Test pile for blocking negative skin friction and its pouring method

Abstract

The application provides a kind of blocking negative friction resistance test test pile and its pouring method, belongs to the technical field of foundation pile pouring, test pile is broken pile structure, including multiple section pile body and the foundation pile negative friction resistance blocking type test element buried between adjacent two section pile body;Pile body includes reinforcement cage and the concrete layer poured outside reinforcement cage;Reinforcement cage includes multiple round equidistant distribution test main reinforcement;Foundation pile negative friction resistance blocking type test element includes element I and element II;Element I and element II all include upper blocking plate, protective partition layer, lower blocking plate and reinforcement stress meter connecting piece.The application can reduce cost, shorten construction period, improve economic benefit and negative friction resistance value accuracy.

Description

Technical Field

[0001] This invention belongs to the technical field of foundation pile casting, and specifically discloses a test pile for blocking negative skin friction and its casting method. Background Technology

[0002] When sites formed by thick, disordered backfilling, such as open-pit mining areas, natural gullies, and reclaimed land, are used as building foundations, site reinforcement can effectively strengthen the site. However, post-construction settlement will still occur, which may result in negative skin friction of the pile foundations constructed later, thus affecting the safety performance of the building structure and causing certain losses to building safety and people's lives and property.

[0003] Currently, there is very little research in the industry on the negative skin friction of post-cast piles in areas with thick, disordered backfill, and the accuracy of negative skin friction values ​​is low. There are only a few common methods for testing the negative skin friction of foundation piles:

[0004] 1. Preliminary calculation: The "Technical Specification for Building Pile Foundations" provides calculation formulas that can be used for estimation during pile foundation design. However, comparison and analysis with the results of on-site testing of pile side stress, tensile load, etc., confirms that the calculation formula is relatively conservative. Designing according to this formula will increase the project cost and cause some waste.

[0005] 2. Pile side loading: The pile body is equipped with blocking components, and pressure is applied to the soil around the pile through pile side loading; it has high site requirements, requires a relatively large site, and is expensive, has a long construction period, and is also inconsistent with the on-site construction environment;

[0006] 3. Simulation device testing: Various pile foundation models are used to test the negative skin friction around the pile. However, the results differ significantly from the actual field conditions, and the accuracy of the negative skin friction value is very low. Summary of the Invention

[0007] This invention provides a test pile for blocking negative skin friction testing and its casting method, so as to reduce costs, shorten the construction period, improve economic benefits and the accuracy of negative skin friction value.

[0008] This invention provides a test pile for testing negative skin friction using a broken pile structure, comprising multiple pile segments and a negative skin friction test element embedded between adjacent pile segments. The pile segment includes a reinforcing cage and a concrete layer poured outside the reinforcing cage. The reinforcing cage includes multiple circular, equally spaced test main reinforcement bars. The negative skin friction test element includes element I and element II. Both element I and element II include an upper blocking plate, a protective partition layer, a lower blocking plate, and a reinforcing bar stress gauge connector. The upper blocking plate, protective partition layer, and lower blocking plate are all annular structures. The blocking plates are installed on the upper and lower surfaces of the protective partition layer, respectively. The central holes of all three are coaxially aligned and axially connected as grouting holes. Axially connected stress gauge perforations are provided according to the number and location of the test main reinforcement bars in each pile segment. The diameter of the central hole in the protective partition layer is smaller than that of the central hole in the upper blocking plate. A connecting wire protection groove is provided on the upper surface of the protective partition layer, corresponding one-to-one with the stress gauge perforations. The first end communicates with the stress gauge perforation, and the second end is located between the central hole of the protective partition layer and the central hole of the upper blocking plate. The reinforcing bar stress gauge connector includes the reinforcing bar stress gauge and its position... The upper and lower connecting bars at both ends of the rebar stress gauge are connected by a rebar stress gauge connector that passes through the stress gauge hole. The upper end of the upper connecting bar and the lower end of the lower connecting bar are located outside the stress gauge hole. The connecting wire of the rebar stress gauge is led out from the second end of the connecting wire protection groove. Component II has an axially penetrating connecting wire hole at the second end of the connecting wire protection groove. Component I is installed at the lowest broken pile position, and Component II is installed at the broken pile position above Component I. The upper ends of the upper connecting bars and the lower ends of the lower connecting bars of Component I and Component II are welded to the test main reinforcement of the two adjacent pile sections, respectively. In Component I, the rebar should... After the connection line of the force gauge is led out from the second end of the connection line protection groove, it passes through the connection line holes of all components II in sequence from bottom to top; in component II installed at the uppermost broken pile position, the connection line of the rebar stress gauge is led out from the second end of the connection line protection groove; in component II located below the uppermost broken pile position, the connection line of the rebar stress gauge is led out from the second end of the connection line protection groove, and passes through the connection line holes of all components II above in sequence from bottom to top; the concrete layer of each pile body is a ring structure, with the inner diameter matching the diameter of the central hole of the protective partition layer and the outer diameter matching the diameter of the pile borehole.

