A post-grouting construction method for cast-in-place pile bottom

Abstract

The present invention relates to the field of construction, and in particular to a post-grouting construction method for bored pile bottoms, comprising the following steps: A. bored pile hole construction; B. installation of bored pile reinforcement cages and grouting conduits; C. concrete pouring of bored piles; D. water splitting; and E. grouting. The post-grouting construction method for bored pile bottoms described herein involves injecting high-pressure water into the grouting conduit before formal grouting. This high-pressure water is used to split the soil layer at the bored pile bottom, forming a vein-like grouting channel. During grouting, the concrete slurry can easily diffuse along the formed grouting channel to a set range, ensuring the quality of the vein-like network stone body.

Description

Technical Field

[0001] The invention relates to the field of building construction, in particular to a post-grouting construction method for a cast-in-place pile bottom. Background Art

[0002] Bored cast-in-place pile construction technology is a low-cost, simple construction method that eliminates vibration, noise, and soil-squeezing effects. Due to their high bearing capacity and wide applicability, cast-in-place piles are widely used in construction projects. However, in the construction of high-rise and super-high-rise buildings or buildings on weak foundations, the bearing capacity of individual cast-in-place piles can be insufficient.

[0003] In order to overcome the deficiencies in the existing technology, patent documents such as publication number CN201810962546.3, invention name “A post-grouting method for bored piles in a carbonaceous limestone geological environment” and publication number CN201910969613.9, invention name “Post-grouting bored pile construction method” disclose a post-grouting technology for bored pile bottoms: after the concrete bored pile is poured and reaches a certain strength, cement slurry is injected into the pile side and pile end through a grouting conduit installed in the pile body within a certain period of time. Through the effects of displacement, compaction, and consolidation, the sediment, mud skin, and soil within a certain range in the hole are combined with the cement slurry to form a vein-like network stone body, which strengthens and reinforces the pile foundation, thereby improving the bearing capacity of a single bored pile. However, there are still deficiencies, as described below:

[0004] The existing technology usually pressurizes cement slurry and then directly injects it into the soil layer. Since the pressure drop of cement slurry in the grouting pipe is large, and the cement slurry ejected from the end of the grouting pipe loses most of the pressure while breaking the soil layer, it is difficult to form an effective grouting channel in the soil layer, resulting in low molding quality of vein network stone bodies, and even the risk of failure of grouting construction after bored piles.

[0005] Therefore, there is an urgent need for a post-grouting construction method for cast-in-place pile bottoms to solve the above-mentioned problems existing in the prior art. Summary of the Invention

[0006] The purpose of the present invention is to address the problem in the prior art that cement slurry is usually pressurized and then directly injected into the soil layer. Since the pressure drop of the cement slurry in the grouting pipe is large, and the cement slurry ejected from the end of the grouting pipe loses most of the pressure while breaking the soil layer, it is difficult to form an effective grouting channel in the soil layer, resulting in low molding quality of the vein network stone body and even failure of the post-grouting construction of the cast-in-place pile. A post-grouting construction method for the pile bottom of the cast-in-place pile is provided.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A post-grouting construction method for a cast-in-place pile bottom comprises the following steps:

[0009] A. Boring construction of bored piles: Drilling and excavation of bored pile holes shall be carried out according to the design requirements, so that the bored pile hole diameter and depth meet the design requirements;

[0010] B. Installation of cast-in-place pile reinforcement cage and grouting conduit: Make the reinforcement cage according to the design requirements, fix the grouting conduit on the reinforcement cage, and then use lifting equipment to place the reinforcement cage into the cast-in-place pile hole;

[0011] C. Cast-in-place pile concrete pouring: pouring concrete to shape the cast-in-place pile body;

[0012] D. Clean water splitting: After the cast-in-place pile concrete reaches the specified strength, high-pressure clean water is injected into the grouting pipe to split the soil layer under the cast-in-place pile using the high-pressure clean water to form a vein-like grouting channel;

[0013] E. Grouting: Use the grouting pipe to inject the pressurized cement slurry into the soil layer at the bottom of the bored pile, so that the cement slurry spreads along the vein-shaped grouting channel until the total grouting amount reaches the design value, or the grouting pressure exceeds the design value.

