Local bending-resistant reinforced foundation pit pouring support pile and construction method thereof

Abstract

The invention discloses a local bending-resistant reinforced foundation pit cast-in-place support pile and a construction method thereof, and the construction method comprises the following specific steps: firstly, forming a local reamed hole near an excavation surface by adopting a small-large-small diameter stepped drilling process; lowering a steel hoop system with a push-in connector at the bottom; the connector is kept in a folded state when passing through the upper straight hole, and when reaching the lower reaming section, the connector loses hole wall constraint and is driven by the built-in torsion spring to be automatically bounced off and clamped on the step of the reaming cavity. Lowering a reinforcement cage; and finally, concrete is poured to form the composite pile body. The problems of high construction cost, tedious construction and long construction period caused by the fact that a traditional cast-in-place support pile in a soft soil area is used for controlling deformation of a foundation pit, enlarging the pile diameter, lengthening the pile body, additionally arranging a support and the like can be effectively solved, meanwhile, the construction is convenient and fast, the reliability is high, the bending resistance of the support pile can be remarkably improved, and remarkable economic benefits and social benefits are achieved.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and building foundation pit support technology, and in particular to a locally flexurally reinforced cast-in-place foundation pit support pile and its construction method. Background Technology

[0002] In deep foundation pit engineering, cast-in-place piles, such as bored piles and rotary piles, are among the most widely used support structures. Their working principle relies on the depth to which the pile is embedded in the soil below the pit bottom to provide the necessary anchoring force to balance the external earth pressure. According to classical foundation pit support design theory, the bending moment distribution borne by the support piles exhibits a non-linear characteristic, with the maximum bending moment typically occurring near the excavation face. This area represents the most critical section of the pile and often controls the design of the entire support system.

[0003] Currently, there are three main conventional methods to improve the bending resistance of retaining piles: 1. increasing the pile diameter; 2. increasing the reinforcement ratio or concrete strength; and 3. adding supports. However, all three methods have significant drawbacks. Increasing the pile diameter significantly increases the amount of concrete used, the amount of earthwork drilled, and the project cost, and also places higher demands on the capabilities of construction equipment. Increasing the reinforcement ratio can improve the pile stiffness to some extent, but its effect is limited, and when the reinforcement ratio exceeds the economical reinforcement ratio, its cost-effectiveness drops sharply. Furthermore, excessively dense reinforcement may lead to loose concrete pouring, which in turn affects the quality of the pile. Supports can provide resistance to reduce foundation pit deformation, but their presence not only increases construction costs but also complicates the construction process, thus extending the construction period.

[0004] On the other hand, the tensile and compressive strengths of steel are far higher than those of concrete. If the pile body can be locally reinforced in the region of maximum bending moment below ground level, its stress performance can be improved most effectively, while avoiding the enormous waste associated with reinforcing the entire pile segment. Therefore, developing a technology capable of precisely and reliably implementing local reinforcement in specific sections of the pile body has significant engineering value and broad market prospects. Summary of the Invention

[0005] This invention aims to address the shortcomings of existing technologies by providing a locally flexurally reinforced cast-in-place pile for foundation pits and its construction method. This cast-in-place pile structure is reinforced only in the region of maximum bending moment, making it economical and efficient. The construction method is simple and easy to operate, and the reinforcing components of the steel hoop system can be accurately positioned and reliably fixed through a mechanical automatic triggering mechanism.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A locally flexurally reinforced cast-in-place support pile for foundation pits is characterized by comprising a stepped pile hole with a "small-large-small" diameter, concrete, a reinforcing cage, and a steel hoop system. The stepped pile hole with a "small-large-small" diameter has a partially enlarged section. A push-in joint is installed at the bottom of the steel hoop system. The push-in joint of the steel hoop system is partially embedded in the partially enlarged section of the pile hole and fixed. The reinforcing cage is lowered into the steel hoop system, and the stepped pile hole is filled with concrete to form a whole.

