A self-balancing bearing capacity detection method suitable for root piles

Abstract

The invention discloses a self-balancing bearing capacity detection method applicable to root piles, belonging to the technical field of civil engineering. The method comprises: defining a self-balancing conversion coefficient applicable to root piles; defining two variables related to root key design parameters that affect the self-balancing conversion coefficient in the root pile self-balancing test; establishing a functional relationship between the overall burial depth of the root key and the root key bearing capacity conversion coefficient; measuring and calculating the bearing capacity contribution of the root key in the self-balancing loading. k ; Calculate the conversion coefficient related to the root key design parameters, and use the conversion coefficient to calculate the bearing capacity of the root pile based on the self-balancing test. Compared with the prior art, the beneficial effect of the present invention is that the self-balancing conversion coefficient of the present invention is applicable to the root pile, and different and accurate self-balancing conversion coefficients can be obtained according to different root key design parameters of the root pile. In addition, the method of the present invention is also applicable to the self-balancing bearing capacity detection of special-shaped piles composed of horizontal rigid beams and pile shafts similar to root piles.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering, and in particular relates to a self-balancing bearing capacity detection method suitable for root piles. Background Art

[0002] For large diameter piles, or when the pile foundation bearing capacity testing conditions are limited, the engineering community usually uses the self-balancing method to test the pile foundation bearing capacity. The self-balancing test method is to load the upper and lower piles through a load box to obtain the corresponding bearing capacities of the upper and lower piles respectively; the upper pile bearing capacity needs to be converted to the equivalent bearing capacity under the heap loading method through a conversion coefficient, and then added to the lower pile bearing capacity to obtain the bearing capacity of the entire pile.

[0003] Therefore, when using the self-balancing technology to detect the bearing capacity of pile foundations, the accuracy of the conversion coefficient directly affects the accuracy of the pile foundation bearing capacity test value. The current specification recommends a conversion coefficient of 0.7 for sand and 0.8 for clay. However, due to the presence of root keys, the bearing characteristics of root piles are significantly different from those of ordinary piles, and the bearing capacity of root piles is closely related to the specific design of the root keys. Therefore, directly using the conversion coefficient of ordinary piles in the current specification to calculate the bearing capacity of the root pile self-balancing test will result in a large error.

[0004] Therefore, it is necessary to provide a self-balancing bearing capacity detection method suitable for root piles to solve the above problems. Summary of the invention

[0005] The purpose of the embodiments of the present invention is to provide a self-balancing bearing capacity detection method applicable to root piles, which can solve at least one technical problem involved in the background technology.

[0006] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0007] The embodiment of the present invention provides a self-balancing bearing capacity detection method applicable to a pile, comprising the following steps:

[0008] Step S1, defining a self-balancing conversion coefficient applicable to the pile, which is expressed by the following formula:

[0009] ①

[0010] In the formula, γ is the self-balancing conversion coefficient of the pile; f d It is the limit value of the negative friction resistance on the pile side provided by the pile shaft during self-balancing loading; P d It is the limit value of negative reaction force of the root key provided by the root key during self-balancing loading; f u It is the limit value of the positive friction resistance of the pile side provided by the pile shaft when loading by the heap loading method;P u It is the limit value of the root bond positive and negative force provided by the root bond when loading by the heap loading method;

[0011] Step S2, defining the conversion coefficient affecting the self-balancing test of the pile γ Two variables related to root key design parameters: root key bearing capacity conversion factor γ g , the bearing capacity contribution rate of the root bond in self-balanced loading k , expressed by the following formula:

[0012] ②

[0013] ③

[0014] By expressing the self-balancing conversion coefficient formula ① of the pile with the above two variables related to the root key design parameters, we can get:

[0015] ④

[0016] In the formula, γ p is the self-balancing conversion coefficient of ordinary piles;

[0017] Step S3: Use mathematical fitting method to establish the conversion coefficient between root key design parameters and root key bearing capacity γ g The functional relationship between

[0018] Step S4: Arrange an axial force meter in the root pile, read the axial force meter value in the self-balancing test of the root pile, measure and calculate the bearing capacity contribution rate of the root key in the self-balancing loading k ;

[0019] Step S5: Calculate the root key bearing capacity conversion coefficient according to the root key design parameters γ g , and the bearing capacity contribution rate of the root bond in the measured self-balancing loading k Substituting it into formula ④, the conversion coefficient related to the root key design parameters is calculated, and the bearing capacity of the root pile based on the self-balancing test is calculated using this conversion coefficient.