[0014] Preferably, in step D, the water splitting operation is performed twice, the first time is 3 to 5 hours, and the second time is 24 hours.

[0015] Preferably, after the water fracturing operation in step D is completed, grouting construction is carried out after waiting for 5 to 7 days.

[0016] Preferably, the number of grouting pipes fixed on the steel cage is greater than or equal to two, and the grouting pipes are symmetrically fixed on the steel cage.

[0017] Preferably, the grouting conduit comprises a pipe body section and a grouting device section, the grouting device section is arranged at the bottom of the pipe body section, and the length of the grouting device section inserted into the bottom soil layer of the pile hole is ≥300 mm.

[0018] Preferably, the length of the top of the tube section above the ground is 200 mm to 300 mm, and a cover is provided on the top of the tube section.

[0019] Preferably, the grouting device section comprises a grouting device body, a tube wall of the grouting device body is provided with grouting holes, and a surface of the grouting device body is covered with a rubber layer, and the rubber layer is used to seal the grouting holes.

[0020] Preferably, the bottom of the grouting device body is shaped like a cone.

[0021] Preferably, the grouting holes include Class I grouting holes and Class II grouting holes. The Class I grouting holes and the Class II grouting holes are both located below the bottom elevation of the bored pile. The Class I grouting holes are arranged on one side corresponding to the bottom of the bored pile, and the Class II grouting holes are arranged away from the bottom of the bored pile. The slurry flow channels formed by the Class I grouting holes are inclined toward the bottom of the bored pile.

[0022] Preferably, a plurality of spring sheets are further provided around the liquid outlet of the grouting hole, with adjacent spring sheets spaced apart, and the length of the spring sheets is smaller than the hole radius of the grouting hole. After the grouting device body is covered by the rubber layer, the spring sheets are compressed and retracted into the grouting hole. After the water splitting construction, the spring sheets return to their extended state, and the spring sheets extend along the length direction of the grouting hole.

[0023] Preferably, the end of the spring sheet is bent toward the tube wall of the grouting device body.

[0024] Preferably, a check valve is provided inside the grouting device body.

[0025] Preferably, the pipe body section and the grouting device section are connected by threads.

[0026] Preferably, the pipe body section is made of seamless steel pipe.

[0027] Preferably, before the grouting operation is performed, clean water is pressed into the grouting conduit to perform a water pressure test, and the working parameters during the grouting are adjusted according to the results of the water pressure test.

[0028] Preferably, during the grouting process, the pile holes at the periphery of the site are grouted first, and then pushed inward layer by layer from the outside to the inside, and finally the pile holes in the central part of the site are grouted.

[0029] Preferably, during grouting construction, the grouting pressure value gradually transitions from small to large to a set grouting pressure value, and the slurry gradually transitions from thin to thick to a set concentration.

[0030] Preferably, during grouting construction, the set grouting pressure value is used as a reference standard. During the grouting process, the changes in grouting pressure are closely monitored and the construction is adjusted in real time according to the following situations:

[0031] (1) The grouting pressure value gradually increases but does not reach the set grouting pressure value: it is judged that the slurry forms vein-like splitting penetration in the clay, or the slurry concentration is low, the gel time is long, or part of the slurry overflows;

[0032] (2) After the grouting starts, the grouting pressure does not increase, or even shows a downward trend from the initial pressure value: it is judged that the slurry has overflowed;

[0033] (3) The grouting pressure value suddenly drops after rising: it is judged that the slurry overflows from the grouting pipe, or the injection speed is too high, disturbing the soil layer, or encountering a weak part with gaps;

[0034] In the above situations, the water-cement ratio of the slurry is adjusted to increase the concentration of the slurry, and / or admixtures are added to the slurry to shorten the setting time of the slurry, and / or the grouting pressure is reduced, the grouting flow rate is limited, and the flow and penetration rate of the slurry in the soil cracks is reduced, so that the slurry particles gradually settle and block the infiltration channels in the soil layer, and / or intermittent grouting is used to allow the slurry particles to settle and gel in a static state, thereby blocking the infiltration channels in the soil layer;

[0035] (4) The grouting pressure value rises to the set grouting pressure value, but the grouting speed cannot reach the set value: it is judged that the soil layer at the bottom of the pile is dense or the grouting time is too short;

[0036] In this case, adjust the water-cement ratio of the slurry, reduce the concentration of the slurry, and / or add admixtures to the slurry to extend the setting time of the slurry, and / or increase the grouting pressure and reduce the pumping volume of the slurry for continuous grouting.

