CN102418349A - Burial depth positioning method of tunnel crossing river - Google Patents

Abstract

The present invention proposes a method for locating the buried depth of a tunnel crossing a river. First, the position where the maximum depth of the engineering section may occur is preliminarily determined, and then according to the scour-silting characteristics of the river section of the engineering, the corresponding relationship with the hydrological year, and the design standards of the engineering, From the perspective of engineering safety, determine the most unfavorable water and sand conditions for engineering safety. Finally, the planar two-dimensional water-sediment mathematical model and unfavorable water-sediment conditions are used to realize the accurate positioning of the maximum depth of the project, and to provide the time when the maximum depth occurs and the elevation of the deepest point.

Description

Buried Depth Locating Method for Tunnels Crossing the River

technical field

The invention relates to a buried depth positioning method of a river-crossing tunnel.

Background technique

In order to adapt to the rapid development of cities along the river (river) and alleviate the increasingly severe traffic pressure across the river, building cross-river tunnels has become a better engineering measure. When planning and designing a tunnel across the river, the maximum buried depth of the tunnel is one of the keys. If the burial depth is determined too small, although the investment can be reduced, once the river bed is scoured so that the covering soil layer on the project is smaller than the design standard or the project is exposed, the project operation safety will be seriously threatened; if the burial depth is determined too large, although the project safety It can be guaranteed, but it will increase project investment and construction difficulty. How to reasonably determine the maximum buried depth to ensure the safety of the project and minimize the investment is the key problem that must be solved in the planning and design of the tunnel project across the river.

The determination of the maximum buried depth is based on the maximum scouring depth of the riverbed at the location of the project. Generally speaking, the maximum scour of riverbed includes two types: local scour caused by engineering and natural scour of river. Since the tunnel is buried under the river bed, it does not interfere with the movement of water and sand in the river, so the erosion problem is mainly the second type of erosion. Due to the complexity of riverbed scour adjustment, there is no unified theoretical calculation formula for this type of riverbed scour. Existing studies have mostly used technical means such as physical models. On the basis of an in-depth understanding of the evolution characteristics of the engineering river section, combined with the geological conditions of the engineering location, the maximum scour depth of the river bed that may occur under certain water and sediment conditions has been studied, and achievements have been made. Relatively rich results have been achieved, but there are still problems in the following aspects: First, the determination of the conditions for scouring water and sand. The selection of the water-sediment process is the prerequisite for the study of the maximum sinking depth, and its correctness is directly related to the rationality of the research results. However, the selection of water-sediment conditions in existing studies has not fully considered the water-sediment transport characteristics of river sections, especially how to determine the water-sediment process of catastrophic floods that have the greatest impact on riverbed scour is still lacking in-depth research; the second is limited by measurement methods , the physical model cannot give the change process of the elevation of the deepest point of the project position with time, so it is also difficult to accurately give the maximum depth of the project position. In view of the above existing deficiencies, how to select more reasonable water and sediment conditions based on an in-depth understanding of the scour-silting characteristics of the project river section, and adopt appropriate simulation methods to accurately and efficiently determine the maximum scour depth of the project location is an urgent need to solve The problem.

Contents of the invention

The purpose of this invention is to provide a buried depth positioning method for cross-river tunnels in view of the existing conditions of the above-mentioned technologies, which can fully consider the erosion-silting characteristics of the engineering river section, and from the perspective of engineering safety, it is more convenient and efficient. Determine the maximum drawing depth and the swing range of the deepest point in the engineering position.

