Method and system for designing multi-stage slope composite retaining structure

Abstract

The invention discloses a method and a system for designing a multi-stage side slope composite retaining structure, aiming at optimizing the design of the retaining structure of a side slope by considering the action of expansive soil. The method disclosed by the invention comprises the following steps: determining the group number of the retaining structures according to the height of the slope, wherein the group number is greater than or equal to 2; wherein at least one retaining structure comprises an anchor rod frame beam and a sheet-pile wall; under the condition that the side slope is not supported, an equation that the sum of gravity external power and expansive soil external power is equal to internal loss power is constructed, and according to an upper limit method for solving a side slope safety coefficient in the equation and basic parameters of a soil body, slip crack surface parameters of the side slope corresponding to the supporting structure at a given critical height are solved; and according to the solved slip crack surface parameters, a load equivalent method and an energy method, the anchor rod tension, the post-pile pressure and the internal force of the inter-pile plate are calculated, and therefore the anchor rod distance of the supporting and retaining structure, the section size of the slide-resistant pile and the inter-pile plate and reinforcing bars are designed.

Description

Technical Field

[0001] The present invention relates to the technical field of slope engineering, and in particular to a design method and system for a multi-level slope composite retaining structure. Background Art

[0002] For the design of multi-level slope retaining structures, if a single retaining structure type (such as anchor frame beam) is used for the entire slope, conventional design methods can be used for design. First, the overall sliding surface of the multi-level slope is determined, the landslide thrust of the entire slope is calculated, and then the landslide thrust is evenly distributed to each level of the slope, and then the retaining structure design of each level is carried out.

[0003] The "Code for Design of Railway Roadbed and Retaining Structures" specifies the applicable regions and general design calculation methods for pile-sheet retaining walls and anchored frame beam retaining structures. However, the code does not provide a corresponding design method for composite retaining structures with multi-level slopes on expansive soils. Furthermore, because the general design methods in the code do not account for the expansive force of expansive soils, they often differ from actual conditions. Field measurements have shown that the expansive force of expansive soil slopes during the rainy season can cause errors in traditional landslide thrust calculations of over 30%. Summary of the Invention

[0004] The present invention aims to disclose a multi-level slope composite retaining structure design method and system, so as to take into account the effect of expansive soil and optimize the retaining structure design of the slope.

[0005] To achieve the above object, the present invention discloses a design method for a multi-level slope composite retaining structure, comprising: Determine the number of retaining structures according to the height of the slope, and the number of retaining structures is greater than or equal to 2; wherein at least one retaining structure includes an anchor frame beam and a pile-sheet wall; In the case of an unsupported slope, an equation is constructed in which the sum of the external power due to gravity and the external power due to expansive soil is equal to the internal power loss. Based on the upper limit method for solving the slope safety factor in this equation and the basic parameters of the soil, the slip surface parameters at a given critical height of the slope corresponding to the retaining structure are solved; Based on the solved sliding surface parameters and the load equivalence method and energy method, the anchor tension, pile pressure and internal force of the pile plate under the slope support condition are calculated, so as to design the anchor spacing, cross-sectional dimensions and reinforcement of the anti-sliding piles and pile plates of the retaining structure.

[0006] The load equivalence method includes: equating the soil covered by the upper retaining structure to the load acting on the lower retaining structure.

[0007] The energy method includes: establishing equations for gravity power, expansion force power and energy dissipation power within the sliding surface based on the limit equilibrium state of the slope.

[0008] In the present invention, each group of retaining structures is designed in order from top to bottom; the above-mentioned load equivalence method includes: when designing the lower-level retaining structure, the load is used to replace the slope soil weight corresponding to the upper-level retaining structure; and when designing the anti-sliding piles, the load is used to replace the slope soil weight behind the anti-sliding piles; and the above-mentioned energy law is based on: when the slope is in the limit state, the power generated by the external load is equal to the internal energy dissipation power.

