Automatic pressure control equipment for horizontal jet grouting

Automation in Construction 69 (2016) 11–20

Contents lists available at ScienceDirect

Automation in Construction
journal homepage: www.elsevier.com/locate/autcon

Automatic pressure-control equipment for horizontal jet-grouting
Yao Yuan a, Shui-Long Shen a,⁎, Zhi-Feng Wang b, Huai-Na Wu a,⁎
a
State Key Laboratory of Ocean Engineering and Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration (CISSE), Department of Civil Engineering, Shanghai Jiao Tong University,
800 Dong Chuan Road, Minhang District, Shanghai 200240, China
b
School of Highway, Chang'an University, China

a r t i c l e

i n f o

Article history:
Received 18 October 2015
Received in revised form 16 May 2016
Accepted 22 May 2016
Available online xxxx
Keywords:
Horizontal jet grouting equipment
Pressure-control
Spoil discharge
Vertical displacement

a b s t r a c t

A new horizontal jet grouting equipment is proposed to eliminate the harmful effect on the surrounding environment due to the injection of large amount of water and/or grout under high jetting pressure. The components of
the proposed equipment and the construction procedures are introduced. During horizontal jet grouting by the
proposed equipment, the inner pressure of the soil stratum can be monitored automatically, the generated spoil
can be transported out, and the impact on surroundings (such as ground upheaval and lateral displacement of the
subsoil) can be mitigated. A field test involving the installation of five horizontal jet grout columns was conducted
in Shanghai to demonstrate the applicability of the new equipment. In addition, monitoring instruments were
installed to observe the vertical displacement of the ground surface. The measured maximum value of the ground
surface upheaval was as low as 9.4 mm, which verifies that the new equipment performed as per expectations.
Finally, the in-situ quality of jet grouted columns was found to be very good based upon the results of field
cone penetration and unconfined compressive strength tests.
© 2016 Elsevier B.V. All rights reserved.

1. Introduction
Jet-grouting is a soft soil improvement technology, which is initially
invented based on jetting cut technology in coal mining [1] and grouting
[2] in soft soil engineering in early 1970s [3]. After jet-grouting technology was invented, it is widely used in many construction projects, e.g.
deep excavations to seal the joints of diaphragm wall to prevent leakage
[4], improvement of stability shaft entrance [5], improvement of bottom
stability of excavation [6], stabilization of micro-tunneling route [7],
tunnel canopy construction [8], recovery of collapsed tunnel [9], improvement of soft subsoil of embankment [10], marine [11] or on-land
foundations [12]. In some circumstance, jet grouting was also applied
to improve soft rocks, e.g. in Athens Metro project [13] and remediation
of existing shield tunnel [14]. The first patent of jet grouting was applied
in 1968, as the ‘Chemical Churning Pile’ (CCP) method [1], which is the
forerunner of the single fluid system [15]. Recently with developments
in construction technology, the double fluid system (involving grout
and air) [16], and the triple fluid system (grout, water and air) [17]
have been used for different geological conditions [18]. During jet
grouting, high velocity fluids shrouded by a compressed air are ejected
from small diameter nozzles to erode the soil and to mix it with the

grout to form a soil-cement column [16]. The shear strength of the
cemented column can reach several MPa [19].
⁎ Corresponding authors.
E-mail addresses: (S.-L. Shen),
(Z.-F. Wang).

/>0926-5805/© 2016 Elsevier B.V. All rights reserved.

Based on construction direction of the rod for jet grouting machines,
jet grouting technology can be classified as: 1) vertical jet grouting
systems [17]; 2) inclined jet grouting systems [20]; and 3) horizontal
jet grouting systems [21]. Fig. 1 depicts the in-situ stress state and
mechanism of stress transferring in ground during horizontal
jet-grouting construction. Before jet grouting, the in-situ overburden
pressure p (shown in Fig. 1) can be expressed as follows:
p ¼ γh