[0037] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0038] 1. The post-grouting construction method for bored piles of the present invention injects high-pressure clean water into the grouting conduit before the formal grouting construction. The high-pressure clean water is used to split the soil layer at the bottom of the bored pile, forming a vein-shaped grouting channel. During the grouting construction, the concrete slurry can be easily diffused along the formed grouting channel to a set range, thereby ensuring the quality of the vein-shaped network stone body.

[0039] 2. The post-grouting construction method for the bottom of a bored pile described in the present invention is to arrange the slurry flow channel formed by the first type of grouting holes to be inclined toward the bottom of the bored pile. During the water splitting construction, the water flow ejected from the first type of grouting holes can flush the bottom of the bored pile, causing the mud / sediment attached to the concrete surface of the bottom of the bored pile to fall off. During the grouting construction, the concrete slurry can better combine with the bottom of the bored pile, making the vein-like network stone body and the bored pile more integrated after the combination, thereby improving the bearing capacity of the bored pile. Furthermore, with this structural setting, during the grouting construction, the concrete slurry can be accumulated at the bottom of the bored pile, thereby improving the density of the concrete structure formed at the bottom of the bored pile. In addition, the concrete slurry can fully combine with the bottom of the bored pile, making the vein-like network stone body and the bored pile more integrated after the combination, further improving the bearing capacity of the bored pile.

[0040] 3. The post-grouting construction method for the cast-in-place pile bottom described in the present invention further includes a plurality of spring plates disposed at the outlet of the grouting hole. When the rubber layer ruptures, the spring plates return to an extended state, propping open the cracks in the rubber layer and fully opening the outlet of the grouting hole. This ensures that the pressure of the water and slurry ejected from the grouting hole can be fully released, and that the water and slurry can be ejected from the grouting hole along a predetermined path, thereby improving the success rate of both water fracturing and grouting. Furthermore, in their extended state, the spring plates can also increase the roughness of the grouting device body wall, allowing the slurry to adhere more tightly to the wall, further enhancing the degree of integration between the vein-like network stone body and the cast-in-place pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a construction process diagram of a post-grouting construction method for cast-in-place piles;

[0042] Figure 2 This is a schematic diagram of the installation structure of the cast-in-place pile reinforcement cage and the grouting conduit;

[0043] Figure 3 It is a structural schematic diagram of a first embodiment of a grouting device segment;

[0044] Figure 4 yes Figure 3 Schematic diagram of the structure of A;

[0045] Figure 5 yes Figure 3 Schematic diagram of the structure of B;

[0046] Figure 6 It is a structural schematic diagram of a second embodiment of a grouting device segment;

[0047] Figure 7 yes Figure 6 Schematic diagram of the structure of C;

[0048] Figure 8 yes Figure 6 Schematic diagram of the structure of D in the middle;

[0049] Figure 9 It is a structural diagram of the spring sheet provided at the grouting hole.

[0050] Markings in the figure: 1- grouting conduit, 2- pipe section, 3- grouting device section, 4- grouting device body, 5- grouting hole, 6- first-class grouting hole, 7- second-class grouting hole, 8- spring sheet, 9- rubber layer, 10- steel cage. DETAILED DESCRIPTION

[0051] The present invention will be described in detail below with reference to the accompanying drawings.

[0052] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0053] Example 1

[0054] like Figure 1 and Figure 2 As shown, the post-grouting construction method of the cast-in-place pile bottom of the present invention comprises the following steps:

[0055] A. Boring construction of bored piles: Drilling and excavation of bored pile holes shall be carried out according to the design requirements, so that the bored pile hole diameter and depth meet the design requirements;

[0056] B. Installation of cast-in-place pile reinforcement cage 10 and grouting conduit 1: Make reinforcement cage 10 according to design requirements, fix grouting conduit 1 on reinforcement cage 10, and then use lifting equipment to place reinforcement cage 10 into the cast-in-place pile hole;

[0057] C. Cast-in-place pile concrete pouring: pouring concrete to shape the cast-in-place pile body;

[0058] D. Water splitting: After the cast-in-place pile concrete reaches the specified strength, high-pressure water is injected into the grouting pipe 1 to split the soil layer under the cast-in-place pile using the high-pressure water to form a vein-like grouting channel;

[0059] E. Grouting: Use the grouting pipe 1 to inject the pressurized cement slurry into the soil layer at the bottom of the bored pile, so that the cement slurry spreads along the vein-shaped grouting channel until the total grouting amount reaches the design value, or the grouting pressure exceeds the design value.

