A method for evaluating the aging deformation risk level of a tunnel bottom constructed in a stress zone layered soft rock formation

Abstract

The present application relates to the technical field of tunnel engineering geological risk assessment, and particularly relates to a method for evaluating the risk grade of time-dependent deformation of a tunnel bottom in a tectonic stress area of a layered soft rock stratum, which obtains the maximum initial ground stress of a target tunnel, the uniaxial saturated compressive strength of rock and the thickness of a rock stratum as control geological parameters, and evaluates the risk of floor heave according to the following criteria: when the maximum initial ground stress is less than 6 MPa, it is determined as low risk; when the maximum initial ground stress is greater than 6 MPa and Rc·h≥1.1 σ max -6.6, it is determined as moderate risk; when the maximum initial ground stress is greater than 6 MPa and Rc·h<1.1 σ max -6.6, it is determined as high risk. The method can realize accurate evaluation of the risk grade of tunnel bottom deformation in the three stages of survey, construction and operation, and the evaluation accuracy is as high as 100% through engineering case verification.

Description

Technical Field

[0001] This invention relates to the field of geological risk assessment technology for tunnel engineering, and in particular to a method for evaluating the risk level of time-dependent deformation of the tunnel floor in layered soft rock strata within a tectonic stress zone. Background Technology

[0002] High-speed railways, with their high speed, high comfort, and high safety, have become an important part of my country's transportation infrastructure. By the end of 2025, my country's high-speed railway operating mileage had exceeded 50,000 kilometers. In complex mountainous terrain, tunnel engineering is extensively used to meet the requirements for line smoothness. To ensure the long-term stability of high-speed railways, ballastless track structures are commonly used in tunnels. Compared with ballasted track, ballastless track has significant advantages such as strong structural durability and less maintenance, essentially achieving the goal of maintenance-free or low-maintenance operation.

[0003] However, with the increase in operating years and the extension of the railway network into more complex geological environments, some operational high-speed railway tunnels have developed a typical engineering defect—tunnel floor heave. This occurs when the tunnel's bottom structure (invert or floor slab) undergoes upward bulging deformation, leading to cracking and arching of the upper ballastless track slab, resulting in track geometry exceeding limits. This defect can range from minor issues affecting train stability and passenger comfort, increasing maintenance costs, to severe issues forcing trains to operate at reduced speeds or even halting operations for emergency repairs, seriously disrupting busy railway transport and causing significant economic losses.

[0004] Engineering case studies show that tunnel floor heave exhibits significant regional and geological lithological characteristics, occurring primarily in tectonic stress zones in southwestern my country. Tunnels experiencing floor heave often traverse soft rock strata, such as carbonaceous shale, mudstone, and argillaceous sandstone. These rock strata typically possess unfavorable engineering characteristics, including low rock strength, easy softening upon contact with water, and significant rheological properties. Furthermore, the affected rock strata often occur as thin to medium-thick layers with gentle dips to near-horizontal dips. Under these specific geological conditions, the stress redistribution process in the surrounding rock after tunnel excavation is complex. The bottom rock mass, under the long-term coupling effect of high ground stress (especially horizontal tectonic stress) and groundwater, is highly susceptible to continuous shear slippage or compressional flow, ultimately leading to floor heave.

[0005] Currently, the engineering community has some understanding of the deformation mechanism of tunnel floor heave. However, because it is a comprehensive result of the nonlinear coupling of multiple factors such as rock mass mechanical properties, geological environment, and engineering factors, the deformation mechanism is extremely complex. Therefore, there is currently a lack of a mature, unified, and widely accepted quantitative evaluation method. Existing technologies for assessing the risk of tunnel floor heave mostly rely on engineering experience analogies or judgment based on a single factor (such as the magnitude of ground stress).

[0006] For example, the current "Code for Investigation of Adverse Geological Conditions in Railway Engineering" (TB10027-2022) mainly classifies high-stress states based on the ratio of maximum initial ground stress to rock strength stress. However, its classification criteria primarily target rockburst and large deformations, and are not entirely applicable to tunnel floor heave, a special type of defect caused by the accumulation of minute deformations. Practice has shown that relying solely on ground stress and rock strength criteria makes it difficult to accurately predict the risk of floor heave, resulting in an inability to effectively mitigate risks during the investigation and design phase, and a lack of precise early warning and control measures during the construction and operation phases.

