Construction method of high-pressure jet grouting pile near bridge pile foundation

Abstract

This invention relates to a high-pressure jet grouting pile construction method for adjacent bridge pile foundations, comprising the following steps: collecting road surface geological data of the construction section and designing a test scheme for a high-pressure jet grouting pile test section; constructing test piles according to the test scheme, and monitoring the settlement and deep horizontal displacement data of the engineering simulation piles, as well as the deep horizontal displacement and pore water pressure of the soil surrounding the test piles during construction, to obtain monitoring data; analyzing the monitoring data and formulating a large-area construction scheme for high-pressure jet grouting piles adjacent to bridge pile foundations; carrying out high-pressure jet grouting pile construction according to the large-area construction scheme; dynamically tracking and analyzing the monitoring data of the monitoring instruments during construction, establishing a data alarm system, and setting alarm values; continuing to track and monitor data such as the horizontal displacement data of the bridge abutment after construction; ensuring that the displacement and settlement of the road surface and bridge abutment are within the allowable monitoring limits.

Description

Technical Field

[0001] This invention relates to the field of civil engineering construction technology, specifically to a high-pressure jet grouting pile construction method for adjacent bridge pile foundations. Background Technology

[0002] With urban economic development, urban transportation networks are becoming increasingly complex, and elevated bridges crossing urban roads are very common. Due to the ever-increasing traffic volume, older urban roads often experience traffic congestion and cannot meet the needs of transportation development, often requiring rerouting and upgrades.

[0003] Secondly, because some urban roads are located in coastal hilly-plain areas, their foundations are often composed of special soil and rock types, such as soft soil, artificial fill, and liquefiable sand. Before road realignment and upgrades, foundation treatment is urgently needed. High-pressure jet grouting piles, as a convenient and reliable foundation reinforcement method, are widely used in various soft soil foundation reinforcement applications. However, the construction of high-pressure jet grouting piles inevitably affects the surrounding soil and rock. The stress on the soil can easily act on the bridge pile foundations of viaducts built above the road, potentially causing excessive deformation and leading to bridge pile foundation failure.

[0004] Therefore, this invention, as a high-pressure jet grouting pile construction method for adjacent bridge pile foundations, solves the aforementioned related problems. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a high-pressure jet grouting pile construction method for adjacent bridge pile foundations that overcomes or at least partially solves the above problems.

[0006] This invention provides a method for constructing high-pressure jet grouting piles near bridge pile foundations, the method comprising the following steps:

[0007] Collect geological data of the road surface of the construction section, select representative soil samples for indoor geotechnical tests, and design test schemes for high-pressure jet grouting pile test sections;

[0008] A section of road surface containing bridge pile foundations was selected as the test section, and the bridge pile foundations were engineering simulation piles. According to the test plan of the high-pressure jet grouting pile test section, test piles were constructed, and the settlement and deep horizontal displacement data of the engineering simulation piles during the construction process, as well as the deep horizontal displacement and pore water pressure of the soil around the test piles during the construction process, were monitored to obtain the monitoring data.

[0009] Analyze the monitoring data to obtain the optimal construction parameters, and formulate a large-area construction plan for high-pressure jet grouting piles near the bridge pile foundation based on the optimal construction parameters.

[0010] Monitoring elements and instruments are deployed on the road surface of the construction section according to general sections and key sections. The general sections are only equipped with instruments for monitoring the horizontal displacement of bridge piers, settlement of bridge piers, pore water pressure of foundation soil, and deep displacement of foundation soil. The key sections are equipped with instruments for monitoring the horizontal displacement of bridge piers, settlement of bridge piers, tilt of bridge piers, automated deep horizontal displacement, pore water pressure of foundation soil, and deep displacement of foundation soil.

[0011] On the road surface of the construction section, high-pressure jet grouting piles were constructed according to the large-area construction plan for high-pressure jet grouting piles.

[0012] During construction, the monitoring data of the monitoring instruments are dynamically tracked and analyzed, a data alarm system is established, and alarm values ​​are set. If abnormal monitoring data is detected, work is stopped in time, the construction parameters are optimized and adjusted, and then the high-pressure jet grouting pile construction is carried out again.

[0013] During construction, the monitoring data from the monitoring instruments were continuously tracked;

[0014] After construction is completed, continue to track and monitor the horizontal displacement data of the bridge abutment, the vertical settlement data of the bridge abutment, the tilt data of the bridge piers, and the settlement data of the shallow soil; establish monitoring and early warning values; and ensure that the displacement and settlement of the road surface and the bridge abutment are within the allowable range of the monitoring limits.

[0015] In one embodiment, the indoor geotechnical tests include: soil moisture content test, soil density test, soil particle size analysis test, soil consolidation test, soil direct shear test, and cement mix proportion test.

[0016] In one embodiment, the test plan for the high-pressure jet grouting pile test section specifically includes a test plan for the influence of jet grouting pressure on bridge pile foundation and foundation soil, and a test plan for the influence of construction distance and sequence on bridge pile foundation.

[0017] In one embodiment, the test plan for the effect of jet grouting pressure on bridge pile foundations and foundation soil includes the following steps:

[0018] Centered on the bridge pile foundation, three high-pressure jet grouting piles, numbered 1#, 2#, and 3# respectively, were constructed in sequence, with an included angle of 120° between the high-pressure jet grouting piles;

[0019] Three monitoring sections were set up between the bridge pile foundation and the three high-pressure jet grouting piles, and inclinometers and earth pressure gauges were installed in each section.

[0020] Four monitoring sections are arranged in a radial pattern at a 60° angle for the No. 1 high-pressure jet grouting pile. Several pore water pressure gauges and soil pressure gauges are installed in each section. Stress relief holes are added to one of the monitoring sections.

[0021] The No. 2 and No. 3 high-pressure jet grouting piles are each arranged in a radial pattern at a 60° angle, with three monitoring sections. Several pore water pressure gauges and soil pressure gauges are installed in each section.

[0022] High-pressure jet grouting piles were constructed sequentially in the order of No. 2, No. 3, and No. 1, with jet grouting pressures of 10MPa, 15MPa, and 20MPa respectively; during construction, automated monitoring was carried out sequentially in each section;

[0023] After construction is completed, record the above monitoring data.