[0009] Furthermore, the steel cage of each pile section also includes multiple auxiliary main bars distributed in a circular shape at equal intervals. The auxiliary main bars and test main bars are staggered, and the two ends of the auxiliary main bars are welded to the upper and lower blocking plates of the two adjacent sets of negative skin friction blocking test elements.

[0010] Furthermore, the two ends of the steel stress gauge are respectively connected to the upper and lower connecting bars via threaded connections.

[0011] Furthermore, the protective partition layer is made of polystyrene board.

[0012] Furthermore, the upper connecting rib and the upper blocking plate are welded together, and the lower connecting rib and the lower blocking plate are welded together.

[0013] The present invention also provides a method for casting the above-mentioned blocking negative skin friction test pile, comprising the following steps:

[0014] S1, Drill holes at the predetermined locations on the site;

[0015] S2, lower the reinforcing cage and install the negative skin friction blocking test element for the foundation pile;

[0016] Weld the upper end of the upper connecting bar and the lower end of the lower connecting bar in component I to the test main bars on both sides of the lowest broken pile position, respectively.

[0017] During the lowering of the reinforcing cage, component II is installed sequentially from bottom to top along the reinforcing cage. The upper end of the upper connecting bar and the lower end of the lower connecting bar in component II are welded to the test main bars on both sides of the broken pile position, respectively.

[0018] For each set of component II installed, the connecting wires of the reinforcing bar stress gauges in component I and component II below the set of component II are passed through the connecting wire holes of the set of component II until all components II are installed.

[0019] S3, Install the grouting conduit along the grouting hole. The bottom end of the grouting conduit is located below component I. The outer diameter of the grouting conduit is adapted to the diameter of the central hole of the protective partition layer.

[0020] S4, concrete is poured through the grouting pipe;

[0021] S5. After the concrete reaches the required age, the grouting pipe and the concrete inside it, as well as the concrete below the grouting pipe, are removed to form a test pile for blocking negative skin friction.

[0022] The above-mentioned pouring method also includes step S0, which involves conducting site dynamic penetration tests and shear wave velocity tests to determine the location of the test pile and the embedment depth of the negative skin friction blocking test element of the foundation pile.

[0023] In step S1, the pile foundation is drilled using a rotary drilling rig. The drilling depth is determined based on the result of step S0 and the pile enters the bearing stratum. After drilling, the pile is cleaned.

[0024] In the above-mentioned pouring method, the grouting pipe is tied to the reinforcing cage, and multiple grouting holes are set at the position between two adjacent sets of negative skin friction blocking test elements of the foundation piles.

[0025] In the above-mentioned pouring method, a conical chute funnel is installed at the top of the grouting conduit; the grouting conduit is made of multiple sections of PVC pipe connected by snap-fit ​​and coated with adhesive.

[0026] The present invention has the following beneficial effects:

[0027] 1. The above-mentioned test pile for the blocking type negative skin friction test is designed with a blocking stress gauge. After the pile is completed, core drilling is required to ensure that the pile breakage location is the axial force of the negative skin friction blocking test element of the foundation pile, so that the steel stress gauge is not affected by the concrete of the cast-in-place pile. The negative skin friction of the soil layer on the side of the pile is calculated through the axial force test results at the pile breakage location, which greatly improves the accuracy of the negative skin friction value.

