Method for analyzing and calculating pre-added anchoring force of underground powerhouse grotto

Abstract

The invention discloses an analysis and calculation method for pre-added anchoring force of an underground powerhouse cavern, and belongs to the technical field of underground engineering construction. The method comprises the following steps: step 1, calculating a geological condition score Sc; 2, calculating the total gross space volume V of the main cavern of the underground powerhouse; 3, selecting unit space anchoring force F according to the geological condition score Sc and the total gross space volume V of the main cavern of the underground powerhouse; and 4, calculating the pre-added anchoring force F anchor of the underground powerhouse cavern, wherein F anchor = V.F. Four parameters including the geological condition score Sc, the total gross space volume V of the underground powerhouse main cavern, the unit space anchoring force F and the underground powerhouse cavern pre-added anchoring force F anchor are defined, a calculation method or a value taking mode of the four parameters is given, the anchoring supporting strength of the underground powerhouse cavern system is conveniently and reasonably determined, the surrounding rock stability condition is accurately predicted, and the underground powerhouse cavern system anchoring supporting strength is improved. The method is of great significance in ensuring safe and effective excavation and support of the large underground powerhouse, reducing the construction cost and the like.

Description

Technical Field

[0001] This invention relates to a method for analyzing and calculating the pre-anchoring force of underground powerhouse caverns, belonging to the field of underground engineering construction technology. Background Technology

[0002] The support design method for underground powerhouse caverns primarily relies on engineering analogy, supplemented by numerical analysis and model testing. For the past two decades, flexible support has been the dominant approach for underground powerhouse cavern support in my country. Technical methods mainly include one or more combinations of reinforced concrete mesh, anchor bolts or steel arches, and prestressed anchor cables. However, given the large scale and prevalent high sidewalls in Chinese underground powerhouses, many projects utilize prestressed anchor cables in addition to systematic anchor bolts. Prestressed anchor cables provide significant support for underground powerhouses with large relaxation ranges, deep depths, poor rock conditions, and high sidewalls. Underground powerhouses with favorable geological conditions do not require prestressed anchoring measures, while those with poor geological conditions necessitate the application of numerous prestressed anchor cables.

[0003] Currently, there is no unified indicator in the industry to measure the strength of anchorage support in underground powerhouse cavern systems. There is only a consensus on the use of prestressed anchor cables, but a reasonable range for their quantity is lacking. Most large-scale hydropower stations in China have deployed a large number of prestressed anchor cables in their underground powerhouses, especially those with poor geological conditions requiring large-scale prestressed anchorage measures. However, some underground projects still experience significant deformation and cracking of the surrounding rock. Due to a lack of definitive experience, and limitations imposed by finite element analysis on geological condition simulation, parameter selection, and verification with existing engineering experience, the stability of the surrounding rock often cannot be accurately predicted.

[0004] There are still a large number of underground powerhouses under construction or planned in China. Rationally determining the anchoring support strength of the underground powerhouse cavern system and accurately predicting the stability of the surrounding rock are of great significance for ensuring the safe and effective excavation and support of large underground powerhouses and reducing construction costs. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a method for analyzing and calculating the pre-anchoring force of underground powerhouse caverns.

[0006] This invention is achieved through the following technical solution:

[0007] A method for analyzing and calculating the pre-anchoring force of underground powerhouse caverns includes the following steps:

[0008] Step 1: Calculate the geological condition score S c ;

[0009] Step 2: Calculate the total gross space volume V of the main caverns in the underground powerhouse;

[0010] Step 3: Score based on geological conditions (S) c The total gross space volume V of the main underground chambers is used to select the unit space anchoring force F;

[0011] Step 4: Calculate the pre-anchoring force F of the underground powerhouse cavern. 锚 F 锚 =V·F.

[0012] In step one, the geological condition score S c The calculation method is as follows:

[0013]

[0014] S = R b / σ max (2),

[0015] In the formula, D is the weighted average value of the burial depth range of the main caverns of the underground powerhouse, in meters; G is the engineering surrounding rock grade score; S is the surrounding rock strength-stress ratio; and R... b σ is the uniaxial saturated compressive strength of the rock. max This represents the maximum principal stress of the surrounding rock.

[0016] The main caverns of the underground powerhouse include the main powerhouse cavern, the main transformer cavern, and the tailrace surge chamber cavern.