[0024] In one embodiment, the experimental scheme for the influence of construction distance and sequence on bridge pile foundations includes the following steps:

[0025] Centered on the bridge pile foundation, high-pressure jet grouting piles numbered 1#, 2#, 3#, and 4# were constructed sequentially around the bridge pile foundation; several array-type displacement gauges and earth pressure gauges were installed at the outer edge section of the bridge pile foundation.

[0026] High-pressure jet grouting piles #1, #2, #3, and #4 were constructed at a jet grouting pressure of 15 MPa. The distances of high-pressure jet grouting piles #1, #2, #3, and #4 from the outer edge of the bridge pile foundation were 1.0 m, 1.5 m, 2.0 m, and 3.0 m, respectively. During construction, automated monitoring within the cross-section was carried out sequentially. The impact of construction distance on the bridge pile foundation was studied accordingly.

[0027] Centered on the bridge pile foundation, high-pressure jet grouting piles numbered 5#, 6#, 7#, and 8# were constructed on the other side of the bridge pile foundation; several array-type displacement gauges and earth pressure gauges were installed at the outer edge section of the bridge pile foundation.

[0028] High-pressure jet grouting piles were constructed in the order of No. 5, No. 7, No. 6, and No. 8, with a jet grouting pressure of 15 MPa. The high-pressure jet grouting piles and the bridge pile foundation were on the same straight line, and the distance between the piles was 1.0 m. During the construction process, the automated monitoring within the cross-section was carried out sequentially. The impact of the construction sequence on the bridge pile foundation was studied accordingly.

[0029] After construction is completed, record the above monitoring data.

[0030] In one embodiment, the large-area construction scheme for the high-pressure jet grouting piles includes the following steps:

[0031] (1) Construction preparation: The construction site is cleared, leveled and compacted, and a slurry preparation system and waste slurry sedimentation tank are set up. Before construction, the control points of the jet grouting pile construction are determined by total station and the pile positions are laid out according to the pile layout diagram.

[0032] (2) Drilling rig is positioned. After the drilling rig is positioned according to the pile layout diagram, the drilling rig is leveled and centered. Before drilling, the air compressor and grout pump should be tested to ensure that the equipment is operating normally. The length of the drill rod is checked to ensure that the bottom elevation of the hole meets the design depth.

[0033] (3) Drilling: After the drilling rig is in place and runs normally during the trial run, the pilot hole drilling begins;

[0034] (4) Inserting the core tube: After drilling with a geological drilling rig, pull out the core tube and replace it with a high-pressure jetting trolley rotary nozzle and insert it to the predetermined depth. During the insertion process, in order to prevent mud and sand from clogging the nozzle, water can be sprayed while inserting the tube, and the water pressure should not exceed 1 MPa.

[0035] (5) Spraying operation: After the nozzle is inserted to the predetermined depth, start the high-pressure pump. After the pump volume and pressure are normal and meet the design requirements, spray the nozzle from bottom to top. The rotary jet drill rod is lifted while spraying until the design elevation is reached.

[0036] (6) After the spraying construction is completed, the grouting pipe and other equipment should be rinsed clean, and no cement slurry should remain in the pipe.

[0037] (7) Move the equipment, such as the drilling rig, to the new hole position, and repeat steps (2) to (6) until all high-pressure jet grouting piles are completed.

[0038] In one embodiment, the specific steps of arranging the pile positions according to the pile layout diagram are as follows: the first row of high-pressure jet grouting piles is arranged 1.0m away from the pile cap, and the spacing between the piles in the first row of high-pressure jet grouting piles is 1.2m; the spacing between the remaining high-pressure jet grouting piles is 1.5m.

[0039] In one embodiment, the construction parameters of the large-area high-pressure jet grouting pile construction scheme are as follows: MGJ-50 type jet grouting drilling rig is used for construction; PO 42.5 grade ordinary Portland cement is used; the cement admixture is 55%, that is, the mix ratio is cement:soil:water = 1:1.83:1, and the cement consumption per meter is 180Kg; the grouting volume is 242L / m-258L / m; the first row of high-pressure jet grouting piles, 1.0m away from the viaduct pile cap, has a jet grouting pressure of 15MPa; the jet grouting pressure of other high-pressure jet grouting piles is 20MPa; high-pressure jet grouting piles are constructed by skipping piles at twice the spacing; the cement slurry flow rate is not less than 50L / min, and the lifting speed is not greater than 0.2m / min.

[0040] In this embodiment, before the formal construction of high-pressure jet grouting piles, indoor geotechnical tests and engineering simulation pile tests are conducted to test the stress and displacement of the pile foundation during construction, analyze the impact of high-pressure jet grouting construction on the existing bridge pile foundation, analyze the influence range of high-pressure jet grouting construction in the horizontal and vertical directions by testing the deep horizontal displacement and pore water pressure of the soil, and evaluate the reinforcement effect of soft soil treatment. This provides a reference for the subsequent large-area high-pressure jet grouting construction parameter optimization design and construction technology, ensuring the stability and safety of the substructure of the existing highway bridge. Attached Figure Description

[0041] The accompanying drawings, which form part of the specification, are used to provide a further understanding of the embodiments of this application and illustrate the implementation methods of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any creative effort. In the drawings:

[0042] Figure 1 This is a plan view of the pile locations and monitoring instruments for the test scheme of the effect of jet grouting pressure on bridge pile foundations and foundation soil according to an embodiment of the present invention.

[0043] Figure 2 This is a diagram showing the vertical arrangement of pile locations and monitoring instruments for an experiment demonstrating the effect of jet grouting pressure on bridge pile foundations and foundation soil, according to an embodiment of the present invention.

[0044] Figure 3 This is a plan view of the pile locations and monitoring instruments for the test scheme of the influence of construction distance and sequence on bridge pile foundations according to an embodiment of the present invention;

[0045] Figure 4 This is a test plan for the impact of construction distance and sequence on bridge pile foundations according to an embodiment of the present invention, showing the vertical layout of pile locations and monitoring instruments;

[0046] Figure 5 This is a graph showing the change in soil pressure increment of simulated pile #0 under different jet grouting pressures according to an embodiment of the present invention.

[0047] Figure 6 This is a graph showing the relationship between the increase in excess pore water pressure and the jet grouting pressure in simulated pile #0 of this invention.

[0048] Figure 7 This is a graph showing the relationship between the increase in excess pore water pressure and the jet grouting distance in simulated pile #0 of this invention.

