Method for predicting damage of special-shaped terrace to dam

Abstract

The invention provides a method for predicting damage of a special-shaped terrace to a dam, and the method comprises the steps: obtaining the settlement S valley of a river valley dam and the settlement S terrace of a terrace dam, calculating the damage influence coefficient K of the special-shaped terrace dam terrace, and predicting the damage degree of the terrace through the damage influence coefficient K. The larger the K value is, the larger the deformation gradient is, and the larger the deformation gradient is. When the K value is larger than or equal to 4, treatment needs to be carried out during design and construction to avoid settlement or tension cracks, and when the K value is smaller than 4, it is indicated that the harm is small, and treatment can not be carried out. According to the method, guidance can be provided for design and subsequent construction, differential settlement of the dam is reduced by taking corresponding measures, the stress states of the dam body and the concrete panel are improved, structural cracks of the dam and the panel due to terrace terrains are prevented, and the seepage-proofing safety of the dam body is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy and hydropower engineering, and particularly relates to a method for predicting the harm of irregular terraces to dams. Background Art

[0002] Topographic conditions are one of the important factors in dam site selection. Due to the limitation of dam site selection, some dams need to be built in narrow valley bends. Compared with wide valleys, valley bends usually have terraces on one side and are relatively steep on the other side. Due to the existence of terraces, the terrain conditions in these areas are complex, and the slopes on both sides of the dam site are asymmetrical, forming a stepped terrace valley, which leads to a large difference in the thickness of the dam body on both sides of the terrace edge. The vertical deformation gradient of the dam body increases within a certain range on both sides of the terrace edge, which affects the continuity and uniformity of the vertical deformation of the dam body along the dam axis. The stress distribution of the dam body and the panel changes, which causes uneven settlement of the rockfill body, which is the weak part of the anti-seepage structure of the panel rockfill dam. In severe cases, it can directly lead to the destruction of the water-stop structure and even the panel, and the destruction of the anti-seepage structure such as the water-stop or panel will aggravate the deformation of the dam, cause cracks in the dam body, and cause leakage, causing great harm to human life and property. Summary of the invention

[0003] The purpose of the present invention is to provide a method for predicting the hazards of irregular terraces to dams, aiming to predict before construction whether the dam body or panel will crack due to the terrace hazards, so as to provide guidance for design and subsequent construction.

[0004] The object of the present invention is achieved by the following technical means: a method for predicting the hazards of irregular terraces to dams, comprising the following steps:

[0005] Get the valley dam settlement S 谷 and the settlement of the terrace dam S 台 ;

[0006] Calculate the influence coefficient K of the dam platform hazard on the irregular terrace:

[0007] K=S 谷 S 台

[0008] Where: K—platform hazard impact coefficient;

[0009] The degree of terrace hazard is predicted by the terrace hazard influence coefficient K. The larger the K value, the greater the deformation gradient and the greater the hazard to the dam body or panel. It is necessary to reduce the terrace hazard during the construction and design process.

[0010] Estimated settlement of the valley dam S 谷 and the expected settlement of the terrace dam S 台 for:

[0011]

[0012] Where: H 谷 — height of river valley dams;

[0013] H 台 — Height of terrace dam;

[0014] E 谷 — deformation modulus of valley dams;

[0015] E 台 —Deformation modulus of terrace dam;

[0016] H1—height of the built dam;

[0017] E1—deformation modulus of the built dam;

[0018] S1—The settlement of the crest of the built dam.

[0019] Since the terrace dam and the valley dam are the same project, the deformation modulus of the dam material is the same.

[0020] K=(H 谷 H 台 ) 2

[0021] When the K value is greater than or equal to 4, it means that the terrace is very harmful and needs to be treated during design and construction to avoid settlement or tension cracks. When the K value is less than 4, it means that the harm is small and no treatment is required.

[0022] The height of the terrace dam is the height from the dam top to the terrace, and the height of the valley dam is the height from the dam top to the bottom of the valley.

[0023] The beneficial effects of the present invention are as follows: a prediction method for the harm of irregular terraces to dams is proposed, and the influence of terraces on the deformation and cracking of dams or panels is estimated in advance through the size of the terrace harm influence coefficient K; and a judgment standard for the influence coefficient K is proposed. When the K value is greater than or equal to 4, it means that the terrace is highly harmful and necessary measures need to be taken to reduce the harm. When the K value is less than 4, it means that the harm is small and no treatment is required. This prediction method is simpler and faster than three-dimensional finite element calculation, and can quickly predict the degree of harm of irregular terraces to dams and panels, thereby providing a reference for subsequent design and construction. By taking corresponding measures, the uneven settlement of the dam is reduced, the stress state of the dam body and concrete panels is improved, and the dam and panels are prevented from being damaged by structural cracks due to irregular terraces, thereby ensuring the anti-seepage safety of the dam body. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the cross-sectional view of the DSX project dam along the dam axis;