[0008] The steel enclosure system includes a steel casing, steel wing plates, and push-in joints. The steel wing plates are fixed to the bottom of the steel casing via push-in joints.

[0009] The push-in joint includes a longitudinal shaft, a bushing, and a torsion spring. One end of the bushing is annular and fitted onto the longitudinal shaft, while the other end is welded to the steel casing. The torsion spring is fitted onto the longitudinal shaft and is pre-compressed and installed between the steel casing and the steel wing plate. Its function is to provide the driving force for the steel wing plate to spring open.

[0010] A construction method for locally flexurally reinforced cast-in-place support piles for foundation pits, comprising the following steps:

[0011] SP1. Drilling construction: Use a drilling rig with a diameter of d to drill and form the borehole wall. Continue drilling until the top of the local enlarged section. Then switch to a drilling rig with a diameter of D to continue drilling and form the local enlarged section. Then switch back to a drilling rig with a diameter of d to drill to the designed pile bottom elevation to complete the pile hole construction.

[0012] SP2. Lowering the steel hoisting system: The steel hoisting system with push-in joints installed at the bottom is hoisted and vertically lowered into the pile hole;

[0013] SP3. Push-in joint trigger: When the push-in joint is lowered to the partially enlarged section, the steel wing plate pops out and is supported on the step surface of the partially enlarged section, thereby fixing the steel hoop system.

[0014] SP4. Lowering the steel cage: The steel cage is pre-tied with longitudinal bars and stirrups, hoisted and lowered into the pile hole;

[0015] SP5. Concrete pouring: Concrete is poured into the pile hole to form a complete cast-in-place pile.

[0016] In step 1, the locally enlarged hole section is located 0.3 to 0.5 times the embedment depth H of the support pile below the excavation surface of the foundation pit.

[0017] The height of the locally enlarged section is at least 20cm. The minimum difference between diameter D and diameter d is 40cm.

[0018] The steel wing plate mentioned in step 3 is arc-shaped and closely adheres to the outside of the steel casing when the steel wing plate is closed. At least four wing plates are symmetrically distributed evenly around the steel casing. The height of the steel wing plate is less than the height of the local enlarged hole section and not less than 10cm. The thickness t is not less than 4mm and the length is less than 0.5 (Dd) and not less than 10cm.

[0019] The top of the steel casing is located 0.3 to 0.5 times the excavation depth h above the excavation surface, and its thickness is not less than 4 mm. The outer diameter of the steel casing is controlled as dt to ensure that the steel hoop system is laid tightly against the borehole wall.

[0020] The push-in joint triggering mechanism described in step 3 is a "constraint-release" mechanism. In the narrow straight hole section with a diameter of d, the lateral constraint provided by the drill groove wall forces the steel wing plate to remain in a retracted state. When the push-in joint enters the pre-drilled local enlarged hole section with a diameter of D below, the lateral constraint disappears, and the built-in steel wing plate pops out instantly and gets stuck on the "shoulder" of the local enlarged hole section, thereby reliably supporting the entire steel hoop system at the predetermined depth.

[0021] In step 3, the push-in connector is completely wrapped with water-resistant grease after assembly to form a physical barrier and prevent sand and mud from entering and causing jamming.

[0022] Before lowering the steel cage in step 4, check the verticality of the steel hoop system and ensure that the error is within 1% before construction can proceed.

[0023] In step 5, shear keys are welded to the inner side of the steel casing to increase the bonding effect between the concrete and the steel hoop system.

