A method for predicting the bearing capacity of single-plate branch piles

Abstract

The present invention generally relates to the technical field of squeezed branch plate piles, and in particular to a method for predicting the bearing capacity of a single-plate branch plate pile. The method comprises: obtaining cohesion, the internal friction angle of the foundation soil, the density of the soil, the width of the plate ring, the cross-sectional area of ​​the pile end, the buried depth of the plate, the plate diameter, and the pile diameter; calculating the ultimate bearing capacity of the soil based on the limit equilibrium theory according to the cohesion, the internal friction angle of the foundation soil, the density of the soil, the width of the plate ring, and the buried depth of the plate; calculating the projected area of ​​the plate according to the plate diameter and the pile diameter; calculating the bearing capacity of the plate according to the ultimate bearing capacity of the soil and the projected area of ​​the plate, and the bearing capacity of the plate is positively correlated with the ultimate bearing capacity of the soil and the projected area of ​​the plate; calculating the bearing capacity of the single-plate branch plate pile according to the cross-sectional area of ​​the pile end, the ultimate bearing capacity of the soil, and the bearing capacity of the plate, combined with the calculation principle of the bearing capacity of ordinary cast-in-place piles. The present invention takes the bearing capacity of the plate into consideration, and the prediction result is more accurate.

Description

Technical Field

[0001] The present invention generally relates to the technical field of squeezed branch plate piles, and in particular to a method for predicting the bearing capacity of a single-plate branch plate pile. Background Art

[0002] Squeezed branch plate piles (SBP) were developed in 1950 and introduced to my country in 1990. Extensive research has shown that, given the same diameter and length, SBP piles have a significantly higher bearing capacity than conventional straight piles. SBP piles are variable-section piles with branches or bearing plates added to the existing bored cast-in-place piles. They are widely used in engineering due to their high bearing capacity, minimal settlement and deformation, and high economic benefits.

[0003] A squeezed branch and plate pile consists of a pile body, a bearing plate, and several branches. The branches and bearing plates are formed by hydraulic expansion in a conventional circular borehole using specialized equipment. As the branches and plates create a cavity, the surrounding soil is also compacted. This compacted surrounding soil integrates tightly with the reinforced concrete pile body and branches poured into the cavity, creating a joint load-bearing effect between the pile and the soil, increasing the pile's lateral friction and end bearing capacity. Therefore, squeezed branch and plate piles can significantly improve the bearing capacity of individual piles. In the design process of squeezed branch and plate piles, the bearing capacity of individual piles is a key design parameter.

[0004] The bearing capacity of a single pile is usually composed of two parts: the pile side friction and the pile end resistance. Due to the presence of branches in squeezed branch plate piles, the single pile bearing capacity of squeezed branch plate piles is composed of three parts: the pile side friction, the pile end resistance, and the branch plate end resistance. Squeezed branch plate piles increase the branch plate end resistance, but the branch plate end resistance affects the side friction within a certain range above and below the branch plate. Existing methods for predicting the bearing capacity of single piles mainly include theoretical formulas and empirical formulas. However, these methods ignore the bearing capacity of the plate. As the main load-bearing component of the branch plate pile, the plate usually bears 30% to 80% of the total load. The accuracy of the plate bearing capacity calculation is directly related to the correct evaluation of the bearing capacity of the branch plate pile.

[0005] In summary, the existing prediction methods have low accuracy. Summary of the Invention

[0006] The present invention provides a method for predicting the bearing capacity of a single-plate branch pile to solve the above problem.

[0007] According to one aspect of the present invention, a method for predicting the bearing capacity of a single-plate branch pile is provided, wherein the method for predicting the bearing capacity of a single-plate branch pile comprises:

[0008] Obtain the basic parameters of the soil constitutive relationship and the geometric parameters of the pile body. The basic parameters of the soil constitutive relationship include cohesion, internal friction angle of foundation soil, and soil density; the geometric parameters of the pile body include disk ring width, pile end cross-sectional area, disk burial depth, disk diameter, and pile diameter;

[0009] The ultimate bearing capacity of the soil is calculated based on the limit equilibrium theory according to the cohesion, the internal friction angle of the foundation soil, the weight of the soil, the width of the disk ring, and the embedding depth of the disk.