[0017] D is the weighted average of the horizontal and vertical burial depth ranges of the main caverns of the underground powerhouse.

[0018] The value of the surrounding rock grade score G is selected based on the surrounding rock category, the total surrounding rock score T, and the surrounding rock strength-stress ratio S.

[0019] The formula for calculating the total gross space volume V of the main caverns in the underground powerhouse in step two is as follows:

[0020] V=ΣL·B·H (3),

[0021] In the formula, L is the maximum excavation length of the cavern, B is the maximum excavation span of the cavern, and H is the maximum excavation height of the cavern.

[0022] According to the pre-anchoring force F of the underground powerhouse cavern in step four... 锚 Calculate the number N of prestressed anchor cables.

[0023]

[0024] In the formula, f is the average anchoring force of a single prestressed anchor cable.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. A geological condition score S was defined. cThe total gross space volume V of the main underground powerhouse caverns, the anchoring force F per unit space, and the pre-anchoring force F of the underground powerhouse caverns. 锚 The four parameters are provided, along with their calculation methods or values, which facilitates the reasonable determination of the anchorage support strength of the underground powerhouse cavern system and the accurate prediction of the surrounding rock stability. This is of great significance for ensuring the safe and effective excavation and support of large underground powerhouses and reducing construction costs.

[0027] 2. At the same time, a calculation method for the number N of prestressed anchor cables is given, which can effectively narrow the range of choices for the number of prestressed anchor cables and scientifically and rationally determine the anchoring force level of the underground powerhouse that is compatible with geological conditions and scale. This plays an important role in the rapid design of underground powerhouses in the early stage and the verification of results in the later stage. Attached Figure Description

[0028] Figure 1 This is a statistical chart showing the anchorage force per unit space in the main caverns of the underground powerhouse. Detailed Implementation

[0029] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0030] Example 1:

[0031] The present invention provides a method for analyzing and calculating the pre-anchoring force of underground powerhouse caverns, comprising the following steps:

[0032] Step 1: Calculate the geological condition score S c ;

[0033] Step 2: Calculate the total gross space volume V of the main caverns in the underground powerhouse;

[0034] Step 3: Score based on geological conditions (S) c The total gross space volume V of the main underground chambers is used to select the unit space anchoring force F;

[0035] Step 4: Calculate the pre-anchoring force F of the underground powerhouse cavern. 锚 F 锚 =V·F.

[0036] A pre-anchoring force F for underground powerhouse caverns is provided. 锚 The calculation method facilitates the reasonable determination of the anchorage support strength of the underground powerhouse cavern system and the accurate prediction of the surrounding rock stability, which is of great significance for ensuring the safe and effective excavation and support of large underground powerhouses and reducing construction costs.

[0037] In step one, the geological condition score S c The calculation method is as follows:

[0038]

[0039] S = R b / σ max (2),

[0040] In the formula, D is the weighted average value of the burial depth range of the main caverns of the underground powerhouse, in meters; G is the engineering surrounding rock grade score; S is the surrounding rock strength-stress ratio; and R... b σ is the uniaxial saturated compressive strength of the rock. max This represents the maximum principal stress of the surrounding rock. During use, geological data such as the main surrounding rock type, horizontal and vertical burial depths, and surrounding rock strength stress of the main caverns of the underground powerhouse are collected to facilitate the calculation of the geological condition score S. c The surrounding rock strength-stress ratio S represents the average ground stress level at the location of the underground powerhouse, and is taken as a weighted average based on the range. When different grades of surrounding rock are present, the engineering surrounding rock grade score G is taken as a weighted average, and the engineering surrounding rock grade score G for a single grade of surrounding rock is selected according to Table 1.

[0041] Table 1. Scoring of Surrounding Rock Grade G in Engineering Projects

[0042]

[0043]

[0044] The main caverns of the underground powerhouse include the main powerhouse cavern, the main transformer cavern, and the tailrace surge chamber cavern.

[0045] D is the weighted average of the horizontal and vertical burial depth ranges of the main caverns of the underground powerhouse.

[0046] The value of the surrounding rock grade score G is selected based on the surrounding rock category, the total surrounding rock score T, and the surrounding rock strength-stress ratio S.

[0047] The formula for calculating the total gross space volume V of the main caverns in the underground powerhouse in step two is as follows:

[0048] V=∑L·B·H (3),

[0049] In the formula, L is the maximum excavation length of the cavern, B is the maximum excavation span of the cavern, and H is the maximum excavation height of the cavern.

