Preparation method of full-replacement variable-cross-section cement-soil pile

Abstract

The invention relates to the technical field of construction engineering, in particular to a preparation method of a full-replacement variable-cross-section cement-soil pile. According to the cement soil pile, a long spiral drilling machine is adopted for drilling a hole in a foundation soil layer, a drill rod is rotated when lifted, and under the action of a cutting tool bit of a special drill bit, the drill rod is rotated, lifted and pumps cement soil slurry at the same time, so that a variable cross-section shape can be formed in the required position of a pile body. Holes are firstly formed, soil is taken out, water, cement, a curing agent and the like are added for stirring outside the holes, and then the soil is poured into pile holes under pressure, so that the full-replacement variable-cross-section cement-soil pile is formed. The novel replacement type variable-cross-section cement-soil pile is formed, the problem that stirring of a stirring pile is not uniform when the stirring pile meets a clay layer is solved, and the construction quality of the cement-soil pile is improved; the bearing capacity of the cement-soil pile is improved through the variable cross section; compared with an in-situ stirring method, the full-replacement cement-soil pile can reduce cement consumption, and conforms to the policy of energy conservation and emission reduction.

Description

Technical Field

[0001] The 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 to apply cement-soil mixing piles to soft soil foundation treatment in the 1980s. In the decades of domestic application, the construction method and pile-making equipment of cement-soil piles have been synchronized with foreign technical levels. It has broken through the "four-spraying and four-stirring" and "high-pressure spraying" modes and achieved the goal of "deep jetting and mixing method".

[0003] Cement soil pile is the most common type of pile among many types of piles. It is divided into shotcrete cement soil pile and powdered cement soil pile according to its pile forming process. The characteristic is that cement curing agent is forcibly mixed with the original soil on site through a mixing nozzle and a device to obtain a cement soil pile body. Due to the uneven mixing of on-site mixing, the strength of the pile body mixed on site will be lower than the indoor mix ratio test strength with the same cement content.

[0004] Due to the characteristics of the process itself, cement-soil mixing piles always remain in the in-situ mixing method. In actual applications, due to problems such as "low pile strength and large discreteness" and "difficult to monitor construction quality", engineering accidents such as "deformation control failure" often occur. Although the mixing process has been continuously improved, the "chronic disease" of uneven mixing has always been unavoidable, resulting in the specification having to accommodate this "retreat" and be modified. The "pile strength reduction coefficient n value" in the "Building Foundation Treatment Code" is: in the 1990s (JGJ 79-1991) n = 0.35 ~ 0.5, adjusted to (JGJ 79-2002) n = 0.25 ~ 0.33 in 2002, and adjusted to (JGJ 79-2012) n = 0.2 ~ 0.25 in 2012. Even if the reduction coefficient is reduced again and again, the construction quality cannot be guaranteed.

[0005] At present, there are CFG piles, mixing piles, and compacted cement soil piles. CFG piles are made of cement, crushed stone, and fly ash. They are drilled with a long spiral drill and pumped into piles. Mixing piles use deep mixers to mix cement and soil in situ to form piles. Compacted cement soil piles use tamping machines to compact in layers. Compacted cement soil piles are suitable for strata without groundwater, and their scope of application is limited. CFG piles are relatively expensive. Mixing piles use in-situ mixing. When encountering clay layers, the mixing is often uneven, and the construction quality is difficult to guarantee.

[0006] At present, when highways encounter soft foundation treatment, mixing piles are mostly used. In order to ensure the construction quality, the method of increasing the amount of cement is adopted, but it cannot fundamentally solve the problem of uneven mixing of the clay layer. Therefore, CFG piles or prefabricated pipe piles can only be used instead, which greatly increases the project cost and causes 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 total station or GPS for positioning and setting out, insert steel chisels or small red flags at the control pile positions, use steel rulers to measure the distance between the middle piles according to the pile spacing, and spray white lime at the pile positions as pile position marks;

[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 of the drill bit center from 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 mixed with a high-speed mixer and prepared by a tank-by-tank mixing method. First, the measured water is put into the mixer, and then cement is added and mixed 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 size in the soil material. The mixing of the cement-soil slurry is completed until all the clay blocks are dissolved.