[0060] By adopting the post-grouting construction method of the bored pile bottom described in the present invention, high-pressure clean water is injected into the grouting conduit 1 before the formal grouting construction is carried out, and the high-pressure clean water is used to split the soil layer at the bottom of the bored pile to form a vein-like grouting channel. Then, during the grouting construction, the concrete slurry can be easily diffused to the set range along the formed grouting channel, thereby ensuring the forming quality of the vein-like network stone body.

[0061] Specifically, in this embodiment, the bored pile hole is dug by a rotary drilling machine. Before the bored pile construction, the pile position is determined and the casing is buried. The inner diameter of the casing is 100 mm larger than the designed diameter of the pile body. The deviation between the center of the casing and the center of the pile position is ≤20 mm. The casing is vertical, the buried depth of the casing exceeds the depth of the impurity soil layer, and the bottom of the casing is buried in the original soil to a depth of ≥200 mm.

[0062] The cast-in-place pile reinforcement cage 10 is made in sections. The length of each section of reinforcement cage 10 should be 5 to 8 meters. When the reinforcement cage 10 is hoisted into the hole, it must not collide with the hole wall. The elevation and plane position of its top and bottom surfaces should meet the design requirements, and the error should not exceed 20 mm.

[0063] The coarse aggregate particle size of the concrete used for cast-in-place piles shall not exceed 40 mm and be less than 1 / 3 of the minimum clear distance between the main reinforcement bars. The cement grade shall not be less than 425, and the cement consumption per cubic meter of concrete shall not be less than 350 kg. During the pouring process of cast-in-place pile concrete, the pouring height shall be monitored at all times. The pouring shall be stopped when the pile reaches 50 cm above the designed top elevation of the pull-out pile. The elevation after removing the floating slurry layer at the top of the pile shall meet the design requirements.

[0064] Grouting is performed using P.O42.5 ordinary Portland cement. Concentrated slurry, slow injection at low pressure, and intermittent grouting are employed to retain a defined volume of cement slurry within the effective area of ​​the pile bottom. The grouting slurry is delivered to the pile bottom via a cement mixer filter, a 500L slurry storage tank, a grouting pump (with a pressure gauge with a maximum pressure of 15 MPa), a pile orifice pressure gauge, and grouting conduit 1. Grouting can be terminated when the grouting pressure reaches ≥2.5 MPa and remains stable for 3-5 minutes, or when the required grouting volume has been injected.

[0065] During construction, the pressure loss caused by the long grouting distance was taken into consideration, and the actual grouting pressure was measured using a pile hole pressure gauge (the actual pressure loss value was about 1.2 to 1.5 MPa), thus avoiding inaccurate grouting pressure values.

[0066] As a preferred embodiment, based on the above method, further, in step D, the water splitting operation is performed twice, the first time lasting 3 to 5 hours, and the second time lasting 24 hours. This construction method can make the vein-shaped grouting channel with higher quality.

[0067] As a preferred embodiment, based on the above method, after the water fracturing operation in step D is completed, the grouting operation is further carried out after waiting for 5 to 7 days. This construction method allows the water injected into the pile bottom to be fully absorbed by the soil, thereby minimizing the dilution of the concrete slurry after injection, further ensuring the formation quality of the vein-like network stone body.

[0068] As a preferred embodiment, based on the above approach, the number of grouting conduits 1 fixed to the steel cage 10 is greater than or equal to two, and the grouting conduits 1 are symmetrically fixed to the steel cage 10. This structural arrangement improves the uniformity of grout distribution at the base of the cast-in-place pile, resulting in excellent bearing capacity. Furthermore, this structural arrangement reduces the risk of clogging and failure of the grouting conduits 1 during actual construction, thereby improving the reliability of grouting operations.