[0050] In step three, the geological conditions are scored as S. c The total gross space volume V of the main underground chambers is used to select the unit space anchoring force F according to Table 2.

[0051] Table 2. Range of Anchoring Force F per Unit Space (kN / m) 3 )

[0052]

[0053] According to the pre-anchoring force F of the underground powerhouse cavern in step four... 锚 Calculate the number N of prestressed anchor cables.

[0054]

[0055] In the formula, f is the average anchoring force of a single prestressed anchor cable.

[0056] like Figure 1 As shown in the figure, based on the analytical calculation method provided by this invention, a statistical analysis was conducted on the unit space anchoring force F and the total gross space volume V of the main caverns in a large number of underground powerhouses in hydropower stations both domestically and internationally. It can be seen from the figure that for underground powerhouses with very good geological conditions (shallow burial depth, relatively good geological conditions, and low ground stress) and a relatively small scale (small to medium-sized underground cavern groups), the unit space anchoring force F is less than 2 kN / m. 3 For underground powerhouses with favorable geological conditions, the anchoring force F per unit space is generally around 2 kN / m. 3 ~4kN / m 3 Between; for geological conditions with poor conditions (great burial depth, fractured surrounding rock, high ground stress) and large scale (large and giant underground cavern groups), the unit space anchoring force F is greater than 4kN / m. 3 The largest even exceeds 10 kN / m 3 It is evident that the anchoring force F per unit space is significantly correlated with the geological conditions and scale of the underground cavern complex.

[0057] Example 2:

[0058] Taking the foundation data of the underground cavern of a large hydropower station in the Dadu River Basin as an example, the support scheme of the underground powerhouse cavern is calculated using the pre-anchoring force analysis and calculation method provided by this invention. The scheme is then verified by combining actual engineering data with the scheme provided by this invention.

[0059] The main surrounding rock category of the underground powerhouse is Class III, with a horizontal burial depth of 280m–510m and a vertical burial depth of 400m–660m. The stress ratio S of the surrounding rock is 3.59. The underground cavern complex consists of three parallel caverns: the main powerhouse cavern measures 224.4m × 29.7m × 74.43m (length × width × height), the main transformer cavern measures 141.1m × 18.8m × 25.2m (length × width × height), and the tailrace surge chamber cavern measures 135m × 23.5m × 73.98m (length × width × height).

[0060] Based on the basic information of the underground cavern, its geological condition score S is calculated. c The four parameters are: the total gross space volume V of the main caverns of the underground powerhouse, the anchoring force F per unit space, and the number of prestressed anchor cables N.

[0061] Step 1: Calculate the geological condition score S c

[0062] Given that the horizontal burial depth of the main underground chamber of the hydropower station is 280m to 510m and the vertical burial depth is 400m to 660m, calculate the weighted average value of the burial depth range of the main underground chamber of the power station, D = 0.25 × (280 + 510 + 400 + 660) = 462.5m.

[0063] It is known that the main surrounding rock category of the underground cavern of the hydropower station is Class III, and its total surrounding rock score T is greater than 55 (65 ≥ 55). Therefore, according to Table 1, the value of the engineering surrounding rock grade score G is selected as 6.

[0064] Given that the strength-stress ratio S of the surrounding rock is 3.59, calculate the geological condition score S. c as follows:

[0065]

[0066] Step 2: Calculate the total gross space volume V of the main caverns in the underground powerhouse.

[0067] The main powerhouse tunnel of the underground powerhouse of the hydropower station measures 224.4m × 29.7m × 74.43m (length × width × height), the main transformer tunnel measures 141.1m × 18.8m × 25.2m (length × width × height), and the tailrace surge chamber tunnel measures 135m × 23.5m × 73.98m (length × width × height).

[0068] The total gross space volume V of the main chambers of the underground powerhouse is calculated as follows:

[0069] V = ∑L·B·H = 224.4 × 29.7 × 74.43 + 141.1 × 18.8 × 25.2 + 135 × 23.5 × 73.98 = 798,000 m³ 3 <1 million m 3 .

[0070] Step 3, Anchoring force F per unit space

[0071] Based on geological conditions, score S c The total gross space volume V of the main underground chambers is calculated from Table 2, where the unit space anchoring force F is 4 kN / m. 3 ~7kN / m 3 .

