A reusable pile shaft axial force testing device and pile shaft axial force testing method

Abstract

The application relates to the technical field of building construction engineering, and particularly discloses a reusable pile shaft axial force testing device and a pile shaft axial force testing method. The reusable pile shaft axial force testing device comprises a pile shaft, the inner side wall of the pile shaft is provided with a protection piece, the protection piece is arranged in parallel with the axis of the pile shaft, a containing cavity is formed between the protection piece and the pile shaft, and the bottom of the protection piece is provided with a wedge block assembly; a guide assembly is arranged in the containing cavity and connected with the pile shaft and the wedge block assembly respectively; at least one pile shaft axial force testing mechanism is arranged in the containing cavity and detachably connected with the inner side wall of the pile shaft, and a connecting rope is arranged on the pile shaft axial force testing mechanism. The application has the advantages that the testing method is intuitive, the pile shaft axial force testing mechanism can be recycled after the pile shaft axial force testing is completed, and the cost of the pile shaft axial force testing is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building construction engineering, in particular to a reusable pile shaft axial force testing device and a pile shaft axial force testing method. BACKGROUND

[0002] Pile foundation has been widely used in various projects due to its high bearing capacity, good anti-seismic performance and small settlement, etc. In order to ensure the safety and applicability of the pile foundation, a large number of sensors and corresponding testing methods are often needed to determine the distribution of the pile shaft axial force and the side friction.

[0003] At present, the pile shaft axial force testing is generally realized by the method of pre-installed sensors. Engineering experience shows that the strain sensors of cast-in-place piles generally have a high survival rate, but the strain sensors of driven piles have a low survival rate after pile sinking. Even if the strain sensors survive, the test data may still lose accuracy. The method of post-installed sensors generally uses the way of secondary filling to ensure the survival rate of the sensors, but it may cause the stress-strain relationship not to be synchronized with the pipe wall, which affects the accuracy of pile foundation measurement. Moreover, no matter the pre-installed method or the current post-installed method, the sensors are consumed as one-time products and cannot be reused, which causes great waste. SUMMARY

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a reusable pile shaft axial force testing device and a pile shaft axial force testing method, which has an intuitive testing method and can be recycled after completing the pile shaft axial force testing, greatly reducing the cost of pile shaft axial force testing.

[0005] One aspect of the present application provides a reusable pile shaft axial force testing device, which comprises:

[0006] a pile body, an inner side wall of the pile body is provided with a protection piece, the protection piece is arranged parallel to the axis of the pile body, a containing cavity is formed between the protection piece and the pile body, and the bottom of the protection piece is provided with a wedge block assembly;

[0007] a guide assembly arranged in the containing cavity and connected with the pile body and the wedge block assembly respectively;

[0008] at least one pile shaft axial force testing mechanism arranged in the containing cavity and detachably connected with the inner side wall of the pile body, and a connecting rope is arranged on the pile shaft axial force testing mechanism.

[0009] Compared with the prior art, the pile shaft force testing mechanism is detachably connected, can be recycled after the pile shaft force testing is completed, effectively reduces the cost of the pile shaft force testing, and can adjust the number of the pile shaft force testing mechanism according to the length of the pile body, effectively improves the applicability of the pile shaft force testing device, and can be applied to piles of different sizes.

[0010] As a preferred scheme of the present application, when the number of the pile shaft force testing mechanism is greater than or equal to two, the two pile shaft force testing mechanisms are connected through the connecting rope.

[0011] By the above scheme, the two pile shaft force testing mechanisms are connected through the connecting rope, and the multiple pile shaft force testing mechanisms can be effectively connected into a whole through the connecting rope, which can be more convenient in the process of testing the pile shaft force.

[0012] As a preferred scheme of the present application, the pile shaft force testing mechanism comprises a strain testing assembly and a fixing assembly, both ends of the strain testing assembly are provided with the fixing assembly, the fixing assembly is detachably connected to the inner side wall of the pile body, and the fixing assembly is provided with the connecting rope.

