DCM construction method of offshore deep cement-soil mixing pile

Abstract

The application discloses a DCM construction method of offshore deep cement soil mixing pile, and comprises the following steps: driving a DCM engineering ship to a predetermined position; determining the construction mode of each mixing pile based on stratum distribution data and the design construction coordinates of each cement soil mixing pile, wherein the construction mode is direct mixing construction or composite reinforcement mixing construction; if the rock stratum slope of the construction position is less than a slope threshold, the direct mixing construction mode is adopted; if the rock stratum slope of the construction position is greater than the slope threshold, the composite reinforcement mixing construction mode is adopted, wherein the composite reinforcement mixing construction mode refers to the following steps: using a variable-diameter drill bit mechanism in a drilling system to drill into the rock stratum surface and drill to form a conical hole on the rock stratum surface, using a four-axis DCM drill bit to conduct downward mixing construction and grouting to form a mixing pile group. The application has the advantages of high intelligence and automation, can adapt to different seabed rock stratum terrains, has good mixing soil body effect, has high construction efficiency, and can realize super-deep reinforcement.

Description

Technical Field

[0001] This invention belongs to the field of marine cement mixing technology, specifically relating to a DCM construction method for deep marine cement-soil mixing piles. Background Technology

[0002] When a tunnel crosses the seabed, the reinforcement of the weak seabed strata plays a crucial role in the safety of the tunnel structure. The cement-soil mixing pile (DCM) method is generally used to reinforce the weak seabed strata to achieve efficient and stable reinforcement, which can effectively ensure the smooth excavation of the shield tunnel and the quality of the completed tunnel.

[0003] The main construction equipment for cement-soil mixing piles (DCM) is the DCM engineering vessel. This vessel is a specialized engineering vessel that assists in the construction and installation of DCM piles. It is a highly automated and intelligent vessel integrating cement storage, cement mixing, screw conveying, underwater spraying, and mixing. It can perform deep cement mixing at depths of up to 30 meters, solidifying deep seabed foundations and playing an irreplaceable role in land reclamation.

[0004] The current cement-soil mixing pile (DCM) method mainly involves drilling cement slurry into the soft seabed strata that needs improvement to a certain depth using a drilling rig. The drill bit blades of the drilling rig fully cut and mix the soil and inject cement slurry to consolidate the soil and achieve a certain stability, as well as a certain shear and compressive strength.

[0005] The drawback of this DCM method is that the cement-soil mixing piles lack an effective connection with the rock strata below the weak seabed strata. Under additional loads or seismic action, the cement-soil mixing piles are prone to slippage or small-scale displacement on the rock surface with a steep slope. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing a DCM construction method for deep marine cement-soil mixing piles. This DCM construction method utilizes a DCM engineering vessel to select the appropriate construction method based on different rock slope data, thereby enabling the mixing piles to be stably installed on the seabed rock strata.

[0007] The objective of this invention is achieved through the following technical solutions:

[0008] A method for deep cement-soil mixing pile construction at sea, characterized in that the method includes the following steps:

[0009] S1: Conduct geological exploration of the seabed surface of the area to be reinforced to obtain the stratigraphic distribution data of the seabed surface, which consists of rock layer, clay layer and silt layer from bottom to top;

[0010] S2: Transport the DCM engineering vessel to the predetermined location; the DCM engineering vessel includes a flat barge, a cement silo system, a mixing and storage system, a slurry pump system, and a drilling rig system;

[0011] S3: Based on the geological distribution data and the design and construction coordinates of each cement-soil mixing pile, determine the construction method of each cement-soil mixing pile. The construction method is either direct mixing construction or composite reinforcement mixing construction.

[0012] S3.1: If the slope of the construction location is less than the slope threshold, the direct mixing construction method shall be adopted;

[0013] S3.2: If the slope of the construction location is greater than the slope threshold, a composite reinforcement and mixing construction method shall be adopted. The composite reinforcement and mixing construction method refers to: using the variable diameter drill bit mechanism in the drilling system to penetrate into the rock surface and drill to form a conical hole on the rock surface, then raising the variable diameter drill bit mechanism, and using the four-axis DCM drill bit in the drilling system to perform downward mixing construction and grouting to form a mixing pile group.

