A construction method for prefabricated bottom-enlarged piles without bottom sealing

Abstract

The present application relates to a method for constructing prefabricated enlarged bottom piles without bottom sealing, which comprises the following steps: S1. Equipment is brought into the site and the pile position is marked according to the construction requirements; S2. The bottom end of the prefabricated pipe pile is not sealed, and after the prefabricated pipe pile is pressed down to the designed bearing layer at the pile position, the loose soil in the hollow part of the prefabricated pipe pile is taken out, and the depth of soil removal exceeds the bottom end of the prefabricated pipe pile; or, a force transfer hammer is inserted into the hollow part of the prefabricated pipe pile, and is pressed down to the designed bearing layer together with the prefabricated pipe pile; S3. Filling material is added into the hollow part of the prefabricated pipe pile in batches, and a force transfer hammer with a length greater than the length of the prefabricated pipe pile is inserted into the hollow part of the prefabricated pipe pile, and the force transfer hammer is squeezed to squeeze the filling material by pressing, spinning or hammering, and the filling material forms a compacted enlarged head at the bottom of the prefabricated pipe pile; S4. Concrete is poured into the hollow part of the prefabricated pipe pile to form an inner pile. The prefabricated pipe pile of the present application has no bottom sealing and no pre-drilling, which can improve the efficiency of pile driving, and can ensure the bearing capacity of the pile end after taking soil from the hollow part of the prefabricated pipe pile.

Description

Technical Field

[0001] The present application relates to the technical field of pile foundation construction, and in particular to a construction method of prefabricated bottom-enlarged piles without bottom sealing. Background Art

[0002] Prefabricated pipe piles, also known as prestressed pipe piles and prefabricated hollow piles, are a type of concrete pile that can be prefabricated in a factory. They have many advantages, such as high construction efficiency, convenient quality monitoring, strong adaptability, and high safety performance. In the current mainstream pile foundation construction, they are widely used. Usually, the prefabricated pipe piles are pressed into the bearing layer by means of pile pressing, and before the pile pressing, it is also necessary to seal the bottom of the prefabricated pipe pile with a steel plate. On the one hand, it can ensure the consistency of the bearing performance of the pile end at the bearing layer, and on the other hand, it can prevent water from flowing through the hollow part of the prefabricated pipe pile to the bearing soil layer at the pile end, thereby reducing the bearing capacity of the bearing layer at the pile end and affecting the bearing capacity of the single pile. Especially for the expanded bottom piles and carrier piles that need to be filled and rammed in the hollow part of the prefabricated pipe piles, the bottom sealing of the prefabricated pipe piles is a crucial link.

[0003] However, with the continuous development of pile foundation construction technology, the two-way requirements for construction efficiency and construction quality are getting higher and higher, and various rock formations of different properties will be encountered during the construction process. If the bearing layer is designed to be in a hard soil layer or rock layer, when the prefabricated pipe pile is pressed after the bottom is sealed, the pile pressure resistance is extremely large, the performance requirements of the pile pressing equipment are high, and there is also the possibility of pile explosion. If you choose to drill holes first and then press the piles, the loose soil on the wall of the pile hole will fall during the pile pressing process, which will also make it difficult for the prefabricated pipe pile to be pressed down when it is pressed down to the vicinity of the bearing layer; if the drilling depth is increased, it is limited by the uncertainty of the amount of loose soil, making it difficult to accurately press the bottom of the prefabricated pipe pile to the bearing layer, and it cannot meet the construction requirements.

[0004] If there is clay or groundwater near the designed bearing layer, after the pile hole is formed, when the prefabricated pipe piles at the bottom are driven into the bearing layer, the flowing groundwater or clay will cause dynamic interference to the bottom of the prefabricated pipe piles at the bottom. When the prefabricated pipe piles are positioned, the groundwater or clay cannot effectively bear the prefabricated pipe piles as the construction process continues, causing the prefabricated pipe piles to become unstable and unable to remain at the set elevation. Moreover, when processing the bottom steel plate, after the heavy hammer breaks the bottom steel plate, a large stress difference will be formed inside and outside the bottom of the prefabricated pipe piles, so that the external mud or groundwater will flow into the hollow part of the prefabricated pipe piles, increasing the difficulty of subsequent construction. Therefore, based on the above factors, it is necessary to further improve and optimize the current construction process of prefabricated pipe piles to improve construction efficiency, increase the universal applicability of construction in different strata, and implement the consistency and standardization of construction standards. Summary of the invention

[0005] In order to improve the problems of low construction efficiency and poor general applicability of existing prefabricated pipe piles when driving them into different strata, the present application provides a construction method for prefabricated bottom-enlarged piles without bottom sealing.

