Method for calculating uplift bearing capacity of socketed pile by considering tensile failure of rock mass

Abstract

The invention discloses a rock-socketed pile uplift bearing capacity calculation method considering rock mass tensile failure. The rock-socketed pile uplift bearing capacity calculation method comprises the steps that S1, the axial uplift ultimate bearing capacity of a rock-socketed section of a rock-socketed pile is calculated through an original calculation method; s2, an anti-pulling failure mode of the socketed pile is determined; and S3, calculating the uplift bearing capacity of the rock-socketed pile when the rock mass is pulled and damaged according to the determined uplift failure mode of the rock-socketed pile and an original calculation method. The problem that when the rock-socketed depth of the rock-socketed pile is smaller than three times of the pile diameter, the formula cannot be applied to determine the uplift bearing capacity of the rock-socketed pile according to field tests, and then the rock-socketed pile is designed is solved.

Description

Technical Field

[0001] The invention relates to a method for calculating the pull-out bearing capacity of rock-embedded piles taking into account the tensile damage of rock mass. Background Art

[0002] Pull-out rock-embedded piles have been widely used in wharf projects, anti-floating foundations, and offshore wind power projects. However, the failure mechanism and bearing capacity calculation method of pull-out rock-embedded piles are still in the exploratory research stage.

[0003] The bearing capacity of rock-embedded piles is related to the engineering properties of rocks, which include hardness, integrity, and special properties such as solubility, disintegration, and expansion. However, my country has a vast territory and a wide variety of rocks. Key parameters such as the side resistance and end resistance of rock-embedded piles vary greatly, making it difficult to summarize the method for determining the key parameters of rock-embedded piles, which has hindered the progress of theoretical research on the bearing capacity calculation of rock-embedded piles.

[0004] At present, among the domestic specifications for the fields of construction, highways, railways, and water transport, only the specifications for water transport stipulate that when the rock embedding depth is greater than 3 times the pile diameter, the calculation method for the pull-out bearing capacity of rock-embedded piles determined based on the uniaxial compressive strength of rock is as follows:

[0005] The calculation method proposed in the existing specifications for pile-rock shear failure is as follows:

[0006] Q=U2ξ' s f rk h r ;

[0007] Where Q is the ultimate axial tensile bearing capacity of the rock-embedded section of the rock-embedded pile, U2 is the circumference of the rock-embedded section, ξ' s is the calculation coefficient of the side resistance and pull-out resistance of the rock-embedded section, which is taken as 0.045, f rk is the standard value of saturated uniaxial compressive strength of rock, h r is the length of the rock-embedded section.

[0008] like Figure 2-4 As shown in the figure, the pull-out failure modes of rock-embedded piles include: shear failure of the pile-rock interface, inverted cone failure of the rock mass on the pile side, and combined failure. Among them, shear failure of the pile-rock interface is the most common failure mode in actual engineering, especially for pull-out rock-embedded piles in hard rocks. The failure mode is that the pile body is pulled out and destroyed; inverted cone failure of the rock mass on the pile side occurs in cast-in-place rock-embedded piles with a shallow rock embedding depth in soft rocks. The failure mode is that the rock mass around the pile body is damaged by shear and tension; combined failure occurs in cast-in-place rock-embedded piles with a certain rock embedding depth in soft rocks, and the pile side is relatively rough. The failure mode is that the rock mass within a certain depth in the upper part is damaged by shear and tension, and the lower pile body is pulled out and destroyed at the same time.

[0009] However, the specification lacks calculation methods for other failure modes. When the rock-embedded depth is less than 3 times the pile diameter, other failure modes may occur. The formula cannot be applied and the rock-embedded pile design can only be carried out by determining the pull-out bearing capacity of the rock-embedded pile based on field tests. Therefore, this formula cannot be used.

[0010] Therefore, a method for calculating the pull-out bearing capacity of rock-embedded piles taking into account the tensile failure of rock mass is provided. Summary of the invention

[0011] The purpose of the present invention is to overcome the existing defects and provide a method for calculating the pull-out bearing capacity of rock-embedded piles taking into account the tensile failure of rock mass, which solves the problem that when the rock embedding depth of the rock-embedded pile is less than 3 times the pile diameter, the formula cannot be applied and the pull-out bearing capacity of the rock-embedded pile can only be determined based on field tests for rock-embedded pile design.