[0028] 2. The reinforcing cage uses a combination of test steel bars and auxiliary steel bars to ensure both the integrity of the test data and the overall structural stability of the pile;

[0029] 3. PVC material is selected for the grouting pipe during pouring, which is easy to remove and more economical than steel pipe;

[0030] 4. In the early stages of pile foundation design, many tests may be required to determine pile foundation parameters, such as self-balancing tests to determine the bearing capacity of the pile foundation. The casting method provided by this invention can perfectly avoid damage to the test equipment during the pile foundation casting process. It is a relatively scientific and advanced method for casting complex test reinforced concrete cast-in-place test piles. It can be used to complete the casting of negative skin friction test piles (discontinuous pile structure) and can also be used for the casting of other test piles that require the embedding of test equipment (self-balancing test equipment, etc.). It is worth promoting and using on a large scale.

[0031] In summary, this invention features a simple structure, reasonable design, high controllability, and relatively high economic benefits. Compared with pile-side counterweight testing, the site requirements for testing negative skin friction using the test pile provided by this invention are significantly reduced, the test area is decreased, the construction period is shortened, and costs are effectively reduced. Compared with pre-calculation and simulation device tests, the accuracy of negative skin friction value is greatly improved. The casting method ensures the overall stability of the test pile and meets the requirements of negative skin friction resistance testing, improving the applicability of the casting method for negative skin friction resistance test piles. This further advances the technology for measuring negative skin friction resistance, which is conducive to improving the research on negative skin friction resistance and can lay a solid foundation for determining its laws in the future. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 A schematic diagram of the structure of the test pile for the blocking negative skin friction test;

[0034] Figure 2This diagram shows the arrangement of the reinforcing cage, the negative skin friction interruption test element for the foundation pile, and the grouting conduit in the foundation pile borehole.

[0035] Figure 3 An enlarged view of the connection between the reinforcing cage and the negative skin friction blocking test element of the foundation pile;

[0036] Figure 4 This is a schematic diagram of component II in the negative skin friction blocking test element for foundation piles.

[0037] Figure 5 This is an exploded view of component II;

[0038] Figure 6 This is a schematic diagram of the protective isolation layer of component I in the negative skin friction blocking test element for foundation piles;

[0039] Figure 7 This is a diagram showing the wiring of the connecting wire when the rebar stress gauge connector passes through component II;

[0040] Figure 8 A schematic diagram showing the connection between the grouting pipe and the conical chute funnel;

[0041] Figure 9 Diagram showing the binding of the grouting conduit;

[0042] Figure 10 for Figure 9 Top view.

[0043] In the diagram: 1-Pile body; 1.1-Test main reinforcement; 1.2-Auxiliary main reinforcement; 2-Pile negative skin friction interruption test element; 2.1-Upper interruption plate; 2.2-Protective partition layer; 2.3-Lower interruption plate; 2.4-Grouting hole; 2.5-Stress gauge perforation; 2.6-Connecting wire protection groove; 2.7-Connecting wire perforation; 2.8-Reinforcing bar stress gauge connector; 2.9-Reinforcing bar stress gauge; 2.10-Upper connecting reinforcement; 2.11-Lower connecting reinforcement; 2.12-Connecting wire; 3-Pile borehole; 4-Grouting guide pipe; 4.1-Grouting hole; 4.2-Snap fastener; 5-Conical chute funnel; 6-Steel wire; 7-Ground. Detailed Implementation

[0044] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] This embodiment provides a test pile for blocking negative skin friction testing, which is a broken pile structure, including multiple pile sections 1 and a negative skin friction blocking test element 2 embedded between two adjacent pile sections 1.

[0047] The pile body 1 includes a steel cage and a concrete layer poured outside the steel cage; the steel cage includes multiple test main bars 1.1 distributed in a circular shape at equal intervals.