[0010] The projected area of ​​the disk is calculated based on the disk diameter and the pile diameter;

[0011] The bearing capacity of the plate is calculated based on the ultimate bearing capacity of the soil and the projected area of ​​the plate. The bearing capacity of the plate is positively correlated with the ultimate bearing capacity of the soil and the projected area of ​​the plate.

[0012] The bearing capacity of a single-plate branch pile is calculated based on the cross-sectional area of ​​the pile end, the ultimate bearing capacity of the soil, and the bearing capacity of the plate, combined with the calculation principle of the bearing capacity of ordinary cast-in-place piles.

[0013] The beneficial effect of the single-plate branch pile bearing capacity prediction method provided by the present invention is that the present invention takes into account the bearing capacity of the plate in the calculation process of the single-plate branch pile bearing capacity, thereby making the prediction result of the single-plate branch pile bearing capacity more accurate.

[0014] Furthermore, the calculation process of the bearing capacity of a single-plate branch pile is as follows:

[0015] Q u =μΣq ik L i +Q ub +A c Z u ;

[0016] Among them, Q u is the bearing capacity of a single-plate branch pile; μ is the circumference of the pile; L i The thickness of the i-th soil layer below the bottom surface of the foundation should be deducted by 1.2 times the height of each support and plate; q ik For L i The corresponding standard value of friction resistance between the soil layer and the pile side; Q ub is the bearing capacity of the disk; A c is the cross-sectional area of ​​the pile end; Z u is the ultimate bearing capacity of the soil.

[0017] Furthermore, the calculation process of the ultimate bearing capacity of soil is:

[0018]

[0019]

[0020] Among them, Z u is the ultimate bearing capacity of the soil; c is the cohesion; is the internal friction angle of the foundation soil; γ is the weight of the soil; B is the width of the disk ring; H is the buried depth of the disk; K0 is the lateral pressure coefficient of the soil; p c is the soil pressure on the pile side of the disk.

[0021] Furthermore, the calculation process of the bearing capacity of the disk is:

[0022] Q ub =SZ u ;

[0023] Among them, Q ub is the bearing capacity of the disk; S is the projected area of ​​the disk; Z u is the ultimate bearing capacity of the soil.

[0024] Furthermore, the calculation process of the projected area of ​​the disk is:

[0025]

[0026] Where S is the projected area of ​​the disk; D1 is the disk diameter; and D2 is the pile diameter.

[0027] Furthermore, the basic parameters of the soil constitutive relation are obtained through cross-plate shear tests.

[0028] Furthermore, with L i The corresponding standard value of friction resistance between the soil layer and the pile side q ik Determined by single pile friction test. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present invention are shown in an illustrative and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0030] Figure 1 This is a flow chart of the method for predicting the bearing capacity of single-plate branch piles;

[0031] Figure 2 It is a force diagram of a single-plate branch pile;

[0032] Figure 3 Schematic diagram of the shape of the shear failure surface and displacement field around the disk. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0034] It should be understood that when the terms "first," "second," and the like are used in the claims, description, and drawings of the present invention, they are merely used to distinguish between different objects, rather than to describe a specific order. The terms "comprise" and "comprising" used in the description and claims of the present invention indicate the presence of the described features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof.

[0035] In one embodiment, a method for predicting the bearing capacity of a single-plate branch pile is provided. Figure 1 As shown, the following steps are included:

[0036] 1) Obtain the basic parameters of the soil constitutive relationship and the geometric parameters of the pile body.

[0037] In this step, the basic parameters of the soil constitutive relationship are obtained through the cross-plate shear test. The basic parameters of the soil constitutive relationship include: cohesion c (i.e. soil cohesion), internal friction angle of foundation soil The specific gravity of the soil is γ.

[0038] The geometric parameters of the pile body include: ring width B, pile end cross-sectional area A c , disk burial depth H, disk diameter D1, pile diameter D2.

[0039] 2) According to the cohesion c and internal friction angle of foundation soil in step 1) The ultimate bearing capacity Z of the soil is calculated based on the limit equilibrium theory, which is the weight of the soil, the width of the disk ring B, and the buried depth H of the disk. u .