[0049] Figure 8 This is a graph showing the horizontal displacement curves of simulated pile #1 at different construction distances under a pressure of 15 MPa, as described in Embodiment 1 of the present invention.

[0050] Figure 9This is a time history curve of the maximum horizontal displacement of simulated pile #1 at different construction distances under a pressure of 15MPa in Embodiment 1 of the present invention.

[0051] Figure 10 This is a graph showing the effect of construction sequence on the horizontal displacement of simulated pile #1 under 15MPa pressure in Embodiment 1 of the present invention.

[0052] Figure 11 This is a displacement rebound curve of the maximum horizontal displacement point under a pressure of 15MPa in Embodiment 1 of the present invention.

[0053] Figure 12 This is a graph showing the change in soil pressure increment of simulated pile #1 at different construction distances under a pressure of 15 MPa, as described in Embodiment 1 of the present invention.

[0054] Figure 13 This is a graph showing the effect of construction sequence on the incremental change of soil pressure in simulated pile #1 under 15MPa pressure in Embodiment 1 of the present invention.

[0055] Figure 14 This is a general section monitoring section layout diagram for the YK35+700~YK38+600 mileage section according to an embodiment of the present invention;

[0056] Figure 15 This is a diagram showing the layout of key monitoring sections in the YK35+700~YK38+600 mileage section according to an embodiment of the present invention.

[0057] Figure 16 This is a general section monitoring section layout diagram for the YK38+600~YK42+487.758 mileage section according to an embodiment of the present invention;

[0058] Figure 17 This is a diagram showing the layout of key monitoring sections for the YK38+600~YK42+487.758 mileage segment in an embodiment of the present invention. Detailed Implementation

[0059] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. It should be understood that the accompanying drawings and the following embodiments are for illustrative purposes only and are not intended to limit the invention.

[0060] This invention provides a method for constructing high-pressure jet grouting piles near bridge pile foundations, comprising the following steps:

[0061] Collect geological data of the road surface of the construction section, select representative soil samples for indoor geotechnical tests, and design test schemes for high-pressure jet grouting pile test sections;

[0062] A section of road surface containing bridge pile foundations was selected as the test section, and the bridge pile foundations were engineering simulation piles. According to the test plan of the high-pressure jet grouting pile test section, test piles were constructed, and the settlement and deep horizontal displacement data of the engineering simulation piles during the construction process, as well as the deep horizontal displacement and pore water pressure of the soil around the test piles during the construction process, were monitored to obtain the monitoring data.

[0063] Analyze the monitoring data to obtain the optimal construction parameters, and formulate a large-area construction plan for high-pressure jet grouting piles near the bridge pile foundation based on the optimal construction parameters.

[0064] Monitoring elements and instruments are deployed on the road surface of the construction section according to general cross-sections and key cross-sections. The general cross-sections are only equipped with instruments for monitoring the horizontal displacement of bridge piers, settlement of bridge piers, pore water pressure of foundation soil, and deep displacement of foundation soil. The key cross-sections are equipped with instruments for monitoring the horizontal displacement of bridge piers, settlement of bridge piers, tilt of bridge piers, automated deep horizontal displacement, pore water pressure of foundation soil, and deep displacement of foundation soil.

[0065] On the road surface of the construction section, high-pressure jet grouting piles were constructed according to the large-area construction plan for high-pressure jet grouting piles.

[0066] During construction, the monitoring data of the monitoring instruments are dynamically tracked and analyzed, a data alarm system is established, and alarm values ​​are set. If abnormal monitoring data is detected, work is stopped in time, the construction parameters are optimized and adjusted, and then the high-pressure jet grouting pile construction is carried out again.

[0067] During construction, the monitoring data from the monitoring instruments were continuously tracked;

[0068] After construction is completed, continue to track and monitor the horizontal displacement data of the bridge abutment, the vertical settlement data of the bridge abutment, the tilt data of the bridge piers, and the settlement data of the shallow soil; establish monitoring and early warning values; and ensure that the displacement and settlement of the road surface and the bridge abutment are within the allowable range of the monitoring limits.

[0069] In one embodiment, the indoor geotechnical tests include: soil moisture content test, soil density test, soil particle size analysis test, soil consolidation test, soil direct shear test, and cement mix proportion test.

[0070] In one embodiment, the test plan for the high-pressure jet grouting pile test section specifically includes a test plan for the influence of jet grouting pressure on bridge pile foundation and foundation soil, and a test plan for the influence of construction distance and sequence on bridge pile foundation.

[0071] In one embodiment, the test plan for the effect of jet grouting pressure on bridge pile foundations and foundation soil includes the following steps:

[0072] Centered on the bridge pile foundation, three high-pressure jet grouting piles, numbered 1#, 2#, and 3# respectively, were constructed in sequence, with an included angle of 120° between the high-pressure jet grouting piles;

[0073] Three monitoring sections were set up between the bridge pile foundation and the three high-pressure jet grouting piles, and inclinometers and earth pressure gauges were installed in each section.

[0074] Four monitoring sections are arranged in a radial pattern at a 60° angle for the No. 1 high-pressure jet grouting pile. Several pore water pressure gauges and soil pressure gauges are installed in each section. Stress relief holes are added to one of the monitoring sections.

[0075] The No. 2 and No. 3 high-pressure jet grouting piles are each arranged in a radial pattern at a 60° angle, with three monitoring sections. Several pore water pressure gauges and soil pressure gauges are installed in each section.

[0076] High-pressure jet grouting piles were constructed sequentially in the order of No. 2, No. 3, and No. 1, with jet grouting pressures of 10MPa, 15MPa, and 20MPa respectively; during construction, automated monitoring was carried out sequentially in each section;

[0077] After construction is completed, record the above monitoring data.

[0078] In one embodiment, the experimental scheme for the influence of construction distance and sequence on bridge pile foundations includes the following steps:

[0079] Centered on the bridge pile foundation, high-pressure jet grouting piles numbered 1#, 2#, 3#, and 4# were constructed sequentially around the bridge pile foundation; several array-type displacement gauges and earth pressure gauges were installed at the outer edge section of the bridge pile foundation.