[0013] By the above scheme, the strain testing assembly can be fixed on the inner side wall of the pile body through the fixing assembly, and the connection between the fixing assembly and the inner side wall of the pile body is detachable, so that the fixing assembly and the strain testing assembly can be recycled after the pile shaft force testing is completed, thereby achieving the purpose of reuse and greatly reducing the cost of the pile shaft force testing.

[0014] As a preferred scheme of the present application, the strain testing assembly comprises a detection plate and a strain gauge, and the strain gauge is arranged on one side of the detection plate close to the inner side wall of the pile body.

[0015] By the above scheme, the strain gauge is arranged on one side of the detection plate close to the inner side wall of the pile body, and when the detection plate is connected to the inner side wall of the pile body through the fixing assembly, the strain gauge can be in contact with the inner side wall of the pile body, thereby better testing the pile shaft force.

[0016] As a preferred scheme of the present application, the fixing assembly comprises an electromagnet, a connecting rod and a guide ring, the connecting rod is connected with the electromagnet and the guide ring respectively, the electromagnet is connected with the strain testing assembly, the guide ring is connected with the guide assembly, the connecting rope is arranged on the electromagnet, and the electromagnet is connected with an external power supply through an electric wire.

[0017] Adopting the scheme, the electromagnet can be connected with the inner sidewall of the pile body by energization, and the electromagnet loses magnetism after being de-energized, that is, the electromagnet can be detached from the inner sidewall of the pile body, so that the detachable connection between the electromagnet and the pile body is realized, and in the process of lowering the device, the cooperation between the guide ring and the guide assembly can ensure that the strain testing assembly is always lowered in the correct posture, so that the pile body axial force testing work is smoothly carried out, and the pile body axial force testing efficiency is improved.

[0018] As a preferred scheme of the present application, the guide assembly comprises a top lifting lug and a bottom lifting lug, the top lifting lug is arranged on the pile body, the bottom lifting lug is arranged in the accommodating cavity and connected with the wedge block assembly, and the top lifting lug and the bottom lifting lug are connected through a guide rope.

[0019] Adopting the scheme, the pile body axial force testing mechanism can be lowered in the correct posture through the guide rope and the guide ring, so that the pile body axial force testing efficiency is effectively improved.

[0020] As a preferred scheme of the present application, the wedge block assembly comprises an inclined plane plate, a top plate, a rib plate and a solid tip, the top plate and the rib plate are connected with the inclined plane plate, the top plate and the rib plate are connected with the inner sidewall of the pile body, and the solid tip is arranged at one end of the inclined plane plate away from the protective piece.

[0021] As a preferred scheme of the present application, the protective piece is connected with the top plate or the inclined plane plate.

[0022] As a preferred scheme of the present application, the protective piece is provided with a protective groove, and the protective groove forms an accommodating cavity with the inner sidewall of the pile body.

[0023] Adopting the scheme, the protective groove can form an accommodating cavity with the inner sidewall of the pile body, so as to provide installation space for the guide assembly and the pile body axial force testing mechanism, and the protective piece can provide protection for the guide assembly and the pile body axial force testing mechanism.

[0024] Another aspect of the present application provides a pile body axial force testing method, which comprises the following steps:

[0025] S1, determining the length of the protective piece according to the pile top elevation and the required testing deepest soil layer elevation;

[0026] S2, if the pile body is a non-steel pipe pile body, an iron sheet equal in length to the pile body needs to be installed on the inner sidewall of the pile body;

[0027] S3, assembling the protective piece and the wedge block assembly, and installing the assembled protective piece and wedge block assembly on the inner sidewall of the pile body according to the type of the driven pile;

[0028] S4. After pile driving is performed, determine the number of segments of the connecting rope and the length of each segment of the connecting rope based on the pile top elevation and the required elevation of each soil layer.

[0029] S5. Determine the number of fixing components and strain testing components based on the number of soil layers required for testing;

[0030] S6. Assemble the fixing components and strain test components;

[0031] S7. Connect the assembled fixing component and the strain test component using the connecting rope;

[0032] S8. Open the guide ring, insert the guide rope, and close the guide ring;

[0033] S9. The fixing components and strain testing components are lowered to the required depth with their faces facing the inner wall of the pile.

