A method for determining a target depth of a deep mixing pile and a deep mixing pile construction method

Abstract

The application provides a deep mixing pile target depth determination method and a deep mixing pile construction method. The deep mixing pile target depth determination method comprises the following steps: in the process of driving the drill rod of the deep mixing pile machine, the real-time working current value I of the rotary power head of the deep mixing pile machine is acquired in real time; when the real-time working current value I meets the following conditions 1-condition 3 at the same time, it is determined that the target depth is reached: condition 1: the real-time working current value I is greater than the set standard current value I0; condition 2: the difference between the real-time working current value I and the no-load current I 空 is greater than the set difference value I 差 ; condition 3: the duration of conditions 1 and 2 is greater than the set time t0 at the same time. Through the setting of the three determination conditions, the target stratum can be accurately identified in the drilling process, the drill rod and the cement slurry are avoided from being wasted due to excessive drilling, and the engineering quality is avoided from being affected due to the identification depth being less than the target stratum.

Description

Technical Field

[0001] This application relates to the field of building construction technology, and in particular to a method for determining the target depth of deep mixing piles and a method for constructing deep mixing piles. Background Technology

[0002] In some coastal cities, unconsolidated soft clay is widespread, and landmark buildings such as the Burj Al Arab, the Ferris wheel, and many others require reinforced soft soil foundations to support them; therefore, the requirements for soft soil foundation reinforcement are very high. Figure 1 The geological structure in the soft soil foundation reinforcement project shown mainly consists of backfill soil from the ground to 90mRL, and alluvial soil (FILL), transition soil (KL), and marine clay (OA) formed by Kallang Formation deposits from 90mRL to 75mRL. The marine clay layer, i.e., the OA layer, is the target stratum for treatment, meaning that the bottom of the deep mixing piles should reach the OA layer. Since the deepest depth of the OA layer can reach 52 meters underground, and the shallowest OA layer is 38 meters below the ground surface, the pile depth of the deep mixing piles is very deep.

[0003] During the construction of deep mixing piles, it is necessary to identify the target stratum. Drilling must be stopped immediately upon identification of the target stratum. The target stratum is determined by the geological conditions of the current drilling hole, generally using the penetration of the drill bit into a layer of hard cohesive soil as the criterion. The target stratum determines the target depth of the deep mixing pile, which is crucial as it relates to construction costs and the reliability of soft soil foundation reinforcement. In existing technologies, the target depth of deep mixing piles is often determined using a single criterion: when the real-time current value of the rotating power head of the deep mixing pile machine exceeds a set value, it is considered that the target stratum has been reached, and the current drill bit depth is taken as the target depth.

[0004] The aforementioned methods for determining the target depth of deep mixing piles rely on a single judgment condition, resulting in low accuracy and a tendency to misjudge the target stratum. This can cause the drill bit to stop drilling before penetrating the hard cohesive soil layer, affecting the reliability of soft soil foundation reinforcement. Therefore, this application proposes a method for determining the target depth of deep mixing piles and a method for constructing deep mixing piles. Summary of the Invention

[0005] The purpose of this application is to address the above problems by providing a method for determining the target depth of deep mixing piles and a method for constructing deep mixing piles.

[0006] In a first aspect, this application provides a method for determining the target depth of deep mixing piles, the method comprising the following steps:

[0007] During the process of driving the drill rod down the deep mixing pile machine, the real-time operating current value I of the rotating power head of the deep mixing pile machine is acquired in real time.

[0008] The target depth is determined when the real-time operating current value I simultaneously meets the following conditions 1-3:

[0009] Condition 1: The real-time operating current value I is greater than the set standard current value I0;

[0010] Condition 2: The real-time operating current value I and the no-load current I 空 The difference is greater than the set difference I 差 ;

[0011] Condition 3: The durations of Condition 1 and Condition 2 are simultaneously greater than the set duration t0.

[0012] According to certain embodiments of the present application, the technical solutions provided are as follows:

[0013] The set standard current value I0 ≥ 200A;

[0014] The set difference I 差 ≥60A;

[0015] The set duration t0 is ≥ 15s.

[0016] Secondly, this application provides a method for constructing deep mixing piles, the method comprising the following steps:

[0017] The main drill rod is drilled into the working hole in a positive circulation manner to the first depth; the main drill rod includes a first drill rod and a second drill rod connected by a third drill rod joint, and the top end of the first drill rod is connected to the rotating power head of the deep mixing pile machine through the first drill rod joint; the first depth is the target depth determined by the deep mixing pile target depth determination method;

[0018] The high-pressure grouting pump on the deep pile mixing machine is turned on to spray cement slurry, and the main drill rod is raised in reverse circulation to spray slurry to the second depth; the second depth is less than the length of the second drill rod.

[0019] The main drill pipe is drilled under positive circulation and cement slurry is sprayed to the first depth;

[0020] Shut down the high-pressure grouting pump and reverse-circulate to raise the main drill pipe to the second depth;

[0021] Remove the third drill pipe joint and drill the first drill pipe into the ground at the first location;

[0022] Remove the first drill rod joint and connect the second drill rod located in the drilling hole to the rotating power head of the deep pile mixing machine through the second drill rod joint;

[0023] The high-pressure grouting pump is turned on, and the second drill rod is drilled down to the third depth in positive circulation; the third depth is deeper than the second depth, and the depth difference between the two is 500mm.

[0024] The second drill pipe is raised using reverse circulation, and cement grout is sprayed to the designed top elevation.

[0025] The second drill pipe is drilled under positive circulation and cement slurry is sprayed to the third depth;

[0026] The high-pressure grouting pump is shut down, and the second drill pipe is raised to the surface via reverse circulation.

[0027] According to the technical solutions provided in certain embodiments of this application, drilling the main drill rod into the working hole to a first depth via positive circulation includes the following steps:

[0028] When the real-time operating current value I simultaneously satisfies both condition 1 and condition 2, it is determined that an obstacle has been encountered, and the real-time depth information is read as the obstacle depth information.