[0006] The present application provides a method for constructing prefabricated bottom-enlarged piles without bottom sealing, which adopts the following technical scheme:

[0007] A method for constructing a prefabricated bottom-enlarged pile without a bottom seal comprises the following steps:

[0008] S1. Equipment enters the site and the pile position is marked according to the construction requirements;

[0009] S2. The bottom of the precast pipe pile is not sealed. After the precast pipe pile is pressed down to the designed bearing layer at the pile position, the loose soil in the hollow part of the precast pipe pile is taken out, and the soil taking depth exceeds the bottom of the precast pipe pile; or, a force transmission hammer is inserted into the hollow part of the precast pipe pile and pressed down together with the precast pipe pile to the designed bearing layer;

[0010] S3. Filling materials are put into the hollow part of the prefabricated pipe pile in batches, and a force hammer having a length greater than the length of the prefabricated pipe pile is inserted into the hollow part of the prefabricated pipe pile, and the force hammer is squeezed to squeeze the filling material by pressing, spinning or hammering, and the filling material is formed at the bottom of the prefabricated pipe pile to expand the head;

[0011] S4. pouring concrete into the hollow part of the prefabricated pipe pile to form an inner pile.

[0012] Furthermore, in step S3, when the bottom of the hammer is flush with or higher than the bottom of the prefabricated pipe pile after the force transmission hammer extrude the filling material, check whether the enlarged head meets the construction standard. If the enlarged head is qualified, proceed to the next step; otherwise, continue to add the filling material and extrude;

[0013] The inspection method is one of the following:

[0014] (i) Load the single pile bearing capacity not less than the design requirement onto the force transfer hammer to extrude the enlarged head. If the sinking amount of the force transfer hammer does not increase after N consecutive extrusions without filling, the enlarged head construction is qualified, where N ≥ 3;

[0015] (ii) Measure three-strike penetration.

[0016] Furthermore, in step S3, before each injection of filler, cement slurry is first poured into the hollow part of the prefabricated pipe pile and then covered with a rear covering filler layer; the amount of cement slurry injected each time is not greater than one fifth of the filling amount of the rear covering filler layer.

[0017] Furthermore, in step S2, if there is a rock layer at the designed bearing layer or the pile foundation needs to pass through an interlayer, a hole is first drilled at the pile position to the designed bearing layer to form a pile hole, and then the prefabricated pipe pile is installed; and the diameter of the pile hole is smaller than the diameter of the prefabricated pipe pile.

[0018] Furthermore, in step S2, if the soil layer at the designed bearing layer is soft soil, the soil excavation depth exceeds the bottom of the prefabricated pipe pile by no less than 100 cm;

[0019] If the soil layer at the designed bearing layer is hard soil, the depth of soil excavation shall not be less than 5cm beyond the bottom of the precast pipe pile.

[0020] Furthermore, in step S3, if there is laminar water in the designed bearing layer, coarse aggregate is firstly put into the hollow part of the prefabricated pipe pile, and then replaced with fine aggregate after compaction.

[0021] Furthermore, in step S3, the timing for stopping squeezing the force transfer hammer and adding filling material is when the force transfer hammer squeezes the filling material for multiple times after adding the material and the sinking amount of the force transfer hammer does not increase, and at this time the bottom end of the force transfer hammer extends out of the bottom end of the prefabricated pipe pile.

[0022] Furthermore, in step S3, after each addition of the filling material, the top of the material layer shall not exceed 10 cm above the bottom end of the prefabricated pipe pile.

[0023] Furthermore, a feeding channel is provided through the middle of the force transmission hammer, a feeding port connected to the feeding channel is provided on the top side wall of the force transmission hammer, and a sealing plate for blocking the feeding channel is movably provided at the bottom of the force transmission hammer;

[0024] When the force transmission hammer is lifted, the sealing plate moves and releases the blockage of the feeding channel.

[0025] Furthermore, the outer diameter of the sealing plate is matched with the inner diameter of the prefabricated pipe pile.

[0026] Furthermore, in step S3, the elevation of the maximum cross section of the spherical enlarged head after forming is calculated according to the designed single pile bearing capacity limit value, and the forming depth is obtained by subtracting the elevation of the bottom end of the prefabricated pipe pile;

[0027] The timing for initially stopping the extrusion of the force transmission hammer and adding the filling material in step S3 is: the depth of the bottom end of the force transmission hammer extending out of the bottom end of the prefabricated pipe pile is greater than or equal to the forming depth.

[0028] Furthermore, the forming depth calculation formula is:

[0029] , formula 1;

[0030] , Formula 2;

[0031] Where:

[0032] H-forming depth;

[0033] K-forming correction coefficient, ranging from 0.4 to 1;

[0034] π - pi;

[0035] R a - Bearing capacity of single bored pile required by design;

[0036] U p - Pile circumference;

[0037] q sia - Characteristic value of pile side resistance;

[0038] L i -Thickness of the i-th rock and soil layer;

[0039] q pa - Characteristic value of pile tip resistance;

[0040] D-pile diameter.