[0014] The main body of the DCM engineering vessel is the flat barge. The cement silo system and the mixing and slurry storage system are interconnected and installed on the flat barge. The drilling rig system includes the variable diameter drill bit mechanism, the four-axis DCM drill bit, and a rotating frame. The rotating frame is horizontally arranged and rotatably connected to the front of the flat barge. The rotating frame is fan-shaped, and the variable diameter drill bit mechanism and the four-axis DCM drill bit are vertically arranged at the front of the rotating frame.

[0015] The front of the flat barge is provided with a set of arc-shaped tracks. The front of the rotating frame is mounted on the arc-shaped tracks via wheels. The rear of the rotating frame is fixed to the flat barge via a pivot. The wheels are driven by a motor fixed below the rotating frame.

[0016] The variable-diameter drill bit mechanism includes a first column support, a first tie rod, a first guide rail, a first slider, a first steel cantilever beam, a first rotary motor, a first drill rod, and a variable-diameter drill bit. The first column support is vertically arranged at the front of the rotary frame. The upper end of the first tie rod is hinged to the upper end of the first column support, and the lower end is hinged to the rotary frame. The first guide rail is vertically arranged along the first column support and is tightly fixed to each other. The first slider is slidably mounted on the first guide rail. The first steel cantilever beam is fixed to the first slider and moves vertically with the first slider. The first rotary motor is fixed to the first steel cantilever beam and drives the first drill rod to rotate. The variable diameter drill bit is located at the lower end of the first drill rod. The variable diameter drill bit includes a drill bit, two long strip-shaped reamers, and two hydraulic telescopic rods. The drill bit is located at the lower end of the first drill rod. The upper end of the long strip-shaped reamer is hinged to the first drill rod. The hydraulic telescopic rod is provided between the lower end of the long strip-shaped reamer and the first drill rod. The hydraulic telescopic rod is used to drive the lower part of the long strip-shaped reamer to gradually expand outward in order to excavate the conical hole in the rock strata.

[0017] The four-axis DCM drill bit includes a second column support, a second tie rod, a second guide rail, a second slider, a second steel cantilever beam, several second rotary motors, and several second drill rods. The second column support is vertically arranged at the front of the rotary frame. The upper end of the second tie rod is hinged to the upper end of the second column support, and the lower end is hinged to the rotary frame. The second guide rail is vertically arranged along the second column support and is tightly fixed to each other. The second slider is slidably mounted on the second guide rail. The second steel cantilever beam is fixed on the second slider and moves vertically with the second slider. Each second rotary motor is fixed on the second steel cantilever beam and drives the corresponding second drill rod to rotate. The second drill rod has a grouting pipe. The mixing and grouting system is rotatably connected to the upper end of the second drill rod through the grouting pipe and pumps the concrete slurry into the grouting pipe inside the second drill rod. The drill bit of the second drill rod has a grout outlet hole.

[0018] The composite reinforcement and mixing construction includes the following steps:

[0019] The traveling wheels on the rotating frame are controlled to move along the arc-shaped track, so that the variable-diameter drill bit mechanism on the rotating frame rotates with the rotating frame to the position to be constructed, so that the first drill rod is lowered to the surface of the rock layer. Then, the drill bit of the variable-diameter drill bit is controlled to drill into the rock layer. At the same time, the lower part of the long strip reamer is gradually lifted outward by the hydraulic telescopic rod to expand it outward until the drill bit drills to a predetermined depth. Then, the long strip reamer is retracted inward by the hydraulic telescopic rod, and the first drill rod is lifted to obtain the tapered hole.

[0020] The traveling wheels on the rotating frame are controlled to move along the arc-shaped track, so that the four-axis DCM drill bit on the rotating frame rotates with the rotating frame to the construction position. The second drill rod is controlled to descend to the surface of the silt layer. Then, the cutter blades on the second drill rod are activated and rotated to drill down. The drill bit on the second drill rod drills down through the silt layer and clay layer in sequence to reach the conical hole in the rock stratum. The drill bit on the second drill rod performs grouting to form a mixing pile located in the conical hole. Then, several drilling and lifting operations are performed in the clay layer and grouting is performed to form a mixing pile in the clay layer. The drill bit on the second drill rod is lifted up and grouting is continued to form a mixing pile located in the silt layer.