[0069] Specifically, the problems that may occur during the grouting construction and their backup measures:

[0070] 1. Failure of Grouting Conduit 1: If one grouting conduit in a pile fails and the other grouting conduit is poorly groutable, use a diluted grout primarily to ensure that the desired cement volume can be injected using a single grouting conduit. If both grouting conduits fail, the remedial measure is to inject an appropriate amount of high-pressure diluted grout into the surrounding piles. If the pile is located in a critical area, additional injection can be performed by drilling a hole through the center of the pile to the bottom, or by adding additional piles. If both grouting conduits fail, the remedial measures must be approved by the design institute and Party A.

[0071] 2. If there is air, bubbles or slurry around the pile, use thick slurry, low pressure and slow injection, and extend the interval time.

[0072] 3. For rock-embedded piles or piles with poor groutability, continuous grouting with thin slurry, high pressure and small pump volume should be used.

[0073] Example 2

[0074] like Figures 3 to 8 As shown, the present invention describes a post-grouting method for bored piles. Based on the above method, the grouting conduit 1 further comprises a pipe section 2 and a grouting device 3. The grouting device 3 is positioned at the bottom of the pipe section 2 and inserted into the soil layer at the bottom of the pile hole for a length of ≥300 mm. This structural arrangement ensures that the concrete slurry can be diffused throughout the bottom of the bored pile. Furthermore, during the pouring of the bored pile concrete, the grouting device inserted into the soil layer at the bottom of the pile hole prevents the steel cage 10 from floating upward.

[0075] As a preferred embodiment, based on the above method, the top of the pipe section 2 is further elevated 200 mm to 300 mm above the ground, and a cover is provided on the top of the pipe section 2. This structural arrangement can prevent foreign matter from entering and clogging the grouting conduit 1.

[0076] As a preferred embodiment, based on the above method, further, the grouting device section 3 includes a grouting device body 4, a grouting hole 5 is provided on the tube wall of the grouting device body 4, and the surface of the grouting device body 4 is covered with a rubber layer 9, and the rubber layer 9 is used to seal the grouting hole 5.

[0077] Specifically, the pipe section 2 described in the present invention should have an inner diameter of 30 mm or greater, or 50 mm or greater when also serving as an acoustic detection pipe; a wall thickness of 3.2 mm or greater, and be made of Q235B. The bottom of the grouting device section 3 should be inserted at least 300 mm below the bottom of the pile hole, equipped with a reverse valve and bamboo joints. Two grouting holes 5 are located between each joint, each with a diameter of 7 mm. These holes are covered with 2 mm thin rubber, the rubber and the joints sealed with silicone, and the ends sealed with threaded seals. The upper end of the grouting pipe should be 0.2 m above the ground. The grouting conduit 1 is lowered simultaneously with the steel cage 10, and a water injection test is performed to prevent leakage.

[0078] As a preferred embodiment, based on the above method, further, the bottom of the grouting device body 4 is shaped as a cone. With this structural setting, the grouting device section 3 can be more easily inserted into the pile bottom soil layer, improving the convenience of the present invention in construction.

[0079] Example 3

[0080] like Figures 3 to 8 As shown, the post-grouting construction method for the bottom of a bored pile described in the present invention is based on the above method. Further, the grouting holes 5 include a first-class grouting hole 6 and a second-class grouting hole 7. The setting positions of the first-class grouting holes 6 and the second-class grouting holes 7 are both located below the elevation of the bottom of the bored pile. The first-class grouting holes 6 are set on one side corresponding to the bottom of the bored pile, and the second-class grouting holes 7 are set away from the side of the bottom of the bored pile. The slurry flow channel formed by the first-class grouting holes 6 is inclined toward the bottom of the bored pile.

[0081] In this embodiment, the slurry flow path formed by the first type of grouting holes 6 is inclined toward the bottom of the bored pile. During water splitting construction, the water jetted from the first type of grouting holes 6 can flush the bottom of the bored pile, causing the mud / sediment attached to the concrete surface at the bottom of the bored pile to fall off. During grouting construction, the concrete slurry can better integrate with the bottom of the bored pile, making the vein-like network stone body and the bored pile more integrated after integration, thereby improving the bearing capacity of the bored pile. Furthermore, adopting this structural arrangement, during grouting construction, the concrete slurry can be accumulated at the bottom of the bored pile, improving the density of the concrete structure formed at the bottom of the bored pile. Moreover, the concrete slurry can fully integrate with the bottom of the bored pile, making the vein-like network stone body and the bored pile more integrated after integration, further improving the bearing capacity of the bored pile.