[0041] In summary, the beneficial technical effects of this application are:

[0042] 1. Through the process of directly installing prefabricated pipe piles without drilling or sealing the bottom, the soil at the pile position can always be filled in the hollow part of the prefabricated pipe pile during the installation process, which can form a good sealing effect on the hollow part of the prefabricated pipe pile, effectively prevent groundwater from flowing into the bearing layer and affecting the bearing capacity of the pile end, and ensure the bearing performance of the prefabricated pipe pile to a certain extent;

[0043] 2. Compared with conventional construction methods, the construction method of the present application does not seal the bottom end of the prefabricated pipe pile, which can greatly reduce the resistance during pile pressing and improve the efficiency of pile driving. Moreover, in strata with good soil properties, no pre-drilling is performed, which not only simplifies the construction steps, but also avoids the defect that the floating soil in the pile hole of the pre-drilled hole affects the positioning of the prefabricated pipe pile and the quality of the pile. At the same time, by taking soil from the hollow part of the prefabricated pipe pile after the pile is in place to exceed the bottom end of the prefabricated pipe pile, it will not affect the positioning of the prefabricated pipe pile at the designed bearing layer, and can also completely eliminate the hidden danger of the floating soil at the bottom of the pile hole affecting the bearing capacity of the bottom end of the prefabricated pipe pile.

[0044] 3. This application uses downward pressure, spinning or hammering to compact the filling material, so that the kinetic energy transferred to the filling material is released slowly, which causes minimal disturbance to the soil at the bottom of the pile hole, and can effectively ensure the effective compaction of the soil at the bottom of the prefabricated pipe pile and the quality of the pile. Therefore, the construction method of this application can significantly improve the construction efficiency, and at the same time increase the general applicability of construction in different strata, making it easier to implement the consistency and standardization of construction standards;

[0045] 4. By setting up an inspection mechanism for whether the enlarged head is qualified, on the one hand, it can be convenient for construction personnel to grasp the construction progress of the expanded pile, control the construction progress and construction quality, and improve construction efficiency; on the other hand, the inspection mechanism can be directly transplanted into the automated pile foundation construction equipment after being programmed, which is convenient for semi-automatic or automated expanded pile construction; at the same time, through this inspection method, the construction quality during the construction of the pile group can be unified, and it also serves as a self-inspection procedure for the construction quality during the construction process, which is conducive to the promotion of standardization and proceduralization of pile foundation construction;

[0046] 5. Through the setting of the force transmission hammer, the gap between the force transmission hammer and the inner wall of the prefabricated pipe pile can be set as small as possible, which not only increases the extrusion area of ​​the filling material and promotes more filling materials to be compacted, but also limits the amount of filling material entering the gap between the force transmission hammer and the inner wall of the prefabricated pipe pile, which can greatly reduce the probability of hammer suction and pile explosion;

[0047] 6. Before each injection of filler, cement slurry is first poured into the hollow part of the prefabricated pipe pile and then covered with filler. The cement slurry injected into the compacted filler layer can be spread on the bottom of the prefabricated pipe pile to form a cement slurry layer, and part of the cement slurry in the cement slurry layer can penetrate into some gaps in the compacted filler layer that cannot be further compacted, so that the density of the previous compacted filler layer can be strengthened layer by layer. When the next layer of filler is injected to form a subsequent covering filler layer, when the force transmission hammer covers the filler layer after extrusion, part of the cement slurry in the cement slurry layer can also continue to penetrate upward or downward or circumferentially, so that the soil layer and the compacted filler layer near the bottom action area of ​​the force transmission hammer can be strengthened. After the enlarged head is formed, the cement slurry solidifies, so that the enlarged head forms a strong whole, which can greatly improve the structural strength of the enlarged head and the bearing capacity of the single pile.

[0048] 7. With the help of simulation of the formed enlarged head, through the requirements for the bearing performance of the single pile of the expanded bottom pile, the equivalent effective area in the bearing capacity of the expanded head pile end in the expanded bottom pile is reversed to calculate the radius of the simulated maximum bearing surface of the enlarged head, which is used as the forming depth extending downward from the bottom of the precast pipe pile. As long as the depth of the hammer bottom exceeds the forming depth during extrusion by the force transmission hammer after the filling material is placed, it indicates that the filling material is still in the stage of filling and compacting the soil around the bottom of the precast pipe pile, and a large amount of filling material needs to be added. At this time, the filling material placement operation can be started directly without waiting for multiple extrusions to make a judgment, which can greatly save the initial operation time of the filling material. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of the construction process of Example 1 of the present application;

[0050] Figure 2 is a construction schematic diagram of step S2 of embodiment 2 of the present application;

[0051] Figure 3 It is a construction diagram of step S3 of Example 3 of the present application.