[0021] The direct mixing construction method includes the following steps: controlling the traveling wheels on the rotating frame to move along the arc-shaped track, so that the four-axis DCM drill bit on the rotating frame rotates with the rotating frame to the construction position; controlling the second drill rod to descend to the surface of the silt layer; then opening the cutter blades on the second drill rod and rotating it to drill down; the drill bit on the second drill rod drills down sequentially through the silt layer and clay layer to reach the surface of the rock layer; then, several drilling and lifting operations are performed in the clay layer, and grouting is carried out to form a mixing pile in the clay layer; the drill bit on the second drill rod is continued to be lifted up and grouting is continued to form a mixing pile located in the silt layer.

[0022] The construction method for piles in the clay layer includes the following steps:

[0023] The drill bit on the second drill rod drills down 1m to the surface of the rock stratum. During this stage, the grouting speed is 1120L / min, the drilling speed is 0.8m / min, and the rotation speed is 30-36rpm.

[0024] The drill bit on the second drill rod is raised 4.1m to the interface between the clay layer and the silt layer. During this stage, the grouting speed is 820L / min, the lifting speed is 1m / min, and the rotation speed is 30-36rpm.

[0025] The drill bit on the second drill rod drills down 3.5m. During this stage, the grouting speed is 1120L / min, the drilling speed is 0.8m / min, and the rotation speed is 30-36rpm.

[0026] The drill bit on the second drill rod is lowered 0.6m to the surface of the rock stratum. During this stage, water spraying and grouting are carried out at a rate of 1120L / min, a drilling speed of 0.8m / min, and a rotation speed of 30-36rpm.

[0027] The drill bit on the second drill rod is raised 1m and then lowered 1m, then raised 1m and then raised 1m. During this stage, grouting is stopped, and the lowering and raising speed is 0.8m / min, with a rotation speed of 30-36rpm.

[0028] The advantages of this invention are: high degree of intelligence and automation, adaptability to different seabed rock strata and terrains, good soil mixing effect, high construction efficiency, and the ability to achieve ultra-deep reinforcement. Attached Figure Description

[0029] Figure 1 This is a vertical cross-sectional view of the seabed topography distribution in the area to be reinforced in this invention.

[0030] Figure 2 This is a schematic diagram of the structure of the DCM engineering vessel in this invention;

[0031] Figure 3 This is a plan view of the rotating frame on the DCM engineering vessel in this invention;

[0032] Figure 4 This is a schematic diagram of the variable diameter drill bit mechanism in this invention;

[0033] Figure 5 This is a schematic diagram of the structure of the four-axis DCM drill bit in this invention;

[0034] Figure 6 This is a schematic diagram of the mixing pile formed by direct mixing construction and the mixing pile formed by composite reinforced mixing construction in this invention;

[0035] Figure 7 This is a control diagram for direct mixing construction in this invention;

[0036] Figure 8 This is a partial structural diagram of the variable diameter drill bit mechanism in this invention. Detailed Implementation

[0037] The features and other related features of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, so as to facilitate understanding by those skilled in the art:

[0038] like Figure 1-8 The markings in the figure are as follows: 1. Flat barge; 2. Cement silo system; 3. Mixing and slurry storage system; 4. Slurry pump system; 5. Rotating frame; 6. Traveling wheel; 7. Arc track; 8. Variable diameter drill bit mechanism; 9. Four-axis DCM drill bit; 10. First mixing pile; 11. Second mixing pile; 12. Conical hole; 13.

[0039] First column support 901, first tie rod 902, first guide rail 903, first slider 904, first steel cantilever beam 905, first rotary motor 906, first drill rod 907, long strip reamer 908, hydraulic telescopic rod 909, variable diameter drill bit 910;

[0040] Second column support 1001, second tie rod 1002, second guide rail 1003, second slider 1004, second steel cantilever beam 1005, second rotary motor 1006, second drill rod 1007, cutter blade 1008, drill bit 1009.