ð1Þ

where γ = unit weight of the overburden soils; and h = overlying
thickness of the soil above the construction site.
Fig. 1(a) shows the longitudinal profile of the ground movement
during conventional jet grouting process. The conventional jet grouting
operation is a two stage process. Stage I is the ground movement during
drilling. As shown in Fig. 1(a), the ground heave at this stage is generally
small, which is induced by the friction between the drilling rod and the
surrounding soils. Stage II is the ground movement during jet grouting
process. When the slurry ejects from the monitor, the inner stratum
pressure around the drilling rod will increase and the ground surface
will be upheaval, which is induced by the expansion of the grouting

slurry and the spoil soils (Fig. 1(b)). The subsequent injection of large
volumes of high pressurized fluids into the soil stratum can lead to
ground upheaval and lateral movement of the surrounding soils.
To solve the ground expansion problems, some modifications of jet
grouting were conducted [21]. In 1995, Nakashima and Nakanishi [20]


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Y. Yuan et al. / Automation in Construction 69 (2016) 11–20

Fig. 1. Mechanism of load transferring during jet grouting: a) longitudinal view of the ground movement; b) Sectional view of the ground upheaval due to grouting slurry; c) ground
movement model of the horizontal jet grouting construction.

developed a jet-grouting technology to make the balance of jetting
pressure with surrounding earth pressure and this system is named
as Metro Jet System Technology (MJS). MJS technology utilizes the
negative pressure induced by highly pressurized water to remove the
spoil [20]. Fig. 2a shows a sectional view of compound pipe used in MJS
technology. The different pipes function as follows: (1) for injecting the
high pressure grout (grout pipe), (2) for injecting high pressure water
to erode soil (water pipe I), (3) for spoil generating water (water pipe
II), (4) for injecting compressed air (air pipe), (5) for the cable set that
link the sensor to measure the earth pressure during jet-grouting (cable
pipe), (6) for transporting the additive (additive pipe), and (7) for
transporting out the spoil induced during jet grouting (spoil pipe). The
equipment required for MJS makes the rod pipe large and heavy. In addition, the existence of earth pressure measuring cable prevents the rod
from continuous 360 degree rotation and the pipe can only swing action
during construction, resulting in reduced construction efficiency.
In order to overcome the drawbacks of the MJS system, Shen et al. [21]

introduced a new horizontal jet grouting technique called the ‘Composite-Pipe Method’ (CPM). Fig. 2b shows the sectional view of compound

pipe used in CPM technology. In CPM, the high pressure water generates
a vacuum state temporary in the entrance of spoil pipe to remove the
spoil generated during construction. This CPM equipment, which can be
regarded as the simplified version of MJS, can help reduce the inner
pressure of the stratum during jet grouting. However, when the overburden soil for jet grouting construction is very thin, the pressure of the jet
grouting fluids may have a major effect on the surrounding environment,
and the volume of spoil to be removed cannot be controlled automatically. Moreover, both spoil pressure and earth pressure do not be monitored
during construction. This may cause obvious ground displacement
around construction site during and after jet grouting (see Fig. 1(c)).
In this paper, to eliminate such impacts (e.g. outflow of the drilling
fluid) and to reduce the impact on surroundings (e.g. large ground
upheaval and lateral displacement), a new construction equipment for
horizontal jet grouting technology named as pressure-control jet
grouting technology (PCJG) is proposed. Fig. 1(c) shows the basic concept of ground movement during jet grouting process in the proposed
PCJG technology. During the jetting process, the ground movement
can be controlled via control of inner stratum pressure near the monitor,

Fig. 2. Sectional view of composite pipes used in MJS and CPM technology, a) MJS; b) CPM (modified from Nakashima and Nakanishi [20]; Wang et al. [24]).


Y. Yuan et al. / Automation in Construction 69 (2016) 11–20

13

Fig. 3. Composition of the equipment for horizontal pressure-control jet grouting.