[0024] The beneficial effects of this invention are as follows: The steel hoop system adopted in this invention can effectively bear the tensile force on the tension side of the cast-in-place pile, reduce concrete cracking and premature yield strength of longitudinal reinforcement, improve the tensile performance of the cast-in-place pile, thereby achieving greater bending stiffness and reducing pile deformation; the steel hoop system can act as a confinement for the concrete, reducing the buckling phenomenon of longitudinal reinforcement caused by its compressive breakage, enhancing the compressive characteristics of the cast-in-place pile, thereby achieving greater bending stiffness and reducing pile deformation; compared with concrete, the steel hoop system has a larger elastic modulus. Replacing a corresponding volume of concrete with steel hoops can improve the bending stiffness of cast-in-place piles. The steel flanges, deployed in the locally enlarged section and erected on the steps, enhance the anchoring effect of the steel casing, allowing it to fully exert its tensile effect, thereby further enhancing the strength utilization efficiency of the cast-in-place pile and reducing pile deformation. The locally bending-enhanced cast-in-place piles used in this invention, by locally reinforcing the pile body at the point of maximum bending moment near the excavation face, can effectively reduce the pile diameter, concrete usage, and steel reinforcement usage. This offers advantages such as easy construction, cost savings, high bending stiffness, and strong deformation control. Attached Figure Description

[0025] Figure 1 This is a schematic cross-sectional view of the locally flexurally reinforced cast-in-place support pile of the present invention;

[0026] Figure 2 This is a schematic diagram of the steel hoop system for cast-in-place piles according to the present invention;

[0027] Figure 3 This is a schematic diagram of the push-in joint of the steel hoop system of the present invention;

[0028] In the diagram: 1-Drill trench wall; 2-Partial reaming section; 3-Steel hoop system; 4-Longitudinal reinforcement; 5-Stirrup; 6-Concrete; 7-Steel casing; 8-Steel flange; 9-Push-in joint; 10-Longitudinal axis; 11-Busset; 12-Torsion spring;

[0029] The following will describe in detail, with reference to the accompanying drawings, embodiments of the invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0031] A locally flexurally reinforced cast-in-place support pile for foundation pits is characterized by comprising a stepped pile hole with a "small-large-small" diameter, concrete 6, a reinforcing cage, and a steel hoop system 3. The stepped pile hole with a "small-large-small" diameter has a partially enlarged section 2. A push-in joint 9 is installed at the bottom of the steel hoop system 3. The push-in joint 9 of the steel hoop system 3 is partially embedded in the partially enlarged section 2 of the pile hole and fixed. The reinforcing cage is lowered into the steel hoop system 3. The stepped pile hole is filled with concrete 6 to form a whole.

[0032] The steel enclosure system 3 includes a steel casing 7, steel wing plates 8, and a push-in connector 9. The steel wing plates 8 are fixed to the bottom of the steel casing 7 via the push-in connector 9.

[0033] The push-in connector 9 includes a longitudinal shaft 10, a bushing 11, and a torsion spring 12. One end of the bushing 11 is annularly fitted onto the longitudinal shaft 10, and the other end is welded to the steel casing 7. The torsion spring 12 is fitted onto the longitudinal shaft 10 and is pre-compressed and installed between the steel casing 7 and the steel wing plate 8, always providing the steel wing plate 8 with an outward opening torque. After assembly, the entire push-in connector 9 is completely wrapped with water-resistant grease to form a physical barrier and prevent sand and mud from entering and causing jamming.

[0034] A construction method for locally flexurally reinforced cast-in-place support piles for foundation pits, comprising the following steps:

[0035] SP1. Drilling construction: Use a drilling rig with a diameter of d to drill and form the borehole wall 1. Continue drilling until the top of the partially enlarged section 2. Then switch to a drilling rig with a diameter of D to continue drilling and form the partially enlarged section 2. Then switch back to a drilling rig with a diameter of d to drill to the designed pile bottom elevation and complete the pile hole construction.

[0036] SP2. Lowering the steel hoisting system 3: The steel hoisting system 3, with the push-in connector 9 installed at the bottom, is hoisted and vertically lowered into the pile hole;

[0037] SP3. Push-in connector 9 trigger: When the push-in connector 9 is lowered to the partially enlarged hole section 2, the steel wing plate 8 pops out and is supported on the step surface of the partially enlarged hole section 2, thereby fixing the steel hoop system 3.