[0052] Description of reference numerals:

[0053] 1. Pile position;

[0054] 2. Prefabricated pipe piles;

[0055] 3. Force transmission hammer; 31. Feeding channel; 32. Feeding port; 33. Sealing plate; 34. Grouting pipe;

[0056] 4. Enlarge the head;

[0057] 51. Compacting the filling material layer; 52. Cement slurry; 53. Covering the filling material layer. DETAILED DESCRIPTION

[0058] The technical solution of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application. Embodiment 1:

[0059] The present application embodiment discloses a method for constructing a prefabricated pile without bottom cover. Figure 1 , which comprises the following steps:

[0060] S1. Equipment enters the site and pile position 1 is marked according to construction requirements.

[0061] S2. The bottom end of the prefabricated pipe pile 2 to be constructed is not sealed, and after the prefabricated pipe pile 2 is pressed down to the designed bearing layer at the pile position 1, the loose soil in the hollow part of the prefabricated pipe pile 2 is taken out, and the soil taking depth exceeds the bottom end of the prefabricated pipe pile 2; the soil taking method can adopt a long spiral or spiral drill to take soil, etc. This pile pressing method without bottom sealing is suitable for strata with good soil properties, and can effectively avoid the problem of loose soil in the pile affecting the pile quality in the process of drilling holes first and then driving piles; and the pile pressing resistance is small and the pile driving efficiency is high.

[0062] S3. Add fillers into the hollow part of the prefabricated pipe pile 2 in batches, insert a force transmitting hammer 3 whose length is greater than that of the prefabricated pipe pile 2 into the hollow part of the prefabricated pipe pile 2, and squeeze the fillers by pressing, spinning or hammering the force transmitting hammer 3, so that the fillers form a densely packed enlarged head 4 at the bottom of the prefabricated pipe pile 2.

[0063] S4. Pour concrete into the hollow part of the prefabricated pipe pile 2 to form an inner pile, and if necessary, place a steel cage.

[0064] Based on this, compared with conventional construction methods, the construction method of the present application does not seal the bottom end of the prefabricated pipe pile 2, which can greatly reduce the resistance during pile pressing and improve the efficiency of pile driving; and, in strata with good soil properties, no pre-drilling is performed, which not only simplifies the construction steps, but also avoids the defect that the loose soil in the pile hole of the pre-drilled hole affects the positioning of the prefabricated pipe pile 2 and the quality of the pile; at the same time, by taking soil from the hollow part of the prefabricated pipe pile 2 after the pile is in place to exceed the bottom end of the prefabricated pipe pile 2, it will not affect the positioning of the prefabricated pipe pile 2 at the designed bearing layer, and can also completely eliminate the hidden danger of the loose soil at the bottom of the pile hole affecting the bearing capacity of the bottom end of the prefabricated pipe pile 2.

[0065] In addition, in the case where there is groundwater, clay, etc. in the designed bearing layer, if the conventional technology of directly using a heavy hammer to lift and then tamp, the potential energy of the free fall will be directly converted into kinetic energy, which will greatly disturb the soil with pressurized water, which is not conducive to the compaction of the soil; while the present application uses the form of downward pressure, spinning or hammering the force transmission hammer 3 to compact the filling material, so that the kinetic energy transmitted to the filling material is in the form of slow release, and the disturbance to the soil at the bottom of the pile hole is minimal, which can effectively ensure the effective compaction of the soil at the bottom of the prefabricated pipe pile 2 and ensure the quality of the pile. Therefore, through the construction method of the present application, the construction efficiency can be significantly improved, and at the same time, the universal applicability of construction in different strata can be increased, which is convenient for implementing the consistency and standardization of construction standards.

[0066] Specifically, in step S3, when the bottom of the hammer is flush with or higher than the bottom of the prefabricated pipe pile 2 after the force transmission hammer 3 extrude the filling material, check whether the enlarged head 4 meets the construction standards. If the enlarged head 4 is qualified, proceed to the next step; otherwise, continue to add filling material and extrude.

[0067] The inspection method for inspecting whether the enlarged head 4 is qualified is one of the following:

[0068] (i) Load the single pile bearing capacity not less than the design requirement onto the force transfer hammer 3 to extrude the enlarged head 4. If the sinking amount of the force transfer hammer 3 does not increase after N consecutive extrusions without filling, the enlarged head 4 is qualified, where N ≥ 3. This method is applicable to static pressure, spinning and hammering methods to press the force transfer hammer 3;

[0069] (ii) Measure three-hit penetration; this method is applicable to the downward pressure force transfer hammer 3 in hammering mode.

[0070] Therefore, by setting up an inspection mechanism for whether the enlarged head 4 is qualified, on the one hand, it can be convenient for construction personnel to grasp the construction progress of the expanded bottom pile, facilitate the control of construction progress and construction quality, and improve construction efficiency; on the other hand, the inspection mechanism can be directly transplanted into the automated pile foundation construction equipment after being programmed, so as to facilitate semi-automatic or automated expanded bottom pile construction; at the same time, through this inspection method, the construction quality during the construction of the pile group can be unified, and it also serves as a self-inspection procedure for the construction quality during the construction process, which is conducive to the promotion of standardization and proceduralization of pile foundation construction.