[0020] Optionally, the root bond design parameters include overall root bond burial depth, root bond size, root bond number, and root bond layer spacing.

[0021] Optionally, step S3 specifically includes:

[0022] Step S31, setting 5 groups of parameter conditions with different root bond overall burial depths;

[0023] Step S32, establishing a finite element model of the parameter working condition, and performing heap loading and self-balancing loading analysis and calculation for each parameter working condition;

[0024] Step S33, based on the calculation results, extract the root key negative reaction force limit value provided by the root key during self-balancing loading under various parameter conditions P d The root bond positive and negative force limit value provided by the root bond during the heap loading method P u , calculate the root bond bearing capacity conversion coefficient under each parameter condition according to formula ② γ g ;

[0025] Step S34: Draw the root bond bearing capacity conversion coefficient of each parameter condition γ g The relationship curve between the root bond and the overall burial depth h is obtained and fitted into a linear function using the least squares method.

[0026] Optionally, the linear function is expressed by the following formula:

[0027] ⑤

[0028] In the formula, h is the overall burial depth of the root bond, L The length of the root pile.

[0029] Optionally, step S4 specifically includes:

[0030] Step S41, axial force gauges are arranged on the upper and lower surfaces of the root keys of all layers in the root pile and on the main reinforcements on both sides of the pile top section and the load box section; corresponding to the first i The axial force gauges at the upper and lower surfaces of the layer root key are numbered as follows: i 1, i 2; the axial force gauge corresponding to the pile top section is numbered 1, and the axial force gauge corresponding to the load box section is numbered n ;

[0031] Step S42, self-balancing loading to the ultimate bearing capacity of the pile, and readings of all axial force gauges;

[0032] Step S43, the reaction force limit value of each layer of the root bond is calculated using formula ⑥, and the root bond negative reaction force limit value provided by the root bond during self-balancing loading is P d Calculate using formula ⑦:

[0033] ⑥

[0034] ⑦

[0035] In the formula, Pd,i For the i The root bond negative reaction force limit value provided by the layer root bond; N i,1 For the i The axial force of the pile at the upper surface of the layer root key; N i,2 For the i The axial force of the pile at the lower surface of the layer root key; m is the number of layers of root bonds above the load box;

[0036] Step S44: During self-balancing loading, the pile side negative friction limit value provided by the pile shaft section between the two root keys is f d,i , the limit value of the negative friction resistance of the pile side provided by the pile shaft section from the pile top to the first root key f d,0 , the limit value of the negative friction resistance of the pile side provided by the pile shaft section of the upper root key of the load box f d,m The negative friction limit value of the pile side provided by the pile shaft during self-balancing loading is calculated using formula (8) f d Calculated using formula (9);

[0037] ⑧

[0038] ⑨

[0039] In the formula, f d,i For the i Layer root key and i +1 layer of pile shaft section between the root keys provides the limit value of pile side negative friction resistance; N 0 is the axial force of the pile at the top section of the pile; N m is the axial force of the pile at the load box section; N m,2 For the m The axial force of the pile at the lower surface of the layer root key;

[0040] Step S45, using formula ③ to calculate the bearing capacity contribution rate of the root key in self-balancing loading k .

[0041] The beneficial effects of the embodiments of the present invention are:

[0042] The self-balancing conversion coefficient of the present invention is different from that of the standard method, which is applicable to ordinary piles. The self-balancing conversion coefficient of the present invention is applicable to root piles, and different and accurate self-balancing conversion coefficients can be obtained according to different root key design parameters of the root piles. In addition, the method of the present invention is not only applicable to root piles, but also to the self-balancing bearing capacity detection of special-shaped piles composed of horizontal rigid beams and pile shafts similar to root piles, which has important significance and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0044] Figure 1 A flow chart of a self-balancing bearing capacity detection method applicable to root piles provided by the present invention;

[0045] Figure 2 (a) to 2(e) are schematic diagrams of parameter conditions provided by the present invention;

[0046] Figure 3 One of the schematic diagrams of the finite element model provided by the present invention;