[0038] SP4. Lowering the steel cage: The steel cage is pre-tied with longitudinal bars 4 and stirrups 5, then hoisted and lowered into the pile hole;

[0039] SP5. Pouring Concrete 6: Pouring concrete 6 into the pile hole to form a complete cast-in-place pile.

[0040] In step 1, the partially enlarged hole section 2 is located 0.3 to 0.5 times the embedment depth H of the support pile below the excavation surface of the foundation pit.

[0041] The height of the partially enlarged hole section 2 is at least 20cm.

[0042] The steel wing plate 8 is arc-shaped and fits tightly against the outside of the steel casing 7 when closed. At least four wing plates are evenly and symmetrically distributed around the steel casing 7 and should be arranged symmetrically. The height of the steel wing plate 8 is less than the height of the local enlarged hole section 2 and not less than 10cm. The thickness t is not less than 4mm and the length is less than 0.5 (Dd) and not less than 10cm.

[0043] The top of the steel casing 7 is located 0.3 to 0.5 times the excavation depth h of the foundation pit above the excavation surface, with a thickness of not less than 4 mm and an outer diameter controlled as dt, to ensure that the steel hoop system 3 is placed tightly against the borehole wall 1.

[0044] The triggering mechanism of the push-in connector 9 in step 3 is a "constraint-release" mechanism. In the narrow straight hole section with a diameter of d, the lateral constraint provided by the drilled groove wall forces the steel wing plate 8 to remain in a retracted state. When the push-in connector 9 enters the pre-drilled local enlarged hole section 2 with a diameter of D below, the lateral constraint disappears, and the built-in steel wing plate 8 pops out instantly and gets stuck on the "shoulder" of the local enlarged hole section 2, thereby reliably supporting the entire steel hoop system 3 at the predetermined depth.

[0045] Before lowering the steel cage in step 4, check the verticality of the steel hoop system 3 and ensure that the error is within 1% before construction can proceed.

[0046] In step 5, shear keys are welded to the inner side of the steel casing 7 to increase the bonding effect between the concrete 6 and the steel hoop system 3.

[0047] Example 1

[0048] A foundation pit has an excavation depth H=9m, and bored cast-in-place piles with a diameter of 1.0m and a length of 18m are used as support piles. To enhance its bending resistance, it is decided to use this invention for local reinforcement.

[0049] (I) Component Preparation

[0050] 1. Steel casing 7: Made of Q235B steel plate, 6m in length (planned coverage depth of about 6m~12m), 0.95m in diameter, and 10mm in wall thickness. Several rows of Φ16mm round steel are evenly welded inside the steel casing 7 as shear keys.

[0051] 2. Push-in connector 9: welded to the bottom of the steel casing 7.

[0052] Bushing 11: Made of 10mm thick steel plate, it is approximately fan-shaped, with one end welded to the bottom of the steel sleeve 7 and the other end fitted onto the longitudinal shaft 10;

[0053] Steel wing plate 8: There are four pieces in total, symmetrically arranged, made of 25mm thick steel plate, and the shape is approximately fan-shaped. When closed, the outer edge of the steel wing plate 8 is flush with the outer wall of the steel casing 7.

[0054] Longitudinal axis 10: Made of solid 45# steel with a diameter of 25mm.

[0055] Torsion spring 12: The torsion spring 12 is made of 316 stainless steel. Its stiffness coefficient k has been calculated and selected to ensure that the driving torque it provides is sufficient to overcome the mud resistance.

[0056] Apply water-resistant grease evenly to the entire push-in connector 9.

[0057] (II) Construction Process

[0058] 1. Drilling (as shown in the attached document) Figure 1 ):

[0059] Drill to a depth of 12m using a rotary drilling rig with d=Φ1.0m;

[0060] Remove the drill rod and replace it with a drill bit with a diameter of 1.2m. Drill down another 0.3m from a depth of 12m to form a local enlarged section 2.

[0061] The drill rod was removed again, and a Φ1.0m drill bit was replaced. Drilling continued until the designed elevation of 18m was reached.

[0062] 2. Lowering the steel hoop system 3 (as attached) Figure 2 ): .