[0071] Meanwhile, in actual operation, in step S3, the timing of stopping squeezing the force transmission hammer 3 and placing the filling material is when the sinking amount of the force transmission hammer 3 does not increase after the force transmission hammer 3 squeezes the filling material for multiple times after the filling material is placed, and at this time, the bottom end of the force transmission hammer 3 extends out of the bottom end of the prefabricated pipe pile 2. In step S3, after each filling material is placed, the top of the material layer shall not exceed 10 cm above the bottom end of the prefabricated pipe pile 2 to prevent the possibility of pile explosion when squeezing the filling material.

[0072] Therefore, a judgment mechanism for placing filling materials is further set up. Relying on the program setting of the automated pile foundation construction equipment, the degree of compaction of the filling material can be intuitively judged. When construction personnel are unable to make direct visual judgment, the automated pile foundation construction equipment can operate autonomously, which can greatly ensure the consistency of construction quality.

[0073] Moreover, when it is applied to actual engineering projects, the construction methods can be adjusted specifically taking into account some special geological conditions.

[0074] For example, in step S2, if there is a rock layer at the designed bearing layer or the pile foundation needs to pass through an interlayer, a pile hole can be first drilled at the pile position 1 to the designed bearing layer, and then the prefabricated pipe pile 2 can be installed; and the pile hole diameter is smaller than the pile diameter of the prefabricated pipe pile 2. This can avoid the prefabricated pipe pile 2 from being inefficient or even exploding when passing through these hard layers; the pile hole diameter is limited to be smaller than the pile diameter of the prefabricated pipe pile 2 in order to ensure the side friction resistance of the prefabricated pipe pile 2 after the pile is formed.

[0075] Furthermore, in step S2, if the soil layer at the designed bearing layer is soft soil, the soil depth beyond the bottom of the prefabricated pipe pile 2 is not less than 100 cm; if the soil layer at the designed bearing layer is hard soil, the soil depth beyond the bottom of the prefabricated pipe pile 2 is not less than 5 cm. This ensures that when the filling material is subsequently filled and compacted, the filling material can first compact the area at the bottom of the prefabricated pipe pile 2 to ensure the molding area of ​​the enlarged head 4.

[0076] And, in step S3, if there is laminated water in the designed bearing layer, coarse aggregate is first added to the hollow part of the prefabricated pipe pile 2, and then replaced with fine aggregate after compaction. Thus, the laminated water and clay can be reinforced with the help of coarse aggregate, promoting the rapid compaction of the soil layer at the bottom of the prefabricated pipe pile 2.

[0077] In addition, in order to facilitate the extrusion of the filling material by the force transmission hammer 3 while also conveniently feeding the filling material, a feeding channel 31 is provided through the middle of the force transmission hammer 3, a feeding port 32 connected to the feeding channel 31 is provided on the top side wall of the force transmission hammer 3, and a sealing plate 33 for blocking the feeding channel 31 is movably provided at the bottom of the force transmission hammer 3; when the force transmission hammer 3 is lifted, the sealing plate 33 moves and releases the blockage of the feeding channel 31.

[0078] Specifically, the sealing plate 33 can be hingedly installed at the bottom of the force transmission hammer 3 through a hinge, and the sealing plate 33 can block the bottom of the force transmission hammer 3 after it is turned horizontally, and the sealing plate 33 serves as a direct contact part for extruding the filling material; in one embodiment, the end of the sealing plate 33 away from the hinge is connected to a pulling rope, and the upper end of the pulling rope extends to the outer side of the upper part of the force transmission hammer 3, so that the construction personnel can control the state of the sealing plate 33; or in another embodiment, a limit block is provided at the bottom of the force transmission hammer 3 to limit the excessive turning of the sealing plate 33, such as limiting the maximum turning of the sealing plate 33 to 60 degrees. In this way, when the force transmission hammer 3 is lifted, the sealing plate 33 turns to a certain angle, and the bottom end of the feeding channel 31 in the force transmission hammer 3 is opened, and an appropriate amount of filling material can be fed into the feeding channel 31 from the feeding port 32; after the feeding is completed, the force transmission hammer 3 is directly pressed down, and the sealing plate 33 turns upward autonomously and squeezes the filling material below under the extrusion of the force transmission hammer 3, so that the flexible switching of feeding and squeezing operations can be completed.