[0007] In view of this, there is an urgent need to develop a scientific, systematic and operable technical solution that can comprehensively consider the key control factors affecting tunnel bottom deformation and establish a precise and quantitative risk level assessment method to run through the entire life cycle of tunnel engineering, effectively guide engineering design, construction and operation and maintenance, and thus ensure the long-term safe operation of major infrastructure such as high-speed railways. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies, such as reliance on single factors or empirical analogies, inaccurate evaluations, and inability to guide engineering practice. It provides a method for evaluating the risk level of time-dependent deformation of tunnel bottoms in layered soft rock strata within structural stress zones.

[0009] In a first aspect, the present invention provides a method for evaluating the risk level of time-dependent deformation of the tunnel floor in layered soft rock strata within a tectonic stress zone, comprising the following steps:

[0010] Obtain the key geological parameters controlling the risk of tunnel floor deformation for the target tunnel, including the maximum initial in-situ stress at the tunnel floor. σ max The uniaxial saturated compressive strength Rc of the rock and the thickness h of the rock layer; Based on the aforementioned geological parameters controlling tunnel floor deformation risk, the risk level of tunnel floor heave deformation is evaluated according to the following criteria: when σ max When the pressure is ≤6MPa, it is judged as low risk; when σ max >6MPa, and Rc·h≥1.1 σ max At -6.6, it is judged as a moderate risk; when σ max >6MPa, and Rc·h <1.1 σ max When the value is -6.6, it is considered a high-risk level.

[0011] Preferably, the maximum initial ground stress σ maxThe unit is MPa, the unit of the uniaxial saturated compressive strength Rc of the rock is MPa, the unit of the rock layer thickness h is cm, and the unit of the maximum initial in-situ stress is... σ max Through formula σ max =0.026H is determined, where H is the maximum burial depth of the tunnel in meters.

[0012] Preferably, the low risk, medium risk, and high risk are classified based on the rock hardness, rock layer thickness, bottom heave deformation, and duration; wherein, the low risk corresponds to a post-construction bottom heave deformation of 15mm-30mm, the medium risk corresponds to a post-construction bottom heave deformation of 30mm-60mm, and the high risk corresponds to a post-construction bottom heave deformation greater than 60mm.

[0013] Preferably, the deformation of the bottom bulge refers to the upward bulging displacement of the tunnel bottom structure after construction.

[0014] Preferably, for the low risk, a tunnel invert arch rise-to-span ratio of 1 / 12-1 / 16 is adopted, and the influence of heave deformation is eliminated by adjusting the track fasteners; for the medium risk, a reinforced concrete invert arch is adopted, and a tunnel invert arch rise-to-span ratio of 1 / 9-1 / 11 is adopted; for the high risk, a reinforced concrete invert arch is adopted, and a tunnel invert arch rise-to-span ratio of 1 / 7-1 / 9 is adopted.

[0015] Preferably, in obtaining the maximum initial ground stress σ max Before determining the uniaxial saturated compressive strength Rc of the rock and the thickness h of the rock strata, the process also includes dividing the tunnel section into several engineering geological units and obtaining corresponding geological characteristics for each unit. σ max The parameters are Rc and h.

[0016] Preferably, the soft rock in the layered soft rock layer of the tectonic stress zone is a rock with a uniaxial saturated compressive strength Rc of less than 30 MPa, and the layering is the occurrence of the rock layer in the form of thin to medium-thick layers.

[0017] Preferably, the method is applicable to at least one of the tunnel exploration, construction, and operation phases to achieve segmented and accurate assessment of tunnel floor heave risk.

[0018] Preferably, after determining that the risk is moderate or high, the method further includes a step of outputting a warning signal, which includes the risk level, the location of the risk segment, and corresponding engineering handling suggestions.

[0019] Preferably, the method is also applicable to the assessment of the time-dependent deformation risk level of the tunnel bottom in the layered soft rock strata of the structural stress zone in highway tunnels, airport tunnels, hydropower station tunnels, water diversion tunnels, or underground caverns.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for evaluating the risk level of time-dependent deformation of tunnel bottoms in layered soft rock strata within tectonic stress zones. By introducing the rock stratum thickness parameter to construct a three-factor coupled criterion of strength, thickness, and stress, it overcomes the shortcomings of existing technologies that rely on single or two-factor criteria for inaccurate evaluation. This method achieves accurate evaluation of the risk level of time-dependent deformation of tunnel bottoms in layered soft rock strata within tectonic stress zones. The accuracy rate of the evaluation has been verified to be 100% through 20 engineering cases.

