Grouting lifting construction method of pile-raft foundation under different working conditions

Abstract

The application discloses a grouting lifting construction method based on pile-raft foundations under different working conditions, detects the state of the original pile foundation through a detection means, judges whether the pile end of the original pile foundation reaches a bearing stratum, adopts a corresponding treatment method according to the detection result, including performing grouting new pile foundation, widening raft plate and other operations, continuously grouting at the end of the new pile foundation during lifting, forming a composite reinforced body, and the composite reinforced body covers the end of the original pile foundation and the new pile foundation; for the fractured original pile foundation, continuously grouting until the top surface of the composite reinforced body exceeds the fracture of the original pile foundation, forming a convex part; finally, grouting at the bottom surface of the composite reinforced body, and performing overall lifting. The application solves the technical problems of building settlement of the pile-raft foundation caused by different working conditions, and the problems of being unable to effectively lift and correct deviation.

Description

Technical Field

[0001] This invention relates to the field of grouting and lifting technology for pile-raft foundation construction, and particularly to grouting and lifting construction methods for pile-raft foundations under different working conditions. Background Technology

[0002] With the continuous development of society, the number of buildings in major cities is constantly increasing. However, in urban construction, problems often arise such as inadequate foundation treatment, high compressibility of the foundation soil, and insufficient bearing capacity of the foundation. Alternatively, changes in groundwater drainage conditions can lead to groundwater erosion, resulting in a reduction in the bearing capacity of the foundation.

[0003] Pile-raft foundations offer advantages such as high bearing capacity, good stability, and simple construction. However, uneven settlement can occur due to factors such as weak interlayers between the pile tip and bedrock, large rock surface inclination leading to insufficient pile penetration depth causing lateral slippage, or soft soil with a low coefficient of friction around the piles, resulting in pile fracture due to heavy superstructure loads. This can cause the building to tilt, resulting in unnecessary losses, necessitating effective reinforcement measures to mitigate the damage. Since settlement in pile-raft foundation structures is generally the result of multiple factors, and pile foundation problems can be comprehensive and diverse, a case-by-case analysis is required for each settlement situation, rather than relying solely on grouting methods.

[0004] In summary, there are currently no effective solutions or measures for building settlement caused by pile foundation problems under various working conditions. Summary of the Invention

[0005] This invention provides a grouting and lifting construction method for pile-raft foundations under different working conditions, which can solve technical problems such as settlement of buildings caused by varying degrees of problems in the pile foundations of pile-raft foundations under various working conditions, and the inability to effectively lift and correct the deviation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The present invention provides a grouting and lifting construction method for pile-raft foundations under different working conditions, including a grouting and lifting structure, which includes a raft slab, original pile foundations, new pile foundations, a soft soil layer, a bearing layer, and a composite reinforced body; wherein, the raft slab is set below the ground, the original pile foundations and new pile foundations are both set on the lower end face of the raft slab and extend into the ground, the bearing layer is located below the soft soil layer, and the ends of all new pile foundations are set in the bearing layer; The construction method includes the following steps: Step one: First, measure the magnitude of the settlement, the length of the original pile foundation, and the location of the original pile foundation in the soil layer using measurement methods; Step two: Using low-strain testing methods, determine the integrity of the original pile foundation to identify any fractures. Then, based on the measurement results, design a grouting reinforcement method. Step 3: If the original pile foundation ends have not reached the bearing layer and the pile body is intact, grouting is required on both sides of the original pile foundation to form a new pile foundation. The length of the new pile foundation exceeds that of the original pile foundation and reaches the bearing layer to stop the settlement of the building. Step 4: If the original pile foundation reaches the bearing layer and low strain testing reveals that the original pile foundation has fractured, and the fractured original pile foundation is in the middle of the raft foundation, the existing grouting lifting method of grouting the pile end can no longer achieve the lifting effect. It is necessary to grout on both sides of the fractured original pile foundation to form a new pile foundation to stop the settlement of the building. Step 5: If the original pile foundation reaches the bearing layer, but low strain testing reveals that the original pile foundation has fractured and the fractured pile is located at the end of the raft foundation, the raft foundation is widened first, and then grout is injected on both sides of the fractured original pile foundation to form a new pile foundation to stop the building settlement. Step 6, Grouting and Lifting: Continue grouting at the end of the new pile foundation to form a composite reinforcement body. The composite reinforcement body covers the ends of both the original pile foundation and the new pile foundation. For the fractured original pile foundation, continue grouting until the top surface of the composite reinforcement body exceeds the fracture point of the original pile foundation, forming a protrusion. Finally, grout the bottom surface of the composite reinforcement body to lift the entire structure. Step 7: After grouting is completed, stress and strain tests are conducted on the pile foundation under various conditions. In particular, the fracture points of the original pile foundation are measured more intensively to determine whether the design requirements for grouting and lifting are met. This completes the grouting and lifting work under various raft foundations.

