Design method of uplift bearing capacity of excavated foundation of power transmission line

Abstract

The present application relates to a kind of transmission line excavated foundation uplift bearing capacity design method, by the equivalent straight line AB of excavated foundation uplift soil mass slip surface, construct straight line slip surface model, deduce a kind of excavated foundation uplift bearing capacity calculation formula from straight line slip surface model, the formula only contains 3 unknown parameters, respectively, according to the equivalent internal friction angle of equivalent internal friction angle excavated foundation bottom diameter D and straight line slip surface model height h that the cohesion and internal friction angle in geology are equivalent according to shear stress equivalence principle, calculation is simple and convenient for engineers to use, by the classification of equivalent internal friction angle, compile into bearing capacity table, for engineering personnel to use, provide great convenience for engineers.

Description

Technical Field

[0001] This invention relates to the field of power transmission line foundation design, specifically to a method for designing the uplift bearing capacity of a power transmission line excavation foundation. Background Technology

[0002] Excavated foundations for overhead transmission lines are mainly used in hilly and mountainous areas with thin overburden. Due to the use of enlarged head type, they can provide relatively large uplift bearing capacity and are widely used in transmission lines. However, the current power industry involves many soil mechanics parameters, and the process of calculating the ultimate uplift bearing capacity of the foundation is complicated and not convenient for actual engineering use. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for designing the uplift bearing capacity of a transmission line excavation foundation, comprising: Based on the principle of equal shear strength, the soil cohesion c and the internal friction angle are considered... Equivalent to equivalent internal friction angle ; The slip surface of the excavated soil on the basis is equivalent to a straight line AB, and a straight slip surface model is constructed. Calculate the volume between the bottom of the excavated foundation and the height of the straight slip surface model. ; Calculate the ultimate pull-out bearing capacity of the excavated foundation Components along the vertical direction ; Based on the volume between the bottom of the excavated foundation and the height of the straight slip surface model The self-weight of the straight slip surface model was obtained by calculating the average unit weight of the soil where the foundation was excavated. ; Utilizing the principle of force balance, based on the ultimate pull-out bearing capacity of the excavation foundation... Components along the vertical direction The self-weight of the straight slip surface model The ultimate pull-out bearing capacity of the excavation foundation of the straight slip surface model was calculated. ; Based on the equivalent internal friction angle Different geological types are classified, and the corresponding ultimate uplift bearing capacity of the excavation foundation is calculated. The corresponding ultimate pull-out bearing capacity of the excavated foundation The results are presented in a load-bearing capacity table for engineers to use.

[0004] Preferably, the equivalent internal friction angle Expressed as a formula: ; In the formula, The average unit weight of the soil. The height of the straight slip surface model. For soil cohesion, It is the internal friction angle.

[0005] Preferably, the linear slip surface model is a frustum-shaped slip surface formed by rotating a straight line AB 360° around the Z-axis, and the angle between the slip surface and the horizontal plane is... .

[0006] Preferably, the volume between the bottom of the excavated foundation and the height of the straight slip surface model is calculated. include: In line AB, the direction closer to the ground surface is direction A, and the direction closer to the bottom of the excavation foundation is direction B. Extend line BA to intersect the Z-axis at point E. Rotate line segment BE around the Z-axis by a small angle dθ to obtain the infinitesimal elements 0AA'MBB', triangular pyramid EMBB', and triangular pyramid EOAA'. The volume of the triangular pyramid EMBB' is calculated and expressed by the formula: ; in: ; ; In the formula, Let E be the height from point E to the bottom of the excavated foundation. D represents the height of the straight slip surface model, and D represents the diameter of the bottom of the excavation foundation. ; The volume of the triangular pyramid EOAA' is calculated and expressed by the formula: ; in: ; The volume of the infinitesimal element 0AA'MBB' is calculated by subtracting the volume of the triangular pyramid EOAA' from the volume of the triangular pyramid EMBB', and can be expressed by the formula:

[0007] ; The volume of the infinitesimal element 0AA'MBB' is rotated around the Z-axis. Integrating within the angular range yields the volume between the bottom of the excavated foundation and the height of the straight slip surface model. Expressed as a formula:

[0008] Preferably, the ultimate pull-out bearing capacity of the excavated foundation is calculated. Components along the vertical direction ,include: The gravity of the infinitesimal element 0AA'MBB' is calculated using the following formula: ; The normal stress component on the slip surface caused by the gravity of the infinitesimal element 0AA'MBB' is obtained through gravity calculation. Expressed as a formula: ; The normal stress component on the slip surface caused by the gravity of the infinitesimal element 0AA'MBB' Calculate the shear strength of the soil where the excavation foundation is located. Expressed as a formula: ; The shear strength of the soil where the excavation foundation is located Perform force analysis to obtain the vertical components. Expressed as a formula: ; The vertical component of the shear strength of the soil where the foundation is located. 0- on both sides around the Z-axis Integrating within the angle range yields the ultimate pull-out bearing capacity of the excavated foundation. Components along the vertical direction Expressed as a formula: =

[0009]

[0010] .

[0011] Preferably, based on the volume between the bottom of the excavated foundation and the height of the straight slip surface model. The self-weight of the straight slip surface model was obtained by calculating the average unit weight of the soil where the foundation was excavated. Expressed as a formula: .

[0012] Preferably, the ultimate pull-out bearing capacity of the excavation foundation is determined by utilizing the principle of force balance. Ultimate pull-out bearing capacity of excavated foundation Components along the vertical direction The self-weight of the straight slip surface model The sum, expressed by the formula: =

[0013] .

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for designing the uplift bearing capacity of excavated foundations for transmission lines. By equating the slip surface of the excavated soil mass to a straight line AB, a straight slip surface model is constructed. From this model, a formula for calculating the uplift bearing capacity of the excavated foundation is derived. This formula contains only three unknown parameters: the equivalent internal friction angle, which is calculated by equivalence of the cohesion and internal friction angle in the geology based on the principle of equal shear stress. The bottom diameter D of the excavated foundation and the height of the straight slip surface model. The calculation is simple and convenient for engineers to use, based on the equivalent internal friction angle. They are categorized and compiled into load-bearing capacity tables for engineers to use, providing great convenience for engineers. Attached Figure Description

[0015] Figure 1 This is a flowchart of a method according to an embodiment of the present invention; Figure 2 The prior art of this invention includes a model of a circular arc slip surface for excavation of a foundation; Figure 3 This is a straight slip surface model of the excavation foundation according to an embodiment of the present invention; Figure 4 It is a micro-element of the linear slip surface model in this embodiment of the invention; Figure 5 This is a force analysis diagram of the micro-element model of the straight slip surface in an embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1 Embodiment 1 of the present invention discloses a method for designing the uplift bearing capacity of a transmission line excavation foundation, comprising: S1. Based on the principle of equal shear strength, the soil cohesion c and the internal friction angle are considered... Equivalent to equivalent internal friction angle Expressed as a formula: ; In the formula, The average unit weight of the soil. The height of the straight slip surface model. For soil cohesion, It is the internal friction angle; S2. Equivalently represent the slip surface of the excavated soil as a straight line AB and construct a straight slip surface model; like Figure 2 As shown, in current standard methods, the fracture surface of the soil removed from the excavation foundation is an arc shape. In this embodiment, the slip surface of the soil removed from the excavation foundation is equivalent to a straight line AB. In the straight line AB, the direction closer to the ground surface is direction A, and the direction closer to the bottom of the excavation foundation is direction B. Rotating the straight line AB 360° around the Z-axis forms a frustum-shaped slip surface, i.e., a straight slip surface model, as shown. Figure 5 As shown, the angle between the slip surface and the horizontal plane is... ,definition ; S3. Calculate the volume between the bottom of the excavated foundation and the height of the straight slip surface model. ; S31, such as Figure 3 As shown, extend the straight line BA to intersect the Z-axis at point E, and rotate the line segment BE around the Z-axis by a small angle dθ to obtain the infinitesimal elements 0AA'MBB', the triangular pyramid EMBB', and the triangular pyramid EOAA'. S32. Calculate the volume of the triangular pyramid EMBB', expressed by the formula: ; in, It is a triangle The surface, expressed by the formula: ; Based on geometric relationships, we can conclude that: ; ; In the formula, Let E be the height from point E to the bottom of the excavated foundation. The height of the straight slip surface model is given by denoted as D, and the bottom diameter of the excavation foundation is given by denoted as D. Based on the above formula, it can be deduced that: ; S33. Calculate the volume of the triangular pyramid EOAA', expressed by the formula: ; in, It is a triangle The surface, expressed by the formula: ; S34. The volume of the infinitesimal element 0AA'MBB' is obtained by subtracting the volume of the triangular pyramid EOAA' from the volume of the triangular pyramid EMBB', and expressed by the formula:

[0018] ; S35. The volume of the infinitesimal element 0AA'MBB' is rotated around the Z-axis. Integrating within the angular range yields the volume between the bottom of the excavated foundation and the height of the straight slip surface model. Expressed as a formula:

[0019] ; S4. Calculate the ultimate pull-out bearing capacity of the excavated foundation. Components along the vertical direction ; S41. Calculate the gravity of the infinitesimal element 0AA'MBB', expressed by the formula: ; S42. Obtain the normal stress component on the slip surface caused by the gravity of the infinitesimal element 0AA'MBB' through gravity calculation. Expressed as a formula: ; S43. Based on relevant knowledge of soil mechanics and Coulomb's theory, determine the shear strength of the soil where the foundation is located. It can be represented as: Based on the normal stress components on the slip surface caused by the gravity of the infinitesimal element 0AA'MBB' Calculate the shear strength of the soil where the excavation foundation is located. Expressed as a formula: ; S44, such as Figure 5 As shown, the shear strength of the soil where the excavation foundation is located... Perform force analysis to obtain the vertical components. Expressed as a formula: ; S45. Vertical component of the shear strength of the soil where the foundation is located. 0- on both sides around the Z-axis Integrating within the angle range yields the ultimate pull-out bearing capacity of the excavated foundation. Components along the vertical direction Expressed as a formula: =

[0020]

[0021] ; S5. Based on the volume between the bottom of the excavated foundation and the height of the straight slip surface model. The self-weight of the straight slip surface model was obtained by calculating the average unit weight of the soil where the foundation was excavated. Expressed as a formula: ; S6. Utilizing the principle of force balance, determine the ultimate tensile bearing capacity of the excavated foundation. Ultimate pull-out bearing capacity of excavated foundation Components along the vertical direction The self-weight of the straight slip surface model The sum, expressed by the formula: =

[0022] ; S7. Based on the equivalent internal friction angle Different geological types are classified, and different excavation foundation bottom diameters (D) and excavation foundation burial depths are classified. Calculate the ultimate pull-out bearing capacity of the corresponding excavated foundation. The corresponding ultimate pull-out bearing capacity of the excavated foundation The results are presented in a load-bearing capacity table for engineers to use.

[0023] The following provides an application of the pull-out bearing capacity design method for excavated foundations of transmission lines described in this invention. Taking a 220kV double-circuit type 1 tension tower as an example, the pull-out design of the excavated foundation is carried out. To facilitate its use in actual design, this embodiment categorizes the ultimate bearing capacity table according to different equivalent internal friction angles. , , , , Divided into five sub-tables, corresponding to Table 1, Table 2, Table 3, Table 4, and Table 5 respectively: Table 1