[0079] Specifically, the sealing plate 33 can be raised and lowered and arranged at the bottom of the force transmitting hammer 3. When the force transmitting hammer 3 is lifted, the sealing plate 33 falls under its own weight. At this time, the bottom end of the feeding channel 31 in the force transmitting hammer 3 is open, and an appropriate amount of filling material can be fed into the feeding channel 31 from the feeding port 32. After the feeding is completed, the force transmitting hammer 3 is directly pressed down, and the sealing plate 33 moves up autonomously and squeezes the filling material below under the extrusion of the force transmitting hammer 3, thereby completing the flexible switching of feeding and squeezing operations.

[0080] In one embodiment, based on the setting of the sealing plate 33 being lifted and lowered at the bottom of the force transmission hammer 3, it can be further set so that the outer diameter of the sealing plate 33 is adapted to the inner diameter of the prefabricated pipe pile 2. In this way, compared with the conventional method of tamping the filling material with a heavy hammer, in order to prevent the heavy hammer from hitting the inner wall of the prefabricated pipe pile 2 during the free fall, a certain gap is usually set between the heavy hammer and the inner wall of the prefabricated pipe pile 2. In this way, in the process of squeezing the filling material, there is always a part of the filling material that cannot be tamped by the heavy hammer, and this part of the filling material will also surround the side of the heavy hammer, forming a suction hammer effect, which not only affects the compaction effect of the filling material, but also hinders the lifting of the heavy hammer; in severe cases, these filling materials may even cause pile explosion when they are squeezed outward.

[0081] On the other hand, in the present application, by setting the force transmission hammer 3, the gap between the force transmission hammer 3 and the inner wall of the prefabricated pipe pile 2 can be set as small as possible, which not only increases the extrusion area of ​​the filling material and promotes more filling materials to be compacted, but also limits the amount of filling material entering the gap between the force transmission hammer 3 and the inner wall of the prefabricated pipe pile 2, which can greatly reduce the probability of hammer suction and pile explosion. Embodiment 2:

[0082] The present application embodiment discloses a method for constructing a prefabricated pile without bottom cover. Figure 2 , which is different from Example 1 in that:

[0083] Step S2 is replaced by: the bottom end of the prefabricated pipe pile 2 is not sealed, a force transmitting hammer 3 is inserted into the hollow part of the prefabricated pipe pile 2, and is pressed down together with the prefabricated pipe pile 2 to the designed bearing layer.

[0084] The consideration for setting this step is that after the pile is driven in without sealing the bottom, it is necessary to use soil-taking equipment to take out the soil in the hollow part of the prefabricated pipe pile 2. If the force transfer hammer 3 is inserted into the hollow part of the prefabricated pipe pile 2 from the beginning and the two are moved down synchronously, the soil-taking step can be omitted. After the prefabricated pipe pile 2 is driven into the bearing layer, the force transfer hammer 3 can be directly slightly lifted and the filling material can be placed, which can further greatly improve the construction efficiency.

[0085] Although, compared with the pile driving without bottom sealing in Example 1, the pile driving resistance is increased to a certain extent, affecting the pile driving efficiency, the improvement effect is still significant in terms of overall construction efficiency; and, compared with the conventional process in which the bottom sealing plate needs to be punched after the bottom end of the prefabricated pipe pile 2 is sealed, the construction method of this embodiment still has the advantages of simple operation and high efficiency in terms of process. Embodiment 3:

[0086] The present application embodiment discloses a method for constructing a prefabricated pile without bottom cover. Figure 3 , which is different from Example 1 in that:

[0087] In step S3 , before each injection of filling material, cement slurry 52 is first poured into the hollow part of the prefabricated pipe pile 2 and then covered with the rear covering filling material layer 53 ; the amount of cement slurry 52 injected each time is not greater than one fifth of the filling amount of the rear covering filling material layer 53 .

[0088] Specifically, a grouting pipe 34 is provided in the feeding channel 31 of the force transmission hammer 3 along its length direction. Before each feeding, the force transmission hammer 3 can be lifted up to open the feeding channel 31, and then a set amount of cement slurry 52 is injected into the bottom end of the prefabricated pipe pile 2 through the grouting pipe 34, and then filling material is added into the feeding channel 31 from the feeding port 32 to cover the cement slurry 52.

[0089] In this way, the cement slurry 52 poured into the compacted filling material layer 51 can be spread flat on the bottom end of the prefabricated pipe pile 2 to form a cement slurry layer, and part of the cement slurry 52 in the cement slurry layer can penetrate into some gaps in the compacted filling material layer 51 that cannot be compacted further, and the density of the previous compacted filling material layer 51 can be strengthened layer by layer; when the next layer of filling material is poured in to form a rear covering filling material layer 53, when the force transmitting hammer 3 covers the filling material layer 53 after extrusion, part of the cement slurry 52 in the cement slurry layer can also continue to penetrate upward or downward or circumferentially, so that the soil layer and the compacted filling material layer 51 near the bottom action area of ​​the force transmitting hammer 3 can be strengthened; when the enlarged head 4 is formed, the cement slurry 52 solidifies, so that the enlarged head 4 forms a strong whole, which can greatly improve the structural strength of the enlarged head 4 and the bearing performance of the single pile.