[0007] Preferably, in steps three, four, and five, the formation of the new pile foundation adopts the forward grouting method, including the following steps: Let L be the drilling length of the drill rod to the bottom of the raft slab. First, fill and grout. Then retract the drill rod upwards, the retraction length being half the drilling length L, and then stop retraction to perform pressure grouting; Within the root-like grouting body formed by pressure grouting, the grout diffuses evenly in all directions, mixes uniformly with the surrounding soil, and solidifies to form a short cylinder with strength. After repeated forward and backward grouting, a continuous short cylindrical structure forms a complete reinforced composite pile foundation. The top surface of the reinforced composite pile foundation supports the raft slab until the grouting reaches the design depth. Finally, the drill rod is pulled out upward, and grout is injected at the same time to fill the borehole tightly.

[0008] Preferably, in step five, when widening the raft slab, connecting steel bars are laid at the edge of the raft slab, and high-strength concrete is poured.

[0009] Preferably, the conditions for stopping grouting are: the grouting pressure reaches a certain level and stabilizes, or the grout injection rate meets the design requirements.

[0010] Preferably, the center of the horizontal cross-section of the short cylinder coincides with the center of the drill pipe.

[0011] Preferably, in step one, the settlement measurement method includes setting up benchmark points, setting up observation points, and using a level instrument for observation.

[0012] Preferably, in step two, a low-strain tester is used to test the integrity of the original pile foundation.

[0013] Preferably, in step three, the new pile foundations are symmetrically arranged in the middle of the raft foundation; in step four, the new pile foundations are symmetrically arranged with the fractured original pile foundations as the axis of symmetry.

[0014] Preferably, in step seven, a three-dimensional model is established to simulate the grouting and lifting process. Control points are set at the fracture point of the original pile foundation, at the pile bottom and at the pile top, and the coordinates of the control points are output. After the grouting process stabilizes, the settlement of the pile top, the strain of the pile body, the stress and the integrity of the pile body are monitored. The on-site measured data of the control points and the simulation data of the three-dimensional model are fitted. If the error is within an acceptable range, the design requirements are met.

[0015] The beneficial effects of this invention are reflected in: 1) The grouting and lifting construction method for pile-raft foundations under different working conditions provided by the present invention detects the state of the original pile foundation through detection means and determines whether it is located in the bearing layer and whether the pile body is intact. According to the detection results, corresponding treatment methods are adopted, including grouting to build new pile foundations and widening the raft slab. It has a good technical effect on the problem of settlement of pile-raft foundation buildings under various working conditions.

[0016] 2) The grouting and lifting construction method for pile-raft foundations under different working conditions provided by the present invention continues grouting after the new pile foundation is formed by grouting. The composite reinforcement body is combined with the original pile foundation and the new pile foundation to form a composite reinforcement body. Grouting is then carried out at the bottom of the composite reinforcement body, which has stronger integrity and can ensure the uniformity and quality of the subsequent lifting.

[0017] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention; the main objects and other advantages of the invention may be realized and obtained by means of the embodiments particularly pointed out in the description. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of grouting and lifting of the original pile foundation before it reaches the bearing layer.

[0019] Figure 2 This is a schematic diagram of the grouting and lifting of the original pile foundation in the middle of the raft foundation, which is fractured according to the present invention.

[0020] Figure 3 This is a schematic diagram of the grouting and lifting of the original pile foundation at the edge of the raft foundation, which is a result of the present invention.