[0082] Example 4

[0083] like Figures 3 to 9As shown, the post-grouting construction method of the bored pile bottom described in the present invention is based on the above method. Further, a plurality of spring sheets 8 are further arranged around the liquid outlet of the grouting hole 5. The adjacent spring sheets 8 are arranged at intervals, and the length of the spring sheets 8 is smaller than the hole radius of the grouting hole 5. After the grouting device body 4 is covered by the rubber layer 9, the spring sheets 8 are compressed and retracted in the grouting hole 5. After the water splitting construction, the spring sheets 8 return to their extended state, and the spring sheets 8 extend along the length direction of the grouting hole 5.

[0084] In the present invention, when pouring concrete in a bored pile, the grouting hole 5 is sealed with the rubber layer 9 to prevent concrete from backflowing from the grouting hole 5 and clogging the grouting device. During water fracturing, a high-pressure water flow tears the rubber layer 9, opening the grouting hole 5. However, using a high-pressure water flow to tear the rubber layer 9 generally makes it difficult to fully open the liquid outlet of the grouting hole 5, and the rips in the rubber layer 9 also produce burrs, which affects the pressure and path of the water / concrete slurry injection during subsequent water fracturing and grouting. Based on this, in this embodiment, a plurality of spring plates 8 are further provided at the outlet of the grouting hole 5. When the rubber layer 9 ruptures, the spring plates 8 return to an extended state, propping up the cracks in the rubber layer 9 and fully opening the outlet of the grouting hole 5. This ensures that the pressure of the water and slurry ejected from the grouting hole 5 can be fully released, and also ensures that the water and slurry can be ejected from the grouting hole 5 along the set path, thereby improving the success rate of the clean water splitting construction and grouting construction. Furthermore, when the spring plates 8 are in their extended state, they can also increase the roughness of the wall of the grouting device body 4, making the slurry more tightly bonded to it, and further improving the degree of integration after the vein-like network stone body and the cast-in-place pile are combined.

[0085] As a preferred embodiment, based on the above approach, the end of the spring piece 8 is further bent toward the wall of the grouting device body 4. This structural arrangement prevents the expanded rubber layer 9 from sliding toward the end of the spring piece 8, thereby affecting the flow of water or slurry. Furthermore, this structural arrangement improves the reliability of the spring piece 8 in expanding the cracks in the rubber layer 9.

[0086] As a preferred embodiment, based on the above-mentioned method, further, a check valve is provided inside the grouting device body 4 .

[0087] As a preferred embodiment, based on the above method, further, the pipe body section 2 and the grouting device section 3 are connected by a thread. This structural setting can improve the convenience of connecting the pipe body section 2 and the grouting device section 3.

[0088] As a preferred embodiment, based on the above method, further, the pipe body section 2 is made of seamless steel pipe.

[0089] Example 5

[0090] like Figures 1 to 9 As shown, the post-grouting construction method for the bored pile bottom described in the present invention is based on the above method. Further, before the grouting operation, clean water is pressed into the grouting pipe 1 to perform a water pressure test, and the working parameters during grouting are adjusted according to the results of the water pressure test.

[0091] Specifically, the pressure of the water pressure test before grouting: The water pressure test before grouting is an important process for pile bottom grouting, which can play three important roles in general grouting projects: 1. Clearing the grouting channel; 2. Pushing the fine particles in the sediment and mud skin out of the reinforcement range; 3. Checking the connectivity of the grouting conduit 1 so as to take measures to give full play to the groutability of the grouting conduit 1.

[0092] As a preferred embodiment, based on the above method, further, during the grouting process, the pile holes around the site are first grouting, and then pushed inward layer by layer from the outside to the inside, and finally the pile holes in the central part of the site are grouting.