[0029] The obstacle depth information is stored in an obstacle record table; the obstacle record table stores the stake number and the corresponding obstacle depth information.

[0030] The number of obstacles within each unit depth range is calculated based on the obstacle record table to obtain the obstacle density corresponding to the stake number and each unit depth range.

[0031] According to the technical solutions provided in certain embodiments of this application, drilling the main drill rod into the working hole to a first depth via positive circulation further includes the following steps:

[0032] Get the current pile number;

[0033] Query the pile distribution table for the number of constructed piles adjacent to the current pile number;

[0034] The adjustment depth range is obtained by querying the obstacle record table for each unit depth range where the obstacle density corresponding to the constructed pile number is greater than the set density value.

[0035] When it is determined that the current drilling depth is within the adjusted depth range, the real-time working current value I is increased by a set ratio.

[0036] According to the technical solutions provided in certain embodiments of this application, the second drill rod is formed by extending several unit sub-drill rods; the bottommost unit sub-drill rod is welded to the drill bit used for drilling.

[0037] According to the technical solutions provided in certain embodiments of this application, the bottom sidewall of the drill bit has only one grouting port; the outer wall of the drill bit has an arc-shaped baffle on one side of the grouting port; the arc-shaped baffle is located in front of the rotation direction when the drill bit drills downward.

[0038] According to the technical solutions provided in certain embodiments of this application, two main drill rods are installed in parallel on the rotating power head of the deep mixing pile machine; the pile diameter of the main drill rod is greater than 1400mm and less than 1600mm; the center distance between the two main drill rods is greater than 1100mm and less than 1300mm.

[0039] According to the technical solutions provided in certain embodiments of this application, the deep mixing pile construction method further includes the following steps:

[0040] When it is determined that there is a protected structure within the construction area or a diaphragm wall structure at the edge of the construction area, before operating the aforementioned access hole:

[0041] A drill rod is lowered at a set distance from the drilling hole and water is sprayed to a set depth to form a pressure-relieving blind hole.

[0042] According to the technical solutions provided in certain embodiments of this application, the deep mixing pile construction method further includes the following steps:

[0043] When it is determined that there is a protected structure within the construction area or a diaphragm wall structure at the edge of the construction area, before operating the drilling hole:

[0044] Several hollow steel pipe piles were intermittently buried within the construction area;

[0045] The soil inside the hollow steel pipe piles was removed.

[0046] Compared with the prior art, the beneficial effects of this application are as follows: During the drilling process of the deep mixing pile machine driving the drill rod, the real-time working current value of the rotating power head of the deep mixing pile machine is obtained in real time, and three judgment conditions are used to determine whether the target stratum has been reached and to determine the target depth of the deep mixing pile. By adopting the technical solution provided by this application, the target stratum can be accurately identified during the drilling process, avoiding excessive drilling and waste of drill rod and cement slurry, and also avoiding the impact on project quality due to insufficient identification depth of the target stratum. Attached Figure Description

[0047] Figure 1 This is a structural schematic diagram of the construction area used in Embodiment 1 of this application;

[0048] Figure 2 This is a schematic diagram of the geological distribution within the construction area in Embodiment 1 of this application;

[0049] Figure 3 This is a flowchart of the method for determining the target depth of deep mixing piles in Embodiment 1 of this application;

[0050] Figure 4 This is a schematic diagram of the deep mixing construction in Embodiment 2 of this application;

[0051] Figure 5This is a schematic diagram of the construction sequence of the drilling holes in Embodiment 2 of this application;

[0052] Figure 6 This is a schematic diagram of the structure of the second drill pipe in Embodiment 2 of this application;

[0053] Figure 7 This is a schematic diagram of the pile distribution in Embodiment 3 of this application;

[0054] Figure 8 This is a schematic diagram of the blind hole structure in an embodiment of this application.

[0055] The text labels in the image represent:

[0056] 100, Second drill pipe; 110, Grout nozzle; 120, Arc-shaped mudguard; 200, Drill bit; 300, Blade. Detailed Implementation

[0057] To enable those skilled in the art to better understand the technical solution of this application, the application will be described in detail below with reference to the accompanying drawings. The description in this section is only exemplary and explanatory, and should not be used to limit the scope of protection of this application.

[0058] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0059] Example 1

[0060] This embodiment uses Figure 1 Taking the construction project shown as an example, this project is a subway subgrade reinforcement project. Through surveying the construction area, the geological distribution within the construction area is roughly as follows: Figure 2 As shown, the geological composition of the construction area is as follows: it includes alluvial deposits (FILL), transitional layers (KL), and marine clay layers (OA), consisting of the Jialun Formation and sedimentary sediments. The marine clay layer (OA) is the target stratum, meaning the bottom of the deep mixing piles should reach the OA layer. Figure 2 It can be seen that the depth of the target strata varies at different locations within the construction area.

[0061] The project involves foundation improvement work on parts of Tunnel 1, equipment rooms, and Tunnel 2. The main work includes approximately 270,000 cubic meters of deep mixing piles, with a maximum depth of 52 meters.

[0062] In this embodiment, the excavation of the soil above the foundation surface of the deep mixing pile is organized to reduce the unnecessary length of empty mixing.

[0063] After leveling the construction site of the deep mixing pile drilling rig and laying a 300mm thick crushed stone cushion layer, the surface was compacted with a 10t steel wheel roller to provide a good working platform for the 130t heavy deep mixing pile machine.

[0064] After completing the above preparatory work, deep mixing operations will be carried out in the construction area. During the deep mixing operation, it is necessary to determine the target depth of the deep mixing piles.