[0021] Attached reference numerals: 1-raft foundation, 2-original pile foundation, 3-new pile foundation, 4-soft soil layer, 5-bearing layer, 6-composite reinforced body, 7-expanded raft foundation, 8-grouting pipe. Detailed Implementation

[0022] The technical solutions of the present invention will be described in detail below through embodiments. The following embodiments are merely exemplary and can only be used to explain and illustrate the technical solutions of the present invention, and should not be construed as limiting the technical solutions of the present invention.

[0023] Example 1 This example uses a building settlement renovation project as an example. The building's foundation is a pile-raft foundation. Testing of the pile bearing capacity and integrity revealed that some piles on one side did not reach the stable bearing layer 5, the bearing layer 5 containing interlayers at the pile bottom was deformed, and the sediment at the pile bottom was generally thick. The end-bearing piles effectively became friction piles, and their bearing capacity did not meet the requirements. According to the geological supplementary investigation report, the uneven thickness and significant differences in physical properties of the compressible layer led to uneven settlement of the foundation, with a larger thickness of the compressible soil layer on the side of greater settlement. The pile end bearing capacity did not meet the design requirements. Furthermore, the insufficient bearing capacity of some piles caused a certain offset between the pile foundation reaction center and the superstructure mass center, exhibiting a significant eccentric effect, which exacerbated the foundation settlement and tilting.

[0024] In this embodiment, a grouting and lifting construction method for pile-raft foundations under different working conditions is adopted, including a grouting and lifting structure. The grouting and lifting structure includes a raft slab 1, original pile foundations 2, new pile foundations 3, soft soil layer 4, bearing layer 5, and composite reinforcement body 6. The raft slab 1 is located below the ground. The original pile foundations 2 and new pile foundations 3 are both located on the lower end face of the raft slab 1 and extend into the ground. The bearing layer 5 is located below the soft soil layer 4, and the ends of all new pile foundations 3 are located in the bearing layer 5. The construction method for grouting and lifting structures includes the following steps: Step 1: First, through measurement methods, including setting up benchmark points and observation points, and using a level to observe, measure the magnitude of the settlement, the length of the original pile foundation 2, and the location of the soil layer where the original pile foundation 2 is located. Step 2: According to the low strain testing method, the integrity of the original pile foundation 2 is tested using a low strain tester to determine the integrity of the original pile foundation 2 and to determine whether there is any fracture in the original pile foundation 2. Then, based on the measurement results, a grouting reinforcement method is designed. Step 3: Since the end of the original pile foundation 2 has not reached the bearing layer 5 and the pile body is intact, grouting is required on both sides of the original pile foundation 2 to form a new pile foundation 3. The length of the new pile foundation 3 exceeds that of the original pile foundation 2 and reaches the bearing layer 5. Step 4, Grouting and Lifting: Continue grouting at the end of the new pile foundation 3 to form a composite reinforced body 6. The composite reinforced body 6 includes the ends of the original pile foundation 2 and the new pile foundation 3. Finally, grouting is performed on the bottom surface of the composite reinforced body 6 to achieve overall lifting. Step 5: After grouting is completed, stress and strain tests are performed on the pile foundation under various conditions to determine whether the design requirements for grouting lifting are met. The specific operation is as follows: A three-dimensional model is established to simulate the grouting lifting process. Control points are set at the pile bottom and pile top, and the coordinates of the control points are output. After the grouting process stabilizes, the settlement of the pile top, the strain of the pile body, the stress, and the integrity of the pile body are monitored. The on-site measured data of the control points and the simulation data of the three-dimensional model are fitted. If the error is within an acceptable range, the design requirements are met, and the grouting lifting work is completed.

