2 depending on the type of soil and its water
saturation; in calculations it is determined on the basis of experimental data –parameters of
soil pressure cells when broadening, n=1.55.
3.2 Calculation Parameters in pile shaft development.
The radial movement of the borehole wall under the action of injection pressure ,
depending on the pile length of solution injection pressure under the condition
>
>
, based on the analytical solutions after Z.G. Ter-Martirosyan, V.G.
Fedorovsky, A.I. Polishchuk [18-19] et al. is evaluated by the formulas.:
in elastic stage of broadening with ≤
=( −
)( + (1+))
(14)
in elastic-plastic stage of broadening with >
>
=
+
−
(15)
where –solution injection pressure acting on the borehole walls, kPa;
–side contact soil pressure, kPa:
=
/(1−) (16)
=
,=
,= +(1+), (17)
=
,=
+,=
+ (18)
=
+
(1−)( +),=(+
) (19)
– critical pressure, kPa, corresponding to the initial plastic strains is evaluated by
the formula:
=()
() (20)
=
(21)
=1−, =−(1+), =−(1+), =(1−) (22)
– hydraulic fracture pressure, kPa, is evaluated by the formula (24);
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Evaluated is the radius of the neighboring compacted soil massif zone due to the pile shaft
diameter increase under solution injection pressure , depending on :
=(
+)
,
=
(23)
3.3 Calculation parameters in hydraulic fractures development
Evaluated is , depending on the depth of the injection horizon z, gravity weight of the
soil massif and its mechanical strength characteristics – и , as well as the strength of
soil-concrete in compression (tension) ,, - necessary to be taken into account in
repeated solution injection in the “fracturing” mode [10,12]:
=1+√3+
√ , (24)
где С =
√
,=√()
() (25)
Evaluated is the radius of hydraulic fracture expansion depending on the
interval of perforations and their quantity in the injector tube section, as well as the type of
injection (single or repeated); due to their random development and uncontrolled
expansion, is taken after the in-situ tests minus ;
The radius of the neighboring compacted soil massif zone is evaluated with regard to:
hydraulic fractures: =
у +
(26)
change of mechanical characteristics ,,С, proceeding from the radius of
their expansion and the solution volume , subjected to injection upon 1rm of the pile
length [20-21]:
=са
, (27)
where ,– air void ratio and modulus of deformation of soil massif reinforced by
hydraulic fractures, MPa. It is evaluated by the formula (28);
с,с – air void ratio and modulus of deformation of soil massif compacted between
fractures, MPa.;
,− initial modulus of deformation and air void ratio of soil;
– modulus of deformation of solution injected into soil massif is taken equal to
=8000 MPa;
– factor reflecting the proportion of hardened solution in the cracks of hydraulic
fracture (minus air void filling) in a given volume of soil massif;
р− air void volume in the soil massif under study , m3;
The coefficient of compaction Сcom. is determined by SP 50-101-2004 with substitution
of value .
3.4 Evaluated is the regularity of settlement development in static loading
The settlement-load comparative diagrams (Fig.3) were plotted on the basis of the elastic-
plastic model after S.P. Timoshenko and the analytical solutions after Z.G. Ter-Martirosyan
[17-18] taking into account the changes in the mechanical properties of the neighboring
compacted soil massif zone and preservation of the residual stresses up to the load the
pressure of which does not exceed the value
in the formulas (12, 27).
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Fig.3. Settlement-load comparative diagrams s=f(p) for drill-injection piles with the controlled
broadening and the repeated solution injection in the “fracturing” mode: a), b) on the 1st site V=10-
20 l; c), d) on the 2d site V=30-40 l.
=()
()
()
()
√.
(28)
=
() ln∗
()
(∗) (29)
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4 The results of in-situ tests
To determine the geometric parameters of the proposed piles and the changes in physical
and mechanical characteristics of the soil massif, excavation of piles was carried out layer
by layer after in-situ tests and installation of piles. (Fig. 4)
Fig. 4. Geometric parameters of the proposed piles: a, b – controlled broadenings V=10-20 l, c, d –
30-40 l, e – pile shaft diameter increase, f – hydraulic fractures development, g, h – expansion of
hydraulic fractures in single and repeated solution injections, i, j – texture of hydraulic fractures of
«А» and «B» types, k – horizontal hydraulic fractures.