[0065] This embodiment provides a method for determining the target depth of deep mixing piles, the method comprising the following steps:

[0066] S101. During the process of driving the drill rod down the deep mixing pile machine, the real-time working current value I of the rotating power head of the deep mixing pile machine is obtained in real time.

[0067] S102. Determine the target depth when the real-time operating current value I simultaneously meets the following conditions 1-3:

[0068] Condition 1: The real-time operating current value I is greater than the set standard current value I0;

[0069] Condition 2: The real-time operating current value I and the no-load current I 空 The difference is greater than the set difference I 差 ;

[0070] Condition 3: The durations of Condition 1 and Condition 2 are simultaneously greater than the set duration t0.

[0071] Furthermore, the set standard current value I0 ≥ 200A; the set difference I 差 ≥60A; the set duration t0 ≥15s.

[0072] In this embodiment, the set standard current value I0 is 210A, and the set difference value I... 差 The current is set to 70A, and the set duration t0 is set to 16s; the no-load current I... 空 This is the current value measured when the drill bit is at its ground position before deep mixing is carried out. In this embodiment, the measured no-load current is 140A.

[0073] Experience shows that during the drilling process of a deep mixing pile machine, when the drill bit encounters the target stratum, the real-time operating current I of the rotating power head of the deep mixing pile machine will continuously increase. This embodiment, by setting the above three judgment conditions, can accurately identify the target stratum during the drilling process, avoid excessive drilling and waste of drill rods and cement slurry, and also avoid affecting the quality of the project due to insufficient identification depth of the target stratum.

[0074] Example 2

[0075] This embodiment, based on Embodiment 1, provides a method for constructing deep mixing piles, the method comprising the following steps:

[0076] S1. Drill the main drill pipe into the working hole in a forward circulation manner to the first depth.

[0077] The main drill rod includes a first drill rod and a second drill rod connected by a third drill rod joint. The top end of the second drill rod is connected to the rotating power head of the deep mixing pile machine through a second drill rod joint.

[0078] In this embodiment, the main drill rod is configured as a two-section extension, comprising a detachably connected first drill rod and a second drill rod. The rotating power head of the deep pile mixing machine can be connected to the first drill rod via the first drill rod joint, and the rotating power head of the deep pile mixing machine can also be connected to the second drill rod via the second drill rod joint. The first drill rod and the second drill rod can also be connected via the third drill rod joint. The length of the first drill rod is greater than the length of the second drill rod.

[0079] When drilling the main drill pipe into the working hole to the first depth using forward circulation, the main drill pipe needs to be assembled. The assembly process of the main drill pipe includes:

[0080] S1-1. Install the first drill rod onto the rotating power head of the deep mixing pile machine through the first drill rod joint.

[0081] In this embodiment, a SWET858 dual-axis deep mixing pile machine is used. The original factory configuration of this deep mixing pile machine is a 1200mm diameter drill bit and a dual-axis center distance of 1000mm. In this embodiment, to improve working efficiency, a 1500mm diameter drill bit will be used, and the power of the power head will be adjusted. Specifically, the power of a single power head will be increased from 110kW to 187.5kW to ensure that sufficient torque can be provided to cut the soil and meet the power requirements of a 1500mm diameter pile.

[0082] In this embodiment, the first drill pipe corresponds to the dual power head configuration, and there are two of them.

[0083] S1-2. Start the grouting pump to spray water and drill the first drill rod into the ground from the first position located next to the drilling hole.

[0084] In this embodiment, the first drill rod is 30 meters long and is drilled into the ground using a deep pile mixing machine. During the lowering of the drill rod, clean water is used, which not only prevents clogging of the drill bit's nozzles but also reduces the load torque, ensuring smooth drilling. When encountering difficult drilling areas, the water flow can be increased to facilitate drilling. In this embodiment, the clean water drilling speed is 1 m / min.

[0085] In this embodiment, the first position can be the position of another drilling hole next to the current drilling hole, or it can be a non-drilling hole position next to the drilling hole.

[0086] S1-3. Turn off the grouting pump, open the first drill rod joint, remove the first drill rod from the rotary power head of the deep pile mixing machine, and install the second drill rod on the rotary power head of the deep pile mixing machine through the second drill rod joint.

[0087] In this step, the drilling of the second drill rod marks the beginning of the deep mixing pile operation. Therefore, before starting this step, it is necessary to inspect and adjust the drilling rig to ensure basic parameters such as the verticality of the drill rod. In this embodiment, the length of the second drill rod is 24 meters.

[0088] In this step, after the first drill rod is removed from the rotating power head of the deep pile mixing machine, in order to prevent it from sinking into the ground due to its own weight, when the first drill rod is lowered in step S1-2, ensure that the top of the first drill rod is slightly exposed above the ground. In this step, after the first drill rod is removed from the rotating power head of the deep pile mixing machine, the top of the first drill rod is held by a limiting plate with a clamp installed to prevent it from sinking.

[0089] In this embodiment, the second drill pipe corresponds to the dual power head setup, and there are also two of them.

[0090] S1-4. Turn on the grouting pump to spray water and drill the second drill rod into the working hole to the second depth, which is slightly less than the length of the second drill rod.

[0091] In this embodiment, the second depth is 21 meters. When the second drill rod is drilled into the working hole to the second depth, the top of the second drill rod emerges from the ground.

[0092] S1-5. Turn off the grouting pump, open the second drill rod joint, and disconnect the second drill rod from the rotating power head of the deep mixing pile machine.

[0093] In this step, after the second drill rod is removed from the rotating power head of the deep pile mixing machine, the top of the second drill rod can be held by the limiting plate with the clamp installed to prevent it from sinking.

[0094] S1-6. Install the first drill rod on the rotating power head of the deep mixing pile machine through the first drill rod joint, and pull the first drill rod out from underground.

[0095] Specifically, the rotating power head of the deep pile mixing machine is first moved above the first drill rod, and the first drill rod is installed on the rotating power head of the deep pile mixing machine through the first drill rod joint. Then the first drill rod is lifted from the first position located next to the drilling hole.

