Design method for rock built-in foundation under slope terrain

Abstract

The invention discloses a method for designing a rock build-in foundation under a slope terrain. The method comprises the following steps: constructing an initial model of a transmission tower rock build-in foundation under a slope condition; a rock built-in foundation damage area under the action of the drawing load is calculated, and a generalized model is constructed according to the size of the damage area; the ultimate uplift bearing capacity T of the built-in foundation is obtained through calculation; 4, according to the environment where the transmission tower is located, the maximum pull-up force of the built-in foundation under the strong wind working condition, the icing working condition and the wire breaking working condition is worked out, whether the pull-up force meets the ultimate pull-up bearing requirement or not is judged, if the pull-up force does not meet the design requirement, the size of the built-in foundation needs to be increased, and then the steps 1-4 are repeated. The construction method has the beneficial effects that the transmission tower rock build-in foundation is designed based on the slope terrain, and the weakening influence of the slope gradient on the ultimate uplift bearing capacity is considered, so that the foundation can be kept stable under extreme conditions.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a rock embedded foundation design method for slope terrain. Background Art

[0002] With the rapid development of my country's economy, the demand for electricity has grown rapidly. Electricity plays an increasingly important role in social production and people's lives. Once there is a power shortage, serious problems will inevitably arise in economic development and people's lives. With the construction of national networking projects, high-voltage transmission towers will inevitably be erected on the edge of ridges and steep slopes. However, due to the potential hazards brought by extreme climate such as strong winds in the southwest region all year round and the tension of wires, the safety and stability of the transmission line foundation project will be affected. In order to ensure that the foundation of the transmission tower can support the overhead power lines and transmission systems, the design of the transmission tower foundation under pull-out resistance is very important.

[0003] At present, the main types of tower foundations in my country's mountainous power transmission line projects are formed by full excavation and large excavation. Large excavation foundations require a large excavation of the foundation surface, causing serious soil and water loss, which is extremely unfavorable to environmental protection and sometimes even threatens the safety of the tower foundation. In response to this problem, some provinces and cities have adopted rock embedded foundations to replace large excavation foundations. Compared with conventional transmission tower foundations, rock embedded foundations have the characteristics of small plane size and greatly reduced mountain excavation. In mountainous power transmission line projects, embedded foundations have broad application prospects due to their unique advantages.

[0004] However, most of the current design methods for embedded foundations are designed for flat land, and the design method mainly designs and calculates the ultimate uplift bearing capacity of rock foundations. However, the existing methods do not consider the weakening effect of slope on the ultimate uplift bearing capacity, and when directly used for the design of rock embedded foundations under slope conditions, it is easy to cause the foundation to become unstable and damaged under extreme conditions. Summary of the invention

[0005] The purpose of the present invention is to provide a rock embedded foundation design method for slope terrain in view of the deficiencies of the prior art, so as to keep the foundation stable under extreme conditions.

[0006] The technical solution adopted by the present invention is: a rock embedded foundation design method for slope terrain, the method comprising the following steps:

[0007] Step 1: Determine the design position of the rock-embedded foundation of the transmission tower according to the slope terrain, and construct an initial model of the rock-embedded foundation of the transmission tower under slope conditions;

[0008] Step 2: According to the initial model of the rock-embedded foundation of the transmission tower under slope conditions, the failure area of ​​the rock-embedded foundation under the pull-out load is calculated, and a generalized model is constructed according to the size of the failure area;

[0009] Step 3: Calculate and obtain the ultimate pull-out bearing capacity T of the embedded foundation;

[0010] Step 4: According to the environment in which the transmission tower is located, calculate the maximum pull-out force of the embedded foundation under strong wind conditions, icing conditions, and broken wire conditions, and determine whether the pull-out force meets the ultimate pull-out bearing requirements. If it does not meet the design requirements, increase the size of the embedded foundation, and then repeat steps 1 to 4 until the requirements are met.

[0011] According to the above scheme, the calculation method of the ultimate pull-out bearing capacity T is:

[0012] T=W+τ f S1cosω (15).