[0063] The prefabricated steel hoisting system 3 is vertically lifted by a crane and slowly placed into the pile hole. At this time, the steel wing plate 8 is in a retracted state under the constraint of the drilled groove wall 1.

[0064] 3. Push-in connector trigger (see appendix) Figure 3 ):

[0065] When the steel casing 7 is lowered to the partially enlarged hole section 2, the hole wall of the constrained steel wing plate 8 suddenly disappears.

[0066] The elastic potential energy stored in the torsion spring 12 is released instantly, generating a huge rotational torque.

[0067] Driven by spring force, the steel wing plate 8 rotates rapidly outward about 90° around the longitudinal axis 10 until it is tightly pressed against the step of the partially enlarged hole section 2.

[0068] The weight of the entire steel hoop system 3 and the subsequent loads will be effectively transferred to the stable soil layer of the borehole wall through these four steel wing plates 8, achieving self-locking fixation.

[0069] 4. Hole cleaning and lowering of the reinforcing cage: standard procedure, which will not be elaborated here.

[0070] 5. Concrete Pouring 6: C30 concrete is poured using the tremie method. The concrete fills the pile hole, encloses the reinforcing cage, and fills all the spaces inside and outside the steel hoop system 3. It is then tightly bonded to the steel hoop system 3 via shear keys, ultimately forming a composite pile.

[0071] The locally reinforced grouted pile used in this invention overcomes the disadvantages of traditional flexural reinforcement technology, such as high cost, complicated construction, and long construction period. The steel hoop system effectively bears the tensile force on the tension side of the grouted pile, slows down concrete cracking and prevents the longitudinal reinforcement from reaching its yield strength prematurely, thereby improving the tensile performance of the grouted pile and achieving greater flexural stiffness and reducing pile deformation. The steel hoop system also acts as a confinement for the concrete, mitigating the buckling of the longitudinal reinforcement caused by compressive breakage, enhancing the compressive characteristics of the grouted pile, and thus achieving greater flexural stiffness and reducing pile deformation. Compared to concrete, the steel hoop system has a higher modulus of elasticity. Replacing a corresponding volume of concrete with steel hoop can improve the bending stiffness of cast-in-place piles. The steel hoop system, in which the flanges are deployed and erected on steps in the locally enlarged section, enhances the anchoring effect of the steel casing, allowing it to fully exert its tensile effect, thereby further enhancing the strength utilization efficiency of the cast-in-place pile and reducing deformation. The new type of locally reinforced bending cast-in-place pile, by locally reinforcing the pile body at the point of maximum bending moment near the excavation face, can effectively reduce the pile diameter, concrete usage, and steel reinforcement requirements. It offers advantages such as easy construction, cost savings, high bending stiffness, and strong deformation control.

[0072] In the description of the invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0073] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0074] In this invention, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0075] The invention has been described above with reference to the accompanying drawings. Obviously, the specific implementation of the invention is not limited to the above-described manner. Any improvements made using the inventive concept and technical solution, or direct application to other situations without modification, are all within the scope of protection of the invention.

Claims

1. A local bending-resistant reinforced type of a cast-in-place foundation pit support pile, characterized by, The invention discloses a method for constructing a cast-in-place pile, which comprises a "small-large-small" diameter stepped pile hole, concrete (6), a steel cage and a steel casing system (3), the "small-large-small" diameter stepped pile hole has a local hole expanding section (2), the bottom of the steel casing system (3) is provided with a push-in joint (9), the push-in joint (9) of the steel casing system (3) is partially embedded in the local hole expanding section (2) of the pile hole and is fixed, the steel cage is lowered into the steel casing system (3), and the stepped pile hole is filled with the concrete (6) to form a whole.

2. The partially anti-buckling reinforced type of cast-in-place foundation pit support pile according to claim 1, characterized in that, The steel casing system (3) comprises a steel casing (7), a steel wing plate (8) and the push-in joint (9), and the steel wing plate (8) is fixed to the bottom of the steel casing (7) through the push-in joint (9).