[0012] The technical solution to achieve the above purpose is:

[0013] A method for calculating the pull-out bearing capacity of rock-embedded piles considering the tensile failure of rock mass includes:

[0014] Step S1, calculating the ultimate axial pull-out bearing capacity of the rock-embedded section of the rock-embedded pile by an existing calculation method;

[0015] Step S2, determining the pull-out failure mode of the rock-embedded pile;

[0016] Step S3, calculating the pull-out bearing capacity of the rock-socketed pile when the rock mass is under tension failure according to the determined pull-out failure mode of the rock-socketed pile and the integrated original calculation method.

[0017] Preferably, in step S2, whether the inverted cone is subjected to tensile shear failure when the rock embedding depth is shallow is determined by the tensile strength of the rock and the shear strength between the rock and the pile body; due to the wide variety of rock types, the rock compressive strength can range from 3MPa to 360MPa, and the tensile strength can range from 0.17MPa to 23MPa.

[0018] Preferably, in step S3, when the rock layer of the rock-embedded section of the rock-embedded pile has a low tensile strength or there is a weak structural surface, the rock mass is prone to tensile failure to form an inverted cone failure surface. When the rock-embedded pile is subjected to an upward pull load, the rock stress of the inverted cone failure surface at the top of the rock layer is greater than the tensile strength of the failure surface, and inverted cone failure occurs.

[0019] in,

[0020] Vertical component of tensile force F on the failure surface of an inverted cone tv The calculation formula is as follows:

[0021] F tv =F t cosα+σ地 π(R 2 -r 2 );

[0022] F t =f t A 倒锥体 ;

[0023] In the formula, F t is the tensile strength of rock, σ 地 is the effective stress of the rock layer at the top of the rock-embedded pile, α is the angle between the failure surface of the inverted cone and the horizontal plane, R is the radius of the inverted cone, r is the radius of the rock-embedded pile, and A 倒锥体 is the lateral area of ​​the truncated cone formed by the inverted cone;

[0024] A 倒锥体 The calculation formula for the lateral area of ​​the truncated cone is as follows:

[0025]

[0026] Where, L is the vertical length of the inverted cone, which is recommended not to exceed 2 times the pile diameter;

[0027] There are also:

[0028]

[0029] Finally, we can get:

[0030] F tv =πf t (R+r)(Rr)+σ 地 π(R 2 -r 2 );

[0031] Right now,

[0032] F tv =π(f t +σ 地 )(R 2 -r 2 ).

[0033] Preferably, in step S3, the shear strength of the rock-embedded section and the tensile strength of the top inverted cone should be calculated simultaneously at the top of the rock-embedded section according to the original calculation method, and the smaller value is used as the ultimate pull-out bearing capacity of the rock-embedded pile. The calculation method is as follows:

[0034]

[0035] In the formula, q s It is the shear strength between the rock-embedded pile and the rock.

[0036] The beneficial effect of the present invention is that the present invention calculates the pull-out bearing capacity of the rock-embedded pile when the rock mass is tensilely damaged by determining the pull-out failure mode of the rock-embedded pile, and takes more comprehensive consideration of the failure mode that may occur when the rock-embedded pile is pulled out, thereby solving the problem that the pull-out bearing capacity calculation of the rock-embedded pile in the current specification cannot calculate the rock-embedded pile within 3 times the pile diameter. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of a method for calculating the pull-out bearing capacity of rock-embedded piles taking into account the tensile failure of rock mass according to the present invention;

[0038] Figure 2 is a schematic diagram of shear failure of the pile-rock interface in the present invention;

[0039] Figure 3 It is a schematic diagram of the inverted cone failure of the rock mass on the pile side in the present invention;

[0040] Figure 4 It is a schematic diagram of composite destruction in the present invention;

[0041] Figure 5 It is the failure force diagram of the inverted cone at the top of the rock layer in the rock-embedded section of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0043] The present invention will be further described below in conjunction with the accompanying drawings.

[0044] like Figure 1 As shown in FIG. 1 , a method for calculating the pull-out bearing capacity of rock-embedded piles considering the tensile failure of rock mass includes:

[0045] Step S1, calculating the ultimate axial pull-out bearing capacity of the rock-embedded section of the rock-embedded pile by the original calculation method.

