Method for determining karst stability of high-speed railway

Abstract

The invention discloses a comprehensive evaluation method for determining the karst stability of a high-speed railway, and the method achieves the precise classification of the karst stability through quantifying seven indexes in a hydrodynamic condition, karst roof features and karst cave features, and combining a weight coefficient to calculate a comprehensive evaluation score. The method solves the problems of high subjectivity, incomplete indexes and the like in the prior art, has the advantages of high objectivity and high operability, and is suitable for design, construction and safety evaluation of high-speed rail engineering.

Description

Technical Field

[0001] This patent relates to a method for determining the karst stability of high-speed railways, specifically a comprehensive stability assessment method that considers multiple indicators that affect karst stability. Background Art

[0002] By 2023, 2,000 km of completed high-speed railway lines in my country will traverse areas prone to karst collapse, and 1,800 km of high-speed railway lines planned for construction in the medium and long term will also be located in areas prone to karst collapse. Due to the constraints of line and station location, high-speed railways inevitably traverse soluble rock areas with well-developed karst. Assessing karst stability is a prerequisite for the design and construction of high-speed railways in karst areas and is crucial for ensuring their smooth and safe operation.

[0003] Karst stability is affected by many factors, including hydrodynamic conditions, karst roof characteristics, karst cave characteristics, etc. Karst stability evaluation must fully consider the influence of various factors. However, existing evaluation methods have the following defects:

[0004] (1) Some evaluation methods are based on the experience of construction workers, which are highly subjective, lack a basis for the selection of evaluation indicators, and are seriously affected by human factors;

[0005] (2) The factors affecting karst stability are not fully considered. For example, the current railway industry standard "Regulations on Unfavorable Geological Survey for Railway Engineering" does not take into account the development of rock cracks around karst and the filling of caves, resulting in inaccurate karst stability evaluation.

[0006] Therefore, it is urgent to propose a more comprehensive and objective high-speed railway karst stability evaluation method to improve the accuracy and credibility of karst stability evaluation. Summary of the Invention

[0007] The present invention proposes a comprehensive assessment method for the karst stability of high-speed railways based on multi-index weight analysis. By quantifying seven indicators in three categories, namely hydrodynamic conditions, karst roof characteristics and cave characteristics, and combining weight coefficients to calculate a comprehensive assessment score, accurate judgment of karst stability can be achieved.

[0008] To achieve the above object, the present invention provides a method for determining the karst stability of a high-speed railway, comprising the following steps:

[0009] S1, seven evaluation indicators were selected from the hydrodynamic conditions, karst roof characteristics and karst cave characteristics, including groundwater level changes, cover layer thickness, fracture development and filling conditions, saturated uniaxial compressive strength of rock, rock integrity index, cave development degree and cave filling conditions;

[0010] S2, score each indicator according to the preset grading standard and obtain the indicator score S i ;

[0011] S3, the score of each indicator S i and the corresponding weight coefficient γ i Multiply and add to calculate the comprehensive evaluation score C = ∑S i γ i

[0012] S4. The karst stability level is divided into stable, relatively stable, relatively unstable, unstable or extremely unstable levels according to the assessment score C.

[0013] Furthermore, the weight coefficient γ i The weight distribution of each indicator is determined by the hierarchical analysis method as follows: Groundwater level change γ i 0.2~0.3; Covering layer thickness γ i is 0.01~0.02; the crack development and filling condition γi is 0.1~0.2; the saturated uniaxial compressive strength of rock γ i 0.05~0.20; rock integrity index γ i 0.1~0.2; the degree of cave development γ i 0.2~0.3; cave filling condition γ i It is 0.05-0.07.

[0014] Furthermore, the scoring criteria for the groundwater level change index are:

[0015] The groundwater level fluctuates near the soil-rock interface and the amplitude is ≥ 1 / 3 of the cover layer thickness, S i The score is 75-100;

[0016] The groundwater level fluctuates near the soil-rock interface and the amplitude is less than 1 / 3 of the cover layer thickness, S i The score is 50-74;

[0017] The groundwater level fluctuates in the overburden or bedrock with an amplitude ≤ the average interface height, S i The score is 25-49;

[0018] The groundwater level is stable and far away from the soil-rock interface, S i The score is 0-24.