The technical solution of the present invention is a method for locating the buried depth of a tunnel crossing a river, comprising the following steps:

Step 1, the initial determination of the maximum depth position, the specific implementation includes the following steps,

Step 1.1, determine the height H and position of the deepest point of the section that have been observed by overlaying the section shape of the engineering position over the years and plotting the _lower envelope map of the section shape;

Step 1.2: Determine the thickness Δh1 of the flushable layer according to the geological conditions near the project, and preliminarily determine the height of the engineering section _according to the elevation H of the deepest point of the current engineering section and the elevation H of the deepest point of the section _given in step 1.1. Maximum sinking depth position and elevation change range [H _lower , H _when - Δh1];

Step 2, determining unfavorable water and sand conditions, the specific implementation includes the following steps,

Step 2.1, carry out the frequency analysis on the runoff of the river section over the years, according to the standard that the frequency is greater than 75% is the year of small water, 25% to 75% is the year of medium water, and the standard of less than 25% is the year of heavy water Typical water-sediment series years with different water-sediment combinations in medium and small waters;

In step 2.2, the engineering calibration flood is used as a typical catastrophic flood, and the hydro-sediment process corresponding to the engineering calibration flood is deduced from the hydro-sediment process in the catastrophic flood year according to the catastrophic flood year in which the scour of the river bed is known to be the largest;

In step 2.3, combine the typical flood and sediment series years obtained in step 2.1 with the typical severe floods obtained in step 2.2 to form the unfavorable water and sediment conditions that most affect the safety of the project;

Step 3, accurate positioning of the maximum drawing depth of the project position, the specific realization includes the following steps,

In step 3.1, according to the unfavorable water and sediment conditions determined in step 2, the planar two-dimensional water and sediment mathematical model is used to calculate the change process of the elevation of the deepest point of the project position with time, and the elevation value of the deepest point of the project section at each time is obtained, from which the occurrence of the maximum sinking depth is obtained. The time and the deepest point elevation;

Step 3.2, judging whether the elevation of the deepest point at the _{maximum depth obtained in step 3.1 is within the range of the maximum elevation elevation of the engineering section preliminarily determined in step 1.2 [H, H when -Δh1} ], if yes, then according to step 3.1 the maximum The time when the sinking depth occurs and the elevation of the deepest point are used to locate the buried depth.

Moreover, in step 2.2, the water and sediment process corresponding to the engineering verification flood includes the flow process and the sand volume process,

When determining the flow process corresponding to the engineering verification flood, it includes taking the flood process line of the catastrophic flood year, and using the same frequency amplification method to calculate the flow process corresponding to the engineering verification flood;

When determining the process of sand volume corresponding to engineering check flood, the following formula is used for calculation:

Q _s =aQ ^b

Among them, Q _s is the sediment transport rate, Q is the flow rate, and the coefficients a and b are determined by establishing the lower envelope of the relationship between the annual flow rate and the sediment transport rate; the sediment transport rate only includes the bed sand transport rate.

The present invention is based on the basic principles of river bed evolution and the basic theory of water and sediment transport, and on the basis of a deep understanding of the evolution of engineering river sections, especially the erosion and deposition characteristics of sections near the project, and proposes water and sediment conditions that can reflect the characteristics of water and sediment transport in river sections Using the mathematical model, the accurate positioning of the position of the maximum drawing depth of the engineering position can be realized, and the change process of the elevation of the deepest point of the engineering position with time and the swing range can be provided. The invention can be used not only in the river crossing tunnel, but also in the river crossing tunnel.

Description of drawings

Fig. 1 is the flowchart of the embodiment of the present invention;

Figure 2 is the shape of the engineering section and the lower envelope diagram;

Figure 3 is a typical geological histogram near the project;

Figure 4 is the process line of checking flood discharge and bed sand content;

Figure 5 is a correlation diagram between flow rate and bed sand transport rate;

Figure 6 shows the elevation change process of the deepest point of the engineering section;

Figure 7 is a diagram of the engineering section change at the maximum drawing depth.

Detailed ways

The technical solution of the present invention will be described in detail below in conjunction with the drawings and embodiments.

Referring to accompanying drawing 1, the embodiment of the present invention is proposed to be built in the river-crossing tunnel project of certain river section, in conjunction with hydrological data, topographical data, geological data, adopt the following steps to determine the maximum depth of the engineering position:

Step 1. Preliminary determination of the maximum sinking depth position. The specific implementation includes the following steps:

Step 1.1: Determine the height H and position of the deepest point of the section that has been observed by overlaying the section shape of the project position over the years and plotting the _lower envelope map of the section shape.

