A preparation method for full-replacement variable-section cement-soil piles

Abstract

The present invention relates to the field of construction engineering technology, and in particular to a method for preparing a fully-replacement variable-section cement soil pile. The cement soil pile uses a long spiral drill to drill a hole in the foundation soil layer, and the drill rod is rotated when it is lifted. Under the action of the cutting head of a special drill bit, the drill rod rotates and lifts while pumping cement soil slurry, forming a variable-section shape at the required position of the pile body. Since a hole is formed first, the soil is taken out, and water, cement, curing agent, etc. are added for mixing outside the hole, and then pressure-injected into the pile hole to form a fully-replacement variable-section cement soil pile. The present invention forms a new replacement variable-section cement soil pile, which solves the problem of uneven mixing of mixing piles when encountering clay layers, and improves the construction quality of cement soil piles; the bearing capacity of cement soil piles is improved by varying the cross-section; compared with the in-situ mixing method, the fully-replacement cement soil pile of the present invention can reduce cement consumption, which complies with the policy of energy conservation and emission reduction.

Description

Technical Field

[0001] The present invention relates to the technical field of construction engineering, and in particular to a preparation method of a full-replacement variable-section cement-soil pile. Background Art

[0002] my country began researching "Bolai" technology in 1978, and cement-soil mixing piles were applied to soft soil foundations in the 1980s. Over the decades of domestic application, cement-soil pile construction methods and equipment have reached parity with international technology. Breakthroughs have been made in methods such as "four-spray, four-mix" and "high-pressure jetting," ultimately achieving the goal of "deep jetting and mixing."

[0003] Cement-soil piles are the most common type of pile and are categorized by the production process into shotcrete-cement-soil piles and powdered-cement-soil piles. These piles are typically produced by forcibly mixing a cement curing agent with the on-site soil using a mixing nozzle and device. Due to the uneven mixing characteristics of on-site mixing, the strength of these piles can be lower than the strength obtained from laboratory mix tests using the same cement content.

[0004] Due to the inherent characteristics of the cement-soil mixing process, cement-soil mixing piles have always relied on an in-situ mixing method. In practice, these practices often result in engineering accidents involving "deformation control failure" due to issues such as low pile strength and high dispersion, and difficulty monitoring construction quality. Despite continuous improvements in mixing technology, the chronic problem of uneven mixing remains unavoidable, forcing the standard to be revised to accommodate this regression. The "pile strength reduction factor n" in the "Code for Building Foundation Treatment" was set at 0.35-0.5 in the 1990s (JGJ79-1991), adjusted to 0.25-0.33 in 2002 (JGJ79-2002), and finally to 0.2-0.25 in 2012 (JGJ79-2012). Even with these repeated reductions, construction quality remains uncertain.

[0005] Current soft foundation treatment methods include CFG piles, mixing piles, and compacted cement-soil piles. CFG piles are made of cement, crushed stone, and fly ash. A long auger is used to drill a hole and then pump and cast the mixture into a pile. Mixing piles use a deep mixer to mix cement and soil in situ. Compacted cement-soil piles are compacted layer by layer using a rammer. Compacted cement-soil piles are suitable for strata without groundwater, but their applicability is limited. CFG piles are relatively expensive. Mixing piles use in-situ mixing, which often results in uneven mixing when encountering clay layers, making construction quality difficult to guarantee.

[0006] Currently, when dealing with soft foundations on highways, mixing piles are often used. To ensure construction quality, increasing the amount of cement added doesn't fundamentally solve the problem of uneven mixing in the clay layer. Consequently, CFG piles or precast pipe piles are often used instead, significantly increasing project costs and causing waste. Summary of the Invention

[0007] In order to make up for the deficiencies of the prior art, the present invention provides a method for preparing a full-replacement variable-section cement-soil pile.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for using a full-replacement variable-section cement-soil pile comprises the following steps:

[0010] (1) Positioning and laying out

[0011] Use a total station or GPS for positioning and setting out. Insert a steel chisel or a small red flag at the control pile position. Use a steel ruler to measure the distance between the middle piles according to the pile spacing, and spray white lime at the pile position as a pile position mark.