[0019] Groundwater level fluctuation is one of the core external factors that induce karst collapse. Its fluctuation near the soil-rock interface will intensify the erosion and transportation of water on the cover layer, directly affecting the stability of the karst system. By dividing the water level into four levels of "≥1 / 3 cover layer thickness", "<1 / 3 cover layer thickness", "≤average interface height", and "stable and far away", the amplitude of water level fluctuation is directly linked to the degree of disaster risk. In accordance with the principles of karst hydraulics, the grades are divided from two dimensions: "fluctuation position" (soil-rock interface / non-interface) and "fluctuation amplitude" (absolute value / relative proportion), avoiding the one-sidedness of a single indicator. At the same time, the fluctuation amplitude is measured based on the "cover layer thickness", so that the scoring standard can be dynamically adjusted with the thickness of the cover layer in different sections, covering multiple states of water level such as "stable", "fluctuating", "near the interface", and "non-interface", which is suitable for karst hydrodynamic evaluation of different landform types such as plains and hilly areas.

[0020] Furthermore, the scoring criteria for the coating thickness index are:

[0021] The covering layer is soil and its thickness is less than 10m, S i The score is 75-100;

[0022] The covering layer is soil with a thickness of 10-30m, S i The score is 50-74;

[0023] The covering layer is soil and the thickness is greater than 30m, S i The score is 25-49;

[0024] The cover layer is non-soluble rock, S i The score is 0-24.

[0025] When the overburden is soil, its thickness directly affects the stress transfer and collapse risk of the karst roof. Thin overburden (less than 10m): The soil has poor self-stabilization capacity, and the karst roof is prone to collapse due to load concentration or hydrodynamic effects. Thick overburden (greater than 30m): The soil can disperse roof stress, forming a natural buffer layer. Non-soluble rock overburden: The rock mass has high strength and low permeability, essentially eliminating the risk of soil erosion. The nonlinear relationship between overburden thickness and collapse risk is converted into a quantitative score, covering common geological scenarios for high-speed railways (such as thin overburden in karst plains and thick overburden in karst valleys). This allows for refined risk grading, distinguishing between soluble and non-soluble rock formations, avoiding the misclassification of hard rock overburdens such as sandstone and shale as high-risk, and improving the targeted nature of assessments.

[0026] Furthermore, the scoring criteria for the fissure development and filling indicators are:

[0027] The cracks are extremely developed and not filled, S i The score is 75-100;

[0028] Fissures are well developed and a few are filled, Si The score is 50-74;

[0029] Cracks are developed but most of them are cemented and filled. i The score is 25-49;

[0030] The cracks are not developed or the cementation is good, S i The score is 0-24.

[0031] The presence of highly developed but unfilled fractures creates a fragmented rock mass, leading to strong groundwater permeability and the formation of concentrated seepage channels, which directly triggers corrosion expansion and roof instability, resulting in an extremely high risk. The presence of developed fractures but mostly cemented fills, with the fracture network filled with cements such as calcareous and siliceous materials, blocks seepage channels and significantly reduces the risk. The absence of fractures or good cementation creates high rock integrity, making it difficult for hydrodynamic forces to penetrate, resulting in an extremely low risk. Converting the causal relationship of "fracture connectivity - filling density - seepage capacity" into a score gradient aligns with the destructive logic of "fracture water conduction - corrosion expansion - structural instability" in karst areas.

[0032] Furthermore, the scoring criteria for the rock saturated uniaxial compressive strength index are:

[0033] Saturated uniaxial compressive strength of rock <30MPa, S i The score is 75-100;

[0034] Saturated uniaxial compressive strength of rock 30-60MPa, S i The score is 50-74;

[0035] Saturated uniaxial compressive strength of rock 60-100MPa, S i The score is 25-49;

[0036] Saturated uniaxial compressive strength of rock>100MPa, S i The score is 0-24.