Embodiment By comparing and analyzing the cross-sectional shape diagrams of engineering positions over the years, and determining the lower envelope diagram of the engineering section according to the deepest points at different positions of the section, see accompanying drawing 2, the abscissa in the figure represents the distance from the left bank, and the ordinate is the elevation. The analysis results show that the overall cross-section shows alternating changes of erosion and siltation, and with the continuous reinforcement of the revetment works on both banks, the shape of the cross-section gradually tends to be stable. From the lower envelope of the engineering section, it can be seen that the elevation of the deepest point of the engineering section once reached _below H. This happened mainly before the revetment works were implemented on both sides of the bank, and the stability of the river regime was relatively poor. There will be relatively large erosion in the engineering section.

Step 1.2: Determine the thickness Δh1 of the flushable layer according to the geological conditions near the project, and preliminarily determine the height of the engineering section _according to the elevation H of the deepest point of the current engineering section and the elevation H of the deepest point of the section _given in step 1.1. Maximum depth position and elevation change range [ _Hdown , _Hdang -Δh1]. By preliminarily determining the position of the maximum sinking depth of the engineering section, it can be estimated that the maximum sinking depth may occur at that part of the riverbed.

It can be seen from accompanying drawing 3 that the geological conditions near the project in the embodiment, the riverbed can be divided into three layers, the first layer is silt with fine particle size, the layer thickness is Δh1, and the bottom elevation is h1 (h1<H _lower ) The second layer (layer thickness Δh2, layer bottom elevation h2) and the third layer (layer thickness Δh3, layer bottom elevation h3) below this elevation are composed of fine round gravel with very good anti-scourability and foundation rock. A schematic diagram of the rock formation section is provided in the figure for reference. Therefore, the flushable layer here is basically above the h1 elevation.

From the above analysis, it can be seen that although the river regime of the engineering section has been generally stable in recent years, and the elevation of the deepest point of the engineering section has not changed much, the riverbed has a flushable layer with a thickness of about Δh1. It is very likely that large-scale erosion will occur, and the elevation of the deepest point may reach _below H.

Step 2, determining unfavorable water and sand conditions, the specific implementation includes the following steps:

Step 2.1, carry out the frequency analysis on the runoff of the river section over the years, according to the standard that the frequency is greater than 75% is the year of small water, 25% to 75% is the year of medium water, and the standard of less than 25% is the year of heavy water Typical year of water-sediment series with different water-sediment combinations in medium and small water.

The general water and sediment series is to choose a typical series of years plus a severe flood year (such as design flood, check flood) as the calculation conditions for simulation. For the selection of the typical series of years, it can be seen from the above analysis of the erosion and deposition characteristics of the engineering sections for many years that the engineering sections have been eroded and silted alternately for many years, and there is no trend of unidirectional changes such as erosion or deposition. Therefore, the selection of embodiments includes large, medium, and Continuous flood and sediment years such as small water can be regarded as typical series of flood and sediment years.

In step 2.2, the engineering calibration flood is used as a typical catastrophic flood, and the hydro-sediment process corresponding to the engineering calibration flood is deduced from the hydro-sediment process in the catastrophic flood year according to the catastrophic flood year in which the scour of the river bed is known to be the largest;

Embodiments For the determination of the severe flood year, according to the design standard of the tunnel, from the perspective of engineering safety, the engineering check flood is selected as the typical flood process. During the specific implementation, it is possible to collect and organize the daily average flow data of the river section of the project for many years, and calculate the frequency of it, determine the years with large peak flow, and compare the magnitude of the river bed scour during the flood in these years to determine The year when the river bed scours is relatively large is regarded as the severe flood year.