After the excavation it was found out that a horizontally elongated elliptical controlled
broadening of 250-350 mm in diameter with the ratio of d / h = 1.3-1.4 was formed at the
pile end in the solution injection of V = 10-20 l into the membrane cup. When the solution
injection was V = 30-40 l, the vertically elongated broadening of 360-390 mm in diameter
with the ratio of d / h = 0.7-08 was formed. The difference in values was due to the
different pile lengths - 2 and 6 m correspondingly. The pile shaft diameter nearly doubled
when the drill-injection pile shaft was formed by the sleeve technology with solution
injection using the "fracturing" mode due to permanent pressure on the borehole walls with
a mean value of 0.2 MPa. Hydraulic fractures up to 40mm in thickness expanded to a
considerable distance from the pile, up to 3 m in a single solution injection. Hydraulic
fractures localized in the neighboring soil massif up to 130mm in thickness at a distance of
0.5 m from the injector in repeated solution injection. In accordance with the classification
of I.I. Sakharov two types of hydraulic fracture textures were found out: type "A" in the
form of the greater crack growth with development of solid lens of 10-130 mm in thickness
and type "B" – numerous thin cracks up to 5mm in thickness, loosely filled with the
solution [10].
Analysis of changes in the physical and mechanical characteristics of the neighboring
soil massif showed that the greatest change occurred in the compacted soil massif zone in
controlled broadening development: the density increased on the average by 25%, the
moisture content decreased on the average by 38%, the modulus of deformation increased
by 60%; the density along the pile shaft increased on the average up to 17%, the moisture
content decreased up to 28%, the modulus of deformation increased up to 35%. – these
must be considered in future in design calculation of the basic parameters of the drill-
injection pile and forecast its interaction with soil foundation [19-23].
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5 Conclusions
1. Developed is a new method for strip foundation strengthening in buildings and structures
erected on silty-clayed soils; it makes it possible to combine drill-injection pile installation
with the controlled broadening, sleeve technology with solution injection using the
"fracturing" mode (including repeated injections) along any layer of the soil massif and to
restore foundation members as an integrated technological unit, thus greatly improving its
effectiveness.
2. It was established that in controlled broadening development of 10-40 l in volume,
minimum diameter of the broadening was from 250 to 390 mm, the compacted soil massif
zone developed with an average radius of expansion of 0.15-0.6 m from the injector tube
and a significant change in physical and mechanical properties: the density increased on the
average by 25%, the moisture content decreased up to 37%, the modulus of deformation
increased by 64%, - these must be considered in future in design calculation of the basic
parameters of the controlled broadening.
3. It was established that in drill injection pile shaft development one should do only the
repeated solution injection using the “fracturing” mode when the number of hydraulic
fractures and their localization increased in the neighboring soil massif at a distance of 0.5
m from the injector tube (at a maximum crack growth up to130 mm) resulting in the pile
bearing capacity increase on the average by 20%. Also it was found out that due to the
permanent pressure on the borehole wall with a mean value of 0.2 MPa, the diameter of the
pile shaft nearly doubled and together with hydraulic fractures resulted in compacted zone
development with the mean radius of 0.2-0.4m from the injector tube and the changes in
physical and mechanical properties within this zone: the density increased on the average
by 17%, the moisture content decreased up to 28%, the modulus of deformation increased
by 35%, - these must be considered in future in design calculation of the pile shaft
parameters.
4.The results obtained after the in-situ tests made it possible to develop the algorithm
for design calculation of the basic parameters allowing the following accuracy: to evaluate
the radius of the compacted zone in the controlled broadening and the neighboring soil
massif - up to 7%; to evaluate radial movements of the membrane cup walls and borehole –
up to 10 and 14% correspondingly; to forecast settlement-load dependency in the proposed
piles in silty-clayed soil loaded statically – up to 25%.
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