[0048] The negative skin friction test element 2 for foundation piles includes element I and element II. Both element I and element II include an upper blocking plate 2.1, a protective partition layer 2.2, a lower blocking plate 2.3, and a rebar stress gauge connector 2.8. The upper blocking plate 2.1, the protective partition layer 2.2, and the lower blocking plate 2.3 are all annular structures. The upper blocking plate 2.1 and the lower blocking plate 2.3 are respectively installed on the upper and lower surfaces of the protective partition layer 2.2. The central holes of the three are coaxially arranged and axially connected as grouting holes 2.4. Axially connected stress gauges are set according to the number and position of the main reinforcing bars 1.1 in each pile section 1. The perforation 2.5 is included; the diameter of the central hole of the protective partition layer 2.2 is smaller than the diameter of the central hole of the upper blocking plate 2.1. A connecting wire protection groove 2.6 is provided on the upper surface of the protective partition layer 2.2, which corresponds one-to-one with the stress gauge perforation 2.5. The first end communicates with the stress gauge perforation 2.5, and the second end is located between the central hole of the protective partition layer 2.2 and the central hole of the upper blocking plate 2.1. The reinforcing bar stress gauge connector 2.8 includes a reinforcing bar stress gauge 2.9 and upper connecting bars 2.10 and lower connecting bars 2.11 located at both ends of the reinforcing bar stress gauge 2.9. Component 2.8 passes through the stress gauge hole 2.5. The upper end of the upper connecting bar 2.10 and the lower end of the lower connecting bar 2.11 are located outside the stress gauge hole 2.5. The connecting line 2.12 of the steel stress gauge 2.9 is led out from the second end of the connecting line protection groove 2.6. The second end of the connecting line protection groove 2.6 in component II is provided with an axially penetrating connecting line hole 2.7. Component I is installed at the lowest broken pile position, and component II is installed at the broken pile position above component I. The upper end of the upper connecting bar 2.10 and the lower end of the lower connecting bar 2.11 of components I and II are respectively connected to the test main of the two adjacent pile sections 1. 1.1 Welding of reinforcing bars; In component I, the connecting wire 2.12 of the reinforcing bar stress gauge 2.9 is led out from the second end of the connecting wire protection groove 2.6 and passes through the connecting wire through holes 2.7 of all components II from bottom to top; In component II installed at the uppermost broken pile position, the connecting wire 2.12 of the reinforcing bar stress gauge 2.9 is led out from the second end of the connecting wire protection groove 2.6; In component II located below the uppermost broken pile position, the connecting wire 2.12 of the reinforcing bar stress gauge 2.9 is led out from the second end of the connecting wire protection groove 2.6 and passes through the connecting wire through holes 2.7 of all components II above from bottom to top.

[0049] Each section of the pile body 1 has a ring-shaped concrete layer with an inner diameter that matches the diameter of the central hole of the protective partition layer 2.2 and an outer diameter that matches the diameter of the pile borehole 3.

[0050] Furthermore, each pile body 1's steel cage also includes multiple auxiliary main bars 1.2 distributed in a circular shape at equal intervals. The auxiliary main bars 1.2 and the test main bars 1.1 are staggered. The two ends of the auxiliary main bars 1.2 are welded to the upper blocking plate 2.1 and the lower blocking plate 2.3 of the adjacent two sets of pile negative skin friction blocking test elements 2, respectively, to ensure the overall stability of the steel cage.

[0051] Furthermore, the two ends of the steel stress gauge 2.9 are respectively connected to the upper connecting bar 2.10 and the lower connecting bar 2.11 via threaded connections.

[0052] Furthermore, both the upper blocking plate 2.1 and the lower blocking plate 2.3 are steel plates, and the protective partition layer 2.2 is a polystyrene board.

[0053] Furthermore, the upper connecting rib 2.10 and the upper blocking plate 2.1 are welded together, and the lower connecting rib 2.11 and the lower blocking plate 2.3 are welded together.

[0054] Example 2

[0055] This embodiment provides a method for casting the above-mentioned blocking negative skin friction test pile, including the following steps:

[0056] S0, conduct site dynamic penetration tests and shear wave velocity tests to determine the location of the test pile and the embedment depth of the negative skin friction blocking test element 2 of the foundation pile;

[0057] S1, Drill holes at the predetermined locations on the site;

[0058] S2, lower the reinforcing cage and install the negative skin friction blocking test element 2 for the foundation pile;

[0059] Weld the upper end of the upper connecting bar 2.10 and the lower end of the lower connecting bar 2.11 in component I to the test main bars 1.1 on both sides of the lowest broken pile position, respectively;

[0060] During the lowering of the reinforcing cage, component II is installed sequentially from bottom to top along the reinforcing cage. The upper end of the upper connecting bar 2.10 and the lower end of the lower connecting bar 2.11 in component II are welded to the test main bars 1.1 on both sides of the broken pile position, respectively.

[0061] For each set of component II installed, the connecting wire 2.12 of the steel stress gauge 2.9 in component I and component II below the set of component II is passed through the connecting wire through hole 2.7 of the set of component II and tied to the corresponding test main reinforcement 1.1 until all components II are installed. The connecting wire 2.12 of the steel stress gauge 2.9 is led out from the second end of the connecting wire protection groove 2.6 of the uppermost component II and connected to the automatic data acquisition instrument.