[0025] Figure 2This is the cross-sectional view of the JSX project dam along the dam axis;

[0026] Figure 3 This is the relationship diagram between the height difference between the valley dam and the terrace dam of the DSX project, the influence coefficient K, and the horizontal displacement difference;

[0027] Figure 4 This is the relationship diagram between the height difference between the valley dam and the terrace dam of the JSX project, the influence coefficient K, and the horizontal displacement difference;

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0029] [Example 1]

[0030] A method for predicting the hazards of irregular terraces to dams comprises the following steps:

[0031] Get the valley dam settlement S 谷 and the settlement of the terrace dam S 台 ;

[0032] Calculate the influence coefficient K of the dam platform hazard on the irregular terrace:

[0033] K=S 谷 S 台

[0034] Where: K—platform hazard impact coefficient;

[0035] The degree of terrace hazard is predicted by the terrace hazard influence coefficient K. The larger the K value, the greater the deformation gradient and the greater the hazard to the dam body or panel. It is necessary to reduce the terrace hazard during the construction and design process.

[0036] Estimated settlement of the valley dam S 谷 and the expected settlement of the terrace dam S 台 for:

[0037]

[0038] Where: H 谷 — height of river valley dams;

[0039] H 台 — Height of terrace dam;

[0040] E 谷 — deformation modulus of valley dams;

[0041] E 台 —Deformation modulus of terrace dam;

[0042] H1—height of the built dam;

[0043] E1—deformation modulus of the built dam;

[0044] S1—The settlement of the crest of the built dam.

[0045] Since the terrace dam and the valley dam are the same project, the deformation modulus of the dam material is the same.

[0046] K=(H 谷 H 台 ) 2

[0047] When the K value is greater than or equal to 4, it means that the terrace is very harmful and needs to be treated during design and construction to avoid settlement or tension cracks. When the K value is less than 4, it means that the harm is small and no treatment is required.

[0048] The height of the terrace dam is the height from the dam top to the terrace, and the height of the valley dam is the height from the dam top to the bottom of the valley.

[0049] Specifically, the DSX concrete face gravel dam has complex topographic and geological conditions at the dam site, poor symmetry of the terrain on both sides, high and steep slopes on the left bank, and a large-scale ancient riverbed terrace on the right bank (about 480m long along the river and about 260m wide across the river). The terrace elevation is 1594m, the river valley elevation is 1460m, the dam top elevation is 1707m, the river valley dam height is 247m, and the terrace dam height is 113m. The calculated terrace hazard impact coefficient K is 4.78. The DSX project terrace structure is as follows Figure 1 shown.

[0050] The water diversion structure of the JSX project is arranged on the left bank of the relatively gentle II and III grade erosion terrace, resulting in discontinuous terrain on the left bank. The top elevation of the horizontal section of the water diversion steel pipe is 1835.00m, and the dam is filled with rockfill above 1835.00m. The river valley elevation is 1758m, and the dam top elevation is 1861m. The river valley dam is 103m high, and the terrace dam is 26m high. The calculated terrace hazard impact coefficient K is 15.69, which is greater than the DSX terrace hazard impact coefficient K. The JSX project terrace structure is as follows Figure 2 shown.

[0051] At present, the existing technology uses the horizontal displacement difference as the control standard for the coordinated deformation of the dam body. It is believed that the allowable horizontal displacement difference is generally about 1%. When the horizontal displacement difference is controlled to be less than 1%, the dam body deformation is small, no large tension cracks will be generated, and the operation safety requirements can be met. Through three-dimensional finite element analysis and calculation, it is found that the horizontal horizontal displacement difference between the DSX platform and the critical area of ​​the river valley in the direction of the dam axis is 1.14%; the horizontal horizontal displacement difference between the JSX platform and the critical area of ​​the river valley in the direction of the dam axis is 2.69%, which is greater than the DSX project; both are greater than 1%, and corresponding measures need to be taken to deal with them. The three-dimensional finite element calculation results are consistent with the calculation law of the platform hazard influence coefficient K.

[0052] Specifically, by constructing a three-dimensional finite element model, the horizontal displacement difference between the terrace and the critical area of ​​the valley in the dam axis direction under different elevation terrace conditions of the DSX and JSX projects was analyzed and calculated to verify the necessity and accuracy of the terrace hazard influence coefficient K. The calculation results are shown in Tables 1 and 2:

[0053] Table 1 The average horizontal displacement difference between the DSX terrace and the valley critical area in the dam axis direction and the terrace hazard influence coefficient K

[0054]

[0055] Table 2 The average horizontal displacement difference between the JSX terrace and the critical area of ​​the river valley in the dam axis direction and the terrace hazard influence coefficient K

[0056]

