Design method for replacement of weak zone in arch dam foundation surface

Abstract

The present invention discloses a design method for replacing weak zones on the foundation surface of an arch dam, which belongs to the technical field of water conservancy and hydropower engineering, and provides a design method for replacing weak zones on the foundation surface of an arch dam realized by combining a finite element analysis method. The present invention combines two-dimensional and three-dimensional finite element methods to adapt to the replacement of weak rock zones of various forms and characteristics, especially steeply inclined weak rock zones that obliquely cross the steep slope section of the foundation surface of the arch dam, and carefully considers the material properties of various rock masses on the foundation surface, and irregular excavation replacement forms. The spatial interpolation of the force on the foundation surface can be adopted, and the actual distribution characteristics of the arch thrust on the foundation surface of the arch end are considered; the replacement scheme comparison based on two-dimensional finite element calculation is adopted to reduce the calculation workload and shorten the calculation cycle. The sub-model method is used for calculation, and the spatial force behavior of the replacement body can be analyzed with a smaller amount of calculation, and a basis can be provided for subsequent possible reinforcement calculations.

Description

Technical Field

[0001] The invention relates to the technical field of water conservancy and hydropower engineering, and in particular to a design method for replacing a weak zone on a foundation surface of an arch dam. Background Art

[0002] The design specification of concrete arch dams requires that the dam foundation, after treatment, has sufficient strength and stiffness to meet the requirements of bearing capacity and deformation control, and meet the anti-sliding stability of the arch seat and the overall stability of the arch dam. The dam foundation treatment plan should be determined based on the geological conditions of the dam site and the physical and mechanical properties of the bedrock, through arch dam structural analysis and stability analysis. Dam foundation treatment measures should be selected according to geological conditions and treatment purposes. Excavation, cushions, thrust piers, gravity piers, wing dams, consolidation grouting, contact grouting, anti-seepage drainage, concrete replacement of weak rock zones, and prestressed anchoring measures can be adopted. Among them, concrete replacement of weak rock zones is the main means of treating foundation surface defects.

[0003] The weak rock belt of the dam foundation includes various scale faults, crack-intensive belts, altered rocks, metamorphic rock belts, etc. Arch dam construction has accumulated a lot of experience in the treatment of weak rock belts. The U.S. Bureau of Reclamation proposed an empirical formula for the empirical formula method of weak rock replacement treatment: when H < 45m: h = 0.3B + 1.5; when H < 45m: h = 0.3B + 1.5, where H is the dam height at the fault fracture zone (m), h is the backfill depth of the concrete plug (m), and B is the width of the fault fracture zone (m). Japan proposed a similar empirical formula. my country's Ertan Project and Xiaowan Project also summarized and proposed a more systematic design method (Zhao Yonggang 2001, He Ruiliang 2017), including engineering experience method, structural mechanics method, elastic foundation beam method, and finite element analysis method. In general, the general methods for treating weak rock belts within the dam foundation range include: ① For weak rock belts with a smaller scale, but the lower filling is loose and weak, and still has an impact on the strength and compression deformation of the dam foundation, an appropriate amount of steel mesh can be laid along the weak rock belt; ② For weak rock belts with a general scale, they should be treated according to engineering experience or specifications. The general treatment method is to carry out trench excavation and concrete replacement along the weak rock belt, and the replacement depth is 1 to 1.5 times the width of the weak rock belt; ③ For weak rock belts extending beyond the upstream and downstream dam foundations, in order to diffuse the dam foundation stress outside the dam foundation range, the excavation treatment range should be expanded, and its horizontal diffusion length is generally 1.5 to 2.0 times the replacement depth of the concrete trench plug; ④ When the weak rock belt of the dam foundation is large in scale, the lower filling is broken soft rock, and has a greater impact on deformation, it should be strictly treated, must meet the structural requirements, and should also be carefully designed and calculated. The replacement depth of the concrete plug can be determined by using calculation methods such as engineering experience method, structural mechanics method, elastic foundation beam method, deep beam method, plane finite element method, and three-dimensional finite element analysis method.