[0041] Example: Figure 1-8 As shown, this embodiment specifically relates to a DCM construction method for deep offshore cement-soil mixing piles, which includes the following steps:

[0042] (S1) As Figure 1 As shown, geological exploration is carried out on the seabed surface of the area to be reinforced to obtain the stratigraphic distribution data of the seabed surface. The seabed surface consists of rock layer, clay layer and silt layer from bottom to top. In addition to the composition of each stratum, the stratigraphic distribution data also includes the thickness of each stratum and the elevation change of the upper surface of the rock layer. The elevation change of the upper surface of the rock layer will also reflect the slope of the upper surface of the rock layer from another perspective.

[0043] (S2) such as Figure 2 As shown, the DCM engineering vessel is driven to the predetermined position, namely the location where the first mixing pile 11 or the second mixing pile 12 is to be constructed. The DCM engineering vessel includes a flat barge 1 and a cement silo system 2, a mixing and storage system 3, a slurry pump system 4, and a drilling rig system that are sequentially arranged and connected on the flat barge 1.

[0044] The main body of the DCM engineering vessel is a flat barge 1. The cement silo system 2 and the mixing and storage system 3 are interconnected and installed on the flat barge 1. The drilling rig system includes a variable diameter drill bit mechanism 9, a four-axis DCM drill bit 10, and a rotating frame 6. Figure 3 As shown, the rotating frame 6 is horizontally positioned and rotatably connected to the front of the flat barge 1; the rotating frame 6 is fan-shaped, and the front part of the rotating frame 6 is vertically equipped with a variable diameter drill bit mechanism 9 and a four-axis DCM drill bit 10.

[0045] A set of arc-shaped tracks 8 is provided at the front of the flat barge 1. The front of the rotating frame 6 is mounted on the arc-shaped tracks 8 via traveling wheels 7. In addition, the rear of the rotating frame 6 is fixed to the flat barge 1 via a rotating shaft 5. The traveling wheels 7 are driven by a motor fixed below the rotating frame 6 (the motor is not shown in the figure; it is a conventional drive method). Through the above-mentioned arrangement of arc-shaped tracks 8, traveling wheels 7, and rotating shaft 5, rotation within a certain rotation angle range can be achieved, thereby enabling the position rotation of the variable diameter drill bit mechanism 9 and the four-axis DCM drill bit 10 without the flat barge 1 moving or turning.

[0046] like Figure 4 As shown, the variable diameter drill bit mechanism 9 includes a first column support 901, a first pull rod 902, a first guide rail 903, a first slider 904, a first steel cantilever beam 905, a first rotary motor 906, a first drill rod 907, and a variable diameter drill bit 910. The first column support 901 is vertically fixed to the front of the rotary frame 6. The upper end of the first pull rod 902 is hinged to the upper end of the first column support 901, and the lower end is hinged to the rotary frame 6. The first guide rail 903 is vertically arranged along the first column support 901 and is tightly fixed to each other. The first slider 904 is slidably mounted on the first guide rail 903. The lifting drive of the first slider 904 can be selected from a combination of a fixed pulley and a cable. The first steel cantilever beam 905 is fixed on the first slider 904 and moves with the first pull rod 906. A slider 904 moves vertically, a first rotary motor 906 is fixed on a first steel cantilever beam 905 and drives the first drill rod 907 to rotate, a variable diameter drill bit 910 is set at the lower end of the first drill rod 907, the variable diameter drill bit 910 includes a drill bit, two long strip reamers 908 and two hydraulic telescopic rods 909. The drill bit is set at the lower end of the first drill rod 907, the upper end of the long strip reamers 908 is hinged to the first drill rod 907, and a hydraulic telescopic rod 909 is set between the lower end of the long strip reamers 908 and the first drill rod 907. The hydraulic telescopic rod 909 and the long strip reamers 908 are connected by a slider and a hinge. The hydraulic telescopic rod 909 is used to drive the lower part of the long strip reamers 908 to gradually expand outward, so as to excavate a conical hole 13 in the rock strata.