[0080] High-pressure jet grouting piles #1, #2, #3, and #4 were constructed at a jet grouting pressure of 15 MPa. The distances of high-pressure jet grouting piles #1, #2, #3, and #4 from the outer edge of the bridge pile foundation were 1.0 m, 1.5 m, 2.0 m, and 3.0 m, respectively. During construction, automated monitoring within the cross-section was carried out sequentially. The impact of construction distance on the bridge pile foundation was studied accordingly.

[0081] Centered on the bridge pile foundation, high-pressure jet grouting piles numbered 5#, 6#, 7#, and 8# were constructed on the other side of the bridge pile foundation; several array-type displacement gauges and earth pressure gauges were installed at the outer edge section of the bridge pile foundation.

[0082] High-pressure jet grouting piles were constructed in the order of No. 5, No. 7, No. 6, and No. 8, with a jet grouting pressure of 15 MPa. The high-pressure jet grouting piles and the bridge pile foundation were on the same straight line, and the distance between the piles was 1.0 m. During the construction process, the automated monitoring within the cross-section was carried out sequentially. The impact of the construction sequence on the bridge pile foundation was studied accordingly.

[0083] After construction is completed, record the above monitoring data.

[0084] In one embodiment, the large-area construction scheme for the high-pressure jet grouting piles includes the following steps:

[0085] (1) Construction preparation: The construction site is cleared, leveled and compacted, and a slurry preparation system and waste slurry sedimentation tank are set up. Before construction, the control points of the jet grouting pile construction are determined by total station and the pile positions are laid out according to the pile layout diagram.

[0086] (2) Drilling rig is positioned. After the drilling rig is positioned according to the pile layout diagram, the drilling rig is leveled and centered. Before drilling, the air compressor and grout pump should be tested to ensure that the equipment is operating normally. The length of the drill rod is checked to ensure that the bottom elevation of the hole meets the design depth.

[0087] (3) Drilling: After the drilling rig is in place and runs normally during the trial run, the pilot hole drilling begins;

[0088] (4) Inserting the core tube: After drilling with a geological drilling rig, pull out the core tube and replace it with a high-pressure jetting trolley rotary nozzle and insert it to the predetermined depth. During the insertion process, in order to prevent mud and sand from clogging the nozzle, water can be sprayed while inserting the tube, and the water pressure should not exceed 1 MPa.

[0089] (5) Spraying operation: After the nozzle is inserted to the predetermined depth, start the high-pressure pump. After the pump volume and pressure are normal and meet the design requirements, spray the nozzle from bottom to top. The rotary jet drill rod is lifted while spraying until the design elevation is reached.

[0090] (6) After the spraying construction is completed, the grouting pipe and other equipment should be rinsed clean, and no cement slurry should remain in the pipe.

[0091] (7) Move the equipment, such as the drilling rig, to the new hole position, and repeat steps (2) to (6) until all high-pressure jet grouting piles are completed.

[0092] In one embodiment, the specific steps of arranging the pile positions according to the pile layout diagram are as follows: the first row of high-pressure jet grouting piles is arranged 1.0m away from the pile cap, and the spacing between the piles in the first row of high-pressure jet grouting piles is 1.2m; the spacing between the remaining high-pressure jet grouting piles is 1.5m.

[0093] In one embodiment, the construction parameters of the large-area high-pressure jet grouting pile construction scheme are as follows: MGJ-50 type jet grouting drilling rig is used for construction; PO 42.5 grade ordinary Portland cement is used; the cement admixture is 55%, that is, the mix ratio is cement:soil:water = 1:1.83:1, and the cement consumption per meter is 180Kg; the grouting volume is 242L / m-258L / m; the first row of high-pressure jet grouting piles, 1.0m away from the viaduct pile cap, has a jet grouting pressure of 15MPa; the jet grouting pressure of other high-pressure jet grouting piles is 20MPa; high-pressure jet grouting piles are constructed by skipping piles at twice the spacing; the cement slurry flow rate is not less than 50L / min, and the lifting speed is not greater than 0.2m / min.

[0094] The present invention will be described in more detail below through specific embodiments, but the embodiments described below are only for illustrating the present invention and the scope of the present invention is not limited thereto.

[0095] Example

[0096] A road realignment project is planned to be implemented under and on both sides of a highway viaduct. Construction adjacent to the viaduct will inevitably have a significant impact on it. The special soil and rock conditions of this road realignment project mainly include soft soil and artificial fill, with liquefiable sandy soil being the primary adverse geological feature. If high-pressure jet grouting is used for the road foundation treatment, it will inevitably affect the surrounding soil. The stress on the soil acting on the pile foundation may cause excessive deformation, leading to pile foundation failure. Therefore, there is an urgent need to solve the above problems using a high-pressure jet grouting construction method located near the bridge pile foundation.

[0097] A high-pressure jet grouting construction method for adjacent bridge pile foundations includes the following steps:

[0098] Geological data of the road surface in the construction section were collected, and representative soil samples were selected for indoor geotechnical tests. These tests included soil moisture content testing, soil density testing, soil particle size analysis, soil consolidation testing, direct shear testing, and cement mix proportioning testing. The physical and mechanical characteristics of undisturbed soil in different strata were obtained from the indoor geotechnical tests. Based on these tests, the following construction parameters were determined: MGJ-50 rotary jet grouting rig was used; PO 42.5 grade ordinary Portland cement was used; the cement content was 55%, i.e., the mix ratio was cement:soil:water = 1:1.83:1, and the cement usage was 180 kg per meter; the grouting volume was 242 L / m - 258 L / m.

[0099] Based on the above parameters, a test plan for the high-pressure jet grouting pile test section was designed. The test plan for the high-pressure jet grouting pile test section includes a test plan for the influence of jet grouting pressure on bridge pile foundation and foundation soil, and a test plan for the influence of construction distance and sequence on bridge pile foundation.

[0100] A section of road surface containing bridge pile foundations was selected as the test section, and the bridge pile foundations were engineering simulation piles. The test site should be selected from strata with representative geological conditions. After on-site reconnaissance, the left 200 meters of the ZK39+000~ZK39+200 section was finally selected as the test section. The test piles were constructed according to the test plan for the influence of jet grouting pressure on bridge pile foundations and foundation soil, and the test plan for the influence of construction distance and sequence on bridge pile foundations. The settlement and deep horizontal displacement data of the engineering simulation piles were monitored during the construction process, as well as the deep horizontal displacement and pore water pressure of the soil around the test piles during the construction process.