P. The inner stratum pressure near the monitor should balance the earth
pressure of the overlying soils, p. If P N p, ground heave in stage II

happens, whereas if P b p, ground settlement happens. At the balance
condition, if p = P, the ground movement in Stage II can be avoided.
Thus decreasing the inner stratum pressure can help eliminate such
impacts (large ground upheaval).
In PCJG, different from MJS and CPM, both spoil pressure and earth
pressure can be monitored and the spoil generated during jet grouting
is transported out promptly. This helps increase the diameter of the
grouting columns and reduce the expansive impact on surroundings.
During jet grouting construction, the inner pressure and the rate
for transporting spoil can be controlled automatically (namely see
Fig. 1(c)), and the drilling fluid for the new equipment is high pressure
water. Meanwhile, the operation becomes simple and easy in comparison to the other two types of aforementioned equipment. Additionally,

the grout pressure in the aforementioned equipment is lower than that
of MJS and CPM, which can help reduce the environmental impact.
The objectives of this paper are: i) to introduce the new equipment;
ii) to describe the construction procedure while using the new equipment; iii) to demonstrate the applicability of the new equipment through
a case study.
2. Pressure-control jet grouting technology
2.1. Composition of PCJG
Fig. 3 shows the composition of the equipment for PCJG. The connection of these different parts is also shown schematically in Fig. 3. Fig. 4
shows photographs of the main components of this system. The main
apparatus applied in PCJG is composed of six parts: (1) the drilling

Fig. 4. Photographs of the main elements of the equipment.


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Y. Yuan et al. / Automation in Construction 69 (2016) 11–20

Fig. 7. Photograph of multiple-functional monitor used in horizontal jet grouting
construction (modified from Wang et al. [24]).

Fig. 5. Sectional view of the sealing device.

and jetting system, (2) grouting system, (3) automatic detection
system, (4) sealing device, (5) pressure-control system, and (6) spoil
discharge system.
(1) Drilling and jetting system
The drilling and jetting system consists of a horizontal drill rig
(#4 in Fig. 3), a triple rod (#11), a three-channel swivel (#12),
and a multiple-functional monitor (#6) with multiple nozzles.
The horizontal drill rig, connected to the triple rod, is used for
supporting and guiding the triple rod. A three-channel swivel is
used to connect the jet grouting system with the triple rod.
There are five nozzles on the multiple-functional monitor.
(2) Grouting system
The grouting system includes a high pressure pump (#7) for
feeding highly pressurized water, a low pressure pump (#8) for
injecting grout, an air compressor (#9) for generating compressed air, grout storage equipment, water bucket, and slurry
mixing station. The grouting facilities are connected to the triple
rod through the three-channel swivel.
(3) Automatic detection system
The automatic detection system contains three flow meters, three
pressure sensors and an in-situ parameter monitor. In order to simultaneously monitor the quality of the jet grouting column, the
following parameters for drilling and jet grouting can be detected

automatically: the retracting velocity of the drill rod, the flow
rate and the pressure of the grout, water and compressed air. The

flow rate of the grout, water and compressed air can be recorded
by the respective flow meters, while the pressure of the grout,
the water, and the compressed air can be monitored simultaneously by the pressure sensors. The parameters are all displayed
in the in-situ parameter monitor. With the automatic detection
system, the position of the nozzles and the relationship between
the column length and the rotation velocity can be displayed
clearly, and the quality of the jet grouting column can be controlled
effectively.
(4) Sealing device
The sealing device (#5) whose details are shown in Fig. 5 includes
a steel tube, a sealing gasket and a pressure sensor. The pressure
sensor is installed on the steel tube. The sealing gaskets, which
are coaxial with the triple rod, are installed around the steel tube
and the triple rod to keep the gap closed. The tube is connected
to the spoil pump. During jet grouting operation, the sealing device
is used to keep the inner pressure of the soil stratum in a steady
state.
(5) Pressure-control system
The pressure-control system is used to record and adjust the inner
pressure of the soil stratum. When the slurry pressure is greater
than a critical pressure of the soil stratum, the system will be utilized to reduce the pressure of the soil stratum by transporting
out the spoil, the ground response around the construction site
can be mitigated.
(6) Spoil discharge system
The spoil storage system is designed to store and recycle the spoil
generated during the construction of jet grouting. When the spoil
is removed from the gap, the spoil discharge system is then turned
on.

Fig. 6. Sectional schematic view of multiple-functional monitors.

Y. Yuan et al. / Automation in Construction 69 (2016) 11–20

15

Fig. 8. Schematic view of the pressure-control system.