[0047] like Figure 5As shown, the four-axis DCM drill bit 10 includes a second column support 1001, a second tie rod 1002, a second guide rail 1003, a second slider 1004, a second steel cantilever beam 1005, four sets of second rotary motors 1006, and four second drill rods 1007. The second column support 1001 is vertically arranged at the front of the rotary frame 6. The upper end of the second tie rod 1002 is hinged to the upper end of the second column support 1001, and the lower end is hinged to the rotary frame 6. The second guide rails 1003 are vertically arranged along the second column support 1001 and are tightly fixed to each other. The second sliders 1004 are slidably assembled. On the second guide rail 1003, the second steel suspension beam 1005 is fixed on the second slider 1004 and moves vertically with the second slider 1004. Each second rotary motor 1006 is fixed on the second steel suspension beam 1005 and drives the corresponding second drill rod 1007 to rotate. The second drill rod 1007 has a grouting pipeline. The mixing and grouting system is rotatably connected to the upper end of the second drill rod 1007 through the grouting pipeline and the grout pump system 4 and pumps the cement grout into the grouting pipeline inside the second drill rod 1007. The drill bit 1009 of the second drill rod has grout outlet holes, namely the upper grout outlet hole and the lower grout outlet hole.

[0048] (S3) Based on the geological distribution data and the design and construction coordinates of each cement-soil mixing pile, determine the construction method of each cement-soil mixing pile. The construction method is either direct mixing construction or composite reinforcement mixing construction.

[0049] S3.1: If the slope of the rock strata at the construction site is less than the slope threshold, then the direct mixing construction method shall be adopted. In short, if the surface slope of the rock strata is relatively gentle, the mixing construction shall be carried out directly, specifically including the following methods:

[0050] like Figure 6 As shown, the traveling wheels 7 on the rotating frame 6 are controlled to move along the arc track 8 so that the four-axis DCM drill bit 10 on the rotating frame 6 rotates with the rotating frame 6 to the position to be constructed. The second drill rod 1007 is controlled to descend to the surface of the silt layer. Then, the cutter blade 1008 on the second drill rod 1007 is opened and rotated to drill down. The drill bit 1009 on the second drill rod 1007 drills down through the silt layer and the clay layer in sequence to reach the surface of the rock layer. Then, several drilling and lifting operations are carried out in the clay layer and grouting is performed to form the first mixing pile 11 in the clay layer. The drill bit 1009 on the second drill rod 1007 is lifted up and grouting is continued to form the first mixing pile 11 located in the silt layer.

[0051] like Figure 7 The diagram shows the control method for the drill bit 1009 of the second drill rod 1007:

[0052] (1) The drill bit 1009 of the second drill rod 1007 is drilled down in the seawater above the silt layer but without spraying slurry. The drilling speed is 0.2-2.0 m / min and the rotation speed is 17-24 rpm.

[0053] Drilling is carried out in the silt layer without grouting, with a drilling speed of 0.2-1.5 m / min and a rotation speed of 12-30 rpm.

[0054] (2) The drill bit 1009 of the second drill rod 1007 is drilled down in the clay layer and water is sprayed until it reaches the interface with the rock layer. The water spraying rate is 240-480L / min, the drilling speed is 0.2-1.0m / min, and the rotation speed is 12-30rpm.

[0055] The drill bit 1009 of the second drill rod 1007 is raised by 1m and grout is sprayed downwards at a rate of 1120L / min, a drilling speed of 0.8m / min, and a rotation speed of 30-36rpm.

[0056] The drill bit 1009 of the second drill rod 1007 drills down 1m to the surface of the rock stratum. During this stage, the grouting speed is 1120L / min, the drilling speed is 0.8m / min, and the rotation speed is 30-36rpm.

[0057] The drill bit 1009 of the second drill rod 1007 is raised 4.1m to the interface between the clay layer and the silt layer. During this stage, the grouting speed is 820L / min, the lifting speed is 1m / min, and the rotation speed is 30-36rpm.