[0101] The test plan for the effect of jet grouting pressure on bridge pile foundations and foundation soil includes the following steps:

[0102] refer to Figures 1 to 2 Centered on the engineering simulation pile (numbered 1#), three high-pressure jet grouting piles numbered 1#, 2# and 3# were constructed in sequence, with the included angle between the high-pressure jet grouting piles being 120°.

[0103] Three monitoring sections were set up between pile #0 and three high-pressure jet grouting piles, and inclinometers and earth pressure gauges were installed in each section.

[0104] Four monitoring sections are arranged in a radial pattern at a 60° angle for the No. 1 high-pressure jet grouting pile. Several pore water pressure gauges and soil pressure gauges are installed in each section. Stress relief holes are added to one of the monitoring sections.

[0105] The No. 2 and No. 3 high-pressure jet grouting piles are each arranged in a radial pattern at a 60° angle, with three monitoring sections. Several pore water pressure gauges and soil pressure gauges are installed in each section.

[0106] High-pressure jet grouting piles were constructed sequentially in the order of No. 2, No. 3, and No. 1, with jet grouting pressures of 10MPa, 15MPa, and 20MPa, respectively. During construction, automated monitoring was carried out in each section at a frequency of 5 minutes per monitoring session. After construction was completed, the above monitoring data were recorded.

[0107] The monitoring items and instruments involved in the test scheme for the impact of jet grouting pressure on bridge pile foundations and foundation soil are shown in the table below:

[0108]

[0109] Table 1

[0110] The experimental plan for the impact of construction distance and sequence on bridge pile foundations includes the following steps:

[0111] refer to Figures 3 to 4Centered on the engineering simulation pile (numbered 1#), high-pressure jet grouting piles numbered 1#, 2#, 3#, and 4# were constructed sequentially around the engineering simulation pile (numbered 1#); several array-type displacement gauges and earth pressure gauges were installed at the outer edge section of the engineering simulation pile (numbered 1#);

[0112] High-pressure jet grouting piles #1, #2, #3, and #4 were constructed at a jet grouting pressure of 15 MPa. The distances of the high-pressure jet grouting piles #1, #2, #3, and #4 from the outer edge of the bridge pile foundation were 1.0 m, 1.5 m, 2.0 m, and 3.0 m, respectively. During construction, automated monitoring within the cross-section was performed sequentially at a frequency of 5 min / time. The impact of construction distance on the bridge pile foundation was studied accordingly.

[0113] Centered on the engineering simulation pile (numbered 1#), high-pressure jet grouting piles numbered 5#, 6#, 7#, and 8# were constructed on the other side of the bridge pile foundation; several array-type displacement gauges and earth pressure gauges were installed at the outer edge section of the engineering simulation pile (numbered 1#);

[0114] High-pressure jet grouting piles were constructed in the order of No. 5, No. 7, No. 6, and No. 8, with a jet grouting pressure of 15 MPa. The high-pressure jet grouting piles and the engineering simulation pile (No. 1) were on the same straight line, and the distance between the piles was 1.0 m. During the construction process, the automated monitoring within the cross-section was carried out sequentially, with a monitoring frequency of 5 min / time. The impact of the construction sequence on the bridge pile foundation was studied accordingly. After the construction was completed, the above monitoring data were recorded.

[0115] The monitoring items and instruments involved in the experimental scheme for the impact of construction distance and sequence on bridge pile foundations are shown in the table below:

[0116]

[0117] Table 2

[0118] Based on the test plans for the effects of jet grouting pressure on bridge pile foundations and foundation soil, and the test plans for the effects of construction distance and sequence on bridge pile foundations, test piles were constructed. Twenty-eight days after pile formation, core samples were drilled within the high-pressure jet grouting pile area of ​​the test section. The piles were found to be uniformly round, without necking or sinking. The pile arrangement, spacing, and diameter met the requirements, and the piles complied with design and construction specifications. Core samples were used to determine the unconfined compressive strength of the pile body; the compressive strength was ≥2MPa. The boreholes after core drilling were sealed with cement mortar. One high-pressure jet grouting pile was also selected for a plate load test. The composite foundation bearing capacity was not less than 120KPa, meeting the design requirements.

[0119] The monitoring data and analysis of the test on the effect of jet grouting pressure on bridge pile foundations and foundation soil are shown below:

[0120]

[0121]

[0122] Table 3. Inclinometer data of simulated pile #0 and soil.

[0123] Analyzing the data in Table 3, the following conclusions can be drawn:

[0124] 1. The maximum horizontal displacement decreases with increasing distance from the high-pressure jet grouting pile. Under the same distance conditions, the maximum horizontal displacement generally increases with increasing jet grouting pressure.

[0125] 2. When the distance increases from 1.0m to 1.5m, the maximum horizontal displacement in the soil decreases significantly, while when it increases from 1.5m to 2.0m, the decrease in the maximum horizontal displacement is relatively small. This indicates that when the construction pressure generated by the high-pressure jet grouting pile propagates in the soil at a distance of 1.0m to 1.5m, the jet grouting energy dissipates significantly, resulting in a significant decrease in the maximum horizontal displacement.

[0126] 3. At distances of 1.0m and 2.0m, the maximum horizontal displacement rebound rate decreases with increasing jet pressure, while at a distance of 1.5m, it first decreases and then increases.

[0127] 4. At the same rotary jet pressure of 10MPa and 15MPa, the maximum horizontal displacement rebound rate shows a trend of first decreasing and then increasing with the increase of distance.

[0128] Figure 5 The graph shows the change in earth pressure increment at simulated pile #0. It can be seen that under both 10MPa and 15MPa conditions, the earth pressure increment reaches its maximum at a depth of 10m. The earth pressure change does not show a decreasing trend with increasing distance; on the contrary, the earth pressure increment at the monitoring point closest to the jet grouting pile (1.0m) is smaller. This is because the earth pressure gauge is close to the jet grouting pile, and the back of the pressure-bearing surface is also soil. Under the action of the jet grouting pressure, the squeezed-in soil moves along with the surrounding soil, resulting in a lower earth pressure at a distance of 1.0m.

[0129] Figure 6 , Figure 7 The graph shows the relationship between the increase in excess pore water pressure of simulated pile #0 and the jet grouting pressure and distance. It can be seen from the graph that: under the same jet grouting pressure, the excess pore water pressure in the soil will decrease as the distance from the jet grouting pile construction increases; while under the same distance, the excess pore water pressure in the soil will increase as the jet grouting pressure increases.