[0016] (4) Drilling, drilling, 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; according to different formations, the drilling speed is 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 send the mixed cement slurry to the bottom of the hole through the guide tube and the drill rod. The pressure of the pumped cement slurry is 7.7-13MPa, and the maximum allowable length of the pipeline is 200m; immediately start the main winch to lift the drill rod, and the lifting speed is generally 1.5-2.0m / min, and match it with the pumping speed; when the drill rod is lifted to the variable diameter, 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 of the foundation, remove the mud and concrete overflowing from the borehole, and finally lift the drill rod; during the lifting of the drill rod, promptly remove the mud on the borehole and spiral blades until the cement slurry at the borehole is exposed; after pouring to the designed elevation of the pile top, it is necessary to pour about 500mm more than the pile diameter to ensure the strength of the concrete on the pile top after the floating slurry is removed. After the pile is formed, the long spiral drill moves to the next pile position.

[0018] Preferably, in step (3), the earth used to prepare the cement soil slurry comes from the earth taken out during the long spiral drilling process, and the water-solid ratio of the cement soil slurry should be determined by the slump of the on-site trial mixing. 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 reasons should be analyzed, the parameters should be adjusted, and the mixture should be remixed.

[0019] Preferably, in step (3), the stirring time of each tank should be determined according to the clay content and slump 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 less 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 the mixing pile when encountering a clay layer, improves the construction quality of the cement soil pile; and improves the bearing capacity of the cement soil pile 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, which is in line with the policy of energy conservation and emission reduction; the raw materials use the soil taken out 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 in conjunction with the accompanying drawings.

[0025] Figure 1 It is a schematic diagram of the structure of a high-speed mixer implemented in 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 construction process flow chart of the full replacement cement soil pile of the present invention; DETAILED DESCRIPTION

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

[0029] Example 1

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

[0031] 1. Improvement of construction technology: In-situ mixing is replaced by full replacement method. The waste soil discharged by the drilling rig can be used to mix the soil with cement, curing agent and water into cement soil slurry, which is then pumped into the borehole through a concrete pump and drill rod to form a pile, forming a full replacement cement soil pile. Compared with the traditional in-situ mixing method, the use of premixed cement soil slurry does not have the problem of cement slurry loss. Under the condition of the same cement soil design strength, the amount of cement added can be reduced, saving cement consumption; it solves the problem of uneven pile strength due to changes in the soil quality of the stratum and uneven mixing in the high plastic clay layer.

[0032] 2. Cement soil slurry mixing equipment: such as Figure 2 As shown, a forced high-speed mixer (see zl202320595525.9 for details) is used, with twin-shaft mixing, driven by 2×37kW motors, a speed of not less than 90r / min, and a volume greater than 4m3. The cement slurry preparation equipment and process adopt an automated control system, the cement feeding is fully enclosed for dust removal, and construction noise and dust emissions are strictly controlled.

[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 to meet the construction process requirements, such as Figure 2As shown in the figure, the drilling rig can meet the requirements of compound action of variable diameter. The power head and main reel of the long spiral drilling rig are equipped with a frequency conversion controller, and the bottom end of the drill bit is provided with a symmetrical double-threaded blade. When the drill rod is rotated and lifted at the same time, the soil outside the pile body will be squeezed to form an expanded diameter. This pile type can expand the diameter at any part of the pile body, for example, it can expand the diameter at the bottom of the pile to form an enlarged head, improve the bearing capacity of the pile end, and further meet the structural and bearing capacity requirements of the foundation pile. When only the drill rod is lifted without rotating, a straight rod section will be formed. There is no squeezing effect when discharging soil during hole formation, but there is a local squeezing effect when expanding the diameter.

[0034] 4. Raw materials and mix ratio test: Mix ratio test is required before construction. It is advisable to use no less than 3 mix ratios for testing. One of them should be the mix ratio determined by the design, and the cement content of the other two mix ratios should be appropriately increased or decreased. The design strength of cement soil is 2.0MPa. The organic matter content in the soil material is not more than 5%; the cement is not less than P.O425 grade cement; the weighing error of the slurry material does not exceed 5%. The slump is 180mm~240mm, which meets the 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 piles 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) Drilling rig in place, vertical adjustment: After the drilling rig is in place, the drill bit tip is aligned with the pile position. If the drill bit tip is found to be off the point, it should be readjusted until the drill bit tip is aligned with the hole position. The drilling rig should be placed steadily, the pile frame guide rod should be straightened, the deviation of the drill bit center from the pile position should not exceed 2cm, and the vertical deviation of the tower frame should be less than 1%.