[0021] This invention provides a method for evaluating the risk level of time-dependent deformation of the tunnel floor in layered soft rock strata within a structural stress zone. The constructed coupled criteria are based on three easily obtainable geological parameters: the maximum initial ground stress of the tunnel, the uniaxial saturated compressive strength of the rock, and the thickness of the rock strata. This method is applicable to the precise segmented evaluation of floor heave risk throughout the entire life cycle of tunnel exploration, construction, and operation, providing a unified quantitative decision-making basis for engineering design, construction, and operation and maintenance. Attached Figure Description

[0022] Figure 1 This is a technical flowchart of the method for evaluating the risk level of time-dependent deformation of the tunnel bottom in the layered soft rock strata of the structural stress zone according to the present invention. Figure 2 This is a diagram showing the relationship between the maximum initial ground stress at the bottom of the tunnel and the tunnel burial depth according to the present invention. Figure 3 This is a classification diagram of the stress coupling criterion for the tunnel floor heave of the present invention; Figure 4 This is a classification diagram of the stress coupling criterion for the strength, thickness, and tunnel floor drum of the present invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0024] This invention addresses the engineering problem of time-related floor heave deformation in tunnels located in layered soft rock strata within tectonic stress zones. It proposes a method for evaluating the risk level of time-related deformation of tunnel floors in such tectonic stress zones. Through systematic statistical analysis of numerous engineering cases, this invention identifies key geological factors controlling the risk of time-related deformation of tunnel floors: in-situ stress level, rock strength, and rock stratum structural characteristics. Furthermore, it establishes a quantitative mathematical relationship between these three factors and the risk level of floor heave, forming a coupled criterion capable of accurately distinguishing between low, medium, and high risk levels. Among these, the rock stratum thickness is a key structural parameter reflecting the deformation resistance of the tunnel floor rock strata. By introducing this parameter, this invention achieves a leap from the traditional two-factor evaluation of strength and stress to a coupled evaluation of strength, thickness, and stress.

[0025] I. Discovery Process of Coupled Criterion Patterns Based on Engineering Case Statistics The core criterion of this invention is: when σ max For strengths >6 MPa, is the product of the rock's uniaxial saturated compressive strength and the rock layer thickness greater than or equal to 1.1? σ max -6.6 serves as the dividing line between moderate and high risk. This pattern is not common knowledge in the field, but was revealed for the first time through in-depth statistical analysis of numerous tunnel floor heave engineering cases. The complete discovery process is as follows.

[0026] Twenty engineering cases of tunnel floor heave defects occurring on seven high-speed railway lines were collected, covering typical projects such as Zhao Jiayan Tunnel, Yunding Tunnel, Xinlongquanshan Tunnel, Laozhouyan Tunnel, Huangcaoshan Tunnel, Meilingguan Tunnel, Xuanzhenguan Tunnel, Sifangshan Tunnel, Shaziguan Tunnel, Fubaoshan Tunnel, Baoanying Tunnel, and Guangzhao Tunnel. These cases are distributed in different tectonic stress zones in southwestern my country, with representative geological conditions, covering different burial depths, different ground stress levels, different rock types, and different rock strata combinations. Since low-risk cases have minimal impact on train operation and can generally be handled independently by railway maintenance departments, relevant monitoring data is difficult to collect systematically. Therefore, the above 20 cases mainly fall into the categories of medium and high risk.

[0027] For each engineering case, geological parameters such as maximum tunnel burial depth, maximum initial ground stress, uniaxial natural compressive strength of rock, uniaxial saturated compressive strength of rock, and rock layer thickness were systematically extracted, and these parameters were compared and analyzed with the floor heave risk level of each case.

[0028] Table 1 summarizes the key parameters of 20 cases of bottom heave defects in 7 high-speed railway lines, including project name, maximum burial depth, maximum initial ground stress, uniaxial saturated compressive strength of rock, rock layer thickness, and qualitative classification results.

[0029] Table 1: Case Studies of Bottom Drumming Projects in Railway Tunnels

[0030] like Figure 2 As shown, the maximum initial ground stress and maximum tunnel burial depth data for each case in Table 1 are plotted on a rectangular coordinate system with burial depth as the abscissa and maximum initial ground stress as the ordinate. From Figure 2 It is clear that the data points for all cases are distributed along a straight line with a slope of approximately 0.026. By performing linear regression analysis on these data points, we can obtain... σ max =0.026H is an empirical relation. Figure 2 The risk level of each case is also indicated, with triangles representing medium risk and circles representing high risk. From Figure 2 It can be seen that the tunnel depth in medium-risk and high-risk cases is generally greater than 240m, and this observation further verifies the positive correlation between burial depth and bottom heave risk.