[0090] Among them, the amount of cement slurry 52 injected each time is limited to no more than one-fifth of the filling amount of the rear covering filler 53 in order to prevent excessive cement slurry 52 from seeping up and adhering to the sealing plate 33 and the force transmission hammer 3 when the force transmission hammer 3 covers the filling material layer 53 after extrusion, thereby affecting the smooth operation of the force transmission hammer 3 and the flexible opening and closing of the sealing plate 33. Embodiment 4:

[0091] The present application embodiment discloses a method for constructing prefabricated bottom-enlarged piles without bottom cover. The difference from the embodiment 1 is that:

[0092] Considering that the judgment mechanism for placing the filling material in Example 1 requires the force transfer hammer 3 to continuously extrude the filling material for multiple times before it can be executed, there is a certain lag compared with the actual timing of placing the filling material, especially in the initial stage of material placement, when there is a lot of loose soil at the bottom of the prefabricated pipe pile 2. Even if a lighter downward pressure is applied to the force transfer hammer 3, the filling material will be quickly compacted. If the judgment mechanism in Example 1 is continued, the lag will obviously be further amplified, thereby affecting the overall construction efficiency.

[0093] To this end, in step S3, the elevation of the maximum cross-section of the spherical enlarged head 4 after molding is calculated according to the design single pile bearing capacity limit value, and the molding depth is obtained by subtracting it from the elevation of the bottom end of the prefabricated pipe pile 2; the timing for initially stopping the extrusion of the force transfer hammer 3 and adding the filling material in step S3 is: the depth of the bottom end of the force transfer hammer 3 extending out of the bottom end of the prefabricated pipe pile 2 is greater than or equal to the molding depth.

[0094] The calculation formula for forming depth is:

[0095] , formula 1;

[0096] , Formula 2;

[0097] Where:

[0098] H-forming depth;

[0099] K-forming correction coefficient, ranging from 0.4 to 1;

[0100] π - pi;

[0101] R a - Bearing capacity of single bored pile required by design;

[0102] U p - Pile circumference;

[0103] q sia - Characteristic value of pile side resistance;

[0104] L i -Thickness of the i-th rock and soil layer;

[0105] q pa - Characteristic value of pile tip resistance;

[0106] D-pile diameter.

[0107] Therefore, with the help of simulation of the formed enlarged head, through the requirements for the bearing performance of the single pile of the enlarged base pile, the equivalent effective area in the bearing capacity of the enlarged head pile end in the enlarged base pile is reversed to calculate the radius of the simulated maximum bearing surface of the enlarged head, which is used as the forming depth extending downward from the bottom end of the precast pipe pile. As long as the depth of the hammer bottom exceeds the forming depth during extrusion by the force transmission hammer after the filling material is placed, it indicates that the filling material is still in the stage of filling and compacting the soil around the bottom end of the precast pipe pile, and a large amount of filling material needs to be added. At this time, the filling material placement operation can be started directly without waiting for judgment after multiple extrusions, which can greatly save the initial operation time of the filling material.

[0108] When the filling material is compacted layer by layer, but the penetration depth of the force transmission hammer still fails to reach the forming depth requirement, it means that the compaction degree of the filling material previously put in is high, and the subsequent material needs to be judged step by step with the help of the judgment mechanism of Example 1 to ensure the construction quality of the enlarged head.

[0109] At the same time, the forming correction coefficient k set in the above formula 1 can be used to correct the forming depth according to the corresponding rock layer in which the design bearing layer is located. For example, when the enlarged head is located in a medium-weathered mudstone layer with a higher saturated uniaxial compressive strength, the medium-weathered mudstone body around the enlarged head is also compacted into a dense compacted rock mass, which can also make more contributions to the pile end bearing performance. At this time, the k value is taken as a smaller value for correction. That is, the harder the soil layer at the design bearing layer, the smaller the k value; conversely, the larger it is.

[0110] Unless otherwise defined, the technical terms or scientific terms used in this application should be understood by people with ordinary skills in the field to which this application belongs. The words "first", "second", "third" and similar words used in the specification and claims of this application do not indicate any order, quantity or importance, but are only used to distinguish different components. "One" or "one" and similar words do not indicate a quantitative limit, but indicate that there is at least one. "Include" or "comprise" and similar words mean that the elements or objects appearing before "include" or "comprise" include the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0111] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for constructing prefabricated bottom-enlarged piles without bottom cover, characterized in that: The following steps are involved: S1. Equipment enters the site and the pile position is marked according to the construction requirements (1); S2. The bottom of the prefabricated pipe pile (2) is not sealed. After the prefabricated pipe pile (2) is pressed down to the designed bearing layer at the pile position (1), the loose soil in the hollow part of the prefabricated pipe pile (2) is removed, and the depth of the soil removal exceeds the bottom of the prefabricated pipe pile (2); or, a force transmission hammer (3) is inserted into the hollow part of the prefabricated pipe pile (2) and pressed down together with the prefabricated pipe pile (2) to the designed bearing layer; S3. Adding fillers into the hollow part of the prefabricated pipe pile (2) in batches, inserting a force transmission hammer (3) whose length is greater than the length of the prefabricated pipe pile (2) into the hollow part of the prefabricated pipe pile (2), and causing the force transmission hammer (3) to squeeze the fillers by pressing, spinning or hammering, so that the fillers form a compacted enlarged head (4) at the bottom of the prefabricated pipe pile (2); before each addition of fillers, first pouring cement slurry (52) into the hollow part of the prefabricated pipe pile (2) and then covering it with the fillers (53); S4. pouring concrete into the hollow part of the prefabricated pipe pile (2) to form an inner pile.

2. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 1, characterized in that: In step S3, when the bottom of the hammer (3) is flush with or higher than the bottom of the prefabricated pipe pile (2) after the force transmission hammer (3) extrude the filling material, check whether the enlarged head (4) meets the construction standard. If the enlarged head (4) is qualified, proceed to the next step; otherwise, continue to add the filling material and extrude; The inspection method is one of the following: (i) A single pile bearing capacity not less than the design requirement is loaded onto the force transmission hammer (3) to extrude the enlarged head (4). If the sinking amount of the force transmission hammer (3) does not increase after N consecutive extrusions without filling, the enlarged head (4) is qualified, where N ≥ 3; (ii) Measure three-strike penetration.

3. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 1, characterized in that: In step S3, the amount of cement slurry (52) injected each time is no more than one fifth of the amount of the post-covering filler (53).

4. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 1, characterized in that: In step S2, if there is a rock layer at the designed bearing layer or the pile foundation needs to pass through an interlayer, a hole is first drilled at the pile position (1) to the designed bearing layer to form a pile hole, and then the prefabricated pipe pile (2) is installed; and the diameter of the pile hole is smaller than the pile diameter of the prefabricated pipe pile (2).

5. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 1, characterized in that: In step S2, if the soil layer at the designed bearing layer is soft soil, the soil is taken to a depth not less than 100 cm beyond the bottom of the prefabricated pipe pile (2); If the soil layer at the designed bearing layer is hard soil, the soil excavation depth shall be not less than 5 cm beyond the bottom of the prefabricated pipe pile (2).

6. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 1, characterized in that: In step S3, if there is laminar water in the designed bearing layer, coarse aggregate is firstly put into the hollow part of the prefabricated pipe pile (2), and then replaced with fine aggregate after compaction.

7. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 1, characterized in that: In step S3, the timing for stopping squeezing the force transmission hammer (3) and adding the filling material is when the sinking amount of the force transmission hammer (3) does not increase after the force transmission hammer (3) squeezes the filling material for multiple times after adding the material, and at this time, the bottom end of the force transmission hammer (3) extends out of the bottom end of the prefabricated pipe pile (2).

8. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 7, characterized in that: In step S3, after each addition of the filling material, the top of the material layer shall not exceed 10 cm above the bottom of the prefabricated pipe pile (2).

9. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 1, characterized in that: A feeding channel (31) is provided through the middle of the force transmission hammer (3), a feeding port (32) communicating with the feeding channel (31) is provided on the top side wall of the force transmission hammer (3), and a sealing plate (33) for sealing the feeding channel (31) is movably provided at the bottom of the force transmission hammer (3); When the force transmission hammer (3) is lifted, the sealing plate (33) moves and releases the blockage of the feeding channel (31).

10. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 9, characterized in that: The outer diameter of the sealing plate (33) is adapted to the inner diameter of the prefabricated pipe pile (2).

11. A method for constructing prefabricated bottom-enlarged piles without bottom cover according to any one of claims 1 to 10, characterized in that: In step S3, the elevation of the maximum cross section of the spherical enlarged head (4) after forming is calculated according to the designed single pile bearing capacity limit value, and the forming depth is obtained by subtracting the elevation of the bottom end of the prefabricated pipe pile (2); The timing for initially stopping the extrusion of the force transmitting hammer (3) and adding the filling material in step S3 is when the depth at which the bottom end of the force transmitting hammer (3) extends out of the bottom end of the prefabricated pipe pile (2) is greater than or equal to the forming depth.

12. The method for constructing prefabricated bottom-enlarged piles without bottom cover according to claim 11, characterized in that: The forming depth calculation formula is: , Formula 1; , Formula 2; Where: H-forming depth; K-forming correction coefficient, ranging from 0.4 to 1; π - pi; R a - Bearing capacity of single bored pile required by design; U p - Pile circumference; q sia - Characteristic value of pile side resistance; L i -Thickness of the i-th rock and soil layer; q pa - Characteristic value of pile end resistance; D-pile diameter.

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