[0012] (2) Position the drilling rig and adjust its verticality

[0013] After the drilling rig is in place, the drill bit tip is aligned with the pile position, the drilling rig is placed stably, the pile frame guide rod is straightened, the deviation between the drill bit center and the pile position is no more than 2cm, and the verticality deviation of the tower is less than 1%;

[0014] (3) Preparation of cement soil slurry

[0015] The cement-soil slurry is prepared by mixing it in a high-speed mixer using a tank-by-tank mixing method. First, measured water is placed in the mixer, and after starting the mixer, cement is added and stirred into a slurry. After the water and cement are fully mixed to form a slurry, the soil material is added in batches and mixed. The mixing time for each tank should be determined based on the clay content and slump of the soil material. The cement-soil slurry is stirred until all the clay lumps are dissolved.

[0016] (4) Drilling, hole formation, lifting and pumping

[0017] After the long spiral drill is in place and the drill rod is aligned with the hole position and the verticality of the drill rod is adjusted, the main motor is started to drive the long spiral drill rod to drill at the normal speed; the drilling speed is controlled within 1.5-2.5m / min according to different strata; after reaching the designed depth, the drill is stopped after idling for 30s; after the hole is formed, the mixed cement soil slurry is immediately delivered to the bottom of the hole through the guide tube and the drill rod using a concrete pump (HBS40). The pressure of the pumped cement slurry is 7.7-13MPa, and the maximum allowable length of the pipeline is 200m; the main winch is immediately started to lift the drill rod, and the lifting speed is generally 1.5-2.0m / min. min, and match the pumping speed. When the drill rod is raised to the diameter change point, start the main motor of the power head to rotate, raising the drill rod while rotating, and simultaneously pumping concrete to form the expanded diameter section. When the drill bit is raised to 0.5-1.0 m from the foundation bottom, remove the excess mud and concrete from the drill hole, and finally remove the drill rod. During the drill rod lifting process, promptly remove the mud from the drill hole and the spiral blades until the cement-soil slurry at the drill hole is exposed. After pouring to the designed elevation of the pile top, pour approximately 500 mm longer than the pile diameter to ensure the strength of the concrete at the pile top after the floating slurry is removed. After the pile is completed, the long spiral drill rig moves to the next pile location.

[0018] Preferably, in step (3), the earth used to prepare the cement-soil slurry is derived from the earth removed during the drilling process of the long spiral drill. The water-to-solid ratio of the cement-soil slurry should be determined by the slump of the on-site trial mix. The prepared cement-soil slurry should have good fluidity and should be able to meet pumping requirements. If the water-to-solid ratio does not meet the use requirements, the cause should be analyzed, the parameters should be adjusted, and the slurry should be remixed.

[0019] Preferably, in step (3), the stirring time of each tank should be determined according to the clay content and slump size in the soil material, and the stirring time is 3-6 minutes; after the cement soil slurry is stirred, the particle size of the residual clay block is not greater than 10 mm.

[0020] Preferably, the organic matter content of the soil material used is not more than 5%; the cement used is not lower than P.O425 grade cement; the weighing error of the slurry material does not exceed 5%; and the slump is 180mm to 240mm.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The present invention forms a new replacement type variable cross-section cement soil pile, which solves the problem of uneven mixing of mixing piles when encountering clay layers and improves the construction quality of cement soil piles; and improves the bearing capacity of cement soil piles by changing the cross-section.

[0023] (2) Compared with the in-situ mixing method, the full replacement cement soil pile of the present invention can reduce cement consumption and comply with the policy of energy conservation and emission reduction; the raw materials use the soil materials extracted by drilling, which reduces energy consumption and is a green and environmentally friendly construction technology; compared with CFG piles and prefabricated pipe piles, it can greatly reduce the project cost, has great promotion value, and can create huge economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings.