[0031] In medium-risk cases, the stress sources were mainly self-weight stress or tectonic stress, while in high-risk cases, the stress sources were all greater than self-weight stress, with tectonic stress being the primary source. This indicates that horizontal tectonic stress is the dominant factor inducing high-risk floor torning.

[0032] Based on the above findings, a strength-stress coupling criterion was first constructed. The maximum initial ground stress of 6 MPa was used as the first dividing line. When the maximum initial ground stress exceeded 6 MPa, the ratio of the uniaxial saturated compressive strength of the rock to the maximum initial ground stress was further used as the distinction between moderate and high risk. This criterion was constructed with reference to the basic principles of high ground stress state classification in the current railway engineering adverse geological investigation regulations, but adjustments were made to account for the characteristics of bottom heave deformation.

[0033] Figure 3 The classification results of the constructed strength-stress coupling criterion are presented. Figure 3 In the figure, the horizontal axis represents the maximum initial ground stress. σ max The vertical axis represents the uniaxial saturated compressive strength Rc of the rock, and the data points for each case are labeled with different symbols according to their actual risk level. Figure 3 It can be seen that this criterion divides the risk area into three zones: low-risk, medium-risk, and high-risk, with the following boundary conditions: σ max =6MPa and Rc=1.5 σ max Project the data points of each case in Table 3 onto... Figure 3In the data, it can be clearly seen that most cases fall within the area corresponding to their actual risk level, but a few cases still deviate from this range.

[0034] The verification results of this criterion were as follows: the accuracy rate was 83.3% in 6 medium-risk cases and 85.7% in 14 high-risk cases. Although this accuracy rate is higher than that of traditional single-factor empirical judgment methods, misjudgments still exist. This result indicates that considering only rock strength and ground stress is not sufficient to completely and accurately evaluate the risk level of tunnel floor heave.

[0035] Further analysis of the geological characteristics of the misjudged cases revealed an important pattern: under conditions of similar rock strength and in-situ stress levels, tunnel sections with thicker rock strata exhibited relatively smaller floor heave deformation and lower risk levels; conversely, tunnel sections with thinner rock strata showed larger floor heave deformation and higher risk levels. For example, in some cases, the uniaxial saturated compressive strength and maximum initial in-situ stress of the rock were similar, but due to differences in rock stratum thickness, the actual floor heave deformation and risk levels varied significantly.

[0036] Based on this phenomenon, the inventors, through in-depth research, realized that the essence of floor heave in soft rock tunnels is the time-dependent deformation process of the surrounding rock at the tunnel floor under unloading conditions, involving bending cracks and shear slippage. This understanding has significant physical implications: the greater the thickness of the rock strata, the greater its section modulus, the higher its bending stiffness, and the stronger its resistance to bending deformation. Therefore, it is less likely to experience floor heave deformation, or the deformation will occur later and with smaller magnitude. Conversely, thin-layered rock strata are more prone to interlayer slippage and bending failure under the same stress conditions, significantly increasing the risk of floor heave. Therefore, the thickness of the rock strata is a key structural parameter reflecting the deformation resistance of the tunnel floor rock strata and an indispensable key control indicator for controlling the risk of floor heave.

[0037] Based on this physical understanding, the inventors combined the thickness of rock strata with the uniaxial saturated compressive strength of the rock in a product form, forming a comprehensive index: the product of Rc and h. This product index has a clear physical meaning: it reflects both the strength properties of the rock material itself and the deformation stiffness properties of the rock strata structure. The product of the two characterizes the ability of a layered rock stratum per unit width to resist bending deformation.

[0038] Furthermore, a regression analysis was performed on this comprehensive index and the maximum initial ground stress. Using cases with a maximum initial ground stress greater than 6 MPa as the sample, the data points for each case were plotted on a Cartesian coordinate system with the product of Rc and h as the ordinate and the maximum initial ground stress as the abscissa. The distribution areas of moderate and high risk were then distinguished based on the actual risk level of each case. Through trial calculations and comparisons of linear boundary lines with different slopes and intercepts, the slope of the boundary line was ultimately determined to be approximately 1.1, and the intercept approximately -6.6.