2.2. Principles of innovation elements of PCJG
The innovative elements of PCJG include: i) multiple-functional
monitor, ii) pressure control system, and iii) spoil discharge system.
The detailed description of the principles of these innovative elements
is given hereafter.
2.2.1. Multiple-functional monitor
Fig. 6 shows the configuration of the multiple-functional monitor,
which is installed at the tip end of the triple rod. Fig. 7 gives a photograph of the monitor used in horizontal jet grouting construction. The
diameter of the monitor (125 mm) is 35 mm larger than that of the
standard triple fluid rod (90 mm), and is 10 mm smaller than the
inner diameter of the steel tube. During jetting, an annular space is created between the rod and the surrounding borehole wall, which allows
the spoil slurry generated to be transported away from the monitor towards the swivel head.
As shown in Fig. 6, there are five injection nozzles on the multiple
monitor; two injection nozzles at the front of the monitor (nozzles 1
and 2), two injection nozzles at the back of the monitor (nozzles 3
and 4) and one injection nozzle at the another end of the monitor (nozzle 5). Nozzles 1 and 2 have dual outlets which are connected to the
grout pipe and the compressed air pipe for injecting lower pressure
grout surrounded by the compressed air. Nozzles 3 and 4 also have
dual outlets which are connected to the high pressure water pipe and
the compressed air pipe. The initial erosion of the soil for drilling is
first conducted by nozzles 3 and 4 with the high pressure water. With
the triple rod in the designated position, the low pressure grout is

ejected from nozzles 1 and 2 to mix with the eroded soil. The grout
from the inner outlet is shrouded by compressed air dispensed from
the outer outlet, which can increase the eroding ability of the grout
and enlarge the diameter of the column. Nozzle 5 ejects high pressure
water to accelerate the removal of the spoil from the gap during jet

grouting construction. Fig. 6 also depicts the configuration of each nozzle. As seen, the nozzles (Nozzle 1–5) have a tapered design such that
the nozzle diameter reduces gradually to 2.6 mm at the exit of the nozzle. The funnel-shaped configuration prevents the backflow of the grout
fluids and the spoil soils.
2.2.2. Pressure-control system
During jet grouting operation, if the inner stratum pressure on the
soil near monitor is larger than the overburden soil pressure, the overburden soil will upheave. If the inner stratum pressure is smaller than
the overburden soil pressure, it will cause the settlement of the overlying soil. Thus, the inner stratum pressure should be controlled to be approximately equal to the overburden soil pressure to reduce the ground
movement. When the slurry pressure in the gap is larger than p, the
valve control is turned on to remove the spoil slurry induced during
jet grouting to control the pressure to the critical state. When the slurry
pressure is smaller than p, the valve control is turned off to stop the
transport of spoil slurry to increase the pressure to the critical state.
With this procedure, the earth pressure of the soil stratum can be balanced and the large ground upheaval or settlement can be avoided.
Fig. 8 illustrates a schematic view of the pressure-control system.
Fig. 9 shows photographs of the pressure-control system in horizontal
jet grouting construction. The main part of the system is a Programmable Logic Controller (PLC) and a frequency converter (Fig. 9a) and control valve (Fig. 9b). The PLC can change the frequency converter
promptly to adjust the front-side pressure of the multiple monitor,
which can keep the inner pressure in a stable state to balance the
inner pressure of the stratum. There are two regulation modes for the
PLC, namely the manual regulation and the automatic regulation. In
the manual regulation mode, the construction workers can adjust the
flow rate of the spoil pumps to control the volume of discharged spoil.
In the automatic regulation mode, the regulation is conducted by the
Proportion Integration Differentiation (PID) automatic control program.

Fig. 9. Photographs of pressure-control system in horizontal jet grouting construction: a) PLC and frequency converter; b) control valve.


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Y. Yuan et al. / Automation in Construction 69 (2016) 11–20

Fig. 10. Configuration of the spoil discharge system.