[0093] Due to the presence of stratum porosity and cracks in the bearing stratum, during grouting of Pile A, cement slurry may spurt from the unplugged but ungrouted pipe of the adjacent Pile B, blocking grouting conduit 1 and potentially causing subsequent grouting failure in Pile B. This cross-hole diffusion phenomenon can also cause consolidation of the surrounding soil, making it difficult for the adjacent pile driver to drill. To avoid grouting failures caused by cross-holes, this project utilizes a continuous flow construction process of unplugging and grouting in sections. Grouting is carried out layer by layer, starting from the periphery of the site and working inward until the entire site is grouted.

[0094] As a preferred embodiment, based on the above method, further, during grouting construction, the grouting pressure value gradually transitions from small to large to the set grouting pressure value, and the slurry gradually transitions from thin to thick to the set concentration.

[0095] As a preferred embodiment, based on the above method, during grouting construction, the set grouting pressure value is used as a reference standard, and the grouting pressure changes are closely monitored during the grouting process, and the construction is adjusted in real time according to the following situations:

[0096] (1) The grouting pressure value gradually increases but does not reach the set grouting pressure value: it is judged that the slurry forms vein-like splitting penetration in the clay, or the slurry concentration is low, the gel time is long, or part of the slurry overflows;

[0097] (2) After the grouting starts, the grouting pressure does not increase, or even shows a downward trend from the initial pressure value: it is judged that the slurry has overflowed;

[0098] (3) The grouting pressure value suddenly drops after rising: it is judged that the slurry overflows from the grouting pipe, or the injection speed is too high, disturbing the soil layer, or encountering a weak part with gaps;

[0099] In the above situations, the water-cement ratio of the slurry is adjusted to increase the concentration of the slurry, and / or admixtures are added to the slurry to shorten the setting time of the slurry, and / or the grouting pressure is reduced, the grouting flow rate is limited, and the flow and penetration rate of the slurry in the soil cracks is reduced, so that the slurry particles gradually settle and block the infiltration channels in the soil layer, and / or intermittent grouting is used to allow the slurry particles to settle and gel in a static state, thereby blocking the infiltration channels in the soil layer;

[0100] (4) The grouting pressure value rises to the set grouting pressure value, and the speed of the grouting pressure value rises faster than the set value, but the grouting speed cannot reach the set value: it is judged that the soil layer at the bottom of the pile is dense or the slurry gelation time is too short;

[0101] In this case, adjust the water-cement ratio of the slurry, reduce the concentration of the slurry, and / or add admixtures to the slurry to extend the setting time of the slurry, and / or increase the grouting pressure and reduce the pumping volume of the slurry for continuous grouting.

[0102] In this embodiment, the pressure value of successful grouting is manifested as follows: the grouting pressure value rises regularly and reaches the set grouting pressure value in time, and the grouting speed is also normal (with little change); or, the grouting pressure value rises and then falls, and then rises again and reaches the set grouting pressure value.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A post-grouting construction method for a bored pile bottom, characterized in that: The steps include: A. Boring construction of bored piles: Drilling and excavation of bored pile holes shall be carried out according to the design requirements, so that the bored pile hole diameter and depth meet the design requirements; B. Installation of cast-in-place pile reinforcement cage and grouting conduit: Make the reinforcement cage according to the design requirements, fix the grouting conduit on the reinforcement cage, and then use lifting equipment to place the reinforcement cage into the cast-in-place pile hole; C. Cast-in-place pile concrete pouring: pouring concrete to shape the cast-in-place pile body; D. Clean water splitting: After the cast-in-place pile concrete reaches the specified strength, high-pressure clean water is injected into the grouting pipe to split the soil layer under the cast-in-place pile using the high-pressure clean water to form a vein-like grouting channel; E. Grouting: Use the grouting pipe to inject pressurized cement slurry into the soil layer at the bottom of the bored pile, so that the cement slurry spreads along the vein-shaped grouting channel until the total amount of grouting reaches the design value, or the grouting pressure exceeds the design value; The grouting conduit includes a pipe section and a grouting device section. The grouting device section is arranged at the bottom of the pipe section. The length of the grouting device section inserted into the bottom soil layer of the pile hole is ≥300mm. The top of the pipe section is 200mm to 300mm above the ground, and a cover is provided on the top of the pipe section. The grouting section includes a grouting body, a grouting hole is provided on the wall of the grouting body, a surface of the grouting body is covered with a rubber layer, the rubber layer is used to seal the grouting hole, and a check valve is provided inside the grouting body; the bottom of the grouting body is shaped like a cone; A number of spring sheets are also provided around the liquid outlet of the grouting hole. Adjacent spring sheets are spaced apart, and the length of the spring sheets is smaller than the hole radius of the grouting hole. After the grouting device body is covered by the rubber layer, the spring sheets are compressed and retracted into the grouting hole. After the water splitting construction, the spring sheets return to their extended state. The spring sheets extend along the length direction of the grouting hole channel, propping up the crack of the rubber layer, so that the liquid outlet of the grouting hole is fully opened, ensuring that the pressure value of the water flow and slurry ejected from the grouting hole can be completely released.