[0037] The saturated uniaxial compressive strength of rock directly reflects its ability to resist compression failure. Lower strength (e.g., soft rock <30 MPa) increases the susceptibility of the karst roof to cracking and collapse due to stress concentration, with a score of 75-100 indicating a very high risk. Higher strength (e.g., hard rock >100 MPa) indicates a greater self-stabilization capacity of the rock mass, with a score of 0-24 corresponding to a very low risk. The use of "saturated uniaxial compressive strength" rather than natural strength emphasizes the deteriorating effects of groundwater on rock mass strength.

[0038] Furthermore, the scoring criteria for the rock integrity index are:

[0039] Rock integrity index <0.35, S i The score is 75-100;

[0040] Rock integrity index 0.35-0.55, S i The score is 50-74;

[0041] Rock integrity index 0.55-0.75, S i The score is 25-49;

[0042] Rock integrity index>0.75, S i The score is 0-24.

[0043] The Rock Integrity Index (RI) is an internationally recognized indicator for evaluating rock mass integrity. This standard directly adopts the critical values ​​from the Engineering Rock Mass Classification Standard (GB / T 50218). A RI of less than 0.35 corresponds to a fragmented structure with dense, interconnected fractures, and a score of 75-100 indicates extremely high risk. A RI of 0.35-0.55 indicates a massive, fragmented structure with moderate to low integrity, with a score of 50-74. A RI of 0.55-0.75 indicates a massive structure with good integrity, with a score of 25-49. A RI of greater than 0.75 indicates a monolithic structure with excellent integrity, with a score of 0-24. These thresholds are fully synchronized with engineering practice to ensure the authority and comparability of the evaluation results.

[0044] Furthermore, the scoring criteria for the cave development index are:

[0045] The development degree of karst caves is strong, S i The score is 75-100;

[0046] The development degree of karst caves is moderate. i The score is 50-74;

[0047] The development degree of karst cave is weak. i The score is 25-49;

[0048] The development degree of karst cave is weak. i The score is 0-24.

[0049] The degree of cave development directly determines the complexity of karst spatial morphology and the risk of roof instability: Strong development (75-100 points): cave density > 5 / km 2 , single-layer height > 5m, multiple layers superimposed, the rock mass is "honeycomb-shaped", which directly threatens the safety of the high-speed rail line; weak development (0-24 points): occasional small solution pores (diameter <1m), no penetration, and the impact on stability can be ignored.

[0050] Furthermore, the scoring criteria for the cave filling condition index are:

[0051] The cave filling condition is unfilled, S iThe score is 70-100;

[0052] The cave filling condition is half-filled, S i The score range is 35-69;

[0053] The cave filling condition is full filling, S i The score is 0-34.

[0054] The filling state of the cave directly affects the stress pattern and hydrodynamic conductivity of the roof: unfilled (70-100 points), the empty cave forms a stress concentration area, and the groundwater can flow freely, exacerbating dissolution, corresponding to an extremely high risk of instability; semi-filled (35-69 points), there is a contact interface between the filling body and the cave wall, which may become a seepage channel or sliding surface, and the risk is medium; fully filled (0-34 points), the filling body (such as clay, sand and gravel) can share the roof load, block the water flow, and the risk is significantly reduced.

[0055] Furthermore, the stability levels are divided into:

[0056] When C ≥ 60, it is extremely unstable;

[0057] When 45≤C<60, it is unstable;

[0058] When 30≤C<45, it is relatively unstable;

[0059] When 15≤C<30, it is relatively stable;

[0060] When C is less than 15, it is stable.

[0061] Beneficial effects of the present invention

[0062] Seven evaluation indicators are subdivided from three aspects: hydrodynamic conditions, karst roof characteristics, and karst cave characteristics. Karst stability is evaluated together with external factors, internal factors, and developmental characteristics of karst collapse. Each evaluation indicator is assigned a different weight coefficient according to the degree of influence on karst stability, which improves the refinement of karst stability evaluation. This patent includes a karst stability evaluation score sheet, an evaluation score calculation method, a correspondence between karst stability and evaluation scores, and an evaluation flow chart. The method of determining the karst stability of high-speed railways in the present invention can solve the problems of poor objectivity of existing evaluation methods and incomplete selection of evaluation indicators. The evaluation method is highly operational and combines external factors, internal factors, and developmental characteristics of karst collapse to evaluate karst stability, achieving high accuracy in karst stability evaluation and high credibility of the results. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is an evaluation flow chart of the present invention. DETAILED DESCRIPTION

[0064] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0065] It will be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections.