[0047] Figure 4 The second schematic diagram of the finite element model provided by the present invention;

[0048] Figure 5 The third schematic diagram of the finite element model provided by the present invention;

[0049] Figure 6 The load-displacement curve diagram of each loading condition provided by the present invention;

[0050] Figure 7 The present invention provides γ g- h / L Graphs;

[0051] Figure 8 (a) to 8 (b) are schematic diagrams of the arrangement of the self-balancing test axial force meter provided by the present invention, wherein: Figure 8 (a) is the elevation view of the pile body where the axial force gauge for the self-balancing test is arranged. Figure 8 (b) Plan view of the pile body for the arrangement of axial force gauges for self-balancing tests;

[0052] Fig. 9 A three-dimensional schematic diagram of a root pile provided by the present invention;

[0053] Fig.10The load-displacement curve diagram of the finite element model provided by the present invention under the heap loading method and the on-site test pile;

[0054] Fig.11 A load-displacement curve diagram of the finite element model under self-balanced loading provided by the present invention;

[0055] Fig.12 The load-displacement curve diagram provided by the present invention after conversion between the method of the present invention and the standard method. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] The terms "first", "second", etc. in the specification and claims of the present invention are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of the same type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0058] As attached Figure 1 As shown, an embodiment of the present invention provides a self-balancing bearing capacity detection method applicable to root piles, comprising the following steps:

[0059] Step S1, defining a self-balancing conversion coefficient applicable to the pile, which is expressed by the following formula:

[0060] ①

[0061] In the formula, γ is the self-balancing conversion coefficient of the pile; f d It is the limit value of the negative friction resistance on the pile side provided by the pile shaft during self-balancing loading; P d It is the limit value of negative reaction force of the root key provided by the root key during self-balancing loading; f u It is the limit value of the positive friction resistance of the pile side provided by the pile shaft when loading by the heap loading method; P uIt is the limit value of the root bond positive and negative force provided by the root bond when loading by the heap loading method;

[0062] It should be noted that for the root pile, when the root key is pushed into the side wall of the pile body, it works together with the surrounding soil to resist the load from the top or bottom of the pile. The pile section that pushes into the root key is equivalent to increasing the pile diameter, thereby increasing the contact area with the soil, and then increasing the lateral friction resistance. Therefore, the reaction force generated by the root key can be equated to the lateral friction resistance, and based on this, combined with the definition of the conversion coefficient, the self-balancing conversion coefficient formula applicable to the root pile is derived.

[0063] Step S2, defining the conversion coefficient affecting the self-balancing test of the pile γ Two variables related to root key design parameters: root key bearing capacity conversion factor γ g , the bearing capacity contribution rate of the root bond in self-balanced loading k , expressed by the following formula:

[0064] ②

[0065] ③

[0066] It should be noted that, when there is sufficient soil covering the root key, the limit value of the root key reaction force provided by the root key when the root pile is subjected to load is related to the relative displacement of the pile-soil at the root key. When the root pile is self-balanced loaded, as the overall burial depth of the root key increases, the displacement of the pile-soil at the root key gradually increases, so the limit value of the root key negative reaction force provided by the root key also gradually increases. When the root pile is loaded by the root pile loading method, as the overall burial depth of the root key increases, the displacement of the pile-soil at the root key gradually decreases, so the limit value of the root key positive reaction force provided by the root key also gradually decreases. Therefore, the ratio of the limit value of the root key negative reaction force provided by the root key to the limit value of the root key positive reaction force will increase with the increase of the overall burial depth of the root key, and it is defined as the root key bearing capacity conversion coefficient. γ g .

[0067] When the overall buried depth of the root key is not changed, the root key reaction limit value provided by the root key during the self-balancing loading of the root pile is related to the root key size, the number of root keys, and the root key layer spacing, while the friction resistance limit value provided by the pile shaft during the self-balancing loading of the root pile is only related to the type of soil layer where the root pile is located. Therefore, the ratio of the root key reaction limit value provided by the root key during the self-balancing loading of the root pile to the side friction resistance limit value provided by the pile shaft is related to the root key size, the number of root keys, and the root key layer spacing, and is defined as the bearing capacity contribution rate of the root key in self-balancing loading. k .