[0096] S1-7. Connect the first drill pipe and the second drill pipe with the third drill pipe joint, and the first drill pipe and the second drill pipe form the total drill pipe.

[0097] Specifically, the rotating power head of the deep mixing pile machine and the first drill rod are first moved above the second drill rod, and the top end of the second drill rod is connected to the bottom end of the first drill rod through the third drill rod connector to form the main drill rod.

[0098] Through steps S1-1 to S1-7 above, the assembly process of the main drill rod is completed. The assembled main drill rod is then drilled into the working hole in a forward cycle to the first depth. When it is determined that the drilling depth has reached the first depth, drilling is stopped. The first depth is the target depth determined by the deep mixing pile target depth determination method described in Example 1. In this example, the first depth is 50 meters. Figure 4 The time period 0-T3 is the time period for lowering the main drill pipe. As shown in steps S1-1 to S1-7 above, lowering the main drill pipe is divided into three stages. The first stage 0-T1 is the time period for lowering the second drill pipe. The second stage T1-T2 is the time period for extending the first and second drill pipes. The third stage T2-T3 is the time period for continuing to lower the drill pipe after extending it.

[0099] By setting the drill rod of the deep mixing pile machine to be extended in two sections, the ultra-deep (maximum 52m) deep mixing depth requirement was achieved at a height of 36m pile machine mast. Furthermore, by setting the length of the first drill rod to be greater than that of the second drill rod, and by connecting the first and second drill rods with several standard-length drill rods through drill rod joints, this embodiment frees up more than half of the time spent connecting drill rods outside of construction operations, saving a significant amount of time and improving work efficiency.

[0100] S2. Turn on the high-pressure grouting pump on the deep pile mixing machine to spray cement slurry, and reverse the circulation to raise the main drill rod to the second depth.

[0101] This step is as follows: Figure 4 The time period T3-T4 is shown in the figure, where the second depth is 21 meters.

[0102] In this embodiment, after the main drill rod sinks to the designed depth, drilling is stopped, but rotation continues. The pressure of the high-pressure mud pump is increased to the construction design value (2-4 MPa). After the bottom is grouted for 30-60 seconds, the main drill rod is lifted again while grouted and rotated for at least 1 minute, so that a thick base is formed at the bottom of the deep mixing pile.

[0103] In this embodiment, the cement used in the cement grout has a grade of not less than 42.5N, and the cement grout mix ratio is water:cement = 1:1; the rotation speed of the total drill rod is 18 rpm, the grouting speed is 0.6 m / min, and the grout flow rate is 120-160 L / min.

[0104] S3. Drill the main drill pipe in positive circulation and spray cement slurry to the first depth.

[0105] This step is as follows: Figure 4 The time period T4-T5 is shown in the figure, where the first depth is 50 meters.

[0106] S4. Turn off the high-pressure grouting pump and reverse the circulation to lift the main drill rod to the second depth.

[0107] This step is as follows: Figure 4 The time period T5-T6 is shown in the figure. The second depth is 21 meters. After this step is completed, the first drill rod is completely above the ground surface, and the top of the second drill rod is exposed above the ground surface.

[0108] S5. Remove the third drill pipe joint and drill the first drill pipe into the ground at the first location.

[0109] This step is as follows: Figure 4 As shown in the time period T6-T7, the second drill rod is left in the drilling hole, and the first drill rod is moved to the underground at the first position next to the drilling hole.

[0110] S6. Remove the first drill rod joint and connect the second drill rod located in the drilling hole to the rotating power head of the deep pile mixing machine through the second drill rod joint.

[0111] In this step, the first drill rod is first removed from the rotating power head of the deep pile mixing machine, and then the top of the second drill rod is connected to the rotating power head of the deep pile mixing machine through the second drill rod connector.

[0112] S7. Start the high-pressure grouting pump and drill the second drill rod to the third depth in positive circulation.

[0113] In this step, the movement of the second drill pipe is relatively small, therefore it was not included. Figure 4 This is specifically reflected in the design. The third depth is deeper than the second depth, and the depth difference is 500mm. In this embodiment, the second depth is 21 meters and the third depth is 21.5 meters. By setting overlapping deep mixing sections between the deep mixing piles formed below and the deep mixing piles above, the integrity and continuity of the pile formation can be guaranteed.

[0114] S8. Reverse circulation to lift the second drill pipe and spray cement slurry to the designed top elevation.

[0115] This step is as follows: Figure 4 As shown in the time period T7-T8, the design top elevation is generally a certain distance below the ground surface. In this embodiment, the design top elevation is 10 meters.

[0116] In this step, when the jet grouting pipe is raised close to the top of the pile, it should be raised slowly from 1.0m below the top of the pile, spraying for a few seconds, and then slowly raised again until the grouting surface at the top of the pile is reached. In this embodiment, the grouting surface is 0.3 meters higher than the designed elevation of the pile. When the grouting nozzle at the end of the second drill bit reaches the top of the pile, the upward movement should be stopped, and the rotation of the grouting should be maintained for 1 minute to form a dense pile head at the top of the pile.

[0117] S9. Drill the second drill pipe in positive circulation and spray cement slurry to the second depth.

[0118] This step is as follows: Figure 4 The time period T8-T9 is shown in the figure.

[0119] S10. Turn off the high-pressure grouting pump and reverse the circulation to raise the second drill rod to the surface.

[0120] In this step, the high-pressure grouting pump is shut off at time T9, and reverse circulation begins to lift the second drill rod. During the lifting of the second drill rod, when the grout nozzle is at a set distance from the ground surface, for example, 4 meters, the high-pressure grouting pump is turned on, and the second drill rod is lifted in reverse circulation while cement grout is sprayed. Light grouting is performed for the set duration. The lifting speed of the drill rod is 0.8 m / min, and the lifting and grouting process is as follows: Figure 4 The portion after time T10. The ground surface is relatively soft, so the above-mentioned technical solution is used to spray cement slurry onto the surface to increase its strength.