[0066] To simplify the drawings, only the parts relevant to the present invention are schematically shown in each figure. They do not represent the actual structure of the product. Furthermore, to simplify the drawings and facilitate understanding, in some figures, only one of the components with the same structure or function is schematically depicted or labeled. As used herein, "one" not only means "only one" but also "more than one."

[0067] It should be further understood that the term "and / or" used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0068] In the embodiments shown in the accompanying drawings, directional indications (such as up, down, left, right, front, and rear) used to explain the structure and movement of various components of the present invention are not absolute but relative. These descriptions are applicable when the components are in the positions shown in the accompanying drawings. If the descriptions of the positions of these components are changed, the directional indications will also change accordingly.

[0069] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0070] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive work.

[0071] Figure 1 This is the method for determining the karst stability of high-speed railways in this embodiment. This method can achieve the effect of accurate evaluation of karst stability and high credibility of the results.

[0072] 1. Construction of evaluation index system

[0073] From the perspectives of hydrodynamic conditions, karst roof characteristics, and karst cave characteristics, the evaluation of karst stability is subdivided into seven specific evaluation indicators: groundwater level changes, cover layer thickness, crack development and filling conditions, saturated uniaxial compressive strength of rock, rock integrity index, cave development degree, and cave filling conditions. The index score S of each indicator under different conditions is given. i , see Table 1 below.

[0074] Table 1 Karst stability evaluation score table

[0075]

[0076]

[0077] After sorting the evaluation indicators by importance, the weight coefficient γ of each indicator is determined by the following formula: i .

[0078]

[0079] Where γ i —The weight coefficient of the i-th evaluation indicator;

[0080] n—number of evaluation indicators (important indicators);

[0081] m—importance ranking number, m≤n.

[0082] The higher the weight coefficient, the more important the evaluation indicator is and the greater its impact on karst stability. The proposed weight coefficient can reflect the contribution of different indicators to karst stability, highlight key risk factors, avoid homogenization errors, and refine the karst stability evaluation method.

[0083] 2. Evaluation score calculation model

[0084] According to the indicator score S i and weight coefficient γ i , the evaluation score C can be determined according to formula (1).

[0085] C=∑S i γ i (1)

[0086] 3. Stability level classification

[0087] Based on the calculated evaluation scores, the karst stability is determined, see Table 2 below.

[0088] Table 2 Correspondence between karst stability and assessment scores

[0089] grade 5 4 3 2 1 Assessment score C C≥60 45≤C＜60 30≤C＜45 15≤C＜30 C＜15 stability Extremely unstable Unstable Less stable relatively stable Stablize DETAILED DESCRIPTION

[0091] Example 1: Karst stability assessment of a high-speed railway section

[0092] Data collection: The overburden of a certain karst area is a soil layer with a thickness of 25m; the groundwater level fluctuation amplitude at the soil-rock interface is 1 / 4 of the overburden thickness; cracks are well developed and a few are filled; the saturated uniaxial compressive strength of the rock is 45MPa, and the integrity index is 0.6; the caves are moderately developed and half filled.

[0093] Indicator scoring (based on Table 1):

[0094] Groundwater level change: 50 points (weight 0.27);

[0095] Cover thickness: 50 points (weight 0.02);

[0096] Crack development and filling: 50 points (weight 0.18);

[0097] Rock compressive strength: 50 points (weight 0.10);

[0098] Rock integrity index: 25 points (weight 0.14);

[0099] Degree of cave development: 50 points (weight 0.23);

[0100] Cave filling condition: 35 points (weight 0.06);

[0101] Calculate the assessment score:

[0102] C=(50×0.27)+(50×0.02)+(50×0.18)+(50×0.10)+(25×0.14)+(50×0.23)+(35×0.06)=43.3;

[0103] Judgment result:

[0104] C=43.3, corresponding to level 3 (relatively unstable), and reinforcement measures are required.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for determining the karst stability of a high-speed railway, characterized in that: The following steps are involved: S1, seven evaluation indicators were selected from the hydrodynamic conditions, karst roof characteristics and karst cave characteristics, including groundwater level changes, cover layer thickness, fracture development and filling conditions, saturated uniaxial compressive strength of rock, rock integrity index, cave development degree and cave filling conditions; S2, score each indicator according to the preset grading standard and obtain the indicator score S i ; S3, the score of each indicator S i and the corresponding weight coefficient γ i Multiply and add to calculate the comprehensive evaluation score C = ∑S i γ i ; S4. The karst stability level is divided into stable, relatively stable, relatively unstable, unstable or extremely unstable levels according to the assessment score C.

2. The method according to claim 1, characterized in that The weight coefficient γ i The weight distribution of each indicator is determined by the hierarchical analysis method as follows: Groundwater level change γ i 0.2~0.3; Covering layer thickness γ i 0.01~0.02; crack development and filling situation γ i is 0.1~0.2; rock saturated uniaxial compressive strength γ i 0.05~0.20; rock integrity index γ i 0.1~0.2; the degree of cave development γ i 0.2~0.3; cave filling condition γ i It is 0.05-0.

07.

3. The method according to claim 1, characterized in that The scoring criteria for the groundwater level change index are: The groundwater level fluctuates near the soil-rock interface and the amplitude is ≥ 1 / 3 of the cover layer thickness, S i The score is 75-100; The groundwater level fluctuates near the soil-rock interface and the amplitude is less than 1 / 3 of the cover layer thickness, S i The score is 50-74; The groundwater level fluctuates in the overburden or bedrock with an amplitude ≤ the average interface height, S i The score is 25-49; The groundwater level is stable and far away from the soil-rock interface, S i The score is 0-24.

4. The method according to claim 1, wherein The scoring criteria for the cover thickness index are: The covering layer is soil and its thickness is less than 10m, S i The score is 75-100; The covering layer is soil with a thickness of 10-30m, S i The score is 50-74; The covering layer is soil and the thickness is greater than 30m, S i The score is 25-49; The cover layer is non-soluble rock, S i The score is 0-24.

5. The method according to claim 1, wherein The scoring criteria for the fissure development and filling indicators are as follows: The cracks are extremely developed and not filled, S i The score is 75-100; Fissures are well developed and a few are filled, S i The score is 50-74; Cracks are developed but most of them are cemented and filled. i The score is 25-49; The cracks are not developed or the cementation is good, S i The score is 0-24.

6. The method according to claim 1, wherein The scoring criteria for the rock saturated uniaxial compressive strength index are: Saturated uniaxial compressive strength of rock <30MPa, S i The score is 75-100; Saturated uniaxial compressive strength of rock 30-60MPa, S i The score is 50-74; Saturated uniaxial compressive strength of rock 60-100MPa, S i The score is 25-49; Saturated uniaxial compressive strength of rock>100MPa, S i The score is 0-24.

7. The method according to claim 1, characterized in that The scoring criteria for the rock integrity index are: Rock integrity index <0.35, S i The score is 75-100; Rock integrity index 0.35-0.55, S i The score is 50-74; Rock integrity index 0.55-0.75, S i The score is 25-49; Rock integrity index>0.75, S i The score is 0-24.

8. The method according to claim 1, characterized in that The scoring criteria for the cave development index are: The development degree of karst caves is strong, S i The score is 75-100; The development degree of karst caves is moderate. i The score is 50-74; The development degree of karst cave is weak. i The score is 25-49; The development degree of karst cave is weak. i The score is 0-24.

9. The method according to claim 1, characterized in that The scoring criteria for the cave filling condition index are: The cave filling condition is unfilled, S i The score is 70-100; The cave filling condition is half-filled, S i The score range is 35-69; The cave filling condition is full filling, S i The score is 0-34.

10. The method according to claim 1, characterized in that The stability levels are divided into: When C ≥ 60, it is extremely unstable; When 45≤C<60, it is unstable; When 30≤C<45, it is relatively unstable; When 15≤C<30, it is relatively stable; When C is less than 15, it is stable.

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