[0009] Preferably, the above-mentioned sliding surface is a logarithmic spiral surface.

[0010] Corresponding to the above method, the present invention further discloses a multi-level slope composite retaining structure design system, comprising: The first module is used to determine the number of retaining structure groups according to the height of the slope, and the number of groups is greater than or equal to 2; wherein at least one retaining structure includes an anchor frame beam and a pile-sheet wall; The second module is used to construct an equation that equates the sum of the external power due to gravity and the external power due to expansive soil to the internal power loss when the slope is not supported. Based on the upper limit method for solving the slope safety factor in this equation and the basic soil parameters, the sliding surface parameters at a given critical height of the slope corresponding to the retaining structure are solved; The third module is used to calculate the anchor tension, pile pressure and internal force of the pile plate under the support condition of the slope based on the solved sliding surface parameters and the load equivalence method and energy method, so as to design the anchor spacing, cross-sectional dimensions and reinforcement of the anti-slip piles and pile plates of the retaining structure.

[0011] The present invention has the following beneficial effects: The multi-level slope combined retaining structure is designed by combining the equivalent load and energy method, and the effect of expansive soil is taken into consideration to optimize the slope retaining structure design and ensure the safety and reliability of the slope retaining structure.

[0012] The present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings: Figure 1 This is a flow chart of a multi-level slope composite retaining structure design method disclosed in an embodiment of the present invention; Figure 2 This is a schematic diagram of the design of the first and second level slope anchor frame beams disclosed in an embodiment of the present invention; Figure 3 Schematic diagram of the design of the upper anti-slide pile disclosed in the embodiment of the present invention; Figure 4This is a schematic diagram of the design of the third and fourth level anchor frame beams disclosed in an embodiment of the present invention; Figure 5 is a schematic diagram of the design of the lower anti-slide pile disclosed in an embodiment of the present invention; Figure 6 It is the logarithmic spiral slip surface disclosed in the embodiment of the present invention; Figure 7 This is a simplified calculation diagram of the force on the cantilever section of the anti-sliding pile disclosed in an embodiment of the present invention; Figure 8 This is a schematic diagram of the calculation of the inter-pile plate disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0015] The embodiment of the present invention discloses a method for designing a multi-level slope composite retaining structure. Figure 1 Shown, including: Step S1: Determine the number of retaining structure groups based on the slope height, the number being greater than or equal to two; wherein at least one retaining structure includes an anchor frame beam and a pile-sheet wall. The anchor frame beam may be replaced with an anchor cable frame beam. Such equivalent transformations fall within the scope of the present invention and will not be further described.

[0016] In this step, the retaining structure may consist entirely of a basic retaining structure comprising a pile-sheet wall and a two-stage anchor frame beam. Alternatively, the retaining structure may consist entirely of a basic retaining structure comprising a pile-sheet wall and a two-stage anchor frame beam, and a modified retaining structure comprising a pile-sheet wall and a single-stage anchor frame beam.

[0017] For example, the number of basic retaining structures is determined based on the slope's height. A basic retaining structure consists of two-stage anchor frame beams and a pile-sheet wall. One basic retaining structure can support a slope height of approximately 20m. The support height of the two-stage anchor frame beams is 2*8=16m (adjustable based on the slope's height), and the anti-slide pile support height is approximately 4m (adjustable based on the slope's height). For a slope height of approximately 40m, two or three basic retaining structures are used, respectively. The anchor frame beam support height can be adjusted based on the slope's height. Similarly, slopes of 60m, 80m, and 100m can be supported. If the slope is approximately 30m high, a combination of a modified basic retaining structure and a basic retaining structure is used from top to bottom. The modified basic retaining structure consists of a primary anchor frame beam (8m high, adjustable) and a pile-sheet wall (2m high, adjustable). Similarly, slopes of 50m, 70m, and 90m can be supported. The slope gradient can be determined by referring to relevant specifications.