[0058] The drill bit 1009 of the second drill rod 1007 drills down 3.5m. During this stage, the grouting speed is 1120L / min, the drilling speed is 0.8m / min, and the rotation speed is 30-36rpm.

[0059] The drill bit 1009 of the second drill rod 1007 drills down 0.6m to the surface of the rock stratum. During this stage, water jetting and grouting are carried out at a rate of 1120L / min, a drilling speed of 0.8m / min, and a rotation speed of 30-36rpm.

[0060] After the drill bit 1009 of the second drill rod 1007 is raised by 1m, it is lowered by 1m, then raised by another 1m and then raised by another 1m. During this stage, the grouting is stopped, the lowering and raising speed is 0.8m / min, and the rotation speed is 30-36rpm.

[0061] (3) The drill bit 1009 of the second drill rod 1007 is lifted up, and grouting is performed simultaneously upward and downward. For details, please refer to the appendix of the instruction manual. Figure 7 The control parameters in.

[0062] S3.2: If the slope of the construction site is greater than the slope threshold, a composite reinforcement and mixing construction method shall be adopted. In short, if the surface slope of the rock layer is steep, a composite reinforcement and mixing construction method shall be adopted. The composite reinforcement and mixing construction method refers to:

[0063] The traveling wheels 7 on the rotating frame 6 are controlled to move along the arc track 8 so that the variable diameter drill bit mechanism on the rotating frame 6 rotates with the rotating frame 6 to the position to be constructed, so that the first drill rod 907 is lowered to the surface of the rock layer. Then, the drill bit 910 is controlled to drill into the rock layer. At the same time, the lower part of the long strip reamer 908 is gradually lifted outward by the hydraulic telescopic rod 909 to expand it outward until the drill bit drills to the predetermined depth. Then, the long strip reamer 908 is retracted inward by the hydraulic telescopic rod 909 and the first drill rod 907 is lifted to obtain the tapered hole 13.

[0064] The traveling wheels 7 on the rotating frame 6 are controlled to move along the arc-shaped track 8 so that the four-axis DCM drill bit 10 on the rotating frame 6 rotates with the rotating frame 6 to the construction position. The second drill rod 1007 is controlled to descend to the surface of the silt layer. Then, the cutter blade 1008 on the second drill rod 1007 is opened and rotated to drill down. The drill bit 1009 on the second drill rod 1007 drills down through the silt layer and the clay layer in sequence to reach the conical hole 13 in the rock layer. The drill bit 1009 on the second drill rod 1007 sprays grout to mix with the broken rock mass to form the second mixing pile 12 located in the conical hole 13. Then, several drilling and lifting operations are carried out in the clay layer and grouting is carried out to form the second mixing pile 12 in the clay layer. The drill bit 1009 on the second drill rod 1007 is lifted up and grouting is carried out continuously to form the second mixing pile 12 located in the silt layer.

[0065] The beneficial effects of this embodiment are as follows:

[0066] (1) High level of intelligence. The DCM method for pile formation control is implemented through the "DCM Engineering Vessel Intelligent Construction Control System" and the "DCM Engineering Vessel Construction Positioning System". This system has various functions such as real-time monitoring, signal data acquisition, data analysis and summary and backup, and construction management. It can monitor construction parameters such as pile number, coordinates, pile length, and current in real time;

[0067] (2) High degree of automation. The entire process, from weighing and measuring the cement grout materials (cement, seawater), mixing, storing, grouting and conveying, drilling the pile driver bit, rotating the blades, treating the bottom of the DCM pile, lifting the drill bit, to the drill bit's dry drilling friction in the stratum and the drill bit flushing, is completed automatically, reducing human error and thus improving the quality of pile formation;

[0068] (3) High construction efficiency. Up to 12 Ø1300mm DCM method piles can be constructed simultaneously, reducing frequent machine relocation and greatly improving work efficiency;

[0069] (4) Good soil mixing effect. The mixing blades and the spray holes evenly arranged on the upper and lower parts of the blades make the soil mixing more thorough. The spray holes evenly arranged on the upper and lower parts allow the grout to spread evenly in the mixing pile body, better combine with the soil, and promote the uniform strength distribution of the mixing pile body.