[0062] S3, install grouting conduit 4 along grouting hole 2.4. The bottom end of grouting conduit 4 is located below component I. The outer diameter of grouting conduit 4 is adapted to the diameter of the central hole of protective partition layer 2.2.

[0063] S4, concrete is poured through grouting pipe 4;

[0064] S5. After the concrete reaches the required age, the grouting pipe 4 and the concrete inside it, as well as the concrete below the grouting pipe 4, are removed to form a test pile for blocking negative skin friction.

[0065] In step S1, the pile drilling rig is used to form the hole 3. The hole depth is determined according to the result of step S0 and enters the bearing layer. After the hole is formed, the hole is cleaned.

[0066] In the above-mentioned pouring method, the grouting pipe 4 is tied to the reinforcing cage, and multiple grouting holes 4.1 are set at the position between the negative skin friction blocking test elements 2 of two adjacent piles.

[0067] In the above-mentioned pouring method, a conical chute funnel 5 is installed at the top of the grouting conduit 4; the grouting conduit 4 is made of multiple sections of PVC pipe connected by snap fasteners 4.2 and coated with adhesive.

[0068] Example 3

[0069] This embodiment takes an example of a test pile with 8 Φ18mm main test bars 1.1 and 8 Φ18mm auxiliary main bars 1.2 in a reinforcing cage, a pile borehole 3 with a diameter of 820-850mm, and a grouting conduit 4 with a diameter of 110mm, to introduce the specific parameters and pouring method of the test pile for the blocking negative skin friction test.

[0070] In step S0, before selecting the location and test point depth of the negative skin friction test pile, a site dynamic penetration test and a shear wave velocity test are conducted. The location of the test pile is selected based on the results of the site dynamic penetration test and the shear wave velocity test. The test point depth of the pile body is selected at locations with a backfill thickness of 20m, 30m, and 40m on the site. A negative skin friction blocking test element 2 is buried every 10m at the test point depth location, and test points are added in relatively loose locations.

[0071] Step S1 is the same as in Example 2.

[0072] The steel cage in step S2 is fabricated in sections according to the following steps:

[0073] Once the skeleton is formed, the support bars are placed on the skeleton forming frame, and the main bars are arranged at equal intervals. The main bars are fixed to the support bars with electric welding. The skeleton is then pushed onto the outer hoop rolling welder, and the hoop is wrapped around it at the specified interval. The main bars and hoop are then fixed in a staggered pattern with arc welding. After the steel cage is formed and inspected and approved, a sign is hung on the steel cage stacking site, and the cages are neatly stacked on wooden blocks.

[0074] The negative skin friction blocking test element 2 for the foundation pile in step S2 is manufactured according to the following steps:

[0075] 1) Machining the upper blocking plate 2.1 and the lower blocking plate 2.3: The upper and lower blocking plates are ordinary carbon steel plates with a diameter of 760mm and a thickness of 30mm. Cut 8 stress gauge holes 5 with a diameter of 30mm at equal intervals at a distance of 320mm from the center, and cut a 200mm center hole in the center.

[0076] 2) Protective partition layer 2.2 in processing component I: The protective partition layer 2.2 is a polystyrene board with a diameter of 800mm and a thickness of 300mm. At a distance of 320mm from the center, corresponding to the stress gauge perforation 2.5 position on the upper and lower blocking plates, eight stress gauge perforations 2.5 with a diameter of 30mm are made with Φ25 ribbed steel bars at equal intervals. A 110mm center hole is cut in the center. Eight connecting line protection grooves 2.6 are installed on the upper surface of the protective partition layer 2.2 through a wooden board. It is immersed in cold water for 72 hours, which plays a role in cooling during the welding process of the steel bar stress gauge connector 2.8.