[0013] In formula (15), the surface area of ​​the failure zone of the embedded foundation is S1; τ f is the shear strength on the failure surface, in units of pa; ω is an intermediate parameter with no specific meaning; W is the gravity of the rock failure zone, in units of N; the embedded foundation and the surrounding destroyed rock mass constitute the total gravity W of the foundation and the failure zone, and its calculation formula is as follows:

[0014] W = W1 + W2 (16);

[0015] In formula (16), W1 is the gravity of the embedded foundation, in N; W2 is the gravity of the rock mass in the damaged area, in N; the two are:

[0016] W1=γ1V1 (17);

[0017] W2=γ2V2 (18);

[0018] In formulas (17) and (18), γ1 is the density of the embedded foundation material, in N / m 3 ; γ2 is the weight of surrounding rock, in N / m 3 ; V1 is the volume of the embedded foundation, in m 3 ; V2 is the volume of the destroyed rock mass, in m 3 ;

[0019] V3 is an imaginary oblique cone, V is the total volume of V1, V2 and V3. According to the mathematical geometric relationship, the expressions of V1 and V2 can be obtained as follows:

[0020]

[0021] V2 = V - V1 - V3 (20);

[0022]

[0023] b2=-2Rcotω2 (24);

[0024] k = tanα (25);

[0025] According to the Mohr-Coulomb theory, the shear strength on the failure surface is calculated as:

[0026]

[0027] In formulas (19) to (27), α is the inclination angle of the slope; r is the top radius of the embedded foundation, in m; h is the height of the embedded foundation, in m; R is the bottom radius of the embedded foundation, in m; c is the cohesion of the surrounding rock, in Pa; The internal friction angle of the surrounding rock; σ is the normal stress of the surrounding rock, in Pa; ω1 and ω2 are the angles between the failure surfaces on both sides of the failure area; b2, b, k, k1, k2 are intermediate parameters with no specific meaning;

[0028] H and ω are intermediate parameters, and their expressions are:

[0029]

[0030] According to the above scheme, the calculation method of the surface area S1 of the damaged area of ​​the embedded foundation is:

[0031] The surface area S1 of the failure zone of the embedded foundation is the area S of the complete oblique cone minus the area S2 of the oblique cone at the tip, that is:

[0032] S1=S-S2 (1);

[0033]

[0034]

[0035] u=d-k2(x0+R′) (11);

[0036]

[0037] x0=dtanω1 (14).

[0038] In the above formulas, r is the top radius of the embedded foundation, in m; h is the height of the embedded foundation, in m; R′ is the distance between the surface point of the failure surface near the slope foot and the embedded foundation, in m; y is the ordinate, in m; among them, R is the bottom radius of the embedded foundation, in m; f1′(y), f2′(y), f3′(y) and f4′(y) are the derivatives of f1(y), f2(y), f3(y) and f4(y), respectively; k1, k2, u, d, m1, n1, n2, x0 are all intermediate parameters without specific meanings.

[0039] According to the above scheme, in step 4, when the calculated maximum pull-out force is less than the ultimate pull-out bearing capacity and does not meet the design requirements, the design height of the embedded foundation is increased, and the latter design height is increased by 5% based on the previous design height.

[0040] According to the above scheme, whether the pull-out force meets the ultimate pull-out bearing requirement is determined as follows: if the calculated maximum pull-out force is greater than the ultimate pull-out bearing capacity, the design requirements are met and the design dimensions meet the requirements; if the calculated maximum pull-out force is less than the ultimate pull-out bearing capacity, the design requirements are not met.

[0041] The beneficial effects of the present invention are as follows: the present invention designs the rock-embedded foundation of the transmission tower based on the slope terrain. Compared with the existing technology, the weakening effect of the slope gradient on the ultimate pull-out bearing capacity is taken into consideration, so that the foundation can ensure stability under extreme conditions while also better saving materials and construction costs. These improvements take into account both economy and safety, and have broad application prospects and significant economic and social benefits in the field of transmission line foundations. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a plan view of the failure surface of the embedded foundation under slope conditions.

[0043] Figure 2 It is a three-dimensional schematic diagram of the failure surface of the embedded foundation under slope conditions.

[0044] Figure 3 Schematic diagram for calculating the fracture surface area.

[0045] Figure 4 This is a schematic diagram of the coordinate rotation of the failure surface of the embedded foundation under slope conditions.