[0040] The calculation process of the ultimate bearing capacity of soil is:

[0041] Z u =Z u1 +Z u2 ;

[0042]

[0043]

[0044]

[0045] Among them, Z u1 is the ultimate bearing capacity component of the foundation related to the cohesion c and the buried depth H of the disk, Z u2 is the ultimate bearing capacity component of the foundation related to the foundation size, p c is the soil pressure on the pile side of the disk, N c 、N q and N γ is the partial coefficient of the ultimate bearing capacity of the foundation; K0 is the lateral pressure coefficient of the soil;

[0046] Finally, we get:

[0047]

[0048] 3) Calculate the projected area S of the disk based on the disk diameter D1 and pile diameter D2 in step 1).

[0049] The calculation process of the projected area S is:

[0050]

[0051] 4) The ultimate bearing capacity Z of the soil obtained according to step 2) u The bearing capacity Q of the disk is calculated based on the projected area S of the disk obtained in step 3) ub .

[0052] The calculation process of the bearing capacity of the disk is:

[0053] Q ub =SZ u .

[0054] The research process of the bearing capacity of the disk of the present invention is as follows:

[0055] First, a model loading test was conducted to study the stress characteristics of the branch pile. Figure 2 As shown, it includes pile side resistance 1, pile side resistance 2 and disk end resistance;

[0056] Then, the displacement of the foundation soil around the disk was studied through transparent soil tests, and the bearing capacity of the disk was theoretically analyzed using Meyerhof's modified method of Terzaghi (Meyerhof further developed Terzaghi's method by modifying the failure surface and applied this solution to the assessment of the bearing capacity of vertical piles. Recent studies have shown that Meyerhof's method is more realistic in predicting the bearing capacity of vertical pile tips). Figure 3 As shown, Figure 3 The geometry of the shear failure surface around the disk is shown, and the displacement field around the disk is similar to the failure surface of the deep foundation;

[0057] Finally, the calculation formula for the bearing capacity of the above disk is obtained.

[0058] 5) The cross-sectional area A of the pile end obtained according to step 1) c , the ultimate bearing capacity Z of the soil obtained in step 2) u , and the bearing capacity Q of the disk obtained in step 4) ub The bearing capacity Q of a single-plate branch pile is calculated based on the calculation principle of the bearing capacity of ordinary cast-in-place piles. u .

[0059] The calculation process of the bearing capacity of a single-plate branch pile is as follows:

[0060] Q u =μΣq ik L i +Q ub +A c Z u ;

[0061] Where μ is the perimeter of the pile; L i The thickness of the i-th soil layer below the bottom surface of the foundation should be deducted by 1.2 times the height of each support and plate; q ik For L i The standard value of friction resistance between the corresponding soil layer and the pile side should be determined by a single pile friction resistance test. When there are no test conditions, it should be selected according to the technical specifications for squeezed branch pile engineering.

[0062] The prediction method of the present invention is described below with reference to a specific embodiment.

[0063] Determine the parameters as follows:

[0064] Basic parameters of soil constitutive relations: cohesion c (ordinary fill: 42.5kPa, silty soil: 15.4kPa, mud soil: 29.6kPa, silty clay: 40kPa), internal friction angle of foundation soil Soil density γ=18kN / m 3 .

[0065] Geometric parameters of the pile body: ring width B = 0.5m, pile end cross-sectional area A c =0.283m 2 , the buried depth of the disk is H = 12m, the disk diameter is D1 = 1.6m; the pile diameter is D2 = 0.6m.

[0066] At the same time, the perimeter of the pile is determined to be μ = 1.88m, the thickness of the i-th soil layer below the bottom of the pedestal is L i =13.04m.

[0067] According to the above parameters, the N of the soil is obtained. c 、N q and N γare 408.7, 142.7 and 303.2 respectively, and then the ultimate bearing capacity Z of the soil is obtained. u =1.150MPa.

[0068] And calculate the bearing capacity Q of the disk ub =855.3kN, and then the ultimate bearing capacity Q of the single-plate branch pile is calculated u =1828kN.