[0072] Based on the geological features revealed during the actual excavation and the analysis of the ground stress test results, the anchoring force F per unit space should be taken as the smaller value within the specified range, i.e., the value range of F is 4 kN / m. 3 ~5kN / m 3 .

[0073] Step 4. Calculate the pre-anchoring force F of the underground powerhouse cavern 锚

[0074] F 锚 = V·F = 79.8×10 4 ×(4 - 5) = 3192000 kN - 3990000 kN.

[0075] Step 5. Calculate the number of prestressed anchor cables N

[0076] The average anchoring force f of prestressed anchor cables commonly used in the project is 3000 kN, 2000 kN, and 1000 kN. In this embodiment, f = 2000 kN is taken for calculation. Then the number of prestressed anchor cables N is calculated as follows:

[0077]

[0078] Step 6. Verify the analysis and calculation method

[0079] The actual support design plan of this hydropower station is to use 76 prestressed anchor cables of 3000 kN, 875 prestressed anchor cables of 2500 kN, 596 prestressed anchor cables of 2000 kN, and 50 prestressed anchor cables of 600 kN. Calculate the pre-anchoring force F of its underground powerhouse cavern 锚 ,

[0080] F 锚 = 3000 kN×76 + 2500 kN×875 + 2000 kN×596 + 600 kN×50 = 3637500 kN, 3192000 kN <3637500> kN <3990000> kN,

[0081] It can be seen that the actual pre-anchoring force of the underground powerhouse cavern of this hydropower station is 3637500 kN, which is between the values of 3192000 kN and 3990000 kN of the pre-anchoring force F of the underground powerhouse cavern calculated by the method provided by the present invention, indicating that the analysis and calculation method of the pre-anchoring force of the underground powerhouse cavern provided by the present invention is reasonable. 锚 ​

Claims

1. A method for analyzing and calculating the pre-anchoring force of an underground powerhouse cavern, characterized in that: The following steps are involved: Step 1: Calculate the geological condition score S c ; Step 2: Calculate the total gross space volume V of the main chambers of the underground powerhouse; Step 3: Score S based on geological conditions c and the total gross space volume V of the main chamber of the underground powerhouse, and select the unit space anchorage force F; Step 4: Calculate the pre-anchoring force F of the underground powerhouse cavern 锚 , F 锚 =V·F.

2. The method for analyzing and calculating the pre-anchoring force of an underground powerhouse cavern according to claim 1, characterized in that: The geological condition score S in step 1 c The calculation method is as follows: S=R b / s max (2), Where D is the weighted average of the depth range of the main chambers of the underground powerhouse, in meters, G is the grade of the surrounding rock, S is the strength stress ratio of the surrounding rock, and R is b is the uniaxial saturated compressive strength of rock, σ max is the maximum principal stress of surrounding rock.

3. The method for analyzing and calculating the pre-anchoring force of underground powerhouse caverns according to claim 1 or 2, characterized in that: The main caverns of the underground powerhouse include the main powerhouse cavern, the main transformer cavern and the tailwater surge chamber cavern.

4. The method for analyzing and calculating the pre-anchoring force of an underground powerhouse cavern according to claim 2, characterized in that: The D is the weighted average of the horizontal burial depth range and the vertical burial depth range of the main chambers of the underground powerhouse.

5. The method for analyzing and calculating the pre-anchoring force of underground powerhouse caverns according to claim 2 is characterized in that: The value of the engineering surrounding rock grade score G is selected according to the surrounding rock type, the total surrounding rock score T and the surrounding rock strength stress ratio S.

6. The method for analyzing and calculating the pre-anchoring force of underground powerhouse caverns according to claim 1, characterized in that: The calculation formula for the total gross space volume V of the main chamber of the underground powerhouse in step 2 is as follows: V=∑L·B·H (3), Where L is the maximum excavation length of the cavern, B is the maximum excavation span of the cavern, and H is the maximum excavation height of the cavern.

7. The method for analyzing and calculating the pre-anchoring force of an underground powerhouse cavern according to claim 1, characterized in that: According to the pre-anchoring force F of the underground powerhouse cavern in step 4 锚 , calculate the number of prestressed anchor cables N, Where f is the average anchoring force of a single prestressed anchor cable.

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