[0068] The defined formula for the self-balancing conversion coefficient of the pile is expressed as a function of two defined variables after algebraic transformation, so that the connection between the self-balancing conversion coefficient and the root key design parameters is realized through the defined intermediate variables.

[0069] Formula ① can be expressed as follows after algebraic transformation: , where f d / f u It is the ratio of the limit value of the pile side negative friction provided by the pile shaft during self-balanced loading to the limit value of the pile side positive friction provided by the pile shaft during heap loading, that is, the conversion coefficient of ordinary piles. Therefore, formula ② can be expressed as: ,in, γ p The self-balancing conversion coefficient of ordinary piles adopts the standard value (in sandy soil γ p =0.7, in clay γ p =0.8). Substituting formula ② and formula ③ into the above formula, the conversion coefficient formula applicable to the pile is expressed as a function of the two variables:

[0070] ④

[0071] In the formula, γ p is the self-balancing conversion coefficient of ordinary piles, using the standard value (in sandy soil γ p =0.7, in clay γ p =0.8);

[0072] Step S3: Establish the root key design parameters and the root key bearing capacity conversion coefficient γ g The functional relationship between them; specifically including:

[0073] Step S31, setting 5 groups of parameter conditions with different root bond overall burial depths;

[0074] Specifically, to obtain the overall burial depth of the root bond h Conversion factor with root bond capacity γ g , 5 groups of parameter analysis conditions were designed, as shown in the attached Figure 2 As shown in the figure, the diameter of the test piles in each working condition is 1.5m, and the pile length is 20m. Among the design parameters of the root key, the root key size is 0.8×0.4×0.4m, the number of root keys is 4×2, and the root key layer spacing is 0.6m. The ratio of the overall burial depth of the root key to the pile length of each working condition (hereinafter referred to as the overall burial depth ratio of the root key) is shown in Table 1.

[0075] Table 1 Overall burial depth ratio of each working condition

[0076]

[0077] Step S32, establishing a finite element model of the parameter working condition, and performing heap loading and self-balancing loading analysis and calculation for each parameter working condition;

[0078] Specifically, ABAQUS finite element software is used to model the soil and pile bodies under various parameter analysis conditions. The schematic diagram of the finite element model is shown in the attached figure. Figures 3 to 5 As shown in the figure, the soil size is 30×30×60m, and the pile size of each working condition is as mentioned above; the soil body model adopts the Mohr-Coulomb model, the pile body adopts the linear elastic model, and the material parameters of the soil and pile body are shown in Table 2; the loading method of self-balanced loading and pile loading method is step-by-step loading, each level of load is 1000kN, the first level of load is 1000kN, and there are 10 levels of load in total. Since only the finite element results need to be extracted P d Value and P u Therefore, the self-balancing and traditional heap loading combined detection method is used to load the root pile, so that the pile end resistance is 0 when the root pile is loaded by the heap loading method, so that it is easier to obtain the root key positive and negative force limit value provided by the root key under the heap loading method. P u .

[0079] Table 2 Soil and pile material parameters

[0080]

[0081] Step S33, based on the calculation results, extract the root key negative reaction force limit value provided by the root key during self-balancing loading under various parameter conditions P d The root bond positive and negative force limit value provided by the root bond during the heap loading method P u , calculate the root bond bearing capacity conversion coefficient under each parameter condition according to formula ② γ g ;

[0082] Specifically, after the numerical model calculation of each parameter analysis condition is completed, the load-displacement curve of the loading point under self-balanced loading and pile loading method is obtained, as shown in the attached figure. Figure 6 As shown in the figure, curves AE are the load-displacement curves of the pile bottom under self-balanced loading of working conditions 1-5, and curves ae are the load-displacement curves of the pile top under pile loading method of working conditions 1-5. The ultimate bearing capacity of the root pile under self-balanced loading and pile loading method of each working condition is determined according to the load-displacement curves, and the ultimate bearing capacity of each working condition is extracted respectively. P d value,P u Substitute the values ​​into formula ② to obtain the root bond bearing capacity conversion coefficient of each working condition. γ g , the results are shown in Table 3.