[0069] In order to verify the accuracy of the prediction of the present invention, four piles were selected to compare the predicted values ​​(i.e., calculated values) obtained by the present invention with the test values. The comparison results are shown in Table 1.

[0070] Table 1 Comparison results

[0071] Pile number <![CDATA[p c (kPa)]]> Calculated value (kN) Test value (kN) error(%) p14 198 816.3 855.3 4.56 p22 342 1065.1 1029.6 3.45 p30 486 1480.4 1356.1 9.17 p38 630 1729.1 1612.3 7.24

[0072] Table 1 shows the comparison between the calculated and tested bearing capacities of the discs. The calculated bearing capacity of the P14 pile disc is 816.3 kN, and the tested value is 855.3 kN; the calculated bearing capacity of the P22 pile disc is 1065.1 kN, and the tested value is 1029.6 kN; the calculated bearing capacity of the P30 pile disc is 1480.4 kN, and the tested value is 1356.1 kN; the calculated bearing capacity of the P38 pile disc is 1729.1 kN, and the tested value is 1612.3 kN. By observing the data of the four piles p14, p22, p30, and p38, the calculated and tested bearing capacities of the discs are very close. In summary, the present invention can simulate field tests relatively accurately and can well predict the bearing capacity of single-disc branch piles.

Claims

1. A method for predicting the bearing capacity of a single-plate branch pile, characterized in that: The forecasting method includes: Obtain the basic parameters of the soil constitutive relationship and the geometric parameters of the pile body. The basic parameters of the soil constitutive relationship include cohesion, internal friction angle of foundation soil, and soil density; the geometric parameters of the pile body include disk ring width, pile end cross-sectional area, disk burial depth, disk diameter, and pile diameter; The ultimate bearing capacity of the soil is calculated based on the limit equilibrium theory according to the cohesion, the internal friction angle of the foundation soil, the weight of the soil, the width of the disk ring, and the embedding depth of the disk. The projected area of ​​the disk is calculated based on the disk diameter and the pile diameter; The bearing capacity of the plate is calculated based on the ultimate bearing capacity of the soil and the projected area of ​​the plate. The bearing capacity of the plate is positively correlated with the ultimate bearing capacity of the soil and the projected area of ​​the plate. The bearing capacity of a single-plate branch pile is calculated based on the cross-sectional area of ​​the pile end, the ultimate bearing capacity of the soil, and the bearing capacity of the plate, combined with the calculation principle of the bearing capacity of ordinary cast-in-place piles. The calculation process of the bearing capacity of a single-plate branch pile is as follows: Q n =μ∑q ik L i +Q nb +A c Z u ; Among them, Q u is the bearing capacity of a single-plate branch pile; μ is the circumference of the pile; L i The thickness of the i-th soil layer below the bottom surface of the foundation should be deducted by 1.2 times the height of each support and plate; q ik For L i The corresponding standard value of friction resistance between the soil layer and the pile side; Q ub is the bearing capacity of the disk; A c is the cross-sectional area of ​​the pile end; Z u is the ultimate bearing capacity of the soil, The calculation process of the ultimate bearing capacity of soil is: Among them, Z u is the ultimate bearing capacity of the soil; c is the cohesion; is the internal friction angle of the foundation soil; γ is the weight of the soil; B is the width of the disk ring; H is the buried depth of the disk; K0 is the lateral pressure coefficient of the soil; p c is the soil pressure on the pile side of the disk, The calculation process of the bearing capacity of the disk is: Q ub =SZ u ; Among them, Q ub is the bearing capacity of the disk; S is the projected area of ​​the disk; Z u is the ultimate bearing capacity of the soil, The calculation process of the projected area of ​​the disk is: Where S is the projected area of ​​the disk; D1 is the disk diameter; and D2 is the pile diameter.

2. The method for predicting the bearing capacity of a single-plate branch pile according to claim 1, characterized in that: The basic parameters of the soil constitutive relationship are obtained through cross-plate shear tests.

3. The method for predicting the bearing capacity of a single-plate and branch-plate pile according to claim 1, characterized in that: With L i The corresponding standard value of friction resistance between the soil layer and the pile side q ik Determined by single pile friction test.

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