[0034] S10. Turn on the power to make the electromagnet in the fixing component magnetic, thereby making the strain test component fit tightly against the pile body.

[0035] S11. Strain gauges at different pile depths are used to detect the strain of the pile, obtaining the strain at different pile depths. ;

[0036] S12, the axial force of the pile at the depth where the strain gauge is located is: ,in and These are the elastic modulus of the pile and the cross-sectional area of ​​the pile, respectively.

[0037] S13. Based on the axial force of the pile body at the depth of each strain gauge obtained in step S12, obtain the distribution of the axial force of the pile body; the difference in the axial force of the pile body at different depths is the side friction resistance of the pile body within the depth range, and obtain the distribution of the side friction resistance along the depth.

[0038] S14. Disconnect the power supply to eliminate the magnetism of the electromagnet, and retrieve the fixing component and strain test component via the connecting rope for future use.

[0039] The present application has the following beneficial effects: the installation and dismounting of the strain testing assembly can be realized by controlling the energization state of the electromagnet, so that the detection plate can be quickly installed during the pile shaft axial force test, and the installation efficiency of the detection plate is improved; when the pile shaft axial force test is completed, the electromagnet can be caused to lose magnetism by cutting off the current on the electromagnet, so that the electromagnet falls off from the inner side wall of the pile body, and the strain testing assembly also falls off from the inner side wall of the pile body, so that the strain testing assembly can be recycled, and the cost of the pile shaft axial force test is greatly reduced; secondly, the electromagnet is connected with the guide ring through the connecting rod, and the guide ring can always face the inner side wall of the pile body under the action of the guide rope, so that the strain gauge of the detection plate can be in contact with the inner side wall of the pile body, and the pile shaft axial force can be better tested. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a structural schematic view of a reusable pile shaft axial force testing device of the present application;

[0041] Figure 2 It is a structural schematic view of a wedge block assembly in a reusable pile shaft axial force testing device of the present application;

[0042] Figure 3 It is a structural schematic view of a strain testing assembly in a reusable pile shaft axial force testing device of the present application;

[0043] Figure 4 It is a structural schematic view of a fixing assembly in a reusable pile shaft axial force testing device of the present application;

[0044] Figure 5 It is a structural schematic view of a top end lifting lug and a bottom end lifting lug in a reusable pile shaft axial force testing device of the present application;

[0045] Figure 6 It is a structural schematic view of a guide ring in a reusable pile shaft axial force testing device of the present application;

[0046] Figure 7 It is a flowchart of a reusable pile shaft axial force testing method of the present application;

[0047] In the figure: 1, pile body; 2, protection piece; 3, wedge block assembly; 31, inclined surface plate; 32, top surface plate; 33, rib plate; 34, solid pointed end; 4, guide assembly; 41, guide rope; 42, bottom end lifting lug; 43, top end lifting lug; 5, pile shaft axial force testing mechanism; 51, strain testing assembly; 511, detection plate; 512, strain gauge; 513, data transmission line; 52, fixing assembly; 521, electromagnet; 522, guide ring; 523, connecting rod; 524, electric wire; 6, connecting rope; 7, sleeve.

[0048] The objectives, functional characteristics and advantages of the present application will be further described with reference to the embodiments in combination with the accompanying drawings. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those of ordinary skill in the art without any creative work fall within the protection scope of the present application.

[0050] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement condition, etc. between components in a certain posture, and if the certain posture changes, the directional indications also change accordingly.

[0051] In addition, if the embodiments of the present application involve descriptions of “first”, “second”, etc., the descriptions of “first”, “second”, etc. are only for description purposes, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by “first” and “second” can explicitly or implicitly include at least one of the features. In addition, if “and / or” or “and / or” appears throughout the text, it means that the three parallel schemes are included, for example, “A and / or B” includes A scheme, or B scheme, or A and B are satisfied at the same time. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of those of ordinary skill in the art, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the protection scope of the present application.

[0052] The present application provides a reusable pile shaft axial force testing device and a pile shaft axial force testing method.