[0004] With the rapid development of computer hardware and software technology, finite element analysis has become an important means of arch dam structure and foundation treatment design. Lijiaxia Arch Dam, the riverbed foundation surface is distributed with multiple faults consisting of f20 fault families, which are staggered and difficult to apply empirical formulas, structural mechanics and other methods. The three-dimensional finite element method has been fully applied in the treatment design of foundation surface replacement and deep grid replacement (Bai Junguang, 2008). The three-dimensional finite element method is used in the design of Jinping first-level foundation treatment under complex geological conditions. The basic treatment schemes are systematically studied and compared, and the treatment design method of the weak rock belt replacement of the foundation surface is studied (Xue Lijun 2005, Mou Gaoxiang 2009, Hu Zhuxiu 2010). Dagangshan (Wang Chao 2012), Baihetan, Yebatan and Mengdigou arch dams under construction also use finite element and other numerical calculation methods to replace the weak rock belt of the arch dam foundation surface.

[0005] In the design of arch dam foundation treatment, the finite element method has many advantages over other methods. It can consider various factors such as complex geometric shapes, material partitions, load combinations and construction processes, and can consider the interaction between arch dams and foundations. On the other hand, the calculation workload is large, especially for the comparison of various treatment schemes. From modeling, loading to results processing, a large amount of comparative analysis is required, and the cycle is relatively long. It is necessary to systematically analyze and summarize the establishment of relatively scientific, simple and standard processes and methods to simplify the calculation of engineering quantities and improve the rationality and scientificity of calculations for reference in subsequent projects. In particular, for relatively simple problems, such as the replacement of a single weak rock belt obliquely crossing the foundation surface, a relatively reasonable analysis process and method should be established; for a general method that can adapt to the treatment design of steeply inclined weak rock belts obliquely crossing the foundation surface of arch dams and steep slope dam sections. Summary of the invention

[0006] The technical problem solved by the present invention is to provide a design method for replacing the weak zone of the arch dam foundation surface in combination with a finite element analysis method.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a design method for replacing the weak zone of the arch dam foundation surface is a design method for replacing the weak zone of the arch dam foundation surface based on a combination of a two-dimensional plane finite element method and a three-dimensional finite element method, comprising the following steps:

[0008] Step 1: Take the area where the weak interlayer is located in the dam toe, dam middle and dam heel sections, and intercept the corresponding section range, where the intercepted section range is not less than twice the length of the weak rock exposed on the foundation surface; according to the relationship between the interlayer and the section on the section, refer to the empirical formula, determine the basic form of excavation replacement, obtain various schemes with different replacement ranges, and establish regular grids respectively;

[0009] Step 2: According to the designed fault of the arch dam body shape, the force on the foundation surface on the calculation grid is interpolated, and the resultant force on each point is calculated, and then decomposed into the plane to obtain the force on the grid node;

[0010] Step 3: compare multiple replacement schemes at the dam toe, dam center and dam heel, and determine the replacement scheme for each section according to the displacement convergence trend;

[0011] Step 4: On the 3D software design and calculation platform, connect the dam toe, dam center and dam heel schemes to construct a 3D model of the replacement body;

[0012] Step 5: Determine whether the structural properties of the replacement body are reasonable, consider various factors such as construction, and improve and modify the treatment plan;

[0013] Step 6: Establish a three-dimensional grid model of the replacement body. According to the three-dimensional finite element calculation results of the arch dam foundation, obtain the boundary conditions of the sub-model, perform structural calculations on the replacement body, and calculate and analyze the stress behavior of the replacement body. If it is unreasonable, modify and improve the replacement plan.

[0014] The beneficial effects of the present invention are as follows: by combining two-dimensional and three-dimensional finite element methods, the present invention can adapt to the replacement of weak rock zones of various shapes and characteristics, especially the steeply inclined weak rock zones that obliquely cross the steep slope section of the arch dam foundation surface, and carefully consider the material properties of various rock masses on the foundation surface, and the irregular excavation replacement form. The spatial interpolation of the force on the foundation surface can be used, taking into account the actual distribution characteristics of the arch thrust on the arch end foundation surface; the replacement scheme comparison based on two-dimensional finite element calculation is used to reduce the calculation workload and shorten the calculation cycle. The sub-model method is used for calculation, and the spatial force behavior of the replacement body can be analyzed with a smaller amount of calculation, and a basis can be provided for subsequent possible reinforcement calculations. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Calculation diagram of deep beam fixed at both ends;

[0016] Figure 2 Replacement of weak rock belt in steep slope section of base surface;