[0130] The monitoring data and analysis of the test on the influence of construction distance and sequence on bridge pile foundations are shown below:

[0131] Figure 8The graph shows the horizontal displacement curves of simulated pile #1 at different construction distances under a pressure of 15 MPa. It can be seen from the graph that the horizontal displacement curve of the pile generally decreases with increasing depth. The maximum horizontal displacements of the high-pressure jet grouting piles constructed at distances of 1.0m, 1.5m, 2.0m and 3.0m are 1.118mm, 0.687mm, 0.624mm and 0.366mm, respectively.

[0132] Figure 9 The figure shows the time history curves of the maximum horizontal displacement of the No. 1 simulated pile body at different construction distances under a pressure of 15MPa. It can be seen from the figure that the cumulative displacement effect of the high-pressure jet grouting pile construction on the pile body is not obvious after the construction distance is greater than 1.5m. Therefore, in the actual construction process, it is advisable to set the distance of 1.5m as the safe construction distance.

[0133] Figure 10 The graph shows the effect of construction sequence on the horizontal displacement of simulated pile #1 under a pressure of 15 MPa. It can be seen from the graph that the maximum horizontal displacements of the pile caused by sequential construction distances of 1.0m, 3.0m, 2.0m, and 4.0m are 0.828mm, 0.473mm, -0.318mm, and -0.218mm, respectively. When the jet grouting pile was constructed at a distance of 2.0m, the pile experienced rebound because the earlier jet grouting pile at a distance of 1.0m experienced lower jet grouting pressure.

[0134] Figure 11 The figure shows the time history curve of the maximum horizontal displacement point on the effect of construction sequence on the horizontal displacement of simulated pile #1 under 15MPa pressure. It can be seen from the figure that because the high-pressure jet grouting piles at distances of 1.0m and 3.0m were constructed first, the jet grouting pressure generated by the high-pressure jet grouting pile at a distance of 2.0m had a reduced effect on the pile body, leading to continuous rebound of the pile body, and the cumulative displacement effect was not significant. Therefore, in actual engineering, adopting skip-driving construction can reduce the impact on surrounding structures.

[0135] Figure 12 The graph shows the change in soil pressure increment of simulated pile #1 at different construction distances under a pressure of 15 MPa. It can be seen from the graph that the maximum value of the soil pressure increment is basically at a depth of 10.0 m, and the soil pressure decreases as the construction distance increases.

[0136] Figure 13The graph shows the effect of construction sequence on the change in soil pressure increment of simulated pile #1 under a pressure of 15 MPa. As can be seen from the graph, the construction of 1.0m and 3.0m high-pressure jet grouting piles first resulted in a decrease in soil pressure increment when constructing high-pressure jet grouting piles with a spacing of 2.0m. The reason is that when constructing the 2.0m jet grouting piles, the already constructed 1.0m and 3.0m high-pressure jet grouting piles are equivalent to two soil reinforcement bonding bodies. The jet grouting pressure needs to do work on these two reinforcement bodies first or bypass them, thus reducing the soil pressure transmitted to the surface of the soil pressure gauge, and consequently reducing the soil pressure increment.

[0137] Based on the test schemes for the effects of jet grouting pressure on bridge pile foundations and foundation soil, and the test schemes for the effects of construction distance and sequence on bridge pile foundations, the following conclusions were drawn after analysis: (1) The maximum horizontal displacement of the pile body increases with the increase of jet grouting pressure and decreases with the increase of the construction distance of the jet grouting pile; (2) High-pressure jet grouting piles of 10MPa, 15MPa and 20MPa were used for construction, respectively. The jet grouting pressure of 20MPa caused the pile body to produce the maximum horizontal displacement, which was 2.934mm. The final displacement after rebound was 1.034mm, and the rebound amount was 1.900m. m, indicating that the impact of jet grouting pressure of 20MPa and below on the pile body is not significant; (3) the cumulative effect of displacement generated by high-pressure jet grouting pile construction on the pile body is not obvious after the construction distance is greater than 1.5m. Therefore, in actual construction, a distance of 1.5m can be considered as a safe construction distance; the test results of construction sequence parameters show that skip-driving construction can reduce the impact on the surrounding structure in actual engineering; (4) when there is a corresponding resistance support on the back of the earth pressure gauge test, the earth pressure increases with the increase of the construction pressure of high-pressure jet grouting pile and decreases with the increase of the construction distance. In addition, in this test, it was found that the maximum earth pressure basically appeared at a depth of 10.0m; (5) under the same jet grouting pressure conditions, the excess pore water pressure in the soil will decrease with the increase of the jet grouting pile construction distance; while under the same distance conditions, the excess pore water pressure in the soil will increase with the increase of the jet grouting pressure.

[0138] Therefore, based on the test results of the indoor geotechnical tests and the test plan of the high-pressure jet grouting pile test section, the optimal construction parameters are as follows: MGJ-50 type jet grouting drilling rig is used; PO 42.5 grade ordinary Portland cement is used; the cement content is 55%, i.e., the mix ratio is cement:soil:water = 1:1.83:1, and the cement usage per meter is 180 kg; the grouting volume is 242 L / m - 258 L / m; the first row of high-pressure jet grouting piles, 1.0 m away from the viaduct pile cap, is constructed using a double-spacing skip pile method, with a high-pressure cement grouting pressure of 15 MPa; the high-pressure cement grouting pressure for other piles is 20 MPa; the cement grout flow rate is not less than 50 L / min, and the lifting speed is not greater than 0.2 m / min.

[0139] Based on the above-mentioned optimal construction parameters, a large-area construction plan for high-pressure jet grouting piles near the bridge pile foundation was formulated.