[0018] Step S2: When the slope is unsupported, construct an equation that equates the sum of the external power due to gravity and the external power due to expansive soil to the internal power loss. Based on the upper limit method for solving the slope safety factor in this equation and the basic soil parameters, calculate the slip surface parameters at a given critical height of the slope corresponding to the retaining structure. In this embodiment, the slip surface is finitely considered to be a logarithmic spiral surface.

[0019] Step S3: Calculate the anchor tension, pile pressure, and internal force of the pile plate under the slope support condition based on the solved sliding surface parameters and the load equivalence method and energy method, so as to design the anchor spacing, cross-sectional dimensions, and reinforcement of the anti-slip piles and pile plates of the support structure.

[0020] In this step, each group of retaining structures is designed in order from top to bottom; the load equivalence method includes: when designing the lower retaining structure, the load is used to replace the slope soil weight corresponding to the upper retaining structure; and when designing the anti-slip piles, the load is used to replace the slope soil weight behind the anti-slip piles; the above-mentioned energy method is based on: when the slope is in the limit state, the power generated by the external load is equal to the internal energy dissipation power.

[0021] For the design sequence of step S3 above, refer to Figures 2 to 5 , for example: The design of the first group of basic retaining structures is briefly described as follows: a1. Determine the first and second level slope sliding surfaces, such as Figure 2 As shown, the landslide thrust of the slope is calculated (taking the expansion force into account) and the first and second level slope anchor frame beams are designed.

[0022] b1. Use load instead of soil weight of first and second level slopes, such as Figure 3As shown in the figure, the soil pressure and expansion force behind the upper anti-slide pile are calculated to design the anti-slide pile.

[0023] c1. Calculate the expansion force behind the plate and use the material mechanics theory to design the inter-pile hanging plate.

[0024] The design of the second group of basic retaining structures is briefly described as follows: a2. Use load to replace the soil weight of the first and second level slopes, and do not consider the influence of the deadweight of the anti-slide piles. Consider the resistance of the piles, and then determine the sliding surface of the third and fourth level slopes, such as Figure 4 As shown, the landslide thrust of the slope is calculated (taking the expansion force into account) and the anchor frame beams of the third and fourth level slopes are designed.

[0025] b2. Use load to replace the soil weight of the first, second, third and fourth level slopes, such as Figure 5 As shown in the figure, the soil pressure and expansion force behind the lower anti-slide piles are calculated, and the lower anti-slide piles are designed.

[0026] c2. Calculate the expansion force behind the plate and use the material mechanics theory to design the inter-pile hanging plate.

[0027] Similarly, n (n>2) groups of basic retaining structures are designed.

[0028] The following uses the fourth-level expansive soil cutting slope test site of the DK221+780 test section of the Yunnan-Guizhou Railway as the engineering background. The above method of this embodiment is used to analyze and calculate the combined retaining structure of the expansive soil slope of the typical section of the test site.

[0029] This section of the slope is located approximately 1 km east of the Baise Railway Station. It is a high slope to the right of DK221+679 to DK221+863 and is 184 meters long. This section of the roadbed is excavated, with a maximum center excavation depth of approximately 20 meters and a maximum side slope excavation depth of 38 meters. The natural slope is 10-30°, with a surface layer of expansive soil covering 3-9 meters. The underlying bedrock is mudstone of the Nadu Formation (E2-3n) of the Middle Tertiary System, interbedded with argillaceous siltstone and lignite. This section of the slope is primarily composed of fully and strongly weathered mudstone interbedded with sandstone of the Tertiary System. The rock formations strike N30°W / 27°SW (25.4°), with a 20° angle between the rock formations and the line's strike, and an apparent dip of 25.4°. There is bedding on the right side of the line. The peak seismic acceleration in this area is 0.10g. The characteristic period of the seismic response spectrum is 0.35s. Since the parameters of the various soil layers are relatively similar, it can be considered a homogeneous slope. The basic parameters of soil are: γ=20kN / m3 (gravity), C=20kPa (cohesion), =16° (internal friction angle), with medium to strong expansion properties, and free expansion rate FS=29.86%.

