Automatic pressure control equipment for horizontal jet grouting

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Automatic pressure-control equipment for horizontal jet-grouting

Yao Yuana, Shui-Long Shena,⁎ , Zhi-Feng Wangb, Huai-Na Wua,⁎

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 b s t r a c t

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

A new horizontal jet grouting equipment is proposed to eliminate the harmful effect on the surrounding environ-ment 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 Afield 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 offield cone penetration and unconfined compressive strength tests

© 2016 Elsevier B.V All rights reserved

Keywords:

Horizontal jet grouting equipment

Pressure-control

Spoil discharge

Vertical displacement

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

technol-ogy 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],

im-provement 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] Thefirst patent of jet grouting was applied

in 1968, as the‘Chemical Churning Pile’ (CCP) method[1], which is the

forerunner of the singlefluid system[15] Recently with developments

in construction technology, the doublefluid system (involving grout

and air)[16], and the triplefluid system (grout, water and air)[17]

have been used for different geological conditions[18] During jet

grouting, high velocityfluids 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]

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 1depicts 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 inFig 1) can be expressed as follows:

whereγ = unit weight of the overburden soils; and h = overlying thickness of the soil above the construction site

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 inFig 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 pressurizedfluids 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]

⁎ Corresponding authors.

E-mail addresses: slshen@sjtu.edu.cn (S.-L Shen), zhifeng.wang@chd.edu.cn

(Z.-F Wang).

http://dx.doi.org/10.1016/j.autcon.2016.05.025

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

addi-tion, 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

‘Compos-ite-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 overbur-den soil for jet grouting construction is very thin, the pressure of the jet groutingfluids may have a major effect on the surrounding environment, and the volume of spoil to be removed cannot be controlled

automatical-ly 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 (seeFig 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 con-cept 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 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.

Fig 2 Sectional view of composite pipes used in MJS and CPM technology, a) MJS; b) CPM (modified from Nakashima and Nakanishi

P The inner stratum pressure near the monitor should balance the earth

pressure of the overlying soils, p If PN p, ground heave in stage II

happens, whereas if Pb 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 drillingfluid for the new equipment is high pressure

water Meanwhile, the operation becomes simple and easy in

compari-son 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 equip-ment; 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 3shows the composition of the equipment for PCJG The connec-tion of these different parts is also shown schematically inFig 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 3 Composition of the equipment for horizontal pressure-control jet grouting.

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 inFig 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 arefive 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

com-pressed 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 threeflow meters, three

pressure sensors and an in-situ parameter monitor In order to

si-multaneously monitor the quality of the jet grouting column, the

following parameters for drilling and jet grouting can be detected

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 respectiveflow meters, while the pressure of the grout, the water, and the compressed air can be monitored simulta-neously 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 inFig 5includes

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 uti-lized 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 5 Sectional view of the sealing device.

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 6shows the configuration of the multiple-functional monitor,

which is installed at the tip end of the triple rod.Fig 7gives a

photo-graph of the monitor used in horizontal jet grouting construction The

diameter of the monitor (125 mm) is 35 mm larger than that of the

inner diameter of the steel tube During jetting, an annular space is

cre-ated between the rod and the surrounding borehole wall, which allows

the spoil slurry generated to be transported away from the monitor

to-wards the swivel head

As shown inFig 6, there arefive 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

(noz-zle 5) Noz(noz-zles 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 6also depicts the configuration of each noz-zle 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 noz-zle 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 over-burden soil will upheave If the inner stratum pressure is smaller than the overburden soil pressure, it will cause the settlement of the overly-ing soil Thus, the inner stratum pressure should be controlled to be ap-proximately 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 bal-anced and the large ground upheaval or settlement can be avoided Fig 8illustrates a schematic view of the pressure-control system Fig 9shows photographs of the pressure-control system in horizontal jet grouting construction The main part of the system is a Programma-ble Logic Controller (PLC) and a frequency converter (Fig 9a) and con-trol 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 8 Schematic view of the pressure-control 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

pres-sure, 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 self-supporting 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 diam-eter 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 dis-charge system is incorporated to remove water from the spoil sludge,

Fig 10 Configuration of the spoil discharge system.

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 10shows the configuration of the spoil discharge system The

spoil discharge system consists offive parts: (1) the preliminary mixing

combination device, (2) the furnishing device, (3) the sludge

concentra-tion device, (4) the integratedfilter-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 thefirst step of mixing the spoil, the mixed spoil is transported

to the concentration device to dehydrate the spoil The sludge

concen-tration device contains: the discharge pump and the inner pressurized

storage tank The discharge pump is set at one side of the inner

pressur-ized storage tank and is connected with the tank through the sludge

valve When the sludgeflows through the inner pressurized storage

tank, the water can transit through thefilter fabric and the large soil

par-ticles will be held back in the device The concentrated spoil then transit

to the integratedfilter-press and sludge discharge device As a result the

filter cake will be formed, and the water can be stored for potential

recycling

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 ef fi-ciency 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, so-dium silicate solution (accelerator) is injected into the soil to promote solidification Use of accelerator can make the soil-cement admixture

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

Fig 13 Test site location where the equipment was used (modified from Wang et al Fig 14 Soil profile and properties of the clay deposits at the test site.

gel within 5 s to seal the hole and to stop the slurry fromflowing 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 12gives 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 inFig 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

4.1 Project background

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 13shows the location of the test site[24].Fig 14

illus-trates 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]

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

inFig 14 The silty clay layer has high water content[29], low strength and high compressibility characteristics[30].Table 1gives the jetting parameters in jet grouting constructions.Fig 15shows 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 thefield test, the vertical displacement of the ground surface was monitored.Fig 16shows 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

4.2 Effectiveness of PCJG

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

field test (data from Wang et al.

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 triplefluid systems), a generalized

formulation was proposed in the form[31]:

Rj¼ ηxLþDr

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 infine-grained soils

formed using conventional jet grouting systems:

Da¼ Dref αΛE0n

7:5  10

qc

1:5

 −0:25

ð3Þ

where Da= average calculated diameter of column; E′ = specific

ener-gy at the nozzles;α = parameter relating to the jet interaction with the

surroundingfluid (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

singlefluid jet grouting having the water-cement ratio of eroding fluid

ofω = 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

theoret-ical 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,

includ-ing water pressure, groutinclud-ing rate, and retractinclud-ing 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

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, par-ticle 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 proof-read 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 Pro-gram of China (973 ProPro-gram: 2015CB057806) Thisfinancial support

is gratefully acknowledged

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