[0024] Table 2

[0025] Table 3

[0026] Table 4

[0027] Table 5

[0028] T1. Design Input Conditions: Geological conditions: silty clay foundation, soil internal friction angle =18°, soil cohesion c=15kPa, average soil unit weight γ=18.0kN / m3; T2. Calculate the range of the equivalent internal friction angle: Due to the equivalent internal friction angle and foundation depth Therefore, it is necessary to calculate the equivalent internal friction angle when the foundation depth is between 2.0m and 6.0m. The range is as follows: =2.0m: 36.5° (Refer to the table as 35°) =2.5m: 33.4° (Refer to table based on 30°) =3.0m: 31.1° (Refer to table based on 30°) =3.5m: 29.3° (Refer to table based on 25°) =4.0m: 28.1° (Refer to table based on 25°) =4.5m: 27.0° (Refer to table based on 25°) =5.0m: 26.2° (Refer to table based on 25°) =5.5m: 25.5° (Refer to the table based on 25°) =6.0m: 24.9° (refer to the table based on 20°); T3. Select the appropriate foundation dimensions based on the magnitude of the foundation force. Here, dimensions refer to the depth of the excavated foundation. and the diameter D of the bottom of the excavated foundation; If the standard value of the pull-out force on the foundation is Tk, since the bearing capacity in the bearing capacity table is the ultimate value and the safety factor for pull-out on the foundation is 2.0, the bearing capacity in the appendix should be divided by 2.0 before comparing it with the standard value of the pull-out bearing capacity on the foundation. This ensures that the standard value of the pull-out bearing capacity on the foundation is not greater than the ultimate bearing capacity in the appendix divided by 2.0, that is:

[0029] T31. When the standard value of the pull-out bearing capacity of the foundation is Tk = 1800kN, for the eight groups in step T2... The values ​​are looked up in the table from smallest to largest until the value corresponding to the diameter D of the bottom of the excavated foundation is found. The value satisfies the requirements of the above formula.

[0030] =2.0m, referring to Table 4, the corresponding maximum bearing capacity is 2488.13 / 2.0=1244.07kN<1800kN, which does not satisfy the above formula; =2.5m, referring to Table 3, the corresponding maximum bearing capacity is 3417.66 / 2.0=1708.83kN<1800kN, which does not satisfy the above formula; =3.0m, referring to Table 3, when D=2.0m: the corresponding maximum bearing capacity is 3689.85 / 2.0=1844.9kN>1800kN, which satisfies the above formula; Therefore, the depth of the excavation foundation =3.0m, with a bottom diameter D=2.0m for the excavated foundation, which can be applied to tower foundations with a standard uplift bearing capacity of Tk=1800kN under this type of geological conditions.

[0031] T32, the standard value of the pull-out force on the foundation is Tk=2800kN, for the eight groups in step T2. The values ​​are looked up in the table from smallest to largest until the corresponding bottom diameter D of the excavated foundation is found. The value satisfies the formula in step T3; =2.0m, referring to Table 4, the corresponding maximum bearing capacity is 2488.13 / 2.0=1244.07kN<2800kN, which does not meet the formula; =2.5m, referring to Table 3, the corresponding maximum bearing capacity is 3417.66 / 2.0=1708.83kN<2800kN, which does not meet the formula; =3.0m, referring to Table 3, the corresponding maximum bearing capacity is 5136.94 / 2.0=2568.47kN<2800kN, which does not satisfy the formula; =3.5m, referring to Table 3, when D=2.2m: the corresponding maximum bearing capacity is 5702.05 / 2.0=2851.02kN>2800kN, which satisfies the formula; Therefore, the depth of the excavation foundation =3.5m, with a bottom diameter of D=2.2m for the excavated foundation, which can be applied to tower foundations with a standard uplift bearing capacity of Tk=2800kN under this type of geological conditions.