[0030] The design of the anchor frame beam in this scenario is detailed as follows: (I) Design of first and second level slope anchor frame beams: like Figure 6 As shown (unit length is taken in the vertical section direction), the slope failure mode is a logarithmic spiral. For the two-level high slope section of expansive soil, the platform widths from top to bottom are d0=L and d1 respectively, and the slope angles of each level from top to bottom are: 、 , the height of each level of slope from top to bottom is 、 ,in 、 is the height coefficient; the above parameters can be determined according to the specific slope size. Assuming that the failure surface AC is a logarithmic spiral surface, the failure surface passes through the slope foot, and the sliding body ABC rotates around the rotation center O relative to the stable body below the logarithmic spiral surface AC. Therefore, the AC surface is a thin layer of velocity discontinuity. The length of the chord OA is r0, and the inclination angles of the chord OA and OC are θ0 and θ h , two-level slope height H. The failure mechanism is determined by three variables, namely: slope height 、 and , square frame beam spacing D L .

[0031] 1. Relationship between slope geometric parameters like Figure 6 As shown, using coordinate transformation, it can be seen from the geometric relationship that the ratio of H / r0 and L / r0 can be expressed by the angles θ0 and θ h express.

[0032] (1); (2); 2. External power (1) Gravity The external power of soil gravity in area ABC is calculated using the superposition method. Therefore, the external power of gravity in area ABC can be expressed as: (3); in: is the angular velocity of the sliding soil; (4); (5); (6); (7); (8); It is worth noting that: in the above formulas (4) to (8), since formula (3) is too long, to The split of formula (3) does not have any other specific meanings. to Similar to this, I will not go into details.

[0033] (2) Expansion force Since the expansion force of expansive soil is also a body force, the expansion direction of expansive soil is the same as the minor principal stress, and the direction of the minor principal stress is perpendicular to the direction of gravity. Although the direction of the expansion force is horizontal to the left, its effect is the same as that of gravity.

[0034] The external power of the expansion force in the ABC region can be expressed as: (9); in: is the expansion coefficient, determined by in-situ expansion test or indoor load expansion test, and is the ratio of the peak expansion force of the soil under saturation to the overburden pressure; (10); (11); (12); (13); (14); (3) Anchor tension The external power of the anchor rod mainly comes from the tension of the anchor rod. The tension of the anchor rod is transmitted to the slope frame beam, and the frame beam exerts a reaction force on the slope to stabilize the sliding body. The tension T of the anchor rod is decomposed into horizontal and vertical components. The horizontal component is in the opposite direction of the expansion force, and the vertical component is in the same direction as gravity. Therefore, the external power of the anchor rod is: (15); Among them, W m is the external power of the anchor, T is the total tension of the anchor, is the horizontal angle of the anchor rod (i.e. the angle between the anchor rod and its horizontal projection), is the volume of the landslide.

[0035] 3. Internal loss rate Internal energy loss occurs on the discontinuous surface AC, and the differential of the energy loss rate CAC can be obtained from the differential area of ​​the surface. With cohesion c and speed The product calculation can be expressed as: (16); 4. Determination of slip surface First, the stability analysis of the slope is carried out under the condition that the slope is not supported, so as to determine that the length of the chord OA is r0, and the inclination angles of the chord OA and OC are θ0 and θ h , from which the position of the slip surface can be determined. In the case of no support on the slope, the external power is equal to the internal energy dissipation power, so:

[0036] Substituting the above formula, we can obtain the critical height of the slope .

[0037] (17); Among them: (Since a is equal to zero, the latter term is equal to 1 and can be canceled) (18); (19); In engineering practice, it is necessary to calculate the safety factor K of the slope. Here, the strength reduction method is used to determine the safety factor.