[0083] Table 3 Conversion coefficient of root bond bearing capacity under various working conditions γ g

[0084]

[0085] Step S34: Draw the root bond bearing capacity conversion coefficient of each parameter condition γ g The relationship curve between the root bond overall burial depth h is fitted into a linear function using the least squares method;

[0086] Specifically, the results in Table 3 are plotted as γ g — h / L Curve, as shown Figure 7 As shown, the least square method is used for fitting, and the fitted function is:

[0087] ⑤

[0088] In the formula, h is the overall burial depth of the root bond, L The length of the root pile.

[0089] Step S4: Arrange an axial force meter in the root pile, read the axial force meter value in the self-balancing test of the root pile, measure and calculate the bearing capacity contribution rate of the root key in the self-balancing loading k ; Specifically include:

[0090] Step S41, axial force gauges are arranged on the upper and lower surfaces of the root keys of all layers in the root pile, as well as on the main bars on both sides of the pile top section and the load box section, as shown in the attached figure. Figure 8 and attached Fig. 9 As shown, Figure 8 In the figure, 1 is the main reinforcement, 2 is the root key, 3 is the axial force gauge, 4 is the upper pile body, 5 is the load box, and 6 is the lower pile body. i The axial force gauges at the upper and lower surfaces of the layer root key are numbered as follows: i 1, i 2. The axial force gauge corresponding to the pile top section is numbered 1, and the axial force gauge corresponding to the load box section is numbered n ;

[0091] Step S42, self-balancing loading to the ultimate bearing capacity of the pile, and readings of all axial force gauges;

[0092] Step S43, the reaction force limit value of each layer of the root bond is calculated using formula ⑥, and the root bond negative reaction force limit value provided by the root bond during self-balancing loading is P d Calculate using formula ⑦:

[0093] ⑥

[0094] ⑦

[0095] In the formula, P d,i For the i The root bond negative reaction force limit value provided by the layer root bond; N i,1 For the i The axial force of the pile at the upper surface of the layer root key; N i,2 For the i The axial force of the pile at the lower surface of the layer root key; m is the number of layers of root bonds above the load box;

[0096] Step S44: During self-balancing loading, the pile side negative friction limit value provided by the pile shaft section between the two root keys is f d,i , the limit value of the negative friction resistance of the pile side provided by the pile shaft section from the pile top to the first root key f d,0 , the limit value of the negative friction resistance of the pile side provided by the pile shaft section of the upper root key of the load box f d,m The negative friction limit value of the pile side provided by the pile shaft during self-balancing loading is calculated using formula ⑧. f d Calculate using formula ⑨;

[0097] ⑧

[0098] ⑨

[0099] In the formula, f d,i For the i Layer root key and i +1 layer of pile shaft section between the root keys provides the limit value of pile side negative friction resistance; N 0 is the axial force of the pile at the top section of the pile; N m is the axial force of the pile at the load box section; N m,2 For the m The axial force of the pile at the lower surface of the layer root key;

[0100] Step S45, using formula ③ to calculate the bearing capacity contribution rate of the root key in self-balancing loading k .

[0101] Step S5: Calculate the root key bearing capacity conversion coefficient according to the root key design parameters γ g , and the bearing capacity contribution rate of the root bond in the measured self-balancing loading k Substituting it into formula ④, the conversion coefficient related to the root key design parameters is calculated, and the bearing capacity of the root pile based on the self-balancing test is calculated using this conversion coefficient.

[0102] Engineering verification: The present invention proposes a self-balancing bearing capacity detection method suitable for root piles, and takes a test pile loaded by the heap loading method between the main pier and the transition pier of the 45+3×80+45m continuous beam bridge of the Chizhou Yangtze River Bridge as the research object. Firstly, the finite element method is used to simulate the heap loading method and the self-balancing loading of the root pile, and based on the finite element simulation results, the load-displacement curves of the heap loading method and the self-balancing loading are extracted respectively. Then the simulated load-displacement curve is compared with the test data of the on-site test pile under the heap loading method to verify the accuracy of the finite element simulation. Finally, the method of the present invention and the standard method are used to convert the self-balancing loading load-displacement curve of the root pile under the finite element simulation, and compared with the load-displacement curve under the on-site test pile heap loading method to verify the correctness, effectiveness and rationality of the method of the present invention.

[0103] The root key arrangement of the test piles is as follows: the pile diameter is 1.5m, the pile length is 44m, the overall burial depth of the root key is 22.35m, the root key dimensions are 0.5m×0.16m×0.16m (root key length×width×height), the number of root keys is 80, and the root key layer spacing is 1.235m.