3. The partially anti-buckling reinforced type of cast-in-place foundation pit support pile according to claim 2, characterized in that, The push-in joint (9) comprises a longitudinal shaft (10), a shaft sleeve (11) and a torsion spring (12), one end of the shaft sleeve (11) is annularly sleeved on the longitudinal shaft (10), the other end is welded on the steel casing (7), the torsion spring (12) is sleeved on the longitudinal shaft (10), and the torsion spring (12) is pre-compressed and arranged between the steel casing (7) and the steel wing plate (8).

4. The construction method of a local anti-bending reinforced foundation bored pile according to claim 3, characterized in that, The steps are as follows: SP1. Drilling construction: a drill with a diameter of d is used to drill a hole to form a hole wall (1), drilling is continued to the top position of the local hole expanding section (2), a drill with a diameter of D is used to continue drilling, the local hole expanding section (2) is formed, and then the drill with the diameter of d is used to drill to the designed pile bottom elevation, and the pile hole construction is completed; SP2. Lowering the steel casing system (3): the steel casing system (3) provided with the push-in joint (9) at the bottom is hoisted and vertically lowered into the pile hole; SP3. Triggering the push-in joint (9): when the push-in joint (9) is lowered to the local hole expanding section (2), the steel wing plate (8) is popped out and supported on the step surface of the local hole expanding section (2), and the fixing of the steel casing system (3) is realized; SP4. Lowering the steel cage: the steel cage is bound with longitudinal reinforcement (4) and stirrup (5) in advance, hoisted and lowered into the pile hole; SP5. Pouring concrete (6): pouring concrete (6) into the pile hole to form a complete cast-in-place pile.

5. The construction method of a local anti-bending reinforced foundation bored pile according to claim 4, characterized in that, The local hole expanding section (2) in step 1 is located below 0.3-0.5 times the embedded depth H of the supporting pile.

6. The construction method of a local anti-bending reinforced foundation bored pile according to claim 5, characterized in that, The height of the local hole expanding section (2) is at least 20 cm, and the minimum difference between the diameter D and the diameter d is 40 cm.

7. The construction method of a local anti-bending reinforced foundation bored pile according to claim 4, characterized in that, In step 3, the steel wing plate (8) is in the shape of a circular arc, closely adheres to the outside of the steel casing (7) when the steel wing plate (8) is closed, is symmetrically distributed along the steel casing (7) for at least four times, the height of the steel wing plate (8) is less than the height of the local hole expanding section (2) and cannot be less than 10 cm, the thickness t is not less than 4 mm, the length is less than 0.5 (D-d) and not less than 10 cm; the top of the steel casing (7) is located above 0.3-0.5 times the excavation depth h of the foundation pit, the thickness is not less than 4 mm, the outer diameter is controlled to be d-t, and the steel casing system (3) is closely adhered to the hole wall during lowering.

8. The construction method of a local anti-bending reinforced foundation bored pile according to claim 4, characterized in that, The push-in joint (9) triggering mechanism in step 3 is a "constraint-release" mechanism, in a narrow straight hole section with diameter d, the lateral constraint provided by the drilling wall forces the steel wing plate (8) to remain in a folded state, when the push-in joint (9) enters the lower pre-drilled partial expansion section (2) with diameter D, the lateral constraint disappears, the built-in steel wing plate (8) is instantly ejected and clamped on the "shoulder" of the partial expansion section (2), thereby reliably supporting the entire steel casing system (3) at the predetermined depth.

9. The construction method of a local anti-bending reinforced foundation bored pile according to claim 4, characterized in that, Before the steel reinforcement cage is lowered in step 4, the verticality of the steel casing system (3) is checked to ensure that the error is within 1% before construction.

10. The construction method of a local anti-bending reinforced foundation bored pile according to claim 4, characterized in that, In step 5, shear keys are welded on the inside of the steel casing (7) to increase the bonding effect of the concrete (6) and the steel casing system (3).

Images