[0017] Figure 3 Design process for concrete replacement in weak rock zones at the arch dam foundation surface;

[0018] Figure 4 The schematic diagram of the cross-section of the arch dam foundation, dam toe, dam center and dam heel. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0020] It should be noted that if there are directional indication terms in the present invention, such as up, down, left, right, front, and back directions and orientation terms, they are for the purpose of facilitating the description of the relative position relationship between components, and are not specific to the absolute position of the related components or the position relationship between components. They are only used to explain the relative position relationship and movement of the components in a certain posture. If the specific posture changes, the directional indication will also change accordingly. If there are terms related to quantity in the present invention, such as "multiple", "multiple", "several", etc., they specifically refer to two or more.

[0021] As 1 to Figure 4 As shown in the figure, the design method for replacing the weak zone of the arch dam foundation surface of the present invention is a design method for replacing the weak zone of the arch dam foundation surface based on a combination of a two-dimensional plane finite element method and a three-dimensional finite element method, comprising the following steps:

[0022] Step 1: Take the area where the weak interlayer is located in the dam toe, dam middle and dam heel sections, and intercept the corresponding section range, where the intercepted section range is not less than twice the length of the weak rock exposed on the foundation surface; according to the relationship between the interlayer and the section on the section, refer to the empirical formula, determine the basic form of excavation replacement, obtain various schemes with different replacement ranges, and establish regular grids respectively;

[0023] Step 2: According to the designed fault of the arch dam body shape, the force on the foundation surface on the calculation grid is interpolated, and the resultant force on each point is calculated, and then decomposed into the plane to obtain the force on the grid node;

[0024] Step 3: compare multiple replacement schemes at the dam toe, dam center and dam heel, and determine the replacement scheme for each section according to the displacement convergence trend;

[0025] Step 4: On the 3D software design and calculation platform, connect the dam toe, dam center and dam heel schemes to construct a 3D model of the replacement body;

[0026] Step 5: Determine whether the structural properties of the replacement body are reasonable, consider various factors such as construction, and improve and modify the treatment plan;

[0027] Step 6: Establish a three-dimensional grid model of the replacement body. According to the three-dimensional finite element calculation results of the arch dam foundation, obtain the boundary conditions of the sub-model, perform structural calculations on the replacement body, and calculate and analyze the stress behavior of the replacement body. If it is unreasonable, modify and improve the replacement plan.

[0028] In addition, for areas with large tensile stress in the replacement body, stress diagram method reinforcement design is carried out to further improve the bearing capacity.

Claims

1. The design method for replacing the weak zone of the arch dam foundation surface is characterized by: A design method for replacing weak zones on the foundation surface of an arch dam based on a combination of a two-dimensional plane finite element method and a three-dimensional finite element method is provided, comprising the following steps: Step 1: Take the area where the weak interlayer is located in the dam toe, dam middle and dam heel sections, and intercept the corresponding section range, where the intercepted section range is not less than twice the length of the weak rock exposed on the foundation surface; according to the relationship between the interlayer and the section on the section, refer to the empirical formula, determine the basic form of excavation replacement, obtain various schemes with different replacement ranges, and establish regular grids respectively; Step 2: According to the designed fault of the arch dam body shape, the force on the foundation surface on the calculation grid is interpolated, and the resultant force on each point is calculated, and then decomposed into the plane to obtain the force on the grid node; Step 3: compare multiple replacement schemes at the dam toe, dam center and dam heel, and determine the replacement scheme for each section according to the displacement convergence trend; Step 4: On the 3D software design and calculation platform, connect the dam toe, dam center and dam heel schemes to construct a 3D model of the replacement body; Step 5: Determine whether the structural properties of the replacement body are reasonable, consider various factors such as construction, and improve and modify the treatment plan; Step 6: Establish a three-dimensional grid model of the replacement body. According to the three-dimensional finite element calculation results of the arch dam foundation, obtain the boundary conditions of the sub-model, perform structural calculations on the replacement body, and calculate and analyze the stress behavior of the replacement body. If it is unreasonable, modify and improve the replacement plan.

2. The design method for replacing the weak zone of the arch dam foundation surface according to claim 1 is characterized by: It also includes step seven, which is to carry out reinforcement design using the stress graph method for areas with large tensile stress in the replacement body.

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