[0053] Please refer to Figure 1The reusable pile shaft 1 axial force testing device provided by the application is described as follows, which comprises a pile shaft 1, a guide assembly 4 and at least one pile shaft axial force testing mechanism 5. The inner side wall of the pile shaft 1 is provided with a protection piece 2, which is arranged parallel to the axis of the pile shaft 1. The protection piece 2 and the pile shaft 1 form a containing cavity therebetween. The bottom of the protection piece 2 is provided with a wedge block assembly 3. The guide assembly 4 is arranged in the containing cavity and connected with the pile shaft 1 and the wedge block assembly 3 respectively. The pile shaft axial force testing mechanism 5 is arranged in the containing cavity and detachably connected with the inner side wall of the pile shaft 1. The pile shaft axial force testing mechanism 5 is provided with a connecting rope 6. The pile shaft axial force testing mechanism 5 is detachably connected, which can be recycled after the pile shaft 1 axial force testing is completed, effectively reducing the cost of the pile shaft 1 axial force testing. In addition, the number of the pile shaft axial force testing mechanism 5 can be adjusted according to the length of the pile shaft 1, effectively improving the applicability of the pile shaft 1 axial force testing device, so that it can be applied to pile shafts 1 of different sizes.

[0054] Referring to Figure 4 In an embodiment, since the number of the pile shaft axial force testing mechanism 5 needs to be determined according to the length of the pile shaft 1, when the number of the pile shaft axial force testing mechanism 5 is greater than or equal to two, the two pile shaft axial force testing mechanisms 5 are connected through the connecting rope 6. The two pile shaft axial force testing mechanisms 5 are connected through the connecting rope 6, which can effectively connect multiple pile shaft axial force testing mechanisms 5 into a whole through the connecting rope 6, so that the pile shaft 1 axial force testing can be more convenient.

[0055] Referring to Figure 1 In an embodiment, the pile shaft axial force testing mechanism 5 comprises a strain testing assembly 51 and a fixing assembly 52. The two ends of the strain testing assembly 51 are provided with the fixing assembly 52. The fixing assembly 52 is detachably connected with the inner side wall of the pile shaft 1. The fixing assembly 52 is provided with the connecting rope 6. The strain testing assembly 51 can be fixed on the inner side wall of the pile shaft 1 through the fixing assembly 52. The connection between the fixing assembly 52 and the inner side wall of the pile shaft 1 is detachable. When the pile shaft 1 axial force testing is completed, the fixing assembly 52 and the strain testing assembly 51 can be recycled for reuse, which greatly reduces the cost of the pile shaft 1 axial force testing.

[0056] Referring to Figure 1 and Figure 3In an embodiment, the strain testing assembly 51 comprises a detection plate 511 and strain gauges 512, the strain gauges 512 are arranged on one side of the detection plate 511 close to the inner side wall of the pile body 1, the strain gauges 512 are connected with an external data processing module through data transmission lines 513, in the embodiment, the external data processing module is a data acquisition instrument, the strain gauges 512 can be installed on the detection plate 511 by bonding, can be installed on the detection plate 511 by screws, or can be installed on the detection plate 511 by embedding, for example, a recess is formed on the detection plate 511, the strain gauges 512 are bonded in the recess, or the strain gauges 512 are installed in the recess by screws to realize the embedded installation of the strain gauges 512, as long as the strain gauges 512 can be fixedly installed on the detection plate 511, the specific connection mode of the strain gauges 512 and the detection plate 511 is not limited herein; in the embodiment, the strain gauges 512 are resistance strain gauges. The strain gauges 512 are arranged on one side of the detection plate 511 close to the inner side wall of the pile body 1, when the detection plate 511 is connected with the inner side wall of the pile body 1 in the fixing assembly 52, the strain gauges 512 can contact with the inner side wall of the pile body 1, so that the axial force of the pile body 1 can be better tested.