The frequency converter is adopted as the drive units to control the
pressure-control system. During jet grouting operation, the rate of
the spoil pumps will be adjusted by the frequency converter to keep
the inner pressure in a stable state automatically. The guidelines for
the control of spoil pumps are as follows:
1) When the pressure is less than 30% of the critical pressure, the valves
of the spoil pump should be shut down to avoid the excessive loss of
spoil at the construction site (Fig. 9b);
2) When the pressure is in the range of 30%–80% of the critical pressure,
the rate of the spoil pump should be set as 30 Hz. This is the optimal
rate for the system which can keep the operation of the electric
motor steady, and maintain the stability of the inner pressure within
the soil stratum.
3) When the pressure is in the range of 80%–120% of the critical pressure, the equipment will adopt the PID mode. The pressure will

decrease to the critical value gradually. This can prevent the adverse
effect of the sudden upheaval or settlement of the ground surface.
Nevertheless, there is still a few limitation in the new equipment.
This equipment need to ensure the path for transporting out the spoil
outside the rod during the jet grouting construction, which means

that during jet grouting the surrounding soil strata must have selfsupporting ability. The surrounding soil should be well consolidated.
The factors influence on stability of surrounding strata include stress
state of soil, particle size of soil and the gap size between diameter of
monitor and rod. Another limitation is the clogging of gap. If the diameter of soil particle (e.g. gravel in soil) is larger than the gap, large soil
particle may cause clogging the spoil slurry path.
2.2.3. Spoil discharge system
Once the spoil transports out from the jet grouting site, a spoil discharge system is incorporated to remove water from the spoil sludge,

Fig. 11. Horizontal jet grouting procedures: a) drilling; b) jet grouting; c) after construction.


Y. Yuan et al. / Automation in Construction 69 (2016) 11–20

17

Fig. 12. Photographs of washing rod in horizontal jet grouting construction.

and transport the spoil away from the construction site. This prevents
secondary pollution from the sludge generated during jet grouting.
The water extracted from the sludge may be recycled and reused in
the jet grouting.
Fig. 10 shows the configuration of the spoil discharge system. The
spoil discharge system consists of five parts: (1) the preliminary mixing
combination device, (2) the furnishing device, (3) the sludge concentration device, (4) the integrated filter-press and sludge discharge device,
and (5) the recording device. The preliminary mixing combination
device is used to store and mixing the spoil transported from the jet
grouting site. The feeding tube is applied to connect the inlet pipe of
the storage tank with the diaphragm pump of the furnishing device.
After the first step of mixing the spoil, the mixed spoil is transported
to the concentration device to dehydrate the spoil. The sludge concentration device contains: the discharge pump and the inner pressurized

storage tank. The discharge pump is set at one side of the inner pressurized storage tank and is connected with the tank through the sludge
valve. When the sludge flows through the inner pressurized storage
tank, the water can transit through the filter fabric and the large soil particles will be held back in the device. The concentrated spoil then transit
to the integrated filter-press and sludge discharge device. As a result the
filter cake will be formed, and the water can be stored for potential
recycling.

Fig. 13. Test site location where the equipment was used (modified from Wang et al. [24]).

3. Construction procedure
The jet grouting operation with the PCJG technology is generally
implemented as following stages:
3.1. Stage 1: drilling
Fig. 11a illustrates the process of drilling in horizontal jet grouting.
During drilling operations, the high pressure pump for water will be
turned on to eject the pressurized water for improving the drilling efficiency. The construction parameters (e.g. drilling velocity and jetting
rate) should be selected based on the designed value. The PLC module
for the pressure-control system should be used to monitor the inner
pressure of the soil stratum and the discharging volume of the sludge
simultaneously. When the drill rod needs to be replaced, the spoil
discharge equipment should be shut down.
3.2. Stage 2: jet grouting
Drilling is stopped when the drill rod reaches the designed position.
Fig. 11b illustrates the horizontal jet grouting process. The jet grouting
parameters, including grouting pressure, retracting rate, flow rate, and
rotation rate should beset to the predesigned values. Meanwhile the
pressure-control system and the spoil discharge system are activated
to keep the inner pressure at a balanced value, while the generated
spoil is transported. Simultaneously, the drill rod is rotated and slowly
retracted from the drilling hole. When the distance between the front

head of the monitor and the retaining wall is reduced to half a meter, sodium silicate solution (accelerator) is injected into the soil to promote
solidification. Use of accelerator can make the soil-cement admixture

Fig. 14. Soil profile and properties of the clay deposits at the test site.