[0121] like Figure 4 As shown, this embodiment adopts a bottom-up, two-stage "inverted V" grouting process, realizing "four stirrings and two sprays" grouting from bottom to top in a two-stage process, achieving one-time pile formation in the environment of extended drill rods, thus achieving efficient pile formation.

[0122] In this embodiment, two main drill rods are installed in parallel on the rotating power head of the deep mixing pile machine. The pile diameter of the main drill rods is greater than 1400mm and less than 1600mm; the center-to-center distance between the two main drill rods is greater than 1100mm and less than 1300mm. Specifically, in this embodiment, the pile diameter of the main drill rods is set to 1500mm, and the center-to-center distance between the two main drill rods is 1200mm. In this embodiment, by adopting a dual-axis large-diameter pile design, combined with a high-power power head, the pile formation efficiency is greatly improved.

[0123] like Figure 5 As shown, in this embodiment, the drilling holes are arranged in rows, and each row of drilling holes is constructed sequentially, for example, the upper row of drilling holes is constructed first, and then the lower row of drilling holes is constructed; the center-to-center distance between adjacent drilling holes is 1300mm to 1400mm.

[0124] In this embodiment, the construction sequence of the holes in the same row is: first end hole, middle hole, second end hole, and other holes. For example... Figure 5 Taking two rows of drilling holes as an example, the construction of the first row of drilling holes is carried out first. Since there are 5 drilling holes in this row, they are constructed in the order of Arabic numerals 1-2-3-4. The two holes numbered 4 can be constructed simultaneously or separately. The second row of drilling holes is constructed in the order of 5-6-7-8. The two holes numbered 8 can be constructed simultaneously. This can greatly reduce the squeezing and pushing effect on the retaining structure. That is, in this embodiment, the number of other drilling holes between two completed drilling holes is 1; in other embodiments, the number of other drilling holes between two completed drilling holes may be 2, 3 or even more. When the number of other drilling holes is less than or equal to 4, they are constructed step by step from the first end to the second end; when the number of other drilling holes is greater than 5, they can be constructed in a sequential manner, preferably in the order of first one end, then the middle, then the other end, and finally the second end.

[0125] In this embodiment, when it is determined that there is a protected structure or a diaphragm wall structure at the edge of the construction area, the construction area close to the protected structure and the diaphragm wall structure is designated as the priority construction area; after dividing the other areas into zones, construction work is carried out at intervals between each zone. The above construction sequence can reduce the squeezing and pushing effect on the protected structure or the diaphragm wall structure, thereby protecting the protected structure or the diaphragm wall structure.

[0126] In this embodiment, when it is determined that a diaphragm wall structure is provided at the edge of the construction area, high-pressure jet grouting is performed near the diaphragm wall structure in the construction area.

[0127] In this embodiment, a dual-pipe high-pressure jetting system is used for construction. During the drilling phase, a 20MPa high-pressure water jet cuts the soil, while a high-pressure air curtain of 8 Bars forms around the water jet, reducing the rate of energy decay and ensuring thorough cutting. During the grouting phase, both high-pressure cement grout and air are jetted laterally to impact and damage the soil. Under the combined action of the high-pressure grout and its surrounding airflow, the energy for soil destruction is significantly increased, ultimately forming a large consolidated body within the soil.

[0128] High-pressure jet grouting construction shall be carried out according to the following steps:

[0129] (1) Drilling rig positioning. Move the jet grouting machine to the designated pile position, align the drill bit with the center of the hole, and level the drilling rig to ensure it is stable and horizontal. The verticality deviation of the drill rod should not exceed 1% to 1.5%. After positioning, first conduct a low-pressure (0.5MPa) water jetting test to check whether the nozzle is unobstructed and whether the pressure is normal.

[0130] (2) Preparation of cement grout. When the pile driver is moved, the cement grout is prepared according to the mix ratio determined in the design.

[0131] (3) Drilling (double-tube method). The drill bit drills to the design elevation at the predetermined pile position (the pre-drilled hole diameter is 15cm). If the treatment depth is greater than the maximum length of the drill rod that the machine can carry, the drill rod needs to be extended halfway through the drilling.

[0132] (4) Lifting and mixing the grouting pipe. After the grouting pipe sinks to the design depth, drilling stops, but rotation continues. The pressure of the high-pressure mud pump is increased to the construction design value (20-40MPa). After grouting for 30 seconds, grouting continues while rotating, and the drill rod is lifted strictly according to the lifting speed determined by the design and test pile. After reaching the design depth, the high-pressure water pipe and air compressor pipe are connected, and the high-pressure clean water pump, mud pump, air compressor and drilling rig are started to rotate. The pressure, flow rate and air volume are controlled by instruments. When the predetermined values ​​are reached, lifting begins. Rotary grouting and lifting continue until the expected reinforcement height is reached and then stop.

[0133] (5) Treatment of the pile head. When the jet grouting pipe is raised close to the top of the pile, it should start from 1.0m below the top of the pile, slowly raise the jet grouting pipe, spray for a few seconds, and then slowly raise it up 0.5m until the grouting surface at the top of the pile stops.

[0134] (7) If encountering gravel strata, in order to ensure the pile diameter, grouting and mixing can be repeated: repeat grouting and mixing according to steps 4 to 6 above until the grouting pipe is raised to the grouting stop surface, turn off the high pressure mud pump (clean water pump, air compressor), stop the delivery of cement slurry (water, air), rotate the grouting pipe to raise it out of the ground, and turn off the drilling machine.

[0135] (8) Cleaning. Pour an appropriate amount of clean water into the grout tank, turn on the high-pressure pump, and clean all the remaining cement grout in the pipeline until it is basically clean. Also clean the soil adhering to the spray nozzle.