[0039] Figure 4 The classification results of the final constructed strength-thickness-stress coupling criterion are presented. Figure 4 In the figure, the horizontal axis represents the maximum initial ground stress. σ max The vertical axis represents the product of the uniaxial saturated compressive strength of the rock and the thickness of the rock strata, Rc·h. Data points for each case are labeled with different symbols according to their actual risk level. Figure 4 As can be seen, this criterion also divides the risk area into three zones: low-risk, medium-risk, and high-risk, with the following demarcation conditions: σ max =6MPa and Rc·h=1.1 σ max -6.6. Project the data points of each case in Table 3 onto... Figure 4 As can be seen, all cases fall within the area corresponding to their actual risk level, with none deviating. This visualization result intuitively demonstrates the 100% accuracy of the three-factor coupling criterion.

[0040] Taking the Genting Tunnel in Table 1 as an example for analysis: The maximum burial depth of the Genting Tunnel is 325m, according to the formula... σ max The maximum initial geostresses calculated by H = 0.026 are 9.5 MPa and 13.7 MPa in two segments; The uniaxial saturated compressive strength of the rock is Rc = 4.4 MPa, and the rock layer thickness is h = 0.30 m.

[0041] For the two analysis sections of the tunnel σ max The values ​​are 9.5 MPa and 13.7 MPa, respectively, both greater than 6 MPa. Calculate Rc·h = 4.4 × 0.30 = 1.32.

[0042] Calculate the limit value 1.1 respectively. σ max -6.6: for σ max When the pressure is 9.5 MPa, the threshold value is 10.45 - 6.6 = 3.85. Since 1.32 < 3.85, it is judged as a high risk. for σ max When the pressure is 13.7 MPa, the threshold value is 15.07 - 6.6 = 8.47. Since 1.32 < 8.47, it is also judged as a high risk.

[0043] The tunnel was actually put into operation in 2010 when floor heave was discovered, and engineering treatment was carried out in 2020, which verified the accuracy of the high-risk assessment conclusion.

[0044] The general operation flow of the method of the present invention will be described in detail below with reference to the accompanying drawings. Figure 1 As shown, the method includes the following steps.

[0045] The first step is to divide the tunnel section into several engineering geological units.

[0046] The implementation method for this step is as follows: Based on the differences in engineering geological factors such as lithology, geological structure, and hydrogeological conditions of the strata traversed by the tunnel, the entire tunnel body is divided into several engineering geological units. The geological conditions within each unit are relatively uniform, while there are identifiable differences between different units in terms of lithological assemblage, stratum occurrence, and geostress field characteristics. When dividing the unit, it is important to ensure that the rock type within the same engineering geological unit is basically consistent, the variation range of stratum thickness should not be too large, and the geostress field characteristics should be similar.

[0047] Taking a specific implementation example provided by this invention, a tunnel with a total length of 12,858m traverses the Upper Jurassic Penglaizhen Formation, whose lithology is mainly mudstone, sandy mudstone, sandstone, and argillaceous sandstone. Based on the engineering geological conditions, including lithology and geological structure, the tunnel is divided into two engineering geological units. The section from DK28+020 to DK31+300 is dominated by horizontal tectonic stress and has a risk of floor heave; the section from DK32+500 to DK35+900 is dominated by self-weight stress and has a lower risk of floor heave. This division lays the foundation for subsequent targeted evaluation. In this case, the final confirmed section length with floor heave risk is 3,280m, of which 2,080m has a medium risk and 1,200m has a high risk.

[0048] Table 2. Geological Unit Division and Preliminary Assessment of Floor Heave Risk in Tunnel Engineering

[0049] The second step is to obtain the control geological parameters for tunnel bottom deformation risk for each engineering geological unit.

[0050] In this step, three key geological parameters need to be obtained for each engineering geological unit, namely, the maximum initial in-situ stress. σ max The uniaxial saturated compressive strength Rc of the rock and the thickness h of the rock layer.

[0051] Maximum initial ground stress σ max This is the maximum principal stress borne by the surrounding rock at the bottom of the tunnel, which typically manifests as horizontal tectonic stress in tectonic stress zones. When obtaining the maximum initial in-situ stress, in-situ stress measurement methods, such as hydraulic fracturing or stress relief methods, are preferred. When in-situ measurement is not feasible, empirical formulas derived through statistical analysis can be used. σ maxThe value is estimated to be 0.026H, where H is the maximum burial depth of the tunnel corresponding to the engineering geological unit, in meters. This empirical formula is derived from a statistical analysis of 20 tunnel floor heave engineering cases and is applicable to the preliminary estimation of tectonic stress zones. In specific implementation cases, the maximum initial ground stress in the section from DK28+020 to DK31+300 ranges from 8.69 MPa to 12.1 MPa.

