A method for anti-heave stability analysis applicable to cantilever revetments in narrow river channels

Abstract

The present invention discloses a method for analyzing the anti-heave stability of a cantilever revetment applicable to a narrow river channel in the field of geotechnical engineering. According to the river channel width, the embedded depth of the retaining structure, and the internal friction angle of the sliding soil mass, three formulas are used to judge the heave instability mode. According to the determined heave instability mode of the river channel, the anti-heave stability safety factor is calculated by selecting one corresponding to one of the four formulas. The method of the present invention improves the accuracy of the calculation result by first judging the heave instability mode and then solving the anti-heave stability safety factor.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering, and particularly to a method for analyzing the anti - heave stability of a cantilever revetment applicable to narrow river channels. Background Technique

[0002] For urban inland rivers, since there are often civil engineering facilities such as houses, roads, pipelines, etc. that cannot be demolished on both banks, cantilever revetments are selected, such as sheet pile revetments and row - pile revetments.

[0003] The anti - heave stability check is an important part of foundation pit design. At present, the Technical Specification for Building Foundation Pit Support JGJ120 provides two methods for calculating anti - heave stability: the Prandtl formula based on the bearing capacity of the foundation and the "Wang - Xia" method based on the circular arc slip surface.

[0004] When applying the current anti - heave calculation method for foundation pits to urban inland river revetments, it should be improved in combination with the actual situation of urban inland rivers. In southern cities with dense river networks, the river channels of urban inland rivers are usually narrow. Taking the urban area of Fuzhou as an example, more than 80% (by length) of the blue - line widths of the river channels are within 16m, and most of the blue - line widths of the river channels are between 10m and 12m. However, the current anti - heave calculation method for foundation pits does not consider the influence of the plane size of the foundation pit, so it is not applicable to the anti - heave analysis of narrow river channels.

[0005] The anti - heave stability of narrow river channels is similar to that of narrow foundation pits (such as subway foundation pits). At present, anti - heave stability analysis methods for narrow foundation pits have been proposed at home and abroad. However, most of these methods are improved based on the circular arc slip surface failure mode (i.e., the "Wang - Xia" method). For those using the circular arc slip mode, the center of the circular arc segment needs to be assumed in advance. For deep subway foundation pits, the center is generally assumed to be located at the intersection of the retaining structure and the lowest support. The depth of urban inland rivers is relatively shallow, and it is not suitable to set internal supports. Therefore, it is difficult to determine the position of the center of the circle for the anti - heave stability analysis based on the circular arc slip failure mode.

[0006] Based on this, the present invention designs a method for analyzing the anti - heave stability of a cantilever revetment applicable to narrow river channels to solve the above problems. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for analyzing the anti - heave stability of a cantilever revetment applicable to narrow river channels to solve the problem that it is difficult to determine the position of the center of the circle for the anti - heave stability analysis based on the circular arc slip failure mode proposed in the above background technique.

[0008] To achieve the above purpose, the present invention provides the following technical solutions: Step 1: Judge the heave instability mode according to the river channel width, the embedded depth of the retaining structure, and the internal friction angle of the sliding soil mass:

[0009] ① When the ratio of the river channel width to the embedded depth of the retaining structure satisfies Equation (1), it is judged as the first mode of heave instability, as shown in Figure 1 . At this time, the heave slip surface at the river bottom does not extend to the retaining structure on the opposite bank, and the angle between the heave slip surface outside the river channel and the ground is . The angle between the heave slip surface at the river bottom and the horizontal plane is

[0010]

[0011] ② When the ratio of the river channel width to the embedded depth of the retaining structure satisfies Equation (2), it is judged as the second mode of heave instability, as shown in Figure 2 . At this time, the heave slip surface reaches the retaining structure on the opposite bank, and the angle between the heave slip surface outside the river channel and the ground still remains . However, the angle between the slip surface at the river bottom and the horizontal plane gradually increases and is between and .

[0012]

[0013] ③ When the ratio of the river channel width to the embedded depth of the retaining structure satisfies Equation (3), it is judged as the third mode of heave instability, as shown in Figure 3 . At this time, the angle between the heave slip surface outside the river channel and the ground still remains unchanged, and the angle between the heave slip surface at the river bottom and the horizontal plane is . The soil mass at the river bottom gradually changes from an approximate triangular failure mode to a trapezoidal failure mode.