[0046] In the embodiment, the calculation method proposed in the existing specification for pile-rock shear failure is as follows:

[0047] Q=U2ξ' s f rk h r ;

[0048] Where Q is the ultimate axial tensile bearing capacity of the rock-embedded section of the rock-embedded pile, U2 is the circumference of the rock-embedded section, ξ' s is the calculation coefficient of the side resistance and pull-out resistance of the rock-embedded section, which is taken as 0.045, f rk is the standard value of saturated uniaxial compressive strength of rock, h r is the length of the rock-embedded section.

[0049] However, the specification lacks calculation methods for other failure modes. When the rock-embedded depth is less than 3 times the pile diameter, other failure modes may occur. The formula cannot be applied and the rock-embedded pile design can only be carried out based on the problem of determining the pull-out bearing capacity of the rock-embedded pile based on field tests. Therefore, this formula cannot be used.

[0050] Step S2, determining the pull-out failure mode of the rock-embedded pile.

[0051] In the embodiment, there are three pull-out failure modes of rock-embedded piles, including shear failure of the pile-rock interface, inverted cone failure of the rock mass on the pile side, and combined failure, wherein:

[0052] like Figure 2 As shown in the figure, shear failure at the pile-rock interface is the most common failure mode in actual engineering, especially for pull-out rock-embedded piles in hard rocks, where the failure mode is the pile body being pulled out.

[0053] like Figure 3 As shown in the figure, the inverted cone failure of the rock mass on the pile side occurs in the cast-in-place rock-embedded pile with a shallow rock embedding depth in soft rock. The failure mode is that the rock mass around the pile body is destroyed by shear and tension.

[0054] like Figure 4 As shown in the figure, composite failure occurs in cast-in-place rock-embedded piles with a certain rock embedding depth in soft rock, and the pile side is relatively rough. The failure mode is that the rock mass within a certain depth in the upper part is subjected to shear and tensile failure, and the lower pile body is pulled out and destroyed at the same time.

[0055] In the embodiment, since the interface shear failure generally occurs when the rock-socketed pile is pulled out, the current research on the pull-out mechanism and failure mode of the rock-socketed pile is mostly focused on the shear failure of the pile-rock interface. It is believed that when the rock-socketed pile and the rock interface are sheared, there are stages such as interface bonding force, interface shear expansion, shear slip, and bedrock failure, and the Hoek-Brown criterion is proposed to derive the pile side friction resistance value considering the slip expansion.

[0056] The inverted cone failure of rock-embedded piles when subjected to tension has been verified in indoor model tests. During the compilation of the current water transport regulations, an applicable range of three times the pile diameter has been proposed for the calculation formula for the pull-out bearing capacity of rock-embedded piles due to the existence of this type of failure mode.

[0057] Whether the inverted cone will fail under tension and shear when the rock is shallow is determined by the tensile strength of the rock and the shear strength between the rock and the pile. Due to the vast land area and various rock types in my country, the rock compressive strength ranges from 3MPa to 360MPa, and the tensile strength ranges from 0.17MPa to 23MPa, with a difference of 100 times. The failure modes of rock-embedded piles in different regions are not necessarily the same when they are pulled out. Therefore, the calculation method of the pull-out bearing capacity of rock-embedded piles should be considered when the inverted cone fails under tension and shear.

[0058] Step S3, calculating the pull-out bearing capacity of the rock-socketed pile when the rock mass is under tension failure according to the determined pull-out failure mode of the rock-socketed pile and the integrated original calculation method.

[0059] In the embodiment, when the rock layer of the rock-embedded section of the rock-embedded pile has a low tensile strength or a weak structural surface, the rock mass is prone to tensile failure to form an inverted cone failure surface. When the rock-embedded pile is subjected to an upward pull load, the rock stress of the inverted cone failure surface at the top of the rock layer is greater than the tensile strength of the failure surface, and an inverted cone failure will occur. The force diagram of the failure surface is shown in FIG. Figure 5 As shown;

[0060] in,

[0061] Vertical component of tensile force F on the failure surface of an inverted cone tv The calculation formula is as follows:

[0062] F tv =F t cosα+σ 地 π(R 2 -r 2 );