[0057] It can be seen from Table 1 and Table 2 that when H 台 ≈1 / 2·H 谷 , that is, when K≈4, the horizontal displacement difference between the two engineering terraces and the critical area of ​​the valley in the direction of the dam axis is ≈1%, and the terrace hazard influence coefficient K increases with △H=H 谷 -H 台 The variation law of the horizontal displacement difference between the terrace and the valley in the direction of the dam axis varies with △H=H 谷 -H 台 The changing pattern of Figure 3 , Figure 4 It can be seen that it is feasible to use the terrace hazard influence coefficient K as a prediction method for the terrace hazard of irregular terrace dams, and it is accurate to use the terrace hazard influence coefficient K equal to 4 as the judgment standard for the terrace hazard of irregular terrace dams. When the K value is greater than or equal to 4, it means that the terrace hazard is large and needs to be treated during design and construction to avoid settlement or tension cracks. When the K value is less than 4, it means that the hazard is small and no treatment is required.

[0058] Compared with three-dimensional finite element calculation, this method uses the terrace hazard influence coefficient K as the prediction standard. It is simpler and more convenient. It can quickly predict the degree of damage of irregular terraces to dams and panels, provide guidance for design and subsequent construction, and take corresponding measures to reduce uneven settlement of the dam, improve the stress state of the dam body and concrete panels, prevent structural cracks in the dam and panels due to terrace terrain, and ensure the anti-seepage safety of the dam body.

[0059] In addition, the Yuanshan Dam in the United States is an earth-rock dam, with a valley dam height of 134m and a terrace dam height of 14m. Its terrace hazard impact coefficient K is 91.6, and cracks greater than 5m deep appeared on the dam crest; the Xinjiang LSG panel dam has a valley dam height of 100m. During the construction, a construction road with a width of 9m was excavated on the left bank of the dam foundation. The construction road is 30m higher than the dam crest, that is, the terrace dam height is 30m. Its terrace hazard impact coefficient K value is 11.1. After the construction is completed, cracks greater than 2cm appeared on the dam body corresponding to the outer edge of the road. Once again, the terrace hazard impact coefficient K can accurately predict the terrace hazard.

[0060] In order to reduce the damage caused by the platform, the following measures can be taken:

[0061] (1) Local terrain modification: The slopes within a certain range of the edge of the terrace can be cut and repaired to slow down the slope, and a low-compression mold-increasing area for the dam body can be set up on the slope between the terrace and the riverbed. Or the slope between the terrace and the riverbed can be filled with plain concrete to make the slope no steeper than 1:0.5, and transition materials can be used within the 3m slope range.

[0062] (2) Modify the order of dam filling: the dam body can be filled to the terrace elevation first, and then the terrace can be filled, and then the dam body; or the platform can be filled into a slope of 1:1.7 first, and then the filling can be evenly increased from the bottom of the riverbed to the top of the dam, etc.

[0063] (3) Carry out pre-settlement or forced pre-settlement. For example, fill the dam with water before pouring the concrete slab to simulate the flooding state of the dam during operation and accelerate the settlement of the dam body.

[0064] (4) Setting narrow panels and special seams: By setting narrow panels and special seams, the ability of the panels to adapt to deformation is enhanced and the harm of uneven settlement is reduced.

Claims

1. A method for predicting the hazards of irregular terraces to dams, characterized in that: The following steps are involved: Get the valley dam settlement S 谷 and the settlement of the terrace dam S 台 ; Calculate the influence coefficient K of the dam platform hazard on the irregular terrace: K=S 谷 S 台 Where: K—platform hazard impact coefficient; The degree of terrace hazard is predicted by the terrace hazard influence coefficient K. The larger the K value, the greater the deformation gradient and the greater the hazard to the dam body or panel. It is necessary to reduce the terrace hazard during the construction and design process.

2. The method for predicting the hazards of irregular terraces to dams according to claim 1, characterized in that: Estimated settlement of the valley dam S 谷 and the expected settlement of the terrace dam S 台 for: Where: H 谷 — height of river valley dams; H 台 — Height of terrace dam; E 谷 — deformation modulus of valley dams; E 台 —Deformation modulus of terrace dam; H1—height of the built dam; E1—deformation modulus of the built dam; S1—The settlement of the crest of the built dam.

3. The method for predicting the hazards of irregular terraces to dams according to claim 2, characterized in that: Since the terrace dam and the valley dam are the same project, the deformation modulus of the dam material is the same. K=(H 谷 H 台 ) 2 。 4. The method for predicting the hazards of irregular terraces to dams according to claim 1, characterized in that: When the K value is greater than or equal to 4, it means that the terrace is very harmful and needs to be treated during design and construction to avoid settlement or tension cracks. When the K value is less than 4, it means that the harm is small and no treatment is required.

5. The method for predicting the hazards of irregular terraces to dams according to claim 2, characterized in that: The height of the terrace dam is the height from the dam top to the terrace, and the height of the valley dam is the height from the dam top to the bottom of the valley.

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