[0025] Figure 1 This is a schematic structural diagram of a high-speed mixer according to the present invention;

[0026] Figure 2 This is a schematic diagram of the double-thread drill bit structure of the present invention;

[0027] Figure 3 This is a flow chart of the construction process of the full replacement cement soil pile of the present invention; DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] Example 1

[0030] The present invention adopts the following technical solutions:

[0031] 1. Improved construction technology: In-situ mixing is replaced with a full replacement method. This utilizes the spoil expelled by the drilling rig, mixing it with cement, a curing agent, and water to create a cement-soil slurry. This slurry is then pumped into the borehole via a concrete pump and drill pipe, creating a fully replaced cement-soil pile. Compared to the traditional in-situ mixing method, premixed cement-soil slurry eliminates the problem of cement slurry loss. While maintaining the same design strength of the cement-soil, the cement dosage can be reduced, saving cement consumption. This method also addresses the issues of uneven pile strength due to variations in soil quality and uneven mixing in highly plastic clay layers, which can occur with in-situ mixing methods.

[0032] 2. Cement soil slurry mixing equipment: such as Figure 2 As shown, a forced high-speed mixer (see zl202320595525.9 for details) with twin horizontal shafts, driven by 2 x 37kW motors with a speed of no less than 90 rpm and a capacity greater than 4 m³, is used. The cement slurry preparation equipment and process utilize an automated control system, and the cement feeder is fully enclosed for dust removal, strictly controlling construction noise and dust emissions.

[0033] 3. Selection of pile construction equipment: Long spiral drilling rigs are selected for pile drilling. Long spiral drilling rigs should meet the requirements of hole formation and diameter change, and special drill bits should be developed according to the construction process requirements, such as Figure 2As shown, the drilling rig is capable of achieving the required complex variable diameter motion. The long auger drill's power head and main reel are equipped with variable frequency controllers, and the bottom end of the drill bit is equipped with symmetrical double-threaded blades. As the drill rod rotates and rises, it squeezes the soil outside the pile shaft, causing the diameter to expand. This type of pile can be expanded at any point in the pile shaft, for example, at the bottom of the pile to form an enlarged head, increasing the bearing capacity of the pile end and further meeting the structural and bearing capacity requirements of the foundation pile. When only the drill rod is raised without rotating, a straight rod section is formed. There is no soil squeezing effect during hole formation, but there is a localized squeezing effect during diameter expansion.

[0034] 4. Raw Materials and Mix Ratio Testing: Mix ratio testing is required before construction. It is recommended to use at least three mix ratios. One of the mix ratios should be based on the design, and the cement content of the other two mix ratios should be adjusted appropriately. The design strength of the cement-soil is 2.0 MPa. The organic matter content of the soil should not exceed 5%. Cement should be graded no lower than P.O425. The weighing error of the slurry material should not exceed 5%. The slump should be 180 mm to 240 mm, meeting pumping requirements.

[0035] Example 2

[0036] like Figure 3 As shown,

[0037] like Figure 1 As shown in the figure, the process flow of full replacement variable cross-section cement soil pile is:

[0038] (1) Positioning and setting out: Use a total station or GPS for positioning and setting out. Insert a steel chisel or a small red flag at the control pile position. Use a steel ruler to measure the distance between the middle piles according to the pile spacing, and spray white lime at the pile position as a pile position mark.

[0039] (2) Position the drilling rig and adjust the verticality: After the drilling rig is in place, align the drill bit tip with the pile position. If the drill bit tip is found to be off the point, readjust it until the drill bit tip is aligned with the hole position. The drilling rig should be placed steadily, and the pile frame guide rod should be adjusted straight. The deviation between the drill bit center and the pile position should not exceed 2 cm, and the verticality deviation of the tower frame should be less than 1%.