[0046] Figure 5 Schematic diagram of the volume ratio of the failure surface. DETAILED DESCRIPTION

[0048] In order to better understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0049] A rock embedded foundation design method for slope terrain, specifically a rock embedded foundation design method for transmission towers in slope terrain, the method comprising the following steps:

[0050] Step 1: Determine the design position of the rock-embedded foundation of the transmission tower according to the slope terrain, and construct the initial model of the rock-embedded foundation of the transmission tower under slope conditions.

[0051] In the present invention, Figure 1 As shown, the inclination angle of the slope 3 (the angle between the slope and the horizontal plane) is α;

[0052] The design position of the rock embedded foundation 2 is determined according to the transmission line and geological conditions; the rock embedded foundation 2 is designed as a truncated cone structure, and the initial design height of the rock embedded foundation 2 is h according to the design requirements; the top diameter, bottom diameter and other parameters of the rock embedded foundation 2 are preliminarily set according to the convenience of construction and the inclination of the rock embedded foundation. A working platform 1 is set up in the top area of ​​the rock embedded foundation, and the height of the working platform 1 is L. The width of the platform is for the convenience of construction, and it must be greater than the top diameter of the foundation by 0.5m. The height L is set according to the slope gradient and the width of the platform.

[0053] Step 2: Based on the initial model of the rock-embedded foundation of the transmission tower under slope conditions, calculate the failure area of ​​the rock-embedded foundation under the pull-out load, and construct a generalized model based on the size of the failure area, such as Figure 1 shown.

[0054] In the present invention, the failure area of ​​the rock embedded foundation is caused by the pull-out load and is determined according to the range of the plastic zone of the rock. In this embodiment, the conventional method is used to calculate the failure area of ​​the rock embedded foundation under the pull-out load. The shape of the failure area is a part of an oblique cone (such as Figure 2 As shown, it is equivalent to cutting off the tip of the oblique cone), and any cross section parallel to the bottom of the oblique cone is a circle; Figure 1 The red dashed line in the figure is the outer contour of the damage area, that is, the damage surface. The generalized model shows the vertical angles ω1 and ω2 of the damage surfaces on both sides, and the depths h1 and h2 of the damage area (h1 and h2 are the depths of the damage surfaces on both sides of the damage area, respectively, as shown in Figure 2. Figure 1 as shown), and the height L of the working platform.

[0055] like Figure 3 As shown in the figure, the surface area S1 (in m) of the embedded foundation damage area 2 ), that is, the area of ​​the failure surface, is the surface area S of the complete oblique cone minus the surface area S2 of the oblique cone at the tip, that is:

[0056] S1=S-S2 (1).

[0057] In order to facilitate calculation, two sets of coordinate axes are used to calculate the area of ​​the failure surface. Figure 1 The coordinate axis shown in the figure, with the center as O1, the left point of the bottom of the embedded foundation as the origin, the horizontal direction of the bottom as the x-axis, and the vertical direction as the y-axis) is used to calculate the surface area S of the entire oblique cone. Rotate the model in 2 clockwise with the origin O1 of the coordinate axis as the origin and the slope slope α to obtain Figure 4 , the original coordinate axis changes to Figure 4 The coordinate axis 2 in corresponds to the origin O; calculate the surface area S2 of the missing oblique cone. According to the mathematical geometric relationship, the relationship between S and S2 can be calculated as follows:

[0058]

[0059] Where R is the bottom radius of the embedded foundation (in m); f1′(y), f2′(y), f3′(y) and f4′(y) are the derivatives of f1(y), f2(y), f3(y) and f4(y) respectively; k1, k2, u, d, m1, n1, n2 and x0 are all intermediate parameters used for convenient calculation and have no specific meaning; their expressions are:

[0060]

[0061] x0=dtanω1 (14).

[0062] In the above formulas, r is the top radius of the embedded foundation (in m); h is the height of the embedded foundation (in m); R′ is the distance between the surface point of the failure surface near the toe of the slope and the embedded foundation (in m); y is the vertical coordinate (in m).

[0063] Step 3: Calculate the ultimate pull-out bearing capacity T (in N) of the embedded foundation.

[0064] According to the limit equilibrium theory, the rock embedded foundation relies on the rock mass failure area, the foundation's own weight, and the vertical component of the shear strength on the failure surface to jointly resist the pull-out effect. From the mechanical equilibrium relationship, we can get:

[0065] T=W+τ f S1cosω (15).