2. The post-grouting construction method for cast-in-place pile bottom according to claim 1, characterized in that: In step D, the water fracturing operation is performed twice, the first time is 3 to 5 hours, and the second time is 24 hours; after the water fracturing operation in step D is completed, the grouting construction is performed after waiting for 5 to 7 days.

3. The post-grouting construction method for cast-in-place pile bottom according to claim 1, characterized in that: The number of grouting pipes fixed on the steel cage is greater than or equal to two, and the grouting pipes are symmetrically fixed on the steel cage.

4. The post-grouting construction method for the bored pile bottom according to claim 3, characterized in that: The grouting holes include Class I grouting holes and Class II grouting holes. The Class I grouting holes and the Class II grouting holes are both located below the bottom elevation of the bored pile. The Class I grouting holes are arranged on one side corresponding to the bottom of the bored pile, and the Class II grouting holes are arranged away from the bottom of the bored pile. The slurry flow channels formed by the Class I grouting holes are inclined toward the bottom of the bored pile.

5. The post-grouting construction method for the bored pile bottom according to claim 4, characterized in that: The end of the spring sheet is bent toward the tube wall of the grouting device body.

6. The post-grouting construction method for cast-in-place pile bottom according to claim 1, characterized in that: Before grouting, clean water is pressed into the grouting pipe to conduct a water pressure test, and the working parameters of the grouting are adjusted according to the results of the water pressure test. During the grouting process, the pile holes around the site are first grouting, and then pushed inward layer by layer from the outside to the inside, and finally the pile holes in the central part of the site are grouting. During the grouting construction, the grouting pressure value gradually transitions from small to large to the set grouting pressure value, and the slurry gradually transitions from thin to thick to the set concentration.

7. The post-grouting construction method for cast-in-place pile bottom according to claim 1, characterized in that: During grouting construction, use the set grouting pressure value as a reference standard. Pay close attention to changes in grouting pressure during the grouting process and adjust the construction in real time according to the following situations: (1) The grouting pressure value gradually increases but does not reach the set grouting pressure value: it is judged that the slurry forms vein-like splitting penetration in the clay, or the slurry concentration is low, the gel time is long, or part of the slurry overflows; (2) After the grouting starts, the grouting pressure does not increase, or even shows a downward trend from the initial pressure value: it is judged that the slurry has overflowed; (3) The grouting pressure value suddenly drops after rising: it is judged that the slurry overflows from the grouting pipe, or the injection speed is too high, disturbing the soil layer, or encountering a weak part with gaps; In the above situations, the water-cement ratio of the slurry is adjusted to increase the concentration of the slurry, and / or admixtures are added to the slurry to shorten the setting time of the slurry, and / or the grouting pressure is reduced, the grouting flow rate is limited, and the flow and penetration rate of the slurry in the soil cracks is reduced, so that the slurry particles gradually settle and block the infiltration channels in the soil layer, and / or intermittent grouting is used to allow the slurry particles to settle and gel in a static state, thereby blocking the infiltration channels in the soil layer; (4) The grouting pressure value rises to the set grouting pressure value, but the grouting speed cannot reach the set value: it is judged that the soil layer at the bottom of the pile is dense or the grouting time is too short; In this case, adjust the water-cement ratio of the slurry, reduce the concentration of the slurry, and / or add admixtures to the slurry to extend the setting time of the slurry, and / or increase the grouting pressure and reduce the pumping volume of the slurry for continuous grouting.

Images