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Y. Yuan et al. / Automation in Construction 69 (2016) 11–20
Table 1
Jetting parameters in the jetting construction (data from Wang et al. [24]).
Properties

Range

Compressed air pressure
Water injection pressure
Water flow rate
Grout injection pressure
Grout flow rate
Rod withdrawal rate
Rod rotation rate
Ratio of water to cement
Nozzle diameter

0.7 MPa
22–25 MPa
75–90 L/min
5–8 MPa
55–65 L/min

0.2 m/min
12 r/min
1:1
1.8 mm

gel within 5 s to seal the hole and to stop the slurry from flowing out
of the grouted column. Thus, even after the pressure-control system
(including valve and rod) is removed, the slurry pressure of jet-grouted
column can keep balance with the earth pressure.
3.3. Stage 3: end of construction
After the construction of one column, the drill rod is withdrawn to
the predesigned position, and the equipment is closed for cleaning.
Fig. 11c shows an illustration of the washing rod after construction.
Fig. 12 gives photographs of drilling rod withdrawn (Fig. 12a) and the
washing rod after construction (Fig. 12b). The drill rod is then moved to
the designed position of the next column and the steps are repeated as
shown in Fig. 10, to complete the next column. This process is repeated
until the target site has been jet grouted to achieve the desired ground
improvement.
4. Case study and discussion

Fig. 16. Plan view of layout of monitoring instruments (modified from Wang et al. [24]).

The horizontally jet grouted columns are constructed in the silty clay
layer at a depth of about 2 m below the ground surface [28], as shown
in Fig. 14. The silty clay layer has high water content [29], low strength
and high compressibility characteristics [30]. Table 1 gives the jetting
parameters in jet grouting constructions. Fig. 15 shows a plan view of
the jet-grouting area. Five columns (labeled C1–C5) were constructed
using this new equipment. The columns were designed to be 6 m in

length and have a target diameter of 1.0 m.
During the field test, the vertical displacement of the ground surface
was monitored. Fig. 16 shows a plan view of the layout of the settlement
gauges (labeled O1–O3). The distances between the jet grouting zone
and the settlement gauges O1, O2, and O3 were 1.8 m, 3.3 m, and
5.8 m, respectively. The spacing between the settlement gauges and
the construction area was 2.5 m.

4.1. Project background
4.2. Effectiveness of PCJG
To demonstrate the capabilities of the new jet grouting equipment, a
field test was conducted at the Qingcaosha Water Source Project [22]
near Longyue Road in Pudong New Development District, Shanghai,
China [23]. Fig. 13 shows the location of the test site [24]. Fig. 14 illustrates the soil profile and the soil properties of the clay deposits at the
test site [25]. A silty clay layer with a thickness of 2.8 m overlies a
10.2 m thick mucky silty clay layer [26]. Under the mucky silty clay
layer, there is a very soft clay layer with a thickness of about 6 m [27].

Fig. 15. Plan view of layout of jet grout columns.

Fig. 17 shows the measured results of ground upheaval. The maximum value of the ground upheaval was 9.4 mm (for column C4) and
the minimum value was 0.4 mm (for C2). Because the new equipment
can easily transport out the spoil and control the inner pressure of the
soil stratum automatically during construction, the adverse ground
movement can be reduced.
Twenty eight days after installation of the trial columns, core
samples are extracted from the jet grout columns for inspection. For
the entire core samples obtained, the total core recovery varied from
70% to 95% and the rock quality designation varied from 79% to 92%.

Fig. 17. The measured upheaval in field test (data from Wang et al. [24]).