[0032] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for designing the uplift bearing capacity of a transmission line excavation foundation, characterized in that, include: Based on the principle of equal shear strength, the soil cohesion c and the internal friction angle are considered... Equivalent to equivalent internal friction angle Expressed as a formula: ； In the formula, The average unit weight of the soil. The height of the straight slip surface model. For soil cohesion, It is the internal friction angle; The slip surface of the excavated soil on the foundation is equivalent to a straight line AB, and a straight slip surface model is constructed. The angle between the slip surface and the horizontal plane is... ; Calculate the volume between the bottom of the excavated foundation and the height of the straight slip surface model. ,include: In line AB, the direction closer to the ground surface is direction A, and the direction closer to the bottom of the excavation foundation is direction B. Extend line BA to intersect the Z-axis at point E. Rotate line segment BE around the Z-axis by a small angle dθ to obtain the infinitesimal elements OAA'MBB', triangular pyramid EMBB', and triangular pyramid EOAA'. The volume of the triangular pyramid EMBB' is calculated and expressed by the formula: ； in: ； ； In the formula, Let E be the height from point E to the bottom of the excavated foundation. D represents the height of the straight slip surface model, and D represents the diameter of the bottom of the excavation foundation. ; The volume of the triangular pyramid EOAA' is calculated and expressed by the formula: ； in: ； The volume of the infinitesimal element OAA'MBB' is calculated by subtracting the volume of the triangular pyramid EOAA' from the volume of the triangular pyramid EMBB', and expressed by the formula: ； The volume of the infinitesimal element OAA'MBB' is rotated around the Z-axis at 0- Integrating within the angular range yields the volume between the bottom of the excavated foundation and the height of the straight slip surface model. Expressed as a formula: ； Calculate the ultimate pull-out bearing capacity of the excavated foundation Components along the vertical direction ; Based on the volume between the bottom of the excavated foundation and the height of the straight slip surface model The self-weight of the straight slip surface model was obtained by calculating the average unit weight of the soil where the foundation was excavated. ; Utilizing the principle of force balance, based on the ultimate pull-out bearing capacity of the excavation foundation... Components along the vertical direction The self-weight of the straight slip surface model The ultimate pull-out bearing capacity of the excavation foundation of the straight slip surface model was calculated. ; Based on the equivalent internal friction angle Different geological types are classified, and the corresponding ultimate uplift bearing capacity of the excavation foundation is calculated. The corresponding ultimate pull-out bearing capacity of the excavated foundation The results are presented in a load-bearing capacity table for engineers to use.

2. The method for designing the uplift bearing capacity of a transmission line excavation foundation according to claim 1, characterized in that, Calculate the ultimate pull-out bearing capacity of the excavated foundation Components along the vertical direction ,include: The gravity of the infinitesimal element OAA'MBB' is calculated using the following formula: ； The normal stress component on the slip surface caused by the gravity of the infinitesimal element OAA'MBB' is obtained through gravity calculation. Expressed as a formula: ； The normal stress component on the slip surface caused by the gravity of the infinitesimal element OAA'MBB' Calculate the shear strength of the soil where the excavation foundation is located. Expressed as a formula: ； The shear strength of the soil where the excavation foundation is located Perform force analysis to obtain the vertical components. Expressed as a formula: ； The vertical component of the shear strength of the soil where the foundation is located. 0- on both sides around the Z-axis Integrating within the angle range yields the ultimate pull-out bearing capacity of the excavated foundation. Components along the vertical direction Expressed as a formula: = 。 3. The method for designing the uplift bearing capacity of a transmission line excavation foundation according to claim 2, characterized in that, Based on the volume between the bottom of the excavated foundation and the height of the straight slip surface model The self-weight of the straight slip surface model was obtained by calculating the average unit weight of the soil where the foundation was excavated. Expressed as a formula: 。 4. The method for designing the uplift bearing capacity of a transmission line excavation foundation according to claim 3, characterized in that, Utilizing the principle of force balance, the ultimate tensile bearing capacity of the excavation foundation is determined. Ultimate pull-out bearing capacity of excavated foundation Components along the vertical direction The self-weight of the straight slip surface model The sum, expressed by the formula: = 。

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