[0136] (9) Relocation. Move the pile driver to carry out the construction of the next pile.

[0137] In this embodiment, the first drill pipe and the second drill pipe are each formed by extending several unit drill pipes. Taking the second drill pipe as an example, as follows... Figure 6 As shown, the second drill rod 100 includes several unit sub-drill rods. The bottom unit sub-drill rod is welded to the drill bit 200 used for drilling. In this embodiment, the bottom unit sub-drill rod adopts an integrated design structure of drill rod and drill bit with a length of 4 meters, which avoids the problem of grout leakage between the short drill bit and the drill rod connected to it, and ensures the pressure and stability of grouting.

[0138] Furthermore, the bottom sidewall of the drill bit has only one grouting port 110; the outer wall of the drill bit has an arc-shaped mudguard 120 on one side of the grouting port 110; the arc-shaped mudguard 120 is located in front of the direction of rotation when the drill bit drills downward.

[0139] Specifically, the grouting nozzle 110 is located on the side of the drill bit, and only one grouting nozzle 110 is provided. This ensures stable pressure at the grouting nozzle, solving the problem of unstable pressure when there are multiple grouting nozzles 110, resulting in a balanced grout output speed and stable pile quality. The second drill rod 100 is equipped with an arc-shaped mudguard 120 corresponding to the grouting nozzle 110. The arc-shaped mudguard 120 has a semi-circular structure and is installed concentrically with the grouting nozzle 110. The arc-shaped mudguard 120 is located at the front end in the rotation direction of the second drill rod. During the downward drilling and rotation of the second drill rod 100, when encountering underground obstacles, the arc-shaped mudguard 120 will clear the debris at the grouting nozzle 110, thereby ensuring that the grouting nozzle 110 can output normally and preventing blockage of the grouting nozzle 110.

[0140] Furthermore, the second drill pipe is equipped with three layers of blades 300, which are used for mixing during construction to ensure that the slurry and soil are fully mixed and to guarantee construction quality. In this embodiment, a steel plate is welded to the edge of the blade, and wear-resistant alloy teeth with high hardness are welded to the outermost edge of the blade. This significantly improves the wear resistance of the blade and avoids the problem of reduced mixing diameter and uneven mixing caused by blade wear and changes in length, thus further ensuring construction quality.

[0141] Example 3

[0142] This embodiment provides a deep mixing pile construction method, which is an improvement on embodiment 2. The similarities between this embodiment and embodiment 2 will not be repeated. The difference lies in the following steps: The main drill rod is drilled into the working hole in a positive circulation manner to the first depth.

[0143] When the real-time operating current value I simultaneously satisfies both condition 1 and condition 2, it is determined that an obstacle has been encountered, and the real-time depth information is read as the obstacle depth information.

[0144] The obstacle depth information is stored in an obstacle record table; the obstacle record table stores the stake number and the corresponding obstacle depth information.

[0145] The number of obstacles within each unit depth range is calculated based on the obstacle record table to obtain the obstacle density corresponding to the stake number and each unit depth range.

[0146] Specifically, during the drilling process, when the real-time operating current value I of the rotating power head of the deep pile mixing machine is greater than the set standard current value I0, and the real-time operating current value I of the rotating power head of the deep pile mixing machine is equal to the no-load current I0, 空 The difference is greater than the set difference I 差 Furthermore, if the duration of the above two conditions is less than or equal to the set duration t0, that is, when the real-time working current value I of the rotating power head of the deep mixing pile machine undergoes a sudden change, it is determined that an obstacle has been encountered. Here, a standard current value I0 and a set difference value I are defined. 差 The value of the set duration t0 is consistent with the value in Example 1.

[0147] According to existing technology, during the drilling process, the control panel of the deep mixing pile machine will display the current drilling depth in real time. When an obstacle is encountered, the real-time depth information, i.e. the current drilling depth, is read and used as the obstacle depth information.

[0148] The control system of the deep mixing pile machine stores an obstacle record table, which is used to record obstacle information within each deep mixing pile in the current construction area. The obstacle record table stores the pile number and corresponding obstacle depth information. The pile number consists of three Arabic numerals, such as 001, 002, etc. As shown in Table 1, when an obstacle is detected and its depth information is obtained, it is stored in the obstacle record table.

[0149] Table 1 Obstacle Record Sheet

[0150]

[0151] The unit depth range refers to a depth range of one meter. For example, if the target depth is 52 meters, then the deep mixing pile contains 52 unit depth ranges, namely 0-1, 1-2, 2-3, ..., 51-52. The obstacle density is the number of obstacles. According to the obstacle depth information of each pile in the obstacle record table, the number of obstacles in each unit depth range of each deep mixing pile can be calculated. Taking the deep mixing pile with pile number 001 in Table 1 as an example, there are three obstacle depth information in the unit depth range of 22-23, which means that there are three obstacles in the unit depth range of 22-23 of the deep mixing pile. Therefore, the obstacle density corresponding to pile number 001 and the unit depth range of 22-23 is 3.

[0152] Furthermore, drilling the main drill pipe into the working hole in a positive circulation manner to the first depth also includes the following steps:

[0153] Get the current pile number;

[0154] Query the pile distribution table for the number of constructed piles adjacent to the current pile number;

[0155] The adjustment depth range is obtained by querying the obstacle record table for each unit depth range where the obstacle density corresponding to the constructed pile number is greater than the set density value.

[0156] When it is determined that the current drilling depth is within the adjusted depth range, the real-time working current value I is increased by a set ratio.

[0157] Before construction, a construction plan is developed based on the size of the construction area, which is generally a rectangular area. When developing the construction plan, the distribution of all piles is typically in the form of an m x n matrix, where m and n are both natural numbers not less than 3. For example... Figure 7 As shown, Figure 7 In the example, all the piles are distributed in 3 rows and 8 columns. During construction, they are generally carried out in a serpentine order, that is, the first row of piles is constructed from left to right, the second row of piles is constructed from right to left, and the third row of piles is constructed from left to right.