[0140] According to the engineering design documents, the starting and ending mileage of this realignment project is from K35+700 to K42+488, with the affected expressway mileage being consistent. A total of 532 bridge piers are located along this section. Monitoring elements and instruments are deployed on the road surface of the construction section according to general and key cross-sections. The general cross-sections are equipped with instruments for monitoring the horizontal displacement of bridge piers, settlement of bridge piers, pore water pressure in the foundation soil, and deep displacement of the foundation soil. The key cross-sections are equipped with instruments for monitoring the horizontal displacement of bridge piers, settlement of bridge piers, tilt of bridge piers, automated deep horizontal displacement, pore water pressure in the foundation soil, and deep displacement of the foundation soil. 532 bridge piers are selected for the regular monitoring section, and 24 are selected for the test section. The monitoring cross-section layout diagram is shown below. Figures 14 to 17 As shown;

[0141] On the road surface of the construction section, high-pressure jet grouting piles were constructed according to the large-area construction plan for high-pressure jet grouting piles.

[0142] The large-area construction plan for high-pressure jet grouting piles includes the following steps:

[0143] (1) Construction preparation

[0144] The construction site was cleared to a depth of 30cm. After leveling and compaction, a grouting system and a waste grout sedimentation tank were set up. Before construction, the control points for the jet grouting pile construction were determined using a total station. The pile positions were laid out according to the pile layout diagram. The first row of high-pressure jet grouting piles was laid out 1.0m away from the pile cap, with a spacing of 1.2m between the first row of high-pressure jet grouting piles. The spacing between the remaining high-pressure jet grouting piles was 1.5m.

[0145] (2) Drilling rig in place

[0146] After the drilling rig is positioned according to the pile layout diagram, it should be leveled and centered. Before drilling, the air compressor and grout pump should be tested to ensure that the equipment is operating normally. The length of the drill rod should be checked to ensure that the bottom elevation of the hole meets the design depth.

[0147] (3) Drilling

[0148] After the drilling rig was in place and ran normally during the trial run, the pilot hole drilling began.

[0149] (4) Intubation

[0150] After drilling with a geological drilling rig, pull out the core tube and replace it with a high-pressure jet rig rotary nozzle inserted to the predetermined depth. During the insertion process, to prevent mud and sand from clogging the nozzle, water can be sprayed while inserting the tube. The water pressure should generally not exceed 1 MPa. If the pressure is too high, the borehole wall may collapse.

[0151] (5) Spraying operation

[0152] Once the nozzle is inserted to the predetermined depth, the high-pressure pump is started. After the pump volume and pressure are normal and meet the design requirements, the jetting operation is carried out from bottom to top. The rotary jetting drill rod is raised while being jetted until the design elevation is reached.

[0153] (6) Rinse

[0154] After the spraying operation is completed, the grouting pipes and other equipment should be thoroughly cleaned, and no cement slurry should remain inside the pipes.

[0155] (7) Mobile equipment

[0156] Move the drilling rig and other equipment to the new hole location and repeat steps (2) to (6) until all high-pressure jet grouting piles are completed.

[0157] During construction, the monitoring data of the monitoring instruments are dynamically tracked and analyzed, a data alarm system is established, and alarm values ​​are set. The control value for differential settlement and horizontal displacement at the surface of the bridge pier is 6mm, the warning value is set at 3mm, and the settlement rate warning value is set at 2mm / d. If abnormal monitoring data is found, work is stopped in time, the construction parameters are optimized and adjusted, and then the high-pressure jet grouting pile construction is carried out again.

[0158] During construction, monitoring data from monitoring instruments were continuously tracked.

[0159] After construction is completed, the horizontal displacement data of the bridge abutment, the vertical settlement data of the bridge abutment, the tilt data of the bridge piers, and the settlement data of the shallow soil will continue to be monitored for 2 years, with a frequency of once every 3 months. Monitoring and early warning values ​​will be set, with the differential settlement and horizontal displacement control value at the bridge pier surface set at 6 mm, the warning value set at 3 mm, and the settlement rate warning value set at 2 mm / d. During the defect period, under the action of vehicle live load, the displacement and settlement of the road surface and the bridge abutment will be within the allowable range of the monitoring limits, thereby ensuring the safety of the lower road and the upper highway bridge.

[0160] In this embodiment, before the formal construction of high-pressure jet grouting piles, indoor geotechnical tests and engineering simulation pile tests are conducted to test the stress and displacement of the pile foundation during construction, analyze the impact of high-pressure jet grouting construction on the existing bridge pile foundation, analyze the influence range of high-pressure jet grouting construction in the horizontal and vertical directions by testing the deep horizontal displacement and pore water pressure of the soil, and evaluate the reinforcement effect of soft soil treatment. This provides a reference for the subsequent large-area high-pressure jet grouting construction parameter optimization design and construction technology, ensuring the stability and safety of the substructure of the existing highway bridge.

[0161] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for constructing high pressure jet grouting pile near a bridge pile foundation, characterized in that, Includes the following steps: Collect geological data of the road surface of the construction section, select representative soil samples for indoor geotechnical tests, and design test schemes for high-pressure jet grouting pile test sections; A section of road surface containing bridge pile foundations was selected as the test section, and the bridge pile foundations were engineering simulation piles. According to the test plan of the high-pressure jet grouting pile test section, test piles were constructed, and the settlement and deep horizontal displacement data of the engineering simulation piles during the construction process, as well as the deep horizontal displacement and pore water pressure of the soil around the test piles during the construction process, were monitored to obtain the monitoring data. Analyze the monitoring data to obtain the optimal construction parameters, and formulate a large-area construction plan for high-pressure jet grouting piles near the bridge pile foundation based on the optimal construction parameters. Monitoring elements and instruments are deployed on the road surface of the construction section according to general sections and key sections. The general sections are only equipped with instruments for monitoring the horizontal displacement of bridge piers, settlement of bridge piers, pore water pressure of foundation soil, and deep displacement of foundation soil. The key sections are equipped with instruments for monitoring the horizontal displacement of bridge piers, settlement of bridge piers, tilt of bridge piers, automated deep horizontal displacement, pore water pressure of foundation soil, and deep displacement of foundation soil. On the road surface of the construction section, high-pressure jet grouting piles were constructed according to the large-area construction plan for high-pressure jet grouting piles. During construction, the monitoring data of the monitoring instruments are dynamically tracked and analyzed, a data alarm system is established, and alarm values ​​are set. If abnormal monitoring data is detected, work is stopped in time, the construction parameters are optimized and adjusted, and then the high-pressure jet grouting pile construction is carried out again. During construction, the monitoring data from the monitoring instruments were continuously tracked; After construction is completed, continue to track and monitor the horizontal displacement data of the bridge abutment, the vertical settlement data of the bridge abutment, the tilt data of the bridge piers, and the settlement data of the shallow soil; establish monitoring and early warning values; and ensure that the displacement and settlement of the road surface and the bridge abutment are within the allowable range of the monitoring limits. The test plan for the high-pressure jet grouting pile test section specifically includes a test plan for the influence of jet grouting pressure on bridge pile foundation and foundation soil, and a test plan for the influence of construction distance and sequence on bridge pile foundation. The test plan for the influence of jet grouting pressure on bridge pile foundations and foundation soil includes the following steps: Centered on the bridge pile foundation, three high-pressure jet grouting piles, numbered 1#, 2#, and 3# respectively, were constructed in sequence, with an included angle of 120° between the high-pressure jet grouting piles; Three monitoring sections were set up between the bridge pile foundation and the three high-pressure jet grouting piles, and inclinometers and earth pressure gauges were installed in each section. Four monitoring sections are arranged in a radial pattern at a 60° angle for the No. 1 high-pressure jet grouting pile. Several pore water pressure gauges and soil pressure gauges are installed in each section. Stress relief holes are added to one of the monitoring sections. The No. 2 and No. 3 high-pressure jet grouting piles are each arranged in a radial pattern at a 60° angle, with three monitoring sections. Several pore water pressure gauges and soil pressure gauges are installed in each section. High-pressure jet grouting piles were constructed sequentially in the order of No. 2, No. 3, and No. 1, with jet grouting pressures of 10MPa, 15MPa, and 20MPa respectively; during construction, automated monitoring was carried out sequentially in each section. After construction is completed, record the above monitoring data.