[0025] Example 2 Similar to Example 1, the difference lies in the following: the original pile foundation 2 reaches the bearing layer 5 at its end. Low-strain testing reveals that the original pile foundation 2 has fractured, and the fractured original pile foundation 2 is located in the middle of the raft foundation 1. Existing grouting and lifting methods that involve grouting and lifting at the pile end can no longer achieve the lifting effect. It is necessary to grout on both sides of the fractured original pile foundation 2 to form new pile foundations 3, which are symmetrically arranged in the middle of the raft foundation 1. After grouting, stress and strain tests are performed on the pile foundations under various conditions. In particular, the fractured part of the original pile foundation 2 is subjected to more intensive measurements to determine whether the design requirements for grouting and lifting have been met. The specific operation is as follows: a three-dimensional model is established to simulate the grouting and lifting process. Control points are set at the fractured part of the original pile foundation 2, at the pile bottom and at the pile top, and the coordinates of the control points are output. After the grouting process stabilizes, the settlement of the pile top, the strain of the pile body, the stress, and the integrity of the pile body are monitored. The on-site measured data of the control points and the simulated data of the three-dimensional model are fitted. If the error is within an acceptable range, the design requirements are met, thus completing the grouting and lifting work.

[0026] Example 3 Similar to Example 2, the difference is that the original pile foundation 2 reaches the bearing layer 5 at its end, but low strain testing reveals that the original pile foundation 2 has fractured, and the fractured pile occurs at the end of the raft foundation 1. First, the raft foundation 1 is widened. When widening the raft foundation 1, connecting steel bars are laid at the edge of the raft foundation 1 and high-strength concrete is poured. Then, grouting is injected on both sides of the fractured original pile foundation 2 to form a new pile foundation 3 to stop the building settlement. The new pile foundation 3 is symmetrically set with the fractured original pile foundation 2 as the axis of symmetry.

[0027] Furthermore, in actual project construction, if two or more of the above three embodiments of the working conditions occur at the same time, it is a relatively complex situation. In this case, it is necessary to first determine the condition of the pile foundation, and then, according to the processing method in the above embodiments, first grout to form a new pile foundation 3. After solving all the pile foundation problems, grout to form a composite reinforced body 6, and then uniform grouting and lifting work is carried out at the bottom of the composite reinforced body 6 to achieve the lifting and correction of the building.

[0028] Furthermore, the formation of the new pile foundation 3 adopts an advancing grouting method, including the following steps: Let the drilling length of the drill rod to the bottom of the raft 1 be L. First, fill grouting is performed. When the grouting reaches a certain grouting pressure and stabilizes, or when the grout injection rate reaches the design requirements, the filling grouting is stopped. Then, the drill rod is pulled back upwards, and the length of the pullback is half of the drilling length L. Then, the pullback is stopped, and pressure grouting is performed. Within the root-like grout body formed by pressure grouting, the grout spreads evenly in all directions and mixes evenly with the surrounding soil. When the grouting reaches a certain pressure and stabilizes, or when the grout injection rate reaches the design requirements, the grout solidifies to form a short cylinder with strength. The center of the horizontal section of the short cylinder coincides with the center of the drill rod. After repeated advancing and pulling grouting, the continuous short cylinder structure forms a complete reinforced composite pile foundation. The top surface of the reinforced composite pile foundation supports the raft 1 until the grouting reaches the design depth. Finally, the drill rod is pulled out upwards, and grout is injected at the same time to fill the borehole densely.