[0066] In formula (15), τ f is the shear strength on the failure surface (in pa); ω is an intermediate parameter used for calculation convenience; W is the gravity of the rock failure zone (in N); the embedded foundation and the surrounding destroyed rock mass constitute the total gravity W of the foundation and the failure zone, and its calculation formula is as follows:

[0067] W = W1 + W2 (16);

[0068] In formula (16), W1 is the gravity of the embedded foundation (in N), and W2 is the gravity of the rock mass in the damaged area (in N), which are:

[0069] W1=γ1V1 (17);

[0070] W2=γ2V2 (18);

[0071] In formulas (17) and (18), γ1 is the density of the embedded foundation material (in N / m 3 ); γ2 is the weight of surrounding rock (in N / m 3 ); V1 is the volume of the embedded foundation (in m 3 ), V2 is the volume of the destroyed rock mass (in m 3 ).

[0072] like Figure 5 As shown in the figure, V3 is an imaginary oblique cone for the convenience of calculation, and V is the total volume of V1, V2 and V3. According to the mathematical geometric relationship, the expressions of V1 and V2 can be obtained as follows:

[0073]

[0074] V2 = V - V1 - V3 (20);

[0075]

[0076] b2=-2Rcotω2 (24);

[0077] k = tanα (25).

[0078] In formulas (19) to (25), b2, b, and k are intermediate parameters used for convenience of calculation and have no specific meanings; the meanings of other parameters such as k1 are the same as in formulas (2) to (18).

[0079] According to the Mohr-Coulomb theory, the shear strength on the failure surface is calculated as:

[0080]

[0081] In formulas (26) to (27), c is the cohesion of the surrounding rock, in Pa; is the internal friction angle of the surrounding rock; σ is the normal stress of the surrounding rock, in Pa; H and ω are intermediate parameters used for convenience of calculation, and the expression is:

[0082]

[0083] Step 4. According to the environment in which the transmission tower is located, calculate the maximum pull-out force of the embedded foundation under strong wind conditions, icing conditions, and broken wire conditions (which can be calculated according to the "110kV-750kV Overhead Transmission Line Design Specifications"), and determine whether the pull-out force meets the ultimate pull-out bearing requirements. If the calculated maximum pull-out force is greater than the ultimate pull-out bearing capacity, the design requirements are met, and the design size is in line with the requirements; if the calculated maximum pull-out force is less than the ultimate pull-out bearing capacity, the design requirements are not met, and the size of the embedded foundation needs to be increased, and then steps 1-4 are repeated until the requirements are met.

[0086] In the present invention, when the calculated maximum pull-out force is less than the ultimate pull-out bearing capacity and does not meet the design requirements, the design height of the embedded foundation is increased, and the latter design height is increased by 5% based on the previous design height.

[0087] Example

[0088] Taking the selection of a railway traction station power supply line foundation as an example, the most unfavorable terrain slope of the foundation is 50°. In step 1, a generalized model of the failure surface of the rock embedded foundation of the transmission tower under the slope adjustment condition is established according to the topographic geological map and the design size of the embedded foundation. Figure 2 As shown, after rotating the ramp clockwise with a slope of α, we get Figure 3 ,from Figure 3 The vertical angles ω1 and ω2 of the failure surface, the depths h1 and h2 of the failure surface, and the distance R′ from the ground point of the failure surface near the slope foot to the foundation are obtained. In step 2, the surface area S1 of the failure surface of the embedded foundation is calculated; according to step 3, the ultimate pull-out bearing capacity T of the foundation is calculated; according to the environment in which the transmission tower is located, the maximum pull-out force of the foundation under extreme conditions such as strong wind, ice cover, and line break is calculated. After calculation, it can be known that the pull-out force on the foundation is the largest at the maximum wind speed, which is 139.2kN, less than the ultimate pull-out force of 348.2kN, which meets the bearing requirements, and the design size of the foundation meets the requirements.