2. The high-pressure jet grouting pile construction method for adjacent bridge pile foundations according to claim 1, characterized in that, The indoor geotechnical tests include: soil moisture content test, soil density test, soil particle size analysis test, soil consolidation test, soil direct shear test, and cement mix design test.

3. The high-pressure jet grouting pile construction method for adjacent bridge pile foundations according to claim 1, characterized in that, The experimental scheme for investigating the impact of construction distance and sequence on bridge pile foundations includes the following steps: Centered on the bridge pile foundation, high-pressure jet grouting piles numbered 1#, 2#, 3#, and 4# were constructed sequentially around the bridge pile foundation; several array-type displacement gauges and earth pressure gauges were installed at the outer edge section of the bridge pile foundation. High-pressure jet grouting piles #1, #2, #3, and #4 were constructed at a jet grouting pressure of 15 MPa. The distances of high-pressure jet grouting piles #1, #2, #3, and #4 from the outer edge of the bridge pile foundation were 1.0 m, 1.5 m, 2.0 m, and 3.0 m, respectively. During construction, automated monitoring within the cross-section was carried out sequentially. The impact of construction distance on the bridge pile foundation was studied accordingly. Centered on the bridge pile foundation, high-pressure jet grouting piles numbered 5#, 6#, 7#, and 8# were constructed on the other side of the bridge pile foundation; several array-type displacement gauges and earth pressure gauges were installed at the outer edge section of the bridge pile foundation. High-pressure jet grouting piles were constructed in the order of No. 5, No. 7, No. 6, and No. 8, with a jet grouting pressure of 15 MPa. The high-pressure jet grouting piles and the bridge pile foundation were on the same straight line, and the distance between the piles was 1.0 m. During the construction process, the automated monitoring within the cross-section was carried out sequentially. The impact of the construction sequence on the bridge pile foundation was studied accordingly. After construction is completed, record the above monitoring data.

4. The high-pressure jet grouting pile construction method for adjacent bridge pile foundations according to claim 1, characterized in that, The large-area construction plan for high-pressure jet grouting piles includes the following steps: (1) Construction preparation: The construction site is cleared, leveled and compacted, and a slurry preparation system and waste slurry sedimentation tank are set up. Before construction, the control points of the jet grouting pile construction are determined by total station and the pile positions are set up according to the pile layout diagram. (2) The drilling rig is positioned according to the pile layout diagram. The drilling rig is then leveled and centered. Before drilling, the air compressor and grout pump should be tested to ensure that the equipment is operating normally. Check the drill rod length to ensure that the bottom elevation of the hole meets the design depth; (3) Drilling: After the drilling rig is in place and runs normally during the trial run, the pilot hole drilling begins; (4) Inserting the core tube: After drilling with a geological drilling rig, pull out the core tube and replace it with a high-pressure jetting trolley rotary nozzle and insert it to the predetermined depth. During the insertion process, in order to prevent mud and sand from clogging the nozzle, water can be sprayed while inserting the tube, and the water pressure should not exceed 1 MPa. (5) Spraying operation: After the nozzle is inserted to the predetermined depth, start the high-pressure pump. After the pump volume and pressure are normal and meet the design requirements, spray the nozzle from bottom to top. The rotary jet drill rod is lifted while spraying until the design elevation is reached. (6) After the spraying construction is completed, the grouting pipe should be rinsed clean and no cement slurry should remain in the pipe. (7) Move the equipment and move the drilling rig to the new hole position. Repeat steps (2) to (6) until all high-pressure jet grouting piles are completed.

5. The high-pressure jet grouting pile construction method for adjacent bridge pile foundations according to claim 4, characterized in that, The specific arrangement of pile positions according to the pile layout diagram is as follows: the first row of high-pressure jet grouting piles is arranged 1.0m away from the pile cap, and the spacing between the piles in the first row of high-pressure jet grouting piles is 1.2m; the spacing between the remaining high-pressure jet grouting piles is 1.5m.

6. A method for constructing high-pressure jet grouting piles near bridge pile foundations according to claim 4 or 5, characterized in that, The construction parameters for the large-area high-pressure jet grouting pile construction scheme are as follows: MGJ-50 type jet grouting drilling rig is used; P.O42.5 grade ordinary Portland cement is used; the cement admixture is 55%, that is, the mix ratio is cement:soil:water = 1:1.83:1, and the cement consumption per meter is 180Kg; the grouting volume is 242L / m-258L / m; the first row of high-pressure jet grouting piles, 1.0m away from the viaduct pile cap, has a jet grouting pressure of 15MPa; the jet grouting pressure of other high-pressure jet grouting piles is 20MPa; high-pressure jet grouting piles are constructed by skipping piles at twice the spacing; the cement slurry flow rate is not less than 50L / min, and the lifting speed is not greater than 0.2m / min.

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