[0038] (20); Substituting formula (20) into formula (17), we can obtain: (twenty one); in: (twenty two); (twenty three); From the above formula (21), we can see that θ h and θ0 are unknown variables, and other parameters can be determined based on the actual slope. According to the upper bound theorem of limit analysis, Equation (21) is the upper bound method expression for solving the safety factor of a given actual slope, where K is the two unknown variables θ h and θ0, and implicitly includes the reduction factor K. When θ h , θ0 satisfies the conditions: (twenty four); (25); When, function There is a minimum value, and then an upper limit solution of the slope safety factor K is obtained. Taking the safety factor K in formula (21) as the objective function, the mathematical programming expression for the slope stability safety factor is: (26); (27); H cr is the critical height of the slope under certain conditions (α, β1, β2, β3, β4, H1, H2, H3, H4, c, φ are known parameters), H = H cr In order to obtain a constraint condition for the upper limit solution of the safety factor K for a specific slope (α, β1, β2, β3, β4, c, φ, H are known parameters). Since the safety factor K is actually an implicit function, this paper uses the quadratic optimization iterative method (or interior point optimization iterative method) to optimize the iterative calculation of Equation (21); thereby, the slip surface parameter θ at the critical height can be solved. h , θ0, r0 and L, by which the position of the slip surface can be determined.

[0039] 5. Calculate anchor tension When the slope is in the limit state, assuming that the anchor tension reaches the ultimate load, the energy consumption is calculated according to the upper limit method so that the power generated by the external load is equal to the internal energy dissipation power, that is: (When the slope is in the limit state, there is a critical height) (28); After simplification, the tension of the anchor rod can be obtained as:

[0040] in: .

[0041] In addition, if the retaining structure needs to be seismically designed, the equation that the power generated by the external load is equal to the power dissipated by the internal energy can be expressed as: (29); The calculation formula for earthquake load is as follows: (30); (31); (32); ——vertical seismic coefficient; ——Horizontal seismic coefficient; for the values ​​of both, please refer to the seismic code.

[0042] After simplification, the tension of the anchor rod can be obtained as:

[0043] Let r0, θ0 and θ hSubstituting this into the equation, we can obtain the total anchor tension, which can then be used to design the anchors. First, determine the anchor spacing, such as 2.5m horizontally and 3.0m vertically. Given a single slope length of 14.4m, n = 2 * 14.4 / 2.5 = 12 anchors. These 12 anchors are evenly distributed on the slope, and the tension of each anchor is T / 12. Next, design the frame beam using elastic foundation beam theory.

[0044] Similarly, this method can be used to design the lower two levels of anchor frame beams.

[0045] 6. Anti-slip pile design The pressure behind the pile can be divided into three parts: expansion force, Rankine active earth pressure behind the pile, and active earth pressure caused by overload on the soil surface.

[0046] (1) Expansion force The interaction between expansive soil and anti-slide piles, in addition to the common properties of other types of clayey soils, also includes a unique property: expansion force. This is primarily due to the fact that expansive soil is significantly affected by humidity, resulting in dramatic changes in its mechanical parameters and more complex engineering properties.

[0047] When considering the trend of expansion force along the depth, according to the analysis of indoor test and field observation results, the expansion force along the depth direction is distributed in the atmospheric influence depth range. = 4m, for soils at different depths, the intensity of atmospheric influence varies. From field tests, it is known that the atmospheric influence on expansive soil follows the rule that the closer to the surface, the greater the influence, and gradually attenuates along the depth direction. In order to facilitate the derivation and calculation of formulas, and to avoid the occurrence of high powers of parameters and excessive cross terms of parameters, the expansion force is simplified here and the expansion force is simplified to the depth. Triangular distribution within the range, such as Figure 7 shown.