[0104] (1) Comparison between the finite element simulation results of the pile loading method and the field test results;

[0105] The finite element model of the on-site test pile and soil layer was constructed using the finite element analysis software ABAQUS, and the pile model was subjected to the heap loading method loading calculation. Based on the finite element analysis results, the load-displacement curve under the heap loading method was extracted, and the load-displacement curve under the heap loading method was compared with the load-displacement curve of the on-site test pile, as shown in the attached figure. Fig.10 As shown. Fig.10 It can be seen that under the loading method, the finite element simulation results of the test piles are very close to the field test results, which shows that the overall effect of the finite element simulation is ideal. Therefore, the finite element results of the self-balancing loading of the test piles can be used to replace the actual self-balancing loading results of the field test piles.

[0106] (2) Finite element results of self-balanced loading of test piles;

[0107] The finite element model of the above test pile is subjected to self-balanced loading calculation at the pile end. After the calculation is completed, the root-bond reaction force under the last level of load is extracted. P d , pile side friction f u , P d is 9642.68kN, f u is 10357.33 kN; and the load displacement curve at the pile end is extracted, as shown in the attached Fig.11 shown.

[0108] (3) The self-balancing conversion coefficient of the test pile based on the method of the present invention and the standard method;

[0109] The root key of the test pile is buried at a depth of 22.35m and the pile length is 44m. Substituting into formula ⑤, the root key bearing capacity conversion coefficient of the test pile is obtained. γ g = 0.7189; Substituting the results in Table 4 into formula ③, we can obtain the bearing capacity contribution rate of the root bond in self-balanced loading. k= 0.931; the soil layer where the test pile is located is clay. According to the specification, the self-balancing conversion coefficient of ordinary piles is γ p = 0.8; the obtained γ g , k、 γ p Substituting the value into formula ④, the self-balancing conversion coefficient of the test pile based on the method of the present invention is obtained to be 0.7587.

[0110] Since the soil layer where the test piles are located is mostly clay, the self-balancing conversion coefficient based on the standard method is 0.8.

[0111] (4) Comparison of self-balancing load conversion results based on the method of the present invention and the standard method;

[0112] Based on the method of the present invention and the standard method, the attached Fig.11 The load-displacement curve in the experiment is converted and compared with the load-displacement curve under the on-site pile loading method. The load-displacement curve comparison diagram is shown in the attached figure. Fig.12 As shown; when the pile top displacement is 19.22mm under the last level of load in the field test pile, the load value of the pile top is used as the comparison index, and the comparison results are shown in Table 4.

[0113] Table 4 Comparison of results

[0114]

[0115] By the attached Fig.11 It can be seen that after the self-balancing loading results are converted based on the conversion coefficient obtained by the method of the present invention, they are closer to the actual results of the field test piles. As shown in Table 4, after the self-balancing loading results are converted based on the conversion coefficients obtained by the method of the present invention and the standard method, under the same pile top displacement, the error between the pile top load converted based on the method of the present invention and the pile top load of the field test pile is 2.84%, while the error between the pile top load converted based on the standard method and the pile top load of the field test pile is 7.45%, indicating that the self-balancing conversion coefficient obtained based on the method of the present invention is more accurate, verifying the correctness and effectiveness of the method of the present invention.