[0040] (3) Preparation of cement slurry: Cement slurry is mixed using a special high-speed mixer. The cement slurry is prepared by the tank-by-tank mixing method. First, the measured water is put into the mixer, and then cement is added and stirred into cement slurry after the mixer is started. After the water and cement are fully mixed to form cement slurry, the soil material is added in batches for mixing. The mixing time of each tank should be determined according to the clay content and slump of the soil material, and the mixing time is 3-6 minutes. After the cement slurry is mixed, the particle size of the residual clay blocks should not be greater than 10mm. Otherwise, the mixing time should be increased until all the clay blocks are dissolved. The soil used to prepare the cement slurry mainly comes from the soil removed during the drilling process of the long spiral drill. The water-solid ratio of the cement slurry should be determined by the slump of the on-site trial mixing. The prepared cement slurry should have good fluidity and should be able to meet the pumping requirements. When the water-solid ratio does not meet the use requirements, the cause should be analyzed, the parameters should be adjusted, and the mixture should be remixed.

[0041] (4) Drilling, forming a hole, lifting and pumping: After the long spiral drill is in place and the drill rod is aligned with the hole position and the verticality of the drill rod is adjusted, the main motor is started to drive the long spiral drill rod to drill at the normal speed. Depending on the different formations, the drilling speed should be controlled within 1.5-2.5m / min. After reaching the designed depth, stop drilling after idling for 30s; after the hole is formed, immediately use a concrete pump (HBS40) to pump the mixed cement soil slurry to the bottom of the hole through the guide tube and drill rod. The pressure of the pumped cement slurry is 7.7-13MPa, and the maximum allowable length of the pipeline is 200m. When the ball valve at the top of the drill pipe is vented (the drill pipe is now full of slurry), the main winch is immediately activated to raise the drill pipe. The lifting speed is generally 1.5-2.0 m / min, matching the pumping speed. When the drill pipe reaches the diameter change point, the main motor of the power head is activated to rotate, lifting the drill pipe while rotating, while simultaneously pumping concrete to form the expanded diameter section. When the drill bit is raised to 0.5-1.0 m from the foundation bottom, excess slurry and concrete are removed from the borehole, and the drill pipe is finally lifted out. During the drill pipe lifting process, construction personnel should promptly remove soil from the borehole and the spiral blades until the cement-soil slurry at the drill hole is exposed. After pouring to the designed pile top elevation, an additional 500 mm of approximately double the pile diameter must be poured to ensure the strength of the concrete at the pile top after the floating slurry is removed. After the pile is completed, the long auger drill is moved to the next pile location.

[0042] The full-replacement cement-soil pile construction technology of this embodiment can solve the problem of poor pile quality of cement-soil mixing piles in clay soil. While mixing piles inject cement slurry into the ground and mix it in situ, the full-replacement method removes the soil, mixes it evenly outside the hole, and then pours it in, completely replacing it.

[0043] The full replacement method has reliable construction quality, solves problems that the in-situ mixing method cannot overcome, and reduces cement consumption.

[0044] Compared with piles of constant cross-section, variable cross-section cement soil piles can significantly improve the bearing capacity of foundation piles, save concrete and reduce project costs.

[0045] Compared with the in-situ mixing method, full-replacement cement-soil piles can reduce cement consumption and comply with the policy of energy conservation and emission reduction; the raw materials are soil materials extracted by drilling, which reduces energy consumption and is a green and environmentally friendly construction technology.

[0046] Highways require a large amount of soft foundation treatment, often requiring hundreds of thousands of meters of cement-soil mixing piles. If the quality of these piles cannot be addressed, replacing them with CFG piles or precast pipe piles would increase project costs by three to four times, resulting in significant waste. The widespread application of full cement-soil replacement piles would have significant economic and social benefits.