[0077] 3) Protective partition layer 2 in processing component II: Protective partition layer 2 is a polystyrene board with a diameter of 800mm and a thickness of 300mm. At a distance of 320mm from the center, corresponding to the stress gauge perforation 2.5 position on the upper and lower blocking plates, eight stress gauge perforations 2.5 with a diameter of 30mm are made with Φ25 ribbed steel bars at equal intervals. A 110mm center hole is cut in the center. Eight connecting wire protection grooves 2.6 are installed on the upper surface of the protective partition layer 2 through a wooden board. At the second end of the connecting wire protection grooves 2.6, 2.8 connecting wire perforations 2.7 are made with Φ25 ribbed steel bars. The grooves are immersed in cold water for 72 hours, which plays a role in cooling during the welding process of the steel bar stress gauge connector 2.8.

[0078] 4) Connecting the rebar stress gauge connector 2.8: Connect the two ends of the rebar stress gauge 2.9 to the upper connecting bar 2.10 and the lower connecting bar 2.11 respectively through threaded connections.

[0079] In step S3, the grouting conduit 4 is provided with perforated holes as grout discharge holes 4.1. The grout discharge holes 4.1 are spaced two meters apart and are 30cm×5cm square holes. To ensure the grouting quality and the integrity of the pile structure 1-2m below the broken pile position, a 30cm×5cm square hole is added below the lower blocking plate 2.3 at the broken pile position for air discharge in this section. The PVC pipe is tied to the reinforcing cage with steel wire in a 6-cross pattern. The operation is simple and quick. The PVC pipe is tied every 3m. The PVC pipe connection is made with clips 4.2 and glued. At the same time, the clips 4.2 need to be tied to the reinforcing cage with steel wire in a 6-cross pattern to ensure that the grouting conduit 4 is in the center of the reinforcing cage.

[0080] In step S4, fine aggregate concrete is selected. The appropriate fine aggregate, cement, and sand ratio is determined through mix proportion tests. C25 concrete is chosen as the strength grade. The maximum particle size of the aggregate in the concrete must not exceed 20mm, and the concrete slump must reach 160mm. Pouring should be as slow as possible, not exceeding 25 minutes. 3 / h, the sound of air being expelled can be heard during the pouring process, and large pieces of concrete that are stuck together should be removed during the pouring.

[0081] In step S5, 14 days after the test pile is poured, core samples are taken by drilling along the grouting guide pipe 4 using the XY-200 engineering drilling rig.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A test pile for testing negative skin friction using a blocking method, characterized in that, The structure is a broken pile, including multiple pile segments (1) and a negative skin friction blocking test element (2) embedded between two adjacent pile segments (1); The pile body (1) includes a steel cage and a concrete layer poured outside the steel cage; The steel cage includes multiple test main bars distributed in a circular shape at equal intervals (1.1); The negative skin friction blocking test element (2) for the foundation pile includes element I and element II; Both component I and component II include an upper blocking plate (2.1), a protective partition layer (2.2), a lower blocking plate (2.3), and a steel reinforcement stress gauge connector (2.8); The upper blocking plate (2.1), the protective partition layer (2.2), and the lower blocking plate (2.3) are all ring structures. The upper blocking plate (2.1) and the lower blocking plate (2.3) are respectively installed on the upper and lower surfaces of the protective partition layer (2.2). The central holes of the three are coaxially arranged and axially connected as grouting holes (2.4). According to the number and position of the test main reinforcement (1.1) in each pile body (1), axially connected stress gauge through holes (2.5) are provided. The diameter of the central hole of the protective partition layer (2.2) is smaller than the diameter of the central hole of the upper blocking plate (2.1). The upper surface of the protective partition layer (2.2) is provided with a connecting wire protection groove (2.6). The connecting wire protection groove (2.6) corresponds one-to-one with the stress gauge through hole (2.5). The first end is connected to the stress gauge through hole (2.5), and the second end is located between the central hole of the protective partition layer (2.2) and the central hole of the upper blocking plate (2.1). The rebar stress gauge connector (2.8) includes a rebar stress gauge (2.9) and an upper connecting bar (2.10) and a lower connecting bar (2.11) located at both ends of the rebar stress gauge (2.9). The rebar stress gauge connector (2.8) passes through the stress gauge through hole (2.5). The upper end of the upper connecting bar (2.10) and the lower end of the lower connecting bar (2.11) are located outside the stress gauge through hole (2.5). The connecting wire (2.12) of the rebar stress gauge (2.9) is led out from the second end of the connecting wire protection groove (2.6). The second end of the connecting wire protection groove (2.6) in component II is provided with an axially through connecting wire hole (2.7); The component I is installed at the lowest broken pile position, and the component II is installed at the broken pile position above the component I. The upper end of the upper connecting bar (2.10) and the lower end of the lower connecting bar (2.11) of the component I and the component II are respectively welded to the test main bar (1.1) of the two adjacent pile body (1). In component I, the connecting wire (2.12) of the steel bar stress gauge (2.9) is led out from the second end of the connecting wire protection groove (2.6) and passes through the connecting wire through holes (2.7) of all components II from bottom to top; In component II installed at the top broken pile position, the connecting wire (2.12) of the steel bar stress gauge (2.9) is led out from the second end of the connecting wire protection groove (2.6); In component II located below the topmost broken pile, the connecting wire (2.12) of the steel stress gauge (2.9) is led out from the second end of the connecting wire protection groove (2.6) and passes through the connecting wire through holes (2.7) of all components II above from bottom to top. The concrete layer of each pile body (1) is a ring structure, with the inner diameter matching the diameter of the central hole of the protective partition layer (2.2) and the outer diameter matching the diameter of the pile borehole (3).