[0040] (3) Preparation of cement soil slurry: Cement soil slurry is mixed with a special high-speed mixer. The cement soil slurry is prepared by the tank-by-tank mixing method. First, the measured water is put into the mixer, and then cement is added after the mixer is started to mix into cement slurry; 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 size in 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 block 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 cement soil slurry mainly comes from the soil taken out during the drilling process of the long spiral drilling machine. The water-solid ratio of the cement soil slurry should be determined by the slump of the on-site trial mixing. The prepared cement soil 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 reasons should be analyzed, the parameters should be adjusted, and the slurry should be remixed.

[0041] (4) Drilling, forming a hole, lifting and pumping: The long spiral drill is in place, 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 send the mixed cement slurry to the bottom of the hole through the guide tube and the 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 rod is exhausted (the drill rod is full of slurry at this time), the main winch is immediately started to lift the drill rod. The lifting speed is generally 1.5-2.0m / min and matches the pumping speed; when the drill rod is lifted to the variable diameter, the main motor of the power head is started to rotate, while lifting the drill rod and rotating, while pumping concrete to form an expanded diameter section; when the drill bit is lifted to 0.5-1.0m from the bottom of the foundation, the mud and concrete overflowing from the borehole are cleared, and finally the drill rod is raised; during the drilling rod lifting process, the construction personnel should promptly clear the soil on the borehole and spiral blades until the cement slurry at the borehole is exposed. After pouring to the designed elevation of the pile top, it is necessary to pour about 500mm more than the pile diameter to ensure the strength of the concrete on the pile top after the floating slurry is removed. After the pile is formed, the long spiral drill moves to the next pile position.

[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. Mixing piles are to inject cement slurry into the stratum in situ for mixing, while the full replacement method is to take out the soil, mix it evenly outside the hole, and then pour it, so as to replace all.

[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 equal 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 use soil extracted by drilling, which reduces energy consumption and is a green and environmentally friendly construction technology.

[0046] There is a huge demand for soft foundation treatment on expressways, and the cement soil mixing pile project often has a length of hundreds of thousands of meters. If the quality problem of mixing piles cannot be solved, and CFG piles or prefabricated pipe piles are used instead, the project cost will increase by 3 to 4 times, causing great waste. If full replacement cement soil piles can be promoted and applied, there will be great 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, and the drill rod is rotated when it is lifted. Under the action of the cutting head of the special drill bit, the drill rod rotates and lifts while pumping cement soil slurry, and a variable cross-section shape is formed at the required position of the pile body. Since the hole is formed first, the soil is taken out, 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 in soft foundation treatment of 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 present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0049] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description 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 may also be appropriately combined to form other implementation modes 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 total station or GPS for positioning and setting out, insert steel chisels or small red flags at the control pile positions, use steel rulers to measure the distance between the middle piles according to the pile spacing, and spray white lime at the pile positions as pile position marks; (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 of the drill bit center from 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 with a high-speed mixer and prepared by a tank-by-tank mixing method. First, measured water is put into the mixer, and then cement is added and mixed into cement slurry after the mixer is started. After water and cement are fully mixed to form cement slurry, soil materials are added in batches for mixing; the mixing time of each tank should be determined according to the clay content and slump size in the soil materials; the cement slurry is mixed until all clay blocks are dissolved; (4) Drilling, drilling, 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; according to different formations, the drilling speed is 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 send the mixed cement slurry to the bottom of the hole through the guide tube and the drill rod. The pressure of the pumped cement slurry is 7.7-13MPa, and the maximum allowable length of the pipeline is 200m; immediately start the main winch to lift the drill rod, and the lifting speed is generally 1.5-2.0m / min, and match it with the pumping speed; when the drill rod is lifted to the variable diameter, 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 of the foundation, remove the mud and concrete overflowing from the borehole, and finally lift the drill rod; during the lifting of the drill rod, promptly remove the mud on the borehole and spiral blades until the cement slurry at the borehole is exposed; after pouring to the designed elevation of the pile top, it is necessary to pour about 500mm more than the pile diameter to ensure the strength of the concrete on the pile top after the floating slurry is removed. After the pile is formed, the long spiral drill moves to the next pile position.

2. The method of use according to claim 1, characterized in that: In step (3), the soil used to prepare the cement soil slurry comes from the soil taken out during the long spiral drilling process. The water-solid ratio of the cement soil slurry should be determined by the slump of the on-site trial mixing. 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 reasons should be analyzed, the parameters should be adjusted, and the slurry should be remixed.

3. The method of use according to claim 1, characterized in that: In step (3), the stirring time of each tank should be determined according to the clay content and slump 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.

4. The method of use according to claim 1, characterized in that: 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%; Slump 180mm~240mm.

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