Design method of asymmetric arch dam force transmission structure

Abstract

The application provides a design method of asymmetric arch dam force transmission structure, and the method is based on the half chord length of several representative elevations in the lower part of the arch dam to obtain the arch thrust influence area coefficient F of the symmetric arch dam as the basis of the force transmission structure design method a ; according to the characteristic curve of the asymmetric arch dam, the thrust ratio Rt of the arch thrust in the lower part of the gentle slope side and the steep slope side is obtained, according to the relationship between the arch thrust and the compressive stress, the horizontal ratio Rc of the compressive stress of the arch end on both banks is obtained, then the force transmission coefficient Cs of the asymmetric arch dam force transmission structure is determined; then the force transmission coefficient is evaluated whether it meets the engineering characteristic requirement; finally, the size Li of the force transmission structure is determined according to the arch end thickness Ti. According to the distribution law of the arch thrust in the low elevation of the asymmetric arch dam, the concrete force transmission structure is arranged in the downstream of the dam, the stress and deformation of the dam foundation are homogenized, the adaptability of the arch dam to the complex dam foundation is enhanced, the overall stability of the dam body and the foundation is improved, the horizontal arch thrust of the left bank and the right bank is basically equivalent, and the better foundation guiding role for the overall safety of the asymmetric arch dam is achieved.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and hydropower engineering design technology, specifically relating to a design method for the force transmission structure of an asymmetric arch dam. It is applicable to the structural design of asymmetric arch dams and has a universal effect. Background Technology

[0002] Concrete arch dams are an economical type of concrete dam, but compared to other dam types, their stress analysis is more complex. Traditional arch dams are generally symmetrical on the left and right banks. However, with the continuous development of the hydropower industry at home and abroad, the number of suitable dam sites for development is becoming increasingly limited according to the traditional design ideas for arch dams. Many dam sites with asymmetrical topographic conditions but relatively intact rock conditions may be adjusted to other dam types, which is economically unreasonable.

[0003] Arch dams are generally located in relatively symmetrical positions on the left and right banks of river valleys. For arch dam sites in asymmetrical valleys, domestically, the steep slope side is often excavated, while in Europe and America, the gentle slope side is often backfilled with concrete to form a foundation. Some arch dam designs, initially considering economic factors, do not employ topographical correction measures such as foundation excavation or concrete backfilling. However, due to the asymmetry between the two banks, the arch dam experiences uneven stress, easily resulting in significantly greater arch thrust on the lower and middle sections of the gentle slope side compared to the steep slope side. This increases the compressive stress level of the concrete dam foundation on the lower and middle sections of the gentle slope side and corresponding locations. While concrete dams, due to their high uniformity, have a relatively high capacity to withstand overload, for rock foundations, the asymmetrical topography, without adjusting the dam's shape, causes an increase in compressive stress in the foundation due to the force transmitted from the arch dam, reducing the overall safety of the arch dam system. Considering this issue, the operation of asymmetrical arch dams on gentle slope sides carries certain risks. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a design method for the force transmission structure of asymmetric arch dams, enhancing the adaptability of arch dams to complex dam foundations, improving the overall stability of the dam body and foundation, and achieving a level where the thrust levels of the left and right bank arches are basically equivalent, thus providing better basic guidance for the overall safety of asymmetric arch dams. To this end, this invention adopts the following technical solution:

[0005] A design method for asymmetric arch dam force transmission structures, characterized by the following steps:

[0006] (1) Calculate the left bank half-chord length C of the corresponding arch ring at different typical elevations in the lower half of the asymmetric arch dam. li (The fixed chord length of the left bank) and the right bank half-chord length C ri(The fixed Chord Length of the right bank);

[0007] (2) Calculate the influence area coefficient F of the arch thrust of the asymmetric arch dam through the left bank half chord length C li and the right bank half chord length C ri (Factor of the arch thrust influence); a (Factor of the arch thrust influence);

[0008] (3) According to the influence area coefficient F of the arch thrust of the asymmetric arch dam a , obtain the thrust ratio R of the arch thrust at the middle and lower elevations on the left and right banks, that is, the gentle slope side and the steep slope side t (thrust ratio of the Asymmetric Arch dam);