2. The test pile for blocking negative skin friction testing according to claim 1, characterized in that, Each pile body (1) also includes multiple auxiliary main bars (1.2) distributed in a circular shape at equal intervals. The auxiliary main bars (1.2) and the test main bars (1.1) are staggered. The two ends of the auxiliary main bars (1.2) are welded to the upper blocking plate (2.1) and the lower blocking plate (2.3) of the two adjacent sets of pile negative skin friction blocking test elements (2).

3. The test pile for blocking negative skin friction testing according to claim 1, characterized in that, The two ends of the steel stress gauge (2.9) are connected to the upper connecting bar (2.10) and the lower connecting bar (2.11) respectively by threaded connections.

4. The test pile for blocking negative skin friction testing according to claim 1, characterized in that, The protective partition layer (2.2) is made of polystyrene board.

5. The test pile for blocking negative skin friction testing according to claim 1, characterized in that, Welding is made between the upper connecting rib (2.10) and the upper blocking plate (2.1), and welding is made between the lower connecting rib (2.11) and the lower blocking plate (2.3).

6. A method for casting a test pile for blocking negative skin friction testing as described in any one of claims 1-5, characterized in that, Includes the following steps: S1, Drill holes at the predetermined locations on the site; S2, lower the steel cage and install the negative skin friction blocking test element of the foundation pile (2); Weld the upper end of the upper connecting bar (2.10) and the lower end of the lower connecting bar (2.11) in component I to the test main bars (1.1) on both sides of the lowest broken pile position respectively; During the lowering of the steel cage, component II is installed sequentially from bottom to top along the steel cage. The upper end of the upper connecting bar (2.10) and the lower end of the lower connecting bar (2.11) in component II are welded to the test main bars (1.1) on both sides of the broken pile position, respectively. For each set of component II installed, the connecting wire (2.12) of the reinforcing bar stress gauge (2.9) of component I and component II below component II is passed through the connecting wire through hole (2.7) of component II until all components II are installed; S3, install grouting conduit (4) along grouting hole (2.4), the bottom end of grouting conduit (4) is located below component I, and the outer diameter of grouting conduit (4) is adapted to the diameter of the central hole of protective partition layer (2.2); S4, concrete is poured through the grouting pipe (4); S5. After the concrete reaches the required age, the grouting pipe (4) and the concrete inside it, as well as the concrete below the grouting pipe (4), are removed to form a test pile for blocking negative skin friction.

7. The casting method according to claim 6, characterized in that, It also includes step S0, which involves conducting site dynamic penetration tests and shear wave velocity tests to determine the location of the test pile and the embedment depth of the negative skin friction blocking test element (2) of the foundation pile.

8. The casting method according to claim 7, characterized in that, In step S1, the pile drilling (3) is carried out by rotary drilling rig. The drilling depth is determined according to the result of step S0 and enters the bearing layer. After drilling, the hole is cleaned.

9. The casting method according to claim 6, characterized in that, The grouting conduit (4) is tied to the reinforcing cage, and multiple grouting holes are set at the position between the negative skin friction blocking test elements (2) of the two adjacent piles.

10. The casting method according to claim 6, characterized in that, A conical chute funnel (5) is installed at the top of the grouting conduit (4); The grouting conduit (4) is made of multiple PVC pipes connected by snap-fit ​​and coated with glue.

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