[0052] The uniaxial saturated compressive strength Rc of rock is obtained as follows: representative rock samples are collected within the engineering geological unit. Following the test methods specified in national or industry standards, the rock samples are processed into standard specimens and subjected to saturation treatment. Then, they are loaded onto a pressure testing machine at a specified loading rate until failure. The maximum load at failure is recorded, and the compressive strength value is calculated. This parameter represents the ultimate ability of rock material to resist compressive failure under saturated conditions. In specific implementation cases, the uniaxial saturated compressive strength of rock in the relevant sections ranges from 5.2 MPa to 13.5 MPa.

[0053] The thickness h of the rock strata is obtained by statistically analyzing the thickness of the main rock strata at the bottom of the tunnel within the engineering geological unit using a borehole core logging system. For gently dipping layered rock strata, the thickness can be determined by combining surface outcrop measurements and borehole data. During the statistical analysis, the thickness of the controlling rock strata should be distinguished, and a representative average value should be taken as the representative thickness of the unit. In specific implementation cases, the rock strata thickness in relevant sections ranges from 0.25m to 0.7m.

[0054] The third step is to evaluate the risk level of bottom heave in each unit based on the three geological parameters and the coupling criteria.

[0055] When the maximum initial geostress σ max When the stress is below 6 MPa, regardless of rock strength and stratum thickness, the tunnel is classified as low-risk. This threshold is based on the following engineering practice: when the maximum initial ground stress is below 6 MPa, the stress environment of the surrounding rock at the tunnel bottom is insufficient to drive significant time-dependent floor heave deformation in soft rock strata. Statistical analysis of engineering cases shows that all tunnels experiencing floor heave of medium to high risk had a maximum initial ground stress greater than 6 MPa.

[0056] When the maximum initial geostress σ max When the pressure is greater than 6 MPa, it is necessary to further calculate the product of the uniaxial saturated compressive strength Rc of the rock and the rock layer thickness h, and then compare this product with the boundary value 1.1 calculated based on the maximum initial in-situ stress. σ max Subtract 6.6 for comparison.

[0057] If Rc·h≥1.1 σ maxA stress level of -6.6 indicates a moderate risk. At this point, although the stress level exceeds the critical value, the rock's strength and the thickness of the rock strata mean that the surrounding rock at the tunnel floor can resist the driving effect of in-situ stress to a certain extent, and the heave deformation is within a controllable range. In a specific implementation case, the maximum initial in-situ stress in the section from DK28+020 to DK29+300 is 8.69 MPa, the uniaxial saturated compressive strength of the rock is 9.6 MPa, the rock stratum thickness is 0.5 m, the product of Rc and h is 4.8, and the critical value is 1.1. σ max -6.6 equals 2.959, which meets the criteria for moderate risk. This segment actually experienced vehicle swaying, thus falling under the category of moderate risk.

[0058] If Rc·h < 1.1 σ max A value of -6.6 indicates a high-risk condition. In this case, the rock strength is low, the rock stratum thickness is thin, or both are present, resulting in insufficient deformation resistance of the tunnel floor surrounding rock to withstand the long-term effects of the tectonic stress field. The floor heave deformation will exceed the allowable value, requiring robust engineering measures. In a specific implementation case, the maximum initial in-situ stress in the section from DK29+300 to DK29+600 is 10.6 MPa, the uniaxial saturated compressive strength of the rock is 5.2 MPa, the rock stratum thickness is 0.3 m, the product of Rc and h is 1.56, while the critical value is 1.1. σ max -6.6 equals 5.06, which meets the high-risk criterion. This section actually experienced defects such as train swaying, track elevation changes, and invert arch cracking.

[0059] For each specific paragraph in Unit 1, obtain σ respectively. max The risk level of bottom heave in each segment is evaluated using three parameters: Rc, h, and the coupling criterion described above. Table 3 details the mileage range, length, layer thickness, maximum principal stress, saturated uniaxial compressive strength of rock, criterion calculation results, and evaluation level for each segment.

[0060] Table 3 Risk Assessment and Verification of Floor Heave in Each Section of the Tunnel

[0061] The evaluation results are summarized in Table 3. There are three medium-risk sections with a total length of 2080m; and three high-risk sections with a total length of 1200m.