[0057] Referring to Figure 1 and Figure 4In an embodiment, the fixing assembly 52 comprises an electromagnet 521, a connecting rod 523 and a guide ring 522, the electromagnet 521 is welded on the detection plate 511, the connecting rod 523 is connected with the electromagnet 521 and the guide ring 522 by welding, in other embodiments, the connecting rod 523 can also be connected with the electromagnet 521 and the guide ring 522 by screws, as long as the connecting rod 523 is connected with the electromagnet 521 and the guide ring 522, the specific connection manner is not limited here; the electromagnet 521 is connected with the strain test assembly 51, the guide ring 522 is connected with the guide assembly 4, the connecting rope 6 is arranged on the electromagnet 521, in the embodiment, the connecting rope 6 is bound on the electromagnet 521 by a knot, the electromagnet 521 is connected with an external power supply by a wire 524, it is worth mentioning that the guide ring 522 can adopt an elastic lock in the prior art, for example, a waist hanging key buckle, a mountaineering buckle and the like, the guide rope 41 is placed in the lock cavity to achieve the purpose of guiding, a metal ring with head and tail in contact can also be adopted, a tester presses the metal ring to make the metal ring elastically deform, at this time, there is an open gap at both ends of the metal ring, the guide rope 41 can pass through the open gap and enter the metal ring, when the tester releases the pressing force of the metal ring, the metal ring can restore the state of head and tail in contact to achieve the purpose of guiding; in the embodiment, the connecting rod 523 and the guide ring 522 are provided with two respectively, in other embodiments, different numbers of the connecting rod 523 and the guide ring 522 can also be provided according to actual needs, the number of the connecting rod 523 and the guide ring 522 is not limited here. The electromagnet 521 can be connected with the inner side wall of the pile body 1 by energization, when the electromagnet 521 is de-energized, the electromagnet 521 loses magnetism and can fall off from the inner side wall of the pile body 1, thereby realizing the detachable connection of the electromagnet 521 with the pile body 1, in addition, in the process of lowering the device, through the cooperation of the guide ring 522 and the guide assembly 4, it can be ensured that the strain test assembly 51 is always lowered in a correct posture, ensuring the smooth progress of the axial force test of the pile body 1 and improving the axial force test efficiency of the pile body 1.

[0058] Referring to Figure 1 , Figure 3 and Figure 4 , in an embodiment, the wire 524 and the data transmission line 513 are located in the sleeve 7, the sleeve 7 is used for protecting and regularizing all the wires 524 and the data transmission line 513, the sleeve 7 can adopt a steel wire sleeve 7.

[0059] Referring to Figure 5In an embodiment, the guide assembly 4 comprises a top hanger 43 welded on the pile body 1 and a bottom hanger 42 arranged in the accommodating cavity and connected with the wedge assembly 3. The top hanger 43 is connected with the bottom hanger 42 through a guide rope 41, both ends of the guide rope 41 are tied on the top hanger 43 and the bottom hanger 42 respectively, and the guide rope 41 is parallel to the axis of the pile body 1. In this embodiment, two top hangers 43 and two bottom hangers 42 are exemplarily arranged, and in other embodiments, the number of the top hangers 43 and the bottom hangers 42 can be increased or decreased according to actual needs, and the number of the top hangers 43 and the bottom hangers 42 is not limited. The pile body axial force testing mechanism 5 can be lowered in a correct posture through the guide rope 41 and the guide ring 522, effectively improving the pile body 1 axial force testing efficiency.

[0060] Referring to Figure 2 In an embodiment, the wedge assembly 3 comprises an inclined plate 31, a top plate 32, a rib plate 33 and a solid tip 34. The top plate 32 and the rib plate 33 are both welded with the inclined plate 31, and the top plate 32 and the rib plate 33 are both welded with the inner side wall of the pile body 1. The solid tip 34 is welded at one end of the inclined plate 31 away from the protector 2. The bottom hanger 42 is welded on the top plate 32, and the top plate 32 and the rib plate 33 are both arc-shaped steel plates.

[0061] Referring to Figure 5 In an embodiment, the protector 2 is welded with the top plate 32, and in other embodiments, the protector can also be welded with the inclined plate 31.

[0062] In an embodiment, the protector 2 is provided with a protection groove forming an accommodating cavity with the inner side wall of the pile body 1. The protection groove can form an accommodating cavity with the inner side wall of the pile body 1 to provide installation space for the guide assembly 4 and the pile body axial force testing mechanism 5, and the protector 2 can provide protection for the guide assembly 4 and the pile body axial force testing mechanism 5.