[0047] The cement soil pile of the present invention uses a long spiral drill to drill a hole in the foundation soil layer. When the drill rod is lifted, it is rotated. Under the action of the cutting head of the special drill bit, the drill rod rotates and lifts while pumping cement soil slurry, which will form a variable cross-section shape at the required position of the pile body. Because the hole is first formed, the soil is taken out, and water, cement, curing agent, etc. are added to stir outside the hole, and then pressure-injected into the pile hole to form a full-replacement variable-section cement soil pile. The developed full-replacement variable-section cement soil pile can be used for soft foundation treatment in construction, highway and other projects, and can be used as a composite foundation to improve the bearing capacity of the foundation.

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0049] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for using a full-replacement variable-section cement-soil pile, characterized in that: The following steps are involved: (1) Positioning and laying out Use a total station or GPS for positioning and setting out. Insert a steel chisel or a small red flag at the control pile position. Use a steel ruler to measure the distance between the middle piles according to the pile spacing, and spray white lime at the pile position as a pile position mark. (2) Position the drilling rig and adjust its verticality After the drilling rig is in place, the drill bit tip is aligned with the pile position, the drilling rig is placed stably, the pile frame guide rod is straightened, the deviation between the drill bit center and the pile position is no more than 2cm, and the verticality deviation of the tower is less than 1%; (3) Preparation of cement soil slurry The cement-soil slurry is mixed using a high-speed mixer and a tank-by-tank mixing method. First, measured water is put into the mixer, and after starting the mixer, cement is added and mixed into the cement slurry. After water and cement are fully mixed to form cement slurry, soil materials are added in batches and mixed. The mixing time of each tank should be determined according to the clay content and slump of the soil material. The cement slurry is mixed until all clay lumps are dissolved. The soil used to prepare the cement-soil slurry comes from the soil removed during the drilling process of the long spiral drill. The water-solid ratio of the cement-soil slurry should be determined by the slump of the on-site trial mix. The prepared cement-soil slurry should have good fluidity and should be able to meet the requirements of pumping. When the water-solid ratio does not meet the use requirements, the cause should be analyzed, the parameters should be adjusted, and remixing should be done; The mixing time of each tank should be determined according to the clay content and slump of the soil material, and the mixing time is 3-6 minutes. After the cement-soil slurry is mixed, the particle size of the residual clay blocks should not exceed 10mm. The organic matter content of the soil used shall not exceed 5%; the cement used shall be no less than P.O425 grade; the weighing error of the slurry material shall not exceed 5%; the slump shall be 180mm to 240mm; (4) Drilling, hole formation, lifting and pumping After the long spiral drill is in place and the drill rod is aligned with the hole position and the verticality of the drill rod is adjusted, the main motor is started to drive the long spiral drill rod to drill at the normal speed; the long spiral drill rig power head and the main reel are equipped with a frequency converter, and the bottom end of the drill bit is equipped with a symmetrical double-threaded blade; the drilling speed is controlled within 1.5-2.5m / min according to different strata; after reaching the designed depth, stop drilling after idling for 30s; after the hole is formed, the mixed cement soil slurry is immediately sent to the bottom of the hole through the guide tube and the drill rod using the concrete pump HBS40. The pressure of the pumped cement slurry is 7.7-13MPa, and the maximum allowable length of the pipeline is 200m. The main winch is immediately started to lift the drill rod and lift it. The speed is 1.5-2.0m / min and matches the pumping speed; when the drill rod is lifted to the diameter change position, start the main motor of the power head to rotate, lift the drill rod while rotating, and pump concrete to form an expanded diameter section; when the drill bit is lifted to 0.5-1.0m from the bottom surface of the foundation, clear the mud and concrete overflowing from the borehole, and finally lift the drill rod; during the drilling rod lifting process, promptly clear the mud on the borehole mouth and spiral blades until the cement soil slurry at the borehole is exposed; after pouring to the designed elevation of the pile top, it is necessary to pour twice the pile diameter length to ensure the strength of the concrete on the pile top after the floating slurry is chiseled off. After the pile is formed, the long spiral drill rig moves to the next pile position.

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