[0062] The last two columns of Table 5 provide the actual floor heave conditions that occurred in the tunnel. According to the records in Table 5, the tunnel experienced swaying between DK28+478 and DK31+478 between 2017 and 2025. Displacement monitoring revealed track elevation changes or invert cracking in sections DK29+325 to DK29+600, DK30+426 to DK30+576, and DK31+079 to DK31+179. By comparing the evaluation levels of each section in Table 5 with the actual conditions of the defects, it is clear that: all sections rated as medium risk experienced varying degrees of swaying without serious defects such as track elevation changes or invert cracking; all sections rated as high risk experienced swaying accompanied by serious defects such as track elevation changes or invert cracking. All sections where tunnel floor heave actually occurred were within the predicted range, with no omissions, and the severity of the damage corresponded perfectly to the risk level.

[0063] The fourth step is to output corresponding engineering disposal recommendations based on the risk level assessment results.

[0064] For low-risk sections, it is recommended to appropriately increase the tunnel support strength and eliminate the impact of heave deformation by adjusting the track fasteners. For medium-risk sections, it is recommended to increase the tunnel support strength and use reinforced concrete inverts, with an invert rise-to-span ratio of 1 / 10, while strengthening deformation monitoring. For high-risk sections, it is recommended to significantly enhance the tunnel support strength, use reinforced concrete inverts, and install reinforcement measures such as long anchor bolts and W-shaped steel strips, with an invert rise-to-span ratio of 1 / 8, increase the density of deformation monitoring points, and closely monitor the time-varying patterns of bottom heave deformation. See Table 4 for details of the surrounding rock and deformation characteristics and engineering measures corresponding to each risk level.

[0065] Table 4. Description of Risk Level Classification for Tunnel Bottom Heave

[0066] The fifth step is to issue an early warning signal after determining that the risk level is moderate or high.

[0067] Warning signals should include at least the following information: risk level, location of the risk zone, and corresponding engineering response recommendations. Warning signals can be output in the form of written reports, electronic documents, or visual graphics for reference and decision-making by engineering designers, construction managers, or operation and maintenance personnel.

[0068] The layered soft rock strata in the tectonic stress zone targeted by the method of this invention have specific geological significance. Soft rock refers to rocks with a uniaxial saturated compressive strength of less than 30 MPa, such as carbonaceous shale, mudstone, sandy mudstone, and argillaceous sandstone. These rocks are characterized by low strength, easy softening upon contact with water, and significant rheological properties, forming the material basis for basal heave deformation. Layered refers to the occurrence of rock strata in thin to medium-thick layers, with dip angles generally ranging from gentle to near horizontal. The layered structure results in significant anisotropy in the mechanical behavior of the rock mass, making it prone to interlayer slippage, bending, and plate cracking failure under long-term tectonic stress.

[0069] In the method of this invention, the post-construction under-drum deformation corresponds to 15-30mm for low risk, 30-60mm for medium risk, and greater than 60mm for high risk. This classification is based on the adjustment capability of the fasteners for high-speed railway ballastless track. Common ballastless track fasteners typically adjust from 4mm to 26mm above the rail surface, allowing for limited adjustment of the under-drum deformation by optimizing the longitudinal slope of the track and raising the elevation of the rail surface adjacent to the starting point. Therefore, 30mm is set as the upper limit for low risk. Special fasteners can achieve maximum adjustment of 40mm and 60mm, but at this point, the track requires speed-limited operation; therefore, 60mm is set as the upper limit for medium risk. When the under-drum deformation exceeds 60mm, it cannot be fully adjusted using track fasteners, requiring engineering measures such as sleeper reconstruction, ballastless track reconstruction, or even under-drum replacement. This generally necessitates track closure for repairs, significantly impacting train operation; therefore, it is set as the lower limit for high risk. The adjustment capabilities of common ballastless track fasteners are shown in Table 5.

[0070] Table 5 Adjustment Capacity of Common Ballastless Track Fasteners

[0071] Bottom heave deformation refers to the upward displacement of the tunnel bottom structure after construction. This displacement can be obtained by periodically observing the structure using precision leveling or automatic total station, with deformation monitoring points set up on the tunnel invert or track slab.

[0072] Furthermore, according to the statistics of other engineering cases in Table 1, for medium-risk cases such as the Xinlongquanshan Tunnel and Huangcaoshan Tunnel, their common characteristic is that the product of Rc·h is relatively large, and even if the ground stress exceeds 6MPa, the underbody deformation is still within a controllable range. However, for high-risk cases such as the Zhaojiayan Tunnel, Laozhouyan Tunnel, Meilingguan Tunnel, and Baoanying Tunnel, their common characteristic is that the product of Rc·h is relatively small, and the underbody deformation is large, often requiring stronger engineering measures for remediation. This comparative analysis further verifies the rationality and effectiveness of the Rc·h product term as an evaluation index in the criterion established in this invention.