[0063] Referring to Figure 7 Now the pile body 1 axial force testing method provided by the present application will be described, which comprises the following steps:

[0064] Step S1, determining the length of the protector 2 according to the pile top elevation and the required deepest soil layer elevation;

[0065] Step S2, if the pile body 1 is a non-steel pipe pile body 1, a piece of iron sheet equal to the length of the pile body 1 needs to be installed on the inner side wall of the pile body 1;

[0066] Step S3, assembling the protector 2 and the wedge assembly 3, and installing the assembled protector 2 and the wedge assembly 3 on the inner side wall of the pile body 1 according to the type of the driven pile;

[0067] Step S4, after the pile is driven, the number of connecting ropes 6 and the length of each connecting rope 6 are determined according to the elevation of the pile top and the elevations of the soil layers to be tested;

[0068] Step S5, the number of fixing assemblies 52 and strain testing assemblies 51 is determined according to the number of soil layers to be tested;

[0069] Step S6, the fixing assemblies 52 and the strain testing assemblies 51 are assembled;

[0070] Step S7, the assembled fixing assemblies 52 and strain testing assemblies 51 are connected through the connecting ropes 6;

[0071] Step S8, the guide ring 522 is opened, the guide rope 41 is put in, and the guide ring 522 is closed;

[0072] Step S9, the fixing assemblies 52 and the strain testing assemblies 51 are lowered to the required depth in a posture facing the inner wall of the pile body 1;

[0073] Step S10, the power is turned on, the electromagnet 521 in the fixing assembly 52 has magnetism, and then the strain testing assembly 51 is tightly attached to the pile body 1;

[0074] Step S11, each strain gauge 512 at different depths of the pile body 1 detects the strain of the pile body 1, and the strain at different depths of the pile body 1 is obtained ;

[0075] Step S12, the axial force of the pile body 1 at the depth of the strain gauge 512 is: , wherein and are the elastic modulus of the pile body 1 and the cross-sectional area of the pile body 1, respectively;

[0076] Step S13, according to the axial force of the pile body 1 at the depth of each strain gauge 512 obtained in step S12, the distribution of the axial force of the pile body 1 is obtained; the difference of the axial force of the pile body 1 at different depths is the side friction resistance of the pile body 1 in the depth range, and the distribution of the side friction resistance along the depth is obtained;

[0077] Step S14, the power is turned off, the magnetism of the electromagnet 521 disappears, and the fixing assemblies 52 and the strain testing assemblies 51 are recovered through the connecting ropes 6 for next use.

[0078] The application can realize installation and dismounting of the strain test assembly 51 by controlling the energization state of the electromagnet 521, thereby quickly installing the detection plate 511 during the pile body 1 axial force test, improving the installation efficiency of the detection plate 511, and when the pile body 1 axial force test is completed, the electromagnet 521 loses magnetism by cutting off the current on the electromagnet 521, so that the electromagnet 521 falls off from the inner side wall of the pile body 1, thereby making the strain test assembly 51 also separate from the inner side wall of the pile body 1, and the strain test assembly 51 can be recycled, greatly reducing the cost of the pile body 1 axial force test; secondly, the electromagnet 521 is connected with the guide ring 522 through the connecting rod 523, and under the action of the guide rope 41, the detection plate 511 is always provided with a side of the strain gauge 512 facing the inner side wall of the pile body 1, thereby ensuring that the strain gauge 512 can contact the inner side wall of the pile body 1, so that the axial force of the pile body 1 can be better tested.

[0079] The above is only the preferred embodiment of the application, and does not limit the patent scope of the application, and any equivalent structural transformation, direct / indirect application in other related technical fields under the inventive concept of the application, and the contents of the specification and drawings are included in the patent protection scope of the application.