[0014]

[0015] In Equation (1), Equation (2), and Equation (3), L is the embedded depth of the retaining structure; B is the river channel width; is the internal friction angle of the sliding soil mass.

[0016] The common feature of the above three heave failure modes is that the sliding soil mass is divided into Zone I, Zone II, and Zone III. The sliding line in Zone I is a straight line, and the angle with the horizontal plane is . The sliding line in Zone II is a logarithmic spiral and is tangent to the straight lines in Zone I and Zone III.

[0017] (2) The differences among the three heave failure modes are as follows:

[0018] ① For the first mode of heave failure: The sliding reference plane is located at the river bottom, and the angle between the sliding soil mass in Zone III and the horizontal plane is

[0019] ② For the second mode of heave failure: The sliding reference plane is located at the river bottom, and the angle between the sliding soil mass in Zone III and the horizontal plane is ψ, where ψ is between and between

[0020] ③ Bulge failure mode three: The sliding reference plane is at a position (L - h) below the river bottom, and the angle between the sliding soil mass in zone III and the horizontal plane is

[0021] Step 2: Determine the bulge instability mode of the river channel according to Step 1, and calculate the anti - bulge stability safety factor according to Equation (4):

[0022]

[0023] ① When the river channel is judged to be in bulge instability mode one, in Equation (4):

[0024]

[0025] ② When the river channel is judged to be in bulge instability mode two, in Equation (4):

[0026]

[0027] ③ When the river channel is judged to be in bulge instability mode three, in Equation (4):

[0028]

[0029] In Equations (4), (5), (6), and (7), H is the river channel depth; q k is the ground surcharge; γ, c are the unit weight and cohesion of the sliding soil mass, N c , N q are bearing capacity factors.

[0030] The specific derivation process is as follows:

[0031] Take the sliding soil mass in zone II (without considering its self - weight), and use the force system balance method to derive the anti - bulge stability safety factor.

[0032] (① The force system of the sliding soil mass in zone II of failure mode one is as Figure 4 shown:

[0033] Take moments about point O,

[0034]

[0035] According to the force system balance equation, it can be obtained that,

[0036] q f = cN c

[0037]

[0038] ② The force system of the sliding soil mass in zone II of failure mode two is asFigure 5 As shown in:

[0039] According to the stress state and strength theory of soil, the stress on the rupture surface in Zone III can be expressed as σ = σ CD sin 2 ψτ = σ CD sinψcosψ

[0040] Satisfying

[0041]

[0042] Therefore,[[]]

[0043]

[0044] Taking the moment about point O,[[]]

[0045]

[0046] According to the force system equilibrium equation, it can be obtained that,[[]]

[0047]

[0048] ③ The force system of the sliding soil mass in Zone II of failure mode three is as Figure 6 shown in:

[0049] According to the stress state and strength theory of soil, the stress on the rupture surface in Zone III can be expressed as

[0050] Therefore,[[]]

[0051]

[0052] According to the force system equilibrium equation, where

[0053]

[0054] According to the force system equilibrium, it can be obtained that

[0055] q f = γ(L - h)N q + cN c

[0056]

[0057] At this time, the safety factor K b is:

[0058]

[0059] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a method for analyzing the anti-heave stability of river channels, filling the gaps at home and abroad; the heave instability mode determined based on the numerical analysis results is more in line with the actual situation, improving the accuracy of the anti-heave stability safety factor. The embedded depth ratio of the retaining structure determined by the present invention is smaller than that applied in the Technical Specification for Building Foundation Pit Support, reducing unnecessary waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0061] Figure 1 It is the first heave failure mode of the present invention;

[0062] Figure 2 It is the second heave failure mode of the present invention;

[0063] Figure 3 It is the third heave failure mode of the present invention;

[0064] Figure 4 It is the sliding soil force system in Zone II of the first heave failure mode of the present invention;

[0065] Figure 5 It is the sliding soil force system in Zone II of the second heave failure mode of the present invention;

[0066] Figure 6 It is the sliding soil force system in Zone II of the third heave failure mode of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0067] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0068] An embodiment of the present invention:

[0069] The width of the river channel B = 10m, and the depth H = 5m; the retaining structure is set as a precast concrete sheet pile; the ground surcharge q k = 10 kPa; the soil body is soft clay, with a unit weight γ = 18 kN / m 3 , cohesion c = 10 kPa, and internal friction angle Calculate the safety factors for three cases where the embedded depth is L = 5m, 6m, and 12m respectively. When the safety factor is greater than 1.20, it is determined that the retaining structure is in a stable state; when the safety factor is less than 1.20, it is determined that the retaining structure is in an unstable state.