[0073] The method of this invention can also be extended to evaluate the risk level of time-dependent deformation of the tunnel floor in layered soft rock strata within structural stress zones in underground engineering projects such as highway tunnels, airport tunnels, hydropower station tunnels, water diversion tunnels, and underground caverns. Although these projects differ from high-speed railway tunnels in structural form and functional requirements, the mechanical mechanism of floor heave deformation is the same, involving the coupled effects of three factors: ground stress, rock strength, and rock stratum structure. Therefore, the evaluation criteria of this invention are equally applicable.

[0074] Furthermore, the method of this invention can perform lateral comparisons between different mileage sections of the same tunnel to form a risk distribution map of the entire tunnel's floor heave, providing a visual decision-making tool for risk management throughout the tunnel's life cycle. With the deepening of engineering practice and the accumulation of more case data, the empirical constants in the coupling criterion disclosed in this invention can be corrected and optimized based on new data to improve evaluation accuracy; these corrections and optimizations all fall within the protection scope of this invention.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for evaluating the risk level of time-dependent deformation of tunnel bottom in layered soft rock strata within a structural stress zone, characterized in that, Includes the following steps: Obtain the key geological parameters controlling the risk of tunnel floor deformation, including the maximum initial in-situ stress at the tunnel floor. σ max The uniaxial saturated compressive strength Rc of the rock and the thickness h of the rock layer; Based on the aforementioned geological parameters controlling tunnel floor deformation risk, the risk level of tunnel floor heave deformation is evaluated according to the following criteria: when σ max When the pressure is ≤6MPa, it is judged as low risk; when σ max >6MPa, and Rc·h≥1.1 σ max At -6.6, it is judged as a moderate risk; when σ max >6MPa, and Rc·h <1.1 σ max When the value is -6.6, it is considered a high-risk level.

2. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, The maximum initial ground stress σ max The unit is MPa, the unit of the uniaxial saturated compressive strength Rc of the rock is MPa, the unit of the rock layer thickness h is cm, and the unit of the maximum initial in-situ stress is... σ max Through formula σ max =0.026H is determined, where H is the maximum burial depth of the tunnel in meters.

3. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, The low-risk, medium-risk, and high-risk categories are classified based on a comprehensive assessment of rock hardness, stratum thickness, bottom heave deformation, and duration. Specifically, the low-risk category corresponds to a bottom heave deformation of 15mm-30mm after construction, the medium-risk category corresponds to a bottom heave deformation of 30mm-60mm after construction, and the high-risk category corresponds to a bottom heave deformation greater than 60mm after construction.

4. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, The deformation of the bottom bulge refers to the upward displacement of the tunnel bottom structure after construction.

5. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, For the aforementioned low-risk conditions, a tunnel invert arch rise-to-span ratio of 1 / 12 to 1 / 16 is adopted; and the influence of heave deformation is eliminated by adjusting the track fasteners. For the aforementioned moderate risk, a reinforced concrete invert arch is adopted, and the tunnel invert arch rise-to-span ratio is 1 / 9-1 / 11; For the aforementioned high risk, a reinforced concrete invert arch is adopted, and the invert arch rise-to-span ratio is 1 / 7-1 / 9.

6. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, In obtaining the maximum initial geostress σ max Before considering the uniaxial saturated compressive strength Rc of the rock and the thickness h of the rock strata, This also includes dividing the tunnel section into several engineering geological units, and obtaining corresponding geological data for each unit based on its geological characteristics. σ max The parameters are Rc and h.

7. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, The soft rock in the layered soft rock strata of the tectonic stress zone is rock with a uniaxial saturated compressive strength Rc of less than 30 MPa, and the layered nature means that the rock strata occur in thin to medium-thick layers.

8. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, The method is applicable to at least one of the tunnel exploration, construction, and operation phases to achieve segmented and accurate assessment of tunnel floor heave risk.

9. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, After determining that the risk is moderate or high, the process also includes the step of outputting a warning signal, which includes the risk level, the location of the risk segment, and corresponding engineering handling suggestions.

10. The method for evaluating the risk level of time-dependent deformation of the tunnel bottom in layered soft rock strata within the tectonic stress zone according to claim 1, characterized in that, The method is also applicable to the assessment of the time-dependent deformation risk level of the tunnel bottom in the layered soft rock strata of the structural stress zone in highway tunnels, airport tunnels, hydropower station tunnels, water diversion tunnels, or underground caverns.

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