[0009] (4) According to the thrust ratio R of the arch thrust in the middle and lower parts of the asymmetric arch dam t and the relationship that is positively correlated with the foundation compressive stress level, the compressive stress level ratio R of both banks c (Compressive stress ratio of the Asymmetric Arch dam) adopts the thrust ratio R under the condition of meeting the engineering accuracy requirements t ;

[0010] (5) Determine the carry coefficient Cs of the force transmission structure on the gentle slope side of the asymmetric arch dam according to the compressive stress level ratio R of both banks c (Carry Coefficient of the structure);

[0011] (6) Judge whether the carry coefficient Cs is reasonable: If the first threshold < Cs ≤ the second threshold, it is relatively reasonable, and a reasonable structural force transmission design coefficient Cs’ is adopted according to Cs;

[0012] (7) Calculate the abutment thickness Ti at each typical elevation within the layout range of the force transmission structure respectively (Thickness of the abutment);

[0013] (8) Determine the control dimension Li of the force transmission structure based on the abutment thickness Ti and the force transmission design coefficient Cs’ of the arch dam force transmission structure.

[0014] Further, considering that the distribution difference of the arch thrust on the left and right banks of the asymmetric arch dam is concentrated in the range below 1 / 2 of the dam height, and the relationship between the difference in arch thrust and the half chord length is relatively good, the different typical elevations are the 4 elevations of 1 / 2 of the dam height, 1 / 3 of the dam height, 1 / 4 of the dam height, and the riverbed dam foundation of the asymmetric arch dam.

[0015] Further, the first threshold value is taken as 0.1 and the second threshold value is taken as 0.3. In step (6), according to the engineering characteristics, it is judged whether the force transfer coefficient Cs is reasonable: if 0.1 < Cs ≤ 0.3, it is relatively reasonable. If the coefficient Cs is too small, the increased concrete structure has limited improvement on the arch dam stress, and the layout of the concrete force transfer structure may not be carried out. If the coefficient Cs is too large, the improvement degree of the increased concrete structure on the stress becomes lower, and it is uneconomical to increase the concrete force transfer structure. The reasonable structural force transfer design coefficient Cs' is obtained according to Cs.

[0016] Further, in step (6), if the first threshold < Cs ≤ the second threshold, Cs' is taken as Cs; otherwise, Cs' is taken as the first threshold or the second threshold.

[0017] The beneficial effects of the present invention are as follows: Based on the design of the asymmetric arch dam and the full utilization of the strength of the mountain bodies on both sides of the dam shoulders, without changing the shape of the arch dam, a design method for the force transfer structure of the asymmetric arch dam is proposed. Based on the semi-chord lengths at several representative elevations in the middle and lower parts of the arch dam, the influence area coefficient F of the arch thrust of the symmetric arch dam is obtained a as the basis of the force transfer structure design method; according to the characteristic curve of the asymmetric arch dam, the thrust ratio R of the arch thrust at the middle and lower elevations on the gentle slope side and the steep slope side is obtained t ; from the relationship between the arch thrust of the arch dam and the foundation pressure stress, the force transfer coefficient Cs of the force transfer structure to be increased on the gentle slope side is obtained; then the force transfer coefficient is evaluated to see if it meets the engineering characteristic requirements; finally, the size Li of the force transfer structure is determined according to the arch end thickness Ti.

[0018] The method of the present invention studies the stress of the asymmetric arch dam shape, and based on the distribution law of the arch thrust at the middle and low elevations of the asymmetric arch dam, a concrete force transfer structure is set downstream of the dam to equalize the foundation stress and deformation, enhance the adaptability of the arch dam to the complex foundation, improve the overall stability of the dam body and the foundation, and achieve the level where the arch thrust levels on the left and right banks are basically equivalent, providing a good basic guiding role for the overall safety of the asymmetric arch dam. Description of the Drawings

[0019] Figure 1 is the plan layout diagram of the arch ring at the 1 / 3 dam height position;

[0020] Reference numerals: 1 - center line of the arch dam; 2 - right bank arch ring (assuming the arch ring on the gentle slope side); 3 - left bank arch ring (assuming the arch ring on the steep slope side); 4 - force transfer structure on the gentle slope side. Detailed Embodiment

[0021] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with the drawings:

[0022] Such as Figure 1As shown, the present invention proposes a design method for an asymmetric arch dam force transmission structure, comprising the following steps:

[0023] a. For an asymmetric arch dam, assume the right bank is a gentle slope (arch 2 is longer) and the left bank is a steep slope (arch 1 is shorter). Decompose the arch dam below half its height into four arches at different elevations: half the dam height, one-third of the dam height, one-quarter of the dam height, and the riverbed / dam foundation. These four arches form a total of four layers. From top to bottom, the half-chord length C of the left bank is obtained. l1 C l2 C l3 C l4 The half-chord length C on the right bank r1 C r2 C r3 C r4 ;

[0024] b. Calculate the influence zone coefficient F of the arch thrust of the asymmetric arch dam. a :

[0025]

[0026] c. Based on the influence zone coefficient F of asymmetric arch dam thrust a Based on the study of the arch thrust on the left and right banks of the asymmetric arch dam, the thrust ratio R of the arch thrust at the lower elevation of the gentle slope side and the steep slope side is... t :

[0027] R t =exp(0.8327×(F) a -1))

[0028] d. According to numerous engineering statistical studies, the magnitude of the arch thrust is positively correlated with the compressive stress level of the dam foundation. The range of tensile stress at the arch end of an arch dam generally does not exceed 10% of the arch end thickness, i.e., the compression zone is 90% of the arch end thickness. Since the distribution range on both banks is basically the same, for ease of engineering application, the ratio R of the compressive stress levels at the arch ends on both banks of an asymmetric arch dam is... c After being homogenized at the arch end, the ratio approximately matches the thrust ratio, and R is also used. t :

[0029] R c =R t

[0030] e. Based on a review of extensive engineering data from both domestic and international sources, the rock mass quality on both banks of an asymmetric arch dam is similar, or the rock mass quality on the gentle slope side may be relatively poor due to weathering and unloading. Previous studies have recognized that due to the asymmetry of the arch dam, the arch thrust (i.e., the stress level of the dam foundation) on the gentle slope side is higher than that on the gentle slope side. Coupled with the relatively weaker rock mass, this exacerbates the safety risks, necessitating effective engineering measures. Therefore, this invention is based on the stress ratio R between the two banks.c Obtain the carry coefficient Cs (Carry Coefficient of the structure) of the force-transfer structure on the gentle slope side of the asymmetric arch dam, and improve the stress level of the dam foundation through the added force-transfer structure.

[0031] Cs = R c -1.1

[0032] f. According to the engineering characteristics, judge whether the carry coefficient Cs needs to be adjusted. When 0.1 < Cs ≤ 0.3, it is relatively reasonable, and take the structural force-transfer design coefficient Cs' = Cs;

[0033] When the carry coefficient Cs ≤ 0.1, the difference between the two banks is relatively small, and the concrete force-transfer structure layout may not be carried out. However, for some projects, in order to further improve safety, the force-transfer structure can also be added according to this invention to increase the safety margin of the asymmetric arch dam, and take Cs' = 0.1;

[0034] When the carry coefficient Cs > 0.3, the improvement of the compressive stress of the dam foundation by the added concrete force-transfer structure becomes less than 2%, and the economy is relatively poor. Therefore, take Cs' = 0.3;

[0035] g. Since the difference in arch thrust is mainly reflected in the range below 1 / 2 of the dam height, calculate the thickness Ti (Thickness of the abutment) of the arch ends at 4 typical elevations within the layout range of the force-transfer structure (the elevations of 1 / 2 of the dam height, 1 / 3 of the dam height, 1 / 4 of the dam height, and the riverbed dam foundation of the asymmetric arch dam);

[0036] h. Calculate the dimensions Li of the force-transfer structure for each elevation respectively:

[0037] L i = T i × C s '<(

[0038] To make the concrete stress transition between the asymmetric dam and the force-transfer structure smooth, control the angle between the connection line of the structure and the dam and the radial direction to be θ, and θ is generally taken as 25 - 30°.