Claims

1. A reusable pile shaft axial force testing device, characterized by, The utility model relates to a reusable pile shaft force testing device and a method for testing pile shaft force, and the reusable pile shaft force testing device comprises: a pile body, an inner side wall of the pile body is provided with a protection piece, the protection piece is arranged in parallel with an axis of the pile body, a containing cavity is formed between the protection piece and the pile body, a wedge block assembly is arranged at a bottom of the protection piece; a guide assembly is arranged in the containing cavity and is connected with the pile body and the wedge block assembly respectively; at least one pile body axial force testing mechanism is arranged in the containing cavity and is detachably connected with the inner side wall of the pile body, and a connecting rope is arranged on the pile body axial force testing mechanism; the pile body axial force testing mechanism comprises a strain testing assembly and a fixing assembly, both ends of the strain testing assembly are provided with the fixing assembly, the fixing assembly is detachably connected with the inner side wall of the pile body, and the connecting rope is arranged on the fixing assembly; the fixing assembly comprises an electromagnet, a connecting rod and a guide ring, the connecting rod is connected with the electromagnet and the guide ring respectively, the electromagnet is connected with the strain testing assembly, the guide ring is connected with the guide assembly, the connecting rope is arranged on the electromagnet, and the electromagnet is connected with an external power supply through an electric wire; the guide assembly comprises a top end lifting lug and a bottom end lifting lug, the top end lifting lug is arranged on the pile body, the bottom end lifting lug is arranged in the containing cavity and is connected with the wedge block assembly, and the top end lifting lug and the bottom end lifting lug are connected through a guide rope.

2. The reusable pile shaft axial force testing device of claim 1, wherein: when the number of the pile body axial force testing mechanisms is greater than or equal to two, the two pile body axial force testing mechanisms are connected through the connecting ropes.

3. The reusable pile shaft axial force testing apparatus of claim 1, wherein: the strain testing assembly comprises a detection plate and a strain gauge, and the strain gauge is arranged on one side of the detection plate close to the inner side wall of the pile body.

4. The reusable pile shaft axial force testing device of claim 1, wherein: the wedge block assembly comprises an inclined plane plate, a top surface plate, a rib plate and a solid tip, the top surface plate and the rib plate are connected with the inclined plane plate, the top surface plate and the rib plate are connected with the inner side wall of the pile body, and the solid tip is arranged at one end of the inclined plane plate away from the protection piece.

5. A reusable pile shaft axial force testing device according to claim 4, characterised in that: the protection piece is connected with the top surface plate or the inclined plane plate.

6. The reusable pile shaft axial force testing device of claim 1, wherein: a protection groove is arranged on the protection piece, and the protection groove forms the containing cavity with the inner side wall of the pile body.

7. A method of pile shaft force testing, characterized by, the method comprises the following steps: S1, determining the length of the protection piece according to the pile top elevation and the required test deepest soil layer elevation; S2, if the pile body is a non-steel pipe pile body, an iron sheet equal to the length of the pile body needs to be installed on the inner side wall of the pile body; S3, assembling the protection piece and the wedge block assembly, and installing the assembled protection piece and wedge block assembly on the inner side wall of the pile body according to the type of the driven pile; S4, after the pile is driven, determining the number of the connecting ropes and the length of each connecting rope according to the pile top elevation and the required test elevation of each soil layer; S5, determining the number of the fixing assemblies and the strain testing assemblies according to the number of the required test soil layers; S6, assembling the fixing assemblies and the strain testing assemblies; S7, connecting the assembled fixing assemblies and strain testing assemblies through the connecting ropes; S8, opening the guide ring, putting in the guide rope and closing the guide ring. S9, the fixed assembly and the strain testing assembly are lowered to the required depth with the posture of facing the inner wall of the pile body; S10, the power is turned on, the electromagnet in the fixed assembly has magnetism, and then the strain testing assembly is tightly attached to the pile body; S11, each strain gauge at different pile body depth detects the strain of the pile body to obtain the strain at different pile body depth ; S12, the axial force of the pile body at the depth where the strain gauge is located is: wherein and E and A are the elastic modulus of the pile body and the cross-sectional area of the pile body, respectively. S13, the distribution of the pile body axial force is obtained according to the pile body axial force at the depth of each strain gauge obtained in step S12; the difference of the pile body axial force at different depths is the side friction resistance of the pile body in the depth range, and the distribution of the side friction resistance along the depth is obtained; S14, the power is turned off, the magnetism of the electromagnet disappears, and the fixed assembly and the strain testing assembly are recovered through the connecting rope for next use.

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