Automatic pressure control equipment for horizontal jet grouting

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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 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: 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 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 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 ẳ h 1ị 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] 12 Y Yuan et al / Automation in Construction 69 (2016) 11–20 Fig 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 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 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 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 Pressure-control jet grouting technology 2.1 Composition of PCJG Fig shows the composition of the equipment for PCJG The connection of these different parts is also shown schematically in Fig Fig shows photographs of the main components of this system The main apparatus applied in PCJG is composed of six parts: (1) the drilling Fig Photographs of the main elements of the equipment 14 Y Yuan et al / Automation in Construction 69 (2016) 11–20 Fig Photograph of multiple-functional monitor used in horizontal jet grouting construction (modified from Wang et al [24]) Fig 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 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 Sectional schematic view of multiple-functional monitors Y Yuan et al / Automation in Construction 69 (2016) 11–20 15 Fig 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 shows the configuration of the multiple-functional monitor, which is installed at the tip end of the triple rod Fig 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 and 2), two injection nozzles at the back of the monitor (nozzles and 4) and one injection nozzle at the another end of the monitor (nozzle 5) Nozzles and 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 and 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 and with the high pressure water With the triple rod in the designated position, the low pressure grout is ejected from nozzles and 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 ejects high pressure water to accelerate the removal of the spoil from the gap during jet grouting construction Fig 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 illustrates a schematic view of the pressure-control system Fig 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 Photographs of pressure-control system in horizontal jet grouting construction: a) PLC and frequency converter; b) control valve 16 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]) 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 18 Y Yuan et al / Automation in Construction 69 (2016) 11–20 Table 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 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 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 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 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 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 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 R j ¼ xL ỵ 2ị 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 = for single fluid jet grouting where no air shroud is used, ii) α N 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 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 [1] T Yahiro, H 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pressure water to erode soil (water pipe I), (3) for spoil generating water (water pipe II), (4) for injecting... (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... 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)