[0048] (33) (2) According to Rankine's active earth pressure theory, the distribution of soil pressure behind the pile is: (34) (3) If Figure 7 As shown in the figure, there is a load on the soil surface. When calculating, draw an auxiliary line ED from the front end of the load, which forms an angle of π / 4+φ / 2 with the horizontal plane. Draw an auxiliary line parallel to ED through the intersection of the cantilever section and the anchor section of the pile. The active earth pressure caused by the soil surface load is distributed in a triangular shape, which is: (35) Therefore, the pressure behind the pile is: (36) The internal forces of the pile can be calculated from the pressure behind the pile, and then the cross-sectional dimensions and reinforcement of the pile can be designed. The same method is used to design the lower-level anti-slip piles.

[0049] 7. Design of pile slabs The load width acting on the pile plate can be calculated according to the calculated plate length. In order to facilitate construction, pile plates are generally not classified too much. The level of the baffle can be divided according to a certain height. When designing and calculating the plate, the soil pressure stress corresponding to the bottom baffle of each level can be taken. It can be simplified according to the simply supported beam with uniform load distribution, such as Figure 8 The load is equal to the sum of the Rankine soil pressure and the expansion force at the depth, that is: (37) In this way, the internal force of the pile slab can be calculated, and then the cross-sectional dimensions and reinforcement of the pile slab can be designed.

[0050] In summary, the multi-level slope composite retaining structure design method disclosed in this embodiment adopts a method combining equivalent load and energy method to design the multi-level slope composite retaining structure, and considers the effect of expansive soil, thereby optimizing the slope retaining structure design and ensuring the safety and reliability of the slope retaining structure.

[0051] Corresponding to the method in the above embodiment, the present invention also discloses a multi-level slope composite retaining structure design system, including the following first to third modules.

[0052] The first module is used to determine the number of retaining structure groups based on the slope height, which number is greater than or equal to two; at least one retaining structure includes an anchor frame beam and a pile-sheet wall. Optionally, the retaining structure can be composed entirely of a basic retaining structure, which includes a pile-sheet wall and a two-stage anchor frame beam; or the retaining structure can be composed of a basic retaining structure and a modified retaining structure, which includes a pile-sheet wall and a two-stage anchor frame beam, and a modified retaining structure including a pile-sheet wall and a single-stage anchor frame beam.

[0053] The second module is used to construct an equation that the sum of the external power of gravity and the external power of expansive soil is equal to the internal loss power when the slope is not supported. Based on the upper limit method for solving the slope safety factor in this equation and the basic parameters of the soil, the parameters of the slip surface (preferably a logarithmic spiral surface) at a given critical height of the slope corresponding to the retaining structure are solved.

[0054] The third module calculates the anchor tension, pile pressure, and internal forces of the pile slab under retaining conditions based on the calculated slip surface parameters and the load equivalence and energy methods. This allows for the design of anchor spacing, cross-sectional dimensions, and reinforcement for the anti-slip piles and pile slabs. Similarly, each retaining structure in the system is designed sequentially from top to bottom. The load equivalence method involves replacing the slope soil weight corresponding to the upper retaining structure with the load when designing the lower retaining structure, and replacing the slope soil weight behind the anti-slip piles with the load when designing the anti-slip piles. The energy law is based on the principle that when the slope is in its limit state, the power generated by the external load is equal to the power dissipated by the internal energy.

[0055] Similarly, the above-mentioned multi-level slope composite retaining structure design system adopts a method combining equivalent load and energy method to design the multi-level slope composite retaining structure, and considers the effect of expansive soil, thereby optimizing the slope retaining structure design and ensuring the safety and reliability of the slope retaining structure.