[0089] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0090] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to replace some of the technical features therein with equivalents. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A rock embedded foundation design method for slope terrain, characterized in that: The method comprises the following steps: Step 1: Determine the design position of the rock-embedded foundation of the transmission tower according to the slope terrain, and construct an initial model of the rock-embedded foundation of the transmission tower under slope conditions; Step 2: According to the initial model of the rock-embedded foundation of the transmission tower under slope conditions, the failure area of ​​the rock-embedded foundation under the pull-out load is calculated, and a generalized model is constructed according to the size of the failure area; Step 3: Calculate and obtain the ultimate pull-out bearing capacity T of the embedded foundation; Step 4: According to the environment in which the transmission tower is located, calculate the maximum pull-out force of the embedded foundation under strong wind conditions, icing conditions, and broken wire conditions, and determine whether the pull-out force meets the ultimate pull-out bearing requirements. If it does not meet the design requirements, increase the size of the embedded foundation, and then repeat steps 1 to 4 until the requirements are met.

2. The rock embedded foundation design method according to claim 1, characterized in that: The calculation method of the ultimate pull-out bearing capacity T is: T=W+τ f S1cosω (15). In formula (15), the surface area of ​​the failure zone of the embedded foundation is S1; τ f is the shear strength on the failure surface, in units of pa; ω is an intermediate parameter with no specific meaning; W is the gravity of the rock failure zone, in units of N; the embedded foundation and the surrounding destroyed rock mass constitute the total gravity W of the foundation and the failure zone, and its calculation formula is as follows: W = W1 + W2 (16); In formula (16), W1 is the gravity of the embedded foundation, in N; W2 is the gravity of the rock mass in the damaged area, in N; the two are: W1=γ1V1 (17); W2=γ2V2 (18); In formulas (17) and (18), γ1 is the density of the embedded foundation material, in N / m 3 ; γ2 is the weight of surrounding rock, in N / m 3 ; V1 is the volume of the embedded foundation, in m 3 ; V2 is the volume of the destroyed rock mass, in m 3 ; V3 is an imaginary oblique cone, V is the total volume of V1, V2 and V3. According to the mathematical geometric relationship, the expressions of V1 and V2 can be obtained as follows: V2 = V - V1 - V3 (20); b2=-2Rcotω2 (24); k = tanα (25); According to the Mohr-Coulomb theory, the shear strength on the failure surface is calculated as: In formulas (19) to (27), α is the inclination angle of the slope; r is the top radius of the embedded foundation, in m; h is the height of the embedded foundation, in m; R is the bottom radius of the embedded foundation, in m; c is the cohesion of the surrounding rock, in Pa; The internal friction angle of the surrounding rock; σ is the normal stress of the surrounding rock, in Pa; ω1 and ω2 are the angles between the failure surfaces on both sides of the failure area; b2, b, k, k1, k2 are intermediate parameters with no specific meaning; H and ω are intermediate parameters, and their expressions are:

3. The rock embedded foundation design method according to claim 2, characterized in that ,,The calculation method of the surface area S1 of the failure zone of the embedded foundation is: The surface area S1 of the failure zone of the embedded foundation is the area S of the complete oblique cone minus the area S2 of the oblique cone at the tip, that is: S1=S-S2 (1); x0=dtanω1 (14). In the above formulas, r is the top radius of the embedded foundation, in m; h is the height of the embedded foundation, in m; R′ is the distance between the surface point of the failure surface near the slope toe and the embedded foundation, in m; y is the ordinate, in m; R is the bottom radius of the embedded foundation, in m; f1′(y), f2′(y), f3′(y) and f4′(y) are the derivatives of f1(y), f2(y), f3(y) and f4(y), respectively; k1, k2, u, d, m1, n1, n2 and x0 are all intermediate parameters without specific meanings.

4. The rock embedded foundation design method according to claim 2, characterized in that: In step 4, when the calculated maximum pull-out force is less than the ultimate pull-out bearing capacity and does not meet the design requirements, the design height of the embedded foundation is increased by 5% based on the previous design height.

5. The rock embedded foundation design method according to claim 1, characterized in that: The method for determining whether the pull-out force meets the ultimate pull-out bearing capacity is as follows: if the calculated maximum pull-out force is greater than the ultimate pull-out bearing capacity, the design requirements are met and the design dimensions meet the requirements; if the calculated maximum pull-out force is less than the ultimate pull-out bearing capacity, the design requirements are not met.

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