[0039] In summary, the design method for the force transmission structure of asymmetric arch dams proposed in this invention addresses the characteristics of the arch thrust distribution in asymmetric arch dams. It divides the area below half the dam height into four arch rings, determines the arch thrust influence zone coefficient, and then determines the thrust ratio Rt based on this coefficient. Based on the relationship between arch thrust and compressive stress, and the horizontal ratio Rc of the compressive stress at the arch ends on both banks, the force transmission coefficient Cs of the asymmetric arch dam force transmission structure is determined. A reasonable range for Cs should be selected. Finally, based on the thickness of the arch ends below half the dam height and the structural force transmission design coefficient Cs', the dimensions of the asymmetric arch dam force transmission structure and its angle with the dam are determined. By applying the force transmission structure, the stress in the dam foundation can be effectively reduced. Without altering the overall dam structure, a simple structural arrangement achieves good engineering results, providing a sound theoretical basis for the design of asymmetric arch dam structures.

[0040] The invention will be further illustrated below with reference to examples:

[0041] Example 1: An asymmetric arch dam project with a height of 168m and a crest elevation of 962m. The influence coefficient of its arch thrust is shown in Table 1.

[0042]

[0043] Based on this, the thrust ratio R of the arch thrust in the lower and middle elevations of the gentle slope side and the steep slope side is determined. t =1.510;

[0044] The force transmission coefficient of the asymmetric arch dam force transmission structure is Cs = 0.410; since Cs > 0.3, the structural force transmission design coefficient is Cs' = 0.3.

[0045] The right bank of this asymmetric arch dam project has a gentle slope, so a force-transfer structure is added below the half elevation of the right bank. The parameters are shown in Table 2.

[0046]

[0047] By designing the force transmission structure, the compressive stress level at low elevations on the gentle slope side of the asymmetric arch dam is effectively reduced, thus improving the dam's safety. Example 2: An asymmetric arch dam project with a height of 220m and a crest elevation of 358m. The influence coefficient of its arch thrust area is shown in Table 3.

[0048]

[0049] Based on this, the thrust ratio R of the arch thrust in the lower and middle elevations of the gentle slope side and the steep slope side is determined. t =1.335;

[0050] The force transfer coefficient Cs of the force transfer structure of the asymmetric arch dam is 0.235. Since 0.1 < Cs ≤ 0.3, the force transfer design coefficient Cs' of the structure is Cs = 0.235.

[0051] The right bank of this asymmetric arch dam project is the gentle slope side, so a force transfer structure is added below the 1 / 2 elevation of the right bank. The parameters are shown in Table 4:

[0052]

[0053] Through the setting of the force transfer structure, the low elevation compressive stress level on the gentle slope side of the asymmetric arch dam is effectively reduced, improving the safety of the arch dam.

Claims

1. A design method for asymmetric arch dam force transmission structures, characterized in that... It includes the following steps: (1) Calculate the left bank half-chord length C of the corresponding arch ring at different typical elevations in the lower half of the asymmetric arch dam. li And the right bank half-chord length C ri The different typical elevations mentioned are the elevations at 1 / 2 dam height, 1 / 3 dam height, 1 / 4 dam height, and riverbed dam foundation of the asymmetric arch dam. (2) The left bank half-chord length C through the different typical elevations li And the right bank half-chord length C ri Calculate the influence zone coefficient of arch thrust in asymmetric arch dams , ； (3) Based on the influence zone coefficient of arch thrust of asymmetric arch dam The thrust ratio of the arch thrust at the lower elevation of the left and right banks, i.e., the gentle slope side and the steep slope side, is obtained. : ； (4) Based on the thrust ratio of the lower arch thrust in the asymmetric arch dam The positive correlation between the compressive stress level of the dam foundation and the ratio of compressive stress levels on both banks Thrust ratio is adopted while meeting engineering accuracy requirements. ; (5) Based on the ratio of compressive stress levels on both sides Determine the force transmission coefficient Cs of the force transmission structure of the arch dam: ； (6) Judge whether the force transfer coefficient Cs is reasonable: When 0.1 < Cs ≤ 0.3, it is relatively reasonable, and take the structural force transfer design coefficient Cs' = Cs; When the force transfer coefficient Cs ≤ 0.1, take Cs' = 0.1; When the force transfer coefficient Cs > 0.3, adopt Cs' = 0.3; (7) Calculate the arch end thickness Ti at each typical elevation within the layout range of the force transfer structure respectively; (8) Determine the control dimension Li of the force transfer structure based on the arch end thickness Ti and the force transfer design coefficient Cs' of the arch dam force transfer structure: 。

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