[0056] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A design method for a multi-level slope composite retaining structure, characterized in that: include: Determine the number of retaining structure groups according to the height of the slope, which should be greater than or equal to 2; At least one retaining structure includes an anchor frame beam and a pile-sheet wall; In the case of an unsupported slope, an equation is constructed in which the sum of the external power due to gravity and the external power due to expansive soil is equal to the internal power loss. Based on the upper limit method for solving the slope safety factor in this equation and the basic parameters of the soil, the slip surface parameters at a given critical height of the slope corresponding to the retaining structure are solved; Based on the solved sliding surface parameters and the load equivalence method and energy method, the anchor tension, pile pressure and internal force of the pile plate under the slope support condition are calculated, so as to design the anchor spacing, cross-sectional dimensions and reinforcement of the anti-sliding piles and pile plates of the retaining structure.

2. The multi-level slope composite retaining structure design method according to claim 1 is characterized in that: Each group of retaining structures is designed in order from top to bottom; the load equivalence method includes: When designing the lower retaining structure, use the load instead of the slope soil weight corresponding to the upper retaining structure; and When designing anti-slide piles, the load is used instead of the weight of the slope soil behind the anti-slide piles; The energy method is based on the fact that when the slope is in the limit state, the power produced by the external load is equal to the power dissipated by the internal energy.

3. The multi-level slope composite retaining structure design method according to claim 1 or 2, characterized in that: The slip surface is a logarithmic spiral surface, and the slip surface parameters include at least the corresponding chord length and inclination angle; wherein the logarithmic spiral surface slip surface parameters are used to calculate the external gravitational power and internal loss power.

4. The multi-level slope composite retaining structure design method according to claim 1 or 2, characterized in that: The retaining structure is entirely composed of a basic retaining structure, which includes a pile-sheet wall and a two-stage anchor frame beam.

5. The multi-level slope composite retaining structure design method according to claim 1 or 2, characterized in that: The retaining structure is composed of a basic retaining structure and a variable retaining structure. The basic retaining structure includes a pile-sheet wall and a two-stage anchor rod frame beam, and the variable retaining structure includes a pile-sheet wall and a one-stage anchor rod frame beam.

6. A multi-level slope composite retaining structure design system, characterized in that: include: The first module is used to determine the number of groups of retaining structures according to the height of the slope, and the number of groups is greater than or equal to 2; At least one retaining structure includes an anchor frame beam and a pile-sheet wall; The second module is used to construct an equation that equates the sum of the external power due to gravity and the external power due to expansive soil to the internal power loss when the slope is not supported. Based on the upper limit method for solving the slope safety factor in this equation and the basic soil parameters, the sliding surface parameters at a given critical height of the slope corresponding to the retaining structure are solved; The third module is used to calculate the anchor tension, pile pressure and internal force of the pile plate under the support condition of the slope based on the solved sliding surface parameters and the load equivalence method and energy method, so as to design the anchor spacing, cross-sectional dimensions and reinforcement of the anti-slip piles and pile plates of the retaining structure.

7. The multi-level slope composite retaining structure design system according to claim 6 is characterized in that: Each group of retaining structures is designed in order from top to bottom; the load equivalence method includes: When designing the lower retaining structure, use the load instead of the slope soil weight corresponding to the upper retaining structure; and When designing anti-slide piles, the load is used instead of the weight of the slope soil behind the anti-slide piles; The energy method is based on the fact that when the slope is in the limit state, the power produced by the external load is equal to the power dissipated by the internal energy.

8. The multi-level slope composite retaining structure design system according to claim 6 or 7, characterized in that: The slip surface is a logarithmic spiral surface, and the slip surface parameters include at least the corresponding chord length and inclination angle.

9. The multi-level slope composite retaining structure design system according to claim 6 or 7, characterized in that: The retaining structure is entirely composed of a basic retaining structure, which includes a pile-sheet wall and a two-stage anchor frame beam.

10. The multi-level slope composite retaining structure design system according to claim 6 or 7, characterized in that: The retaining structure is composed of a basic retaining structure and a variable retaining structure. The basic retaining structure includes a pile-sheet wall and a two-stage anchor rod frame beam, and the variable retaining structure includes a pile-sheet wall and a one-stage anchor rod frame beam.

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