Determine the flow process corresponding to the engineering check flood:

Use the same frequency amplification method that is widely used at present to amplify the flow process into the flow process corresponding to the calibration flood, see Figure 4. The existing hydrological observation data are generally short, at most about a hundred years, which cannot meet the design requirements for flood frequency. Therefore, when determining the flow process corresponding to a typical flood, it must be amplified according to the flood process that has occurred in the project river section. The same-frequency amplification method belongs to the prior art, for which reference can be made to Ye Shouze, Zhan Daojiang, Textbook for Colleges and Universities-Engineering Hydrology (Third Edition), Beijing: China Water Conservancy and Hydropower Press, 1987.

The process of determining the amount of sand corresponding to the engineering check flood:

According to the measured data, the boundary particle size D _boundary is determined according to the division method of bed sand and flushing quality, and the correlation relationship between flow rate and bed sand transport rate is plotted, as shown in Figure 5. Considering that the lower the sediment concentration at the same flow rate, the more significant the scouring effect of the river bed is, from the perspective of engineering safety, the lower envelope (power) of the flow-sediment rate relationship in Figure 5 is used as the basis for determining the sediment flow process.

In the process of calculating the amount of sediment, the following formula is used for calculation: Q _s = aQ ^b , where Q _s is the sediment transport rate, Q is the flow rate, and the coefficients a and b are determined by establishing the lower envelope of the relationship between the flow rate and the sediment transport rate for many years . When calculating the sediment transport rate, since the sediment involved in the deformation of the river bed is mainly bed sand, only the bed sand transport rate needs to be calculated. Firstly, according to the hydrology and riverbed composition data of the engineering river section, the sediment particle size of the riverbed sediment composition less than 5% to 10% can be used as the boundary particle size of the river bed sand and flushing sand to determine the bed sand quality. , and then by establishing the correlation between bed sand transport rate and flow rate, the process of sediment volume corresponding to typical floods can be deduced. The prior art generally adopts the particle size of less than 5% to 10% of the sediment as the boundary particle size, which will not be described in detail in the present invention.

The relational expression of flow rate and sediment transport rate in the embodiment is Q _s =7E-14Q ^2.81 . Accompanying drawing 4 is exactly the process line of bed sandy sediment concentration corresponding to the calibration flood calculated according to the enveloping line.

In step 2.3, combine the typical flood and sediment series years obtained in step 2.1 with the typical severe floods obtained in step 2.2 to form the unfavorable water and sediment conditions that most affect the safety of the project. That is, according to the results of the above steps, the embodiment determines that the unfavorable water and sediment conditions include large, medium and small water and other continuous flood and sediment years + calibration floods.

Step 3, accurate positioning of the maximum drawing depth of the engineering position, the specific realization includes the following steps:

In step 3.1, according to the unfavorable water and sediment conditions determined in step 2, the planar two-dimensional water and sediment mathematical model is used to calculate and analyze the change process of the elevation of the deepest point of the engineering position with time, and obtain the elevation value of the deepest point of the engineering section at each moment, from which the maximum sinking depth is obtained The time of emergence and the elevation of the deepest point.

The two-dimensional water-sediment mathematical model of the plane is an existing technology. For specific implementation, please refer to: Li Yitian, Zhao Mingdeng, Cao Zhifang, Two-dimensional water-sediment mathematical model of the river course, Beijing: China Water Conservancy and Hydropower Press, 2001. The embodiment adopts the plane two-dimensional water-sediment mathematical model and the above-mentioned water-sediment conditions, and when calculating the maximum sinking depth of the project location, the terrain at the current moment is selected as the starting terrain for model calculation. The elevation of the deepest point of the section calculated by the model varies with time in Figure 6, and the profile of the section at the maximum depth and at the beginning of calculation is shown in Figure 7.

It can be seen that the maximum washout depth of the section generally appears at the end of the flood period, and the elevation of the deepest point of the receding water gradually returns to siltation after the flood, while the maximum washout depth of the engineering section by the check flood occurs under the check flood condition, and the elevation of the deepest point is h _max (h _max > _H ), the thickness relative to the initial terrain scour is Δh _max (Δh _max <Δh1).