Y. Yuan et al. / Automation in Construction 69 (2016) 11–20

The measured values of unconfined compressive strength (qu) range
from 0.9 MPa to 1.5 MPa [24].
Shen et al. (2013a) [31] pointed out that there exists two methods
for prediction of the diameter of jet grout column, i.e. empirical
approach [17], theoretical approach based on submerged flow [32] or
turbulent flow theory [31], and numerical approach [33]. Ochmański
proposed an approach to predict the diameter of Jet Grouting columns
with Artificial Neural Networks [34]. To predict the diameter of
jet grout columns installed using the various conventional jet grouting
systems (i.e. single, double and triple fluid systems), a generalized
formulation was proposed in the form [31]:
Dr
2

R j ¼ ηxL þ

ð2Þ

where Rj = calculated radius of column; η = reduction coefficient
accounting for the effect of the injection time; xL = ultimate erosion
distance; Dr. = diameter of monitor. All of the operational parameters,
fluid properties, soil strength and particle size distribution were
incorporated in the reduction coefficient (η) and the ultimate erosion
distance (xL). The reader can refer to Shen et al. (2013b) [31] for an
in-depth description of this method.

Similarly, Flora et al. [17] proposed an alternate formulation to
predict the average diameter of jet grout column in fine-grained soils
formed using conventional jet grouting systems:

Da ¼ Dref

0:2  −0:25
αΛ Ã E0n
qc
7:5 Â 10
1:5

ð3Þ

where Da = average calculated diameter of column; E′ = specific energy at the nozzles; α = parameter relating to the jet interaction with the
surrounding fluid (either grout spoil or air): i) α = 1 for single fluid jet
grouting where no air shroud is used, ii) α N 1 for double and triple fluid
jet grouting; Λ⁎ = parameter relating to composition of the eroding
fluid (either water or grout); Dref = reference diameter obtained with
single fluid jet grouting having the water-cement ratio of eroding fluid
of ω = 1, and corresponding to E′ = 10 MJ/m and qc = 1.5 MPa. The
reader is referred to Flora et al. (2013) for further details of this method
[17].
In adopting Eq. (2) for the present trial parameters, a predicted
diameter of 1.04 m (i.e. Rj = 0.52 m). The alternate prediction using
Eq. (3) gave a diameter of Da = 1.13 m. These predicted diameter
are a little bit smaller than the measured diameters of 1.1 m to 1.4 m
observed in the trial columns [24]. This shown that removal of spoil
increases the erodibility of jetting, which was considered in the theoretical prediction equations.
5. Conclusions

Newly designed automatic pressure-control equipment has been
developed to reduce construction related ground movement and
environmental impact during horizontal jet grouting operations. The
applicability of this new equipment was verified through a case study
in a well consolidated soil strata with over-consolidation ratio greater
than unity. Detailed conclusions can be drawn as follows:
1) The innovative elements of the horizontal jet grouting equipment
include: i) multiple-functional monitor, ii) pressure control system,
and iii) spoil discharge system.
2) The developed automatic pressure-control jet grouting equipment is
based on the concept of self-balanced pressure and automatic spoil
drainage. During jet grouting, the construction parameters, including water pressure, grouting rate, and retracting velocity can be
detected, recorded and controlled automatically. The generated
spoil can be removed from the stratum to maintain the stability of
the ground and to effectively reduce environmental impact.

19

3) The field test was conducted in the well-consolidated soil strata with
over consolidation ratio greater than unity. Monitoring results from
field test indicate that the measured upheaval of the ground surface
is less than 10 mm, which is significantly smaller than those required
from code for protecting surroundings. These results verify the
effectiveness of the new equipment.
4) The key aspect of the successful application of the new equipment is
to ensure the spoil path out road during jet grouting. Thus, the
clogging of gap between diameters of monitor and rod should be
avoided. There are two possible reasons for clogging: collapse of
soil strata and large diameter of soil particle (e.g. gravel particle).
The factor influence of clogging may include stress state of soil, particle size of soil and size of the gap, which need to be investigated

further in the future to develop universal applicable equipment in
various soil strata.
Acknowledgements
The authors thank Dr. Anil Misra for assistance in review and proofread the manuscript for improvement of the quality of the manuscript
in both English and technical aspect. The research work described
herein was funded by the National Nature Science Foundation of
China (NSFC) (Grant No. 41372283) and National Basic Research Program of China (973 Program: 2015CB057806). This financial support
is gratefully acknowledged.
References
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