[0070] (5) Ultra-deep reinforcement. Equipped with a high-power four-axis DCM drilling rig and a continuously variable speed grout pump, the drill rod can be extended to meet the needs of different construction depths, and the grout pump can adjust the flow rate and pressure of the grout according to the requirements of the construction process to ensure construction quality.

Claims

1. A DCM construction method of offshore deep cement-soil mixing piles, characterized in that The DCM construction method comprises the following steps: S1: geological exploration is performed on a seabed surface of a region to be reinforced to obtain stratum distribution data of the seabed surface, the seabed surface comprising, from bottom to top, a rock layer, a clay layer and a silt layer; S2: a DCM engineering ship is driven to a predetermined position; the DCM engineering ship comprising a flat barge, a cement silo system, a mixing slurry storage system, a slurry pump system and a drilling system; S3: based on the stratum distribution data and design construction coordinates of each mixing pile, a construction mode of each cement-soil mixing pile is determined, the construction mode being one of direct mixing construction or composite reinforcement mixing construction; S3.1: if a rock layer slope of a position to be constructed is less than a slope threshold, the direct mixing construction mode is adopted; S3.2: if the rock layer slope of the position to be constructed is greater than the slope threshold, the composite reinforcement mixing construction mode is adopted, the composite reinforcement mixing construction mode being that a variable-diameter drill bit mechanism in the drilling system is used to drill into a rock layer surface and drill to form a conical hole in the rock layer surface, then the variable-diameter drill bit mechanism is lifted, and a four-axis DCM drill bit in the drilling system is used to downward mixing construction and grouting to form a mixing pile group.

2. The DCM construction method of offshore deep cement-soil mixing piles according to claim 1, characterized in that The main body of the DCM engineering ship is the flat barge, the cement silo system and the mixing slurry storage system are connected with each other and arranged on the flat barge, the drilling system comprises the variable-diameter drill bit mechanism, the four-axis DCM drill bit and a rotating frame, the rotating frame is arranged in a horizontal state and rotatably connected to a front portion of the flat barge; the rotating frame is in a fan shape, and the front portion of the rotating frame is vertically provided with the variable-diameter drill bit mechanism and the four-axis DCM drill bit, respectively.

3. The DCM construction method of a deep sea cement-soil mixing pile according to claim 2, characterized in that The front portion of the flat barge is provided with a set of arc-shaped tracks, the front portion of the rotating frame is assembled on the arc-shaped tracks through traveling wheels, the rear portion of the rotating frame is fixed to the flat barge through a rotating shaft, and the traveling wheels are driven to travel by a motor fixed below the rotating frame.

4. The DCM construction method of a deep sea cement-soil mixing pile according to claim 3, characterized in that The variable-diameter drill bit mechanism comprises a first column support, a first pull rod, a first guide rail, a first sliding block, a first steel suspension beam, a first rotary motor, a first drill rod and a variable-diameter drill bit. The first column support is vertically arranged at the front of the rotary frame. The upper end of the first pull rod is hingedly connected to the upper end of the first column support, and the lower end is hingedly connected to the rotary frame. The first guide rail is vertically arranged along the first column support and is fixedly connected to each other. The first sliding block is slidably arranged on the first guide rail. The first steel suspension beam is fixed to the first sliding block and moves vertically with the first sliding block. The first rotary motor is fixed to the first steel suspension beam and drives the first drill rod to rotate. The variable-diameter drill bit is arranged at the lower end of the first drill rod. The variable-diameter drill bit comprises a drill bit, two long strip-shaped reamers and two hydraulic telescopic rods. The upper end of the long strip-shaped reamer is hingedly connected to the first drill rod. The lower end of the long strip-shaped reamer is provided with the hydraulic telescopic rod between the first drill rod. The hydraulic telescopic rod is used to drive the lower part of the long strip-shaped reamer to gradually expand outward to form the tapered hole on the rock stratum.