Step 3.2, judging whether the elevation of the deepest point at the maximum depth obtained in step 3.1 is _{within the range of the maximum elevation elevation of the engineering section preliminarily determined in step 1.2 [H, H when -Δh1} ], if yes, then according to step 3.1 the maximum The time when the sinking depth occurs and the elevation of the deepest point are used to locate the buried depth. The rationality of the calculation and analysis results can be checked by corroborating the calculation results in step 3.1 with the preliminary determination results in step 1.2. If there is a discrepancy in rare cases, you can adjust the parameters of the two-dimensional water-sediment mathematical model, and return to step 3.1 to recalculate until a consistent result appears, and the elevation of the deepest point at the maximum depth calculated by the model is within the predicted range . The specific adjustments can be realized by those skilled in the art, and the references are described in detail.

The various conditions used in this method are all based on the most unfavorable angle to the engineering safety, and the results calculated by the model are also consistent with the characteristics of the actual phenomenon, which shows that the determined maximum depth is reasonable and is very important for the project. If it is relatively safe, it can provide a scientific basis for the rational burial of the tunnel across the river.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention belongs can make various modifications or supplements to the described specific embodiments or adopt similar methods to replace them, but they will not deviate from the spirit of the present invention or go beyond the definition of the appended claims range.

Claims (2)

1. A buried depth positioning method for crossing a river tunnel, is characterized in that, comprises the following steps: Step 1, the initial determination of the maximum depth position, the specific implementation includes the following steps, Step 1.1, determine the observed elevation of the deepest point of the section by overlaying the cross-sectional shape of the engineering position over the years and plotting the envelop map of the cross-sectional shape

and location; Step 1.2, according to the geological conditions near the project, determine the thickness of the flushable layer

, and according to the elevation of the deepest point of the current engineering section

and the elevation of the deepest point of the section given in step 1.1

and position, and preliminarily determine the maximum depth position and elevation variation range of the engineering section[ ,

]; Step 2, determining unfavorable water and sand conditions, the specific implementation includes the following steps, Step 2.1, carry out the frequency analysis on the runoff of the river section over the years, according to the standards that the frequency is greater than 75% is the year of small water, 25%~75% is the year of medium water, and the standard of less than 25% is the year of heavy water Typical water-sediment series years with different water-sediment combinations in medium and small waters; In step 2.2, the engineering calibration flood is used as a typical catastrophic flood, and the hydro-sediment process corresponding to the engineering calibration flood is deduced from the hydro-sediment process in the catastrophic flood year according to the catastrophic flood year in which the scour of the river bed is known to be the largest; In step 2.3, combine the typical flood and sediment series years obtained in step 2.1 with the typical severe floods obtained in step 2.2 to form the unfavorable water and sediment conditions that most affect the safety of the project; Step 3, accurate positioning of the maximum drawing depth of the project position, the specific realization includes the following steps, In step 3.1, according to the unfavorable water and sediment conditions determined in step 2, the planar two-dimensional water and sediment mathematical model is used to calculate the change process of the elevation of the deepest point of the project position with time, and the elevation value of the deepest point of the project section at each time is obtained, from which the occurrence of the maximum sinking depth is obtained. The time and the deepest point elevation; Step 3.2, judging whether the elevation of the deepest point at the maximum depth obtained in step 3.1 is within the variation range of the maximum depth elevation of the engineering section preliminarily determined in step 1.2[ , ], if yes, locate the buried depth according to the time when the maximum sinking depth appears in step 3.1 and the elevation of the deepest point. 2. The method for locating the buried depth of the tunnel crossing the river as claimed in claim 1, characterized in that: in step 2.2, the water and sediment process corresponding to the engineering check flood includes a flow process and a sand volume process, When determining the flow process corresponding to the engineering verification flood, it includes taking the flood process line of the catastrophic flood year, and using the same frequency amplification method to calculate the flow process corresponding to the engineering verification flood; When determining the process of sand volume corresponding to engineering check flood, the following formula is used for calculation:

in is the sand transport rate,

For discharge, the coefficients a and b are determined by establishing the lower envelope of the relationship between annual discharge and sediment transport rate; the sediment transport rate only includes bed sand transport rate.

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