[0063] F t =f t A 倒锥体 ;

[0064] In the formula, F t is the tensile strength of rock, σ 地 is the effective stress of the rock layer at the top of the rock-embedded pile, α is the angle between the failure surface of the inverted cone and the horizontal plane, R is the radius of the inverted cone, r is the radius of the rock-embedded pile, and A 倒锥体 is the lateral area of ​​the truncated cone formed by the inverted cone;

[0065] A 倒锥体 The calculation formula for the lateral area of ​​the truncated cone is as follows:

[0066]

[0067] Where, L is the vertical length of the inverted cone, which is recommended not to exceed 2 times the pile diameter;

[0068] There are also:

[0069]

[0070] Finally, we can get:

[0071] F tv =πf t (R+r)(Rr)+σ 地 π(R 2 -r 2 );

[0072] Right now,

[0073] F tv =π(f t +σ 地 )(R 2 -r 2 ).

[0074] In the embodiment, the original calculation method is combined, and the shear strength of the rock-embedded section and the tensile strength of the top inverted cone should be calculated at the same time at the top of the rock-embedded section. The smaller value is used as the ultimate pull-out bearing capacity of the rock-embedded pile. The calculation method is as follows:

[0075]

[0076] In the formula, q s It is the shear strength between the rock-embedded pile and the rock.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the pull-out bearing capacity of rock-embedded piles considering the tensile failure of rock mass, characterized in that: include: Step S1, calculating the ultimate axial pull-out bearing capacity of the rock-embedded section of the rock-embedded pile by an existing calculation method; Step S2, determining the pull-out failure mode of the rock-embedded pile; Step S3, calculating the pull-out bearing capacity of the rock-socketed pile when the rock mass is under tension failure according to the determined pull-out failure mode of the rock-socketed pile and the integrated original calculation method.

2. A method for calculating the pull-out bearing capacity of rock-embedded piles considering the tensile failure of rock mass according to claim 1, characterized in that: In step S2, whether the inverted cone is subjected to tensile shear failure when the rock embedding depth is shallow is determined by the tensile strength of the rock and the shear strength between the rock and the pile body; due to the wide variety of rock types, the rock compressive strength ranges from 3MPa to 360MPa, and the tensile strength ranges from 0.17MPa to 23MPa.

3. The method for calculating the pull-out bearing capacity of rock-embedded piles considering the tensile failure of rock mass according to claim 1, characterized in that: In step S3, when the rock layer of the rock-embedded section of the rock-embedded pile has a low tensile strength or there is a weak structural surface, the rock mass is prone to tensile failure to form an inverted cone failure surface. When the rock-embedded pile is subjected to an upward pull load, the rock stress of the inverted cone failure surface at the top of the rock layer is greater than the tensile strength of the failure surface, and an inverted cone failure will occur. in, Vertical component of tensile force on the failure surface of an inverted cone F tv The calculation formula is as follows: F tv =F t cosα+σ 地 π(R 2 -r 2 ); F t =f t A 倒锥体 ; In the formula, F t is the tensile strength of rock, σ 地 is the effective stress of the rock layer at the top of the rock-embedded pile, α is the angle between the failure surface of the inverted cone and the horizontal plane, R is the radius of the inverted cone, r is the radius of the rock-embedded pile, and A 倒锥体 is the lateral area of ​​the truncated cone formed by the inverted cone; A 倒锥体 The calculation formula for the lateral area of ​​the truncated cone is as follows: Where, L is the vertical length of the inverted cone, which is recommended not to exceed 2 times the pile diameter; There are also: Finally, we can get: F tv =πf t (R+r)(R-r)+σ 地 π(R 2 -r 2 ); Right now, F tv =π(f t +s 地 )(R 2 -r 2 )。 4. The method for calculating the pull-out bearing capacity of rock-embedded piles considering the tensile failure of rock mass according to claim 3, characterized in that: In step S3, based on the original calculation method, the shear strength of the rock-embedded section and the tensile strength of the top inverted cone should be calculated simultaneously at the top of the rock-embedded section, and the smaller value is used as the ultimate pull-out bearing capacity of the rock-embedded pile. The calculation method is as follows: In the formula, q s It is the shear strength between the rock-embedded pile and the rock.

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