[0029] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A grouting and lifting construction method for pile-raft foundations under different working conditions, characterized in that, The structure includes a grouting lifting structure, which comprises a raft foundation (1), original pile foundation (2), new pile foundation (3), soft soil layer (4), bearing layer (5), and composite reinforcement body (6). Among them, the raft foundation (1) is set below the ground, the original pile foundation (2) and the new pile foundation (3) are both set on the lower end face of the raft foundation (1) and extend into the ground, the bearing layer (5) is located below the soft soil layer (4), and the ends of all the new pile foundations (3) are set in the bearing layer (5). The construction method includes the following steps: Step 1: First, measure the magnitude of the settlement, the length of the original pile foundation (2), and the location of the soil layer where the original pile foundation (2) is located. Step 2: According to the low strain test method, determine the integrity of the original pile foundation (2), determine whether the original pile foundation (2) is fractured, and then design the grouting reinforcement method based on the measurement results; Step 3: If the end of the original pile foundation (2) does not reach the bearing layer (5) and the pile body is intact, grouting is required on both sides of the original pile foundation (2) to form a new pile foundation (3). The length of the new pile foundation (3) exceeds that of the original pile foundation (2) and reaches the bearing layer (5) to stop the settlement of the building. Step 4: If the end of the original pile foundation (2) reaches the bearing layer (5), but the low strain test finds that the original pile foundation (2) has broken, and the broken original pile foundation (2) is in the middle of the raft slab (1), the existing grouting lifting method can no longer achieve the lifting effect by grouting the pile end. It is necessary to grout on both sides of the broken original pile foundation (2) to form a new pile foundation (3) to stop the settlement of the building. Step 5: If the end of the original pile foundation (2) reaches the bearing layer (5), but the low strain test finds that the original pile foundation (2) has broken, and the broken pile occurs at the end of the raft foundation (1), the raft foundation (1) is widened first, and then grout is injected on both sides of the broken original pile foundation (2) to form a new pile foundation (3) to stop the building from settling. Step 6, grouting and lifting: Insert the grouting pipe (8) and continue grouting at the end of the new pile foundation (3) to form a composite reinforcement body (6). The composite reinforcement body (6) covers the ends of the original pile foundation (2) and the new pile foundation (3). For the broken original pile foundation (2), continue grouting until the top surface of the composite reinforcement body (6) exceeds the broken part of the original pile foundation (2) to form a protrusion. Finally, grout the bottom surface of the composite reinforcement body (6) to lift the whole structure. Step 7: After grouting is completed, stress and strain tests are performed on the pile foundation under various conditions. Among them, the fracture point of the original pile foundation (2) is measured in detail to determine whether the design requirements for grouting and lifting are met, thereby completing the grouting and lifting work under the pile raft foundation.

2. The grouting and lifting construction method for pile-raft foundations under different working conditions as described in claim 1, characterized in that, In steps three, four, and five, the formation of the new pile foundation (3) adopts the forward grouting method, including the following steps: Let L be the drilling length of the drill rod to the bottom of the raft (1). First, fill and grout. Then retract the drill rod upwards, with the retraction length being half the drilling length L, and then stop retraction to perform pressure grouting; Within the root-like grouting body formed by pressure grouting, the grout diffuses evenly in all directions, mixes uniformly with the surrounding soil, and solidifies to form a short cylinder with strength. After repeated forward and backward grouting, the continuous short cylindrical structure forms a complete reinforced composite pile foundation. The top surface of the reinforced composite pile foundation supports the raft slab (1) until the grouting reaches the design depth. Finally, the drill rod is pulled out upward, and grout is injected at the same time to fill the borehole tightly.

3. The grouting and lifting construction method for pile-raft foundations under different working conditions as described in claim 1, characterized in that, In step five, when widening the raft slab (1), connecting steel bars are laid on the edge of the raft slab (1), and high-strength concrete is poured.

4. The grouting and lifting construction method for pile-raft foundations under different working conditions as described in claim 2, characterized in that, The conditions for stopping grouting are: the grouting pressure reaches a certain level and stabilizes, or the grout injection rate meets the design requirements.

5. The grouting and lifting construction method for pile-raft foundations under different working conditions as described in claim 2, characterized in that, The center of the horizontal cross-section of the short cylinder coincides with the center of the drill pipe.

6. The grouting and lifting construction method for pile-raft foundations under different working conditions as described in claim 1, characterized in that, In step one, the settlement measurement method includes setting up benchmark points, setting up observation points, and using a level instrument for observation.

7. The grouting and lifting construction method for pile-raft foundations under different working conditions as described in claim 1, characterized in that, In step two, a low-strain tester is used to test the integrity of the original pile foundation (2).

8. The grouting and lifting construction method for pile-raft foundations under different working conditions as described in claim 1, characterized in that, In steps four and five, the new pile foundation (3) is set symmetrically with the fractured original pile foundation (2) as the axis of symmetry.

9. The grouting and lifting construction method for pile-raft foundations under different working conditions as described in claim 1, characterized in that, In step seven, a three-dimensional model is established to simulate the grouting and lifting process. Control points are set at the fracture point of the original pile foundation (2), at the bottom of the pile and at the top of the pile. The coordinates of the control points are output. After the grouting process is stable, the settlement of the pile top, the strain of the pile body, the stress and the integrity of the pile body are monitored. The on-site measured data of the control points and the simulation data of the three-dimensional model are fitted. If the error is within the acceptable range, the design requirements are met.

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