[0158] The control system of the deep mixing pile machine also stores a pile distribution table, which contains information on all piles within the current construction area. Each pile information consists of four Arabic numerals: the first three digits represent the pile number, and the last digit indicates whether the pile has been constructed. "1" represents that the pile has been constructed, and "0" represents that the pile has not been constructed. For example, if a pile information is "0071", it means that the pile has been constructed and its pile number is 007; if a pile information is "0200", it means that the pile has not been constructed and its pile number is 020. The pile distribution table is shown in Table 2.

[0159] Table 2 Pile Distribution Table

[0160]

[0161] When constructing a specific pile, the current pile number is first obtained, for example, pile number 012. Then, the pile distribution table is consulted to find the constructed pile numbers adjacent to pile number 012. Piles located in front of, behind, to the left of, and to the right of the current pile are considered adjacent piles. In this embodiment, the piles adjacent to pile number 012 include piles 005, 011, 013, and 021, of which piles 005 and 011 are already constructed. Finally, the obstacle record table is consulted to find the obstacle density of piles 005 and 011 within each unit depth range. In this embodiment, the target depth for pile 005 is 50 meters. The target depth for stake 011 is 48 meters. Therefore, there are 50 unit depth ranges corresponding to stake 005 and 48 unit depth ranges corresponding to stake 011. The obstacle density values ​​for each unit depth range of the two stakes are retrieved from the obstacle record table. The obstacle density value for each unit depth range is compared with the set density value. If it is greater than the set density value, the unit depth range is stored in the adjustment depth range. It should be noted that for the same unit depth range, as long as the obstacle density value of any stake is greater than the set density value, it is stored in the adjustment depth range. The adjustment depth range includes several unit depth ranges.

[0162] In this embodiment, the set density value ranges from 2 to 4, and in this embodiment, the set density value is 3.

[0163] After determining the adjustment depth range, deep mixing pile construction begins. During construction, when the current drilling depth reaches any unit depth within the adjustment depth range, the real-time working current I is increased by a set ratio in advance. That is, before drilling into the obstacle, the real-time working current value I of the rotating power head of the deep mixing pile machine is increased in advance to protect the drill bit and the main drill rod. In this embodiment, the value range of the set ratio is generally 1.2-1.5, preferably 1.35.

[0164] Example 4

[0165] This embodiment provides a method for constructing deep mixing piles. This embodiment is an improvement on embodiment 2. The similarities between this embodiment and embodiment 2 will not be repeated. The difference is that the method for constructing deep mixing piles further includes the following steps:

[0166] When it is determined that there is a protected structure within the construction area or a diaphragm wall structure at the edge of the construction area, before operating the aforementioned access hole:

[0167] A drill rod is lowered at a set distance from the drilling hole and water is sprayed to a set depth to form a pressure-relieving blind hole.

[0168] In this embodiment, the set distance can be, for example, 1-1.5 meters. Because pressure relief blind holes are set near the drilling holes, the pressure on the underground soil during deep mixing will be released through these blind holes, thus avoiding damage to the protected structure or diaphragm wall structure. The protected structure can be, for example, an underground pipeline; specifically, for example, a 6.6kV cable buried at a depth of 1.5-2m approximately 2m from the edge of the foundation treatment. During the grouting of the two rows at the edge, blind holes are drilled, with one blind hole between every two deep mixing piles, such as... Figure 8 As shown, the bottom elevation of the blind hole is the top elevation of the grouting. The blind hole is constructed first, followed by grouting.

[0169] This embodiment, based on Embodiment 2, adds a pressure release step. When the construction area is an equipment room or a shield tunnel section, the cement grout is ejected at a relatively high pressure from the grouting nozzle at the bottom of the drill rod underground, reaching a pressure of 6 Bar. In particular, the cutting action of the drill bit blades drives the nearby soil, thereby squeezing and pushing the outer soil layer, generating tangential and radial forces. Simultaneously, the cement grout permeates into soil cracks and pores. The pore water pressure in the undisturbed soil will suddenly increase, accumulating in the underconsolidated soft clay and not easily dissipating, resulting in radial and tangential plastic displacement of the nearby soil. Macroscopically, this manifests as soil heave and lateral displacement, road cracking, and the soil squeezing effect caused by deep mixing pile construction, which will have a significant impact on the surrounding environment. The technical solution provided in this embodiment can solve the above problems.

[0170] Example 5

[0171] This embodiment provides a method for constructing deep mixing piles. This embodiment is an improvement on embodiment 2. The similarities between this embodiment and embodiment 2 will not be repeated. The difference is that the method for constructing deep mixing piles further includes the following steps:

[0172] When it is determined that there is a protected structure within the construction area or a diaphragm wall structure at the edge of the construction area, before operating the drilling hole:

[0173] Several hollow steel pipe piles were intermittently buried within the construction area;

[0174] The soil inside the hollow steel pipe piles was removed.

[0175] In this embodiment, a total of 21 800mm diameter steel pipe piles were pre-installed within the construction area of ​​the station foundation, with a spacing of approximately 10m between the piles. After pile installation, the soil inside the pipes was emptied to provide storage space for soil upwelling during deep mixing, and the internal silt was promptly removed. The steel pipe piles function similarly to blind holes and can also be used as release holes for underground soil pressure during deep mixing. Steel pipe piles have a longer service life and more stable performance than blind holes. The installation depth of the steel pipe piles is also to the design elevation of the deep mixing piles. By adopting the technical solution provided in this embodiment, the same technical problems as in Embodiment 4 can be solved.