5. The DCM construction method of a deep sea cement-soil mixing pile according to claim 4, characterized in that The four-axis DCM drill bit comprises a second column support, a second pull rod, a second guide rail, a second sliding block, a second steel suspension beam, a plurality of second rotary motors and a plurality of second drill rods. The second column support is vertically arranged at the front of the rotary frame. The upper end of the second pull rod is hingedly connected to the upper end of the second column support, and the lower end is hingedly connected to the rotary frame. The second guide rail is vertically arranged along the second column support and is fixedly connected to each other. The second sliding block is slidably arranged on the second guide rail. The second steel suspension beam is fixed to the second sliding block and moves vertically with the second sliding block. Each second rotary motor is fixed to the second steel suspension beam and drives the corresponding second drill rod to rotate. The second drill rod has a grouting pipeline. The mixing and storage system is rotatably connected to the upper end of the second drill rod through the grouting pipeline and pumps the concrete slurry into the grouting pipeline in the second drill rod. The second drill rod has a grouting hole on the drill bit.

6. The DCM construction method of a deep cement mixing pile at sea according to claim 5, characterized in that The composite reinforcement mixing construction comprises the following steps: The running wheels on the rotary frame are controlled to move along the arc-shaped track, so that the variable-diameter drill bit mechanism on the rotary frame is rotated to the position to be constructed with the rotary frame, the first drill rod is lowered to the surface of the rock stratum, then the drill bit of the variable-diameter drill bit is drilled into the rock stratum, at the same time, the lower part of the long strip-shaped reamer is gradually jacked outward by the hydraulic telescopic rod to expand outward until the drill bit is drilled to the predetermined depth, then the long strip-shaped reamer is retracted inward by the hydraulic telescopic rod, and the first drill rod is lifted to obtain the tapered hole. The method comprises the following steps: controlling the traveling wheels on the rotating frame to move along the arc-shaped track so that the four-axis DCM drill bit on the rotating frame rotates to a position to be constructed, controlling the second drill rod to be lowered to the surface of the silt layer, then turning on the reamer blades on the second drill rod and rotating the drill bit on the second drill rod to drill through the silt layer and the clay layer and reach the surface of the rock layer, and then performing jet grouting on the drill bit on the second drill rod to form a mixing pile in the conical hole.

7. The DCM construction method of a deep cement mixing pile at sea according to claim 5, characterized in that The method comprises the following steps: controlling the traveling wheels on the rotating frame to move along the arc-shaped track so that the four-axis DCM drill bit on the rotating frame rotates to a position to be constructed, controlling the second drill rod to be lowered to the surface of the silt layer, then turning on the reamer blades on the second drill rod and rotating the drill bit on the second drill rod to drill through the silt layer and the clay layer and reach the surface of the rock layer, and then performing jet grouting on the drill bit on the second drill rod to form a mixing pile in the conical hole.

8. The DCM construction method of a deep cement mixing pile at sea according to claim 7, characterized in that The method comprises the following steps: The drill bit on the second drill rod drills 1 m to the surface of the rock layer, during which the jet grouting is performed at a flow rate of 1120 L / min, the drilling speed is 0.8 m / min, and the rotation speed is 30-36 rpm; The drill bit on the second drill rod is lifted 4.1 m to the interface between the clay layer and the silt layer, during which the jet grouting is performed at a flow rate of 820 L / min, the lifting speed is 1 m / min, and the rotation speed is 30-36 rpm; The drill bit on the second drill rod drills 3.5 m, during which the jet grouting is performed at a flow rate of 1120 L / min, the drilling speed is 0.8 m / min, and the rotation speed is 30-36 rpm; The drill bit on the second drill rod drills 0.6 m to the surface of the rock layer, during which the jet grouting is performed, the drilling speed is 0.8 m / min, and the rotation speed is 30-36 rpm; The drill bit on the second drill rod is lifted 1 m and then drills 1 m, and then is lifted 1 m and then drills 1 m, during which the jet grouting is stopped, the drilling and lifting speed is 0.8 m / min, and the rotation speed is 30-36 rpm.

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