[0070] Step 1: Determine the heave failure mode.

[0071] According to equations (1), (2), and (3),

[0072] When L = 5m, It is determined to be failure mode 1.

[0073] When L = 6m, It is determined to be failure mode 2.

[0074] When L = 12m, It is determined to be failure mode 3.

[0075] Step 2: Calculate the anti-heave stability safety factor.

[0076] When L = 5m,

[0077]

[0078] The retaining structure is in an unstable state.

[0079] When L = 6m,

[0080] By using the trial method for the second formula of equation (6), ψ = 43.75°

[0081]

[0082] The retaining structure is in an unstable state.

[0083] When L = 12m,

[0084]

[0085] The retaining structure is in a stable state.

[0086] Compare the anti-heave stability safety factors of the method of the present invention, the code method, and the numerical simulation method. The table is as follows. It can be seen from the table that the result obtained by the method of the present invention is closer to the numerical simulation method, indicating that the method of the present invention is more accurate.

[0087]

[0088] In the description of this specification, the descriptions referring to the terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0089] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for analyzing the anti-heave stability of a cantilever revetment applicable to narrow river channels, characterized in that: It includes the following steps: Step 1: Determine the heave instability mode based on the river channel width, the embedment depth of the retaining structure, and the internal friction angle of the sliding soil mass: ①When the ratio of the river channel width to the embedded depth of the retaining structure satisfies Equation (1), it is judged as the first mode of heave instability: the heave slip surface at the river bottom does not extend to the retaining structure on the opposite bank, and the angle between the heave slip surface outside the river channel and the ground is The angle between the heave slip surface at the river bottom and the horizontal plane is ② When the ratio of the river channel width to the embedded depth of the retaining structure satisfies Equation (2), it is judged as the second mode of heave instability: the heave slip surface reaches the retaining structure on the opposite bank, and the angle between the heave slip surface outside the river channel and the ground still remains However, the angle between the slip surface at the river bottom and the horizontal plane gradually increases and is in and between; ③When the ratio of the river channel width to the embedded depth of the retaining structure satisfies Equation (3), it is judged as the third mode of heave instability: the angle between the heave slip surface outside the river channel and the ground remains unchanged, and the angle between the heave slip surface at the river bottom and the horizontal plane is The soil at the river bottom gradually changes from an approximately triangular failure mode to a trapezoidal failure mode; In Formula (1), Formula (2), and Formula (3), L is the embedded depth of the retaining structure; B is the river width; is the internal friction angle of the sliding soil mass; Step 2: Determine the heave instability mode of the river channel according to Step 1, and calculate the anti-heave stability safety factor according to Equation (4): ① When the river channel is judged to be in heave instability mode one, in Equation (4): ② When the river channel is judged to be in heave instability mode two, in Equation (4): ③ When the river channel is judged to be in heave instability mode three, in Equation (4): In Formula (4), Formula (5), Formula (6), and Formula (7), H is the river depth; q k is the ground surcharge; γ and c are the unit weight and cohesion of the sliding soil mass, N c , N q are bearing capacity factors; ψ is the angle between the slip surface in Zone III and the horizontal plane; h is the radial radius when the tangent direction of the logarithmic spiral is horizontal.

2. The anti-heave stability analysis method for a cantilever revetment applicable to a narrow river channel according to claim 1, wherein: The common feature of the three bulging instability modes is that the sliding soil mass is divided into Zone I, Zone II, and Zone III. The sliding line in Zone I is a straight line, and the angle with the horizontal plane is The sliding line in Zone II is a logarithmic spiral, tangent to the straight lines in Zone I and Zone III; The differences among the three heave instability modes are as follows: ① Bulging failure mode 1: The sliding reference plane is located at the river bottom, and the angle between the sliding soil mass in zone III and the horizontal plane is ② Heave instability mode two: The sliding reference plane is located at the river bottom, and the angle between the sliding soil mass in zone III and the horizontal plane is ψ, where ψ is between (π / 4 - φ / 2) and (π / 4 + φ / 2); ③ Heave instability mode three: The sliding reference plane is located at a position (L - h) below the river bottom, and the angle between the sliding soil mass in zone III and the horizontal plane is (π / 4 + φ / 2).

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