[0116] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0117] In addition, it should be noted that the scope of the methods and systems in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0118] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A self-balancing bearing capacity detection method suitable for root piles, characterized in that: The steps include: Step S1, defining a self-balancing conversion coefficient applicable to the pile, which is expressed by the following formula: ① In the formula, γ is the self-balancing conversion coefficient of the pile; f d It is the limit value of the negative friction resistance on the pile side provided by the pile shaft during self-balancing loading; P d It is the limit value of negative reaction force of the root key provided by the root key during self-balancing loading; f u It is the limit value of the positive friction resistance of the pile side provided by the pile shaft when loading by the heap loading method; P u It is the limit value of the root bond positive and negative force provided by the root bond when loading by the heap loading method; Step S2, defining the conversion coefficient affecting the self-balancing test of the pile γ Two variables related to root key design parameters: root key bearing capacity conversion factor γ g , the bearing capacity contribution rate of the root bond in self-balanced loading k , expressed by the following formula: ② ③ By expressing the self-balancing conversion coefficient formula ① of the pile with the above two variables related to the root key design parameters, we can get: ④ In the formula, γ p is the self-balancing conversion coefficient of ordinary piles; Step S3: Use mathematical fitting method to establish the conversion coefficient between root key design parameters and root key bearing capacity γ g The functional relationship between Step S4: Arrange an axial force meter in the root pile, read the axial force meter value in the self-balancing test of the root pile, measure and calculate the bearing capacity contribution rate of the root key in the self-balancing loading k ; Step S5: Calculate the root key bearing capacity conversion coefficient according to the root key design parameters γ g , and the bearing capacity contribution rate of the root bond in the measured self-balancing loading k Substituting it into formula ④, the conversion coefficient related to the root key design parameters is calculated, and the bearing capacity of the root pile based on the self-balancing test is calculated using this conversion coefficient.

2. The self-balancing bearing capacity detection method for root piles according to claim 1, characterized in that: The root bond design parameters include the overall burial depth of the root bond, the root bond size, the number of root bonds, and the root bond layer spacing.

3. The self-balancing bearing capacity detection method for root piles according to claim 2, characterized in that: Step S3 specifically includes: Step S31, setting 5 groups of parameter conditions with different root bond overall burial depths; Step S32, establishing a finite element model of the parameter working condition, and performing heap loading and self-balancing loading analysis and calculation for each parameter working condition; Step S33, based on the calculation results, extract the root key negative reaction force limit value provided by the root key during self-balancing loading under various parameter conditions P d The root bond positive and negative force limit value provided by the root bond during the heap loading method P u , calculate the root bond bearing capacity conversion coefficient under each parameter condition according to formula ② γ g ; Step S34: Draw the root bond bearing capacity conversion coefficient of each parameter condition γ g The relationship curve between the root bond and the overall burial depth h is obtained and fitted into a linear function using the least squares method.

4. The self-balancing bearing capacity detection method for root piles according to claim 3, characterized in that: The linear function is expressed by the following formula: ⑤ In the formula, h is the overall burial depth of the root bond, L The length of the root pile.

5. The self-balancing bearing capacity detection method for root piles according to claim 4, characterized in that: Step S4 specifically includes: Step S41, axial force gauges are arranged on the upper and lower surfaces of the root keys of all layers in the root pile and on the main reinforcements on both sides of the pile top section and the load box section; corresponding to the first i The axial force gauges at the upper and lower surfaces of the layer root key are numbered as follows: i 1, i 2; the axial force gauge corresponding to the pile top section is numbered 1, and the axial force gauge corresponding to the load box section is numbered n ; Step S42, self-balancing loading to the ultimate bearing capacity of the pile, and readings of all axial force gauges; Step S43, the reaction force limit value of each layer of the root bond is calculated using formula ⑥, and the root bond negative reaction force limit value provided by the root bond during self-balancing loading is P d Calculate using formula ⑦: ⑥ ⑦ In the formula, P d,i For the i The root bond negative reaction force limit value provided by the layer root bond; N i,1 For the i The axial force of the pile at the upper surface of the layer root key; N i,2 For the i The axial force of the pile at the lower surface of the layer root key; m is the number of layers of root bonds above the load box; Step S44: During self-balancing loading, the pile side negative friction limit value provided by the pile shaft section between the two root keys is f d,i , the limit value of the negative friction resistance of the pile side provided by the pile shaft section from the pile top to the first root key f d,0 , the limit value of the negative friction resistance of the pile side provided by the pile shaft section of the upper root key of the load box f d,m The negative friction limit value of the pile side provided by the pile shaft during self-balancing loading is calculated using formula ⑧. f d Calculate using formula ⑨; ⑧ ⑨ In the formula, f d,i For the i Layer root key and i +1 layer of pile shaft section between the root keys provides the limit value of pile side negative friction resistance; N 0 is the axial force of the pile body at the cross section position of the pile top; N m is the axial force of the pile at the load box section; N m,2 For the m The axial force of the pile at the lower surface of the layer root key; Step S45, using formula ③ to calculate the bearing capacity contribution rate of the root key in self-balancing loading k .

Images