[0176] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of written expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A method for constructing deep mixing piles, characterized in that, The method includes the following steps: The main drill rod is drilled into the working hole in a forward circulation manner to the first depth; the main drill rod includes a first drill rod and a second drill rod connected by a third drill rod joint, the top end of the first drill rod is connected to the rotating power head of the deep mixing pile machine through the first drill rod joint; the length of the first drill rod is greater than the length of the second drill rod, and the second drill rod is formed by extending several unit sub-drill rods; the bottommost unit sub-drill rod is welded to the drill bit used for drilling; the first depth is the target depth determined by the deep mixing pile target depth determination method; The method for determining the target depth of deep mixing piles includes: During the process of driving the drill rod down the deep mixing pile machine, the real-time operating current value I of the rotating power head of the deep mixing pile machine is acquired in real time. The target depth is determined when the real-time operating current value I simultaneously meets the following conditions 1-3: Condition 1: The real-time operating current value I is greater than the set standard current value I0; Condition 2: The real-time operating current value I and the no-load current I 空 The difference is greater than the set difference I 差 ; Condition 3: The durations of conditions 1 and 2 are simultaneously greater than the set duration t0; When drilling the main drill pipe into the working hole to the first depth using forward circulation, the main drill pipe needs to be assembled. The assembly process of the main drill pipe includes: S1-1. Install the first drill rod onto the rotating power head of the deep pile mixing machine through the first drill rod joint; S1-2. Start the grouting pump to spray water and drill the first drill rod into the ground from the first position located next to the drilling hole in a positive circulation manner. S1-3. Turn off the grouting pump, open the first drill rod joint, remove the first drill rod from the rotating power head of the deep pile mixing machine, and install the second drill rod on the rotating power head of the deep pile mixing machine through the second drill rod joint. S1-4. Turn on the grouting pump to spray water and drill the second drill rod into the working hole to the second depth, which is slightly less than the length of the second drill rod. S1-5. Turn off the grouting pump, open the second drill rod joint, and disconnect the second drill rod from the rotating power head of the deep mixing pile machine. S1-6. Install the first drill rod on the rotating power head of the deep pile mixing machine through the first drill rod joint, and pull the first drill rod out from the ground; S1-7. Connect the first drill pipe and the second drill pipe with the third drill pipe joint, and the first drill pipe and the second drill pipe form a total drill pipe. The high-pressure grouting pump on the deep pile mixing machine is turned on to spray cement slurry, and the main drill rod is raised in reverse circulation to spray slurry to the second depth; the second depth is less than the length of the second drill rod. The main drill pipe is drilled under positive circulation and cement slurry is sprayed to the first depth; Shut down the high-pressure grouting pump and reverse-circulate to raise the main drill pipe to the second depth; Remove the third drill pipe joint and drill the first drill pipe into the ground at the first location; Remove the first drill rod joint and connect the second drill rod located in the drilling hole to the rotating power head of the deep pile mixing machine through the second drill rod joint; The high-pressure grouting pump is turned on, and the second drill rod is drilled down to the third depth in positive circulation; the third depth is deeper than the second depth, and the depth difference between the two is 500mm. The second drill pipe is raised using reverse circulation, and cement grout is sprayed to the designed top elevation. The second drill pipe is drilled under positive circulation and cement slurry is sprayed to the third depth; The high-pressure grouting pump is shut down, and the second drill pipe is raised to the surface via reverse circulation.

2. The deep mixing pile construction method according to claim 1, characterized in that, The set standard current value I0 ≥ 200A; The set difference I 差 ≥60A; The set duration t0 is ≥ 15s.

3. The deep mixing pile construction method according to claim 1, characterized in that, The main drill pipe is drilled into the working hole in a positive circulation manner to the first depth, including the following steps: When the real-time operating current value I simultaneously satisfies both condition 1 and condition 2, it is determined that an obstacle has been encountered, and the real-time depth information is read as the obstacle depth information. The obstacle depth information is stored in an obstacle record table; the obstacle record table stores the stake number and the corresponding obstacle depth information. The number of obstacles within each unit depth range is calculated based on the obstacle record table to obtain the obstacle density corresponding to the stake number and each unit depth range.

4. The deep mixing pile construction method according to claim 3, characterized in that, The process of drilling the main drill pipe into the working hole to the first depth via positive circulation also includes the following steps: Get the current pile number; Query the pile distribution table for the number of constructed piles adjacent to the current pile number; The adjustment depth range is obtained by querying the obstacle record table for each unit depth range where the obstacle density corresponding to the constructed pile number is greater than the set density value. When it is determined that the current drilling depth is within the adjusted depth range, the real-time working current value I is increased by a set ratio.

5. The deep mixing pile construction method according to any one of claims 1-4, characterized in that, The bottom sidewall of the drill bit has only one grouting port; the outer wall of the drill bit has an arc-shaped baffle on one side of the grouting port; the arc-shaped baffle is located in front of the direction of rotation when the drill bit drills downward.

6. The deep mixing pile construction method according to any one of claims 1-4, characterized in that, The deep pile mixing machine has two main drill rods installed in parallel on its rotating power head; the pile diameter of the main drill rods is greater than 1400mm and less than 1600mm; the center distance between the two main drill rods is greater than 1100mm and less than 1300mm.

7. The deep mixing pile construction method according to any one of claims 1-4, characterized in that, It also includes the following steps: When it is determined that there is a protected structure within the construction area or a diaphragm wall structure at the edge of the construction area, before operating the aforementioned access hole: A drill rod is lowered at a set distance from the drilling hole and water is sprayed to a set depth to form a pressure-relieving blind hole.

8. The deep mixing pile construction method according to any one of claims 1-4, characterized in that, It also includes the following steps: When it is determined that there is a protected structure within the construction area or a diaphragm wall structure at the edge of the construction area, before operating the drilling hole: Several hollow steel pipe piles were intermittently buried within the construction area; The soil inside the hollow steel pipe piles was removed.

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